Biological term for close species rivalry

Biological term for close species rivalry

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Is there any phenomenon/force in biology when two very close species fiercely fight each other (as a sign of a strong tendency to deepen the difference between species)? If there is, what's the name of the phenomenon or any similar phenomenon? (Question from a layman in biology, thanks for an answer.)

Citing wikipedia

Character displacement refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species' distributions do not overlap. This pattern results from evolutionary change driven by competition among species for a limited resource (e.g. food). The rationale for character displacement stems from the competitive exclusion principle, also called Gause's Law, which contends that to coexist in a stable environment two competing species must differ in their respective ecological niche; without differentiation, one species will eliminate or exclude the other through competition.

In ecology, the competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law,[2] is a proposition that states that two species competing for the same resource cannot coexist at constant population values, if other ecological factors remain constant. When one species has even the slightest advantage or edge over another then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolutionary or behavioral shift toward a different ecological niche. The principle has been paraphrased into the maxim "complete competitors cannot coexist"

Sibling Rivalry

Suzanne D. Dixon , Martin T. Stein , in Encounters with Children (Fourth Edition) , 2006


Sibling rivalry is a predictable, normal and healthy response to the birth of a new brother or sister. In most families it demonstrates that the older child is appropriately attached to the parents and is responsive to a perceived threat to the parent-child relationship. It is a normal response to having your place as the baby of the family usurped. In this context, the emergence of behavior that reflects sibling rivalry should be viewed positively. Ambivalence toward the baby as evidenced by an ongoing shift between positive and negative behavior is to be expected. Indeed, its absence may be worrisome. Sibling rivalry is not a disease, but a manifestation of psychological health.

Behavioral manifestations of sibling rivalry can take several forms, such as the following:

Aggressive behavior is directed most commonly toward the mother, but it may also be directed toward the baby, father, playmates, self or toys. Aggressive behavior most often occurs when the older sibling is a toddler. Increases in this behavior will probably occur when the new baby becomes more socially engaging at 4 to 5 months of age and again when he becomes mobile during the last half of the first year. Open hostility may be reduced to more subtle behavior directed at the infant, such as pulling the pacifier out of the baby's mouth or taking a toy away.

Naughtiness, or doing things contrary to family rules, occurs frequently at times when the mother is busy with the baby. This strategy serves to both increase tension in the household and verify the continuing power of the toddler to alter the behavior of those around her. A careful history of when such behavior occurs may highlight to the family for the first time that it is not “random,” but dependent on a particular situation.

Some children are overly compliant to or overly solicitous of the infant. Perhaps the child fears being totally replaced if she misbehaves, so the child becomes “extra good” to ensure her place in the family. Then again, she may be so frightened of her own aggressive and angry feelings that she holds them tightly in check. This may become a costly strategy and may evolve into an actively aggressive pattern or an irritable, depressed mood.

Regressive and dependent behavior is usually seen in the form of clinging and demanding. Other possible types of regressive behavior include sleep disturbances, stuttering, thumb sucking, bedwetting, eating refusals or demands and baby talk. These responses serve to see whether one can get the same attention and care as the infant. They are also the expected response to any stress and demand for adjustment.

Behavioral manifestations of sibling rivalry reflect a child's limited and primitive response to change in the family structure, including her own position. They generally decrease, but may not entirely disappear during the year after the new sibling's birth. There may be periods of readjustment as the infant's abilities change. Over this period the older child becomes confident of a new place in the family, with its status and privileges. Additionally, the older sibling usually develops a separate relationship with the younger child as the latter becomes more fun, more responsive and interactive. Young babies aren't much fun and are usually quite a disappointment to a child initially.

. “Mom changing baby's diaper.” By Eric Ries, age 6½.

The arrival of a younger sibling can evoke positive behavioral changes, as well as negative ones, even in the early, get-acquainted period. Dunn and Kendrick report gains in the older child's independence and mastery, particularly with regard to self-help skills (e.g., dressing and feeding). The child may gain new skills and a growing sense of competency through participation in “her” baby's care. She may be able to reflect on her own growth and development as she sees the baby's emerging capabilities. The older sibling may try out new ways of dealing with the little stranger, such as initiating and maintaining interactions in which she bears the burden of greater understanding. She will learn to laugh at the antics of the baby and grow in confidence as she learns to make the infant laugh, play games and imitate. This is an opportunity for growth if such behavior is understood and supported. Ways to support the older child are laid out in Box 9-3 .

The biology of cultural conflict

Although culture is usually thought of as the collection of knowledge and traditions that are transmitted outside of biology, evidence continues to accumulate showing how biology and culture are inseparably intertwined. Cultural conflict will occur only when the beliefs and traditions of one cultural group represent a challenge to individuals of another. Such a challenge will elicit brain processes involved in cognitive decision-making, emotional activation and physiological arousal associated with the outbreak, conduct and resolution of conflict. Key targets to understand bio-cultural differences include primitive drives—how the brain responds to likes and dislikes, how it discounts the future, and how this relates to reproductive behaviour—but also higher level functions, such as how the mind represents and values the surrounding physical and social environment. Future cultural wars, while they may bear familiar labels of religion and politics, will ultimately be fought over control of our biology and our environment.

1. Cultural conflict and why biology matters

In the most general sense, culture can be thought of as the knowledge, customs and traditions of a group of people [1], which systematically drive and channel collective dispositions of thoughts and behaviours into the future. Culture includes social, legal and economic institutions, as well as non-institutionalized trends and movements. Culture encompasses technology, literature and art, as well as disparate political, ethnic and religious beliefs and biases that both infuse and connect the higher cognitive functions and emotions of individual brains [2].

Although culture is usually thought of as the collection of knowledge and traditions that are transmitted outside of biology, one cannot credibly deny that the thoughts and behaviours of individuals contribute to the creation of culture, and that every person must process and react to cultural phenomena. Over 100 years ago, William James said it clearly, ‘There is not a single one of our states of mind, high or low, healthy or morbid, that has not some organic process or condition… They [beliefs] are equally organically founded, be they of religious or non-religious content’ [3, p. 16].

Thus, cultural conflict should manifest in two ways. First, if there are systemic and substantial cultural differences between groups of people, this would result in different types of processing in individual brains that form the group. Take, for example, religion. When presented with a concept like God, a Christian and an atheist would surely react differently, and this will probably manifest as differences in brain activation [4]. Similarly, in the US political realm, probing the role of government spending could well elicit different brain activations for Republicans, Democrats and Tea Party members. Second, mere cultural differences in brain activation do not necessarily imply conflict. Cultural conflict would be hypothesized to occur only when certain beliefs and traditions of one culture represent a challenge to individuals of another culture. Such a challenge would elicit brain processes involved in the cognitive decision-making, emotional activation and physiological arousal associated with the outbreak, conduct and resolution of conflict.

Because biological processes govern our perceptions, interpretations and reactions to cultural events, understanding these processes will not only help us understand cultural conflicts but also potentially mitigate them. In this issue, we have collected a series of papers that begins to tackle issues surrounding cultural conflict from a biological perspective. The cultural themes range from political partizanship to sacred values and religious conflicts, and the tools used to study them include brain imaging with functional magnetic resonance imaging and measures of physiological arousal (skin conductance responses (SCRs) and eye-tracking).

2. Primitive drives

We begin with the most primitive biologic processes linked to decision-making: good versus bad. Every animal makes decisions about things that it wants and things it avoids. In human economics, we designate these categories as ‘goods’ and ‘bads’, but behaviourally these categories can be mapped out by things that individuals approach or avoid. For humans, there are certain universals. We generally like (and approach) things linked to survival and prosperity: food, mates and money and we generally dislike (and avoid) things linked to mortality and loss. Although universal, cultural differences shape their relative importance to individuals, and so we begin by examining responses to these biologically primitive drives. For example, which is more important—seeking out the good things or avoiding the bad? Differences over this basic decision may cause conflicts both within and between cultures. Dodd et al. [5] approach the question in terms of political affiliation.

Even within a society, individuals may hold different beliefs about politics that lead to cultural conflict. Strictly defined, politics refers to governing institutions and policies. However, political affiliations often align with other cultural and religious beliefs, so that when we talk about political differences, these may include broad cultural differences even within a society. There appears to be a strong disposition to categorize in terms of binary oppositions: to dichotomize [6], essentialize [7] and thereby deepen outward differences that may have initially been superficial or arbitrary. Ever since the French Revolution, it is common to divide secular political camps into the ‘left’ and ‘right’. The left/right division has different meanings in different countries but generally maps onto bigger or smaller roles of government. In the USA, it is liberals and conservatives, or Democrats and Republicans. In the UK, Labour and Conservative parties in France, left (e.g. Socialist Party) and right (e.g. RPR) in Germany, the left (SPD) and the right (CDU/CSU) in Spain, the left (PSOE) and the right (PP) in Israel, Labor and Likud, and so on.

Do such divisions of left and right on the political spectrum merely reflect the human tendency to categorize, or might there be fundamentally two contrasting types of politically relevant cognitive and social dispositions that differentially characterize individuals in every culture? Dodd et al. [5] provide physiological evidence for the latter. Using SCRs, which are a measure of physiological arousal, they find significant differences between people on the left and the right. Importantly, the differences appear only when subdivided into ‘good’ and ‘bad’ provocateurs. Those on the right show arousal responses to pictures of aversive stimuli like maggot-ridden meat and angry mobs, while those on the left show arousal responses to positive pictures like rabbits and happy children. A follow-up study using eye-tracking to measure attention confirmed that attention and arousal are yoked together along these same dimensions.

These findings may help to explain differential support for policy differences between the political left and right. Individuals on the political right appear to be more sensitive and attuned to the unpleasant things in life. As Dodd et al. [5] note, ‘this responsiveness, in turn, is consistent with the fact that right-of-centre policy positions are often designed to protect society from out-group threats (e.g. by supporting increased defence spending and opposing immigration) and in-group norm violators (e.g. by supporting traditional values and stern penalties for criminal behaviour)’. If true, then the rules and policies advocated by the two poles of the political spectrum are there to mitigate biological sensitivity to unpleasantries.

Another primitive biological process that all animals must face is how to value the future. Humans have extensive cognitive capacity for both remembering the past and imagining the future, and how we value the future has ramifications for individuals and societies. When the future is expected to be better than the present, there is motivation to invest in the future. Such investments include having children, emphasizing their education, investing and building infrastructure, saving for retirement and adopting behaviours that prolong and increase the quality of life. On the other hand, when the future is expected to be worse than the present, the incentives move towards living in the present: profligate consumption and reduced infrastructure investment.

One way to measure the value of the future is through an individual's discount rate. This is the rate at which time devalues future expected values for that individual. Kim et al. [8] examine biological differences in discount rates between Koreans and Americans. They find that Americans have discount rates over twice that of Koreans, and that these differences are mirrored in the activity of the ventral striatum—a brain structure well-known to be associated with value-based decisions. These findings lay the groundwork for understanding differences in culturally situated beliefs towards savings and investment, which may be a source of conflict.

Another biological primitive, which may also relate to future discounting, is reproductive behaviour. Henrich et al. [9] examine the cultural conditions that foster and inhibit monogamous marriage. Like discount rates, a society's institutions for marriage provide a window into how the culture values the future. Fundamentally, marriage is a framework that allows society to recognize reproductive rights, and secondarily, to provide for an orderly passing of property to offspring. Although marriage is a cultural institution, reproduction is generally expected to be a consequence of the arrangement, and therefore, intertwined with biology. Given that males can reproduce with relatively low cost, and that historically 85 per cent of societies have allowed men to have multiple wives, how could monogamy ever be adaptive? Henrich et al. [9] suggest a theory with a simple premise: polygamy creates a residual pool of males with no possibility of having a wife. With limited prospects of future reproductive success, these males should have steeper discount rates (substantially higher valuation of the present), which is associated with more impulsive behaviours: criminal activity, violence and drug use. Henrich et al. [9] argue that these are destabilizing influences in a society. Adopting monogamy as the cultural norm ensures a mate for everyone, and crime and violence decrease, benefitting all. In contrast, polygamous societies will have a large pool of males with no hope for reproduction. These males can be channelled into armies and sacrifice their genes for ‘their brothers’.

Carrying the theme of conflict forward to violent means, there is considerable historical, cross-cultural and psychological evidence that males and females differ in aggressive tendencies, especially in the most violent behaviours of aggravated assault and homicide [10], war and terrorism [11]. McDonald et al. [12] propose an evolutionary-based argument for why this is the case. It has been suggested that females are a resource for which males aggressively compete. However, ‘this competition need not take the form of direct contests for instances of sexual access, but may include conflicts over feeding territories, nest sites and more intangible resources, such as social influence, power and status—resources that can be converted into reproductive opportunities over time’. They suggest that intergroup conflict has affected the social psychologies of men and women differently. Because men are the more common perpetrators and victims of intergroup aggression, coalitional psychology is likely to be more pronounced among men. From this, McDonald et al. [12] argue that selection has favoured the evolution of cognitive processes for ‘the formation of male coalitions capable of planning, initiating and executing attacks on out-groups with the aim of acquiring or protecting reproductive resources’, which is referred to as the ‘male warrior hypothesis’.

3. ‘Give me liberty or give me death’

In The Origin of Species, Charles Darwin considered adaptations—including warlike and altruistic behaviour in humans—only for the individual's own use in its struggle to gain resources to produce offspring: ‘good for itself’, but ‘never … for the exclusive good of others’ [13, p. 230]. Later, however, he puzzled over the problem of how self-interest alone could account for humankind's aptitude for self-sacrifice to the point of giving up one's life—the totality of a person's self interests—for tribe, nation, religion or for humanity. The puzzle led Darwin to modify his view that natural selection only produces selfish individuals. In The Descent of Man, he suggested that humans have a naturally selected propensity to the virtue of ‘morality’, that is, a willingness to sacrifice self-interest in the cause of group interests. This includes heroism in battle, and martyrdom, where prospects for personal survival are very low but somewhat higher for those in the group who may be neither kin nor kith. Groups possessing an abundance of individuals with such moral virtue, Darwin argued, would be better endowed in history's spiralling competition for survival and dominance [14].

The nature of moral values is, in large part, defined by the culture in which individuals engage them in decisions, but virtue theory suggests two very different ways in which moral values might be processed [15]. Moral values could be either deontological in nature [16] or they could be utilitarian [17]. Deontic processing is defined by an emphasis on absolute rights and wrongs, whereas utilitarian processing is characterized by costs and benefits. Models of rational behaviour predict many of society's patterns, such as favoured strategies for maximizing profit or likelihood for criminal behaviour in terms of opportunity costs [18]. But the prospects of crippling economic burdens and huge numbers of deaths do not necessarily sway people from their positions on whether going to war, or opting for revolution or resistance, is the right or wrong choice [19]. One possible explanation is that people are not weighing the pros and cons for advancing material interests at all, but rather using a moral logic of ‘sacred values’—convictions that trump all other considerations—that cannot be quantified in straightforward ways [20].

In potentially violent situations of intergroup conflict, sacred values appear to operate as moral imperatives that generate actions independently, or out of proportion, to their evident or likely results, because it is the right thing to do whatever the consequences [21]. For example, regardless of the utilitarian calculations of terror-sponsoring organizations, suicide terrorists appear willing to make extreme sacrifices that use a ‘logic of appropriateness’ rather than a calculus of probable costs and benefits [22]. Or consider the American revolutionaries who, despite belonging to a society that had the highest standard of living in the world, defied the greatest empire, army and navy of the age in pledging ‘our lives, our fortunes, our sacred honour’ for the cause of ‘liberty or death’, where the desired outcome was highly improbable by any measure of manpower or available means of material warfare [23].

The problem with sacred values, from an experimental point of view, is that they are difficult to study in the laboratory. Berns et al. [24] describe a novel paradigm in which they use integrity as a proxy for the strength of an individual's commitment to a particular cultural value. Integrity refers to an individual's consistency of values and actions. For example, although we cannot test whether an individual is willing to kill an innocent human being (a common cultural taboo), we can test their willingness to sign a document that says they would. Although signing such a document does not bind the person to that action, it creates an inconsistency between value and action that signals a loss of integrity. It is reasonable to assume that if something is truly sacred, then an individual would maintain their integrity for that value and not sign such a document. What if they were offered money to sign? It then becomes a trade-off between the monetary gain and the cost in personal integrity.

If sacred values are represented in a utilitarian manner, then prior neuroeconomic research suggests that they should be associated with increased neural activity in brain regions associated with the calculation of utility alternatively, if sacred values are represented as deontic rules, then brain regions associated with the processing of moral permissibility (rights and wrongs). Interestingly, Berns et al. [24] find evidence for the deontic processing of sacred values. Moreover, they find that the stronger the deontic processing in brain regions associated with the engagement of rules, the more active an individual tends to be in group organizations. This suggests that groups carry and inculcate cultural rules in the brains of individuals.

Cultural conflict is likely to emerge when the rules and values of one cultural group are substantially different from another, and members of the cultures come in contact with each other. How individuals react depends greatly on the specific context, but the findings in this issue point to generic biological mechanisms. As Berns et al. [24] show, the amygdala—a key structure for physiological arousal—is activated when individuals are presented with statements contrary to their own personal sacred values. Although amygdala activation is not specific for a particular emotional state, it is consistent with heightened arousal. But in a conflict situation, it is most likely a negative emotional state of high arousal. This is important because this is the physiological state associated with ‘fight or flight’. Confronting individuals' sacred cultural values with conflicting ones, places the individuals in a state in which they are more likely to experience ‘moral outrage’ and engage in violence [25].

One constellation of values that appears to acquire sacred status in a variety of different cultural settings, and whose violation often generates moral outrage that can lead to extreme violence, concerns the conception of ‘honour’ [26]. Gelfand et al. [27] discuss the importance of honour in Middle Eastern countries. They find that in Middle Eastern cultures honour is not only a status indicator for individuals, but that it is a transferable resource to immediate family members. Moreover, honour is a shared resource with ‘ripple effects on the extended family, friends and social circles, the community, neighbourhood, tribe and organizations’. When honour is lost through the actions of an individual, the extended community suffers. Thus, there is a strong incentive for the establishment of cultural rules that treat honour as a sacred value. Any perceived violation of the code of honour by those outside the society may be grounds for violence and even war [28], whereas violation by individuals within a culture of honour may be considered an attack upon the moral foundation of the society that merits extreme punishment [29].

4. Enforcement of cultural rules

Social groups that affirm and maintain their identity through cultural rules must also have the means to enforce compliance. Like the primitive drives noted earlier, enforcement mechanisms must be either rewarding or punishing in nature. Rewards for group membership can be explicit through recognition and conferring of status vis-à-vis titles through conspicuous displays of status in the form of material wealth or number of children, for example or indirectly through reciprocal relationships with other members of the group—for example, business deals or marriages. Punishments, on the other hand, diminish social status by taking away the opportunity to reap these rewards. Punishments can be explicit and public, e.g. prison or corporal punishment, or implicit through shunning and loss of relationships within the community, which closes the opportunity to do business or have a spouse.

Huettel & Kranton [30] address this relationship between individuals and their social groups by suggesting a new framework based on ‘identity neuroeconomics’. They adapt the standard expected utility model of decision-making to include a cultural term that interacts with individual utility. In this model, ‘identity utility’ depends on the extent to which one's own and others' actions match prescribed behaviour. Identity utility also depends on the status of one's social group, and the match between the individual's attributes to the ideal of the social group. Whether it is honour or status or material markers of status, their framework suggests ways in which one might measure how culture affects individual decision-making.

Along these lines, the way culture affects the individual can be measured in the laboratory by controlling specific elements of culture. Kishida et al. [31] do exactly this by creating an experimental culture in which status is defined by performance on an intelligence test. In many cultures, intellectual achievement is a marker of status and success, and so this is a reasonable place to start. Specifically, they explore the neural effects of publicly broadcasting this status marker. Behaviourally, they find that broadcasting ranks of intelligence globally depressed everyone's performance, and only a subset of individuals were able to recover. The implication is that broadcasting social rank, whether by intelligence or some other metric, is a powerful tool to both reward and punish culturally sanctioned behaviours. Kishida et al. [31] shows that the biological effect of cultural enforcement may lie in the amygdala. Individuals who are able to inhibit the amygdala, through activation of the left prefrontal cortex, may be relatively immune to cultural norms. If so, this may ultimately shed light on what types of individuals comply with cultural norms, resist them or react violently when the norms are threatened.

5. From differences to conflict

Just because cultures are different does not necessarily mean they will end up in conflict. Thus, while cultural differences may be a facilitating condition for conflict to occur, differences alone are insufficient. The same logic applies to biological differences: the mere demonstration of biological differences between cultural groups does not mean that a conflict will follow. As noted above, cultures manifest a variety of mechanisms to instill and maintain their internal set of beliefs, which, when challenged, set in motion a series of physiological responses that prime individuals for violent action. Who engages in violence and who approaches conflict from the standpoint of negotiation?

Two papers in this issue examine brain responses across cultural groups already in conflict and provide important new insights into the cognitive processes evoked when individuals are forced to consider the perspectives and beliefs of someone that, in other circumstances, might be considered an enemy. The advantage of studying members of groups already in conflict is that they provide a cross-sectional snapshot of both cognitive and emotional responses to established in- and out-groups.

Bruneau et al. [32] suggest that when groups are in conflict, cultural biases serve to further drive the groups apart and prevent reconciliation. They theorize that these biases inhibit the individual's capacity to either mentalize about the states of mind of someone from the conflicting culture or empathize with their pain. Using Arab and Israeli subjects, they examine the neural circuits associated with processing poignant stories of members of the corresponding in- and out-groups. If these longstanding cultural conflicts have resulted in an inability to empathize the pain of the opposing group, then, as Bruneau et al. [32] suggest, this should lead to blunted responses in the brain's pain matrix to depictions of pain in the opposing group. Although a variety of behavioural metrics are consistent with warmer feelings towards the in-group, and less empathy for the out-group, the neuroimaging results suggest a more nuanced explanation.

Responses in brain regions associated with mentalizing were equally large for both Arab and Israeli participants reading about Israeli and Arab targets, but less so for a distant, third-party group (South Americans). This suggests that the brain processes associated with mentalizing have more to do with the salience and proximity of the group rather than ‘friend’ or ‘enemy’ labels. More than these labels, empathic responses may be driven by personal significance. This dovetails with Gelfand's results, suggesting that personal salience can be amplified by the construct of honour, especially as it can be shared.

Another testbed of cultural conflict can be found in the USA between Democrats and Republicans, especially those who have strong party affiliations. As Dodd et al. [5] showed, skin conductance measures suggest differences in arousal to good and bad stimuli, thus setting the stage for a biologically mediated conflict between Democrats and Republicans. Examining the issue directly, Falk et al. [33] focus on brain responses in Democrats and Republicans in the months leading up to the 2008 presidential election. As they note, the election provides a focal point that increases the personal salience of whatever conflict is perceived between members of the two parties. Thus, whatever differences exist between Democrats and Republicans, an election forces them into conflict because only one can win. Falk et al. [33] had Democrats and Republicans consider issues from the stance of their own party's candidate or the other (McCain and Obama). Interestingly, they find that regions associated with mentalizing functions, especially the medial prefrontal cortex, were more active when taking the perspective of one's own candidate. Moreover, the effect was exaggerated in individuals who measured higher on scales of perspective taking. One of the presumed impasses to negotiation between conflicted groups is the inability to see things from the other side. As Falk et al. [33] note, even individuals who exhibit temperaments that are more empathic may deploy this ability selectively—an effect that was amplified as the election grew closer.

If the ability to empathize with, or take the perspective of, someone from an out-group is reflected in the responsiveness of prefrontal circuits, then what about trusting them? Stanley et al. [34] examine neural responses in a ‘trust game’ and how these responses are affected by the race of the individual to be trusted. In the trust game, participants are given an endowment of money, from which they can share with a trustee. Any money sent to the trustee is quadrupled, and then the trustee can either keep it or split the proceeds 50/50. The exchanges are anonymous, except that the participant is shown a picture of the partner's face before deciding how much to send. Racial bias can be measured by the difference in amounts of money sent to black versus white trustees. Stanley finds that the ventral striatum activity correlates with the individual's race bias: this structure was more active when making decisions about individuals from whichever race they trusted less. Although striatal activity is typically related to the expected value of outcomes, growing evidence suggests that the striatum also signals the salience of the action itself [35]. This is consistent with Bruneau's findings that groups in conflict with each other are highly salient to each other.

6. What does it mean?

The 50 years following World War II were a period of modern history that was unprecedented for its constancy in terms of the bipolar rivalry between global secular ideologies, and the dominance of a ‘rational actor’ paradigm for dealing with that rivalry. It seems increasingly obvious that such an era is over. As we noted earlier, cultural differences do not always lead to conflict, but several factors on both a local and global scale have increased the likelihood of conflict. A vastly increased population means more people competing for limited resources, and the globalization of the economy means that local conflicts ripple throughout the world, affecting markets and distribution of raw materials. Modern communication through text messaging, social networking and new Internet technologies ensure that news of conflict spreads almost instantly. Thus, where geographical remoteness previously had a strong role in keeping conflicts local, we are now in the situation where riots in Greece or Mumbai, for example, have immediate global consequences. Consequently, the two basic requirements for the initiation of cultural conflict—substantial differences in beliefs and active challenges to those beliefs—are now done electronically. Physical proximity is no longer a necessary condition for the engagement of the biological requirements for conflict.

Cultural conflicts are not simply the result of different traditions. The proverbial ‘clash of civilizations’ may be less appropriate as a characterization of post-Cold War conflicts throughout the world than a crisis, or even collapse, of traditional territorial cultures. Vertical, generation-to-generation forms of social structure and information hierarchies are breaking down and many, especially the young, are forming their identities in global, media-driven political cultures through horizontal peer-to-peer relationships that ignore historical and spatial constraints [36]. But whereas Internet communication and revivalist religious ideologies may increasingly serve as facilitators and vehicles for conflict, root causes may remain primitive and biologic. Fundamentally, people want to survive, prosper and create a better future for their children and those they care for, including genetic strangers that form part of primary reference groups, be it their tribe, nation, religion or conception of ‘humanity’. When these basic goals are threatened, conflict is more likely.

Many of the papers in this special issue deal with the way in which cultural differences map onto biological differences in the brain. We will set aside the question of causality and take these observations at face value. For example, biological differences in discount rates have direct implications for behaviour. All things being equal, a society in which individuals tend to have steeper discount rates will behave more impulsively. Because the future is worth relatively little, such cultures would resist investing in infrastructure would tend to devalue education would engage in more rapid depletion of their resources and would generally ‘live for the moment’.

Just because there are biological differences does not mean they are immutable. We know, for example, that individual discount rates can be altered by drugs. Unfortunately, most of the documented effects of drugs, such as tobacco, are associated with increased discount rates, making individuals even more impulsive [37]. However, given evidence for the close link between discount rates and foraging behaviour in animals, it is possible that even simple changes in human nutrition would affect an individual's behaviour on a societal scale. Beyond calorie counts, how might different amino acids and fatty acids affect discount rates? Viewed through the lens of biology, dietary choices may be directly related to resource consumption, birthrates and violence simply by the effect of nutrition on the dopamine system and its discount rate for the future.

Another area for future inquiry is the possible effect of sacred values on discount rates. For example, people may perceive temporally distant but culturally significant events to actually feel closer in time than do more recent events, especially in contexts of group conflict: for example, important episodes in religious or national history. This may be especially salient when people visit, or think about, ‘sacred places’ that evoke significant cultural events, such as a hallowed shrine or battlefield. Evocation of these sentiments might have profound biological effects in the form of memory reactivation (good and bad) and physiological arousal, leading to fight or flight responses. Understanding these biological mechanisms helps us understand why one cultural group might be willing to invest in social infrastructure, while another wants to destroy it. Ultimately, biological responses determine who is ready to engage in war, and who wishes to seek peace.

As we begin to unravel the links between culture and biology, we are seeing how culture affects the brain. But what about the other direction? If the biology of the brain is changed, whether through diet, climate, chemicals or, inevitably, genetic engineering, will culture change? If, as we believe, culture and biology are yoked together, then future cultural conflicts will also play out biologically. Some cultures will embrace ways to change their biology and, in the process, change their culture. Others will reject such engineering. As a preview of what to expect, we might look to the conflicts that took place (and are still occurring) over contraception. Almost 100 years ago, Marget Sanger forcefully argued, ‘contraception needs no external justification—it is a civilizing force in itself, and carries with it its own immediate benefits, its own rewards to the parents, to the children, and to the community at large’ [38, p. 536]. The development of the birth control pill in the 1950s, set the stage for a full-blown cultural war over the right of women to control reproductive biology. Downstream cultural effects resulted in more women delaying marriage, going to college and entering the workforce [39]. Future cultural wars, while they may bear familiar labels of religion and politics, will ultimately be fought over control of our biology and our environment. The sooner we understand these relationships, the better position humankind will be in to mitigate these looming conflicts.


Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated commercial fisheries monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Most fisheries are managed as a common (shared) resource even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. The natural outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction.

Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4,000 species—despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.

View a brief video discussing the role of marine ecosystems in supporting human welfare and the decline of ocean ecosystems.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin.

Related Biology Terms

  • Evolution – The gradual change in characteristics or genes within and between species.
  • Competition – The interaction between two or more species that results from both (or all) attempting to exploit a resource.
  • Predation – The process of one animal capturing and feeding on another ‘prey’ animal.
  • Altruism – Behavior of animal that benefits another, either with no benefit or with detriment to the original animal.

1. A symbiosis that benefits one organism and kills the other is:
A. Ammensalism
B. Parasitism
C. Commensalism
D. Dimorphism

2. The interaction between cleaner fish and their hosts is:
A. Resource-resource symbiosis
B. Resource-Service symbiosis
C. Service-service symbiosis

3. In the coral-zooxanthellae symbiosis, the relationship is:
A. Parasitic
B. Facultative
C. Altruistic
D. Obligate

4. What type of symbiosis does ‘commensalism’ involve?
A. Benefits to both partners
B. Benefits to neither partner
C. Benefits to one partner while the other is unaffected
D. Benefits to one partner at the expense of the other

Extreme cost of rivalry in a monandrous species: male–male interactions result in failure to acquire mates and reduced longevity

Mating system variation is profound in animals. In insects, female willingness to remate varies from mating with hundreds of males (extreme polyandry) to never remating (monandry). This variation in female behaviour is predicted to affect the pattern of selection on males, with intense pre-copulatory sexual selection under monandry compared to a mix of pre- and post-copulatory forces affecting fitness under polyandry. We tested the hypothesis that differences in female mating biology would be reflected in different costs of pre-copulatory competition between males. We observed that exposure to rival males early in life was highly costly for males of a monandrous species, but had lower costs in the polyandrous species. Males from the monandrous species housed with competitors showed reduced ability to obtain a mate and decreased longevity. These effects were specific to exposure to rivals compared with other types of social interactions (heterospecific male and mated female) and were either absent or weaker in males of the polyandrous species. We conclude that males in monandrous species suffer severe physiological costs from interactions with rivals and note the significance of male–male interactions as a source of stress in laboratory culture.

1. Introduction

Female mating behaviour varies widely among taxa [1]. The rate at which females remate is a fundamental parameter in evolution and ecology, impacting on disease transmission (e.g. [2]), male/female dimorphism (e.g. [3]), the degree of sexual conflict [4] and potentially the rate of evolution of a species (reviewed in [5]) and its propensity both to speciate (e.g. [6]) and go extinct (e.g. [7]). Within the genus Drosophila alone, species exist where females mate once in their lifetime, and others where females will mate with a different male within 30 minutes of completing copulation [8,9]. These patterns of mating behaviour influence the pattern of selection on males. Where females are monandrous, male reproductive fitness depends solely on pre-copulatory sexual selection (success in acquiring mates), which often involves male–male competition. By contrast, male fitness under female polyandry depends on both pre- and post-copulatory sexual selection, which involves sperm competition and cryptic female choice of sperm [1]. Post-copulatory sexual selection can be intense, driving the evolution of, for example, increased testes size and unusual ejaculate properties [10,11].

Recently, it has been recognized that female mating behaviour may profoundly affect male life history. In Antechinus marsupial mice, synchronous polyandry by females drives intense post-copulatory sexual selection in males, leading to the death of the males within the breeding season [12]. More recently, longevity effects associated with continued mate-seeking behaviour have been observed in Drosophila melanogaster [13]. Males maintained in the presence of female pheromones, but in the absence of a mate, died before males that were sexually satiated or maintained without the stimulus to seek mates.

In this paper, we examined whether monandry might likewise produce strong life-history impacts, where male–male interactions occur over a protracted period, rather than during a confined breeding bout. Our study was motivated by the recent observation that males in the monandrous species Drosophila subobscura mate for twice as long when previously housed with rival males [14]. Previous work has demonstrated that increases in copulation duration can represent an adaptive response to the risk of sperm competition (reviewed in [15]). However, this explanation is unlikely to apply to the generally monandrous D. subobscura [16]. It was proposed that the effect in D. subobscura may instead derive from poorer condition of males that had been subject to social interactions. For instance, increasing male age is known to be associated with increased copulation duration in flies [17]. We reasoned that social interaction may be producing a similar effect to ageing in male D. subobscura.

Because condition is an important determinant of male ability to provide nuptial gifts and gain matings in D. subobscura [18], we predicted that the impact of prior social interactions may go beyond copulation duration, and be reflected in an array of traits. To this end, we examined the impact of social environment on a male's ability to acquire matings and on longevity. We compared social environment effects across two Drosophila species: the monandrous D. subobscura, and the closely related polyandrous species Drosophila pseudoobscura [16,19,20]. As males of a monandrous species are only subjected to pre-copulatory sexual selection while males of polyandrous species are subjected to both pre- and post-copulatory sexual selection, we expected that the presence of rivals before copulation would have a more profound impact on the fitness (reproductive success and survival) of males of the monandrous species than the polyandrous one.

2. Material and methods

(a) Species examined and mating procedure

Multi-female lines of D. subobscura (initially established from nine inseminated wild females from British Columbia) and D. pseudoobscura (N = 100) were collected in 2008 from Vancouver Island (British Columbia, Canada) and Show Low (AZ, USA), respectively. Flies were maintained in large outbred populations in a humidified room at 21°C with a 12 L : 12 D photoperiod, on standard corn–sugar–yeast–agar medium (ASG medium). Experimental adult flies were raised at standard densities of 50 larvae per vial and isolated as virgins within 24 h of eclosion. Females were kept at a standard density of five per vial. Males were kept in a vial in the conditions described later in the methods. Experiments were performed at 21°C.

(i) Experiment 1: male response to social environment

Previous work showed that the presence of a single rival affected copulation duration in both species [14,16,21]. Here, we examined the specificity of the male response to rivals by exposing males to various social environments.

For each species, males were placed either individually (treatment ‘single’), or with one rival male (treatment ‘one rival’), four rival males (treatment ‘four rivals’), one heterospecific male (treatment ‘heterospecific’) or one conspecific mated female (treatment ‘mated female’), from within 8 h of eclosion to 8 days old (N total D. subobscura: single = 126, one rival = 152, four rivals = 99, heterospecific = 57, mated female = 63 N total D. pseudoobscura: single = 58, one rival = 56, four rivals = 41, heterospecific = 19, mated female = 16). Numbers of trials were higher for D. subobscura to reduce the risk that the lower mating rate in this species would reduce the number of matings below which reasonable analysis of copulation duration and latency was difficult. It was also partly owing to the difficulty of synchronizing eclosion of the two species. ‘Heterospecifics’ corresponded to a D. pseudoobscura male for D. subobscura and vice versa. The females used to alter social environment in the ‘mated female’ treatment were mated a day before exposure they were conspecific and the same age as the males tested. As D. subobscura females are monandrous [16], they were thus inaccessible to the tested male. However, D. pseudoobscura females typically remate after 5 days, and so it is likely that they will have mated with the experimental male. This means that the experimental D. pseudoobscura male for the ‘mated female’ treatments would not have been a virgin. Moreover, the relatively low sample size for the D. pseudoobscura trials investigating the impact of heterospecific males and mated females also means that the results need to be interpreted cautiously. Conspecific and heterospecific males were right or left wing-clipped at emergence to allow distinction (the clipped wing was randomized across replicates).

After the exposure period, the male was placed in a vial into which a single virgin female was then added. Where males were exposed to multiple conspecific males, only one male was randomly chosen from each vial to avoid pseudoreplication. Sexual partners had a 3 h window to copulate, mimicking their natural ecology. This procedure was followed for all treatments detailed above. Male responses to treatments were assessed by measuring their propensity to acquire a mate (proportion mating) (N mated males D. subobscura: single = 97, one rival = 64, four rivals = 26, heterospecific = 38, mated female = 39 N mated males D. pseudoobscura: single = 53, one rival = 53, four rivals = 39, heterospecific = 18, mated female = 14). For each mating observed, we also recorded copulation latency (time from male introduction into a female vial until mating occurred) and copulation duration.

(ii) Experiment 2: the effect of rivals on male ability to compete for a female

Males were either kept singly (‘single’ males) or exposed to ‘four rivals’ as described above, before being placed in competition for female access in the arena of mating. To this end one ‘single’ and one ‘four rival’ male were placed in each vial prior to adding one virgin female (ND. subobscura: 24 ND. pseudobscura: 40). The success of ‘four rivals’ and ‘single’ males in acquiring the female as a mate was then scored. Copulation latency and duration were also recorded for each mating.

(iii) Experiment 3: effect of exposure to rivals early in life on male longevity

Males were either kept singly (‘single’ males) or exposed to ‘four rivals’ as described above. After the exposure period, males were isolated (for the ‘four rivals’ males) and transferred to a new fresh vial (ND. subobscura: singlelongevity = 40, four rivalslongevity = 37 ND. pseudobscura: singlelongevity = 35, four rivalslongevity = 40). Every Monday, Wednesday and Friday, the number of dead males in each group for each species was recorded. Live males were transferred to a new fresh vial of food weekly until all males died. This experiment was run from mid June 2012 to mid November 2012. Longevity assessments were performed at 18°C for D. subobscura and 21°C for D. pseudoobscura.

(b) Relevance of the methods to the ecology of the species

Conditions used here are likely to approximate situations experienced by these flies in nature. The two species inhabit the same forests on Vancouver Island [22], almost certainly interacting on breeding sites. Our rival/no rival conditions are likely to occur to flies in nature as local density and sex ratio can be highly variable in both species (ranging from intense male–male interactions to almost complete absence of rivals) [23,24]. Mating trials in vials do increase the likelihood of copulation occurring during an interaction, but the impact is modest (female flies provided with a refuge have a 20% lower mating rate) [25]. Both species are crepuscular, with mating typically occurring at 21°C during a few hours around dusk and dawn [23,24]. However D. subobscura is less tolerant to high temperatures than D. pseudoobscura, so we used 18°C for the D. subobscura longevity trials.

Drosophila subobscura females mature at 8 days post eclosion, with males maturing at 2–3 days [26]. Drosophila pseudoobscura females mature at 3 days post eclosion, and males at 1–2 days [26]. Both species have a highly male-biased operational sex ratio, owing to monandry in D. subobscura [16], and a 3–5 day female remating latency in D. pseudoobscura [22]. Both species can live for three months in ideal laboratory conditions [27], but are much shorter lived as adults in nature [28,29]. Assuming an 8% death rate in nature as measured for D. pseudoobscura, 40% of flies will die within a week of eclosion, which is relevant to the mating ages we use for both species. Our longevity study probably overestimates longevity, but longevity is frequently used as an indicator of stress occurring at a younger age in Drosophila [30].

(c) Statistical analysis

All statistical analyses were performed using v. R 2.12.1 [31]. Data on the proportion of males copulating were analysed using a generalized linear model (GLM) procedure assuming a binomial error distribution with a logit link function. Copulation latencies and duration data were tested for normality using Shapiro tests, and for variance heteroscedasticity using Bartlett tests, and they were non-normally distributed. A range of transformations was tried, with copulation duration normalized by Ln transformation, and copulation latency normalized by log 10 transformation. The transformed data were then analysed using a GLM procedure assuming a normal distribution with an identity link function [32]. Differences in responses under different treatments were assessed by analysis of variance (ANOVA) followed by a Tukey HSD test. Mating success in two male mating trials was evaluated using an exact binomial test. Cox proportional-hazard regressions were used to assess variation in longevity for ‘single’ males and for ‘four rivals’ males. Survival analysis involves the modelling of time to event data, with death (the hazard function) being considered the ‘event’, so that each death corresponded to one ‘event’ modelled against time with treatments (‘single’ or ‘four rivals’) as factor (using the Survdiff function).

3. Results

(a) Experiment 1: male response to social environment

We first examined the effect of social environment on the ability to acquire a mate in the absence competition. We observed that exposure to ‘one rival’ or ‘four rivals’ significantly reduced male ability to acquire a mate in the monandrous species, D. subobscura (figure 1a electronic supplementary material, table S1a). In this species, exposure to one or more rivals led to a nearly threefold reduction in male ability to acquire a mate compared with ‘single’ males. The other types of social environment had an effect comparable with the ‘single’ male treatment (electronic supplementary material, table S1a). By contrast, there was no difference among treatments in male ability to acquire a mate in D. pseudoobscura, to gain a mating (figure 1b electronic supplementary material, table S1b).

Figure 1. Probability of successfully mating when alone with a female for (a) D. subobscura and for (b) D. pseudoobscura, when males were kept singly (single) or with one rival (one rival), four rivals (four rivals), a heterospecific male (heterospecific) or a mated female (mated female) prior to copulation. Different letters represent significant differences within each graph. For statistical results, see the electronic supplementary material, table S1a,b.

Any type of social environment increased copulation latency in D. subobscura compared with ‘single’ males (figure 2a electronic supplementary material, table S2a). By contrast, exposure to a ‘heterospecific’ male or ‘mated female’ increased copulation latency in D. pseudoobscura compared with ‘single’ males and to ‘one rival’ males, while exposure to ‘four rivals’ had no effect (figure 2b electronic supplementary material, table S2b).

Figure 2. Copulation latency (mean ± s.e) for (a) D. subobscura and (b) D. pseudoobscura when males were kept singly (single) with one rival (one rival), four rivals (four rivals), a heterospecific male (heterospecific) or a mated female (mated female) prior to copulation. Different letters represent significant differences within each graph. For statistical analysis, see the electronic supplementary material, table S2a,b.

In D. subobscura, exposure to a rival increased copulation duration as previously reported, but this increase was even stronger following exposure to ‘four rivals’, whereas exposure to a ‘heterospecific’ male had no effect on copulation duration (figure 3a). However, exposure to a ‘mated female’ increased copulation duration to the same extent as exposure to ‘one rival’ did (electronic supplementary material, table S3a). By contrast, the effect of additional rivals was not profound in D. pseudoobscura (figure 3b). The null hypothesis that a single rival affected copulation duration was not rejected, while exposure to ‘four rivals’ did increase copulation duration. As in D. subobscura, exposure to a ‘heterospecific’ male had no effect on copulation duration, but exposure to a ‘mated female’ significantly decreased copulation duration (electronic supplementary material, table S3b).

Figure 3. Copulation duration (mean ± s.e) for (a) D. subobscura and (b) D. pseudoobscura when males were kept singly (single), with one rival (one rival), four rivals (four rivals), a heterospecific male (heterospecific) or a mated female (mated female) prior to copulation. Different letters represent significant differences within each graph. For statistical analysis, see the electronic supplementary material, table S3a,b.

(b) Experiment 2: the effect of rivals on male ability to compete for a female

Competition assays revealed that males of both species which had been exposed to rivals before copulation were less successful in acquiring matings when in competition with ‘single’ males. In the monandrous species D. subobscura, the male exposed to ‘four rivals’ was successful in only two of 24 trials (8.33%, exact binomial test: p = 0.001). The male exposed to ‘four rivals’ were also less successful in the polyandrous species D. pseudoobscura, but the effect was smaller, with males exposed to ‘four rivals’ successfully mated in 11 of 40 trials (27.5%, exact binomial test: p = 0.006).

(c) Experiment 3: effect of exposure to rivals early in life on male longevity

Exposure to rivals during the first 8 days of life significantly decreased the longevity of males of the monandrous species (D. subobscura) (Survdiff p = 6.84×10 −11 ) (figure 4a) but not of males of the polyandrous species (D. pseudoobscura) (Survdiff p = 0.264) (figure 4b).

Figure 4. Longevity represented as proportion dead of males over time (in days) for (a) D. subobscura and for (b) D. pseudoobscura, when males were kept singly (single: triangles) or with four rivals (four rivals: circles) for 8 days after having reached sexual maturity.

4. Discussion

For males in a monandrous species, the fitness benefit of a single mating is very high. This generates strong competition for mating opportunities, and high level of investment in obtaining matings, as reflected in adaptations such as provision of nuptial gifts. We predicted that presence of one or more rival males in monandrous species would lead to costs associated with this competition. Our results demonstrated that these costs are profound, with prior exposure to rivals associated with decreased ability to obtain matings, and reduced longevity. Furthermore, these costs are greater in the monandrous D. subobscura than in the polyandrous D. pseudoobscura. Although based on a comparison of only two species, the result is consistent with the hypothesis that pre-copulatory male competition should be vital to male success in monandrous species, and so be associated with significant effort and costs.

Previous studies in Drosophila have demonstrated a cost of sex, in that individuals that mate more frequently die younger (e.g. [30,33]). In D. melanogaster, there is also a longevity impact in males associated with mate-seeking and courtship activity [13]. Our results demonstrate that there is also a direct cost of intrasexual social interaction in the monandrous species D. subobscura, even in the absence of mate finding, courtship and sex. Thus, intrasexual social interaction intensity should be accounted for as one of the major factors associated with reproduction that affect longevity.

Sexual selection leading to ‘suicidal reproduction’ in males has been demonstrated in the Australian redback spider, where cannibalized males manipulate female behaviour to increase paternity [34]. Very recently, this has also been observed in semelparous marsupials, where females manipulate male behaviour to increase their own reproductive success [12]. Males in these species increase mating effort at the expense of survival, not because adult male or female survival is low for environmental reasons or because males are altruistic, but ultimately because females profit from sperm competition and their remating behaviour selects for males that invest all their reserves into mating effort [35]. In these two examples, the reproductive system is polyandrous, with females remating with several males. Our results demonstrate that even in monandrous species, pre-copulatory sexual selection may lead to male behaviours that severely impact upon their longevity.

There are two possible explanations for why males of monandrous species would have their reproductive ability heavily reduced when exposed to rivals. First, pre-copulatory male–male interactions may be more intense in monandrous species. The increased effort involved in this competition may be reflected in more profound effects on physiological condition, reducing their ability to seek matings. Second, monandry is associated with increased choosiness of females in mating, and increased probability of a virgin female rejecting a male [10,30]. If exposure to rivals impacts on male condition, this reduction in condition may drastically reduce his mating success in the face of highly selective monandrous females. Evidence for increased effects of rivals on condition derives from the profound longevity impact of housing with rivals. Evidence for differential choosiness is suggested by the requirement for female D. subobscura to be provided with nuptial gifts [18], and the lower acceptance rate by D. subobscura females than D. pseudoobscura females even for males kept alone (77 versus 91%, respectively).

Previous work on polyandrous species highlighted the adaptive benefits of plasticity in mating duration following exposure to a rival (reviewed in [15]). We observed that plasticity in mating duration was most profoundly observed in D. subobscura, a monandrous species where there is little or no sperm competition [14,16]. The general deterioration in male condition following housing with rivals provides the most parsimonious explanation for the prolonged copulation duration following exposure to rivals in D. subobscura. In other words, exhausted D. subobscura males mate for longer and die earlier. Fatigue also increases the length of copulation in the wolf spider [36]. Our favoured hypothesis is that rival presence may impact on sleep patterns. Sleep is essential for longevity in D. melanogaster [37]. In our experiment, exposure to rivals led to increased aging rate in this monandrous species, which could indirectly be caused by shortened periods of sleeping. To our knowledge, the results presented in this study are the first to demonstrate a link between exhaustion induced by social interactions, reproductive deficiency and decreased longevity. Our results also imply that plasticity in mating duration can have both adaptive (sperm competitive advantage) and non-adaptive (exhaustion) causes. Thus, selection for plasticity in mating duration may be driven by more complex forces than simply for increasing male success in sperm competition.

In this study, the results for D. pseudoobscura are similar to those in previous published studies, with exposure to a rival increasing latency to mating and copulation duration [21]. However, we found little evidence that exposure to four males had a greater impact on male mating behaviour than exposure to a single rival. This has also been observed in D. melanogaster [38] and is predicted by theory on risk and intensity of sperm competition [39]. The data on response by males to exposure to a previously mated female has to be interpreted cautiously, because focal males are likely to have remated with this female. Drosophila pseudoobscura females typically remate after 4 days [20], and so are likely to have mated with the focal male at least once. Males of this species can mate with three females a day, each day for several days without any loss of ability to mate [40], so the impact of this may have been minor. More detailed experiments would be needed to fully understand the impact of the presence of females on subsequent male mating behaviour in this species.

Our data provide support for the notion that social environment (presence of rivals) has a large impact on condition in a monandrous species. The data are notable because D. subobscura is commonly used as a model of stress tolerance in nature [41–43]. However, stress tolerance studies in this species have focused on thermal effects on genetic and phenotypic polymorphisms of wings and desiccation resistance [43–45]. Our data suggest that experimental analysis of stress impacts should both control and incorporate social environment in their design.

In conclusion, we find remarkably strong impacts of social environment on the ability of males to obtain mates, on their ability to compete with rivals, and on their longevity. These impacts are far stronger in a monandrous species than in a polyandrous relative, which is likely to reflect the importance of pre-copulatory success in monandrous species. We suggest that mating system can be used to predict the costs of social interactions in a species, and this could be useful for the design of effective laboratory studies, and potentially for animal husbandry for conservation or human use.

Symbiotic and Antagonistic Relationship between Two Species

Inter-specific relationships between two (or more) species can be discovered in any community and belong to two main categories —symbiosis and antagonism.

Symbiotic Relationships:

Symbiosis means ‘living together’. It is a beneficial relationship between two different species in which one or both the species are benefited and neither species is harmed.

Symbiotic relationships include commensalism (one species benefited, another called host not affected), proto-cooperation the species are benefited, the relationship is favourable to both but not obligatory) and mutualism (both the species or symbionts are benefited, the relationship is favourable to both and obligatory).

Commensalism occurs when one species is benefited from a symbiotic relationship. All communalistic relationships are facultative, as the commensalism neither harm nor help their hosts: die hosts also appear neither to resist nor to foster the relationship in any way. Examples of commensalism showing more or less continuous contact with the host are offered by a great variety of epiphytes and epizoans. All epiphytes use trees only for attachment and manufacture their own food by photosynthesis.

In Vanda, an epiphytic orchid, special kind of aerial roots hang freely in the air and absorb moisture with the help of their special absorptive tissue called velamen. Sessile invertebrates that grow on plants or other animals represent many permanently fixed commensals. For example, hydroids like Hydractinia live as commensals on the gastropod shells occupied by crabs.

Barnacles attached to the skin of whales provide another example, an association, which provides wider distribution and feeding opportunities for the sessile crustaceans. Examples of commensalism without continuous contact also occur.

An interesting example of a commensal living within its host is that of a small tropical fish, Fierasfer. This species finds shelter in the doaca of a sea cucumber, moving out for food and returning to the cloacal cavity at its own will. Tie suckerfish, Echeneis, attaches to the underside of a shark, thereby securing protection, wide pro-graphical dispersal and scrapes of food. The shark neither benefits nor suffers in any respect.

Protocooperation is a relationship between two species, which is favourable to both but not obligatory. The association of a crab and a coelenterate shows an interesting example of potocooperation. The sea anemone, Adamsia palliata, grows on the back of the hermit crab, Eupagurus prideauxi, or is sometime ‘planted’ there by the crab. It protects the crab with the help of its nematocysts that prevent the approach of predatory fish, which feed on the crab.

The sea anemone is transported by the crab from place to place and obtains particles of food when the crab captures and eats another animal. In this case the crab is not absolutely dependent on the coelenterate, or vice-versa. Hence the association, through favourable to both, is not obligatory for their existences.

Mutualism occurs when both the species benefit from a symbiotic relationship. Mutualism may be facultative, where the species involved in the association can exist independently. It may be obligatory, where the relationship is imperative to the existence of one or both the species. Mutualism may occur between two animal species, between two plant species, or between animal and a plant species. An example of obligatory mutualism between two animal species, without continuous contact, is the association between aphids and dairy ants (Fig. 2.2).

Dairy ants keep the tiny green aphids (plant lice) as food suppliers. Aphids secrete honeydew, a sugar and protein mixture, on which the ants depend. A common species of garden ant, for example, places aphids on the roots of com. Aphids feed there and the ants thereafter “milk” these “ant cows” by gently stroking them. At the approach of winter the aphids are carried into the ant nest and are put back on com roots the following spring. Thus, ants obtain food from the aphids, and the aphids in turn secure protection, food and care from the ants.

Lichens such as Graphis, Parmelia and Cladonia exhibit a more intimate form of mutualism between two plant species. Each lichen is a symbiotic association between a fungus and an alga. In many species of lichens, the algal symbiont is Trebouxia. The algae manufacture food for themselves as well as for the fungus. The fungus in turn contributes water and carbon dioxide that enable the alga to synthesize food. If they are separated from their association, they lead a precarious life, more particularly the fungus.

Nitrogen fixing mutualistic bacteria of the genus Rhizobium infects the roots of many leguminous plants. They enter the roots through the root hair and the infected root cells respond by developing root nodules (Fig. 2.3). In these root nodules, the host plant provides nutrients for the bacteria and the bacteria in turn contribute fixed nitrogen to the host plant, which becomes independent of supplies of nitrogen from the soil.

There are many examples of symbiotic mutualism between an animal and a plant species. In green hydra, Chlorohydra viridissima, the cells of gastrodermis contain many unicellular algae, oochlorellae, which are transferred by the host eggs from one generation to another. The algae supply food and oxygen, and in turn receive protection, water and other materials essential for continued photosynthesis.

Pollination of flowers by insects is yet another manifestation of plant animal mutualism. In many cases, the relationship between the insect mouth parts and the shape the flower is complimentary with an adaptation to each other. For example, bee- pollinated s, such as Orchidaceae, usually have zygomorphic flowers.

These are tubular, so the bee can adjust itself to the flower shape and then push its head into the flower. Similar adaptations occur butterfly and moth- pollinated flowers and pollinator’s mouth parts. Interdependence of the yucca moth, Pronuba yuccasella, and the yucca flower is very fascinating. These are co-evolutionary relationships. In some cases flower species have coevolved to avoid competition among themselves flowering at different times of the year, or by attracting different species of insect as their pollinator.

Antagonistic Relationships:

The antagonistic relationships are manifested through parasitism, predation, competition and antibiosis between two different species. Parasitism is a relationship in which one species (parasite) is always benefited at the cost of other species (host). A parasite derives nourishment from the host and in many cases finds protection and living space on or inside the host.

The host is usually larger than the parasite and 1 efficient parasite does not kill its host. Many parasites require a secondary host for dispersal completion of their life cycle. For example, mosquito species serve as vectors for the protozoan malaria parasite, Plasmodium. Animals that become infected and serve as a source from which animals can be infected are known as reservoir hosts. Animals may also be parasitic on plants.

Nematodes infest the roots of plants. Wasps or gnats, especially on oak, roses form galls. A variety of insect larvae are leaf miners, wood borers, cambium feeders, and fruit eaters. Plants themselves may be parasites either on other plants or on animals. Bacteria and fungi are among the most important disease-producing organisms in animals.

Filamentous bacteria, Actinomycetes are chiefly decomposers in the soil. Some of them produce chemicals to reduce severe competition for food from other microbes. Man in combating several bacterial diseases uses these chemicals called antibiotics (e.g., streptomycin). Some basidiomycetes such as Puccinia graminis and Ustilago maydis produce rust of wheat and smut in com respectively.

Parasitic adaptations are too many and beyond the scope of this treatise. The size of the parasite also influences its mode of reproduction. The host-parasite relationships have great ecological significance and are influenced by a number of environmental factors. The density of host population also affects the parasite population density.

The term predation is generally used to describe the killing and eating of one species by mother. Typical predation occurs when a carnivore kills a herbivore or another carnivore for food. The study of prey-predator relationships is very fascinating and examples of this relationship may be discovered in many natural communities.

Allelopathy or chemical competition occurs when one organism uses chemicals to cause harm 10 another. This phenomenon is widely reported in terrestrial plants (Seigler, 1996). The occurrence of chemical competition has also been reported in aquatic plants (Gopal and Goel, 1993). In general sense, allelopathy means causing of injury (pathy) to other organisms (allelo) by chemical means, but it can be more complex.

For example, a common alga, Chlorella, produces a bactericide that not only kills bacteria but also retards the growth of Daphnia, which feed on Chlorella. A chemical produced by a diatom, Nitzschia, slowed the division rate of Chlorella grown in the same culture. This type of interspecies antagonism probably exerts control on the abundance of different phytoplankton species in water bodies, and in some cases may influence the seasonal succession of species, so common in nature.

There are many examples of chemical interaction among crop plants. Barley, Hordeum vulgare may inhibit germination and growth rate of several weeds, even in the absence of competition for nutrients or water. Allelopathic effects of crop plants against weeds, called heterotoxicity, may be of great benefit in agricultural systems.

Some researcher suggested that the abundant oils in the leaves of eucalyptus trees in Australia promote frequent fires in the leaf litter, killing the seedlings of competitors. The study of allelopathic agents is currently a very active field in plant ecology, and it is too early to say how much the distributional patterns of plants are determined by interactions involving toxins or antibiotic substances.

Competition is another manifestation of antagonistic relationship. Competition may occur among species and between species. However, in nature competition may not be always apparent although it is occurring. Increased growth rate of some tree species after the removal of other species provides direct evidence of competition for water, light and nutrients. Individuals of the same species may compete for food, living space and mate. Competition for food also applies to animals of different species that depend on the same type of food.

Competition may result in death of some competitors, but this is usually from fighting or being deprived of food rather than being killed for food as in predation, or by disease as in extreme parasitism. The severity of inter-specific competition depends on the extent of similarity or overlap of resource requirements of different organisms and the shortage of supply in the habitat. Such a competition may have several effects on the populations of competing individuals.

Schoener (1983) divided competition into six categories. These are consumptive competition (based on the utilisation of some renewable resource), pre-emptive competition (based on the occupation of open space), overgrowth competition (occurring when one organism grows over another thereby depriving it of light, water, or some other resource).

Chemical competition (by production of a toxin acting at a distance), territorial competition (defense of territory), and encounter competition (involving transient interactions over a resource resulting in loss of time or energy, physical harm, or theft of food).

These competition mechanisms are defined in terms of the capabilities of organisms and the habitats in which they occur (Ricklefs and Miller, 2000). In terrestrial environments, consumptive competition is most common. However, pre-emptive and overgrowth competition are more common in marine habitats. Territorial and encounter con-petitions occur only among animals of all habitats, predominating in terrestrial ones.

Darwin emphasized that competition is usually most intense between closely related species or organisms. As they have similarity in structure and habits, the competition is more severe among species of the same genus than between species of different genera. Substitution experiments, developed by Wit (1960), are helpful for studying plant competition. In such experiments, ratios of two plant species are varied, but their total density is kept constant.

The results are portrayed on replacement series diagrams showing the relative strengths of inter-specific and intra-specific competition. Experimental work with agriculture crops suggested these competitive interactions are very acute in field populations. Experiments with oats (Avena) and other plants have demonstrated strong asymmetry in inter-specific competition.

It is the most critical factor confining a species to a particular niche. According to the competitive exclusion principle of Gause (1934), stabilised populations of more than one species cannot simultaneously and completely occupy an ecological niche. Thus, inter-specific competition results in the segregation of species into different niches.

When two populations compete, it is likely that one of them is more strongly affected by competition than the other. This is called asymmetrical competition. In plants, root competition for nutrients and water is generally symmetrical, whereas shoot competition for light is asymmetrical. Examples of asymmetrical competition are available in animal kingdom also (Resetarits, 1997).


There is a developing, if nascent, interest in invasive species research that goes beyond individual managers and their practices to examine the relationships between various actors in invasive species management and the diverse configurations of collective action they form. Our typology, which extends similar efforts by Epanchin-Niell et al. ( 2010 ), Marshall et al. ( 2016 ), and Uetake ( 2013 ), demonstrated the diversity of approaches to collective action. These approaches have reoriented invasive species policy, institutions, and management away from a narrow focus on educating and assisting individual managers and enforcing invasive species regulations on individual properties to more holistic, multiscalar, cross-boundary, and collaborative efforts. In a broad sense, the works we reviewed made valuable contributions to conceptualizations of contemporary environmental management problems (including invasive species) that are defined by complexity and uncertainty and require inclusive, adaptive solutions (Woodford et al. 2016 ). Interorganizational and intersectoral collective action strategies have become more common, both as a policy tool for governments and as a means for organizations and resource managers to increase capacity, scope, and efficiency.

The articles reviewed provided insight for those seeking to enhance collective responses to invasive species. Local ownership (e.g., Lachapelle & McCool 2005 ) and capacity, social and financial, were critical for collective responses to endure, especially in instances where external support was high, but not assured in perpetuity. Financial capacity was important, but not sufficient for success. For example, collective efforts thrived when supported by normative beliefs among managers and stakeholders that invasive species ought to be controlled and that others were making investments to do so. Agencies or community leaders can elevate these normative beliefs with simple tools such as yard signs, public commitments, and participatory mapping (Niemiec et al. 2016 ) or existing communication networks. Across articles, collective responses were enhanced when stakeholders appreciated the cross-boundary nature of the problem, were aware of the benefits that might arise from coordinated action, and were presented with achievable goals. Where organizations collaborated, clear problem definitions and roles of collaborators fostered more successful responses. Efforts to enhance these contextual factors are likely to boost collective invasive species control.

Although some of the invasive species collective action research reviewed was linked to broader CPR theory, in most cases these links remained opaque. Most articles discussed factors commonly associated with successful CPR collective action including norms and social capital, shared knowledge of the socioecological system, monitoring, and third-party sanctioning (Tables 2 & 3). However, other factors identified as centrally or contextually important for effective CPR collective action, such as collective choice arrangements, low-cost conflict-resolution mechanisms, and collective-choice rules, received less attention (Tables 2 & 3). Thus, there is significant scope for invasive species research to engage more substantively with CPR collective-action theory and to clarify the type of collective-action problems that exist with respect to invasive species and under what circumstances.

Invasive species management research could benefit from more deliberate engagement with PG theory and literature. Most reviewed articles uncritically engaged CPR theory in their discussions about the need for collective action in invasive species management. Our findings suggest that although some elements of CPR theory are relevant and applicable to collective control of invasive species, others have been confounded with PG-specific characteristics and dynamics (i.e., establishing clear boundaries and number of users), and some may be incompatible (i.e., agencies or organizations monitoring and sanctioning individual behavior). More research is needed to explore and detail the aspects of CPR and PG theories that are complimentary when used to investigate collective responses to invasive species, which are contradictory, and, in cases of the latter, which is more fruitful. The relevance of these questions likely extends beyond invasive species control to other environmental resources.

Invasive species control represents a complex, interjurisdictional challenge that demands a range of collective actions linking diverse actors at various scales. This collective action requires a diversity of expertise that is functionally linked as an integrated system of management or mitigation. Thus, questions regarding the diverse forms of interactor collective action for invasive species management become highly germane. There is a need to better understand, connect, and model the conceptual foundations, forms, and actions of such collectives as a form of environmental network governance (Lubell et al. 2017 ).

Based on the results of our review, a key aim for the development of invasive species policy and governance should be to facilitate collective action between and among landowners, organizations, and government agencies to achieve management objectives at various scales. The legislative and policy foundations of invasive species management have remained largely unchanged, and there is a mismatch between their focus on individual-level action and the complex, transboundary nature of invasive species and their management. There is considerable scope for future research on invasive species management to explore how policy and practice can more substantively draw on, be evaluated through, and contribute to rich bodies of existing theory and knowledge concerning environmental governance and collective action to empower effective responses to invasions and realize desired ecological outcomes.

Historical GDP and population data were obtained from the World Bank Databank (, and forecasted values are accessible through the IIASA SSP database ( Data on inter-country distance, trade agreements, common language, common border and common colonial history are obtainable through the CEPII research centre’s GeoDist and Gravity datasets ( Data on historical ballast releases can be accessed through the NBIC Database ( Current and forecasted environmental variables used in this study are available from the AquaMaps Environmental Dataset ( Data on ship movements and attributes were purchased from IHS Sea-web, are used under license and cannot be publicly shared by the authors. However, these data can be purchased from IHS (

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Defining and recognizing a species has been a controversial issue for a long time. To determine the variation and the limitation between species, many concepts have been proposed. When a taxonomist study a particular taxa, he/she must adopted a species concept and provide a species limitation to define this taxa. In this paper some of species concepts are discussed starting from the typological species concepts to the phylogenetic concept. Positive and negative aspects of these concepts are represented in addition to their application.