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The estimated number of species on Earth, as reported in this article is around 8.7 million. I am fascinated by how nature produces such a wide variety of species.
As per my understanding, many species have gone extinct, that is, were not able to adapt to changing conditions on Earth. Perhaps the number of species before few thousands of years were larger than today. Can we estimate the approximate number of species at a given point in the past, using available data?
according to the National Science Foundation press release"Species Have Come and Gone at Different Rates than Previously Believed" indeed show what Atl LED suggests, that the progression is not linear, with the study showing that:
The previously thought exponential increase in diversity is not there.
Further, there is the "Palaeobiology Database, that
seeks to provide researchers and the public with information about the entire fossil record.
The site also has links to further papers of the topic.
How Many Species on Earth?
Eight million, seven hundred thousand species! (Give or take 1.3 million.)
That is a new, estimated total number of species on Earth—the most precise calculation ever offered—with 6.5 million species found on land and 2.2 million dwelling in the ocean depths.
Until now, the number of species on Earth was said to fall somewhere within the large range of 3 and 100 million.
The new study, published yesterday in the open access journal PLoS Biology, says a staggering 86% of all species on land and 91% of those in the seas have yet to be discovered, described and catalogued.
Says lead author Camilo Mora of the University of Hawaii and Dalhousie University in Halifax, Canada: “The question of how many species exist has intrigued scientists for centuries and the answer, coupled with research by others into species’ distribution and abundance, is particularly important now because a host of human activities and influences are accelerating the rate of extinctions. Many species may vanish before we even know of their existence, of their unique niche and function in ecosystems, and of their potential contribution to improved human well-being.”
“This work deduces the most basic number needed to describe our living biosphere,” says co-author Boris Worm of Dalhousie University. “If we did not know—even by an order of magnitude (1 million? 10 million? 100 million?)—the number of people in a nation, how would we plan for the future? It is the same with biodiversity. Humanity has committed itself to saving species from extinction, but until now we have had little real idea of even how many there are.”
The team refined the estimated species total to 8.7 million by identifying numerical patterns within the taxonomic classification system (which groups forms of life in a pyramid-like hierarchy, ranked upwards from species to genus, family, order, class, phylum, kingdom and domain).
Analyzing the taxonomic clustering of the 1.2 million species today in the Catalogue of Life and the World Register of Marine Species, the researchers discovered reliable numerical relationships between the more complete higher taxonomic levels and the species level.
Carl Zimmer explains the method in his Discover blog, The Loom:
The method is based on Linnean taxonomy. While we have lots of new species left to find, we may have found most of the classes, orders, and phyla. It turns out that for a number of groups–mammals, birds, and so on–the numbers of each of these rankings rise as you descend the hierarchy.
(See the graph above, courtesy of the Census of Marine Life, via The Loom.)
(In case you lost track… Organisms in the eukaryote domain have cells containing complex structures enclosed within membranes. The study looked only at forms of life accorded, or potentially accorded, the status of “species” by scientists. Not included: certain micro-organisms and virus “types,” for example, which could be highly numerous.)
But not everyone buys into this calculation. First of all, it doesn’t include the entire picture of life, according to Nature News.
The method does not work for prokaryotes (bacteria and archaea) because the higher taxonomic levels are not well catalogued as is the case for eukaryotes. A conservative ‘lower bound’ estimate of about 10,000 prokaryotes is included in Mora's total but, in reality, they are likely to number in the millions.
Jonathan Eisen, an expert on microbial diversity at the University of California, Davis, said he found the new paper disappointing.
“This is akin to saying, ‘Dinosaurs roamed the Earth more than 500 years ago,’ ” he said. “While true, what is the point of saying it?”
But one of their biggest fans, the well-respected Lord Robert May of Oxford, past-president of the UK’s Royal Society, published a commentary adjacent to the study, praising the researchers’ “imaginative new approach.”
Random Sampling Technique
A technique called sampling can be used to estimate population size. In this procedure, the organisms in a few small areas are counted and projected to the entire area. For instance, if a biologist counts 10 squirrels living in a 200-square foot area, she could predict that there are 100 squirrels living in a 2000 square foot area. This is a simple ratio.
2. A biologist collected 50 liters of pond water and counted 10 mosquito larvae. How many larvae would you estimate to be in that pond if the total volume of water in the pond was 80,000 liters? Show work.
3. What are some problems with this technique? What could affect its accuracy?
|Trial Number||Number Captured||Number Recaptured with mark|
Alaska Fish & Wildlife News March 2017
One of the great perks of living in Alaska is sharing our space with a variety of wildlife. Whether we are curious about our next hunting opportunities, or eager to watch wildlife, we often wonder about the animals living in our own backyards. Have you ever considered how many bears are hibernating near you on cold winter evenings? When you see a moose outside your window do you imagine there might be more you do not see? Wildlife managers and researchers work diligently to find out how many individuals of a particular species live in a certain area. Their jobs are necessary to ensure the conservation of wildlife, particularly for animals that are hunted.
Tim Peltier, a biologist for the Alaska Department of Fish and Game (ADF&G) in Palmer, explains one of the reasons why biologists have such an important job.
&ldquoWe count moose, caribou, sheep, and to a lesser extent bears and wolves,&rdquo he said. &ldquoThe Board (of Game) has determined the population and harvest objective in each area and we are tasked with determining how close we are to those objectives. We need to have an idea of the population size.&rdquo
How do biologists determine the number of animals living in an area? A variety of methods are used to determine populations. A biologist must consider the ecosystem, terrain, the species being counted and must also factor in weather, costs, and time.
It would be ideal to see and count each individual animal in a population. This is called a census. Unfortunately, there is no simple way to do this. Animals move from place to place, they hide, they hibernate, and they are often camouflaged and difficult to see in their environment. The closest thing to conducting a census in Alaska is counting caribou such as the Western Arctic Herd on the North Slope. During the summer, caribou huddle up on snow fields for relief from mosquitoes and other insect pests. Viewed from above, the brown caribou on the white, snowy background are relatively easy to see. Biologists fly over these groups of caribou, systematically taking pictures as they go. Back in the office, every picture is analyzed and biologists zoom in and count each caribou individually. It is an important and time consuming project &ndash hundreds of thousands of caribou can be counted in more than 1,000 pictures.
Another efficient method researchers have developed to estimate populations is called &ldquocapture-mark-recapture.&rdquo Instead of trying to count every animal, biologists randomly capture a sample group of the population, mark it, release it, and then do a series of recaptures that will allow them to estimate the entire population in a particular study area. One easy way to understand this method is to see how Alaska teachers are learning to use ADF&G&rsquos curriculum Wildlife for the Future in their classroom lessons.
Last fall in Nome, 16 teachers were each given a container filled with beans. Their first task was to write down the number of beans they thought were in their container. The teachers used a variety of strategies to come up with their visual estimates. Many took random guesses without much forethought, some relied solely on their sight by counting as many beans as were visible to them, and others counted the rows and columns of the beans and multiplied to determine their estimate.
Then they applied the &ldquomark-recapture&rdquo technique. Each teacher reached into the bowl of beans to &ldquocapture&rdquo a handful of &ldquoanimals.&rdquo They counted the captured beans and recorded this number on a data sheet. Before putting the beans back in the bowl, they &ldquomarked&rdquo the captured beans by replacing them with the same number of beans of a different color &ndash these then became the &ldquomarked animals.&rdquo After thoroughly mixing the beans they did a series of &ldquorecaptures&rdquo by again grabbing a handful of beans, counting the total number of &ldquoanimals&rdquo captured, recording that number, and then recording the number of marked &ldquoanimals&rdquo in each recapture. They did this 10 times. Once all 10 recaptures were finished they calculated the average number of beans for the recaptures and then the average number of &ldquomarked,&rdquo or different colored beans, in the recaptures. They put these two averages along with the number in the first sample count in to a mathematical formula and calculated the scientific estimate of the population of beans in the container. Finally, they dumped the beans out and counted each individual bean for an accurate count, or census, of the bean &ldquopopulation.&rdquo Nearly every teacher came up with a less than five percent error rate between their scientific estimate and the actual count, a much narrower margin of error than their own visual estimate.
State wildlife biologist Stephen Bethune, based in Sitka, explains how this works in real life. On Baranof Island mountain goats are captured and fitted with bright red or orange collars and ear tags.
&ldquoWe know we never see all the goats in a given area, but having marked goats on the landscape allows us to determine the sightability of goats during that survey,&rdquo he said. &ldquoFor example, if there are 10 marked goats in an area and we see seven, we would apply a 70% sightability correction factor to a survey. So if we counted 50 goats, applying the correction factor we can estimate there were 71 goats in the area.&rdquo
Biologists then use the collars to conduct what are called aerial surveys, where they monitor survival and kid production to help build population models. &ldquoThe more sightability surveys we conduct, the more refined our sightability factors can be calculated,&rdquo Bethune said. &ldquoWe are able to monitor the general health of the population to help set appropriate harvest quotas in hunt zones.&rdquo
Other animals, such as brown bears on Kodiak Island, are surveyed from above. Biologist Nathan Svoboda uses intensive aerial surveys (ISA) to derive estimates for brown bears on Kodiak Island. His goal is to manage for a sustainable harvest and population and, &ldquoto ensure a healthy, robust, viable brown bear population exists in perpetuity, as brown bears are the cornerstone of ecological integrity on the archipelago,&rdquo he said.
These ISA&rsquos must be done after bears exit winter dens in the spring, but before vegetation green-up so surveyors can identify both individual bears and family groups without vegetation obstructing their view. Time is of the essence. In recent years, earlier green-up than normal has presented some challenges for biologists. They must start surveying earlier in the year while making sure they acquire accurate estimates of all bears, as some bears may not have exited dens yet, specifically females with young. In spite of challenges, Svoboda continues managing for a sustainable harvest and sustainable population and is investigating options to develop a robust population estimate for the Kodiak Island brown bears.
Obtaining a population estimate is a big job for management and research biologists. Whether conducting a census, an aerial survey, a capture-mark-recapture survey or one of the many other methods used to obtain an accurate estimate, each one provides important information to better understanding wildlife. So, next time you see a moose outside your door and you wonder if more are out there, rest assured that Alaska&rsquos wildlife biologists are curious about that too. And, they will continue to work to help keep Alaska&rsquos wildlife populations healthy and sustainable, now, and for future generations of wildlife enthusiasts.
Species Data Overview
GAP has delineated species range and predicted distribution maps for more than 2,000 species that occur within the continental US as well as Alaska, Hawaii, and Puerto Rico. Our goal is to build species range maps and distribution models with the best available data for assessing conservation status, conservation planning, and research.
Why are these Data Important?
Knowledge of a species geographic and ecological location is fundamental to many aspects of biodiversity conservation and for understanding spatial patterns of species occurrences. Furthermore, they will provide the basis of a national biodiversity assessment (gap analysis of species protection status).
How National GAP Species Data are being used
- To enhance understanding of spatial patterns of species occurrence (e.g., species richness).
- As a core data input to a national biodiversity assessment of vertebrate species occurring in United States.
- To provide information about the location of a species to enhance understanding of how that species will adapt to the effects of climate change.
- As core datasets from which new iterations of the maps and models can be developed as additional data become available.
Description of the CONUS Data Set
We started with a species list for each of the four terrestrial vertebrate classes of interest (i.e. mammals, amphibians, reptiles, birds). The list was compiled from three standard checklists including:
Banks, R. C., R. T. Chesser, C. Cicero, J. L. Dunn, A. W. Kratter, I. J. Lovette, P. C. Rasmussen, J. V. Remsen, Jr., J. D. Rising, D. F. Stotz, and K. Winker. 2008. Forty-ninth supplement to the American Ornithologists Union Check-list of North American Birds. The Auk 125:758-768. DOI: 10.1525/auk.2008.9708
Crother, B. I. 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 6th edition. Herpetological Circular No. 37, Society for the Study of Amphibians and Reptiles.
Wilson, D. E., and D. M. Reeder. 2005. Mammal Species of the World. A Taxonomic and Geographic Reference, 3rd edition. Johns Hopkins University Press.
Known Range Maps
GAP species range data are coarse representations of the total areal extent a species occupies - in other words, the geographic limits within which a species can be found (Morrison and Hall 2002). These data provide the geographic extent within which we delineate areas of suitable habitat for terrestrial vertebrate species in their species’ habitat maps. The range maps are created by attributing a vector file derived from the 12-digit Hydrologic Unit Dataset (USDA NRCS 2009). Modifications to that dataset are described here. Attribution of the season range for each species was based on the literature and online sources (See Cross Reference section of the metadata). Attribution for each hydrologic unit within the range included values for occurrence (extant, possibly present, potentially present, extirpated), season (year-round, summer, winter, migratory, vagrant), origin (native, introduced, reintroduced, vagrant), and reproductive use (breeding, non-breeding, both). These species range data provide the biological context within which to build our species distribution models.
Predicted Habitat Maps
Gap Analysis Project (GAP) habitat maps are predictions of the spatial distribution of suitable environmental and land cover conditions within the United States for individual species. Mapped areas represent places where the environment is suitable for the species to occur (i.e. suitable to support one or more life history requirements for breeding, resting, or foraging), while areas not included in the map are those predicted to be unsuitable for the species. While the actual distributions of many species are likely to be habitat limited, suitable habitat will not always be occupied because of population dynamics and species interactions. Furthermore, these maps correspond to midscale characterizations of landscapes, but individual animals may deem areas to be unsuitable because of presence or absence of fine-scale features and characteristics that are not represented in our models (e.g. snags, vernal pools, shrubby undergrowth). These maps are intended to be used at a 1:100,000 or smaller map scale.
These habitat maps are created by applying a deductive habitat model to remotely-sensed data layers within a species’ range. The deductive habitat models are built by compiling information on species’ habitat associations into a relational database. Information is compiled from the best available characterizations of species’ habitat, which included species accounts in books and databases, as well as primary peer-reviewed literature. The literature references for each species are included in the “Species Habitat Model Report” and “Machine Readable Habitat Database Parameters” files attached to each habitat map item in the ScienceBase repository. For all species, the compiled habitat information is used by a biologist to determine which of the ecological systems and land use classes represented in the National Gap Analysis Project’s (GAP) Land Cover Map Ver. 1.0 that species is associated with. The name of the biologist who conducted the literature review and assembled the modeling parameters is shown as the “editor” type contact for each habitat map item in the repository.
For many species, information on other mapped factors that define the environment that is suitable is also entered into the database. These factors included elevation (i.e. minimum, maximum), proximity to water features, proximity to wetlands, level of human development, forest ecotone width, and forest edge and each of these factors corresponded to a data layer that is available during the map production. The individual datasets used in the modeling process with these parameters are also made available in the ScienceBase repository. The “Machine Readable Habitat Database Parameters” JSON file attached to each species' habitat map item has an “input_layers” object that contains the specific parameter names and references (via Digital Object Identifier) to the input data used with that parameter. The specific parameters for each species were output from the database used in the modeling and mapping process to the “Species Habitat Model Report” and “Machine Readable Habitat Database Parameters” files attached to each habitat map item in the repository.
How To Cite These Data:
Known Range Maps
U.S. Geological Survey – Gap Analysis Project, 2018, U.S.Geological Survey – Gap Analysis Project Species Range Maps CONUS_2001: U.S. Geological Survey data release, https://doi.org/10.5066/F7Q81B3R
Predicted Habitat Maps
U.S. Geological Survey – Gap Analysis Project, 2018, U.S. Geological Survey – Gap Analysis Project Species Habitat Maps CONUS_2001: U.S. Geological Survey data release, https://doi.org/10.5066/F7V122T2
It should be noted that all our ranges and distribution models are predictions about the occurrence of a species within the U.S. GAP ranges and distribution models are intended for use at the landscape scale (i.e., areas the size of square kilometers). They are not intended to be precise predictions of species occurrence/absence at local scales (areas the size of square meters). It is important for GAP data users to evaluate the suitability of the data for their intended purpose.
GAP aims to use the best available information to create species ranges and distribution models. GAP relies on existing data and expert opinions from partners and collaborators (e.g., State Natural Heritage Programs).
Species range maps and distribution models are viewed as a single iteration based on the best available information. We encourage biologists and data users to assess GAP’s species ranges and distribution models, and to give us feedback so that we can continually improve our models and ultimately our ability to conserve biodiversity.
All of GAP’s ranges and distribution models have been reviewed by experts and compared to other data sources for accuracy. The accuracy of the species ranges and distribution models varies from species to species in part because habitat preferences and behaviors vary seasonally and annually (Edwards et al. 1996). However, those species for which thorough knowledge of habitat preferences exists are better represented than those for which little is known (i.e., rare or small populations) or vary widely both spatially and temporally. Species with highly restrictive distributions are very difficult to model accurately because their habitat cannot be predicted within the 30 m resolution of our land cover data and distribution maps. We accept the uncertainty within some ranges and distribution models because we believe these data provide basic information and serve an important purpose by highlighting where more data are needed.
Despite these limitations, we believe GAP species ranges and distribution models are valuable and relevant for addressing broad landscape level conservation questions and research.
Banks, R. C., R. T. Chesser, C. Cicero, J. L. Dunn, A. W. Kratter, I. J. Lovette, P. C. Rasmussen, J. V. Remsen, Jr., J. D. Rising, D. F. Stotz, and K. Winker. 2008. Forty-ninth supplement to the American Ornithologists’ Union Check-list of North American Birds. The Auk 125:758-768. Available from: https://pubs.er.usgs.gov/publication/5224902.
Crother, B. I. 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 6th edition. Herpetological Circular No. 37, Society for the Study of Amphibians and Reptiles. Available from: www.ssarherps.org/pages/comm_names/Index.php
Morrison, M. L., and L. S. Hall. 2002. Standard terminology: Toward a common language to advance ecological understanding and application. Pages 43-52 in Predicting Species Occurrences: Issues of accuracy and scale. Editors: J. M. Scott, P. J. Heglund, and M. L. Morrison, et al., Island Press.
A point quadrat is a frame shaped like a T. The bar of the T has ten holes in it, and to sample vegetation a long pin much like a knitting needle is stuck through each hole. The different plants that the pin 'hits' as it is pushed towards the ground are identified and counted.
To collect data on abundance, count the first hit made by the pin on each different plant. Count the first hit only.
Local frequency can be calculated for each species.
`"Local frequency" = ("total number of hits of a species" xx 100) / "total number of pin drops"`
For example, if at a single station sea holly is hit 2 times out of 10 pin drops
`"Local frequency" = 2/10 xx 100 = 20%`
The local frequency of sea holly is 20%
If you have classified each species into communities (e.g. pioneers, mobile sand dunes, dune slack plants, etc.) you can use point quadrat data to calculate percentage composition. This shows what percentage of plants at each station are from each community.
`"Local composition" = (% "frequency of a community" xx 100) / % "frequency of all communities"`
For example, if at a single station, the % frequency for all pioneers is 40 and the % frequency for all communities is 80.
`"Local composition" = 40/80 xx 100 = 50%`
Pioneers make up 50% of all plants found at that station.
FSC believes that the more we understand about and take inspiration from the world around us the more we can appreciate its needs and protect its diversity and beauty for future generations. Find out more
© 2016 Field Studies Council, a Limited Company, reg. England and Wales No.412621, and a Charity No.313364 and a charity registered in Scotland (SC039870). Registered Office: Preston Montford, Shrewsbury, Shropshire, SY4 1HW
Total Number of Species Estimated in the World
Scientists are fairly certain of how many mammals, birds and coniferous plants in the world, as they have discovered and described nearly all of the species for these groups. The other species estimates listed here are informed guesses, as only a fraction of all species have been formally identified and recorded. Thousands of species of fish, flowers and others still remain undiscovered by science.
No reliable estimate exists of how many species exist of plant algae, the green and red algae. So the total number of plant species given here doesn't include those species. Estimates of plant algae species range from 40 thousand to 140 thousand.
Categories of Invertebrate Animals
- Arachnids are spiders, mites and scorpions
- Molluscs are shellfish, snails and squid
- Crustaceans are crabs, shrimp and lobsters
- Echinoderms includes starfish, sea urchins and sea cucumbers
- Others includes worms, centipedes, sponges and jellyfish
Arthur D Chapman. 2009. Numbers of Living Species in Australia and the World. 2nd edition. Australian Government, Department of the Environment, Water, Heritage and the Arts. Canberra, Australia.
How many species on Earth? A simple question that's hard to answer
How many species still to name? That’s a good question. Credit: Shutterstock/ju see
You'd think it would be a simple piece of biological accounting – how many distinct species make up life on Earth?
But the answer may come as a bit of a shock.
We know more accurately the number of books in the US Library of Congress than we know even the order or magnitude – millions and billions and so on – of species living on our planet, wrote the Australian-born ecologist Robert May.
Current estimates for the number of species on Earth range between 5.3 million and 1 trillion.
That's a massive degree of uncertainty. It's like getting a bank statement that says you have between $5.30 and $1 million in your account.
So why don't we know the answer to this fundamental question?
It's hard to count life
Part of the problem is that we cannot simply count the number of life forms. Many live in inaccessible habitats (such as the deep sea), are too small to see, are hard to find, or live inside other living things.
So, instead of counting, scientists try to estimate the total number of species by looking for patterns in biodiversity.
In the early 1980s, the American entomologist Terry Erwin famously estimated the number of species on Earth by spraying pesticides into the canopy of tropical rainforest trees in Panama. At least 1,200 species of beetle fell to the ground, of which 163 lived only on a single tree species.
Assuming that each tree species had a similar number of beetles, and given that beetles make up about 40% of insects (the largest animal group), Erwin arrived at a controversial estimate of 30 million species on Earth.
Many scientists believe the 30 million number is far too high. Later estimates arrived at figures under 10 million.
In 2011, scientists used a technique based on patterns in the number of species at each level of biological classification to arrive at a much lower prediction of about 8.7 million species.
All creatures great and very, very small
But most estimates of global biodiversity overlook microorganisms such as bacteria because many of these organisms can only be identified to species level by sequencing their DNA.
As a result the true diversity of microorganisms may have been underestimated.
After compiling and analysing a database of DNA sequences from 5 million microbe species from 35,000 sites around the world, researchers concluded that there are a staggering 1 trillion species on Earth. That's more species than the estimated number of stars in the Milky Way galaxy.A jewel beetle, one of the more colourful species of insect alive today. Credit: Shutterstock/Suttipon Thanarakpong
But, like previous estimates, this one relies on patterns in biodiversity, and not everyone agrees these should be applied to microorganisms.
It's not just the microorganisms that have been overlooked in estimates of global biodiversity. We've also ignored the many life forms that live inside other life forms.
Most – and possibly all – insect species are the victim of at least one or more species of parasitic wasp. These lay their eggs in or on a host species (think of the movie Aliens, if the aliens had wings). Researchers suggest that the insect group containing wasps may be the largest group of animals on the planet.
What do we mean by species?
A more fundamental problem with counting species comes down to a somewhat philosophical issue: biologists do not agree on what the term "species" actually means.
The well-known biological species concept states that two organisms belong to the same species if they can interbreed and produce fertile offspring. But since this concept relies on mating, it cannot be used to define species of asexual organisms such as many microorganisms as well as some reptiles, birds and fish.
It also ignores the fact that many living things we consider separate species can and do interbreed. For example, dogs, coyotes and wolves readily interbreed, yet are usually considered to be separate species.
Other popular species definitions rely on how similar individuals are to one another (if it looks like a duck, it is a duck), their shared evolutionary history, or their shared ecological requirements.
Yet none of these definitions are entirely satisfactory, and none work for all life forms.
There are at least 50 different definitions of a species to choose from. Whether or not a scientist chooses to designate a newly found life form as a new species or not can come down to their philosophical stance about the nature of a species.
The cost of species loss
Our ignorance about the true biodiversity on our planet has real consequence. Each species is a potential treasure trove of solutions to problems including cures for disease, inspirations for new technologies, sources of new materials and providers of key ecosystem services.
Yet we are living in an age of mass extinction with reports of catastrophic insect declines, wide-scale depopulation of our oceans and the loss of more than 50% of wildlife within the span of a single human life.
Our current rate of biodiversity loss means we are almost certainly losing species faster than we are naming them. We are effectively burning a library without knowing the names or the contents of the books we are losing.Three six-to-seven-month-old hybrids between a male western gray wolf and a female western coyote resulting from artificial insemination. Credit: PLOS One (L. David Mech et al), CC BY
So while our estimate of the number of species on the planet remains frustratingly imprecise, the one thing we do know is that we have probably named and described only a tiny percentage of living things.
New species are turning up all the time, at a rate of roughly 18,000 species each year. For example, researchers in Los Angeles found 30 new species of scuttle fly living in urban parks, while researchers also in the US discovered more than 1,400 new species of bacteria living in the belly buttons of university students.
Even if we take the more conservative estimate of 8.7 million species of life on Earth, then we have only described and named about 25% of life forms on the planet. If the 1 trillion figure is correct, then we have done an abysmally poor job, with 99.99% of species still awaiting description.
It's clear our planet is absolutely teeming with life, even if we cannot yet put a number to the multitudes. The question now is how much of that awe-inspiring diversity we choose to save.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
How to calculate Simpson's Diversity Index (AP Biology)
Simpson's Diversity Index (SDI) is one approach to quantifying biodiversity. There are a number of other options that may be used (such as species richness and Shannon's Diversity Index), but the AP Biology Equation and Formula Sheet includes Simpson's, so AP Biology students should be prepared to use it for the AP Biology exam. SDI takes both the number of species and the population size of each species into account. The resulting value is between 0 and 1, with 0 representing no diversity (all individuals in an area are the same species) and 1 representing maximum diversity.
This post uses the version of SDI found on the AP Biology formula sheet. Another version of the equation is used for small communities. The two versions are sometimes called finite (small samples) and infinite (large samples). AP Biology uses the infinite version of the equation. The specific formula that appears on the AP exam will be used here, even though the simulations used for these examples produce small sample sizes. The Resources page (and Google drive) includes worksheets for both versions of SDI as well as species richness options.
Quick ecology vocab review before getting into the equation a community is a group of different species in a given area and a population is a group of individuals of the same species in an area.
Two variables are needed for this formula. First is the total number of individuals in the community. Second is the population size for each species. In a real study, scientists use various sampling techniques to estimate population sizes. For the purposes of practice, we will use a simulation to collect data.
There are two simulations on Biology Simulations that lend themselves well to practicing diversity calculations. For our first example, we'll use the Biodiversity simulation. In this simulation, each time the "Produce Community" button is clicked, an animal community is produced in the forest ecosystem. Random components include the total number of individuals and the number of species represented. Pictured below is a sample run of the simulation, with each species circled in a different color. Identifying each species by name isn't important to completing the calculation, you just need to keep track of how many individuals are in each population.