Abundance (ecology)

In ecology, local abundance is the relative representation of a species in a particular ecosystem.[1] It is usually measured as the number of individuals found per sample. The ratio of abundance of one species to one or multiple other species living in an ecosystem is referred to as relative species abundances.[1] Both indicators are relevant for computing biodiversity.

A variety of sampling methods are used to measure abundance. For larger animals, these may include spotlight counts, track counts and roadkill counts, as well as presence at monitoring stations.[2] In many plant communities the abundances of plant species are measured by plant cover, i.e. the relative area covered by different plant species in a small plot.[3] Abundance is in simplest terms usually measured by identifying and counting every individual of every species in a given sector. It is common for the distribution of species to be skewed so that a few species take up the bulk of individuals collected.[4]

Relative species abundance is calculated by dividing the number of species from one group by the total number of species from all groups.

Community ecology

These measures are all a part of community ecology. Understanding patterns within a community is easy when the community has a relatively low number of species. However most communities do not have a low number of species.[4] Measuring species abundance allows for understanding of how species are distributed within an ecosystem.[4] For example, salt water marshes have an influx of sea water, causing only a few species which are adapted to be able to survive in both salt and fresh water to be abundant. Inversely in land locked wetlands, the species abundance is more evenly distributed among the species who live within the wetland.[4]

In most ecosystems in which abundance has been calculated, most often only a small number of species are abundant, while a large number are pretty rare.[4] These abundant species are often generalists, with many rare species being specialists.[4] High density of a species in multiple localities will usually lead to it being relatively abundant over all in an ecosystem.[4] Therefore, high local abundance can be directly linked to high regional distribution. Species with high abundance are likely to have more offspring, and these offspring in turn are more likely to colonize a new sector of the ecosystem then a species which is less abundant. Thus begins a positive feedback loop leading to a species distribution in which a few "core species" are wide spread, and the other species are restricted and scarce known as satellite species.[1]

Species abundance distribution

Species abundance distribution (SAD) is one of the main uses of this measurement. SAD is a measurement of how common, or rare species are within a ecosystem.[5] This allows researchers to assess how different species are distributed throughout an ecosystem. SAD is one of the most basic measurements in ecology and is used very often, therefor many different methods of measurement and analysis have developed.[5]

Measurement

There are several methods for measuring abundance. An example of this is Semi-Quantitive Abundance ratings.[6] These are measurement methods which involve estimation based on viewing a specific area of a designated size.[6] The two Semi-Quantitive Abundance ratings used are known as the D.A.F.O.R, and the A.C.F.O.R.[6]

The A.C.F.O.R. scale is as follows:

  • A – Species observed is "Abundant" within the given area.
  • C – Species observed is "Common" within the given area.
  • F – Species observed is "Frequent" within the given area.
  • O – Species observed is "Occasional" within the given area
  • R – Species observed is "Rare" within the given area.

D.A.F.O.R scale:

  • D - Species observed is "Dominant" in a given area.
  • A - Species observed is "Abundant" in a given area.
  • F - Species observed is "Frequent" in a given area.
  • O - Species observed is "Occasional" in a given area.
  • R - Species observed is "Rare" in a given area.

These methods are great for getting a rough estimate of the species abundance in a designated area (quadrant). However, they are not exact, or objective measurements. Therefor if another method of measuring abundance is available, it should be used. This will lead to more useful and quantifiable data.[6]

See also

References

  1. ^ a b c Preston, F.W. (July 1948). "The Commonness, and Rarity, of Species" (PDF). Ecology. 29 (3): 254–283. doi:10.2307/1930989. JSTOR 1930989 – via Ben-Gurion University of the Negev.
  2. ^ Wright, David Hamilton (July 1991). "Correlations Between Incidence and Abundance are Expected by Chance". Journal of Biogeography. Journal of Biogeography, Vol. 18, No. 4. 18 (4): 463–466. doi:10.2307/2845487. JSTOR 2845487.
  3. ^ Damgaard, Christian (2009). "On the distribution of plant abundance data". Ecological Informatics. 4 (2): 76–82. doi:10.1016/j.ecoinf.2009.02.002.
  4. ^ a b c d e f g Verberk, W (2011). "Explaining General Patterns in Species Abundance and Distributions". Nature Education Knowledge. 3 (10): 38 – via researchgate.
  5. ^ a b Baldridge E, Harris DJ, Xiao X, White EP. 2016. An extensive comparison of species-abundance distribution models. PeerJ 4:e2823 https://doi.org/10.7717/peerj.2823
  6. ^ a b c d Morris, Peter (1995). Methods of Environmental Assessment. University College London Press. p. 236.

External links

Common species

Common species and uncommon species are designations used in ecology to describe the population status of a species. Commonness is closely related to abundance. Abundance refers to the frequency with which a species is found in controlled samples; in contrast, species are defined as common or uncommon based on their overall presence in the environment. A species may be locally abundant without being common.

However, "common" and "uncommon" are also sometimes used to describe levels of abundance, with a common species being less abundant than an abundant species, while an uncommon species is more abundant than a rare species.Common species are frequently regarded as being at low risk of extinction simply because they exist in large numbers, and hence their conservation status is often overlooked. While this is broadly logical, there are several cases of once common species being driven to extinction such as the passenger pigeon and the Rocky Mountain locust, which numbered in the billions and trillions respectively before their demise. Moreover, a small proportional decline in a common species results in the loss of a large number of individuals, and the contribution to ecosystem function that those individuals represented. A recent paper argued that because common species shape ecosystems, contribute disproportionately to ecosystem functioning, and can show rapid population declines, conservation should look more closely at how the trade-off between species extinctions and the depletion of populations.

Depensation

In population dynamics, depensation is the effect on a population (such as a fish stock) whereby, due to certain causes, a decrease in the breeding population (mature individuals) leads to reduced production and survival of eggs or offspring. The causes may include predation levels rising per offspring (given the same level of overall predator pressure) and the allee effect, particularly the reduced likelihood of finding a mate.

Mark and recapture

Mark and recapture is a method commonly used in ecology to estimate an animal population's size. A portion of the population is captured, marked, and released. Later, another portion is captured and the number of marked individuals within the sample is counted. Since the number of marked individuals within the second sample should be proportional to the number of marked individuals in the whole population, an estimate of the total population size can be obtained by dividing the number of marked individuals by the proportion of marked individuals in the second sample. The method is most useful when it is not practical to count all the individuals in the population. Other names for this method, or closely related methods, include capture-recapture, capture-mark-recapture, mark-recapture, sight-resight, mark-release-recapture, multiple systems estimation, band recovery, the Petersen method, and the Lincoln method.

Another major application for these methods is in epidemiology, where they are used to estimate the completeness of ascertainment of disease registers. Typical applications include estimating the number of people needing particular services (i.e. services for children with learning disabilities, services for medically frail elderly living in the community), or with particular conditions (i.e. illegal drug addicts, people infected with HIV, etc.).

Niche apportionment models

Mechanistic models for niche apportionment are biological models used to explain relative species abundance distributions. These niche apportionment models describe how species break up resource pool in multi-dimensional space, determining the distribution of abundances of individuals among species. The relative abundances of species are usually expressed as a Whittaker plot, or rank abundance plot, where species are ranked by number of individuals on the x-axis, plotted against the log relative abundance of each species on the y-axis. The relative abundance can be measured as the relative number of individuals within species or the relative biomass of individuals within species.

Occupancy frequency distribution

In macroecology and community ecology, an occupancy frequency distribution (OFD) is the distribution of the numbers of species occupying different numbers of areas. It was first reported in 1918 by the Danish botanist Christen C. Raunkiær in his study on plant communities. The OFD is also known as the species-range size distribution in literature.

Rare species

A rare species is a group of organisms that are very uncommon, scarce, or infrequently encountered. This designation may be applied to either a plant or animal taxon, and is distinct from the term endangered or threatened. Designation of a rare species may be made by an official body, such as a national government, state, or province. The term more commonly appears without reference to specific criteria. The IUCN does not normally make such designations, but may use the term in scientific discussion.Rarity rests on a specific species being represented by a small number of organisms worldwide, usually fewer than 10,000. However, a species having a very narrow endemic range or fragmented habitat also influences the concept. Almost 75% of known species can be classified as "rare."The International Union for Conservation of Nature uses the term "rare" as a designation for species found in isolated geographical locations. They are not endangered but classified as "at risk."A species may be endangered or vulnerable, but not considered rare if it has a large, dispersed population. Rare species are generally considered threatened because a small population size is more likely to not recover from ecological disasters.Rare species are species with small populations. Many move into the endangered or vulnerable category if the negative factors affecting them continue to operate. Examples of rare species include the Himalayan brown bear, Fennec fox, Wild Asiatic buffalo and Hornbill.

A rare plant's legal status can be observed through the USDA's Plants Database.

Status

Status (Latin plural: statūs), is a state, condition, or situation.

Status may also refer to:

Status (law)

City status

Legal status, in law

Political status, in international law

Small entity status, in patent law

Status conference

Status crime

Marital status

Observer status, in international organizations

Senior status

Social status, in sociology

Achieved status

Ascribed status

Master status

Socioeconomic status

Sociometric status

Status attainment

Status offense

Status shift

Status brand, in marketing

Status constructus, a noun form

Status match, in loyalty programs

Status quo

Status symbol

White-tailed eagle

The white-tailed eagle (Haliaeetus albicilla) is a very large eagle widely distributed across Eurasia. As are all eagles, it is a member of the family Accipitridae (or accipitrids) which includes other diurnal raptors such as hawks, kites, and harriers. One of up to eleven members in the genus Haliaeetus, which are commonly called sea eagles, it is not infrequently also referred to as the white-tailed sea-eagle. It is also sometimes known as the ern or erne (depending on spelling by sources), gray sea eagle and Eurasian sea eagleWhile found across a very wide range, today breeding as far west as Greenland and Iceland across to as far east in Hokkaido, Japan, they are often scarce and very spottily distributed as a nesting species, mainly due to human activities. These have included habitat alterations and destruction of wetlands, about a hundred years of systematic persecution by humans (from the early 1800s to around World War II) followed by inadvertent poisonings and epidemics of nesting failures due to various manmade chemical pesticides and organic compounds, which have threatened eagles since roughly the 1950s and continue to be a potential concern. Due to this, the white-tailed eagle was considered endangered or extinct in several countries. However, some populations have recovered well due to some governmental protections and dedicated conservationists and naturalists protecting habitats and nesting sites and partially regulating poaching and pesticide usage, as well as careful reintroductions into parts of their former range.White-tailed eagles usually live most of the year near large bodies of open water, including both coastal saltwater areas and inland freshwater, and require an abundant food supply and old-growth trees or ample sea cliffs for nesting. They are considered a close cousin of the bald eagle (Haliaeetus leucocephalus), which occupies a similar niche in North America.

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