Species–area relationship

The species–area relationship or species–area curve describes the relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical relationships.[1] The species–area relationship is usually constructed for a single type of organism, such as all vascular plants or all species of a specific trophic level within a particular site. It is rarely, if ever, constructed for all types of organisms if simply because of the prodigious data requirements. It is related but not identical to the species discovery curve.

Ecologists have proposed a wide range of factors determining the slope and elevation of the species–area relationship.[2] These factors include the relative balance between immigration and extinction,[3] rate and magnitude of disturbance on small vs. large areas,[3] predator–prey dynamics,[4] and clustering of individuals of the same species as a result of dispersal limitation or habitat heterogeneity.[5] The species–area relationship has been reputed to follow from the 2nd law of thermodynamics.[6] In contrast to these "mechanistic" explanations, others assert the need to test whether the pattern is simply the result of a random sampling process.[7]

Authors have classified the species–area relationship according to the type of habitats being sampled and the census design used. Frank W. Preston, an early investigator of the theory of the species–area relationship, divided it into two types: samples (a census of a contiguous habitat that grows in census area, also called "mainland" species–area relationships), and isolates (a census of discontiguous habitats, such as islands, also called "island" species–area relationships).[1] Michael Rosenzweig also notes that species–area relationships for very large areas—those collecting different biogeographic provinces or continents—behave differently from species–area relationships from islands or smaller contiguous areas.[2] It has been presumed that "island"-like species–area relationships have higher slopes (in log–log space) than "mainland" relationships,[2] but a 2006 metaanalysis of almost 700 species–area relationships found the former had lower slopes than the latter.[8]

Regardless of census design and habitat type, species–area relationships are often fit with a simple function. Frank Preston advocated the power function based on his investigation of the lognormal species-abundance distribution.[1] If is the number of species, is the habitat area, and is the slope of the species area relationship in log-log space, then the power function species–area relationship goes as:

Here is a constant which depends on the unit used for area measurement, and equals the number of species that would exist if the habitat area was confined to one square unit. The graph looks like a straight line on log–log axes, and can be linearized as:

In contrast, Henry Gleason championed the semilog model:

which looks like a straight line on semilog axes, where area is logged and the number of species is arithmetic. In either case, the species–area relationship is almost always decelerating (has a negative second derivative) when plotted arithmetically.[9]

Species–area relationships are often graphed for islands (or habitats that are otherwise isolated from one another, such as woodlots in an agricultural landscape) of different sizes.[3] Although larger islands tend to have more species, it is possible that a smaller island will have more than a larger one. In contrast, species-area relationships for contiguous habitats will always rise as areas increases, provided that the sample plots are nested within one another.

The species–area relationship for mainland areas (contiguous habitats) will differ according to the census design used to construct it.[10] A common method is to use quadrats of successively larger size, so that the area enclosed by each one includes the area enclosed by the smaller one (i.e. areas are nested).

In the first part of the 20th century, plant ecologists often used the species–area curve to estimate the minimum size of a quadrat necessary to adequately characterize a community. This is done by plotting the curve (usually on arithmetic axes, not log-log or semilog axes), and estimating the area after which using larger quadrats results in the addition of only a few more species. This is called the minimal area. A quadrat that encloses the minimal area is called a relevé, and using species–area curves in this way is called the relevé method. It was largely developed by the Swiss ecologist Josias Braun-Blanquet.[11]

Estimation of the minimal area from the curve is necessarily subjective, so some authors prefer to define minimal area as the area enclosing at least 95 percent (or some other large proportion) of the total species found. The problem with this is that the species area curve does not usually approach an asymptote, so it is not obvious what should be taken as the total.[11] In fact, the number of species always increases with area up to the point where the area of the entire world has been accumulated.[12]

In 2017, it was proposed that, although broad-scale patterns of the distribution of biodiversity across the earth focused on a bi-dimensional space, the species-volume relationship (SVR) has rarely been considered.[13] The environmental and evolutionary biologist Dr. Roberto Cazzolla Gatti and his colleagues of the Euro-Mediterranean Centre on Climate Change (CMCC) tested a global correlation between vascular plant species richness (S) and average forest canopy height (H), the latter regarded as a proxy of volume, using the NASA product of Global Forest Canopy Height map and the global map of plant species diversity. They found a significant correlation between H and S both at global and macro-climate scales, with strongest confidence in the tropics. Dr. Cazzolla Gatti and colleagues suggested that the volume of forest ecosystems should be considered in ecological studies as well as in planning and managing protected areas and natural sites.

SAR(Species-area curve)
The species–area relationship for a contiguous habitat

See also


  1. ^ a b c Preston, F.W. 1962. The canonical distribution of commonness and rarity: Part I. Ecology 43:185–215 and 410–432.
  2. ^ a b c Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge University Press, Cambridge.
  3. ^ a b c MacArthur and Wilson. 1967. The Theory of Island Biogeography. Princeton University Press: Princeton, NJ.
  4. ^ Brose, U., A. Ostling, K. Harrison, and N.D. Martinez. 2004. Unified spatial scaling of species and their trophic interactions. Nature 428:167–171.
  5. ^ Green, J.L. and A. Ostling. 2003. Endemics-area relationships: The influence of species dominance and spatial aggregation. Ecology 84:3090–3097.
  6. ^ Würtz, P. & Annila, A. (2008). "Roots of diversity relations". J. Biophys. 2008: 1–8. arXiv:0906.0251. doi:10.1155/2008/654672.
  7. ^ Connor, E.F. and E.D. McCoy. 1979. The statistics and biology of the species–area relationship. American Naturalist 113:791–833.
  8. ^ Drakare S, Lennon J.L., Hillebrand H., 2006 The imprint of the geographical, evolutionary and ecological context on species–area relationships Ecology Letters 9 (2), 215–227
  9. ^ Arrhenius, O. 1921. "Species and Area" J. Ecol. 9: 95–99
  10. ^ Scheiner, S.M. 2003. Six types of species–area curves. Global Ecology and Biogeography 12:441–447.
  11. ^ a b Barbour, M. G., Burk, J. H., & Pitts, W. D. (1980). Terrestrial plant ecology. Menlo Park CA: Benjamin/Cummings. Pp. 158–160.
  12. ^ Williamson, M., K.J. Gaston, and W.M. Lonsdale. 2001. The species–area relationship does not have any asymptote! Journal of Biogeography 28:827–830.
  13. ^ Cazzolla Gatti, R., Di Paola, A., Bombelli, A., Noce, S., & Valentini, R. (2017). Exploring the relationship between canopy height and terrestrial plant diversity. Plant Ecology, 218(7), 899-908.

External links

Allopatric speciation

Allopatric speciation (from Ancient Greek ἄλλος, allos, meaning "other", and πατρίς, patris, "fatherland"), also referred to as geographic speciation, vicariant speciation, or its earlier name, the dumbbell model, is a mode of speciation that occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with gene flow.

Various geographic changes can arise such as the movement of continents, and the formation of mountains, islands, bodies of water, or glaciers. Human activity such as agriculture or developments can also change the distribution of species populations. These factors can substantially alter a region's geography, resulting in the separation of a species population into isolated subpopulations. The vicariant populations then undergo genetic changes as they become subjected to different selective pressures, experience genetic drift, and accumulate different mutations in the separated populations gene pools. The barriers prevent the exchange of genetic information between the two populations leading to reproductive isolation. If the two populations come into contact they will be unable to reproduce—effectively speciating. Other isolating factors such as population dispersal leading to emigration can cause speciation (for instance, the dispersal and isolation of a species on an oceanic island) and is considered a special case of allopatric speciation called peripatric speciation.

Allopatric speciation is typically subdivided into two major models: vicariance and peripatric. Both models differ from one another by virtue of their population sizes and geographic isolating mechanisms. The terms allopatry and vicariance are often used in biogeography to describe the relationship between organisms whose ranges do not significantly overlap but are immediately adjacent to each other—they do not occur together or only occur within in a narrow zone of contact. Historically, the language used to refer to modes of speciation directly reflected biogeographical distributions. As such, allopatry is a geographical distribution opposed to sympatry (speciation within the same area). Furthermore, the terms allopatric, vicariant, and geographical speciation are often used interchangeably in the scientific literature. This article will follow a similar theme, with the exception of special cases such as peripatric, centrifugal, among others.

Observation of nature creates difficulties in witnessing allopatric speciation from "start-to-finish" as it operates as a dynamic process. From this arises a host of various issues in defining species, defining isolating barriers, measuring reproductive isolation, among others. Nevertheless, verbal and mathematical models, laboratory experiments, and empirical evidence overwhelmingly supports the occurrence of allopatric speciation in nature. Mathematical modeling of the genetic basis of reproductive isolation supports the plausibility of allopatric speciation; whereas laboratory experiments of Drosophila and other animal and plant species have confirmed that reproductive isolation evolves as a byproduct of natural selection.


An ectomycorrhiza (from Greek ἐκτός ektos, "outside", μύκης mykes, "fungus", and ῥίζα rhiza, "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobiont, and the roots of various plant species. The mycobiont is often from the phyla Basidiomycota and Ascomycota, and more rarely from the Zygomycota. Ectomycorrhizas form on the roots of around 2% of plant species, usually woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine, Douglas fir and rose families. Research on ectomycorrhizas is increasingly important in areas such as ecosystem management and restoration, forestry and agriculture.

Unlike other mycorrhizal relationships, such as arbuscular mycorrhiza and ericoid mycorrhiza, ectomycorrhizal fungi do not penetrate their host's cell walls. Instead they form an entirely intercellular interface known as the Hartig net, consisting of highly branched hyphae forming a latticework between epidermal and cortical root cells.

Ectomycorrhizas are further differentiated from other mycorrhizas by the formation of a dense hyphal sheath, known as the mantle, surrounding the root surface. This sheathing mantle can be up to 40 µm thick, with hyphae extending up to several centimeters into the surrounding soil. The hyphal network helps the plant to take up nutrients including water and minerals, often helping the host plant to survive adverse conditions. In exchange, the fungal symbiont is provided with access to carbohydrates.

Well known EcM fungal fruiting bodies include the economically important and edible truffle (Tuber) and the deadly death caps and destroying angels (Amanita).

Insular biogeography

Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness and diversification of isolated natural communities. The theory was originally developed to explain the pattern of the species–area relationship occurring in oceanic islands. Under either name it is now used in reference to any ecosystem (present or past) that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, seamounts, oases, fragmented forests, and even natural habitats isolated by human land development. The field was started in the 1960s by the ecologists Robert H. MacArthur and E. O. Wilson, who coined the term island biogeography in their inaugural contribution to Princeton's Monograph in Population Biology series, which attempted to predict the number of species that would exist on a newly created island.

Lac la Ronge

Lac la Ronge is a glacial lake in Saskatchewan, Canada. It is the fifth largest lake in the province.

It is approximately 250 kilometres (160 mi) north of Prince Albert, on the edge of the Canadian Shield. La Ronge, Air Ronge and the Lac La Ronge First Nation are on the west shore. The lake is a popular vacation spot. Recreational activities include fishing, boating, canoeing, hiking, and camping.

The Lac la Ronge Dam, an embankment dam, was constructed at the source of the Rapid River in 1966 to regulate the lake's water level. The dam is 3.1 metres high and contains four gates. The dam was upgraded in 2007 and a fish ladder was installed.

Mamirauá Sustainable Development Reserve

The Mamirauá Sustainable Development Reserve (Portuguese: Reserva de Desenvolvimento Sustentável Mamirauá) in the Brazilian state of Amazonas, near the city of Tefé, is a 4,300-square-mile (11,000 km2) reserve near the village of Boca do Mamirauá. It includes mostly Amazonian flooded forest and wetlands.

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.

Population model

A population model is a type of mathematical model that is applied to the study of population dynamics.

Reconciliation ecology

Reconciliation ecology is the branch of ecology which studies ways to encourage biodiversity in human-dominated ecosystems. Michael Rosenzweig first articulated the concept in his book Win-Win Ecology, based on the theory that there is not enough area for all of earth’s biodiversity to be saved within designated nature preserves. Therefore, humans should increase biodiversity in human-dominated landscapes. By managing for biodiversity in ways that do not decrease human utility of the system, it is a "win-win" situation for both human use and native biodiversity. The science is based in the ecological foundation of human land-use trends and species-area relationships. It has many benefits beyond protection of biodiversity, and there are numerous examples of it around the globe. Aspects of reconciliation ecology can already be found in management legislation, but there are challenges in both public acceptance and ecological success of reconciliation attempts.

Reserve design

Reserve design is the process of planning and creating a nature reserve in a way that effectively accomplishes the goal of the reserve.

Reserve establishment has a variety of goals, and planners must consider many factors for a reserve to be successful. These include habitat preference, migration, climate change, and public support. To accommodate these factors and fulfill the reserve's goal requires that planners create and implement a specific design.

Species diversity

Species diversity is the number of different species that are represented in a given community (a dataset). The effective number of species refers to the number of equally abundant species needed to obtain the same mean proportional species abundance as that observed in the dataset of interest (where all species may not be equally abundant). Species diversity consists of three components: species richness, taxonomic or phylogenetic diversity and species evenness. Species richness is a simple count of species, taxonomic or phylogenetic diversity is the genetic relationship between different groups of species,whereas species evenness quantifies how equal the abundances of the species are.

Food webs
Example webs
Ecology: Modelling ecosystems: Other components


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