Limits...
The shape of terrestrial abundance distributions.

Alroy J - Sci Adv (2015)

Bottom Line: However, previous studies have focused on either a few theoretical distributions or a few empirical distributions.However, unlike any other model, it assumes both that richness is finite and that species compete unequally for resources in a two-dimensional niche landscape, which implies that niche breadths are variable and that trait distributions are neither arrayed along a single dimension nor randomly associated.The hypothesis that niche space is multidimensional helps to explain how numerous species can coexist despite interacting strongly.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia. E-mail: john.alroy@mq.edu.au.

ABSTRACT
Ecologists widely accept that the distribution of abundances in most communities is fairly flat but heavily dominated by a few species. The reason for this is that species abundances are thought to follow certain theoretical distributions that predict such a pattern. However, previous studies have focused on either a few theoretical distributions or a few empirical distributions. I illustrate abundance patterns in 1055 samples of trees, bats, small terrestrial mammals, birds, lizards, frogs, ants, dung beetles, butterflies, and odonates. Five existing theoretical distributions make inaccurate predictions about the frequencies of the most common species and of the average species, and most of them fit the overall patterns poorly, according to the maximum likelihood-related Kullback-Leibler divergence statistic. Instead, the data support a low-dominance distribution here called the "double geometric." Depending on the value of its two governing parameters, it may resemble either the geometric series distribution or the lognormal series distribution. However, unlike any other model, it assumes both that richness is finite and that species compete unequally for resources in a two-dimensional niche landscape, which implies that niche breadths are variable and that trait distributions are neither arrayed along a single dimension nor randomly associated. The hypothesis that niche space is multidimensional helps to explain how numerous species can coexist despite interacting strongly.

No MeSH data available.


Related in: MedlinePlus

Characteristic rank abundance distributions of four disparate taxonomic groups in tropical and temperate zones.Each value is the median proportional abundance at the appropriate position in the rank abundance distribution. Data are truncated at the point where the median falls to 0. Patterns are similar for the remaining groups (fig. S2). Thick lines, tropical zone data; thin lines, temperate zone data. (A) Trees. (B) Bats. (C) Frogs. (D) Dung beetles.
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Figure 2: Characteristic rank abundance distributions of four disparate taxonomic groups in tropical and temperate zones.Each value is the median proportional abundance at the appropriate position in the rank abundance distribution. Data are truncated at the point where the median falls to 0. Patterns are similar for the remaining groups (fig. S2). Thick lines, tropical zone data; thin lines, temperate zone data. (A) Trees. (B) Bats. (C) Frogs. (D) Dung beetles.

Mentions: The major distributions are tested against one another using 1055 community samples of 10 taxonomic groups that are reposed at The Ecological Register (http://ecoregister.org) (see Materials and Methods). Composite rank abundance distributions showing the median relative abundance at each position are remarkably linear across all taxonomic groups (Fig. 2 and fig. S2). Thus, the most common species are less common and the rarest species are less rare than one would expect based on the lognormal (Fig. 1B). Instead, there is only a very subtle upward curvature at the left side, and it is only visible in some cases (for example, tropical trees; birds, ants, and butterflies in general). This curvature is consistent with the modestly high dominance predicted by the double geometric (Fig. 1A). Small drops at the ends of many curves, especially in temperate data, are also consistent with the double geometric. They are certainly not consistent with the geometric series and log series because these two assume there are no detectable limits to the size of the species pool. Although one could argue in an ad hoc way that such limits could be imposed on the geometric series and log series in the real world (that is, that the underlying distributions could be truncated), adding a truncation parameter would render those models less testable.


The shape of terrestrial abundance distributions.

Alroy J - Sci Adv (2015)

Characteristic rank abundance distributions of four disparate taxonomic groups in tropical and temperate zones.Each value is the median proportional abundance at the appropriate position in the rank abundance distribution. Data are truncated at the point where the median falls to 0. Patterns are similar for the remaining groups (fig. S2). Thick lines, tropical zone data; thin lines, temperate zone data. (A) Trees. (B) Bats. (C) Frogs. (D) Dung beetles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643760&req=5

Figure 2: Characteristic rank abundance distributions of four disparate taxonomic groups in tropical and temperate zones.Each value is the median proportional abundance at the appropriate position in the rank abundance distribution. Data are truncated at the point where the median falls to 0. Patterns are similar for the remaining groups (fig. S2). Thick lines, tropical zone data; thin lines, temperate zone data. (A) Trees. (B) Bats. (C) Frogs. (D) Dung beetles.
Mentions: The major distributions are tested against one another using 1055 community samples of 10 taxonomic groups that are reposed at The Ecological Register (http://ecoregister.org) (see Materials and Methods). Composite rank abundance distributions showing the median relative abundance at each position are remarkably linear across all taxonomic groups (Fig. 2 and fig. S2). Thus, the most common species are less common and the rarest species are less rare than one would expect based on the lognormal (Fig. 1B). Instead, there is only a very subtle upward curvature at the left side, and it is only visible in some cases (for example, tropical trees; birds, ants, and butterflies in general). This curvature is consistent with the modestly high dominance predicted by the double geometric (Fig. 1A). Small drops at the ends of many curves, especially in temperate data, are also consistent with the double geometric. They are certainly not consistent with the geometric series and log series because these two assume there are no detectable limits to the size of the species pool. Although one could argue in an ad hoc way that such limits could be imposed on the geometric series and log series in the real world (that is, that the underlying distributions could be truncated), adding a truncation parameter would render those models less testable.

Bottom Line: However, previous studies have focused on either a few theoretical distributions or a few empirical distributions.However, unlike any other model, it assumes both that richness is finite and that species compete unequally for resources in a two-dimensional niche landscape, which implies that niche breadths are variable and that trait distributions are neither arrayed along a single dimension nor randomly associated.The hypothesis that niche space is multidimensional helps to explain how numerous species can coexist despite interacting strongly.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia. E-mail: john.alroy@mq.edu.au.

ABSTRACT
Ecologists widely accept that the distribution of abundances in most communities is fairly flat but heavily dominated by a few species. The reason for this is that species abundances are thought to follow certain theoretical distributions that predict such a pattern. However, previous studies have focused on either a few theoretical distributions or a few empirical distributions. I illustrate abundance patterns in 1055 samples of trees, bats, small terrestrial mammals, birds, lizards, frogs, ants, dung beetles, butterflies, and odonates. Five existing theoretical distributions make inaccurate predictions about the frequencies of the most common species and of the average species, and most of them fit the overall patterns poorly, according to the maximum likelihood-related Kullback-Leibler divergence statistic. Instead, the data support a low-dominance distribution here called the "double geometric." Depending on the value of its two governing parameters, it may resemble either the geometric series distribution or the lognormal series distribution. However, unlike any other model, it assumes both that richness is finite and that species compete unequally for resources in a two-dimensional niche landscape, which implies that niche breadths are variable and that trait distributions are neither arrayed along a single dimension nor randomly associated. The hypothesis that niche space is multidimensional helps to explain how numerous species can coexist despite interacting strongly.

No MeSH data available.


Related in: MedlinePlus