The consistency of relative species abundance patterns suggests that some common macroecological "rule" or process determines the distribution of individuals among species within a trophic level. Relative species abundance distributions are usually graphed as frequency histograms "Preston plots"; Figure 2  or rank-abundance diagrams "Whittaker Plots"; Figure 3.
When plotted in these ways, relative species abundances from wildly different data sets show similar patterns: Figure 2 and rank-abundance diagrams tend to conform to the curves illustrated in Figure 4. Researchers attempting to understand relative species abundance patterns usually approach them in a descriptive or mechanistic way. Using a descriptive approach biologists attempt to fit a mathematical model to real data sets and infer the underlying biological principles at work from the model parameters.
By contrast, mechanistic approaches create a mathematical model based on biological principles and then test how well these models fit real data sets.
Motomura developed the geometric series model based on benthic community data in a lake. Thus if k is 0. Although Motomura originally developed the model as a statistical descriptive means to plot observed abundances, the "discovery" of his paper by Western researchers in led to the model being used as a niche apportionment model — the "niche-preemption model". The geometric series rank-abundance diagram is linear with a slope of — k , and reflects a rapid decrease in species abundances by rank Figure 4.
The logseries was developed by Ronald Fisher to fit two different abundance data sets: Together, this produced the logseries distribution Figure 4. The logseries predicts the number of species at different levels of abundance n individuals with the formula:. Using several data sets including breeding bird surveys from New York and Pennsylvania and moth collections from Maine, Alberta and Saskatchewan Frank W.
Preston argued that species abundances when binned logarithmically in a Preston plot follow a Normal Gaussian distribution , partly as a result of the Central Limit Theorem Figure 4. According to his argument, the right-skew observed in species abundance frequency histograms including those described by Fisher et al.
Given that species toward the left side of the x -axis are increasingly rare, they may be missed in a random species sample. As the sample size increases however, the likelihood of collecting rare species in a way that accurately represents their abundance also increases, and more of the normal distribution becomes visible.
As the sample size increases Preston's veil is pushed farther to the left and more of the normal curve becomes visible   Figure 6. Williams' moth data, originally used by Fisher to develop the logseries distribution, became increasingly lognormal as more years of sampling were completed.
Preston's theory has an application: Assuming the shape of the total distribution can be confidently predicted from the collected data, the normal curve can be fit via statistical software or by completing the Gaussian formula: The number of species missing from the data set the missing area to the left of the veil line is simply N minus the number of species sampled.
The Yule model is based on a much earlier, Galton—Watson model which was used to describe the distribution of species among genera. As the number of species within a genus, within a clade, has a similar distribution to the number of individuals within a species, within a community i.
This section provides a general summary of niche apportionment theory, more information can be found under niche apportionment models. Most mechanistic approaches to species abundance distributions use niche-space, i.
If species in the same trophic level consume the same resources such as nutrients or sunlight in plant communities, prey in carnivore communities, nesting locations or food in bird communities and these resources are limited, how the resource "pie" is divided among species determines how many individuals of each species can exist in the community. Species with access to lots of resources will have higher carrying capacities than those with little access.
Mutsunori Tokeshi  later elaborated niche apportionment theory to include niche filling in unexploited resource space. Numerous niche apportionment models have been developed. Each make different assumptions about how species carve up niche-space. The Unified Neutral Theory of Biodiversity and Biogeography UNTB is a special form of mechanistic model that takes an entirely different approach to community composition than the niche apportionment models.
A community in the UNTB model can be best visualized as a grid with a certain number of spaces, each occupied with individuals of different species. The model is zero-sum as there are a limited number of spaces that can be occupied: The model then uses birth, death, immigration, extinction and speciation to modify community composition over time. Relative species abundances in the UNTB model follow a zero-sum multinomial distribution.
If a species' density declines, then the food it most depends on will become more abundant since there are so few individuals to consume it. As a result, the remaining individuals will experience less competition for food. Although "resource" generally refers to food, species can partition other non-consumable objects, such as parts of the habitat. For example, warblers are thought to coexist because they nest in different parts of trees.
As stated in the introduction, anole lizards appear to coexist because each uses different parts of the forests as perch locations. Predator partitioning occurs when species are attacked differently by different predators or natural enemies more generally. For example, trees could differentiate their niche if they are consumed by different species of specialist herbivores , such as herbivorous insects.
If a species density declines, so too will the density of its natural enemies, giving it an advantage. Thus, if each species is constrained by different natural enemies, they will be able to coexist. Conditional differentiation sometimes called temporal niche partitioning occurs when species differ in their competitive abilities based on varying environmental conditions.
For example, in the Sonoran Desert , some annual plants are more successful during wet years, while others are more successful during dry years. When environmental conditions are most favorable, individuals will tend to compete most strongly with member of the same species.
For example, in a dry year, dry-adapted plants will tend to be most limited by other dry-adapted plants. Species can differentiate their niche via a competition-predation trade-off if one species is a better competitor when predators are absent, and the other is better when predators are present.
Defenses against predators, such as toxic compounds or hard shells, are often metabolically costly. As a result, species that produce such defenses are often poor competitors when predators are absent. Species can coexist through a competition-predation trade-off if predators are more abundant when the less defended species is common, and less abundant if the well-defended species is common.
One instance is in a group of hispine beetle species Strong These beetle species, which eat the same food and occupy the same habitat, coexist without any evidence of segregation or exclusion. The beetles show no aggression either intra- or inter-specifically. Coexistence may be possible through a combination of non-limiting food and habitat resources and high rates of predation and parasitism , though this has not been demonstrated. This example illustrates that the evidence for niche differentiation is by no means universal.
Niche differentiation is also not the only means by which coexistence is possible between two competing species see Shmida and Ellner However, niche differentiation is a critically important ecological idea which explains species coexistence, thus promoting the high biodiversity often seen in many of the world's biomes. Research using mathematical modelling is indeed demonstrating that predation can indeed stabilize lumps of very similar species. Willow warbler and chiffchaff and other very similar warblers can serve as an example.
The idea is that it is also a good strategy to be very similar to a successful species or have enough dissimilarity. Also trees in the rain forest can serve as an example of all high canopy species basically following the same strategy. Other examples of nearly identical species clusters occupying the same niche were water beetles, prairie birds and algae. The basic idea is that there can be clusters of very similar species all applying the same successful strategy and between them open spaces.
Here the species cluster takes the place of a single species in the classical ecological models. From Wikipedia, the free encyclopedia. Resource competition 1st ed. Biotic interactions in the tropics: Lawrence 14 July Proceedings of the National Academy of Sciences.
In Grace, James; Tilman, David. Perspectives on Plant Competition. Chemoorganoheterotrophy Decomposition Detritivores Detritus. Archaea Bacteriophage Environmental microbiology Lithoautotroph Lithotrophy Microbial cooperation Microbial ecology Microbial food web Microbial intelligence Microbial loop Microbial mat Microbial metabolism Phage ecology.
Ascendency Bioaccumulation Cascade effect Climax community Competitive exclusion principle Consumer-resource systems Copiotrophs Dominance Ecological network Ecological succession Energy quality Energy Systems Language f-ratio Feed conversion ratio Feeding frenzy Mesotrophic soil Nutrient cycle Oligotroph Paradox of the plankton Trophic cascade Trophic mutualism Trophic state index.
Animal coloration Antipredator adaptations Camouflage Deimatic behaviour Herbivore adaptations to plant defense Mimicry Plant defense against herbivory Predator avoidance in schooling fish.
Abundance Allee effect Depensation Ecological yield Effective population size Intraspecific competition Logistic function Malthusian growth model Maximum sustainable yield Overpopulation in wild animals Overexploitation Population cycle Population dynamics Population modeling Population size Predator—prey Lotka—Volterra equations Recruitment Resilience Small population size Stability.
Biodiversity Density-dependent inhibition Ecological effects of biodiversity Ecological extinction Endemic species Flagship species Gradient analysis Indicator species Introduced species Invasive species Latitudinal gradients in species diversity Minimum viable population Neutral theory Occupancy—abundance relationship Population viability analysis Priority effect Rapoport's rule Relative abundance distribution Relative species abundance Species diversity Species homogeneity Species richness Species distribution Species-area curve Umbrella species.
Ecological niche Ecological trap Ecosystem engineer Environmental niche modelling Guild Habitat Marine habitats Limiting similarity Niche apportionment models Niche construction Niche differentiation.