Species abundance patterns in an ecosystem simulation studied through Fisher’s logseries

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. b s t r a c tWe have developed an individual-based evolving predator-prey ecosystem simulation that integrates, for the first time, a complex individual behaviour model, an evolutionary mechanism and a speciation process, at an acceptable computational cost. In this article, we analyse the species abundance patterns observed in the communities generated by our simulation, based on Fisher's logseries. We propose a rigorous methodology for testing abundance data against the logseries. We show that our simulation produces coherent results, in terms of relative species abundance, when compared to classical ecological patterns. Some preliminary results are also provided about how our simulation is supporting ecological field results.

Speciation with gene flow in a heterogeneous virtual world: can physical obstacles accelerate speciation?

“…Our species recognition method involves the use of a 2-means clustering algorithm in which an initial species is split into two new species, each one of them containing the agents that are mutually the most similar. Since the birth and death of individuals influences the general composition of species [19] and speciation and extinction can occur at any time step, species membership is evaluated at each time step. Although speciation events are discrete, the complete speciation process is spread over multiple time steps.…”

“…This thorough tracking system enables us to extract, to measure and to correlate parameters that are useful to understand the underlying properties of such a complex system. Several studies evaluated the capacity of the EcoSim platform to model real ecosystems and make realistic predictions regarding species abundance patterns [19] and the complexity levels of the simulation [18]. These studies show that the communities of species generated by the simulation follow the same lognormal law as natural communities and that EcoSim can help evaluate the overall level of diversity of a given community.…”

A New Species Abundance Distribution Model Based on Model Combination

“…The first parameter, α, is constant for all samples from a given community (it is a characteristic of the community and not of the sample). α is correlated with the total number of species in the considered community and is called the "index of diversity" of the community [26].…”

“…Modeled distribution provides an acceptable fit to an observed SAD if the absolute difference between the observed and the calculated values of n 1 is less than 15% of the observed value which means that n obs 1 À n calc 1 0:15 n obs 1 [26]. n 1 is historically meaningful; it has always been an important statistic of a sample, and the SAD models had to give good approximations of n 1 to be validated [7].…”

“…We say that the model distribution provides a basic good fit to an observed SAD, if it presents an acceptable fit, and if a basic X 2 test (chi-square test), applied on both distributions, gives a X 2 that is not significant (for example, 5% significance) [26,27]. The X 2 test is then performed, calculating the observed and expected counts and computing the chisquare test statistic.…”