Paul Higgs | Searcharxiv

arXiv2004

Topological structure and interaction strengths in model food webs

We report the results of carrying out a large number of simulations on a coevolutionary model of multispecies communities. A wide range of parameter values were investigated which allowed a rather complete picture of the change in behaviour of the model as these parameters were varied to be built up. Our main interest was in the nature of the community food webs constructed via the simulations. We identify the range of parameter values which give rise to realistic food webs and give arguments which allow some of the structure which is found to be understood in an intuitive way. Since the webs are evolved according to the rules of the model, the strengths of the predator-prey links are not determined a priori, and emerge from the process of constructing the web. We measure the distribution of these link strengths, and find that there are a large number of weak links, in agreement with recent suggestions. We also review some of the data on food webs available in the literature, and make some tentative comparisons with our results. The difficulties of making such comparisons and the possible future developments of the model are also briefly discussed.

q-bio.PE↗

arXiv2004

Deleting species from model food webs

We use food webs generated by a model to investigate the effects of deleting species on other species in the web and on the web as a whole. The model incorporates a realistic population dynamics, adaptive foragers and other features which allow for the construction of model webs which resemble empirical food webs. A large number of simulations were carried out to produce a substantial number of model webs on which deletion experiments could be performed. We deleted each species in four hundred distinct model webs and determined, on average, how many species were eliminated from the web as a result. Typically only a small number of species became extinct; in no instance was the web close to collapse. Next, we examined how the the probability of extinction of a species depended on its relationship with the deleted species. This involved the exploration of the concept of indirect predator and prey species and the extent that the probability of extinction depended on the trophic level of the two species. The effect of deletions on the web itself was studied by searching for keystone species, whose removal caused a major restructuring of the community, and also by looking at the correlation between a number of food web properties (number of species, linkage density, fraction of omnivores, degree of cycling and redundancy) and the stability of the web to deletions. With the exception of redundancy, we found little or no correlation. In particular, we found no evidence that complexity in terms of increased species number or links per species is destabilising.

q-bio.PE↗