Does interference competition in animals meet Chesson's criteria for coexistence?

Background/Question/Methods

Contrary to indirect resource competition, interference competition involves direct negative interactions among competing individuals for limiting resources. Chesson (2000) showed that coexistence by niche partitioning required that, 1) coexisting species must be able to recover from low densities when other competing species are at their average densities (invasibility), and 2) density-dependent forces must reduce population growth such that intra-specific competition > interspecific competition as competing species approach their average densities. Also, equalizing coexistence will reduce fitness differences between competing species. Coexistence likely results from a balance between fitness similarity and niche differences. We surveyed the literature for interference competition among animals to determine if, 1) rare species can increase when their competitors are at average densities, and 2) if intra-specific aggression > inter-specific aggression when resources limit population growth. We searched the ISI Web of Science using ((“animal” OR “animals”) and “coexistence”) OR ((“animal” OR “animals”) AND “interfere*”) OR ((“animal” OR “animals”) AND ((“intra*” AND “inter*” AND “*specific”) OR (“con*” AND “hetero*” AND “*specific”)) AND (“competit*” OR “effect”)).

Results/Conclusions

We screened 191 articles eliminating studies with uncertain results to produce a non-exhaustive list of 39 articles involving a variety of animals and ecosystem types. In 15 studies, the frequency of intraspecific aggression > the frequency of interspecific aggression. However, there was no difference in the frequency of intra versus interspecific aggression 9 studies. Also, the ability of rare populations to increase depended on the availability of refuge habitat where they could avoid detection. However, one of the competing species were driven locally extinct in 6 studies. Some animals can seek out and attack small populations of competitors. These preliminary results suggest that in some cases of interference competition species do not coexist, and in some cases where they do coexist, intraspecific aggression is not > interspecific aggression. It appears that equal fitness in form of equal aggressors may permit species coexistence in these latter cases.