Daniel Janzen posed this question in a 1980 Evolution article. Once researchers of coevolution understand what coevolution is and understand the results of ecological interactions between populations, they must understand that the results of coevolution can also be caused by a number of other factors, often referred to as confounding factors. For example, just because traits in two species seem to have matching distributions, does not necessarily mean that they evolved to be that way because of their interaction. In order to be termed coevolution, the species must have experienced reciprocal evolutionary change as a result of their interactions. In 2003, Thomson, during a presidential address for the American Society of Naturalists, continued this call by posing the question ''When is it mutualism?,'' challenging empiricists to critically examine ecological data that seem to support claims of ecological interactions leading to coevolution.
In another example, recall that as a result of antagonistic interactions, allele frequencies can oscillate. If only a snapshot of evidence is available, subpopulations at different points of their cycling frequencies may appear to be different species or subspecies because of the different allele frequencies found when sampling the populations. When Gomulkiewicz et al. examined variable mutualisms, they noted that even in regions of antagonistic interaction, trait matching persisted. Therefore, not all cases of trait matching result from strictly mutualistic interactions, so it would be misleading to draw conclusions from only temporal or spatial snapshots of genetic information. The best progress will be made if interactions are studied from multiple perspectives, using mathematical models, behavioral observations of the ecological interactions, and genetic data of coevolution throughout time and space.
See also: Biodiversity; Death; Demography; Environmental Tolerance; Grazing Models; Microbial Communities; Microbial Cycles; Microbial Models; Statistical Prediction.
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