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Competition has long been recognized as a central force in shaping
evolution, particularly through character displacement. Yet research on
character displacement is biased as it has focused almost exclusively on
pairs of interacting species, while ignoring multispecies interactions.
Communities are seldom so simple that only pairs of species interact, and
it is not clear if inferences from pairwise interactions are sufficient to
explain patterns of phenotypes in nature. Here we test for character
displacement in a natural system of freshwater fishes in western Mexico
that contains up to four congeneric species of the genus Poeciliopsis. We
analyzed body shape differences between populations with different numbers
of competitors while accounting for confounding environmental variables.
Surprisingly, we found evidence for convergent character displacement in
populations of P. prolifica, P. viriosa and P. latidens. We also found
that the convergence in body shape was not consistently in the same
direction, meaning that when three or more competitors co-occurred, we did
not find more extreme body shapes compared to when there were only two
competitors. Instead, when three or more competitors co-occur, body shape
was intermediate to the shape found with a pair of species or no
competitor present. This intermediate shape suggests that evolution in
multispecies communities likely occurs in response to several competitors,
rather than to simple pairwise interactions. Overall, our results suggest
that competition among multiple species is more complex than simple
pairwise competitive interactions.
391 views reported since publication in 2019.