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Ecogeographic analyses have recovered common environmental trends with
respect to morphology; however discrepancies among trends exist.
Hypothesized reasons for these divergences vary, but most relate a taxon’s
morphology to its ecological niche. Morphology is known to diverge when
species co-occur with competitors or predators and when species occur
across different habitats and environments. A less understood divergence
from ecogeographic trends is niche fixation, wherein species become locked
into particular niches due to their community interactions or foraging
ecology. A form of niche fixation has been hypothesized in the theory of
Interspecies Social Dominance Mimicry (ISDM), in which mimics maintain
relatively constant size ratios with models to perpetuate their mimicry.
If true, mimics should display variation and trends in tandem with their
models. Here, I use mass as a proxy for body size and examine
ecogeographic trends in two sets of woodpeckers (Picidae): a Nearctic
group which has been reported to interact via ISDM, and a Neotropical
group which, based on similar appearances and overlapping distributions,
is a potential ISDM system. I found ecogeographic trends suggestive of
differential evolutionary responses, and I found evidence against niche
fixation in the Nearctic clade. The Neotropic clade showed limited
evidence for tandem size evolution between models and mimics, but
inconsistencies in the size ratios between mimic and model populations.
Here, I discuss the implications of observing divergent ecogeographic
trends within mimicry systems, with specific emphasis on how environment,
ecology, and community interactions guide evolution.
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