Niche theory and its relation to morphology and phenotype in geographic space: a case study in woodpeckers (Picidae)

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.