The spatial analysis of biological interactions: morphological variation responding to the co-occurrence of competitors and resources

By sharing geographic space, species are forced to interact with one
another and the contribution of this process to evolutionary and
ecological patterns of individual species is not fully understood. At the
same time, species turnover makes that species composition varies from one
area to another, so the analysis of biological interaction cannot be
uncoupled from the spatial context. This is particularly important for
clades that show high degree of specialization such as hummingbirds, where
any variation in biotic pressures might lead to changes in morphology.
Here, we describe the influence of biological interactions on the
morphology of Hylocharis leucotis by simultaneously considering potential
competition and diet resources. We characterized the extent of local
potential competition and local available floral resources by correlating
two measurements of hummingbird diversity, floral resources and the size
of morphological space of H. leucotis along its geographic distribution.
We found that H. leucotis shows an important morphological variability
across its range and two groups can be recognized. Surprisingly,
morphological variation is not always linked to local hummingbird richness
or the phylogenetic similarity of. Only in the southern part of its
distribution, H. leucotis is morphologically more variable in those
communities where it coexist with closely related hummingbird species. We
also found that morphological variation in H. leucotis is independent from
the availability of floral resources. Our results suggest that abiotic
factors might be responsible for morphological differences across
populations in Hylocharis leucotis being biological interactions of minor
importance.