The Ecology of Morphology: The Ecometrics of Locomotion and Macroenvironment in North American Snakes

Abstract

Morphological traits that have a functional relationship with the environment can be used to study relationships between organisms and environments through time and across space. Dynamics of the trait-environment complex can be studied with ecometrics in individuals, in populations, and in communities. We explored how closely correlated three skeletal traits are with substrate use, and thus macrohabitat, among communities of snakes with the goal of better understanding how climate and macrovegetation might affect snake assemblages. Substrate use explained a large part of the variance in mean length-to-width ratio of vertebrae (R 2 = 0.66), PC1 of vertebral shape of a mid trunk vertebra (R 2 = 0.46), and relative tail length (R 2 = 0.71). Furthermore, mean relative tail length in snake assemblages across North America is strongly associated with ecoregions and vegetation cover (R 2 = 0.65 and 0.47, respectively). The close relationship with macrovegetation makes relative tail length a useful tool for predicting how snake assemblages will change as climates and biomes change across space or through time. This “ecometric” approach provides a medium-scale link between data collected from ecological studies over decades to data assembled from the fossil record over thousands, tens of thousands, or even millions of years. We show how historical vegetation changes between the early twentieth and twenty-first centuries at five preserves in North America resulted in ecometric changes that parallel the geographic distribution of relative tail length in snake communities across North America.