Analyzing time-energy constraints to understand the links between environmental change and local extinctions in terrestrial ectotherms

Accelerated extinction rates have prompted an increased focus on the interplay between environmental change and species response. The effects of environmental change on thermal opportunity are typically considered through a climate change context. However, habitat alteration can also have strong effects on the thermal environment. Additionally, habitat alteration is considered a leading factor of species extinction, yet few studies address the influence of habitat alteration on thermal opportunity and time-energy budgets in at-risk species. Here we show the strong effects that habitat degradation can have on thermal opportunity, time energy-budgets, and life history demographics of local populations. In the Ozark Mountains of northern Arkansas, woody vegetation encroachment has resulted in a shift in life history traits that appears to play an important role in recent extirpations of Eastern Collared Lizards (Crotaphytus collaris). Populations in degraded habitats experienced a decline in thermal opportunity and less time-at-body temperatures (time-at-Tb) suitable for digestion compared to those in intact habitats. We used our data to model the effect of reduced time-at-Tb on the net assimilated energy available for growth and reproduction. Our model predicts a ca. 46% decline in annual fecundity of individuals – which is similar to empirical observations of reproduction of C. collaris populations in degraded habitats (~49%). We conclude that C. collaris in degraded habitats experienced reduced growth and reproduction primarily as a result of constrained thermal opportunity leading to a decline in digestive processing rates. Our study applies an under-appreciated approach to identify the biophysical and time-energy effects of habitat alteration.