Meeting Abstract
Rising temperatures and shifting rainfall patterns due to climate change have altered the ecological milieu that organisms exploit for resources and reproduction. Many studies have examined actual and potential range shifts or changes in the phenology of species due to climate change. However, few have examined changes in phenotypic traits associated with habitat exploitation. Body size is a key phenotypic trait, because many physiological and ecological attributes scale with size. Several recent studies have shown a decrease in mean body size that has accompanied warmer climates. This pattern has been documented in invertebrates and vertebrate species. In this study, I compared the temporal pattern of body size of the tree lizard (Urosaurus ornatus ) from a Sonoran desert habitat in southeastern Arizona. I measured boy size (snout-vent length) on males and females at a study site in Saguaro National Park from 1985 – 2017. In addition, I supplemented these data with measurements taken from museum specimens from 1889 – 1980. During the 100+ year interval, average mean maximum and minimum temperatures have significantly increased in nearly all months of the year. Mean body size varied from 1889 – 1980, but showed no specific trend. A segmented regression revealed a shift in body size after 1985. Male tree lizards increased in size, whereas female lizards decreased in size. In addition, the magnitude of sexual size dimorphism also increased. Population size also declined during the 1985 – 2017 period. The changes in body size were consistent with an increase in the frequency and intensity of droughts that began after 1989. The increase in male body size may represent lower intraspecific competition resulting in higher per capita food availability. In contrast, female size may be a result of early onset of reproductive maturity and annual higher mortality.
