Beyond guilds: the promise of continuous traits for mammalian functional diversity

Abstract

Studies on mammalian community ecology and biogeography are increasingly using functional diversity to advance our understanding of how diversity is maintained and how it varies across space and over time. Functional diversity quantifies the range and prevalence of species traits in an assemblage and provides a means of linking patterns of diversity to the ecological processes that generate them. Measuring the most appropriate and informative traits is critically important, yet the variety of traits applied to mammalian systems has been relatively limited and most are categorical rather than continuous. As a result, finer variation among species is often overlooked, which may obscure more detailed and accurate conclusions, particularly for studies on smaller species pools. We seek to improve the quality of trait information for mammals by investigating the value of three continuous ecomorphological traits: the relative medullary thickness of the kidney (an indicator of urine concentrating ability) as a metric of habitat moisture requirements, hair density as a measure of temperature limitations, and an integrated suite of cranial and dental measurements as an indicator of dietary specialization. We measured these traits for the small mammal assemblage of the Great Basin ecoregion using fluid-preserved and skeletal specimens housed in natural history collections and accounted for phylogenetic and allometric relationships. Kidney morphology, hair density, and craniodental morphology each exhibited phylogenetic signal and revealed ecologically meaningful variation that is overlooked by associated categorical traits. The greater resolution of these continuous trait data will facilitate more refined assessments of functional diversity and improve efforts to test ecological theories or track responses to environmental change.