Species Traits versus Environmental Properties as Factors Influencing Species Abundance
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A longstanding goal in ecological research is to explain the abundance of a species found in a particular place and time. To do so, researchers identify factors that influence species abundance and attempt to describe their relationship quantitatively. The main objective of my study was to compare the relative effects of intrinsic species traits (morphological, physiological, behavioral and life history attributes) and extrinsic environmental properties (climatic, biotic and geographic aspects) on species abundance. From a literature search, 915 independent abundance observations were compiled for 83 species from 170 survey locations distributed throughout the western United States. Besides abundance information, data on species traits associated with body size, reproductive capacity, diet, and geographic range were acquired along with properties of each survey location including climatic, spatial, and biotic (number of other rodent species and individuals) variables. To make the comparison, four composite variables (an intrinsic ecological variable, intrinsic geographic variable, extrinsic abiotic variable and extrinsic biotic variable) were created using Principal Components Analysis (PCA), and a fifth variable that was the distance between each species location (from a particular survey) and the center of that species geographic range was also included. Model comparison and model-averaging procedures were then conducted using all 31 possible linear regression models of the five predictor variables with standardized abundance (corrected for extraneous design variables) as the response variable. For the dataset consisting of all species, the intrinsic ecological variable was found to have the greatest influence on abundance (N=915, βeco = 0.116, SE= 0.042). For datasets limited to certain genera (Dipodomys, Neotoma, Perognathus, and Peromyscus), different variables were identified as most influential. These results indicate that environmental properties and species traits can influence abundance independently and in combination with one another. Moreover, there is no single combination of extrinsic and intrinsic variables that most influences abundance in all genera. Nonetheless, the distinction between intrinsic and extrinsic variables is a useful dichotomy in studying the factors affecting species abundance.