Meeting Abstract

133.1  Monday, Jan. 7  Examining factors influencing body size change for insular rodents DURST, PAP*; ROTH, VL; Duke University; Duke University paul.durst@duke.edu

When organisms colonize an island, they often undergo dramatic shifts in size. This phenomenon has been observed in birds, reptiles, amphibians and even plants, but it is especially evident among mammals, where insular shifts towards larger body sizes in small species and smaller body sizes in large species have come to be known as the “island rule”. Despite early assertions that mammals followed this rule with law-like regularity, it is now clear that the island rule is an oversimplification of a complex process where exceptions abound. Multiple processes have been hypothesized to influence these size shifts, but no single variable has proven to be capable of explaining a significant portion of the size variance observed on islands. The order Rodentia has presented particular challenges to the island rule because among rodents on islands exist cases of both size increase and decrease with little apparent relation to original body size. To address this issue, we previously assembled a data set of insular rodent populations and made use of classification tree methods to identify which hypothesized processes were most useful in predicting the direction of size change for insular rodents. We found the most important factor predicting direction of change to be mainland body mass and while other variables had some predictive power, their roles in determining direction of size change were more context-dependent. Here, we expand our data set and confirm some previous findings, we use more traditional linear methods to focus on how these predictor variables influence the degree of size change, and we explore to what extent different degrees of size change reflect a significant difference between island and mainland rodent populations.