PARENT SESSION
Poster Session # 21: Biogeography, Biodiversity, Populations, and Genetics.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Small island biogeography in the Gulf of California: Lizards, the subsidized island biogeography hypothesis, and the small island effect.

Barrett, Kyle^{*,1, 3}, Wait, D. Alexander¹, Anderson, Wendy², ¹ Southwest Missouri State University, Springfield, MO³ Auburn University, Auburn, AL² Drury University, Springfield, MO

ABSTRACT- We used insular lizard communities in the Gulf of California to test predictions of the subsidized island biogeography (SIB) hypothesis and the small island effect (SIE). The SIB hypothesis suggests spatial subsidies may alter species richness patterns on small islands, while the SIE suggests a break-point model more accurately depicts species-area relationships by representing inter-island variation in the species richness of small islands. To evaluate the SIB hypothesis, we identified subsidized and unsubsidized islands based on surrogate measures of allochthonous productivity (i.e., island size and bird presence). Subsequently, we created species-area curves for Gulf island lizards. We used the residuals and slopes from these analyses to compare species richness on subsidized and unsubsidized islands. To test for a SIE, we used breakpoint regression to model the relationship between lizard species richness and island area. We compared these results to results from the log-linear regression model. Subsidized islands had a lower, but not significantly different, slope than unsubsidized islands. In addition to comparing slopes, we tested for differences in the magnitude of the residuals (from the species-area regression of all islands) for subsidized versus unsubsidized islands. We found no significant patterns in the residual values for small versus large islands; however, we found that islands without seabirds have significantly greater variance from the species-area linear regression relative to seabird-inhabited islands. We found the SIE to be a better predictor of lizard species richness than the log-linear model, although it did not explain a significantly greater amount of variation. Predictions of the SIB hypothesis were not strongly supported by the data; however, the absence of a significant SIE may be a result of spatial subsidies as explained by the SIB hypothesis and data presented here. We suggest potential scenarios to test for interactions between these two small island hypotheses.

Key words: lizard, spatial subsidies, island biogeography, small island effect