Diversity, distributions, and activity of bats in the San Juan Islands

Abstract

The loss and fragmentation of natural habitats are some of the greatest threats to terrestrial biodiversity. Much of the practice of conservation science is rooted in Island Biogeography Theory (IBT). IBT postulates that species richness on islands is driven by a dynamic equilibrium between the effects of area on extinction rates and the effects of isolation on colonization rates. However, studies of plants and animals on oceanic islands and man-made habitat islands suggest that IBT needs to be broadened to consider additional habitat characteristics beyond area and isolation. Additionally, species-specific differences in ecology, life-history, morphology, and mobility are all implicated to mediate how species respond to habitat fragmentation. In Chapter one, I investigated how island area, isolation, and habitat quality influence species richness in a naturally fragmented landscape - The San Juan Archipelago. I also examined whether ecological traits or morphological traits associated with mobility mediate species-specific distribution and activity patterns on the islands. I found that species richness increased on larger islands, but was not affected by habitat quality or isolation at this scale. I also found that species with more specialized diets were less prevalent among the islands. I did not find that any morphological traits related to mobility influenced species distribution patterns. In Chapter two, I analyzed activity patterns of bats on the San Juan islands. I found that the combined activity of all bat species was higher on larger islands and was not reduced on more isolated islands. My results suggest that islands with a greater abundance of potential roosting habitat (i.e., snag density) also have higher bat activity. I found that activity of larger bats tended to increase on islands with higher snag densities, but snag density had no influence on Myotis spp. activity. At the site scale, I found that Myotis spp. activity was positively related to canopy cover, whereas large bat activity tended to increase in more open habitats. Overall bat activity was also significantly higher adjacent to fresh water resources. Considering the results of Chapters one and two together, large islands are necessary to maintain higher bat species richness, but small isolated islands also provide habitat for bats. Importantly, availability of fresh water resources is also important for bat activity in the region. In Chapter three, I investigated how environmental characteristics in turn influence bat morphology. Specifically, I examined the intraspecific morphological variation in the Pallid Bat (Antrozous pallidus) and tested whether temperature, seasonality, or resource availability drive size variation differences in this wide-ranging Western bat species. I found that primary productivity and, to a lesser extent, temperature (via heat conservation) explain Pallid bat size variation across its distribution. My results also indicate that larger bats possess morphological traits associated with greater bite force production. The results of this study suggest that variation in resource availability may be a key factor underlying spatial patterns in size, morphology and, possibly, feeding performance in bats.