Island biogeography theory and the urban landscape: stopover site selection by the silver-haired bat (Lasionycteris noctivagans)

Many migratory bats require forested sites for roosting and foraging along their migration path, but increased urbanization and intensive agricultural practices may reduce the availability of stopover sites. Urban forests may provide important stopover habitat, maintaining landscape connectivity in regions where the majority of natural habitat has been cleared for development. Island biogeography theory can be applied to urbanized temperate forest biomes where small urban forests represent islands separated from the larger “mainland” forest. We used acoustic monitoring during the fall migration period to investigate the use of urban forest habitat by the migratory species Lasionycteris noctivagans Le Conte, 1831. We predicted that recorded activity would have a positive relationship with forest patch area and shape and a negative relationship with isolation from other forest patches, as suggested by island biogeography theory. We observed greater activity at larger forest patches, and although relationships for shape and isolation were not statistically supported the observed patterns were consistent with predictions. Our results demonstrate the need for more in-depth research on the habitat requirements for both migratory and resident bat species and the impact that ongoing urbanization has on local bat populations.

Saprotrophic fungal diversity predicts ectomycorrhizal fungal diversity along the timberline in the framework of island biogeography theory

Island biogeography theory (IBT) is one of the most fruitful paradigms in macroecology, positing positive species-area and negative species-isolation relationships for the distribution of organisms. Biotic interactions are also crucial for diversity maintenance on islands. In the context of a timberline tree species (Betula ermanii) as “virtual island”, we surveyed ectomycorrhizal (EcM) fungal diversity along a 430-m vertical gradient on the top of Changbai Mountain, China, sampling fine roots and neighboring soils of B. ermanii. Besides elevation, soil properties and plant functional traits, endophytic and saprotrophic fungal diversity were assessed as candidate predictors to construct integrative models. EcM fungal diversity decreased with increasing elevation, and exhibited positive diversity to diameter at breast height and negative diversity to distance from forest edge relationships in both roots and soils. Integrative models further showed that saprotrophic fungal diversity was the strongest predictor of EcM fungal diversity, directly enhancing EcM fungal diversity in roots and soils. Our study supports IBT as a basic framework to explain EcM fungal diversity. The diversity-begets-diversity hypothesis within the fungal kingdom is more predictive for EcM fungal diversity within the IBT framework, which reveals a tight association between saprotrophic and EcM fungal lineages in the timberline ecosystem.

TEST OF THE ISLAND BIOGEOGRAPHY THEORY WITH BOULDERS IN A SEAGRASS BED

We used shore boulders that had been previously colonized, and were scattered in a seagrass bed as models for islands. We tested two predictions of Island Biogeography theory: (1) small boulders harbored fewer species than large boulders, and (2) small boulders had higher rates of extinction than large boulders, as reflected in higher faunal replacement variability. We detected a definite relation between species richness and boulder size although not for all statistical models. We did not confirm higher compositional variability in small boulders.

Global synthesis of conservation studies reveals the importance of small habitat patches for biodiversity

Island biogeography theory posits that species richness increases with island size and decreases with isolation. This logic underpins much conservation policy and regulation, with preference given to conserving large, highly connected areas, and relative ambivalence shown toward protecting small, isolated habitat patches. We undertook a global synthesis of the relationship between the conservation value of habitat patches and their size and isolation, based on 31 systematic conservation planning studies across four continents. We found that small, isolated patches are inordinately important for biodiversity conservation. Our results provide a powerful argument for redressing the neglect of small, isolated habitat patches, for urgently prioritizing their restoration, and for avoiding simplistic application of island biogeography theory in conservation decisions.