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Island biogeography has strongly influenced the study of biodiversity because
archipelagos provide natural model systems for investigating patterns of diversity and the
processes that shape ecological communities. I investigated the influence of area and
isolation of islands (n = 32) in the Gulf of California, Mexico on patterns of richness,
nestedness, and incidence of desert bats to determine factors important in shaping
community structure and patterns of occurrence of bats in a naturally insular landscape.
Species richness of bats was positively influenced by island size and declined
with isolation from the Baja peninsula in two distinct subarchipelagos. Southern islands,
which are associated with greater density of vegetation from summer rainfall, supported
more species than dry, barren islands in the northern subarchipelago, suggesting that both
area and habitat characteristics contribute to species richness of bats.
Community composition of bats was nested by area and isolation, such that
species found on smaller and more isolated islands were subsets of communities found on
large, less isolated islands that harbored higher richness. The influences of area and
isolation on community nestedness suggest species differ in immigration and persistence
rates on islands. Bat communities were also nested at 27 sites in coastal habitat on the
Baja peninsula, indicating that nestedness may occur in contiguous habitats that lack
immigration and extinction filters.
Probability of species occurrence on islands was influenced by area for five
species of insectivorous bat (Pipistrellus hesperus, Myotis californicus, Macrotus
californicus, Antrozous pallidus, and Mormoops megalophylla), suggesting occupancy of
islands by these species is limited by resource requirements. The threshold of island size
for occupancy of most species was ca. 100 ha, which is similar to area thresholds of
incidence for many landbirds in the same archipelago. Isolation also influenced
incidence of insectivorous bat species.
My research shows that area and isolation influence both community structure
and occupancy of bat species in a near-shore archipelago. My results raise important
questions about connectivity and persistence of populations of bats in isolated habitats,
especially when patch size is small. |
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