Effects of Fragmentation on the Richness of Vertebrates in the Florida Scrub Habitat

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Structures of habitat fragments interact with autecologies of resident species to produce patterns in taxonomic richness. Understanding this interaction is crucial to habitat conservation. We studied the vertebrates inhabiting fragments of the severely threatened sand pine scrub habitat of interior peninsular Florida. We surveyed 16 scrubs in south—central Florida that were categorized as either “large,” “medium,” or “small.” For each scrub, we determined (1) vegetational structure, (2) vegetational composition, (3) distance to the nearest scrub, (4) distance to the nearest larger scrub, (5) presence/absence of potential “corridor“ habitats between scrubs, (6) types of habitats between scrubs, (7) distance to the nearest permanent water, (8) percent coverage of surrounding habitats, and (9) area reduction over time. The principal methods used to census nonavian taxa were pitfall and double—ended funnel traps, while the principal method for avian taxa was transect surveys. Many of the nine scrub attributes were intercorrelated. Scrub size was the only attribute that correlated strongly with vertebrate richness. Distance, both to permanent water and to the nearest scrub, correlated strongly with nonavian richness after the influence of size was removed, however. We detected significant nestedness, but when the taxon—area relationship was taken into consideration, we could not demonstrate that any taxa were excluded from small scrubs. We constructed joint lists of taxa from various hypothetical “archipelagos” of the 16 individual scrubs, and found that the archipelagos often supported more taxa than large individual scrubs. We found no tendency for small scrubs to be depauperate, in general, and no matter how rare taxa were identified, they were more common than expected in medium and small scrubs, and less common than expected in large scrubs. The mere observation of either a taxon—area relationship or a nested taxonomic composition reveals little about underlying ecological processes. Our detailed analysis leads us to conclude that no evidence indicates the need for single large scrub reserves for resident vertebrates: an archipelago of individually smaller reserves could support at least as many taxa. This conclusion is based solely on the simple presence—absence of taxa in scrubs that were treated as replicates within size categories, however, and consideration of the abundances and distributions of individual taxa, and of the variation among scrubs of similar size, may lead to a different conclusion.

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Citation / Publisher Attribution

Ecology, v. 75, issue 2, p. 446-257