PARENT SESSION
Oral Session #21: Conservation of Biodiversity: Human landscapes, reserve design. Presiding: C. Meine.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Madison Ballroom D.
Relative Influences of Site, Landscape Context and Historical Factors on Birds in a Fragmented Landscape.
Mac Nally, Ralph1, Horrocks, Gregory1, 1
ABSTRACT- We considered the influence of habitat structure, landscape context, history and an aggressive, despotic bird (the Noisy Miner) on three characteristics of woodland-dependent bird assemblages in the fragmented, eucalypt-forest landscape of central Victoria, Australia. The response variables were species richness and sums-of-densities (i.e. total number of individual birds) and an index of rare-species occurrence. Species richness was less than expected (relative to same-sized areas in continuous forest) in smaller fragments and this was apparently due to current fragment area, density of Noisy Miners and habitat quality. The rare-species index exhibited similar dependencies, while sums-of-densities appeared to be related to the number and quality of wooded linkages to fragments. The historical variable was change in fragment area between 1963 and 1996, and was found to be irrelevant to all response variables. The lack of historical influence suggested that the avifaunas of the fragments were not relaxing from isolation effects and local extinctions, but are more likely to be dominated by dynamic recolonization and abandonment throughout the year. Thus, it is expected that species-richness and the rare-species index will be functions of contemporary ecological factors that generate typical species-area curves (area, competitive species). The dependence of sums-of-densities on the linkage variable appeared to be largely due to the responses of two species, the Red Wattlebird and the Yellow-tufted Honeyeater. These species are among the three most common in the large forest blocks (> 6000 ha), but are much rarer in fragments. The connectedness effect suggests that these species may depend upon linkages to occupy fragments that are only moderately distant from large forested areas within this region.
KEY WORDS: habitat fragmentation, birds, Australia, eucalypt woodlands