My research focused on the persistence of bird species in fragmented environments by examining their ecological tolerances to an intermediate scale of fragmentation of subtropical rainforest at Ravensbourne plateau, southeast Queensland, Australia. Previous studies of forest fragmentation have been inspired by theories of island biogeography, metapopulations and the principles of landscape ecology. They emphasize the effects of spatial scale of forests, assume that forest fragments provide habitats like those which existed before deforestation and assume that the spatial scale of those habitats as perceived by animals is analogous to the geographical perceptions of humans. Autecological studies of species' responses to fragmentation and studies of local extinctions of species suggest that these assumptions are untenable. In addition, most studies have been conducted well after the impact of deforestation and assume that the effects of fragmentation exceed those which occur as a result of natural fluctuations in the absence of deforestation. To address this assumption in the present study, I first asked whether small-scale deforestation caused a detectable impact on species richness and the abundances of individuals of foraging birds in an impacted fragment.
The ecological tolerances of species were investigated by establishing the functional habitats of different species to meet food and nesting requirements in fragments and continuous forest of simple notophyll evergreen vine forest. The extent and intensity of use of foraging and nesting habitats provided a basis from which to examine the abilities of species to respond either rigidly or flexibly to forest fragmentation. Once differences in the ecological tolerances of species were known, I then asked whether foraging and nesting traits of species, their preferences for vegetational features and their responses to spatial isolation and area of forest influenced differences in ecological tolerances.
The impact of deforestation was investigated by conducting an asymmetrical beyond BACIP experimental design which entailed sampling at randomly selected times before and after deforestation in controls and the impacted fragment. Both species richness and abundance of individuals fluctuated over time after deforestation and also gradually increased within the impacted fragment. The magnitude of these changes was greater than expected on the basis of observations conducted at the same time at locations which had not been deforested for at least 40 years. Further, changes were most pronounced near the source of the impact. Thus, the impacted fragment experienced an increase in the carrying capacity of species and individuals in response to small-scale deforestation, suggesting that the assumption of an impact of deforestation is justified.
The foraging and nesting habitats used to diagnose ecological tolerances of different species to fragmentation, were measured by the ways in which species used fragments and continuous forest. Ranges of foraging and nesting habitats were determined for 33 species. Species were diagnosed as having either euryoecious, high oligoecious, moderately oligoecious, narrow oligoecious or stenoecious range of foraging and nesting habitats. Euryoecious species were considered to exhibit greater ecological tolerance to fragmentation than stenoecious species. With the exception of three species, the functional habitats for foraging and nesting were dissimilar. Species which exhibited euryoecious foraging habitats had either moderately oligoecious, narrow oligoecious or stenoecious nesting habitats. Nesting habitats of species in the mosaic were therefore narrower than foraging habitats, suggesting that the ecological tolerance of species to fragmentation for nesting was less flexible than foraging requirements. Species tended to forage between the fragments and continuous forest more by chance whereas they placed nests throughout the mosaic in a non-random manner. Although all fragments and the continuous forest were used by at least some species for foraging and nesting, most species showed individuality in the combination of fragments and continuous forest used for these activities.
Floristics and vegetational structure both contributed to the explanation of differences in ecological tolerances of most species to fragmentation of forest as foraging habitats. To a lesser degree, the intermediate spatial scale of forest fragmentation also explained species' ecological tolerances for foraging habitat. Ecological tolerances of species to fragmentation of forest as nesting habitat differed substantially from those for foraging habitats. Ecological tolerances of species to fragmentation to meet their requirements for nesting were largely explained by placement of nests in multiple life forms of vegetation and substrates, preferences for combinations of vegetational structure of nesting habitat and, to a lesser degree, the spatial scale of forest.
By using an autecological approach to study the persistence of species, I found that species exhibited individuality in their ecological tolerance to fragmentation. I argue that such individuality in tracking food and suitable locations for nesting by species inhabiting a fragmented forest environment challenges the utility of the theories of island biogeography and metapopulations as explanatory tools. The Recognition Concept of Species is suggested as a useful framework for understanding the ecological tolerances of species to fragmentation of forest as foraging and nesting habitat.