Bird Survival in an Isolated Javan Woodland: Island or Mirror?

Abstract

Differential extinction of forest species following forest fragmentation raises the questions of which populations are most prone to disappeaq and why. Hence we studied an 86–hectare woodland in west Java, the Bogor Botanical Garden (BBG), that became isolated when suwounding woodland was destroyed 50 years ago. Out of 62 bird species breeding in the BBG during 1932–1952, 20 had disappeared by 1980–1985, four were close to extinction, and five more had declined noticeably. The two main variables that identifl extinction‐prone populations in the BBG are 1) small initial population size in the BBG and 2) rareness or absence in the surrounding counttyside. Although the BBG retained wooded habitat, it is evidently too small to retain self‐sustaining populations of many woodland bird species. Small populations at high risk of extinction for stochastic reasons are doomed to disappear permanently unless subsidized by re‐colonization from the surroundings Thus, a too‐small reserve cannot function as a distributional island but comes to mirror the species composition of its surroundings More such case studies documenting species losses from small habitat fragments are required to demonstrate to nonbiologists the need for reserves large enough to support self‐sustaining populations.

Avian life‐history determinants of local extinction risk in a hyper‐fragmented neotropical forest landscape

“…Species that occur at naturally low abundances may be disadvantaged within a fragmented landscape because when isolated in fragments their populations are reduced in comparison to co-occurring species with higher abundance, rendering them more extinction-prone to environmental or demographic stochasticity (e.g. Diamond, Bishop & van Balen, 1987). A severe reduction in the species richness of terrestrial/understorey foragers, as observed in this study, is consistent with most tropical forest fragmentation studies (e.g.…”

Habitat use and species richness of bats in a patchy landscape

“…The degree of influence depends on time since isolation (Saunders 1989), distance between patches, size, shape (Wilcove et al 1986), occurrence of corridors (Saunders and de Rebeira 1991), etc. There are many examples of the impact of fragmentation on wildlife (Whitcomb et al 1981, Diamond 1984, Diamond et al 1987, Rolstad 1991 and Wilcox and Murphy (1985) argue that this is the most important factor contributing to the increasing loss of biological diversity.…”

Rapid land-use change and its impacts on tropical biodiversity

“…As deforestation proceeds, some species that are initially present in a landscape may be completely extirpated by habitat loss, and others may persist in tiny numbers in fragments, especially if they are rare or patchily distributed [Wilcox, 1980]. Populations of many forest-dependent species are completed isolated in fragments, whereas others are only partially isolated depending on their tolerance of degraded habitats and vagility [Diamond et al, 1987;Laurance, 1991]. The degree to which populations in fragments are connected demographically and genetically is also influenced by the distance to which the fragment is isolated from other forest tracts, and the types of degraded land surrounding the fragment.…”