Showing papers by "Stephen E. Williams published in 2005"

Ecological traits of declining amphibians in upland areas of eastern Australia

Abstract: Catastrophic declines of amphibian populations have been reported from upland areas around the world, yet within regions not all species have been affected. Herein, we examine the relationships between conservation status and ecological traits for over 60 amphibian species from upland areas of eastern Australia. Among the 24 phylogenetic groups examined, eight groups contained only declining species, eight groups contained both declining and non-declining species and eight groups had no declining species, suggesting species declines are influenced by their evolutionary history. Declines have been reported for only one species (Philoria frosti) of 20 species (i.e. from genera Assa, Cophixalus, Austrochaperina and remaining Philoria/Kyaranus) with direct development in the terrestrial environment. Of the remaining 40 species that include an aquatic stage in the life history, species-specific traits associated with declines suggest species with stream-dwelling tadpoles are more likely to be declining than species that breed in ephemeral and isolated ponds. However, low ovarian clutch size is the most important ecological trait significantly associated with the tendency for a species to be declining (independent of phylogeny). Species with restricted geographic ranges are also more likely to be declining than widespread species (independent of phylogeny). While ovarian clutch size and geographic range are correlated they are both good predictors for the likelihood of decline for upland species independent of their phylogenetic history. We propose that low ovarian clutch size is an index of low fecundity, and indicates a reduction in population resilience, making those species more susceptible to population declines and extinction than highly fecund species. This provides the first ecological explanation for why some species are declining while other sympatric species are not. Geographic range provides an easily applied tool that can be used to predict the likelihood of species decline in other regions. These results support the hypothesis that a causal factor may be affecting all species of frogs, yet only those species with naturally low population resilience are susceptible to declines.

Potential decoupling of trends in distribution area and population size of species with climate change

Abstract: Global climates are changing rapidly and biological responses are becoming increasingly apparent. Here, we use empirical abundance patterns across an altitudinal gradient and predicted altitudinal range shifts to estimate change in total population size relative to distribution area in response to climate warming. Adopting this approach we predict that, for nine out of 12 species of regionally endemic birds, total population size will decline more rapidly than distribution area with increasing temperature. Two species showed comparable loss and one species exhibited a slower decline in population size with change in distribution area. Population size change relative to distribution area was greatest for those species that occurred at highest density in the middle of the gradient. The disproportional loss in population size reported here suggests that extinction risk associated with climate change can be more severe than that expected from decline in distribution area alone. Therefore, if we are to make accurate predictions of the impacts of climate change on the conservation status of individual species, it is crucial that we consider the spatial patterns of abundance within the distribution and not just the overall range of the species.

Vertebrate fauna survey of White Mountains National Park in the Desert Uplands Bioregion, central-north Queensland

Abstract: The patterns of composition and distribution of vertebrate fauna in Queensland's tropical savannas are poorly known. The sandstone landscapes of White Mountains National Park are considered to be significant for fauna given its geographical position on the Great Dividing Range. A survey at White Mountains National Park was undertaken in order to determine the species present, and place them in the context of the assemblages recorded within the Desert Uplands Bioregion. Standardised trapping and incidental data collection techniques were used and a total of 122 vertebrate fauna species (53 being new to the park) were identified. The fauna assemblage contains a mix of vertebrates with some affiliation to north-eastern Queensland tropical savannas (e.g. Anomalopus gowi, Uperoleia lithomoda, Chaerephon jobensis), more mesic east coastal environments (e.g. Glaphyromorphus punctulatus, Planigale maculata, Rattus sordidus) and species distributed generally within and west of the Desert Uplands (e.g. Pseudomys desertor, Ctenotus rosarium, Gehyra variegata, Lerista wilkinsi).

Post-fire Plant Regeneration in Montane Heath of the Wet Tropics, North-Eastern Queensland

Abstract: This paper documents post-fire plant regeneration within a montane heath community of the Wet Tropics. A large proportion of heath plants on Bishop's Peak, Cardwell Range north of Ingham, was observed to resprout after fire, with only one species, Banksia plagiocarpa, a rare shrub that co-dominates the community, identified as a fire-killed, "obligate seeder". Species richness and the seedling density of the co-dominant shrub Allocasuarina littoralis were higher in recently burnt heath compared with sites that remained unburnt for eight years; and five species displayed significantly greater abundance in either recently burnt or unburnt heath. Two years after fire, the height of most A. littoralis plants, both resprouts and seedlings, was below 61cm, and of most B. plagiocarpa seedlings was below 21cm. Seedlings of these shrubs are not expected to begin producing seed for several more years or gain their mature heights until more than eighty years after fire. Therefore, although fire can promote seed germination and species richness in this significant community, fire at intervals of more than eight years are required to allow the maturation of shrubs.