Showing papers by "Stephen E. Williams published in 2010"

Dynamic refugia and species persistence: tracking spatial shifts in habitat through time

Abstract: Historical climate is known to influence contemporary patterns of biological diversity. Species distribution modeling methods, combined with paleoclimatic surfaces, have been used to identify regions that were likely stable across long periods of time. To date, this approach has produced a static representation of refugia by identifying regions of suitable climate across a series of time-slices. However, suitable habitat for a given species (or suite of species) may have shifted contiguously in response to changing climates through geologic time. We develop a new approach that takes into consideration habitat connectivity through time. We use the Australian Wet Tropics as a case study to demonstrate how our method works and suggest additional insights the method might give for understanding the determinants of biological diversity.

Patterns of persistence and isolation indicate resilience to climate change in montane rainforest lizards

Abstract: Globally, montane tropical diversity is characterized by extraordinary local endemism that is not readily explained by current environmental variables indicating a strong imprint of history. Montane species often exist as isolated populations under current climatic conditions and may have remained isolated throughout recent climatic cycles, leading to substantial genetic and phenotypic divergence. Alternatively, populations may have become contiguous during colder climates resulting in less divergence. Here we compare responses to historical climate fluctuation in a montane specialist skink, Lampropholis robertsi, and its more broadly distributed congener, L. coggeri, both endemic to rainforests of northeast Australia. To do so, we combine spatial modelling of potential distributions under representative palaeoclimates, multi-locus phylogeography and analyses of phenotypic variation. Spatial modelling of L. robertsi predicts strong isolation among disjunct montane refugia during warm climates, but with potential for localized exchange during the most recent glacial period. In contrast, predicted stable areas are more widespread and connected in L. coggeri. Both species exhibit pronounced phylogeographic structuring for mitochondrial and nuclear genes, attesting to low dispersal and high persistence across multiple isolated regions. This is most prominent in L. robertsi, for which coalescent analyses indicate that most populations persisted in isolation throughout the climate cycles of the Pleistocene. Morphological divergence, principally in body size, is more evident among isolated populations of L. robertsi than L. coggeri. These results highlight the biodiversity value of isolated montane populations and support the general hypothesis that tropical montane regions harbour high levels of narrow-range taxa because of their resilience to past climate change.

Distributions, life‐history specialization, and phylogeny of the rain forest vertebrates in the Australian Wet Tropics

Abstract: The purpose of this data set was to compile distributional, general life-history characteristics and phylogenies for Australian tropical rain forest vertebrates to inform a wide range of comparative studies on the determinants of biodiversity patterns and to assess the impacts of global climate change. We provide three distinct data sets: (1) a table of species specific distributional and life-history traits for 242 vertebrate species found in the rain forests of the Australian Wet Tropics; (2) species distribution maps (GIS raster files) for 202 of the species displaying both the realized and potential distributions; and (3) phylogenies for these species. These species represent 93 birds, 31 amphibians, 31 mammals (including one monotreme), and 47 reptiles. Where information exists, the distributional and life-history data compiled here present information on: indices of environmental specialization (ENFA), habitat specialization, average body mass and size, sexual dimorphism, reproductive characteristics such as age at first reproduction, clutch/litter size, number of reproductive bouts per year and breeding seasonality, longevity, time of day when most active, and dispersal ability; distributional characteristics such as range size (potential and realized for both total and core ranges) and observed ranges in temperature, precipitation, and elevation; and niche attributes such as environmental marginality and specialization. The distribution maps provided represent a combination of presence-only ecological niche modeling (using MaxEnt) to estimate the potential distribution of a species followed by biogeographic clipping by expert opinion based on extensive field data and a subregional classification relevant to the topography and biogeographic history of the region to produce best-possible estimates of the realized distribution. Our assemblage contains many species with a shared evolutionary history, and thus many analyses of these data will need to account for phylogeny. Although a comprehensive phylogeny with branch length information does not exist for this diverse group of species, we present a best-estimate composite phylogeny constructed primarily from recently published molecular phylogenies of included groups.

Potential for mountaintop boulder fields to buffer species against extreme heat stress under climate change

Abstract: Species may circumvent or minimize some impacts resulting from climate change by utilizing microhabitats that buffer against extreme events (e.g., heat waves). Boulder field habitats are considered to have functioned as important refugia for rainforest fauna during historical climate fluctuations. However, quantitative data on microhabitat buffering potential in these habitats is lacking. We characterized temperature buffering over small distances (i.e., depths) within an exposed and forested boulder field on a tropical mountain. We demonstrate that temperatures are cooler and become more stable at increasing depths within boulder fields. The magnitude of difference is most pronounced in exposed situations where temperatures within boulder fields can be as much as 10°C lower than near surface conditions. Our data provide a first step toward building models that more realistically predict exposure to heat stress for fauna that utilize rocky habitats.

Elevational gradients in species abundance, assemblage structure and energy use of rainforest birds in the Australian Wet Tropics bioregion

Abstract: Elevational patterns of species richness, local abundance and assemblage structure of rainforest birds of north-eastern Australia were explored using data from extensive standardized surveys throughout the region. Eighty-two species of birds were recorded with strong turnover in assemblage structure across the elevational gradient and high levels of regional endemism in the uplands. Both species richness and bird abundance exhibited a humped-shaped pattern with elevation with the highest values being between 600 and 800 m elevation. While much of the variability in species richness could be explained by the species-area relationship, analyses of net primary productivity (NPP) and total daily energy consumption of the bird community (energy use) suggest that ecosystem energy flow or constraints may be a significant determinant of species richness. Species richness is positively correlated with local bird abundance which itself is closely related to total energy use of the bird community. We suggest the hypothesis that lower NPP limits bird abundance and energy use in the uplands (>500 m) and that low bird energy use and species richness in the lowlands is limited by a seasonal bottleneck in available primary productivity and/or a species pool previously truncated by an extinction filter imposed by the almost complete disappearance of rainforest in the lowlands during the glacial maxima. We suggest that some of the previously predicted impacts of global warming on biodiversity in the uplands may be partially ameliorated by increases in NPP because of increasing temperatures. However, these relationships are complex and require further data specifically in regard to direct estimates of primary productivity and detailed estimates of energy flow within the assemblage.