Don A. Driscoll

EXTINCTION AND OUTBREAKS ACCOMPANY FRAGMENTATION OF A REPTILE COMMUNITY

Land clearing depletes and fragments habitat, resulting in the loss of biodiversity. Corridors of native vegetation can ameliorate the impacts of land clearing by reducing isolation of remnant vegetation. However the effectiveness of linear remnants as corridors or connecting habitat is influenced by remnant size and condition. In central New South Wales, Australia, 84–95% of native vegetation has been cleared, with remnants occurring as isolated reserves and interconnecting strips beside roads and paddocks. Do the linear remnants provide connectivity throughout the landscape for reptile populations? In three 100-km2 agricultural locations, I classified all remnants into one of 10 “landscape elements” based on shape, management, and vegetation. I used generalized linear models and permutation tests to examine differences in reptile abundance among landscape elements. Only two blind snakes were captured in paddocks, suggesting that the matrix between remnants is virtually devoid of reptiles. Remnant shape ...

Land management practices associated with house loss in wildfires

Losses to life and property from unplanned fires (wildfires) are forecast to increase because of population growth in peri-urban areas and climate change. In response, there have been moves to increase fuel reduction—clearing, prescribed burning, biomass removal and grazing—to afford greater protection to peri-urban communities in fire-prone regions. But how effective are these measures? Severe wildfires in southern Australia in 2009 presented a rare opportunity to address this question empirically. We predicted that modifying several fuels could theoretically reduce house loss by 76%–97%, which would translate to considerably fewer wildfire-related deaths. However, maximum levels of fuel reduction are unlikely to be feasible at every house for logistical and environmental reasons. Significant fuel variables in a logistic regression model we selected to predict house loss were (in order of decreasing effect): (1) the cover of trees and shrubs within 40 m of houses, (2) whether trees and shrubs within 40 m of houses was predominantly remnant or planted, (3) the upwind distance from houses to groups of trees or shrubs, (4) the upwind distance from houses to public forested land (irrespective of whether it was managed for nature conservation or logging), (5) the upwind distance from houses to prescribed burning within 5 years, and (6) the number of buildings or structures within 40 m of houses. All fuel treatments were more effective if undertaken closer to houses. For example, 15% fewer houses were destroyed if prescribed burning occurred at the observed minimum distance from houses (0.5 km) rather than the observed mean distance from houses (8.5 km). Our results imply that a shift in emphasis away from broad-scale fuel-reduction to intensive fuel treatments close to property will more effectively mitigate impacts from wildfires on peri-urban communities.

The role of connectivity in Australian conservation

The existing system of nature reserves in Australia is inadequate for the long-term conservation and restoration of native biological diversity because it fails to accommodate, among other elements, large scale and long-term ecological processes and change, including physical and biotic transport in the landscape. This paper is an overview of the connectivity elements that inform a scientific framework for significantly improving the prospects for the long-term conservation of Australias biodiversity. The framework forms the basis for the WildCountry programme. This programme has identified connectivity at landscape, regional and continental scales as a critical component of an effective conservation system. Seven categories of ecological phenomena are reviewed that require landscape permeability and that must be considered when planning for the maintenance of biological diversity and ecological resilience in Australia: (1) trophic relations at regional scales; (2) animal migration, dispersal, and other large scale movements of individuals and propagules; (3) fire and other forms of disturbance at regional scales; (4) climate variability in space and time and human forced rapid climate change; (5) hydroecological relations and flows at all scales; (6) coastal zone fluxes of organisms, matter, and energy; and, (7) spatially-dependent evolutionary processes at all scales. Finally, we mention eight cross-cutting themes that further illuminate the interactions and implications of the seven connectivity-related phenomena for conservation assessment, planning, research, and management, and we suggest how the results might be applied by analysts, planners, scientists, and community conservationists.

How does ecological disturbance influence genetic diversity

Environmental disturbance underpins the dynamics and diversity of many of the ecosystems of the world, yet its influence on the patterns and distribution of genetic diversity is poorly appreciated. We argue here that disturbance history may be the major driver that shapes patterns of genetic diversity in many natural populations. We outline how disturbance influences genetic diversity through changes in both selective processes and demographically driven, selectively neutral processes. Our review highlights the opportunities and challenges presented by genetic approaches, such as landscape genomics, for better understanding and predicting the demographic and evolutionary responses of natural populations to disturbance. Developing this understanding is now critical because disturbance regimes are changing rapidly in a human-modified world.

Genetic structure, metapopulation processes and evolution influence the conservation strategies for two endangered frog species

The survival and continued evolution of a species is a pivotal tenet of conservation biology. Therefore, we need to understand the factors affecting survival and evolution of species to conserve them adequately. In this study I use allozyme electrophoresis to investigate the metapopulation structure and evolutionary processes that operate within the endangered frog species Geocrinia alba and G. vitellina. Genetically, G. alba and G. vitellina are highly subdivided. A number of intraspecific genetic groups can be recognised, although even within these groups there are significant differences in allele frequencies among populations. These differences imply that migration between populations is likely to be extremely restricted, if it occurs at all. The intraspecific genetic patterns suggest an evolutionary history of population bottlenecks followed by range expansion. Therefore, in the short term neither species exists as a metapopulation. However, at a larger time scale, migration, extinction and recolonisation may be central to the evolution and survival of both species. Maintenance of these processes is a challenge to which conservation managers must rise for the criteria of long-term survival and evolution to be met.

Empirical tests of metacommunity theory using an isolation gradient

All metacommunity theories incorporate dispersal as a key process influencing community composition. If communities are examined across a habitat-patch isolation gradient, different metacommunity theories predict contrasting patterns of community divergence and responses of rare species. We used bird and reptile data collected in three years from 168 habitat patches in a fragmented agricultural landscape, and bird data gathered from 63 remnants embedded in a pine plantation over two years to examine predictions arising from six metacommunity theories: A, neutral; B, species sorting; C, species sorting at low isolation but neutral at high isolation; D, neutral at low isolation but species sorting at high isolation; E, mass effects; and F, patch dynamics. We identified three classes of predictions arising from these theories that we could test using community survey data: (1) trajectories of rare species across an isolation gradient; (2) the influence of geographic distance, environmental parameters, and patch isolation on pair-wise comparisons of community divergence; and (3) the influence of isolation and environmental parameters on the divergence of communities from a regional species pool. Some analyses indicated moderately common support for neutral and species-sorting concepts, often acting simultaneously. Opposite responses by different groups of rare species to the isolation gradient showed that neutral and patch-dynamic processes may act on different components of the same community. Different analyses provided support for different theories, and so helped us to avoid being misled by a single analysis. However, generally we found very little consistent support for any of the metacommunity theories. Our analyses suggested that different metacommunity mechanisms act ephemerally, sometimes simultaneously and on different subsets of the fauna in different regions. The complexity of responses means that metacommunity ideas cannot yet be used predictively in a management context. We encourage further testing of the multiple predictions that arise from current metacommunity concepts, using additional data sets. However, if metacommunity processes act simultaneously and ephemerally, the predictions of any one metacommunity theory may be hard to detect at the community level. In that case, examining the ecology of multiple species in the same landscape may be needed to characterize metacommunity processes in nature.

The trajectory of dispersal research in conservation biology. Systematic review.

Dispersal knowledge is essential for conservation management, and demand is growing. But are we accumulating dispersal knowledge at a pace that can meet the demand? To answer this question we tested for changes in dispersal data collection and use over time. Our systematic review of 655 conservation-related publications compared five topics: climate change, habitat restoration, population viability analysis, land planning (systematic conservation planning) and invasive species. We analysed temporal changes in the: (i) questions asked by dispersal-related research; (ii) methods used to study dispersal; (iii) the quality of dispersal data; (iv) extent that dispersal knowledge is lacking, and; (v) likely consequences of limited dispersal knowledge. Research questions have changed little over time; the same problems examined in the 1990s are still being addressed. The most common methods used to study dispersal were occupancy data, expert opinion and modelling, which often provided indirect, low quality information about dispersal. Although use of genetics for estimating dispersal has increased, new ecological and genetic methods for measuring dispersal are not yet widely adopted. Almost half of the papers identified knowledge gaps related to dispersal. Limited dispersal knowledge often made it impossible to discover ecological processes or compromised conservation outcomes. The quality of dispersal data used in climate change research has increased since the 1990s. In comparison, restoration ecology inadequately addresses large-scale process, whilst the gap between knowledge accumulation and growth in applications may be increasing in land planning. To overcome apparent stagnation in collection and use of dispersal knowledge, researchers need to: (i) improve the quality of available data using new approaches; (ii) understand the complementarities of different methods and; (iii) define the value of different kinds of dispersal information for supporting management decisions. Ambitious, multi-disciplinary research programs studying many species are critical for advancing dispersal research.

How to find a metapopulation

Where habitat loss and fragmentation is severe, many native species are likely to have reduced levels of dispersal between remnant populations. For those species to avoid regional extinction in fragmented landscapes, they must undergo some kind of metapopulation dynamics so that local extinctions are countered by recolonisation. The importance of spatial dynamics for regional survival means that research into metapopulation dynamics is essential. In this review I explore the approaches taken to examine metapopulation dynamics, highlight the analytical methods used to get the most information out of field data, and discover some of the major research gaps. Statistical models, including Hanski’s incidence function model (IFM) are frequently applied to presence–absence data, an approach that is often strengthened using long-term data sets that document extinctions and colonisations. Recent developments are making the IFM more biologically realistic and expanding the range of situations for which the model is...

Is the matrix a sea? Habitat specificity in a naturally fragmented landscape

Abstract.  1. Metapopulation and island biogeography theory assume that landscapes consist of habitat patches set in a matrix of non‐habitat. If only a small proportion of species conform to the patch–matrix assumptions then metapopulation theory may only describe special cases rather than being of more general ecological importance.

GENETIC STRUCTURE OF THE FROGS GEOCRINIA LUTEA AND GEOCRINIA ROSEA REFLECTS EXTREME POPULATION DIVERGENCE AND RANGE CHANGES, NOT DISPERSAL BARRIERS

I describe the genetic structure of two frog species, Geocrinia rosea and Geocrinia lutea, using allozyme electrophoresis to understand population structure and thereby possible mechanisms of divergence and speciation. The sampling regimes represented the entire range of both species and provided replicated tests of the impact of ridges, rivers, and dry forest on gene flow. Geocrinia rosea and G. lutea were highly genetically subdivided (FST = 0.69, 0.64, respectively). In the extreme, there were fixed allelic differences between populations that were only 4 km (G. rosea) or 1.25 km (G. lutea) apart. In addition to localized divergence, two‐dimensional scaling of genetic distance allowed the recognition of broad‐scale genetic groups, each consisting of several sample sites. Patterns of divergence were unrelated to the presence of ridges, rivers, or dry forest. I argue that range contraction and expansion, combined with extreme genetic divergence in single, isolated populations, best accounts for the genetic structure of these species.