Papers by Martin J Westgate
Conservation biology : the journal of the Society for Conservation Biology, Jan 14, 2015
Keeping track of conceptual and methodological developments is a critical skill for research scie... more Keeping track of conceptual and methodological developments is a critical skill for research scientists, but this task is increasingly difficult due to the high rate of academic publication. As a crisis discipline, conservation science is particularly in need of tools that facilitate rapid yet insightful synthesis. We show how a common text-mining method (latent Dirichlet allocation, or topic modeling) and statistical tests familiar to ecologists (cluster analysis, regression, and network analysis) can be used to investigate trends and identify potential research gaps in the scientific literature. We tested these methods on the literature on ecological surrogates and indicators. Analysis of topic popularity within this corpus showed a strong emphasis on monitoring and management of fragmented ecosystems, while analysis of research gaps suggested a greater role for genetic surrogates and indicators. Our results show that automated text analysis methods need to be used with care, but ...
Science of The Total Environment, 2015
Surrogate concepts are used in all sub-disciplines of environmental science. However, controversy... more Surrogate concepts are used in all sub-disciplines of environmental science. However, controversy remains regarding the extent to which surrogates are useful for resolving environmental problems. Here, we argue that conflicts about the utility of surrogates (and the related concepts of indicators and proxies) often reflect context-specific differences in trade-offs between measurement accuracy and practical constraints. By examining different approaches for selecting and applying surrogates, we identify five trade-offs that correspond to key points of contention in the application of surrogates. We then present an 8-step Adaptive Surrogacy Framework that incorporates cross-disciplinary perspectives from a wide spectrum of the environmental sciences, aiming to unify surrogate concepts across disciplines and applications. Our synthesis of the science of surrogates is intended as a first step towards fully leveraging knowledge accumulated across disciplines, thus consolidating lessons learned so that they may be accessible to all those operating in different fields, yet facing similar hurdles.
Understanding the influence of landscape change on animal populations is critical to inform biodi... more Understanding the influence of landscape change on animal populations is critical to inform biodiversity conservation efforts. A particularly important goal is to understand how urban density affects the persistence of animal populations through time, and how these impacts can be mediated by habitat provision; but data on this question are limited for some taxa. Here, we use data from a citizen science monitoring program to investigate the effect of urbanization on patterns of frog species richness and occurrence over 13 years. Sites surrounded by a high proportion of bare ground (a proxy for urbanization) had consistently lower frog occurrence, but we found no evidence that declines were restricted to urban areas. Instead, several frog species showed declines in rural wetlands with low-quality habitat. Our analysis shows that urban wetlands had low but stable species richness; but also that population trajectories are strongly influenced by vegetation provision in both the riparian zone and the wider landscape. Future increases in the extent of urban environments in our study area are likely to negatively impact populations of several frog species. However, existing urban areas are unlikely to lose further frog species in the medium term. We recommend that landscape planning and management focus on the conservation and restoration of rural wetlands to arrest current declines, and the revegetation of urban wetlands to facilitate the re-expansion of urban-sensitive species.
Journal of Animal Ecology, May 2015
Unlike philopatric migrants, the ecology of nomadic migrants is less well understood. This life-h... more Unlike philopatric migrants, the ecology of nomadic migrants is less well understood. This life-history strategy reflects responses to spatiotemporal variation in resource availability and the need to find resource rich patches to initiate breeding. The fitness consequences of movements between regions of patchily distributed resources can provide insight into ecology of all migrants and their responses to global change.
We link broad-scale data on spatiotemporal fluctuation in food availability to data on settlement patterns and fitness outcomes for a nomadic migrant, the endangered swift parrot Lathamus discolor. We test several predictions to determine whether facultative movements are adaptive for individual swift parrots in an environment where resources are patchily distributed over time and space.
Variation in the availability of swift parrot food resources across our study period was dramatic. As a consequence, swift parrots moved to breed wherever food was most abundant and did not resettle nesting regions in successive years when food availability declined. By moving, swift parrots exploited a variable food resource and reproduced successfully.
Exploiting the richest patches allowed swift parrots to maintain stable fitness outcomes between discrete breeding events at different locations. Unlike sedentary species that often produce few or lower quality offspring when food is scarce, nomadic migration buffered swift parrots against extreme environmental variation.
We provide the first detailed evidence that facultative movements and nomadic migration are adaptive for individuals in unpredictable environments. Our data support the widely held assumption that nomadic migration allows animals to escape resource limitation.
Basic and Applied Ecology, May 2015
Spatial population synchrony is defined as the coincidental changes of population density or othe... more Spatial population synchrony is defined as the coincidental changes of population density or other demographic parameters over time. Synchrony between local populations is believed to be widespread in nature because it has been found across a range of ecological guilds and across large spatial scales. However, a detailed understanding is still lacking of the extent of synchronous patterns in population parameters across animal communities, and of the relative importance of the several potential causes of population synchrony.
This study aimed to contribute to the understanding of how widespread spatial synchrony is in bird communities and to identify the main ecological drivers of synchrony. To achieve this we examined patterns of synchrony among bird populations inhabiting two contrasting areas of southeast Australia: the Victoria Central Highlands and Booderee National Park. Bird populations were studied through yearly point counts spanning 2004–2012 in Victoria and 2003–2012 in Booderee National Park.
Our empirical assessment showed that spatial proximity, synchrony in weather (cumulative rainfall) and habitat type influenced the level of spatial synchrony in 11 out of the 38 species examined (i.e. 29% of the species). Synchrony was primarily driven by spatial proximity, followed by synchrony in rainfall; habitat similarity played a small role as driver of synchrony in both areas.
Oikos, Feb 23, 2015
Surrogates are used widely in ecology to detect or monitor changes in the environment that are to... more Surrogates are used widely in ecology to detect or monitor changes in the environment that are too difficult or costly to assess directly. Yet most work on surrogates to date has been correlative, with little work on their predictive capacity or the circumstances under which they work. Our suggestion is to revisit and learn from research in the clinical medical sciences, including the causal statistical frameworks available to validate relationships between treatments, surrogate variables, and the outcome of interest. We adapt this medical thinking to ecology by providing a new framework that involves specification of the surrogate model, statistical validation, and subsequent evaluation in a range of spatial and temporal contexts. An inter-disciplinary surrogate concept will allow for a more rigorous approach to validating and evaluating proxy variables, thus advancing the selection and application of surrogates in ecology.
Ecology and Evolution, Jul 29, 2014
Quantifying and visualizing species associations are important to many areas of ecology and conse... more Quantifying and visualizing species associations are important to many areas of ecology and conservation biology. Species networks are one way to analyze species associations, with a growing number of applications such as food webs, nesting webs, plant–animal mutualisms, and interlinked extinctions. We present a new method for assessing and visualizing patterns of co-occurrence of species. The method depicts interactions and associations in an analogous way with existing network diagrams for studying pollination and trophic interactions, but adds the assessment of sign, strength, and direction of the associations. This provides a distinct advantage over existing methods of quantifying and visualizing co-occurrence. We demonstrate the utility of our new approach by showing differences in associations among woodland bird species found in different habitats and by illustrating the way these can be interpreted in terms of underlying ecological mechanisms. Our new method is computationally feasible for large assemblages and provides readily interpretable effects with standard errors. It has wide applications for quantifying species associations within ecological communities, examining questions about particular species that occur with others, and how their associations can determine the structure and composition of communities.
Journal of Applied Ecology, Jul 28, 2014
Conversion of natural and agricultural areas to conifer plantations is an important element of gl... more Conversion of natural and agricultural areas to conifer plantations is an important element of global change. Despite their widespread distribution and global importance, it is still unclear whether conifer plantations hinder or enhance movement by biota.
Population connectivity is difficult to quantify without detailed studies such as those using capture–mark–recapture methods. A novel solution is to quantify the synchrony in abundance between populations over time. Using this approach, more connected populations are expected to display synchrony, whereas disconnected populations are expected to fluctuate asynchronously. Here, we compared the relative effects of spatial proximity and matrix type on the population synchrony of a suite of forest-dependent birds in a long-term, fully controlled, and replicated landscape-scale experiment in south-eastern Australia.
Our experiment consisted of comparing bird populations inhabiting remnant eucalypt patches surrounded by Radiata pine Pinus radiata plantations (50 patches) with bird populations inhabiting remnant eucalypt patches where the surrounding landscapes are grazing fields (55 patches). Our data set encompassed 10 years and included 52 bird species characterized by different life history traits. After controlling for the effects of rainfall and patch characteristics on population dynamics, we found that spatial proximity, not matrix type, was the main driver of population synchrony for 16 species. The effect of the pine plantation matrix was negative (it reduced synchrony). However, the magnitude of its effect was particularly low (being significant only in four species).
Synthesis and applications. Our results show that pine plantations do not increase connectivity. In fact, they have little effect, with the exception of a few species, for which they may constitute a barrier. The implications of our findings for landscape management are that the conversion of agricultural areas to plantation forestry does not promote substantial movement of individuals (to the extent that would synchronize populations). Therefore, plantation expansion should not be promoted on the belief that it increases connectivity relative to an agricultural matrix.
Conservation Biology, Jul 21, 2014
Biodiversity surrogates and indicators are commonly used in conservation management. The focal sp... more Biodiversity surrogates and indicators are commonly used in conservation management. The focal species approach (FSA) is one method for identifying biodiversity surrogates, and it is underpinned by the hypothesis that management aimed at a particular focal species will confer protection on co-occurring species. This concept has been the subject of much debate, in part because the validity of the FSA has not been subject to detailed empirical assessment of the extent to which a given focal species actually co-occurs with other species in an assemblage. To address this knowledge gap, we used large-scale, long-term data sets of temperate woodland birds to select focal species associated with threatening processes such as habitat isolation and loss of key vegetation attributes. We quantified co-occurrence patterns among focal species, species in the wider bird assemblage, and species of conservation concern. Some, but not all, focal species were associated with high levels of species richness. One of our selected focal species was negatively associated with the occurrence of other species (i.e., it was an antisurrogate)—a previously undescribed property of nominated focal species. Furthermore, combinations of focal species were not associated with substantially elevated levels of bird species richness, relative to levels associated with individual species. Our results suggest that although there is some merit to the underpinning concept of the FSA, there is also a need to ensure that actions are sufficiently flexible because management tightly focused on a given focal species may not benefit some other species, including species of conservation concern, such of which might not occur in species-rich assemblages.
Nature Communications, May 21, 2014
Knowledge of the number and distribution of species is fundamental to biodiversity conservation e... more Knowledge of the number and distribution of species is fundamental to biodiversity conservation efforts, but this information is lacking for the majority of species on earth. Consequently, subsets of taxa are often used as proxies for biodiversity; but this assumes that different taxa display congruent distribution patterns. Here we use a global meta-analysis to show that studies of cross-taxon congruence rarely give consistent results. Instead, species richness congruence is highest at extreme spatial scales and close to the equator, while congruence in species composition is highest at large extents and grain sizes. Studies display highest variance in cross-taxon congruence when conducted in areas with dissimilar areal extents (for species richness) or latitudes (for species composition). These results undermine the assumption that a subset of taxa can be representative of biodiversity. Therefore, researchers whose goal is to prioritize locations or actions for conservation should use data from a range of taxa.
Journal of Applied Ecology
Many animal taxa respond strongly to spatial and temporal variation in vegetation structure and f... more Many animal taxa respond strongly to spatial and temporal variation in vegetation structure and floristic composition, suggesting that changes in vegetation could be a cheap and readily observable surrogate for changes in animal assemblages. Yet there is considerable uncertainty about how different taxa respond to vegetation over time, potentially limiting the application of habitat-based surrogates to many areas of applied ecology.
We examined the strength and temporal consistency of habitat-based surrogates of three different vertebrate taxa in a landscape with multiple vegetation types. We used regression models to quantify the relationships between six vegetation attributes (species richness and percentage cover of overstorey, midstorey and understorey) and three measures of bird, mammal and reptile assemblages (abundance, species richness and composition).
We found that overstorey richness and cover had both consistent and strong positive effects on bird assemblages. Vegetation effects were generally weaker and more variable for mammals and reptiles compared with birds. Each taxon displayed different temporal dynamics following fire, with negative effects on birds and mammals, but positive short-term effects on reptiles. Surprisingly, fire increased vegetation effects on birds, but did not consistently alter vegetation effects on mammals or reptiles, indicating a lack of concordant responses among taxa.
Synthesis and applications. Empirical testing of habitat-based surrogates of multiple animal taxa is needed to identify reliable and consistent management proxies. Our study suggests that habitat-based surrogates could be useful metrics for quantifying changes in bird assemblages through time and after fire, but that the same metrics could not be applied to mammal and reptile assemblages. The absence of both strong and consistent effects of vegetation attributes across the three groups of vertebrates suggests that taxon-specific habitat surrogates may be required to detect changes over time and after disturbance within heterogeneous landscapes.
PLOS ONE, Apr 17, 2014
Dispersal knowledge is essential for conservation management, and demand is growing. But are we a... more 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.
PLOS ONE, Feb 24, 2014
A holy grail of conservation is to find simple but reliable measures of environmental change to g... more A holy grail of conservation is to find simple but reliable measures of environmental change to guide management. For example, particular species or particular habitat attributes are often used as proxies for the abundance or diversity of a subset of other taxa. However, the efficacy of such kinds of species-based surrogates and habitat-based surrogates is rarely assessed, nor are different kinds of surrogates compared in terms of their relative effectiveness. We use 30-year datasets on arboreal marsupials and vegetation structure to quantify the effectiveness of: (1) the abundance of a particular species of arboreal marsupial as a species-based surrogate for other arboreal marsupial taxa, (2) hollow-bearing tree abundance as a habitat-based surrogate for arboreal marsupial abundance, and (3) a combination of species- and habitat-based surrogates. We also quantify the robustness of species-based and habitat-based surrogates over time. We then use the same approach to model overall species richness of arboreal marsupials. We show that a species-based surrogate can appear to be a valid surrogate until a habitat-based surrogate is co-examined, after which the effectiveness of the former is lost. The addition of a species-based surrogate to a habitat-based surrogate made little difference in explaining arboreal marsupial abundance, but altered the co-occurrence relationship between species. Hence, there was limited value in simultaneously using a combination of kinds of surrogates. The habitat-based surrogate also generally performed significantly better and was easier and less costly to gather than the species-based surrogate. We found that over 30 years of study, the relationships which underpinned the habitat-based surrogate generally remained positive but variable over time. Our work highlights why it is important to compare the effectiveness of different broad classes of surrogates and identify situations when either species- or habitat-based surrogates are likely to be superior.
Biological Conservation, 2013
Adaptive Management (AM) is widely considered to be the best available approach for managing biol... more Adaptive Management (AM) is widely considered to be the best available approach for managing biological systems in the presence of uncertainty. But AM has arguably only rarely succeeded in improving biodiversity outcomes. There is therefore an urgent need for reflection regarding how practitioners might overcome key problems hindering greater implementation of AM. In this paper, we present the first structured review of the AM literature that relates to biodiversity and ecosystem management, with the aim of quantifying how rare AM projects actually are. We also investigated whether AM practitioners in terrestrial and aquatic systems described the same problems; the degree of consistency in how the term ‘adaptive management’ was applied; the extent to which AM projects were sustained over time; and whether articles describing AM projects were more highly cited than comparable non-AM articles. We found that despite the large number of articles identified through the ISI web of knowledge (n = 1336), only 61 articles (<5%) explicitly claimed to enact AM. These 61 articles cumulatively described 54 separate projects, but only 13 projects were supported by published monitoring data. The extent to which these 13 projects applied key aspects of the AM philosophy – such as referring to an underlying conceptual model, enacting ongoing monitoring, and comparing alternative management actions – varied enormously. Further, most AM projects were of short duration; terrestrial studies discussed biodiversity conservation significantly more frequently than aquatic studies; and empirical studies were no more highly cited than qualitative articles. Our review highlights that excessive use of the term ‘adaptive management’ is rife in the peer-reviewed literature. However, a small but increasing number of projects have been able to effectively apply AM to complex problems. We suggest that attempts to apply AM may be improved by: (1) Better collaboration between scientists and representatives from resource-extracting industries. (2) Better communication of the risks of not doing AM. (3) Ensuring AM projects ‘‘pass the test of management relevance’’.
Biological Conservation, 2012
Quantifying functional connectivity is essential for understanding factors that limit or promote ... more Quantifying functional connectivity is essential for understanding factors that limit or promote animal dispersal in fragmented landscapes. Topography is a major factor influencing the movement behaviour of many animal species, and therefore the extent of functional connectivity between habitat patches. For pond-breeding frogs, areas of low topographic relief (such as streams or drainage lines) offer damp microhabitats that can facilitate movement through otherwise dry landscapes. However, the extent of topographic bias of frog movements has rarely been quantified. We used a replicated study to compare captures in high- and low-relief transects, for three species from a pond-breeding frog community in southeastern Australia. We captured frogs significantly more often on low-relief transects. However, capture rates decreased with increasing distance from water at similar rates on both high-relief and low-relief transects, and we observed few differences between adult and juvenile movements. Our results suggest that although low-relief drainage lines are important for the pond-breeding frogs in question, ecologists and landscape managers should not discount the role of high-relief locations. Because low-relief drainage lines represent a low proportion of the pond margin, >90% of movements are likely to occur across high-relief locations. Therefore, for the species that we studied, buffer zones designed to conserve only hydrological networks would provide insufficient protection of frequently used pond margins, while drainage lines are unlikely to act as vital networks facilitating connectivity between breeding ponds. Our study suggests that movement across slopes may be most important for facilitating functional connectivity.
Oikos, Apr 3, 2012
Fire is a common form of recurrent disturbance in many ecosystems, but ecological theory has a po... more Fire is a common form of recurrent disturbance in many ecosystems, but ecological theory has a poor record of predicting animal responses to fire, at both species and assemblage levels. As a consequence, there is limited information to guide fire regime management for biodiversity conservation. We investigated a key research gap in the fire ecology literature; that is, the response of an anuran assemblage to variation in the fire return interval. We tested two hypotheses using a spatially-explicit fire database collected over a 40 year period: (1) Species richness would peak at intermediate levels of disturbance. (2) Species with traits which enabled them to escape fire – burrowing or canopy dwelling – would be better able to survive fires, resulting in higher levels of occurrence in frequently burned sites. We found no evidence for either a reduction in species richness at locations with short fire return intervals, or a peak in species richness at intermediate levels of disturbance. Although we found some support for individual species responses to fire return intervals, these were inconsistent with the interpretation of burrowing or climbing being functional traits for fire-avoidance. Instead burrowing and climbing species may be more likely to be disadvantaged by frequent fire than surface dwelling frogs. More generally, our results show that many species in our study system have persisted despite a range of fire frequencies, and therefore that active management of fire regimes for anuran persistence may be unnecessary. The responses of anurans to fire in this location are unlikely to be predictable using simple life-history traits. Future work should focus on understanding the mechanistic underpinnings of fire responses, by integrating information on animal behavior and species’ ecological requirements.
Biodiversity and Conservation, Jan 1, 2009
Recent reviews of the conservation literature indicate that significant biases exist in the publi... more Recent reviews of the conservation literature indicate that significant biases exist in the published literature regarding the regions, ecosystems and species that have been examined by researchers. Despite the global threat of climatic change, similar biases may be occurring within the sub-discipline of climate-change ecology. Here we hope to foster critical thought and discussion by considering the directions taken by conservation researchers when addressing climate change. To form a quantitative basis for our perspective, we assessed 248 papers from the climate change literature that considered the conservation management of biodiversity and ecosystems. We found that roughly half of the studies considered climate change in isolation from other threatening processes. We also found that the majority of surveyed scientific publications were conducted in the temperate forests of Europe and North America. Regions such as Latin America that are rich in biodiversity but may have low adaptive capacity to climate change were not well represented. We caution that such biases in research effort may be distracting our attention away from vulnerable regions, ecosystems and species. Specifically we suggest that the under-representation of research from regions low in adaptive capacity and rich in biodiversity requires international collaboration by those experienced in climate-change research, with researchers from less wealthy nations who are familiar with local issues, ecosystems and species. Furthermore, we caution that the propensity of ecologists to work in essentially unmodified ecosystems may fundamentally hamper our ability to make useful recommendations in a world that is experiencing significant global change.
Conference Presentations by Martin J Westgate
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Papers by Martin J Westgate
We link broad-scale data on spatiotemporal fluctuation in food availability to data on settlement patterns and fitness outcomes for a nomadic migrant, the endangered swift parrot Lathamus discolor. We test several predictions to determine whether facultative movements are adaptive for individual swift parrots in an environment where resources are patchily distributed over time and space.
Variation in the availability of swift parrot food resources across our study period was dramatic. As a consequence, swift parrots moved to breed wherever food was most abundant and did not resettle nesting regions in successive years when food availability declined. By moving, swift parrots exploited a variable food resource and reproduced successfully.
Exploiting the richest patches allowed swift parrots to maintain stable fitness outcomes between discrete breeding events at different locations. Unlike sedentary species that often produce few or lower quality offspring when food is scarce, nomadic migration buffered swift parrots against extreme environmental variation.
We provide the first detailed evidence that facultative movements and nomadic migration are adaptive for individuals in unpredictable environments. Our data support the widely held assumption that nomadic migration allows animals to escape resource limitation.
This study aimed to contribute to the understanding of how widespread spatial synchrony is in bird communities and to identify the main ecological drivers of synchrony. To achieve this we examined patterns of synchrony among bird populations inhabiting two contrasting areas of southeast Australia: the Victoria Central Highlands and Booderee National Park. Bird populations were studied through yearly point counts spanning 2004–2012 in Victoria and 2003–2012 in Booderee National Park.
Our empirical assessment showed that spatial proximity, synchrony in weather (cumulative rainfall) and habitat type influenced the level of spatial synchrony in 11 out of the 38 species examined (i.e. 29% of the species). Synchrony was primarily driven by spatial proximity, followed by synchrony in rainfall; habitat similarity played a small role as driver of synchrony in both areas.
Population connectivity is difficult to quantify without detailed studies such as those using capture–mark–recapture methods. A novel solution is to quantify the synchrony in abundance between populations over time. Using this approach, more connected populations are expected to display synchrony, whereas disconnected populations are expected to fluctuate asynchronously. Here, we compared the relative effects of spatial proximity and matrix type on the population synchrony of a suite of forest-dependent birds in a long-term, fully controlled, and replicated landscape-scale experiment in south-eastern Australia.
Our experiment consisted of comparing bird populations inhabiting remnant eucalypt patches surrounded by Radiata pine Pinus radiata plantations (50 patches) with bird populations inhabiting remnant eucalypt patches where the surrounding landscapes are grazing fields (55 patches). Our data set encompassed 10 years and included 52 bird species characterized by different life history traits. After controlling for the effects of rainfall and patch characteristics on population dynamics, we found that spatial proximity, not matrix type, was the main driver of population synchrony for 16 species. The effect of the pine plantation matrix was negative (it reduced synchrony). However, the magnitude of its effect was particularly low (being significant only in four species).
Synthesis and applications. Our results show that pine plantations do not increase connectivity. In fact, they have little effect, with the exception of a few species, for which they may constitute a barrier. The implications of our findings for landscape management are that the conversion of agricultural areas to plantation forestry does not promote substantial movement of individuals (to the extent that would synchronize populations). Therefore, plantation expansion should not be promoted on the belief that it increases connectivity relative to an agricultural matrix.
We examined the strength and temporal consistency of habitat-based surrogates of three different vertebrate taxa in a landscape with multiple vegetation types. We used regression models to quantify the relationships between six vegetation attributes (species richness and percentage cover of overstorey, midstorey and understorey) and three measures of bird, mammal and reptile assemblages (abundance, species richness and composition).
We found that overstorey richness and cover had both consistent and strong positive effects on bird assemblages. Vegetation effects were generally weaker and more variable for mammals and reptiles compared with birds. Each taxon displayed different temporal dynamics following fire, with negative effects on birds and mammals, but positive short-term effects on reptiles. Surprisingly, fire increased vegetation effects on birds, but did not consistently alter vegetation effects on mammals or reptiles, indicating a lack of concordant responses among taxa.
Synthesis and applications. Empirical testing of habitat-based surrogates of multiple animal taxa is needed to identify reliable and consistent management proxies. Our study suggests that habitat-based surrogates could be useful metrics for quantifying changes in bird assemblages through time and after fire, but that the same metrics could not be applied to mammal and reptile assemblages. The absence of both strong and consistent effects of vegetation attributes across the three groups of vertebrates suggests that taxon-specific habitat surrogates may be required to detect changes over time and after disturbance within heterogeneous landscapes.
Conference Presentations by Martin J Westgate
We link broad-scale data on spatiotemporal fluctuation in food availability to data on settlement patterns and fitness outcomes for a nomadic migrant, the endangered swift parrot Lathamus discolor. We test several predictions to determine whether facultative movements are adaptive for individual swift parrots in an environment where resources are patchily distributed over time and space.
Variation in the availability of swift parrot food resources across our study period was dramatic. As a consequence, swift parrots moved to breed wherever food was most abundant and did not resettle nesting regions in successive years when food availability declined. By moving, swift parrots exploited a variable food resource and reproduced successfully.
Exploiting the richest patches allowed swift parrots to maintain stable fitness outcomes between discrete breeding events at different locations. Unlike sedentary species that often produce few or lower quality offspring when food is scarce, nomadic migration buffered swift parrots against extreme environmental variation.
We provide the first detailed evidence that facultative movements and nomadic migration are adaptive for individuals in unpredictable environments. Our data support the widely held assumption that nomadic migration allows animals to escape resource limitation.
This study aimed to contribute to the understanding of how widespread spatial synchrony is in bird communities and to identify the main ecological drivers of synchrony. To achieve this we examined patterns of synchrony among bird populations inhabiting two contrasting areas of southeast Australia: the Victoria Central Highlands and Booderee National Park. Bird populations were studied through yearly point counts spanning 2004–2012 in Victoria and 2003–2012 in Booderee National Park.
Our empirical assessment showed that spatial proximity, synchrony in weather (cumulative rainfall) and habitat type influenced the level of spatial synchrony in 11 out of the 38 species examined (i.e. 29% of the species). Synchrony was primarily driven by spatial proximity, followed by synchrony in rainfall; habitat similarity played a small role as driver of synchrony in both areas.
Population connectivity is difficult to quantify without detailed studies such as those using capture–mark–recapture methods. A novel solution is to quantify the synchrony in abundance between populations over time. Using this approach, more connected populations are expected to display synchrony, whereas disconnected populations are expected to fluctuate asynchronously. Here, we compared the relative effects of spatial proximity and matrix type on the population synchrony of a suite of forest-dependent birds in a long-term, fully controlled, and replicated landscape-scale experiment in south-eastern Australia.
Our experiment consisted of comparing bird populations inhabiting remnant eucalypt patches surrounded by Radiata pine Pinus radiata plantations (50 patches) with bird populations inhabiting remnant eucalypt patches where the surrounding landscapes are grazing fields (55 patches). Our data set encompassed 10 years and included 52 bird species characterized by different life history traits. After controlling for the effects of rainfall and patch characteristics on population dynamics, we found that spatial proximity, not matrix type, was the main driver of population synchrony for 16 species. The effect of the pine plantation matrix was negative (it reduced synchrony). However, the magnitude of its effect was particularly low (being significant only in four species).
Synthesis and applications. Our results show that pine plantations do not increase connectivity. In fact, they have little effect, with the exception of a few species, for which they may constitute a barrier. The implications of our findings for landscape management are that the conversion of agricultural areas to plantation forestry does not promote substantial movement of individuals (to the extent that would synchronize populations). Therefore, plantation expansion should not be promoted on the belief that it increases connectivity relative to an agricultural matrix.
We examined the strength and temporal consistency of habitat-based surrogates of three different vertebrate taxa in a landscape with multiple vegetation types. We used regression models to quantify the relationships between six vegetation attributes (species richness and percentage cover of overstorey, midstorey and understorey) and three measures of bird, mammal and reptile assemblages (abundance, species richness and composition).
We found that overstorey richness and cover had both consistent and strong positive effects on bird assemblages. Vegetation effects were generally weaker and more variable for mammals and reptiles compared with birds. Each taxon displayed different temporal dynamics following fire, with negative effects on birds and mammals, but positive short-term effects on reptiles. Surprisingly, fire increased vegetation effects on birds, but did not consistently alter vegetation effects on mammals or reptiles, indicating a lack of concordant responses among taxa.
Synthesis and applications. Empirical testing of habitat-based surrogates of multiple animal taxa is needed to identify reliable and consistent management proxies. Our study suggests that habitat-based surrogates could be useful metrics for quantifying changes in bird assemblages through time and after fire, but that the same metrics could not be applied to mammal and reptile assemblages. The absence of both strong and consistent effects of vegetation attributes across the three groups of vertebrates suggests that taxon-specific habitat surrogates may be required to detect changes over time and after disturbance within heterogeneous landscapes.