... ALAN N. ANDERSEN 1 ,; RICHARD W. BRAITHWAITE 1 ,; GARRY D. COOK 1 ,; LAURIE K. CORBETT 1 ,; R... more ... ALAN N. ANDERSEN 1 ,; RICHARD W. BRAITHWAITE 1 ,; GARRY D. COOK 1 ,; LAURIE K. CORBETT 1 ,; RICHARD J. WILLIAMS 1 ,; MICHAEL ... Currently the dominant fire management paradigm is one of extensive prescribed burning early in the dry season (May-June), in order ...
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 5, 2015
Protected areas remain a cornerstone for global conservation. However, their effectiveness at hal... more Protected areas remain a cornerstone for global conservation. However, their effectiveness at halting biodiversity decline is not fully understood. Studies of protected area benefits have largely focused on measuring their impact on halting deforestation and have neglected to measure the impacts of protected areas on other threats. Evaluations that measure the impact of protected area management require more complex evaluation designs and datasets. This is the case across realms (terrestrial, freshwater, marine), but measuring the impact of protected area management in freshwater systems may be even more difficult owing to the high level of connectivity and potential for threat propagation within systems (e.g. downstream flow of pollution). We review the potential barriers to conducting impact evaluation for protected area management in freshwater systems. We contrast the barriers identified for freshwater systems to terrestrial systems and discuss potential measurable outcomes and ...
Comparative studies of plant resource use and ecophysiological traits of invasive and native resi... more Comparative studies of plant resource use and ecophysiological traits of invasive and native resident plant species can elucidate mechanisms of invasion success and ecosystem impacts. In the seasonal tropics of north Australia, the alien C4 perennial grass Andropogon gayanus (gamba grass) has transformed diverse, mixed tree-grass savanna ecosystems into dense monocultures. To better understand the mechanisms of invasion, we compared resource acquisition and usage efficiency using leaf-scale ecophysiological and stand-scale growth traits of A. gayanus with a co-habiting native C4 perennial grass Alloteropsis semialata. Under wet season conditions, A. gayanus had higher rates of stomatal conductance, assimilation, and water use, plus a longer daily assimilation period than the native species A. semialata. Growing season length was also ~2 months longer for the invader. Wet season measures of leaf scale water use efficiency (WUE) and light use efficiency (LUE) did not differ between the two species, although photosynthetic nitrogen use efficiency (PNUE) was significantly higher in A. gayanus. By May (dry season) the drought avoiding native species A. semialata had senesced. In contrast, rates of A. gayanus gas exchange was maintained into the dry season, albeit at lower rates that the wet season, but at higher WUE and PNUE, evidence of significant physiological plasticity. High PNUE and leaf (15)N isotope values suggested that A. gayanus was also capable of preferential uptake of soil ammonium, with utilization occurring into the dry season. High PNUE and fire tolerance in an N-limited and highly flammable ecosystem confers a significant competitive advantage over native grass species and a broader niche width. As a result A. gayanus is rapidly spreading across north Australia with significant consequences for biodiversity and carbon and retention.
Background/Question/Methods Although most ecologists agree that both top-down and bottom-up facto... more Background/Question/Methods Although most ecologists agree that both top-down and bottom-up factors (consumers and resource limitation, respectively) influence biomass of primary producers, few studies experimentally examine both in concert. Here the relative importance of top-down and bottom-up factors was experimentally examined in two reaches in a 4th order oligotrophic river in the Australian wet-dry tropics during base flow conditions. The top-down factor (i.e. macroconsumer grazing) was examined using split-stream, large scale exclusion cages. The bottom-up factor (i.e. nutrient limitation) was manipulated using nutrient diffusing substrates with control, low N and P and high N and P addition treatments. Results/Conclusions Macroconsumer grazing was found to be important but varied depending on reach and substrate tested. Chlorophyll a biomass on natural rocky substrates within exclusion cages was significantly greater than in controls but only in the downstream reach. On the ...
1. Understanding the processes that structure community assembly across landscapes is fundamental... more 1. Understanding the processes that structure community assembly across landscapes is fundamental to ecology and for predicting and managing the consequences of anthropogenically induced changes to ecosystems. 2. We assessed the community similarity of fish, macroinvertebrate and vegetation communities against geographic distances ranging from 4 to 480 km (i.e. distance–decay relationships) to determine the balance between local environmental factors and regional dispersal processes, and thus whether species-sorting (niche processes) or dispersal limitation (neutral processes) was more important in structuring these assemblages in Australia's wet-dry tropics. We investigated whether the balance between niche and dispersal processes depended on the degree of hydrological connectivity, predicting that dispersal processes would be more important at connected sites, and also whether there was spatial concordance among these three assemblage types. 3. There was significant but weak s...
ABSTRACT 1.Invasive weeds are a major cause of biodiversity loss and economic damage worldwide. T... more ABSTRACT 1.Invasive weeds are a major cause of biodiversity loss and economic damage worldwide. There is often a limited understanding of the biology of emerging invasive species, but delay in action may result in escalating costs of control, reduced economic returns from management actions and decreased feasibility of management. Therefore, spread models that inform and facilitate on-ground control of invasions are needed.2.We developed a spatially explicit, individual based spread model that can be applied to both data-poor and data-rich situations to model future spread and inform effective management of the invasion. The model is developed using a minimum of two mapped distributions for the target species at different times, together with habitat suitability variables and basic population data. We present a novel method for internally calibrating the reproduction and dispersal distance parameters. We use a sensitivity analysis to identify variables that should be prioritized in future research to increase robustness of model predictions.3.We apply the model to two case studies, gamba grass and para grass, to provide management advice on emerging weed priorities in northern Australia. For both species we find that the current extent of invasion in our study regions is expected to double in the next ten years in the absence of management actions. The predicted future distribution identifies priority areas for eradication, control and containment to reduce the predicted increase in infestation.4.The model was built for managers and policy makers in northern Australia working on species where expert knowledge and environmental data are often lacking, but is flexible and can be easily adapted for other situations e.g. where good data are available. The model provides predicted probability of occurrence over a user-specified, typically short-term, time horizon. This output can be used to direct surveillance and management actions to areas that have the highest likelihood of rapid invasion and spread. Directing efforts to these areas provides the greatest likelihood of management success and maximises the return on investment management response.This article is protected by copyright. All rights reserved.
... ALAN N. ANDERSEN 1 ,; RICHARD W. BRAITHWAITE 1 ,; GARRY D. COOK 1 ,; LAURIE K. CORBETT 1 ,; R... more ... ALAN N. ANDERSEN 1 ,; RICHARD W. BRAITHWAITE 1 ,; GARRY D. COOK 1 ,; LAURIE K. CORBETT 1 ,; RICHARD J. WILLIAMS 1 ,; MICHAEL ... Currently the dominant fire management paradigm is one of extensive prescribed burning early in the dry season (May-June), in order ...
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 5, 2015
Protected areas remain a cornerstone for global conservation. However, their effectiveness at hal... more Protected areas remain a cornerstone for global conservation. However, their effectiveness at halting biodiversity decline is not fully understood. Studies of protected area benefits have largely focused on measuring their impact on halting deforestation and have neglected to measure the impacts of protected areas on other threats. Evaluations that measure the impact of protected area management require more complex evaluation designs and datasets. This is the case across realms (terrestrial, freshwater, marine), but measuring the impact of protected area management in freshwater systems may be even more difficult owing to the high level of connectivity and potential for threat propagation within systems (e.g. downstream flow of pollution). We review the potential barriers to conducting impact evaluation for protected area management in freshwater systems. We contrast the barriers identified for freshwater systems to terrestrial systems and discuss potential measurable outcomes and ...
Comparative studies of plant resource use and ecophysiological traits of invasive and native resi... more Comparative studies of plant resource use and ecophysiological traits of invasive and native resident plant species can elucidate mechanisms of invasion success and ecosystem impacts. In the seasonal tropics of north Australia, the alien C4 perennial grass Andropogon gayanus (gamba grass) has transformed diverse, mixed tree-grass savanna ecosystems into dense monocultures. To better understand the mechanisms of invasion, we compared resource acquisition and usage efficiency using leaf-scale ecophysiological and stand-scale growth traits of A. gayanus with a co-habiting native C4 perennial grass Alloteropsis semialata. Under wet season conditions, A. gayanus had higher rates of stomatal conductance, assimilation, and water use, plus a longer daily assimilation period than the native species A. semialata. Growing season length was also ~2 months longer for the invader. Wet season measures of leaf scale water use efficiency (WUE) and light use efficiency (LUE) did not differ between the two species, although photosynthetic nitrogen use efficiency (PNUE) was significantly higher in A. gayanus. By May (dry season) the drought avoiding native species A. semialata had senesced. In contrast, rates of A. gayanus gas exchange was maintained into the dry season, albeit at lower rates that the wet season, but at higher WUE and PNUE, evidence of significant physiological plasticity. High PNUE and leaf (15)N isotope values suggested that A. gayanus was also capable of preferential uptake of soil ammonium, with utilization occurring into the dry season. High PNUE and fire tolerance in an N-limited and highly flammable ecosystem confers a significant competitive advantage over native grass species and a broader niche width. As a result A. gayanus is rapidly spreading across north Australia with significant consequences for biodiversity and carbon and retention.
Background/Question/Methods Although most ecologists agree that both top-down and bottom-up facto... more Background/Question/Methods Although most ecologists agree that both top-down and bottom-up factors (consumers and resource limitation, respectively) influence biomass of primary producers, few studies experimentally examine both in concert. Here the relative importance of top-down and bottom-up factors was experimentally examined in two reaches in a 4th order oligotrophic river in the Australian wet-dry tropics during base flow conditions. The top-down factor (i.e. macroconsumer grazing) was examined using split-stream, large scale exclusion cages. The bottom-up factor (i.e. nutrient limitation) was manipulated using nutrient diffusing substrates with control, low N and P and high N and P addition treatments. Results/Conclusions Macroconsumer grazing was found to be important but varied depending on reach and substrate tested. Chlorophyll a biomass on natural rocky substrates within exclusion cages was significantly greater than in controls but only in the downstream reach. On the ...
1. Understanding the processes that structure community assembly across landscapes is fundamental... more 1. Understanding the processes that structure community assembly across landscapes is fundamental to ecology and for predicting and managing the consequences of anthropogenically induced changes to ecosystems. 2. We assessed the community similarity of fish, macroinvertebrate and vegetation communities against geographic distances ranging from 4 to 480 km (i.e. distance–decay relationships) to determine the balance between local environmental factors and regional dispersal processes, and thus whether species-sorting (niche processes) or dispersal limitation (neutral processes) was more important in structuring these assemblages in Australia's wet-dry tropics. We investigated whether the balance between niche and dispersal processes depended on the degree of hydrological connectivity, predicting that dispersal processes would be more important at connected sites, and also whether there was spatial concordance among these three assemblage types. 3. There was significant but weak s...
ABSTRACT 1.Invasive weeds are a major cause of biodiversity loss and economic damage worldwide. T... more ABSTRACT 1.Invasive weeds are a major cause of biodiversity loss and economic damage worldwide. There is often a limited understanding of the biology of emerging invasive species, but delay in action may result in escalating costs of control, reduced economic returns from management actions and decreased feasibility of management. Therefore, spread models that inform and facilitate on-ground control of invasions are needed.2.We developed a spatially explicit, individual based spread model that can be applied to both data-poor and data-rich situations to model future spread and inform effective management of the invasion. The model is developed using a minimum of two mapped distributions for the target species at different times, together with habitat suitability variables and basic population data. We present a novel method for internally calibrating the reproduction and dispersal distance parameters. We use a sensitivity analysis to identify variables that should be prioritized in future research to increase robustness of model predictions.3.We apply the model to two case studies, gamba grass and para grass, to provide management advice on emerging weed priorities in northern Australia. For both species we find that the current extent of invasion in our study regions is expected to double in the next ten years in the absence of management actions. The predicted future distribution identifies priority areas for eradication, control and containment to reduce the predicted increase in infestation.4.The model was built for managers and policy makers in northern Australia working on species where expert knowledge and environmental data are often lacking, but is flexible and can be easily adapted for other situations e.g. where good data are available. The model provides predicted probability of occurrence over a user-specified, typically short-term, time horizon. This output can be used to direct surveillance and management actions to areas that have the highest likelihood of rapid invasion and spread. Directing efforts to these areas provides the greatest likelihood of management success and maximises the return on investment management response.This article is protected by copyright. All rights reserved.
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