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Browsing Environment Institute Leaders publications by Author "Akcakaya, H."
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Item Metadata only Adapted conservation measures are required to save the Iberian lynx in a changing climate(Nature Publishing Group, 2013) Fordham, D.; Akcakaya, H.; Brook, B.; Rodriguez, E.; Alves, P.; Civantos, E.; Trivino, M.; Watts, M.; Araujo, M.The Iberian lynx (Lynx pardinus) has suffered severe population declines in the twentieth century and is now on the brink of extinction1. Climate change could further threaten the survival of the species2, but its forecast effects are being neglected in recovery plans3, 4. Quantitative estimates of extinction risk under climate change have so far mostly relied on inferences from correlative projections of species’ habitat shifts5. Here we use ecological niche models coupled to metapopulation simulations with source–sink dynamics6, 7 to directly investigate the combined effects of climate change, prey availability and management intervention on the persistence of the Iberian lynx. Our approach is unique in that it explicitly models dynamic bi-trophic species interactions in a climate change setting. We show that anticipated climate change will rapidly and severely decrease lynx abundance and probably lead to its extinction in the wild within 50 years, even with strong global efforts to mitigate greenhouse gas emissions. In stark contrast, we also show that a carefully planned reintroduction programme, accounting for the effects of climate change, prey abundance and habitat connectivity, could avert extinction of the lynx this century. Our results demonstrate, for the first time, why considering prey availability, climate change and their interaction in models is important when designing policies to prevent future biodiversity loss.Item Metadata only Critiques of PVA ask the wrong questions: throwing the heuristic baby out with the numerical bath water(Blackwell Publishing Inc, 2002) Brook, B.; Burgman, M.; Akcakaya, H.; O'Grady, J.; Frankham, R.Item Metadata only Dynamics of range margins for metapopulations under climate change(Royal Soc London, 2009) Anderson, B.; Akcakaya, H.; Araujo, M.; Fordham, D.; Martinez-Meyer, E.; Thuiller, W.; Brook, B.We link spatially explicit climate change predictions to a dynamic metapopulation model. Predictions of species' responses to climate change, incorporating metapopulation dynamics and elements of dispersal, allow us to explore the range margin dynamics for two lagomorphs of conservation concern. Although the lagomorphs have very different distribution patterns, shifts at the edge of the range were more pronounced than shifts in the overall metapopulation. For Romerolagus diazi (volcano rabbit), the lower elevation range limit shifted upslope by approximately 700 m. This reduced the area occupied by the metapopulation, as the mountain peak currently lacks suitable vegetation. For Lepus timidus (European mountain hare), we modelled the British metapopulation. Increasing the dispersive estimate caused the metapopulation to shift faster on the northern range margin (leading edge). By contrast, it caused the metapopulation to respond to climate change slower, rather than faster, on the southern range margin (trailing edge). The differential responses of the leading and trailing range margins and the relative sensitivity of range limits to climate change compared with that of the metapopulation centroid have important implications for where conservation monitoring should be targeted. Our study demonstrates the importance and possibility of moving from simple bioclimatic envelope models to second-generation models that incorporate both dynamic climate change and metapopulation dynamics.Item Metadata only Frillneck Lizard Chlamydosaurus Kingii in Northern Australia: determining optimal fire management regimes(Oxford University Press, 2004) Brook, B.; Griffiths, A.; Akcakaya, H.; Burgman, M.; Kindvall, O.; Wood, C.; Sjogrem Gulve, P.; Hatfield, J.; McCarthy, M.Item Metadata only Integrating bioclimate with population models to improve forecasts of species extinctions under climate change(The Royal Society, 2009) Brook, B.; Akcakaya, H.; Keith, D.; Mace, G.; Pearson, R.; Araujo, M.Climate change is already affecting species worldwide, yet existing methods of risk assessment have not considered interactions between demography and climate and their simultaneous effect on habitat distribution and population viability. To address this issue, an international workshop was held at the University of Adelaide in Australia, 25–29 May 2009, bringing leading species distribution and population modellers together with plant ecologists. Building on two previous workshops in the UK and Spain, the participants aimed to develop methodological standards and case studies for integrating bioclimatic and metapopulation models, to provide more realistic forecasts of population change, habitat fragmentation and extinction risk under climate change. The discussions and case studies focused on several challenges, including spatial and temporal scale contingencies, choice of predictive climate, land use, soil type and topographic variables, procedures for ensemble forecasting of both global climate and bioclimate models and developing demographic structures that are realistic and species-specific and yet allow generalizations of traits that make species vulnerable to climate change. The goal is to provide general guidelines for assessing the Red-List status of large numbers of species potentially at risk, owing to the interactions of climate change with other threats such as habitat destruction, overexploitation and invasive species.Item Metadata only Managing the long-term persistence of a rare cockatoo under climate change(Blackwell Publishing Ltd, 2012) Harris, J.; Fordham, D.; Mooney, P.; Pedler, L.; Araujo, M.; Paton, D.; Stead, M.; Watts, M.; Akcakaya, H.; Brook, B.1. Linked demographic-bioclimatic models are emerging tools for forecasting climate change impacts on well-studied species, but these methods have been used in few management applications, and species interactions have not been incorporated. We combined population and bioclimatic envelope models to estimate future risks to the viability of a cockatoo population posed by climate change, increased fire frequency, beak-and-feather disease and reduced management. 2. The South Australian glossy black-cockatoo Calyptorhynchus lathami halmaturinus is restricted to Kangaroo Island, Australia, where it numbers 350 birds and is managed intensively. The cockatoo may be at particular risk from climate change because of its insular geographic constraints and specialised diet on a single plant species, Allocasuarina verticillata. The cockatoo population model was parameterised with mark-resight-derived estimates of survival and fecundity from 13 years of demographic data. Species interactions were incorporated by using a climate-change-driven bioclimatic model of Allocasuarina verticillata as a dynamic driver of habitat suitability. A novel application of Latin Hypercube sampling was used to assess the model’s sensitivity to input parameters. 3. Results suggest that unmitigated climate change is likely to be a substantial threat for the cockatoo: all high-CO2-concentration scenarios had expected minimum abundances of <160 birds. Extinction was virtually certain if management of nest-predating brush-tail possums Trichosurus vulpecula was stopped, or adult survival reduced by as little as 5%. In contrast, the population is predicted to increase under low-emissions scenarios. 4. Disease outbreak, increased fire frequency and reductions in revegetation and management of competitive little corellas Cacatua sanguinea, were all predicted to exacerbate decline, but these effects were buffered by the cockatoo population’s high fecundity. 5. Spatial correlates of extinction risk, such as range area and total habitat suitability, were nonlinearly related to projected population size in the high-CO2-concentration scenario. 6. Synthesis and applications. Mechanistic demographic-bioclimatic simulations that incorporate species interactions can provide more detailed viability analyses than traditional bioclimatic models and be used to rank the cost-effectiveness of management interventions. Our results highlight the importance of managing possum predation and maintaining high adult cockatoo survival. In contrast, corella and revegetation management could be experimentally reduced to save resources.Item Metadata only Methods for determining viability of wildlife populations in large landscapes(Academic Press, 2009) Akcakaya, H.; Brook, B.; Millspaugh, J.; Thompson, F.This chapter reviews methods of population viability analysis (PVA) as applied to wildlife populations in large landscapes. For these populations, viability analysis requires careful consideration of the issues of spatial heterogeneity and scaling of ecological processes, habitat connectedness, and temporal dynamics of the landscape. Spatially structured models used for large-scale PVA include occupancy models, grid-based lattice models, demographically structured metapopulation models, and individual-based models. Population viability analyses in large landscapes often require the definition of distinct subpopulations, which in turn depend critically on the spatial scale of, and barriers to, dispersal in relation to the distribution of suitable habitat. Another important factor is the effect of landscape dynamics on the temporal variability of the habitat, and hence on the dynamics of the wildlife populations. Viability of species in dynamic landscapes depends on the interaction between landscape change (the pattern, scale, rate, and direction of landscape changes in size, structure, and quality) and the species' ecology (its ability to disperse between and grow in the habitat patches or make use of the matrix). Spatial separation of populations can also provide the opportunity to validate the generality and applicability of model predictions in the absence of long-term monitoring data. © 2009 Elsevier Inc. All rights reserved.Item Metadata only Plant extinction risk under climate change: are forecast range shifts alone a good indicator of species vulnerability to global warming?(Blackwell Science Ltd, 2012) Fordham, D.; Akcakaya, H.; Araujo, M.; Elith, J.; Keith, D.; Pearson, R.; Auld, T.; Mellin, C.; Morgan, J.; Regan, T.; Tozer, M.; Watts, M.; White, M.; Wintle, B.; Yates, C.; Brook, B.AbstractModels that couple habitat suitability with demographic processes offer a potentially improved approach for estimating spatial distributional shifts and extinction risk under climate change. Applying such an approach to five species of Australian plants with contrasting demographic traits, we show that: (i) predicted climate‐driven changes in range area are sensitive to the underlying habitat model, regardless of whether demographic traits and their interaction with habitat patch configuration are modeled explicitly; and (ii) caution should be exercised when using predicted changes in total habitat suitability or geographic extent to infer extinction risk, because the relationship between these metrics is often weak. Measures of extinction risk, which quantify threats to population persistence, are particularly sensitive to life‐history traits, such as recruitment response to fire, which explained approximately 60% of the deviance in expected minimum abundance. Dispersal dynamics and habitat patch structure have the strongest influence on the amount of movement of the trailing and leading edge of the range margin, explaining roughly 40% of modeled structural deviance. These results underscore the need to consider direct measures of extinction risk (population declines and other measures of stochastic viability), as well as measures of change in habitat area, when assessing climate change impacts on biodiversity. Furthermore, direct estimation of extinction risk incorporates important demographic and ecosystem processes, which potentially influence species’ vulnerability to extinction due to climate change.Item Metadata only The theta-logistic is unreliable for modelling most census data(British Ecological Society, 2010) Clark, F.; Brook, B.; Delean, J.; Akcakaya, H.; Bradshaw, C.Summary1.The theta‐logistic is a simple and flexible model for describing how the growth rate of a population slows as abundance increases. Starting atrm(taken as the maximum population growth rate), the growth response decreases in a convex or concave way (according to the shape parameter θ) to zero when the population reaches carrying capacity.2.We demonstrate that fitting this model to census data is not robust and explain why. The parameters θ andrmare able to play‐off against each other (providing a constant product), thus allowing both to adopt extreme and ecologically implausible values.3.We use simulated data to examine: (i) a population fluctuating around a constant carrying capacity (K); (ii) recovery of a population from 10% of carrying capacity; and (iii) a population subject to variation inK. We show that estimates of extinction risk depending on this or similar models are therefore prone to imprecision. We refute the claim that concave growth responses are shown to dominate in nature.4.As the model can also be sensitive to temporal variation in carrying capacity, we argue that the assumption of a constant carrying capacity is both problematic and presents a fruitful direction for the development of phenomenological density‐feedback models.Item Metadata only Tools for integrating range change, extinction risk and climate change information into conservation management(Blackwell Munksgaard, 2013) Fordham, D.; Akcakaya, H.; Araujo, M.; Keith, D.; Brook, B.; Environment InstituteEcological niche models (ENMs) are the primary tool used to describe and forecast the potential influence of climate change on biodiversity. However, ENMs do not directly account for important biological and landscape processes likely to affect range dynamics at a variety of spatial scales. Recent advances to link ENMs with population models have focused on the fundamental step of integrating dispersal and metapopulation dynamics into forecasts of species geographic ranges. Here we use a combination of novel analyses and a synthesis of findings from published plant and animal case studies to highlight three seldom recognised, yet important, advantages of linking ENMs with demographic modelling approaches: 1) they provide direct measures of extinction risk in addition to measures of vulnerability based on change in the potential range area or total habitat suitability. 2) They capture life‐history traits that permit population density to vary in different ways in response to key spatial drivers, conditioned by the processes of global change. 3) They can be used to explore and rank the cost effectiveness of regional conservation alternatives and demographically oriented management interventions. Given these advantages, we argue that coupled methods should be used preferentially where data permits and when conservation management decisions require intervention, prioritization, or direct estimates of extinction risk.