School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemStructure and fragmentation of growling grass frog metapopulations(SPRINGER, 2013-04)Metapopulations occur in fragmented landscapes, and consist of demographically-independent populations connected by dispersal. Nevertheless, anthropogenic habitat fragmentation may be fatal to metapopulations, as it disrupts dispersal and gene flow, and undermines the balance between population extinction and colonization. Understanding the extent to which particular land-use practices disrupt dispersal and gene flow is therefore crucial for conserving metapopulations. We examined the structure and fragmentation of metapopulations of the endangered growling grass frog (Litoria raniformis) in an urbanizing landscape in southern Australia. Population clustering analyses revealed three distinct genetic units, corresponding to the three wetland clusters sampled. Isolation-by-distance was apparent between populations, and genetic distance was significantly correlated with the presence of urban barriers between populations. Our study provides evidence that urbanization fragments metapopulations of L. raniformis. Managers of L. raniformis in urbanizing landscapes should seek to mitigate effects of urbanization on dispersal and gene flow.
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ItemMulti-Scale, Direct and Indirect Effects of the Urban Stream Syndrome on Amphibian Communities in Streams(PUBLIC LIBRARY SCIENCE, 2013-07-29)Urbanization affects streams by modifying hydrology, increasing pollution and disrupting in-stream and riparian conditions, leading to negative responses by biotic communities. Given the global trend of increasing urbanization, improved understanding of its direct and indirect effects at multiple scales is needed to assist management. The theory of stream ecology suggests that the riverscape and the surrounding landscape are inextricably linked, and watershed-scale processes will also affect in-stream conditions and communities. This is particularly true for species with semi-aquatic life cycles, such as amphibians, which transfer energy between streams and surrounding terrestrial areas. We related measures of urbanization at different scales to frog communities in streams along an urbanization gradient in Melbourne, Australia. We used boosted regression trees to determine the importance of predictors and the shape of species responses. We then used structural equation models to investigate possible indirect effects of watershed imperviousness on in-stream parameters. The proportion of riparian vegetation and road density surrounding the site at the reach scale (500-m radius) had positive and negative effects, respectively, on species richness and on the occurrence of the two most common species in the area (Criniasignifera and Limnodynastesdumerilii). Road density and local aquatic vegetation interacted in influencing species richness, suggesting that isolation of a site can prevent colonization, in spite of apparently good local habitat. Attenuated imperviousness at the catchment scale had a negative effect on local aquatic vegetation, indicating possible indirect effects on frog species not revealed by single-level models. Processes at the landscape scale, particularly related to individual ranging distances, can affect frog species directly and indirectly. Catchment imperviousness might not affect adult frogs directly, but by modifying hydrology it can disrupt local vegetation and prove indirectly detrimental. Integrating multiple-scale management actions may help to meet conservation targets for streams in the face of urbanization.
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ItemAre incentive programs working? Landowner attitudes to ecological restoration of agricultural landscapes.(Elsevier, 2013-09-30)Private property accounts for much of the planet's arable land, and most of this has been cleared for agricultural production. Agricultural areas retain only fragments of their original vegetation and this has been detrimental to many native plant and animal species. Habitat restoration and revegetation may be able to reconnect and enlarge existing remnant areas in agricultural landscapes and, thereby, enhance native plant and animal communities. However, conservation initiatives will be successful only if landowners actively participate in restoration actions. This study used four hundred postal questionnaires to assess the degree to which landowners in two regions of south-eastern Australia adopt restoration activities, their opinions regarding remnant and revegetated land and their management actions in these areas. One hundred and seventy nine completed questionnaires were received. Three quarters of respondents had undertaken restoration on their property or were planning to revegetate in the future. Landcare members were most likely to have previously revegetated and future revegetation intentions were best predicted by previous restoration activities and a primary income source that was off-farm. Landowners were more likely to manage restored and remnant areas if they perceived threats such as weeds, pest animals and fire risk would be detrimental to their property, than to enhance environmental outcomes. These results indicate that landowners are interested in restoring natural areas, but without greater assistance to restore ground layers and manage perceived threats posed by fire and invasive plants and animals, restoration actions will not have their desired biodiversity benefits.
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ItemAre only the strong surviving? Little influence of restoration on beetles (Coleoptera) in an agricultural landscape(ELSEVIER SCI LTD, 2013-06)Habitat restoration has become an important part of biodiversity conservation in the face of extensive habitat loss and fragmentation, especially in agricultural landscapes. Study of invertebrates such as beetles (Coleoptera) may be important to assess the effectiveness of restoration techniques in maintaining native fauna, because they provide a variety of trophic roles and ecosystem services. In this study we examined the conservation value for beetles of revegetation in linear strips and alongside remnant patches compared with remnant vegetation and cleared roadsides. We also assessed how habitat variables structured beetle community composition. Beetle species richness and abundance did not substantially differ between revegetated, remnant and cleared areas, and was not substantially influenced by vegetation type and structure. Herbivorous beetles and the family Curculionidae were more species rich in cleared linear strips. Beetle fauna in these agricultural landscapes may be a robust subset of the pre-clearing beetle community, possibly due to the widespread degradation of remnant areas and the ground layer habitats within them. One beetle species had slightly higher abundance in remnant linear strips, suggesting that remnant habitats may be important for some beetle species. Importantly, environmental variables strongly influenced beetle community composition, signifying that beetle communities are still responding to factors such as soil type and native vegetation, rather than variables mainly associated with land management. The restoration practices currently being undertaken in agricultural areas may not maintain beetle species that require specific habitat variables to survive. Ground-layer attributes need to be included in future revegetation projects, and translocation of specialist species of beetles may be required to restore communities.
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ItemA Bayesian model of metapopulation viability, with application to an endangered amphibian(WILEY, 2013-06-01)Abstract Aim Population viability analysis (PVA) is used to quantify the risks faced by species under alternative management regimes. BayesianPVAs allow uncertainty in the parameters of the underlying population model to be easily propagated through to the predictions. We developed a Bayesian stochastic patch occupancy model (SPOM) and used this model to assess the viability of a metapopulation of the growling grass frog (Litoria raniformis) under different urbanization scenarios. Location Melbourne, Victoria, Australia. Methods We fitted a Bayesian model that accounted for imperfect detection to a multiseason occupancy dataset forL. raniformiscollected across northern Melbourne. The probability of extinction was modelled as a function of effective wetland area, aquatic vegetation cover and connectivity, using logistic regression. The probability of colonization was modelled as a function of connectivity alone. We then simulated the dynamics of a metapopulation ofL. raniformissubject to differing levels of urbanization and compensatory wetland creation. Uncertainty was propagated by conducting simulations for 5000 estimates of the parameters of the models for extinction and colonization. Results There was considerable uncertainty in both the probability of quasi‐extinction and the minimum number of occupied wetlands under most urbanization scenarios. Uncertainty around the change in quasi‐extinction risk and minimum metapopulation size increased with increasing habitat loss. For our focal metapopulation, the analysis revealed that significant investment in new wetlands may be required to offset the impacts of urbanization. Main conclusions Bayesian approaches toPVAallow parametric uncertainty to be propagated and considered in management decisions. They also provide means of identifying parameters that represent critical uncertainties, and, through the use of informative priors, can easily assimilate new data to reduce parametric uncertainty. These advantages, and the ready availability of software to run Bayesian analyses, will ensure that Bayesian approaches are used increasingly forPVAs.
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ItemPredicting the Effect of Urban Noise on the Active Space of Avian Vocal Signals(UNIV CHICAGO PRESS, 2013-10-01)Urbanization changes the physical environment of nonhuman species but also markedly changes their acoustic environment. Urban noise interferes with acoustic communication in a range of animals, including birds, with potentially profound impacts on fitness. However, a mechanistic theory to predict which species of birds will be most affected by urban noise is lacking. We develop a mathematical model to predict the decrease in the active space of avian vocal signals after moving from quiet forest habitats to noisy urban habitats. We find that the magnitude of the decrease is largely a function of signal frequency. However, this relationship is not monotonic. A metaregression of observed increases in the frequency of birdsong in urban noise supports the model's predictions for signals with frequencies between 1.5 and 4 kHz. Using results of the metaregression and the model described above, we show that the expected gain in active space following observed frequency shifts is up to 12% and greatest for birds with signals at the lower end of this frequency range. Our generally applicable model, along with three predictions regarding the behavioral and population-level responses of birds to urban noise, represents an important step toward a theory of acoustic communication in urban habitats.