Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population

Authors

  • David C. Pavlacky Jr,

    Corresponding author
    1. School of Biological Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
    2. Centre for Applied Environmental Decision Analysis, University of Queensland, Brisbane, Qld 4072, Australia
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    • Present address: Rocky Mountain Bird Observatory, PO Box 1232, Brighton, CO 80601, USA.

  • Hugh P. Possingham,

    1. School of Biological Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
    2. Centre for Applied Environmental Decision Analysis, University of Queensland, Brisbane, Qld 4072, Australia
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  • Andrew J. Lowe,

    1. School of Earth and Environmental Sciences, Australian Centre for Evolutionary Biology and Biodiversity, University of Adelaide, Adelaide, SA 5000, Australia
    2. State Herbarium of South Australia, Science Resource Centre, Department of Environment and Natural Resources, Adelaide, SA 5005, Australia
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  • Peter J. Prentis,

    1. Faculty of Science and Technology, Queensland University of Technology, Brisbane, Qld 4001, Australia
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  • David J. Green,

    1. Department of Biological Sciences, Centre for Wildlife Ecology, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
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  • Anne W. Goldizen

    1. School of Biological Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
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Correspondence author. E-mail: david.pavlacky@uqconnect.edu.au

Summary

1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations.

2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration.

3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes.

4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners.

5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes.

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