Beetle’s responses to edges in fragmented landscapes are driven by adjacent farmland use, season and cross-habitat movement
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Farming practices influence the degree of contrast between adjoining habitats, with consequences for biodiversity and species movement. Little is known, however, on insect community responses to different kinds of edges over time, and the extent of cross-habitat movement in agricultural landscapes.
To determine temporal changes in beetle responses to different farmland-woodland edges, and document cross-habitat movement.
We examined species richness, abundance, and movement across edges between remnant woodlands and four farmland uses (plantings, fallow, annual crops, woody debris applied over crops post-harvest) in southeastern Australia. We used directional pitfall traps to infer movement, and sampled at edges, and 20 and 200 m on both sides of edges, during spring and summer.
Detritivore and predator abundance varied between seasons across the edge between woodlands and all farmlands, but seasonal differences were weaker for fallow-woodland and woody debris-woodland edges. Detritivores moved from farmlands towards woodlands, but not across fallow-woodlands and woody debris-woodlands edges during summer. During summer, predators showed short-range movement towards edges from all farmlands except plantings, and towards woody debris from woodlands. Edges showed temporally stable predator richness and higher herbivore richness than adjoining habitats.
Farmland use and season interactively affect beetle abundance across farmland-woodland edges. Woody debris can reduce seasonal fluctuations in beetle edge responses and increase permeability for cross-habitat movement, while plantings provide habitat during summer. Edges provide important resources for beetles in adjoining habitats, however, seasonal movement of predators specifically into edges may affect prey assemblages—a link requiring further study.
KeywordsAgroecosystem Coleoptera Dispersal Spatial subsidies Spillover
This work was supported by Central Tablelands Local Land Services (through Australian Government funding), Lake Cowal Foundation and Mount Mulga Pastoral Company. KN was supported by an Australian Government Research Training Program (RTP) scholarship. Thanks to landholders (Day, Foy, Conlan, Hall, Lucas, Nowlan, Aylott, Grimm, Robinson, Crawford, Daley families) for property access. We are grateful to Alicia Ng, Nicholas Shore, Margaret Ning, Phil Pritchard, Dimitrios Tsifakis, Mal Carnegie, Hanh Huynh, Greg Burgess, Hannah Selmes, Yong Ding Li, Jake Lennon, Temma Carruthers-Taylor and Michael Lai for fieldwork assistance; Daniel Martinez-Escobar, Shauna Priest, Imogen Moore and Jake Lennon for lab assistance; Maldwyn John Evans, Kim Pullen, Michael Nash, Lingzi Zhou, Rolf Oberprieler, Margaret Thayer, Vladimir Gusarov and Roberto Pace for beetle identification; Wade Blanchard for statistical advice; and Clive Hilliker for Fig. 2 illustration. We thank Raphael Didham, Matt Hill and anonymous reviewers for helpful comments on the manuscript.
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