Research article - Peer-reviewed, 2016
Predator refuges for conservation biological control in an intermediately disturbed system: the rise and fall of a simple solutionLiman, Anna-Sara; Eklund, Karin; Björkman, Christer
Abstract1. Managed systems harvested at intermediate time-scales have advantages over annualshort-cycled systems in maintaining top-down control of insect herbivores, and the flexibleharvest regimes in these systems provide opportunities for habitat management that can stabilizepredator-prey population dynamics across harvests - resulting in reduced risk of pest outbreaks.
2. In a large-scale field experiment, we explored whether retaining refuges, that is preservingparts of the stand to reduce predator mortality, could reduce the risk of pest insect outbreaksin willow short-rotation coppice. Population densities of three omnivorous predator speciesand three outbreaking herbivorous leaf beetle species were monitored over four years aftercoppice (stem harvest) in eight stands with refuges (treatment) and eight stands withoutrefuges (control). Predation pressure was estimated in years three and four.
3. Contrary to our predictions, leaf beetle densities were higher in stands with refuges andpredator densities were higher in stands without refuges. Leaf beetle egg mortality increasedwith total predator density, but did not differ between stands with and without refuges.
4. These unexpected results can be attributed to interactions between dispersal and patchage. The altered phenology of coppiced stems may have triggered leaf beetle aggregation inrefuges and migration from stands without refuges. A behavioural response to resource concentrationin retained old patches likely transformed the predator refuge from a ‘source' to a‘sink'.
5. Synthesis and applications. This study shows that retaining refuges in willow short-rotationcoppice to facilitate predator population recovery after harvest can come at the cost of moreattractive herbivore habitats - and thus increased pest problems. We conclude that croprefuges in systems with intermediate disturbance regimes pose new challenges for conservationbiological control, in particular the need to consider how patch age affects dispersal andrecolonization of both pest and predators.
Keywordsconservation biological control; harvest; insect outbreak; omnivore; patch age; perennial crop; recolonization; refuge; short-rotation coppice
Published inJournal of Applied Ecology
2016, volume: 53, number: 6, pages: 1823-1830
SLU Network Plant Protection
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