Indirect effects of prey swamping: differential seed predation during a bamboo masting event

KITZBERGER, T.; ENRIQUE JOSE CHANETON; CACCIA, F. L.

Ecology

Allen Press

Lugar: New York; Año: 2007 vol. 88 p. 2541 - 2554

0012-9658

Resource pulses often involve extraordinary 1 rdinary increases in prey availability that “swamp”consumers and reverberate through indirect interactions affecting other community members. We developed a model that predicts predator-mediated indirect effects induced by an epidemic prey on co-occurring prey types differing in relative profitability/preference, and validated our model by examining current-season and delayed effects of a bamboo mass seeding event on seed survival of canopy tree species in mixed Patagonian forests. The model shows that predator foraging behavior, prey profitability, and the scale of prey swamping influence the character and strength of short-term indirect effects on various alternative prey. When in large, prey-swamped patches, non-selective predators decrease predation on all prey types. Selective predators, instead, only benefit prey of similar quality to the swamping species, while very low or high preference prey remain unaffected. Negative indirect effects (apparent competition) may override such positive effects (apparent mutualism), especially for highly preferred prey, when prey-swamped patches are small enough to allow predator aggregation and/or predators show a reproductive numerical response to elevated food supply. Seed predation patterns during bamboo masting were consistent with predicted short-term indirect effects mediated by a selective predator foraging in large, prey-swamped patches. Bamboo seeds and similarly-sized Austrocedrus chilensis (ciprés) and Nothofagus obliqua (roble) seeds suffered lower predation in bamboo flowered than non-flowered patches. Predation rates on the small-seeded Nothofagus dombeyi (coihue) and the large-seeded Nothofagus alpina (raulí) were independent of bamboo flowering. Indirect positive effects were transient; three months after bamboo seeding, granivores preyed heavily upon all seed types, irrespective of patch flowering condition. Moreover, one year after bamboo seeding, predation rates on the most preferred seed  (raulí) was higher in flowered than in nonflowered patches. Despite rapid predator  numerical responses, short-term positive effects can still influence community recruitmentent dynamics because surviving seeds may find refuge beneath the litter  produced by bamboo dieback. Together, our theoretical analysis and experiments indicate that indirect effects experienced by alternative prey during and after prey-swamping episodes need not be universal, but change across a prey quality spectrum, and critically depend on predator foraging rules and spatial scale of swamping.