Foraging mode of spiders affects risk of predation by birds
Artikel i vetenskaplig tidskrift, 2015
Avian insectivores are top predators of arboreal arthropods in different forest ecosystems. The selective effects of
bird predation in relation to foraging behaviour in canopy-living spiders were studied in a 2-year field experiment
using exclosures in a spruce forest in southern Sweden. Three different hunting strategies – free-hunting,
two-dimensional web, three-dimensional web – were included in the analysis. Comparisons of bird predation rate
(ratio ln (abundance net-enclosed branch/abundance control)) showed considerable variation between spider
groups. Free-hunting spiders suffered most from avian insectivores and predation rate was significantly higher
than in spiders with two-dimensional webs. Spiders with three-dimensional webs were exposed to a predation rate
in between those of the two other hunting strategies. Generally, the experimental effect was significantly higher
in spring samples than in autumn, suggesting a stronger predation pressure in winter. The high variation in
susceptibility to predation by insectivores implies that selection on behaviour of spider individuals is strong. Web
building in itself is probably part of the protective mechanism, suggesting that webs have dual functions. We
conclude that the risk of bird predation is a selective force on foraging behaviour of spiders in a forest canopy
system.
spruce canopies
spider webs
hunting strategy
avian insectivores
differential mortality
Araneae