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Resum
Food-chain length, or the trophic level of an apex predator, is among the most important properties of food-webs
with implications for community structure, ecosystem processes and pollutant accumulation in forests. Three
main hypotheses (ecosystem-size, productivity, and disturbance) have been erected to explain variation in food chain length in freshwater ecosystems, yet the support for these hypotheses in less spatially restricted terrestrial
ecosystems has not been extensively studied. Here, we used nitrogen (δ15N) and carbon (δ13C) stable isotopes to
explore variation in the realized trophic positions (δ15N) of a beetle Carabus lineatus lateralis and a wasp Vespula
vulgaris in 32 chestnut woodland patches in northwestern Spain, while accounting for the insects’ relative mo bility by using inferences based on δ13C. We used five potential predictors of ecosystem-size productivity, seven
of disturbance and six covariates in anticipation that biological assemblages in woodlands might be influenced
by ecosystem-size productivity, and from a change from the human management to a much-increased activity of
ecosystem engineers, especially wild boar. Our results provided support for the disturbance hypothesis and
suggested that the beetle FCL seems to be more affected by wild boar disturbance than by human-forest man agement, possibly due to increased forest cover and to rural abandonment in recent decades. Moreover, we
found a negative association between the wasp FCL and the ecosystem-size productivity hypothesis, as indicated
by the plant Ellengberg’s indicator value for nitrogen, which contrasts to the hypothesis that ecosystem-size
productivity should increase FCL. Our findings are discussed in relation to: (1) differences in intensity and
frequency between human- and wild boar-induced disturbances; (2) the diets and mobilities of the two pre dators; and (3) the near lack of hard ecological boundaries in terrestrial ecosystems, such as chestnut wood
Citació
Forest ecology and management, vol. 479 (2021)
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