Abstract
Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a variation cascade that propagated across the food web, including fish, zooplankton and phytoplankton species. In fisheries that removed a large amount of top-predatory and cannibalistic fish, the biomass oscillations started to decrease after fishing was started. In fisheries that mainly targeted large planktivorous fish, the biomass oscillations did not dampen but slightly increased over time. Removing species with specific ecological functions might alter the food web dynamics and potentially affect the ecological resilience of aquatic ecosystems.
Highlights
The widespread importance of trophic cascades (‘indirect species interactions that originate with predators and spread downward through food webs’ sensu Ripple et al 2016) has become increasingly recognized since they were first identified as primary determinant of community structure and ecosystem dynamics (Hairston et al 1960; Paine 1980; Pace et al 1999)
We studied the effects of different fishing gear on food web dynamics after adding environmental stochasticity in the model
Because our model consists of a complex food web, not of a simple food chain, it is difficult to demonstrate a wide top-down cascade, where, for example, the removal of piscivorous fish increases the abundance of the smaller fish they prey upon, which would reduce the zooplankton biomass
Summary
The widespread importance of trophic cascades (‘indirect species interactions that originate with predators and spread downward through food webs’ sensu Ripple et al 2016) has become increasingly recognized since they were first identified as primary determinant of community structure and ecosystem dynamics (Hairston et al 1960; Paine 1980; Pace et al 1999). The alteration of one species can spread throughout the food web via interactions that connect the species (Fig. 1b) These interactions are not limited to typical predator-prey interactions, as in a classic trophic cascade concept, but those can be competitive or other indirect interactions (e.g., Borer et al 2005, 2006). Complex food web models have been used to study the effects of human activities, such as fisheries regulation or ocean acidification, on food web properties but not to directly study human-induced trophic cascades (Kaplan et al 2010; Ainsworth et al 2011)
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