Stabilizing mechanisms in a food web with an introduced omnivore

Abstract

Intraguild predation (IGP) is an omnivorous food web configuration in which the top predator consumes both a competitor (consumer) and a second prey that it shares with the competitor. This omnivorous configuration occurs frequently in food webs, but theory suggests that it is unstable unless stabilizing mechanisms exist that can decrease the strength of the omnivore and consumer interaction. Although these mechanisms have been documented in native food webs, little is known about whether they operate in the context of an introduced species. Here, we study a marine mussel aquaculture system where the introduction of omnivorous mussels should generate an unstable food web that favors the extinction of the consumer, yet it persists. Using field and laboratory approaches, we searched for stabilizing mechanisms that could reduce interaction strengths in the food web. While field zooplankton counts suggested that mussels influence the composition and abundance of copepods, stable isotope results indicated that life‐history omnivory and cannibalism facilitated the availability of prey refugia, and reduced competition and the interaction strength between the mussel omnivore and zooplankton consumers. In laboratory experiments, however, we found no evidence of adaptive feeding which could weaken predator–consumer interactions. Our food web study suggests that the impact of an introduced omnivore may not only depend on its interaction with native species but also on the availability of stabilizing mechanisms that alter the strength of those interactions.

Nutrient-Loading Mitigation by Shellfish Aquaculture in Semi-Enclosed Estuaries

“…The low impact on it likely results from its fast turn-over rates and the feedback mechanism mentioned above. Conversely, zooplankton exchange is the most affected due to its slower dynamics, the competition for food with the bivalves (Gianasi et al in review; Granados et al, 2017a;Granados et al, 2017b) and, although marginal, the direct bivalve predation on zooplankton (Pace et al, 1998;Davenport et al, 2000;Trottet et al, 2008;Peharda et al, 2012). Despite the overall low contribution of zooplankton, representing only 1.8 to 3.9% of total N exported in all scenarios tested, this last result indicates that the bivalve aquaculture signal can be amplified through the trophic levels both in and out of these nearshore systems.…”

Modelling mixotrophic functional diversity and implications for ecosystem function

“…Food webs comprise complex arrays of interactions between resources and consumers (Worm et al, 2002;Araújo et al, 2011). Despite the recognised importance of predation and competition in defining the ecological niches of different functional taxa (Hunter and Price 1992;Cloern and Dufford, 2005), the overall structure and dynamics of food webs are also greatly affected by additional factors, such as intraguild predation and omnivory (Polis et al, 1989;Williams and Martinez, 2000;Johnson et al, 2010;Granados et al, 2017). Mixotrophy, defined here as the combination of phototrophy and phagotrophy in a single organism (Table I), is another 'twist' that can shift our understanding of ecosystem dynamics from terrestrial to aquatic environments (Tittel et al, 2003;Selosse et al, 2017).…”

Size and variation in individual growth rates among food web modules

“…Here, both the mussel and zooplankton feed on phytoplankton, while the mussel has the capacity to consume zooplankton. The blue mussel is an omnivore with an equal preference for phytoplankton or zooplankton irrespective of their relative densities; however, as blue mussels grow, they can accept a wider size range of zooplankton (Granados et al 2017). To complete the experimental design, we also created a consumer-resource module by effectively shutting down interactions with the mussel as a predator or competitor in the three-species interaction web.…”