Variation in the Vulnerability of Prey to Different Predators: Community‐Level Consequences

Abstract

Midge larvae (Diptera, Chironomidae) that weave filamentous algae into retreats of tufts, are dominant primary consumers in a river food web. In a previous study, densities of tuft—weaving midges increased in the presence of large fish. In the absence of large fish, midges decreased as densities of predatory invertebrates built up, and higher standing crops of algae were maintained. To examine the mechanisms underlying these dynamics, we compared the vulnerability of tuft—weaving midges (naked or in algal tufts) to fish and predatory invertebrates, in field and laboratory experiments. When midges were exposed for 1 h in the river to fish, 15 out of 15 midges in tufts survived, while 15 of 15 naked midges were consumed. Tufts afforded only partial protection to midges exposed to invertebrate predators, however. After 1 h, enhancement of survivorship by tufts was moderately significant for midges exposed to aeshnids, and insignificant for midges exposed to lestids and naucorids. We suggest that the vulnerability of tuft—weaving midges to invertebrate predators, and their relative invulnerability to fish, sets the stage for trophic cascades observed in the system. Fish, by consuming small predators, release midges, which graze down algae. The strong effects of fish as fourth—level consumers would not be predicted from their diets, in which algivorous mayflies dominate (>60% of the insect biomass found in each of the two most common fish species). Nevertheless, fish in this food web act as fourth—level, rather than third—level, consumers because of the differential vulnerability of one guild of primary consumer, which, when released from predation, can suppress plants.

Productivity, consumers, and the structure of a river food chain.

“…For example, experiments in lake mesocosms have demonstrated a variety of taxon-specific responses of plankton to manipulation of trophic architecture and nutrients (41)(42)(43). In some cases, taxon-specific differences in the susceptibility of prey to predators at different trophic levels can produce chain-like dynamics even in food webs with omnivores (24,44 …”

Induced Defenses in Herbivores and Plants Differentially Modulate a Trophic Cascade

“…Ecologists have also strongly focused on the biotic and abiotic factors that explain variation in cascade strengths within certain types of ecosystems (Power et al 1992, Polis and Strong 1996, Chase 2003. Potential explanations for variation in the strength of community-wide trophic cascades include predator species diversity (Finke and Denno 2004, Bruno and O'Connor 2005, Byrnes et al 2006, Snyder et al 2006, herbivore species diversity (Schmitz et al 2000), intraguild predation (McCann et al 1998, Hart 2002, refuges against intraguild predation Denno 2002, 2006), and heterogeneity in edibility within trophic levels (Leibold 1989, Power et al 1992, Bell 2002). …”

“…The importance of variation in (induced) defenses and thus edibility as modulators of top-down control has been recognized for a long time (Murdoch 1966, Power et al 1992, Strong 1992, Polis and Strong 1996, Bell 2002, Vos et al 2002, Schmitz et al 2004. Under a regime of increasing predation, species that differ in their defense levels may change in relative abundance (Abrams and Vos 2003), or species turnover may change community composition altogether (Leibold et al 1997, Chase et al 2000.…”

The ShearStress importance on the spatial distribution pattern of the invader Limnoperna fortunei in the Upper Paraná River Basin. - An assessment based on the Spatial Distribution Models

“…In general, potential distribution models can be considered as the adjustment of a function between the points of occurrence of a species and a multivariate group of environmental data (Phillips et al 2006). However, an invading species must overcome some filters in order to settle in a new region (Power et al 1992). These filters include: geographical barriers; the physical environment, which characterizes the target habitat and may constitute a more or less favorable environment to a certain invading species; the demographical resistance; and, finally, the biological filter, which can be defined by the competition and predation between previously settled species and invading species (Williamson 1996).…”