Dependence of stream predators on terrestrial prey fluxes: food web responses to subsidized predation

Abstract

Abstract. Resource subsidies in the form of energy, materials, and organisms can support the productivity of recipient ecosystems. When subsidies increase the abundance of top predators, theory predicts that top-down interactions will be strengthened. However, the degree to which subsidies intensify predation should be constrained by the strength of interactions between predators and their prey. To test the potential for subsidies to drive strong top-down control by two stream predators, steelhead (Oncorhynchus mykiss) and Pacific giant salamander (Dicamptodon tenebrosus) we reduced terrestrial prey and manipulated the presence of predators in 32 stream reaches. Prey subsidies supported elevated growth of predatory steelhead in our study system and in the absence of allochthonous prey steelhead experienced a 187% reduction in growth. Despite the high biomass of subsidized predators, there was little support for strong top-down control of herbivore biomass, or a trophic cascade as measured by changes in AFDM and chlorophyll-a. This result was consistent across subsidy treatments, suggesting that predatory steelhead are unable to increase exploitation of aquatic prey in the absence of terrestrial prey subsidies. The potential for top-down control was apparently limited by the fact that most (82%) herbivores in our study system were armored and relatively invulnerable to predation. These results demonstrate the potential importance of behavioral and morphological adaptations that can temper predator prey interactions in highly subsidized ecosystems.

Mainstem‐tributary linkages by mayfly migration help sustain salmonids in a warming river network

“…a) after the method of Atlas et al . (). Roofs had no effect on temperature, water flow, or chlorophyll‐a in benthic algae in enclosed pools (Table.…”

“…Therefore the predators in the small tributaries largely depend on allochthonous subsidies (Atlas et al . ) for their food.…”

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…These inputs can be particularly important to consumers during certain periods of low resource availability in recipient ecosystems [53]. The flow of food resources from freshwater to terrestrial ecosystems has the potential to create the high abundance of consumers along the edge of aquatic habitats [17,[54][55][56]. Since the flux of adult aquatic insects is an important subsidy for many terrestrial consumers / predators [2,10,19,23,27], managing aquatic and riparian habitats must consider trophic linkage of aquatic resource and terrestrial organisms [1,4,17].…”

“…Plants -While most studies focused on the importance of riparian forests as donor ecosystems to transfer leaf litter, large wood, seeds, pollen and terrestrial insects to aquatic ecosystems [5,10,39,56,108,109], or as recipient ecosystems for terrestrial consumers to enjoy the aquatic subsidy feast [7,9,23,27,54], ecologists investigated effects of aquatic subsidies (e.g. organic matter, emerging aquatic insects, salmon carcasses) on riparian plants [97,100,110,111].…”

Correlates and consequences of injury in a large, predatory stream salamander (Dicamptodon tenebrosus)

“…Although the density of both YOY and 1-|-steelhead were positively linked to the probability of salamander injury, the large differences in body size and behaviour between the two size classes of steelhead likely result in different mechanisms of salamander injury. As with many stream-dwelling salmonids, juvenile steelhead feed primarily on drifting aquatic and terrestrial invertebrate prey, and 1-1-steelhead are known to have a high degree of dietary overlap with giant salamanders (Atlas et al, 2013;Munshaw et al, 2013). Consequently, high densities of 1 -|-steelhead may intensify direct exploitation competition for prey with salamanders, leading to more aggressive encounters between individuals, or a higher frequency of salamander cannibalism attempts under preylimited conditions (Wildy et al, 2001).…”