Consumer return chronology alters recovery trajectory of stream ecosystem structure and function following drought

Abstract

Consumers are increasingly being recognized as important drivers of ecological succession, yet it is still hard to predict the nature and direction of consumer effects in nonequilibrium environments. We used stream consumer exclosures and large outdoor mesocosms to study the impact of macroconsumers (i.e., fish and crayfish) on recovery of intermittent prairie streams after drying. In the stream, macroconsumers altered system recovery trajectory by decreasing algal and macroinvertebrate biomass, primary productivity, and benthic nutrient uptake rates. However, macroconsumer influence was transient, and differences between exclosures and controls disappeared after 35 days. Introducing and removing macroconsumers after 28 days resulted mainly in changes to macroinvertebrates. In mesocosms, a dominant consumer (the grazing minnow Phoxinus erythrogaster) reduced macroinvertebrate biomass but had little effect on algal assemblage structure and ecosystem rates during recovery. The weak effect of P. erythrogaster in mesocosms, in contrast to the strong consumer effect in the natural stream, suggests that both timing and diversity of returning consumers are important to their overall influence on stream recovery patterns. Although we found that consumers significantly altered ecosystem structure and function in a system experiencing rapid changes in abiotic and biotic factors following disturbance, consumer effects diminished over time and trajectories converged to similar states with respect to primary producers, in spite of differences in consumer colonization history. Thus, consumer impacts can be substantial in recovering ecosystems and are likely to be dependent on the disturbance regime and diversity of the consumer community.

Dynamic influences of nutrients and grazing fish on periphyton during recovery from flood

“…In general, nutrient influence intensified with time, whereas dace influence attenuated. A weakening dace effect is contrary to the observed strong effect of grazing minnows on algal biomass during baseflow conditions in some streams (Power et al 1988b, Gelwick andMatthews 1992), but is consistent with results reported by Murdock et al (2010), who found decreasing large-consumer effects during prairie stream recovery from drought. Murdock et al (2010) attributed this pattern to changing grazer communities and increasing macroinvertebrate grazing during succession.…”

“…A weakening dace effect is contrary to the observed strong effect of grazing minnows on algal biomass during baseflow conditions in some streams (Power et al 1988b, Gelwick andMatthews 1992), but is consistent with results reported by Murdock et al (2010), who found decreasing large-consumer effects during prairie stream recovery from drought. Murdock et al (2010) attributed this pattern to changing grazer communities and increasing macroinvertebrate grazing during succession. Dace appeared to have little influence on periphyton recovery because their effect was greatest soon after flooding, and the change from weak dace control to strong nutrient control coincided with the start of exponential algal growth.…”

The Stream Biome Gradient Concept: factors controlling lotic systems across broad biogeographic scales

“…Information comparing effects of stream consumers on ecosystem structure and function across biomes is limited. Grazing fishes can have strong effects on periphyton communities and nutrient cycling in desert (Grimm 1988) and grassland streams (Power et al 1985, Murdock et al 2010, Kohler et al 2011) that have relatively high rates of autochthonous production. The role of shrimp and crayfish in litter processing probably increases in forested tropical and temperate streams (Huryn andWallace 1987, Crowl et al 2001).…”

Quantifying the top-down and bottom-up effects of a non-native grazer in freshwaters

“…3, 4) could have been due to changes in algal community composition. For instance, grazers may have selected against long filamentous algae, resulting in a different algal community (Murdock et al 2010;Power et al 1985). Additionally, pevious work has documented conflicting patterns of the effects of native grazers on GPP.…”