Reach‐scale manipulations show invertebrate grazers depress algal resources in streams

Taylor, Barrie F.; McIntosh, Angus R.; Peckarsky, Barbara L.

doi:10.4319/lo.2002.47.3.0893

Cited by 44 publications

(34 citation statements)

References 31 publications

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“…In both experiments of this study all grazer treatments reduced mean algal biomass at the scale of microcosm chambers, consistent with other experiments conducted at larger scales (e.g., Lamberti et al 1987;Taylor et al 2002). Interestingly, all grazers used in this study prevented the accumulation of algal biomass, reducing chl a to levels similar to the rocks from the source stream.…”

Section: Discussionsupporting

confidence: 77%

How do grazers affect periphyton heterogeneity in streams?

Álvarez

Peckarsky

2004

Oecologia

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The effects of grazing by stream invertebrates on algal biomass and spatial heterogeneity were tested experimentally in flow-through microcosms with natural substrates (rocks). One experiment tested the effects of fixed densities of three species of grazers (the caddisfly Allomyia sp. and two mayflies, Epeorus deceptivus and Baetis bicaudatus) on periphyton. Baetis was tested with and without chemical cues from fish predators, which reduced grazer foraging activity to levels similar to the less mobile mayfly (Epeorus). Mean algal biomass (chlorophyll a; chl a) was reduced in grazer treatments compared to ungrazed controls, but there were no differences among grazer treatments. Algal heterogeneity (Morisita index) increased with grazer mobility, with the highest heterogeneity occurring in the Baetis-no fish treatment (most mobile grazer) and the lowest in the caddisfly treatment (most sedentary grazer). A second experiment used a three factorial design, and tested whether initial resource distribution (homogeneous vs. heterogeneous), Baetis density (high vs. low) and fish odor (present vs. absent) affected grazer impact on algal resources. Abundances of Baetis and chl a on individual rocks were recorded to explore the mechanisms responsible for the observed distributions of algae. Initial resource heterogeneity was maintained despite being subjected to grazing. Mean chl a was highest in controls, as in experiment I, and effects of Baetis on algal biomass increased with grazer density. There were no fish effects on algal biomass and no effects of grazer density or fish on algal heterogeneity. At the scale of individual rocks Baetis was unselective when food was homogeneously distributed, but chose high-food rocks when it was heterogeneously distributed. Results of these mechanistic experiments showed that Baetis can track resources at the scale of single rocks; and at moderate densities mobile grazers could potentially maintain periphyton distributions observed in natural streams.

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Section: Discussionsupporting

confidence: 77%

How do grazers affect periphyton heterogeneity in streams?

Álvarez

Peckarsky

2004

Oecologia

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“…Because we did not conduct small-scale experiments in riZes, we cannot make Wrm conclusions about their predictive capability in this habitat. However, because we did examine riZes in the large-scale perturbation , we can conclude that any eVects of experimental scale would not have been of the same nature as those observed by Kohler and Wiley (1997) or Taylor et al (2002). On the large scale, our work showed no eVects in riZes, whereas the aforementioned studies showed strong eVects.…”

Section: Discussioncontrasting

confidence: 53%

“…Because of their openness, the electric exclusions and the shrimp addition experiments were unaVected by typical mesocosm artifacts, which may have been a factor limiting extrapolation in the Colorado stream (Taylor et al 2002). The electric exclusion technique avoids mesocosm/cage artifacts such as altered water velocity, dissolved oxygen, sedimentation rates, and insect movements (Pringle et al 1999).…”

Section: Discussionmentioning

confidence: 99%

“…Similar to our study, both examine eVects of strongly interacting, numerically-dominant, grazing stream invertebrates. In Colorado (USA), microcosm experiments underestimated the eVects on algae of a whole-reach experiment (Taylor et al 2002). In Michigan (USA), small-scale experiments predicted eVects on algae, but substantially underestimated most eVects on invertebrates on the large scale (Kohler and Wiley 1997).…”

Section: Discussionmentioning

confidence: 99%

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Do small-scale exclosure/enclosure experiments predict the effects of large-scale extirpation of freshwater migratory fauna?

2006

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A variety of theoretical and empirical studies indicate that the abilities of small-scale experiments to predict responses to large-scale perturbations vary. Small-scale experiments often do not predict the directions of large-scale responses, and relatively few empirical studies have examined whether small-scale experiments predict the magnitudes of large-scale responses. Here we present an empirical example of small-scale manipulations predicting not only the directions but also the magnitudes of the effects of whole-catchment, decades-long decimation of migratory freshwater shrimp populations. In streams of Puerto Rico (USA), we used arena sizes of <2 m2 in 1- to 4-week exclosure/enclosure experiments. Effects of small-scale experiments largely matched those of large-scale shrimp loss above dams for a variety of response variables (abiotic and biotic factors including epilithic fine sediments, algae and organic matter, and invertebrate grazers, detritivores, and predators). The results of our extrapolation contrast with studies of small- versus large-scale perturbations in the temperate zone. Our findings are likely explained by: a set of response variables that are more dominated by within-patch processes than exchange processes, an experimental manipulation that encompassed the characteristic scales of response variables, our use of open arenas lacking cage artifacts, and/or our combination of two distinct experimental approaches (exclosures and enclosures). Based on our study design, we suggest that extrapolation across experimental scales can be greatly enhanced by embedding open arenas within large-scale conditions that represent all treatment levels.

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“…When we added nutrients to mesocosms, increased algal growth potential limited the magnitude of herbivore effects, thereby weakening the strength of the grazer-algal interactions (as in Taylor et al 2002. The rates of accrual of benthic algae reflect counteracting dynamic processes including nutrient supply, physical disturbance and grazing (Peterson 1996, Biggs et al 1999.…”

Section: Discussionmentioning

confidence: 99%

Disturbance legacies and nutrient limitation influence interactions between grazers and algae in high elevation streams

et al. 2015

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Debate about control of interaction strength among species is fueled by variation in environmental contexts affecting food webs. We used extensive surveys and two field experiments to test the individual and interactive influences of variation in the assemblages and associated traits of grazers as shaped by the legacy of disturbance, nutrient limitation and the presence of top predators on the accrual of basal resources. We quantified hydrologic variation and streambed movement to describe the legacy of disturbance and sampled biota of 20 streams over five years in a high‐elevation catchment in Colorado, USA. Grazer assemblages switched from caddisfly‐dominated to mayfly‐dominated as disturbance increased. We manipulated the composition of grazer assemblages and the availability of nutrients (N and P) within flow‐through mesocosms assembled adjacent to 10 streams, and also deployed larger in‐stream channels manipulating the presence of top predators (brook trout) in five streams varying in disturbance regimes. In both experiments we compared the rate of accrual of benthic algae and the strength of grazer‐algal interactions among treatments. We observed no indirect effects of top predators on grazer mobility, grazer consumption of algae, or accrual of algal biomass (no trophic cascades). However, in both experiments accrual rates of algae yielded a unimodal pattern and grazer impacts on algae decreased with increasing disturbance, but only at ambient (limiting) nutrient conditions. When nutrients were amended in the mesocosm experiment, algal accrual was uniformly high and grazer impacts on algae were consistently low. Reduced algae accrual at high disturbance levels may be explained by direct effects of environmental harshness on algae, and at low disturbance by indirect effects on grazer traits (behaviors) rather than on grazer density. In more benign streams per capita and per unit biomass grazer impacts on algae were high and drift dispersal was low, both behaviors that reduced accrual of algae. We conclude that nutrient limitation and indirect effects of disturbance on accrual of algae mediated by grazer traits can be stronger than indirect effects of predators on algae, providing a new contribution to the debate about the influence of environmental context on the strength of food web interactions.

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Reach‐scale manipulations show invertebrate grazers depress algal resources in streams

Cited by 44 publications

References 31 publications

How do grazers affect periphyton heterogeneity in streams?

How do grazers affect periphyton heterogeneity in streams?

Do small-scale exclosure/enclosure experiments predict the effects of large-scale extirpation of freshwater migratory fauna?

Disturbance legacies and nutrient limitation influence interactions between grazers and algae in high elevation streams

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