Extreme Climatic Events Alter Aquatic Food Webs

Ledger, Mark E.; Brown, Lee E.; Edwards, François; Hudson, Lawrence N.; Milner, Alexander M.; Woodward, Guy

doi:10.1016/b978-0-12-417199-2.00006-9

Cited by 43 publications

(9 citation statements)

References 107 publications

(157 reference statements)

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“…Our findings nonetheless challenge the consensus that drought disproportionately affects high trophic levels and contribute to a growing body of evidence (e.g. Gibb et al, 2017;Nelson et al, 2017;O'Gorman et al, 2017) documenting exceptions to the general principle that climate change and environmental disturbance discriminate against large body size (Daufresne, Lengfellner, & Sommer, 2009;Ledger et al, 2013;Woodward et al, 2005).…”

Section: Ta B L E 1 Summary Of Fitted Linear and Segmented Regressioncontrasting

confidence: 70%

Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

et al. 2019

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Predicted trends towards more intense droughts are of particular significance for running water ecosystems, as the loss of critical stream habitat can provoke sudden changes in biodiversity and shifts in community structure. However, analysing ecological responses to the progressive loss of stream habitat requires a continuous disturbance gradient that can only be generated through large‐scale manipulations of streamflow. In the first experiment of its kind, we used large artificial stream channels (mesocosms) as analogues of spring‐fed headwaters and simulated a gradient of drought intensity that encompassed flowing streams, disconnected pools, and dry streambeds. We used breakpoint analysis to analyse macroinvertebrate community responses to intensifying drought, and identify the taxa and compositional metrics sensitive to small changes in drought stress. We detected breakpoints for >60% of taxa, signalling sudden population crashes or irruptions as drought intensified. Abrupt changes were most pronounced where riffle dewatering isolated pools. In the remnant wetted habitat, we observed a shift to larger body sizes across the community, primarily driven by irruptions of predatory midge larvae and coincident population collapses among prey species (worms and smaller midges). Our results suggest that intense predation in confined, fragmented stream habitat can lead to unexpected changes in body sizes, challenging the conventional wisdom that droughts favour the small. Pool fragmentation might thus be the most critical stage of habitat loss during future droughts, as the point at which impacted rivers and streams begin to exhibit major shifts in fundamental food web properties.

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Section: Ta B L E 1 Summary Of Fitted Linear and Segmented Regressioncontrasting

confidence: 70%

Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

et al. 2019

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“…Simplification of stream food webs has also been observed in response to acidification (Layer et al, 2010) and drought (Ledger et al, 2013). Both studies showed streams under stress to have smaller food webs with fewer trophic interactions.…”

Section: Potamopyrgus)mentioning

confidence: 85%

“…Both studies showed streams under stress to have smaller food webs with fewer trophic interactions. In theory, simplification may make food webs more stable if interaction strengths remained constant, but if the number and positioning of strong links is altered, the consequences for ecosystem stability and functioning could be far-reaching (Ledger et al, 2013;McCann, 2000). Quantifying interaction strengths and site-specific foraging behaviour is therefore a priority for food web studies.…”

Section: Potamopyrgus)mentioning

confidence: 99%

The effects of pastoral intensification on the feeding interactions of generalist predators in streams

et al. 2017

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Land‐use change can alter trophic interactions with wide‐ranging functional consequences, yet the consequences for aquatic food webs have been little studied. In part, this may reflect the challenges of resolving the diets of aquatic organisms using classical gut contents analysis, especially for soft‐bodied prey. We used next‐generation sequencing to resolve prey use in nearly 400 individuals of two predatory invertebrates (the Caddisfly, Rhyacophila dorsalis, and the Stonefly Dinocras cephalotes) in streams draining land with increasingly intensive livestock farming. Rhyacophila dorsalis occurred in all streams, whereas D. cephalotes was restricted to low intensities, allowing us to test whether: (i) apparent sensitivity to agriculture in the latter species reflects a more specialized diet and (ii) diet in R. dorsalis varied between sites with and without D. cephalotes. DNA was extracted from dissected gut contents, amplified without blocking probes and sequenced using Ion Torrent technology. Both predators were generalists, consuming 30 prey taxa with a preference for taxa that were abundant in all streams or that increased with intensification. Where both predators were present, their diets were nearly identical, and R. dorsalis's diet was virtually unchanged in the absence of D. cephalotes. The loss of D. cephalotes from more intensive sites was probably due to physicochemical stressors, such as sedimentation, rather than to dietary specialization, although wider biotic factors (e.g., competition with other predatory taxa) could not be excluded. This study provides a uniquely detailed description of predator diets along a land‐use intensity gradient, offering new insights into how anthropogenic stressors affect stream communities.

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“…This summer window is particularly stressful to organisms, as they can reach their physiological limits due to thermal stress and/or insufficient dissolved oxygen (Trimmel et al 2018). Warming also alters individual growth rate, behavior, and fecundity in aquatic insects and fish (Hogg and Williams 1996; Woodward et al 2010; Ledger et al 2013) with effects potentially scaling up to whole‐ecosystem functioning (e.g., changes in decomposition rates and cross ecosystem subsidies; Dewson et al 2007; Pyne and Poff 2017; Sardina et al 2017). While climate warming is a prominent stressor in stream ecosystems of major mountain ranges globally (including the Sierra Nevada), uncertainty exists around when and how warmer air may threaten stream thermal regimes, that is, the characteristic patterns of variation in temperature over time (Caissie 2006; Steel et al 2017).…”

Section: Figmentioning

confidence: 99%

Dynamic, downstream‐propagating thermal vulnerability in a mountain stream network: Implications for biodiversity in the face of climate change

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Safeeq

et al. 2022

Limnology & Oceanography

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As climate change continues to increase air temperature in high‐altitude ecosystems, it has become critical to understand the controls and scales of aquatic habitat vulnerability to warming. Here, we used a nested array of high‐frequency sensors, and advances in time‐series models, to examine spatiotemporal variation in thermal vulnerability in a model Sierra Nevada watershed. Stream thermal sensitivity to atmospheric warming fluctuated strongly over the year and peaked in spring and summer—when hot days threaten invertebrate communities most. The reach scale (~ 50 m) best captured variation in summer thermal regimes. Elevation, discharge, and conductivity were important correlates of summer water temperature across reaches, but upstream water temperature was the paramount driver—supporting that cascading warming occurs downstream in the network. Finally, we used our estimated summer thermal sensitivity and downscaled projections of summer air temperature to forecast end‐of‐the‐century stream warming, when extreme drought years like 2020–2021 become the norm. We found that 25.5% of cold‐water habitat may be lost under high‐emissions scenario representative concentration pathway (RCP) 8.5 (or 7.9% under mitigated RCP 4.5). This estimated reduction suggests that 27.2% of stream macroinvertebrate biodiversity (11.9% under the mitigated scenario) will be stressed or threatened in what was previously cold‐water habitat. Our quantitative approach is transferrable to other watersheds with spatially replicated time series and illustrates the importance of considering variation in the vulnerability of mountain streams to warming over both space and time. This approach may inform watershed conservation efforts by helping identify, and potentially mitigate, sites and time windows of peak vulnerability.

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Extreme Climatic Events Alter Aquatic Food Webs

Cited by 43 publications

References 107 publications

Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

The effects of pastoral intensification on the feeding interactions of generalist predators in streams

Dynamic, downstream‐propagating thermal vulnerability in a mountain stream network: Implications for biodiversity in the face of climate change

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