Holy flux: spatial and temporal variation in massive pulses of emerging insect biomass from western U.S. rivers

Walters, David; Wesner, Jeff S.; Zuellig, Robert E.; Kowalski, Dan A.; Kondratieff, Matt C.

doi:10.1002/ecy.2023

Cited by 26 publications

(21 citation statements)

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“…During emergence events, salmonfly larvae crawl out of the river and leave their exuvia clinging to features within a short distance (typically 0–2 m) from the water's edge. These large abandoned exuvia are conspicuous along the shoreline, and therefore systematic counts of exuvia are a useful method to quantify salmonfly emergence timing and abundance (Nehring et al, ; Walters, Wesner, Zuellig, Kowalski, & Kondratieff, ). We recorded first emergence date at five sites (1, 3, 5, 7, and 8) along the Madison River in the summer of 2017 to determine a relationship between water temperature and salmonfly emergence timing.…”

Section: Methodsmentioning

confidence: 99%

“…Salmonfly exuvia length was quantified at Sites 1, 3, 5, 7, and 8 in the summer of 2017 to determine a relationship between water temperature and salmonfly body size. Adult female salmonflies can be over 2× larger than males (Walters et al, ), so we measured 30 randomly selected salmonfly exuvia of each sex at each site. Total exuvia length, excluding cerci, was measured with digital callipers to the nearest 1/10th of a millimetre.…”

Section: Methodsmentioning

confidence: 99%

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Water temperature drives variability in salmonfly abundance, emergence timing, and body size

Anderson

Albertson

Walters

2019

River Research & Apps

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Freshwater organisms are disproportionately impacted by climate change and human disturbance, resulting in shifts in species' distributions and life histories. We coupled contemporary and historical datasets documenting physical and ecological variables over four decades to quantify changes in the abundance, emergence timing, and body size of salmonflies (Pteronarcys californica) in the Madison River in southwest Montana. In contemporary surveys, water temperature was the main driver of salmonfly abundance, emergence timing, and body size. Salmonfly densities were negatively correlated with summer water temperature, which explained 60% of variation in larval density among sites, whereas substrate type played a negligible role. Emergence occurred 20 days earlier, and male and female exuvia length were 13.8% and 11.3% shorter, respectively, at the warmest site relative to the coolest site (4°C difference). These patterns were supported by historical data. For example, a 1.2°C increase in mean annual water temperature in the Madison River between 1977 and 2017 coincided with evidence for upstream range contraction. Between 1973 and 2017, emergence timing varied widely among years, occurring up to 41 days earlier in years when spring water temperatures were relatively warm. As climate change progresses,we predict that salmonflies could be extirpated from an additional 28 km of currently occupied habitat, representing a 22.6% reduction in suitable habitat along the Madison River. This study provides evidence of long-term biological change of an aquatic insect and highlights the importance of combining spatial and historical datasets to better understand species' responses to environmental stressors across both space and time.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Water temperature drives variability in salmonfly abundance, emergence timing, and body size

Anderson

Albertson

Walters

2019

River Research & Apps

Self Cite

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“…Because salmonflies are so large, these abandoned exuviae are conspicuous along the shoreline, and therefore, systematic counts of exuvia can be a useful method to quantify salmonfly emergence timing and abundance (Walters et al. ). At each site, 100‐m sample reaches were established along stream banks adjacent to riffles (typical salmonfly larval habitat) and exuviae were collected and removed at the same 10 randomly selected 1‐m bank transects within each reach.…”

Section: Methodsmentioning

confidence: 99%

“…Although emergence events are brief (~1 week at any one location; Sheldon ), salmonflies can dominate annual aquatic insect subsidies to terrestrial ecosystems where they are abundant (Walters et al. ). Thus, variability in the timing and duration of salmonfly emergence could have important implications for consumers and their ability to prolong access to high‐quality foraging opportunities.…”

Section: Introductionmentioning

confidence: 99%

Thermal variability drives synchronicity of an aquatic insect resource pulse

2019

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Spatial heterogeneity in environmental conditions can prolong food availability by desynchronizing the timing of ephemeral, high-magnitude resource pulses. Spatial patterns of water temperature are highly variable among rivers as determined by both natural and anthropogenic features, but the influence of this variability on freshwater resource pulse phenology is poorly documented. We quantified water temperature and emergence phenology of an aquatic insect (salmonfly, Pteronarcys californica) resource pulse in two rivers characterized by differing catchment topography and human impact. Along both rivers, salmonfly emergence occurred earlier where spring temperatures were warmer. Emergence events were brief (4-8 d) at sites in the more human-impacted river, but occurred asynchronously along the entire river, lasting 27 d in total. In contrast, emergence events were more prolonged (6-11 d) at sites on the more natural and topographically complex river, but occurred synchronously along the entire river, lasting 13 d in total. These scale-specific differences in subsidy duration could have opposing consequences for salmonfly consumers depending on their mobility and foraging habits. Asynchronous emergence at a large scale is potentially most important for mobile consumers like birds and fish that can migrate to feed on aquatic insects and track resource waves across a landscape, whereas prolonged emergence duration at a smaller scale may be most important for immobile or opportunistic consumers like spiders and ants. Relating environmental heterogeneity and resource pulse phenology across a gradient of human impact and at multiple spatial scales is needed for a better understanding of how food availability, aquatic-terrestrial linkages, and consumer-resource dynamics may change with climate variability and increasing human activity in the future.

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“…, Walters et al. ). Identifying the conditions that promote successful foraging can be challenging without careful observational studies of predator foraging behavior and prey availability.…”

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confidence: 99%

Feeding on the edge: foraging White Ibis target inter‐habitat prey fluxes

2019

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Avian population dynamics are influenced by the availability of spatiotemporally variable prey resources, but the conditions producing abundant and accessible prey are not always clear. In the Florida Everglades, wading birds nest in the dry season when receding water levels concentrate prey and facilitate improved foraging efficiency. White Ibis (Eudocimus albus) feed extensively on crayfish in sloughs, and previous studies have demonstrated that crayfish move downgradient from higher elevation, heavily vegetated ridge habitats into adjacent less-vegetated sloughs when ridges are almost dry. Most White Ibis foraging is thought to occur in sloughs with relatively shallow water (< 19 cm), but crayfish move and their densities peak when water in sloughs is deeper (~21-32 cm). We conducted an observational study of White Ibis foraging in drying wetlands to determine if White Ibis restricted their foraging to shallow water or if they foraged in relatively deep water when crayfish were migrating. In a series of large drying wetlands, we used time-lapse imagery to quantify White Ibis foraging activity over 61 d from February to April 2017 and we also quantified crayfish biomass density in sloughs. Crayfish biomass density peaked when ridges were almost dry. Most White Ibis foraging occurred over 2-3 d when ridges were almost dry and water in sloughs averaged ≥ 29 cm deep. White Ibis selected slough edges for foraging, suggesting that they were capturing crayfish migrating between habitats. Our results point to a new mechanism of prey exploitation driven by inter-habitat prey flux when ridge habitat dries. Although the results of previous studies suggest that White Ibis will not forage on fish in deeper water (> 25 cm), we found that White Ibis will forage on crayfish in water at those depths. Maintenance of habitat elevational differences and hydro-patterns that promote crayfish production will be necessary to promote this predator-prey interaction in the ridge-slough landscape of the Everglades.

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Holy flux: spatial and temporal variation in massive pulses of emerging insect biomass from western U.S. rivers

Cited by 26 publications

References 0 publications

Water temperature drives variability in salmonfly abundance, emergence timing, and body size

Water temperature drives variability in salmonfly abundance, emergence timing, and body size

Thermal variability drives synchronicity of an aquatic insect resource pulse

Feeding on the edge: foraging White Ibis target inter‐habitat prey fluxes

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