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Understanding the mechanisms that enable species coexistence is essential for explaining community structure and biodiversity. We tested the hypothesis that dietary niche partitioning facilitates coexistence between two dominant stream predators in western North America: Coastal Giant Salamanders (Dicamptodon tenebrosus) and Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii). These aquatic predators are important regulators of community dynamics and ecosystem processes in stream networks. We analyzed stomach contents from 81 salamanders and 96 trout collected via electrofishing in a 6-km section of Lookout Creek, Oregon, during low flow conditions in summer. We predicted that salamanders, primarily nocturnal benthic feeders, and trout, visual consumers of both terrestrial and aquatic prey, would exhibit distinct diets reducing direct diet overlap. We identified 4,897 prey items, classifying them into aquatic (50) and terrestrial (77) sources across 127 categories. Salamanders primarily preyed on aquatic invertebrates (Trichoptera, Ephemeroptera, and Plecoptera), while trout consumed a mix of terrestrial and aquatic invertebrates (Diptera, Trichoptera, and Plecoptera). Partial dietary overlap confirmed niche differentiation as a likely mechanism facilitating the coexistence of trout and salamanders. These findings highlight the role of dietary partitioning in structuring predator communities and inform predictions of how environmental changes may impact stream ecosystems.
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Do Electrofishing Activities Disrupt Stream Biofilm Standing Stocks? An Assessment from Two Headwater Streams in Western Oregon
Abstract Humans affect ecosystems in many ways, and scientific field studies are no exception. If data collection disrupts environments or biota too much, it can lead to inaccurate conclusions in the study of interest or in subsequent studies. We evaluated whether stream electrofishing surveys could measurably disturb the benthic biofilms in two forested headwaters in western Oregon, USA. While the consequences of electrofishing to macroinvertebrates and fish have been assessed, to date no studies have quantified its influence on benthic biofilms. We observed declines in the standing stocks of accrued benthic chlorophyll a directly after electrofishing in both streams. After electrofishing, the standing biofilm stocks declined by an average of ~15% in Oak Creek, a small third-order stream in the Oregon Coast Range Mountains, and by an average of ~34% in a third-order section of Lookout Creek, which is located in the western Cascade Mountains of Oregon, USA. In returning to Oak Creek 2 weeks after electrofishing, the standing stocks had fully recovered to their prefishing levels. While the benthic biofilm standing stocks did decline in association with electrofishing, the effects were small when compared with those of disturbances from common flow events and when scaling to the whole stream system. In Oak Creek, the proportional biofilm standing stock decline from electrofishing activity was about 26% of what was observed following a moderate flow event (40% of bank-full discharge), and about 15% of the decline in biofilm standing stocks following a complete bank-full discharge event (140% of bank-full discharge).
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- Award ID(s):
- 2025755
- PAR ID:
- 10567920
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- North American Journal of Fisheries Management
- Volume:
- 41
- Issue:
- 2
- ISSN:
- 0275-5947
- Format(s):
- Medium: X Size: p. 466-473
- Size(s):
- p. 466-473
- Sponsoring Org:
- National Science Foundation
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