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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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Dietary partitioning promotes the coexistence of planktivorous species on coral reefs.
Theories involving niche diversification to explain high levels of tropical diversity propose that species are more likely to co-occur if they partition at least one dimension of their ecological niche space. Yet, numerous species appear to have widely overlapping niches based upon broad categorizations of resource use or functional traits. In particular, the extent to which food partitioning contributes to species coexistence in hyperdiverse tropical ecosystems remains unresolved. Here, we use a molecular approach to investigate inter- and intraspecific dietary partitioning between two species of damselfish (Dascyllus flavicaudus, Chromis viridis) that commonly co-occur in branching corals. Species-level identification of their diverse zooplankton prey revealed significant differences in diet composition between species despite their seemingly similar feeding strategies. Dascyllus exhibited a more diverse diet than Chromis, whereas Chromis tended to select larger prey items. A large calanoid copepod, Labidocera sp., found in low density and higher in the water column during the day, explained more than 19% of the variation in dietary composition between Dascyllus and Chromis. Dascyllus did not significantly shift its diet in the presence of Chromis, which suggests intrinsic differences in feeding behaviour. Finally, prey composition significantly shifted during the ontogeny of both fish species. Our findings show that levels of dietary specialization among coral reef associated species have likely been underestimated, and they underscore the importance of characterizing trophic webs in tropical ecosystems at higher levels of taxonomic resolution. They also suggest that niche redundancy may not be as common as previously thought.
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- Award ID(s):
- 1637396
- PAR ID:
- 10155986
- Date Published:
- Journal Name:
- Molecular ecology
- Volume:
- 28
- Issue:
- 10
- ISSN:
- 1365-294X
- Page Range / eLocation ID:
- 2694-2710
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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