1. A framework for integrating stream ecosystem theories into spatial modeling of fish richness and assemblage structure.
- Author
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Yancy, Lauren E., Santee, Noah S., Parker, Emily B., Madewell, M. Jake, Chavez, Fernando E., Stevens, Lucas W., Wolff, Jacob P., Evans, Hannah A., and Perkin, Joshuah S.
- Subjects
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CONTINUUM hypothesis , *RIVER conservation , *FRESHWATER fishes , *FISH conservation , *SPECIES diversity - Abstract
Freshwater streams are frequently fragmented by infrastructure that has the potential to alter stream fish assemblage structure. However, separating natural vs anthropogenically derived assemblage structuring mechanisms within fragmented riverscapes can be challenging. Riverscape concepts such as the river continuum concept (RCC), serial discontinuity concept (SDC), and network dynamics hypothesis (NDH) conceptualize the roles of natural and anthropogenic regulators of assemblage structure along longitudinal gradients in streams. Each of these theories approaches the influence of stream continuity and discontinuity differently, and their application to metacommunity ecology might identify natural vs anthropogenic drivers of assemblage structure. Over 3 y, we surveyed fish assemblages and habitat variables from 40 sites along the longitudinal dimension of White Creek, a headwater stream in College Station, Texas, USA, to test theory-based hypotheses regarding the structuring of fish metacommunities. To achieve this goal, we constructed asymmetric eigenvector maps (AEMs) that integrated aspects of the RCC, NDH, and SDC theories and used these AEMs to test 3 hypotheses: (H1) fish species richness increases longitudinally downstream, but fragmentation by road–stream crossings causes repeated disruptions to this increase, as predicted by the SDC; (H2) spatial contexts based on the SDC explain more variation in metacommunity structure compared with RCC, NDH, or a neutral model; and (H3) distinct fish assemblages exist within fragments of stream created by impassable road–stream crossings. Competing generalized additive models based on stream theories indicated the SDC was the top-ranked model for predicting longitudinal increase in species richness, supporting H1. Spatial variables from the theory-integrated AEMs explained more variation in assemblage structure relative to the neutral model (particularly for the SDC model), supporting H2. Assemblage clustering and ordination showed unique assemblage structure in 3 of the 4 fragments, providing partial support for H3. Our results advance the goal of bridging the gap between theory and conservation of stream fishes by indicating that integration of stream ecosystem theories provides insight to the origins of spatial processes that regulate assemblage structure. Moreover, our results highlight that management of fragmented stream ecosystems might benefit from perspectives that frame anthropogenic alterations within the context of the natural architecture of riverscapes. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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