Modelling patterns of coexistence of three congeneric headwater fishes

• Published in: Freshwater biology Vol. 65; no. 6; pp. 1017 - 1027
• Main Authors: Hubbell, Joshua P., Schaefer, Jacob F., Warren, Melvin L., Sterling, Kenneth A.
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01-06-2020
• Subjects: Catchment area; Coastal plains; Coexistence; Competitors; Current velocity; Detection; Distribution patterns; Dominant species; Evaluation; Freshwater; Freshwater fish; Geographical distribution; Groundwater; Habitats; headwater streams; Headwaters; Heterogeneity; Influence; Inland water environment; Modelling; Occupancy; Rivers; Spatial data; Streams
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.13486

Mechanisms driving patterns of occurrence and co‐occurrence among North American freshwater fishes are poorly understood. In particular, the influence of biotic interactions on coexistence among stream reaches and their effects on regional species distribution patterns is not well understood for congeneric headwater fishes.
Occupancy models provide a useful framework for examining patterns of co‐occurrence while also accounting for imperfect detection. Occupancy models may be extended to test for evidence that a dominant species influences the occurrence of a subordinate species and thus evaluate support for the hypothesis that species interactions drive patterns of coexistence.
We examined patterns of occurrence and co‐occurrence at the stream‐reach scale among three species of darters (Percidae: Etheostomatinae) that occupy headwater streams within a Gulf Coastal Plain drainage in the south‐eastern U.S.A. We assessed species occurrences at 97 sites in first‐ to third‐order streams on one occasion each and used data from four sub‐reaches sampled with equal effort at each site to estimate species‐specific detection probabilities. Following sampling, a suite of habitat variables was collected at three equidistant points along each of the three transects established within a sub‐reach. Coarse (stream‐segment, catchment, network) scale variables were also incorporated using geospatial data. Single‐species and two‐species occupancy models were used to examine patterns of occupancy and coexistence.
The occupancy of each species was influenced by distinct habitat variables. Goldstripe darters (Etheostoma parvipinne) were constrained by a stream size gradient, groundwater input appeared to influence the occurrence of Yazoo darters (Etheostoma raneyi), and local habitat heterogeneity (e.g. variation in depth and current velocity) appeared to influence the occupancy of redspot darters (Etheostoma artesiae).
We found no evidence that the presence of one species influenced the occurrence of another within a stream‐reach based on two‐species occupancy models. Rather, species co‐occurrences were best explained as independent occurrences within a stream‐reach according to species‐specific habitat associations.
Occupancy modelling may provide a suitable framework for evaluating the influence of biotic interactions among congeneric stream fishes along species‐specific habitat gradients at the stream reach scale. Our study offers insight into how habitat variation can influence coexistence of potential competitors across a large river system.