Regime change in a large-floodplain river ecosystem: patterns in body-size and functional biomass indicate a shift in fi
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ORIGINAL PAPER
Regime change in a large-floodplain river ecosystem: patterns in body-size and functional biomass indicate a shift in fish communities Kristen Bouska
Received: 5 December 2019 / Accepted: 29 July 2020 This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2020
Abstract Changes in species dominance may drive regime shifts because dominant biotic feedbacks reflect functional traits of a community. Changes in species dominance has been documented by a 25-year fish community dataset encompassing six reaches of the Upper Mississippi and Illinois Rivers. Specifically, common carp (Cyprinus carpio) abundance has declined across all reaches, whereas silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) have increased in abundance in the southern three reaches. To test whether signals in the data were consistent with regime transitions, changes in body-size patterns and trends in functional biomass and variance of functional biomass of the fish community were assessed. I further explored biomass thresholds relative to transitions. Shifts in body-size aggregations and trends in functional biomass support hypotheses that transitions from common carp dominance to a more functional diverse community represent alternate regimes. Results indicate such transitions occurred in the early
2000s for the two most northern reaches, and that the third most northern reach is nearing this transition. In the southern reaches, results indicate that transitions from common carp dominance to silver and bighead carp dominance also represent alternate regimes. Regime transitions support biomass thresholds between 8000 and 10,000 g per unit of day electrofishing effort of common carp and between 20 and 2000 g per unit effort in silver and bighead carp. Consistencies across reaches with similar dominance patterns provide support that reinforcing feedbacks, unique to the functional attributes of the dominant species, occur at similar biomass levels. Building knowledge of such feedback mechanisms is imperative to effectively manage for desired regimes. Keywords Ecological resilience Alternate regimes Common carp Silver carp Mississippi river Illinois river
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10530-020-02330-5) contains supplementary material, which is available to authorized users. K. Bouska (&) U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, WI 54603, USA e-mail: [email protected]
Abrupt and unexpected changes in ecosystems, referred to as regime shifts, occur when dominant feedbacks that maintain ecological structure and function are disrupted and new feedbacks emerge to support a different structure and function (i.e., alternate regime) that is often undesirable. Human
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K. Bouska
degradation of resilience frequently results in ecological regim
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