Coextirpation of host–affiliate relationships in rivers: the role of climate change, water withdrawal, and host-specificity

Authors

  • DANIEL E. SPOONER,

    1. Department of Biology, Trent University, Peterborough, ON, Canada K9J 7B8
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    • 1Present address: United States Geological Survey Northern Appalachian Lab 176 Straight Run Road, Wellsboro, PA 16901, USA.

  • MARGUERITE A. XENOPOULOS,

    1. Department of Biology, Trent University, Peterborough, ON, Canada K9J 7B8
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  • CHRISTOF SCHNEIDER,

    1. Center for Environmental Systems Research, University of Kassel, Kassel, Germany
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  • DAELYN A. WOOLNOUGH

    1. Department of Biology, Trent University, Peterborough, ON, Canada K9J 7B8
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    • 2Present address: Biology Department, Central Michigan University, Mount Pleasant, Michigan 48859, USA.


Daniel E. Spooner, e-mail: dspooner45@gmail.com

Abstract

The role of climate-related disturbances on complex host–affiliate relationships remains understudied, largely because affiliate species vary in host use and are often differentially susceptible to disturbance relative to their hosts. Here we report the first set of host–affiliate species–discharge relationships (SDR) in freshwater and examine how anticipated shifts in water availability (flow) will impact coextirpations. We used SDR for freshwater mussels and fish across 11 regions (over 350 rivers) in the continental United States that we coupled to future water availability (2070) to model mussel and fish coextirpations. We also used river-specific host–affiliate matrices (presence–absence) to evaluate how host-specificity (mean number of hosts used by an affiliate) and host-overlap (extent to which affiliates share hosts) relate to extirpation vulnerability. We found that the strength and predictability of SDR models vary geographically and that mussels were more susceptible to flow alterations than fish. These patterns of extirpations were strongest in the southeast where: (1) flow reductions are expected to be greatest; (2) more species are lost per unit flow; (3) and more mussels are expected to be lost per unit of fish. We also found that overall mussel losses associated with reduction in habitat (water availability) were greater than those associated with loss of fish hosts which we assumed to be a function of host redundancy. These findings highlight the utility of SDR as a tool for conservation efforts but they also demonstrate the potential severity of reductions in mussel and fish richness as consequence of climate change and water use. Mussels provide key ecosystem services but face multiple pronged attacks from reductions in flow, habitat, and fish hosts. These losses in biodiversity and ecosystem functions can translate into major effects on food webs and nutrient recycling.

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