SFS Annual Meeting

6/05/2024  |   13:30 - 13:45   |  Salon 3/4

Maximum entropy models reveal spatial variation of metabolic scaling in stream fish communities Metabolic scaling provides valuable information about the physiological and ecological functions of organisms, although few studies have quantified the metabolic scaling exponent (b) of communities under natural conditions. Maximum entropy theory of ecology (METE) is a constraint-based unified theory with the potential to empirically assess the spatial variation of the metabolic scaling. Our main goal is to develop a novel method of estimating b within a community by integrating metabolic scaling and METE. We developed a new METE framework to estimate b in 118 stream fish communities in the north-eastern Iberian Peninsula. We extended the original maximum entropy model by parameterizing b in the model prediction of the community-level individual size distributions and compared our results with empirical and theoretical predictions. We found that community-level b of the best maximum entropy models showed great spatial variability, ranging from 0.25 to 2.38. The mean exponent (b = 0.93) resembled the community-aggregated mean values from three previous metabolic scaling meta-analyses, all of which were greater than the theoretical predictions of 0.67 and 0.75. The large spatial variation of b may reflect the combined effects of environmental constraints and species interactions, which likely have important feedback on the structure and function of natural communities. Our newly developed framework can also be applied to study the impact of global environmental pressures on metabolic scaling and energy use in other ecosystems.

Meng Xu (Primary Presenter/Author), Pace University, mxu@pace.edu;

Ignasi Arranz (Co-Presenter/Co-Author), Universidad Rey Juan Carlos, ignasi.arranz@urjc.es;

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6/05/2024  |   13:45 - 14:00   |  Salon 3/4

N-15 IS STRONGLY CORRELATED WITH BODY SIZE WHEN INDIVIDUAL-LEVEL DATA ARE EXAMINED IN TEMPERATE STREAMS Efforts to confirm the generality of a positive relationship between body size and trophic position have been equivocal. This may be due, in part, to the use of species-level averages (one estimate of average size and trophic position per species) in among-species tests. In this study, individual-level estimates of body size and relative trophic position, inferred from bulk-tissue nitrogen stable isotopes, were collected for vertebrates in six temperate streams. Ordinary least squares regression and linear mixed-effects modelling were used to test for positive relationships between body size and relative trophic position, both within and among species. Significant relationships were confirmed in 15 of 22 (species × site) tests. Furthermore, species exhibiting positive size vs. relative trophic position relationships accounted for >50% of the standing stock vertebrate biomass in 5 of 6 streams. Thus, individual-level data may be necessary to fully understand trophic dynamics in temperate streams.

Daniel McGarvey (Primary Presenter/Author), Center for Environmental Studies, Virginia Commonwealth University, djmcgarvey@vcu.edu;

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6/05/2024  |   14:00 - 14:15   |  Salon 3/4

LONG-TERM DECLINES IN BODY SIZE OF THE INVASIVE RUSTY CRAYFISH (FAXONIUS RUSTICUS) IN TEMPERATE LAKES Invasive species often experience phenotypic change during the invasion process. For example, many invasive species are larger in their non-native than native ranges, but some invasive species experience body size declines with time since invasion. We use a long-term dataset (1980-2020) in 17 lakes of Wisconsin, United States to investigate trends in body size for an invasive species, the rusty crayfish (Faxonius rusticus). We relate F. rusticus body size to crayfish relative abundance as catch-per-unit effort (CPUE) from baited trapping, as well as modeled lake temperatures and pelagic primary productivity, using a structural equation model. We found that F. rusticus body size has declined over the past four decades in our study lakes, from a mean of 36.6 mm total carapace length in 1980 to 32.8 mm in 2020. Faxonius rusticus individuals were larger when lakes were warmer and more productive, but the overall effect of time on declining F. rusticus body size was stronger than either of these two predictors. Relative abundance as CPUE had no effect on F. rusticus body size, rejecting a role for density dependence in explaining adult body size of this invasive crayfish. Declining F. rusticus body sizes have accompanied population declines of this invasive crayfish in some Wisconsin lakes, and both trends provide potential for post-invasion ecosystem recovery. As one example, smaller F. rusticus individuals may be less effective or active predators on fish nests. By contrast, declining F. rusticus body size may also create opportunities for serial or over-invasion by future crayfish invaders.

Elle Sawyer (Co-Presenter/Co-Author), University of Michigan, ellesa@umich.edu;

Timothy Kreps (Co-Presenter/Co-Author), Bridgewater College, tkreps@bridgewater.edu;

David Lodge (Co-Presenter/Co-Author), Cornell University, dml356@cornell.edu;

Eric Larson (Primary Presenter/Author), University of Illinois, erlarson@illinois.edu;

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6/05/2024  |   14:15 - 14:30   |  Salon 3/4

WING SIZE AND SHAPE DO NOT PREDICT POPULATION-GENETIC STRUCTURE AMONG FIVE CO-OCCURRING CADDISFLY SPECIES Body size is a readily quantifiable trait that varies greatly among aquatic insects. It is tempting to extrapolate body size and/or shape parameters to infer other species-level traits such as dispersal ability, which could confer resilience to disturbance and allow range shifts in response to broad-scale change. For example, larger wings with greater aspect ratio increase the potential for long-distance flight. If dispersal and gene flow directly reflect this potential, we expect a negative relationship between these morphological traits and population-genetic structure. We tested this hypothesized relationship by measuring wing size and shape and using microsatellites to quantify population structure of five Trichoptera species collected from the same 10 headwater streams in SE Australia, spanning a maximum pairwise geographic distance of 81 km. Among species, mean wingspan varied 7.8-13.7 mm, wing area 26.5-69.7 mm2, and aspect ratio 4.5-6.3. Species ranked from smallest to largest were: Hydrobiosella waddama (Philopotamidae), Koetonga clivicola (Hydrobiosidae), Notalina bifaria (Leptoceridae), Caenota plicata (Calocidae), Triplectides proximus (Leptoceridae). As expected, the species with largest wings was panmictic (no genetic structure) and the species with smallest wings showed some degree of structure. However, K. clivicola with relatively small wings and low aspect ratio, was also panmictic. Conversely, the species with greatest wing aspect ratio and relatively large wings (N. bifaria) exhibited population structure, suggesting weaker dispersal than expected based on size and shape. These empirical results point to dispersal as a complex process that probably should not be approximated solely with simple proxies such as wing morphology.

Debra Finn (Primary Presenter/Author), Missouri State University, dfinn@missouristate.edu;

Jill Lancaster (Co-Presenter/Co-Author), University of Melbourne, JIlll@unimelb.edu.au;

Barbara Downes (Co-Presenter/Co-Author), The University of Melbourne, barbarad@unimelb.edu.au;

Rosalind St Clair (Co-Presenter/Co-Author), University of Melbourne, ros.stclair@gmail.com;

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6/05/2024  |   14:30 - 14:45   |  Salon 3/4

Intraspecific variation in size and density of stream insects are not strongly correlated Individual size should be a sensitive measure of habitat suitability. However, few studies have quantified how size within species of aquatic insects varies across different environmental gradients. We hypothesized that mean individual size within a species would vary systematically across streams concordant with density patterns. To test our hypothesis, we used random forests to model how both size and abundance of 60 taxa varied across 350 stream habitat patches in 45 streams in relation to temperature, conductivity, substrate size, current velocity, and species density. We also included day of year as a predictor to account for differences in size and density associated with life-cycle timing across sites. Preliminary analyses on a subset of samples showed that log density models typically outperformed size models (mean and range of model R2 = 36% (0-86%) for log density and 17% (0-74%) for size). After controlling for day of year, conductivity and stream temperature were most often associated with variation in density, but none of the predictors were most consistently associated with variation in size. The top performing log density models were for Agapetus and Ephemerella inermis/dorothea, whereas the top performing size models were for Glossosoma and Serratella. Optima and limits for size and density inferred from partial dependence plots were not strongly correlated and were sometimes negatively correlated. Individual size, a surrogate for fitness, appears to vary across streams somewhat independently from density and may provide a complementary, individual-level, endpoint for use when assessing effects of environmental degradation on aquatic insects.

Katlyn Gardner (Primary Presenter/Author), Utah State University, katy.gardner@usu.edu;

Charles Hawkins (Co-Presenter/Co-Author), Utah State University, chuck.hawkins@usu.edu;

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