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SFS Annual Meeting

Wednesday, June 5, 2024
10:30 - 12:00

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S03 From Individuals to Ecosystems: A Size-Based Understanding of Freshwaters

10:30 - 10:45 | Salon 3/4 | SEARCHING FOR A UNIVERSAL INDICATOR OF STREAM STATUS: COMMUNITY SIZE STRUCTURE ACROSS LATITUDES AND HUMAN IMPACTS

6/05/2024  |   10:30 - 10:45   |  Salon 3/4

Searching for a universal indicator of stream status: Community size structure across latitudes and human impacts Human activities are driving pronounced changes in the structure and functioning of freshwater communities worldwide. However, recent empirical and theoretical syntheses suggest that human impacts on stream communities might differ between latitudes, indicating that knowledge from the Global North might not be readily transferable to the developing tropics, where rapid land transformations are occurring. Body size distributions and size spectra offer a general tool to understand anthropogenic impacts (including land use change), bridging individual-level physiological processes to ecosystems. Here, we present results from a global analysis of community size spectra for freshwater streams spanning gradients of human pressure and latitude. This dataset includes tens of millions individual size measurements of macroinvertebrates and fish, from thousands of sites, across 6 continents. We investigate how individual size distribution parameters (i.e. exponent & total biomass) change across an index of human footprint and latitude, and the direct and indirect role of temperature, diversity and food web structure. In doing so, this study sheds light on the key drivers shaping the size structure of stream communities and their response to human impacts across the globe.

Justin Pomeranz (Primary Presenter/Author), Colorado Mesa University, jfpomeranz@gmail.com;

Dan Perkins (Co-Presenter/Co-Author), University of Roehampton, daniel.perkins@roehampton.ac.uk;

Ignasi Arranz (Co-Presenter/Co-Author), King Juan Carlos University, ignasiarranz@gmail.com;

Ioar de Guzman (Co-Presenter/Co-Author), University of the Basque Country, mirenioar.deguzman@ehu.eus;

Vojsava Gjoni (Co-Presenter/Co-Author), University of South Dakota, vojsava.gjoni@usd.edu;

Dean Jacobsen (Co-Presenter/Co-Author), Freshwater Biological Laboratory, University of Copenhagen, Denmark, djacobsen@bio.ku.dk;

Pavel Kratina (Co-Presenter/Co-Author), Queen Mary, University London, p.kratina@qmul.ac.uk;

Aitor Larranaga (Co-Presenter/Co-Author), University of the Basque Country, aitor.larranagaa@ehu.es;

Ciaran Murray (Co-Presenter/Co-Author), NIVA Denmark Water Research, cjm@niva-dk.dk;

Jes Rasmussen (Co-Presenter/Co-Author), NIVA Denmark Water Research, jes.rasmussen@niva-dk.dk;

Victor Saito (Co-Presenter/Co-Author), Universidade Federal de São Carlos, victor.saito@gmail.com;

Francisco Valente (Co-Presenter/Co-Author), Universidade Federal de São Carlos, fvalenteneto@gmail.com;

10:45 - 11:00 | Salon 3/4 | SIZE SPECTRA PATTERNS IN TEMPERATE AND TROPICAL RIVER NETWORKS

6/05/2024  |   10:45 - 11:00   |  Salon 3/4

Size spectra patterns in temperate and tropical river networks Body size is one of the most important aspects of an organism’s biology and determines metabolism, a vital life function. Analyzing organism mass with respect to abundance at a given scale is known as a size spectra analysis. Steeper size spectra slopes indicate less efficient energy transfer between trophic levels. Biological processes such as growth and reproduction cycles, consequences of an organism’s body size and therefore metabolism, occur differently in temperate climates than tropical ones. Spatial variation in size spectra has been researched, but much remains unknown regarding temporal trends of community size spectra in lotic systems. To investigate how size spectra compare between tropical and temperate streams, we sampled macroinvertebrates at 8 sites in two river networks: one in Virginia, USA and one in Sao Paulo, Brazil. Using data from three benthic macroinvertebrate sampling events that occurred every two months, we produced community size spectra slopes to illustrate temporal patterns between the two river networks. Community dynamics in temperate streams are largely driven by seasonal changes, while tropical sites without marked temperature-based seasonality are influenced by flow regimes. Tropical sites are more prone to environmental stochasticity, which is expected to produce steeper size spectra slopes and less temporal variability. Temperate sites are expected to have more variability over time as discrete cohorts age and emerge together whereas tropical insects often emerge year-round. Climate change is predicted to affect temperature and precipitation patterns, thus temporal study such as this one is necessary to understand these trends.

Gretel Baur (Primary Presenter/Author), Virginia Tech, gretel.baur@yahoo.com;

11:00 - 11:15 | Salon 3/4 | RESPONSES OF INDIVIDUAL SIZE DISTRIBUTIONS ACROSS A CONTINENTAL GRADIENT OF TEMPERATURE AND RESOURCE SUPPLY

6/05/2024  |   11:00 - 11:15   |  Salon 3/4

Responses of individual size distributions across a continental gradient of temperature and resource supply A common pattern in ecology is the negative relationship between individual body size and abundance. This pattern is known as the individual size distribution (ISD, N ~ M^?), where ? is the rate of decline in relative abundance from small to large individuals. The ISD is a powerful tool for assessing changes in spatiotemporally and taxonomically disparate ecosystems. This is because ? is thought to vary as a function of trophic transfer efficiency, predator-prey mass ratio, and metabolism-mass scaling, universal processes across ecosystems. Temperature and resource availability affect ?, but the direction and magnitude of their effects are varied. We leverage 2.4 million individual body sizes from freshwater streams in NEON, spanning natural gradients of temperature and resource availability. Despite broad environmental conditions and complete species turnover, we find little variation in ? (mean = -1.2, sd = 0.04) and no change with temperature or resource supply. The value of ? = -1.2 represents higher than expected relative abundance of large individuals. The only way to achieve this is by relaxing the assumption that metabolic scaling is 0.75 and by assuming subsidy inputs to large predators. We support these hypotheses with a simulation study and mesocosm experiment that suggests a metabolic scaling coefficient of ~0.4 for freshwater macroinvertebrates. Our results emphasize remarkable uniformity in the prevalence of larger individuals within freshwater streams, persisting across both spatial and temporal dimensions. A critical next step is to understand the mechanisms for upholding the constancy of ? under varying environmental conditions.

Jeff Wesner (Primary Presenter/Author), University of South Dakota, Jeff.Wesner@usd.edu;

Vojsava Gjoni (Co-Presenter/Co-Author), University of South Dakota, vojsava.gjoni@usd.edu;

James Junker (Co-Presenter/Co-Author), University of North Texas, james.junker1@gmail.com;

Justin Pomeranz (Co-Presenter/Co-Author), Colorado Mesa University, jfpomeranz@gmail.com;

11:15 - 11:30 | Salon 3/4 | UNVEILING THE RELATIONSHIP BETWEEN BODY SIZE AND BIOMASS TURNOVER IN A NEOTROPICAL RIVERINE CONTINUUM

6/05/2024  |   11:15 - 11:30   |  Salon 3/4

Unveiling the relationship between body size and biomass turnover in a neotropical riverine continuum The metabolic theory of ecology (MTE) offers a comprehensive framework for analyzing the relationships between body size, biomass turnover and energy flow within and across aquatic ecosystems. The primary predictions of MTE are: (i) Density (N) decreases as body mass (M) increases; (ii) Population biomass (B) increases with M; (iii) Biomass turnover rate (P/B) decreases with increasing M; and (iv) Production (P) remains independent of body size. To test these predictions, we are conducting monthly field sampling of aquatic macroinvertebrate community composition and population sizes along a riverine continuum (1st to 5th order streams) within a Neotropical protected area of Atlantic Forest. The preliminary results showed that the presence of overabundant large taxa, such as net-spinning caddisflies and other small rare taxa may disrupt the first MTE prediction that density declines as body mass increases. Additionally, we observed that the asynchronous life cycles and overlapping cohorts are ubiquitous among the collected taxa, suggesting that biomass turnover and secondary production may not conform to the MTE predictions. Given the large variation in body sizes observed across populations, we expect that the study sites will not necessarily align with MTE predictions. This study provides a comprehensive spatiotemporal investigation of the relationship between body size and biomass turnover in Neotropical streams. Our results will contribute to understanding the reference conditions of ecosystem functions in streams located in a region particularly threatened by the global change effects.

José Leonardo Mello (Primary Presenter/Author), Federal University of São Carlos (Brazil), josemello@protonmail.com;

Erika Mayumi Shimabukuro (Co-Presenter/Co-Author), Federal University of São Carlos (Brazil), erika.msh@gmail.com;

Victor Satoru Saito (Co-Presenter/Co-Author), Federal University of São Carlos (Brazil), victor.saito@gmail.com;

11:30 - 11:45 | Salon 3/4 | TEMPERATURE AND PREDATION AFFECT INDIVIDUAL METABOLIC CONSTRAINTS, SHAPING COMMUNITY SIZE SPECTRA PATTERNS UNDER THEIR INFLUENCE

6/05/2024  |   11:30 - 11:45   |  Salon 3/4

Temperature and predation affect individual metabolic constraints, shaping community size spectra patterns under their influence Size spectra capture the interplay between body mass and abundance in ecosystems, reflecting size-dependent metabolic demands. While they can be observed across various biological levels, deviations from physiological predictions due to factors like predation pressure and temperature remain unexplored at the community level, hindering a comprehensive understanding of ecological mechanisms. Our study investigates the impact of temperature on the ontogenetic scaling of resting metabolic rate in freshwater macroinvertebrate communities, particularly in relation to predation regimes. We find that increasing temperature leads to a reduction in the metabolic scaling exponent in systems under predation pressure, resulting in steeper size spectra. This underscores the interactive influence of temperature and predation on ecophysiological processes, potentially altering the exponent of size spectra and affecting energy exchange equilibrium within ecological communities. Our research highlights the importance of understanding individual energetics in deciphering community structure and provides a basis for further exploration into ecological systems.

Vojsava Gjoni (Primary Presenter/Author), University of South Dakota, vojsava.gjoni@usd.edu;

Jeff Wesner (Co-Presenter/Co-Author), University of South Dakota, Jeff.Wesner@usd.edu;

Justin Pomeranz (Co-Presenter/Co-Author), Colorado Mesa University, jfpomeranz@gmail.com;

James Junker (Co-Presenter/Co-Author), University of North Texas, james.junker1@gmail.com;

11:45 - 12:00 | Salon 3/4 | DEVELOPING COMMUNITY SIZE SPECTRA AS A TOOL FOR AQUATIC INVASIVE SPECIES MANAGEMENT IN FRESHWATERS

6/05/2024  |   11:45 - 12:00   |  Salon 3/4

Developing community size spectra as a tool for aquatic invasive species management in freshwaters Aquatic invasive species are one of the greatest global threats to freshwater biodiversity and management comes at incredible economic costs. Once established eradication is seldom possible and management efforts turn toward containment and reduction of impacts. However, management targets for invasive species reduction/control goals are seldom established resulting in inefficient resource allocation. Establishing reduction or control targets is hampered by (1) limited mechanistic understanding of impacts of invasive species that can be translated into measurable attributes, e.g. often impacts are assessed in terms of individual native species, and (2) similarly the historic species-specific management paradigm. Community size spectra (CSS) is a relatively simple ataxic approach describing food web structure through assessment of assemblage-wide body size distributions and can be used as a tool to guide aquatic invasive species management. CSS represent emergent food web characteristics such as predator-prey biomass ratios and trophic transfer efficiency. They are also sensitive and reactive to changes in food web composition including invasive species, thus provide a quantitative measure of food web change. The CSS framework provides (1) an assessment of food web level impacts, (2) additional means of assessing the specific species most impacted, (3) identity of restoration targets, and (4) reduction/control targets for the invader. In this presentation I will share functional relationships derived from a variety of taxa, ecosystems, and applications to illustrate these points, as well as logical next steps to fully develop the CSS framework for aquatic invasive species management.

Brent Murry (Primary Presenter/Author), West Virginia University, brent.murry@mail.wvu.edu;