Resource supply governs the apparent temperature dependence of animal production in stream ecosystems

Abstract

Rising global temperatures are changing how energy and materials move through ecosystems, with potential consequences for the role of animals in these processes. We tested a central prediction of the metabolic scaling framework—the temperature independence of animal community production—using a series of geothermally heated streams and a comprehensive empirical analysis. We show that the apparent temperature sensitivity of animal production was consistent with theory for individuals (Epind = 0.64 vs. 0.65 eV), but strongly amplified relative to theoretical expectations for communities, both among (Epamong = 0.67 vs. 0 eV) and within (Epwithin = 1.52 vs. 0 eV) streams. After accounting for spatial and temporal variation in resources, we show that the apparent positive effect of temperature was driven by resource supply, providing strong empirical support for the temperature independence of invertebrate production and the necessary inclusion of resources in metabolic scaling efforts.

Individual size distributions across North American streams vary with local temperature

“…Quantifying resource supply is less straightforward as stream consumers utilize both autochthonous and allochthonous resources. Generally, rates of stream primary production increase with temperature (Demars et al, 2016) suggesting a positive relationship between temperature and resource supply which may confound expected temperature responses (e.g., Junker et al, 2020) and explain net positive relationships between invertebrate community productivity and temperature (e.g., Patrick et al, 2019). Whether these processes can explain the positive relationship between community biomass and temperature is unknown but is worth exploring.…”

Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide

“…However, if, as the season progresses, daily average temperatures exceed grazer tolerances, grazer assemblages can collapse, allowing filamentous algae to flourish (Werner et al 2016 ). The complexity of temperature effects is illustrated in a comparison of geothermally heated streams; benthic invertebrate production was positively correlated with temperature, because algal primary production increased with increased annual stream temperature (Junker et al 2020 ). Despite the positive effect of temperature on invertebrate production, attached algal biomass increased a hundredfold across the 25°C temperature gradient among streams, suggesting a weakening of top-down control with increasing average temperature.…”

The Ecology of River Ice

“…However, applicability of this work to other aquatic species and its generality within and across watersheds in different biomes is not well understood (Brown et al., 2010). In addition, despite the increasingly well‐documented predicted change in ice cover, there are few quantitative studies relating ice dynamics to ecological and food web processes in rivers (Blackadar et al., 2020; Elser et al., 2020; Honeyfield & Maloney, 2015; Hood et al., 2018; Junker et al., 2020; Prowse, 2001). The presence of ice and snow can dramatically alter the physical river template on which ecological processes occur.…”

“…The consideration of aquatic consumers as seasonal specialists and seasonal variation in food web processes raises concerns regarding the effects of climate change on organism physiology (Blackadar et al., 2020; Elser et al., 2020; Honeyfield & Maloney, 2015; Hood et al., 2018; Junker et al., 2020; Prowse, 2001) and community phenology in seasonally frozen streams and rivers. For example, the life cycle of winter specialists is timed to coincide with the presence of suitable food and absence of predators (Cummins et al., 1989).…”