The ants underfoot forage faster as the ground warms each day. Likewise, the fish in nearby streams and the worms and other organisms that parasitize these fish speed their activities as the water warms. Above the stream, dragonflies engage in more aerial battles each hour for prime perches as the air warms. We have all witnessed these quickenings, as insects and other ectotherms, organisms whose body temperature are primarily environmentally determined, become more active and interact more quickly in hotter environments. How much faster do such biotic interactions increase with temperature, and why? This is studied in the Early View paper “Rates of biotic interactions scale predictably with temperature despite variation” by Bill Burnside and co-workers. Their sumary of the study continues here:
In this meta-analysis, we look across taxa and habitats to assess the temperature dependence of biotic interaction rates, such as herbivory and competition, between two species. We hypothesize that these rates will increase approximately exponentially with temperature, mirroring the temperature dependence of respiratory metabolism generally. This hypothesis is inspired by the metabolic theory of ecology, which suggests that many ecological patterns and processes are functions of individual metabolic rates of the organisms involved. These rates vary characteristically with body temperature, which affects the rates of cellular chemical reactions. Biotic interactions are metabolic because they involve exchanges of energy and materials between organisms and their environment and because they are inspired by basic metabolic demands, like the need to eat.
This work was intriguing because even though we were not interacting ourselves with all the amazing organisms in our analysis, like those pictured here, we did not know what we would find. The studies were often focused on a related question and just happened to include temperature as a variable or did not include graphs, so it was tough to visualize how some rates varied with temperature. And the rate terms varied by their nature, from the rate ground beetles catch and eat fruit flies to the rate sea lice parasitize fish.
Seeing the results for the first time—the generally parallel lines, each with a slope indicating how interaction rate scales with temperature—was amazing. Our results generally supported our hypothesis, but there was also a great deal of variation. We could only find a fairly small sample of studies on most interaction types, which probably accounts for some of this variation, but organisms vary in their level of thermal performance and peak response, among other traits, which surely accounts for variation when different species interact.
Understanding how temperature affects biotic interaction rates is more important than ever in our warming world. The answers won’t be entirely straightforward and may vary among places, species, and communities, but this study offers basic insight to inform our search.