An Integrative Perspective on the Mechanistic Basis of Context Dependent Species Interactions

Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates

Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour-a key process mediating nutrient cycling-associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.

Weather influences survival probability in two coexisting mammals directly and indirectly via competitive asymmetry

Ecologists have studied the role of interspecific competition in structuring ecological communities for decades. Differential weather effects on animal competitors may be a particularly important factor contributing to the outcome of competitive interactions, though few studies have tested this hypothesis in free-ranging animals. Specifically, weather might influence competitive dynamics by altering competitor densities and/or per-capita competitive effects on demographic vital rates. We used a 9-year data set of marked individuals to test for direct and interactive effects of weather and competitor density on survival probability in two coexisting mammalian congeners: Columbian ground squirrels (Urocitellus columbianus) and northern Idaho ground squirrels (Urocitellus brunneus). Ambient temperature and precipitation influenced survival probability in both species, but the effects of weather differed between the two species. Moreover, density of the larger Columbian ground squirrel negatively impacted survival probability in the smaller northern Idaho ground squirrel (but not vice versa), and the strength of the negative effect was exacerbated by precipitation. That is, cooler, wetter conditions benefited the larger competitor to the detriment of the smaller species. Our results suggest weather-driven environmental variation influences the competitive equilibrium between ecologically similar mammals of differential body size. Whether future climate change leads to the competitive exclusion of either species will likely depend on the mechanism(s) explaining the coexistence of these competing species. Divergent body size and, hence, differences in thermal tolerance and giving up densities offer potential explanations for the weather-dependent competitive asymmetry we documented, especially if the larger species competitively excludes the smaller species from habitat patches of shared preference via interference.

Mutualisms in a warming world

Predicting the impacts of global warming on mutualisms poses a significant challenge given the functional and life history differences that usually exist among interacting species. However, this is a critical endeavour since virtually all species on Earth depend on other species for survival and/or reproduction. The field of thermal ecology can provide physiological and mechanistic insights, as well as quantitative tools, for addressing this challenge. Here, we develop a conceptual and quantitative framework that connects thermal physiology to species' traits, species' traits to interacting mutualists' traits and interacting traits to the mutualism. We first identify the functioning of reciprocal mutualism-relevant traits in diverse systems as the key temperature-dependent mechanisms driving the interaction. We then develop metrics that measure the thermal performance of interacting mutualists' traits and that approximate the thermal performance of the mutualism itself. This integrated approach allows us to additionally examine how warming might interact with resource/nutrient availability and affect mutualistic species' associations across space and time. We offer this framework as a synthesis of convergent and critical issues in mutualism science in a changing world, and as a baseline to which other ecological complexities and scales might be added.