From individuals to ecosystems: carrion beetle responses to heatwaves impact nutrient cycling

Climate extremes, such as heatwaves, are becoming more frequent and severe, leading to significant disruptions in key ecosystem processes. The direct effects of heatwaves on these processes have thus received increasing attention, yet the indirect effects of heatwaves, as mediated through animal behavioural responses, are still unknown. Insects play a fundamental role in carrion decomposition by modifying carcasses and regulating nutrient transfer to soils. Understanding how insect responses to climate extremes scale up to ecosystem processes is therefore crucial. In this study, we used a widespread carrion beetle, the burying beetle Nicrophorus vespilloides, to experimentally investigate the direct and indirect effects of a simulated heatwave on carrion decomposition dynamics, and the consequences for soil nutrient cycling. We found that burying beetle presence increased carcass mass loss by 355% under ambient temperatures, and that this was accompanied by significant increases in dissolved organic carbon (+86%), ammonium (+71%), and nitrate (+47%) concentrations. However, the positive effects of burying beetle presence on carcass mass loss were severely diminished by heat stress. Path analyses revealed that this was related to marked reductions in certain beetle behaviours, such as carcass preparation, as well as a reduction in brood size. These behavioural and reproductive shifts were, in turn, linked to decreased soil nitrate concentrations and soil moisture. Together, these findings demonstrate that the indirect effects of heatwaves on decomposition processes, as mediated by shifts in the behaviour and traits of animal ecosystem engineers, can be as important as their direct effects. Such indirect effects must therefore be incorporated into our understanding of how key ecosystem processes respond to climate extremes.