Contrasting effects of temperature across trophic levels in geothermally warmed soil food webs

Abstract

Global warming is altering the structure and dynamics of ecological communities, with significant consequences for soil food webs. Rising temperatures are expected to accelerate metabolic rates in organisms, potentially altering species interactions, and the structure and energetics of food webs. However, most studies assessing warming impacts on soil invertebrates have been short‐term, taxonomically narrow, or confounded by large‐scale variability. We investigated how long‐term warming affects soil invertebrate community structure across trophic levels. We sampled soil invertebrate along natural temperature gradients (17–40°C) of geothermal surface features of New Zealand, and we analysed community composition and population densities in relation to soil temperature, pH, water content, and microbial biomass. We found that the invertebrate community composition was significantly influenced by temperature and associated environmental variables. Total invertebrate density increased with warming, primarily driven by decomposers, while diversity metrics generally declined (except for omnivores). Decomposer diversity declined due to reductions in both dominant and rare species (Hill q = 1 and q = 2), whereas predator richness decreased mainly due to the loss of rare species (Hill q = 1) that resulted in higher evenness. In contrast, omnivores exhibited increased species richness. Our results highlight that warming effects are trophic‐level specific and environmentally context‐dependent. This suggests that long‐term warming may disrupt key ecosystem functions – such as decomposition, predator–prey interactions, and top‐down control by reshaping community composition and inducing the loss of decomposer taxa and rare predatory taxa. Such alterations could compromise soil food web stability and the resilience of those communities to disturbance events in a changing climate.