Drought and Nitrogen Addition Modulate Wolf Spider‐Associated Responses in a Detrital Food Web Without Detectable Functional Cascades

ABSTRACT

Predators play a key role in sustaining biodiversity and ecological functioning in grasslands, yet their ecological roles may shift under increasingly severe droughts and nitrogen (N) deposition. However, how top‐down effects of predators on detrital food webs respond to these global change factors remains unclear. Here, we conducted a field mesocosm experiment in a temperate grassland where we manipulated the presence/absence of locally dominant ground‐dwelling wolf spiders (Lycosidae) under drought and N addition. We examined how these predators influence soil fauna and microbial communities, and how such changes cascade to soil N availability and litter decomposition. Drought and N addition independently modulated wolf spider‐associated effects on the detrital food web by altering soil fauna and microbial community responses. However, these community‐level changes did not cascade to detectable shifts in soil inorganic N availability or litter decomposition rates. Drought altered spider‐induced changes in fungal and bacterial diversity and also altered spider effects on the community composition of Collembola, fungi, and bacteria. In contrast, N addition mainly increased the sensitivity of Collembola abundance to spider presence, while having little effect on the microbial communities. Overall, our findings highlight that drought and N addition can modulate detrital food webs and predator–prey interactions, providing new insight into how global change may alter predator‐associated effects in detrital food webs. These findings suggest that functional redundancy within detritivore and microbial assemblages may help buffer soil ecosystem functioning under global change, highlighting the importance of conserving biodiversity even if it is in a state of redundancy.