Relative Importance of Resource and Condition Niche for Invertebrates in Water‐Filled Treeholes

ABSTRACT Water‐filled treeholes offer an ideal system to disentangle the roles of resource availability and abiotic conditions in community assembly. This study hypothesized that niches related to consumable resources and microhabitat conditions play distinct roles in shaping community structure, with niche differentiation being more strongly influenced by resources than conditions. We conducted a field experiment by independently manipulating resource levels (cotton powder addition) and condition variables (plastic leaf addition) as well as their combination, and analysed species‐specific responses with a trait‐based species distribution model (SDM). We found that species‐specific responses varied with body size: smaller species were more responsive to resource and condition manipulations, and resource additions disproportionately benefited these smaller species, potentially intensifying competition and reshaping niche dynamics. In contrast, larger species, such as Tripteroides bambusa , were less responsive to single treatments but declined significantly under combined treatments. Interactions between resource and condition niches demonstrated both additive and synergistic effects, highlighting their distinct yet interconnected contributions to community assembly. Furthermore, species responses to treatments were more strongly associated with resource niches than with condition niches, confirming the critical role of resources in niche differentiation within water‐filled treeholes. These findings underscore the importance of distinguishing resource and condition niches to advance our understanding of community assembly and provide broader insights into niche differentiation mechanisms across ecological systems.