A trait-based perspective toward the mechanistic understanding of benthic macroinvertebrate assemblage in a tropical rice field

Approximately 15% of the world's wetlands are rice fields, vital in providing food for 40% of the human population. Due to farming practices-induced habitat disturbances, rice cultivation acts as a habitat filter that retains only taxa possessing specific traits to overcome the constraints. Being aquatic biota, benthic macroinvertebrates are also impacted by the intermittent presence of water in rice fields. The biological traits and trait combinations of benthic macroinvertebrates enabling their existence during the rice cultivation cycle in seasonal rice fields of Maranchery Kole (The Ramsar site Vembanad Kole wetland’s part) were studied. Based on the literature, 63 categories of 11 biological traits assignable at the genus level were used to characterize benthic macroinvertebrates. The taxa by traits data matrix was subjected to Gower's distance‐based hierarchical agglomerative cluster analysis to categorize faunal groups with similar trait assembly. According to the abundance weighted trait modality scores, the predominant traits were small body size, life duration of more than 1 year, multivoltine life cycle, aquatic larval stage, aquatic passive dispersal, cocoons as resistant form, locomotion by full water swimming, tegumental respiration, asexual reproduction, detritus as food and deposit-feeding. Trait-based classification of taxa resulted in 5 clusters. Characteristic trait combinations in each cluster particularly those beneficial for survival in unstable lentic freshwaters enabled the existence of taxa. Cluster I, the most abundant group (oligochaetes), was benefited from trait combinations including resistance forms to survive the intermittent presence of water in rice fields. Asexual reproduction and early onset of reproduction ensured their higher abundance from the transplanting phase. Detrital feeding also facilitated their rapid buildup in newly flooded fields rich in decomposing detritus. Cluster groups II and III, actively flying colonists characterized by competitive traits like predation, were more in tillering and preharvest phases. Apart from resistant and resilient traits ensuring survival in the temporary and disturbed habitat, exclusive trait combinations favored the faunal groups through different phases.