Functional response of benthic macroinvertebrates to fire disturbance in patagonian streams

Abstract

Disturbances often act as ecological filters through which only certain combinations of biological traits may pass. Here, we aimed to determine if an unprescribed human-started wildfire can act as a filter for stream-dwelling macroinvertebrates. To do this, we sampled three burnt and two reference streams in Los Alerces National Park (Patagonia, Argentine side). Sampling began shortly after the fire was extinguished and comprised four visits during the following seven months. We explored how functional richness, evenness, and dispersion at the community level responded to post-fire environmental changes using generalized linear mixed models. We also used RLQ and fourth-corner analysis to identify which trait modalities were specifically affected, either positively or negatively, by the fire. We found that functional richness and dispersion decreased with increasing disturbance intensity, which in this case, was best represented by increased suspended solids. In addition, all three functional metrics were significantly lower in fire-affected sites. Burnt streams were characterized by bi-multivoltine taxa and collector-gatherers, among others. Overall, our study showed how a wildfire can directly constrain the functional composition of macroinvertebrate communities, and highlighted the importance of incorporating trait-based approaches into the study of large-scale disturbances.