Biological traits of benthic macroinvertebrates in California mediterranean-climate streams: long-term annual variability and trait diversity patterns

Abstract

We examined long-term variability of the biological traits of benthic macroinvertebrate communities using data collected annually (20-, 7-, and 8-years in duration, respectively) from three study regions in northern California's mediterranean-climate region. We related temporal variability to several climatic and physical variables representing precipitation and hydrologic conditions, and assessed the stability of biological-trait composition using time-lag regression analysis. We also examined the temporal variability of trait diversity metrics and their relationship to taxa richness. Trait modalities exhibited high temporal variability (∼ 20 % of all trait modalities had a CV > 50 %) and biological-trait composition varied along a gradient from dry (extreme drought) to wet (above average) years. Traits conferring resistance or resilience to drying (e.g. desiccation resistance, aerial respiration) were more common in drought years, whereas traits conferring resistance or resilience to floods (e.g. flattened body shape, drift dispersal) were more common in wet years. Furthermore, prolonged drought and the patterns of increasing or decreasing precipitation over time in the study regions resulted in patterns of directional change in biological-trait composition. Although biological traits had high temporal variation within each region, between-region variation was higher than temporal variation in a single region. As found in other studies, trait diversity and richness metrics were relatively invariable over time despite high taxonomic turnover. However, there was considerable regional variation in trait diversity metrics along a gradient of increasing taxonomic diversity. The four functional metrics studied showed high redundancy. Taxa richness was positively correlated with three functional metrics (trait richness and two trait diversity measures), and trait richness and diversity became saturated taxa richness increased (∼50 taxa). In communities largely controlled by abiotic factors, such as stream invertebrates in mediterranean-climate, high redundancy may be the result of strong filtering of traits at larger spatial scales.