Invertebrate functional trait variation along successional gradients in stream ecosystems

Abstract

As glaciers recede the environmental conditions in stream ecosystems shift from variable and harsh through to more stable and benign. The process through which communities assemble and develop along this successional gradient is governed primarily by changes in the environmental conditions, but mediated by the traits of organisms. Certain traits allow for organisms to be colonisers and persist under harsh environmental conditions, whereas others allow organisms to resist ecological interactions, and extreme events in later successional stages. As such, we can use trait analyses to understand the processes and mechanisms responsible for community assembly and structure. Here, we used a unique natural laboratory, Glacier Bay National Park, to further develop our understanding of how traits vary and functional diversity assembles as glaciers recede and the riverine landscape develops. Macroinvertebrate and meiofauna were investigated across two scales: (1) landscape – 16 streams of different successional stages (years since glacial recession); and (2) long-term – one postglacial stream over 40 years. Across both datasets, clear patterns were observed in community structure, trait variation and functional diversity. Traits conveying resilience to harsh environmental conditions (e.g., size, voltinism and short generation times) were shown to decrease in prevalence over time as environmental conditions changed and new taxa colonised. Functional diversity did not unilaterally increase along the successional gradient for either macroinvertebrates or meiofauna. However, the general patterns in functional richness and divergence indicated diversification in the trait space. Through comparing differences in the structure and function of meiofauna and macroinvertebrates along successional gradients, we were able to gain an improved understanding the dominant processes influencing communities within these postglacial systems.