Intraspecific variability across seasons and geographically distinct populations can modify species contributions to ecosystems

Abstract

Environmental change profoundly alters biodiversity and, by extension, species contributions to ecosystem functioning. While it is well-established that these impacts can be geographically and temporally nuanced, most assessments of species contributions to ecosystems assume that species traits are temporally and spatially fixed, and those that do acknowledge intraspecific variability have failed to fully determine its relevance to ecosystem functioning. Here, using three geographically distinct populations of sediment-dwelling invertebrates, we combine a laboratory experiment with Bayesian hierarchical modelling to empirically quantify the prevalence of intraspecific trait variability in relation to geographic locality and seasonal conditions. Furthermore, we assessed the role of intraspecific trait variability in mediating sediment particle mixing, nutrient generation and benthic oxygen uptake. We found that geographic and seasonal variability in body size and sediment particle reworking modified macrofaunal contributions to sediment total oxygen uptake and nutrient generation. These associations, however, were not consistent across all measured traits and ecosystem functions. Our findings highlight asymmetries in both the absolute magnitude and/or direction of species responses to changing seasonal conditions, indicating that the relative functional contributions species make to ecosystems can be temporally or spatially transient and may, therefore, diverge from expectations based on contemporary functional group typologies. These findings highlight a critical knowledge gap in our understanding of the key sources of variability affecting functionally important aspects of species behaviour and physiology and call for the development of dynamic ecological assessment and management approaches that account for individual as well as species responses to changing environments. Read the free Plain Language Summary for this article on the Journal blog.