Abstract
Northern ecosystems are experiencing rapid and large-scale changes driven by accelerated warming, which have profound effects on the terrestrial and freshwater biodiversity. A comprehensive understanding of the distribution of aquatic biodiversity of subarctic ecosystems is therefore needed to better predict future trajectories of their unique biodiversity. In this study, we examined the functional diversity of chironomid communities in subarctic lakes across a 1000 m-elevation gradient, reflecting gradual changes in temperature and landscape characteristics. Using fuzzy correspondence analyses, we investigated spatial variability in trait composition of chironomid communities from 100 lakes in northern Sweden, and tested the hypotheses that (1) climate directly and indirectly shapes chironomid trait composition across the studied gradient, and (2) that generalist taxa with smaller body size and broader food preferences are more able to persist in cold environments. Our results showed that complex interplays between direct (e.g. temperature) and indirect climate processes (e.g. elevation-driven changes in vegetation/habitats) affect the functional diversity of chironomid communities. Specifically, traits such as larval size, food preference and feeding habits were well separated along the gradient, and this pattern revealed that low elevation lakes with forested catchments tended to have more sediment-feeding taxa and larger larvae than those above the tree line. As expected, food resource availability in lakes is strongly linked to vegetation composition/cover, and traits related to resource exploitation in chironomid communities are therefore well constrained by landscape characteristics. Furthermore, our findings suggested that short life cycles could facilitate the development of viable population in northern and high-elevation lakes where the short ice-free period is a limiting factor, thus contradicting patterns showing smaller organisms in warmer environments reported for other invertebrates. As a consequence of climate warming, the highest elevation lakes in subarctic landscapes will likely lose their typical cold-adapted chironomid taxa along with their functional attributes leading to potential impacts on the food web structure and the overall functioning of northern lake ecosystems.
Highlights
Patterns in biodiversity are determined by a combination of large-scale landscape attributes and habitat propertiesHandling Editor: Jamie Kneitel.Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.(Townsend et al 2003), among which climate plays a central role
PCA revealed the existence of two distinct gradients: the first axis explained elevation, total organic carbon concentration in water (TOC), organic matter concentration in sediments and climate parameters, whereas the second axis was strongly correlated with specific conductance, pH, and concentrations of major principal component analysis (PCA1 vs. PCA2) performed on lake characteristics, and correlation circle representing variable contributions to the first two PCA axes
Resource availability in lakes is strongly linked to vegetation composition/cover, and predominant traits related to resource exploitation in chironomid communities are strongly constrained by landscape characteristics
Summary
Northern ecosystems are experiencing rapid and large-scale changes driven by accelerated warming (AMAP 2011), and climate change is already responsible for ecological shifts observed on freshwater biodiversity (Heino et al 2009; Lento et al 2019; Lau et al 2020). The effects of environmental changes on ecosystem functions are partly set by the functional diversity in a community (Hulot et al 2000; Reynolds et al 2002; Hooper et al 2005), and trait composition of communities helps to define ecological resilience (McLean et al 2019). Functional diversity responses to changing environmental conditions have been well documented for temperate lakes (see Schmera et al 2017), we are still lacking information about their effects on ecosystem properties of subarctic lakes
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