No biotic homogenisation across decades but consistent effects of landscape position and pH on macrophyte communities in boreal lakes

Abstract

It has been predicted that spatial beta diversity shows a decreasing trend in the Anthropocene due to increasing human impact, causing biotic homogenisation. We aimed to discover if vascular aquatic macrophyte communities show different spatial patterns in beta diversity in relation to land use and environmental characteristics in different decades from 1940s to 2010s. We aimed to discover if spatial structures differ between species-, phylogeny-and functional-based beta diversity. We used presenceabsence data of aquatic macrophytes from five decades from small boreal lakes. We utilized generalised dissimilarity modelling to analyse spatial patterns in beta diversity in relation to environmental gradients. We found that lake elevation and pH were the most important variables in each decade, while land use was not particularly important in shaping beta diversity patterns. We did not find signs of a decreasing trend in spatial beta diversity in our study area during the past 70 yr. We did not find signs of either biotic homogenisation or biotic differentiation (taxonomic, phylogenetic or functional). Vascular aquatic macrophyte communities showed only slightly different beta diversity patterns in relation to human impact across decades. The patterns of different facets of beta diversity diverged only slightly from each other. Lake position in the landscape, reflecting both natural connectivity and lake characteristics, explained the patterns found in beta diversity, probably because our study area has faced only modest changes in land use from 1940s to 2010s when compared globally. Our study highlights the fact that biotic homogenisation is not an unambiguous process acting similarly at all spatial and temporal scales or in different environments and different organism groups.

Lakes in the era of global change: moving beyond single‐lake thinking in maintaining biodiversity and ecosystem services

“…Therefore, sets of lakes should be understood as being connected in unique waterscapes, making the understanding of metacommunity organization context dependent and highly challenging. Recent findings in macrosystems ecology (Fergus et al ., 2018; Soranno et al ., 2019) and metacommunity ecology (García‐Girón et al ., 2020; Lindholm et al ., 2020) have increased knowledge on the spatial and temporal variability of physical, chemical, and biological features of lakes, which has further consequences for understanding a set of lakes as a meta‐ecosystem.…”

Effects of the Temporal Scale of Observation on the Analysis of Aquatic Invertebrate Metacommunities

“…However, environmental changes can also determine the temporal turnover due to species sorting, potentially reaching rates higher than those predicted by stochastic dynamics (Dornelas et al, 2014). At the metacommunity level, long-term studies have shown either stable (e.g., Azeria and Kolasa, 2008;Huttunen et al, 2018;Lindholm et al, 2020) or changing metacommunities through time, due to environmental fluctuations or disturbances observed (e.g., Datry et al, 2016;Sarremejane et al, 2017;Cañedo-Argüelles et al, 2020). Nevertheless, the spatio-temporal scale of observation in each study could explain these differences, depending on whether or not the study duration covered those relevant environmental fluctuations (Korhonen et al, 2010).…”

Changes in the functional features of macrophyte communities and driving factors across a 70-year period

“…Thus, naturally more eutrophic lakes are located at lower elevations and are mainly surrounded by agricultural land or settlements, while smaller and more oligotrophic lakes at higher elevations in the landscape are less affected by human activity and are surrounded by coniferous forest and peatlands. Key characteristics of these lakes are described in Table 2, and more information of the study area can be found in Lindholm et al (2019).…”

“…To represent functional diversity of aquatic macrophytes, we used four functional traits: growth form, perennation, common method of propagation and potential size (Supplementary material Appendix 2; Lindholm et al 2019). Growth form division consists of the following classes: ceratophyllid, elodeid, helophyte (incl.…”

“…We used the following environmental variables: lake area (ha), elevation (m), maximum depth (m), pH, water transparency (m), land use variables and geographical coordinates of lakes' centres, as we had only a limited number of environmental variables available from the 1940s (Table 2; Lindholm et al, 2019). Measurements of pH were done in the 1940s in summertime, while in 2017 during the fall overturn.…”