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 presence–absence 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.
Highlights
Biological communities are temporally dynamic, as they gain and lose species over time when the environments around them change (Bengtsson et al 1997).human actions have increased these changes by intensifying land use, introducing new species to ecosystems and altering the climate especially during the last century (Vitousek 1994, Chapin et al 2000)
We had two main questions: Are spatial beta diversity patterns different between decades, i.e. has there been biotic homogenisation? What are the main drivers for spatial beta diversity and are those drivers the same over the decades? We aimed to discover if these patterns differ between species, phylogenyand trait-based beta diversity
Similar patterns occurred for functional beta diversity as the average values vary between 0.38 and 0.44 (Fig. 2, Supplementary material Appendix 3), and it was more contributed by the richness difference (75.4–79.2%) than the replacement (20.8–24.6%) in each decade (Supplementary material Appendix 3)
Summary
Biological communities are temporally dynamic, as they gain and lose species over time when the environments around them change (Bengtsson et al 1997).human actions have increased these changes by intensifying land use, introducing new species to ecosystems and altering the climate especially during the last century (Vitousek 1994, Chapin et al 2000). One major consequence of human impact on biodiversity through time is that ecosystems are losing their biological uniqueness in a process called biotic homogenisation (McKinney and Lockwood 1999, Olden and Rooney 2006). Biotic homogenisation has gained much attention in recent decades (Castaño-Sánchez et al 2018, Richardson et al 2018), it is still unclear how this process is acting at different levels of biodiversity through time in different ecosystems. This is especially the case in the lake-rich boreal region, which covers large areas across the Northern Hemisphere and is only moderately impacted by human activities compared to many other regions and ecosystems
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