Abstract
The impact of global change on biodiversity is commonly assessed in terms of changes in species distributions, community richness and community composition. Whether and how much associations between species are also changing is much less documented. In this study, we quantify changes in large‐scale patterns of species associations in bird communities in relation to changes in species composition. We use network approaches to build three community‐aggregated indices reflecting complementary aspects of species association networks. We characterise the spatio–temporal dynamics of these indices using a large‐scale and high‐resolution dataset of bird co‐abundances of 109 species monitored for 17 years (2001–2017) from 1969 sites across France. We finally test whether spatial and temporal changes in species association networks are related to species homogenisation estimated as the spatio–temporal dynamics of species turnover (β‐diversity) and community generalism (community generalisation index). The consistency of these relationships is tested across three main habitats, namely woodland, grassland and human settlements. We document a directional change in association‐based indices in response to modifications in species turnover and community generalism in space and time. Weaker associations and sparser networks were related to lower spatial species turnover and higher community generalism, suggesting an overlooked aspect of biotic homogenisation affecting species associations and may also have an impact on species interactions. We report that this overall pattern is not constant across habitats, with opposite relationships between biotic homogenisation and change in species association networks in urban versus forest communities suggesting distinct homogenisation processes. Although species associations contain only partial signatures of species interactions, our study highlights that biotic homogenisation translates to finer changes in community structure by affecting the number, strength and type of species associations.
Highlights
Among the major effects of global change on biological diversity, the modification or even the extinction of species interactions has early on been identified as being pervasive, but is still poorly understood (Janzen 1974, Diamond 1989)
Weaker associations and sparser networks were related to lower spatial species turnover and higher community generalism, suggesting an overlooked aspect of biotic homogenisation affecting species associations and may have an impact on species interactions. We report that this overall pattern is not constant across habitats, with opposite relationships between biotic homogenisation and change in species association networks in urban versus forest communities suggesting distinct homogenisation processes
The structure and dynamics of species interactions are among the main drivers of community dynamics (Davis et al 1998, Barabás et al 2016), and represent a critical subject of study for ecology and biodiversity conservation (Kissling and Schleuning 2015, García-Girón et al 2020)
Summary
Among the major effects of global change on biological diversity, the modification or even the extinction of species interactions has early on been identified as being pervasive, but is still poorly understood (Janzen 1974, Diamond 1989). In some cases (e.g. in simple trophic networks with few taxa), observations or experiments can address both issues as the existence and type of species interactions are clearly identified These cases provide inference of species interactions in local and specific systems, which makes it difficult to derive general rules for interactions in larger communities (Whittaker et al 2005, Denny and Benedetti-Cecchi 2012). An alternative approach is to assume that species associations (inferred from their spatial aggregation) are shaped, at least to some extent, by the combination of true interactions (i.e. clear ecological relationships such as competition or predation) In this case, studying communities with a large number of species and broad spatial coverage should be a good framework for estimating species associations, the ability of spatial co-occurrence patterns to infer pairwise species interactions is still controversial (Blanchet et al 2020)
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