Species‐level drivers of avian centrality within seed‐dispersal networks across different levels of organisation

Abstract

Bird–plant seed‐dispersal networks are structural components of ecosystems. The role of bird species in seed‐dispersal networks (from less [peripheral] to more connected [central]), determines the interaction patterns and their ecosystem services. These roles may be driven by morphological and functional traits as well as evolutionary, geographical and environmental properties acting at different spatial extents. It is still unknown if such drivers are equally important in determining species centrality at different network levels, from individual local networks to the global meta‐network representing interactions across all local networks. Using 308 networks covering five continents and 11 biogeographical regions, we show that at the global meta‐network level species' range size was the most important driver of species centrality, with more central species having larger range sizes, which would facilitate the interaction with a higher number of plants and thus the maintenance of seed‐dispersal interactions. At the local network level, body mass was the only driver with a significant effect, implying that local factors related to resource availability are more important at this level of network organisation than those related to broad spatial factors such as range sizes. This could also be related to the mismatch between species‐level traits, which do not consider intraspecific variation, and the local networks that can depend on such variation. Taken together, our results show that the drivers determining species centrality are relative to the levels of network organisation, suggesting that prediction of species functional roles in seed‐dispersal interactions requires combined local and global approaches.

Moving towards a comprehensive view of the spatial processes in seed dispersal networks: Embracing metacommunities

“…Most of interaction patterns in seed dispersal systems have been assessed for local assemblages; however, growing data sets available on this kind of interaction has recently allowed for the construction of large-scale meta-networks that combine all the locally observed interactions in one single network (Emer et al, 2018;Fricke & Svenning, 2020;Vizentin-Bugoni et al, 2021). Moulatlet et al (2023) contribute to this cross-scale approach by moving from local networks to a broader spatial scale, one global meta-network, when investigating the importance of different properties and traits as drivers of bird species centrality in seed dispersal networks (Figure 1). The authors assessed the role of morphological, geographical, climatic and evolutionary properties as predictors of species centrality and, following their expectations, the factors determining centrality were different between spatial scales.…”

“…Focusing on node-level descriptors, Moulatlet et al (2023) showed the effects of spatial scale on the predictors of bird species centrality in seed dispersal networks (Figure 1). However, we still need to further investigate how the spatial scale of observation affects the overall structure of ecological networks, a relevant topic if we are to understand the implications of the current biodiversity crisis on the persistence and functioning of ecological systems (Galiana et al, 2018).…”

“…Therefore, given the key role of dispersal in this approach, metacommunities can be defined at an intermediate scale of analysis, above the level of local communities and below the level of large-scale biogeographic studies (Chase & Bengtsson, 2009). In this perspective, the work of Moulatlet et al (2023) sheds light on processes operating at the local and global spatial scales. Future efforts to include one more spatial scale (i.e.…”

“…Ecological boundaries set the template for the interactions to occur within ecoregions, whereas human disturbances, particularly those contributing to biotic homogenization, may weaken those biogeographical patterns (Fricke & Svenning, 2020;Martins et al, 2022). Indeed, at the global scale, Moulatlet et al (2023) improved their meta-network model by considering the biogeographical affiliation, suggesting its importance as a driver of bird species centrality. At regional scales, besides interactions between resident species, connections in meta-networks depicting metacommunities are mainly determined by spatial processes such as the dispersal of individuals among local communities, rather than by events of migration or by human-mediated factors, as it happens in the global meta-network (Martins et al, 2022).…”

“…In summary, the work of Moulatlet et al (2023) advances the interface between ecological interactions and biogeography by considering local and global spatial scales while investigating the factors that determine species centrality in seed dispersal networks. Body mass and range size were the main drivers of avian centrality in local and global networks respectively.…”