Portfolio effect and asynchrony as drivers of stability in plant–pollinator communities along a gradient of landscape heterogeneity

Abstract

Understanding how pollination services can be maintained in increasingly anthropogenic landscapes is a current challenge for basic and applied ecology. The stability of plant-pollinator communities might increase in heterogeneous landscapes with a high diversity of species and alternative habitats, both through larger independent fluctuations of populations (portfolio effect) and increased species asynchrony. However, how the drivers of stability (portfolio effect and synchrony) vary along land-use gradients remains largely unknown. Using independent samplings for plants, pollinators and their interactions in Mediterranean communities along a gradient of landscape heterogeneity, we assessed the relationships between within-year stability and its drivers, and between the drivers of stability, landscape heterogeneity and species diversity. In addition, we evaluated the relationship between the stability of plant-pollinator interactions (temporal mean/SD of pairwise interactions) and the structure of mutualistic networks (modularity, nestedness, connectance). As expected, stability increased with larger portfolio effects and asynchronies. Interaction stability was positively related to pollinator stability, but not to plant stability. Landscape evenness increased the stability of plants, pollinators and their interactions, through increased portfolio effects. However, for plants and pollinators, the effect was detected at a smaller scale (1-km) than for interactions (2-km); and for pollinators and interactions, the effect was only evident from medium-to-high levels of landscape evenness. Temporal synchrony of species/pairwise interactions was an important driver of stability, tightly linked to species/interaction diversity. More asynchronous communities showed a larger portfolio effect and were also those with higher species evenness for all plants, pollinators and their interactions; while synchrony was also weakly positively related to species richness for plants. Interestingly, more modular mutualistic network structures conferred enhanced overall community stability, through higher portfolio effect and asynchrony. Preserving diverse communities within the heterogeneous Mediterranean landscapes may help maintain the stability of pollination services, both through effects on synchrony and the portfolio effect.

Pollinator asynchrony drives the temporal stability of flower visitation rates, but not of plant reproductive success

“…This stability-asynchrony relationship has been found by different theoretical and empirical studies (Blüthgen et al, 2016;De Mazancourt et al, 2013;Kigel et al, 2021;Lepš et al, 2018;Sasaki et al, 2019;Valencia et al, 2020). For example, Lázaro et al (2022) also found for plants, pollinators, and their interactions, that more asynchronous communities are more temporally stable. In this sense, species asynchrony can increase the temporal stability of the visitation rate when the abundance of one species increases as a result of decreases in the abundance of another species (i.e.…”

Habitat loss increases seasonal interaction rewiring in plant–pollinator networks

“…Therefore, and for simplicity, we will refer to them as pollinators hereafter, although we lack information about their pollination efficiency. Rarefaction curves and sampling completeness estimates per site were adequate and can be found in Lázaro et al (2022).…”

“…However, it is still unclear whether static interaction structures calculated by accumulating data over time (still the most frequent way of studying network properties) actually reflect the rewiring dynamics of the networks. Understanding whether this link exists is crucial because several static network structures are often related to community stability (Bascompte et al, 2006; Grilli et al, 2016; Krause et al, 2003; Lázaro et al, 2022; Mariani et al, 2019). Interestingly, we found that as interaction rewiring increases, nestedness decreases and network specialization (H2') also tends to decrease.…”

“…Also, Schwarz et al (2020) showed that there is an interplay between sampling effort and temporal dynamics that shapes network structure across different temporal scales. However, it is still unclear the extent to which seasonal interaction rewiring influences the structure of static networks built by accumulating interactions through the season, which is still the most common way of analysing network structure and is supposed to be related to the stability and robustness of communities (Bascompte et al, 2006; Krause et al, 2003; Lázaro et al, 2022; Tylianakis et al, 2010). In addition, determining the species more prone to rewiring may help to comprehend how future anthropogenic changes will affect the interactions and functioning of communities.…”

Global change and plant–pollinator communities in Mediterranean biomes

“…For example, mosaics of patches at different successional stages can promote species richness (Dantas de Miranda et al, 2019; Penado et al, 2022), while landscape evenness (i.e. the degree to which the distribution of different landscape elements is uniform) can enhance the stability of pollination networks (Lázaro et al, 2022). Late successional stages of Mediterranean‐type vegetation are not optimal for bee diversity (Penado et al, 2022), although p–p networks can exhibit relative robustness to shrub encroachment (Lara‐Romero et al, 2016).…”