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

Abstract

The stability of ecological communities over time, often quantified using their aggregated abundance or biomass, is thought to be influenced by species richness and the asynchrony of species abundance fluctuations. However, the relationship between community stability and the stability of ecosystem functioning provided by this community has been little explored, especially for functions involving several trophic levels such as plant pollination. Understanding the mechanisms driving community stability and how this should be related to the stability of ecosystem functions is important to predict the resilience of communities in front of the increasing threats to biodiversity. Using a 5‐year dataset across 13 Mediterranean shrublands and 12 plant species, we assessed the effect of pollinator richness and asynchrony as drivers of stability in plant visitation rates and plant reproductive success. Additionally, we analysed whether the effects of species richness and visitation rate on plant reproductive success were consistent over the years. The stability of plant visitation rates is driven by the asynchrony of pollinator species abundances, but the effect of pollinator species richness is only indirect, as richer communities also tend to have more asynchronous populations. In contrast, the stability of plant reproductive success is not related to the stability of pollinator visitation rates. A year‐by‐year analysis reveals that plants in the studied system are unlikely to be limited by pollinator abundance except in specific years, blurring any potential effect of visitation rate stability on reproductive success stability. Synthesis: We highlight the importance of asynchronous fluctuating species that are redundant in their function as an important factor for the stability of ecosystems. This is particularly important for pollinators with diverse responses to environmental fluctuations, as their asynchrony between years ensures stable levels of flower visitation rates. However, we warn that final ecosystem functions such as plant reproductive success, which depends not only on pollinators but on plant competition or resource availability, might be decoupled from first order ecosystem functions (i.e. visitation rates and pollen deposition) when pollination is not a limiting factor.

Stability in plant–pollinator communities across organizational levels: present, gaps, and future

“…Thirdly, the majority of research has focused on single organizational levels, notably populations, leaving gaps in understanding stability’s scaling across higher levels (e.g. communities, though exceptions exist, such as Lázaro et al 2022 ; Tobajas et al 2023 ). In contrast, other systems like plants and biomass production have extensively explored how stability scales with organizational levels driven by various factors ( Tilman 1995 ; Wang et al 2019a ).…”

“…Part of this ladder towards an understanding of stability within multi-trophic communities has recently started to be climbed in the case of plant–pollinator communities (e.g. Lázaro et al 2022 ; Tobajas et al 2023 ). This research includes intra and inter-annual measures of stability of plant–pollinator species population abundances, their interactions and the structure of these communities.…”

“…We considered that a visit was successful if the pollinator species touched the reproductive parts of the plants. In addition, we recorded measures of fruit set for a subset of eight plant species ( Cistus salviifolius , C. crispus , C. ladanifer , C. libanotis , Halimium halimifolium , H. calcynum , H. comutatum , and Lavandula stoechas ), whose flowering period is mostly comprised within our study window (see for example Tobajas et al 2023 for similar sampling efforts in the same study area). To do this, we marked open flowers within different individuals and fruits were collected once mature.…”

“…Although the bulk of studies on stability within complex communities has focused on single trophic levels, some research has started to address stability in communities with more than one trophic level (e.g. Lázaro et al 2022 ; Tobajas et al 2023 ). Overall, these studies reveal that ecological stability within these multi-trophic systems depends on factors such as the trophic level/group considered ( Firkowski et al 2021 ; Siqueira et al 2023 ), the spatial scale of analysis ( Siqueira et al 2023 ), landscape heterogeneity ( Lázaro et al 2022 ), habitat fragmentation ( Ren et al 2022 ), the diversity and proportion of interaction types ( Lurgi et al 2015 ) and the structure of species interactions networks ( Neutel et al 2002 ; McWilliams et al 2019 ; Duchenne et al 2022 ; Lázaro et al 2022 ; Nie et al 2023 ).…”