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

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. La estabilidad de las comunidades ecologicas, a menudo cuantificada como la abundancia agregada o biomasa, esta influenciada por la riqueza y por la asincronia de la abundancia de especies. Sin embargo, la relacion entre la estabilidad de la comunidad y la estabilidad de las funciones ecosistemicas ha sido poco explorada, especialmente en funciones que implican varios niveles troficos, como la polinizacion de las plantas. Comprender los mecanismos que impulsan la estabilidad de la comunidad y su relacion con la estabilidad de las funciones ecosistemicas es importante para predecir la capacidad de recuperacion de las comunidades frente a las crecientes amenazas a la biodiversidad.Empleando datos de 12 especies de plantas recolectados durante 5 anos en 13 zonas de matorral mediterraneo, evaluamos el efecto de la riqueza de polinizadores y la asincronia sobre la estabilidad de la tasa de visitas y el exito reproductivo de las plantas. Ademas, analizamos si los efectos eran consistentes a lo largo de los anos.La estabilidad de la tasa de visitas a las plantas esta impulsada por la asincronia de la abundancia de especies, pero el efecto de la riqueza de polinizadores es indirecto, ya que las comunidades mas ricas tienden a tener poblaciones mas asincronicas. En cambio, la estabilidad del exito reproductor de las plantas no esta relacionada con la estabilidad de la tasa de visita de los polinizadores. Un analisis ano por ano revela que es poco probable que las plantas en nuestro sistema de estudio esten limitadas por la abundancia de polinizadores excepto en anos especificos, lo cual puede desvanecer cualquier efecto potencial de la estabilidad de la tasa de visitas sobre la estabilidad del exito reproductivo de las plantas.Sintesis: Destacamos la asincronia en la fluctuacion de las especies como un factor importante para la estabilidad de los ecosistemas. Esto es particularmente importante para los polinizadores con respuestas diversas a las fluctuaciones ambientales, ya que su asincronia entre anos asegura niveles estables de tasas de visita a las flores. Sin embargo, funciones del ecosistema como el exito reproductivo de las plantas, la cual no solo depende de los polinizadores sino tambien de la competencia entre plantas o de la disponibilidad de recursos, podrian desajustarse de las funciones de primer orden (es decir, las tasas de visita y los depositos de polen) cuando la polinizacion no es un factor limitante. 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. Photo: Osmia bicornis on Lavadula pedunculata (by Curro Molina).image

Automated summary

The stability of ecological communities is influenced by species richness and the asynchrony of species abundance fluctuations. However, the relationship between community stability and the stability of ecosystem functioning has been little explored, especially for functions involving several trophic levels. Using data from Mediterranean shrublands and plant species, this study found that plant visitation rates stability is driven by the asynchrony of pollinator species abundances, but pollinator species richness has only an indirect effect. On the other hand, the stability of plant reproductive success is not related to the stability of pollinator visitation rates.