Plant-pollinator networks: Does land use impede an insurance against climate change?

Background/Question/Methods

Functional redundancy (FR), the diversity of species performing a particular function, improves the functional stability of ecosystems by providing an insurance against disturbances, local population declines or species extinctions. Land use intensification represents such a threat to many species, often reduces the local biodiversity and consequently FR. Plant-pollinator networks are particularly suitable models for biodiversity effects on ecosystem services.

Results/Conclusions

We show that land use intensity in central European grasslands strongly reduces the diversity of flowering plants and affects the composition of pollinators. While flies tend to increase in abundance and diversity, butterflies and bees are particularly sensitive, are more specialized and often require flower species that are themselves vulnerable to land use. Losses in FR may translate into a more narrow tolerance of environmental stress (lower ‘response diversity’), a high risk for altered conditions following climate change. Apart from lower FR in terms of flower or pollinator species richness, biotic homogenization may represent a lower resilience of their functional services – exemplified by reduced phylogenetic diversity of pollinators. Here we test (1) whether FR in plant-pollinator networks decreases with land use intensity, (2) whether reduced FR derives from lower flower abundance or pollinator activity densities, lower overall diversity and/or increased selectivity of pollinator visits, and (3) whether reduced FR is associated with poor taxonomic diversity. We found that FR of floral resources for each pollinator is more severely reduced than FR of pollinators for each plant. The findings suggest that synergistic effects of land use impacts and climate change via decreased FR may compromise the maintenance of ecosystem functioning such as pollination services in the future.