Landscape simplification leads to loss of plant-pollinator interaction diversity and flower visitation frequency despite buffering by abundant generalist pollinators

Global change, especially landscape simplification, is a main driver of
species loss that can alter ecological interaction networks, with
potentially severe consequences to ecosystem functions. Therefore,
understanding how landscape simplification affects the rate of loss of
plant-pollinator interaction diversity (i.e., number of unique
interactions) compared to species diversity alone, and the role of
persisting abundant pollinators, is key to assess the consequences of
landscape simplification on network stability and pollination services. We
analysed 24 landscape-scale plant-pollinator networks from standardised
transect walks along landscape simplification gradients in three
countries. We compared the rates of species and interaction diversity loss
along the landscape simplification gradient and then stepwise excluded the
top 1-20% most abundant pollinators from the data set to evaluate their
effect on interaction diversity, network robustness to secondary loss of
species, and flower visitation frequencies in simplified
landscapes. Interaction diversity was not more vulnerable than
species diversity to landscape simplification, with pollinator and
interaction diversity showing similar rates of erosion with landscape
simplification. We found that 20% of both species and interactions are
lost with an increase of arable crop cover from 30 to 80% in a landscape.
The decrease in interaction diversity was partially buffered by persistent
abundant generalist pollinators in simplified landscapes, which were
nested subsets of pollinator communities in complex landscapes, while
plants showed a high turnover in interactions across landscapes. The top
5% most abundant pollinator species also contributed to network robustness
against secondary species loss, but could not prevent flowers from a loss
of visits in simplified landscapes. Although persistent abundant
pollinators buffered the decrease in interaction diversity in simplified
landscapes and stabilised network robustness, flower visitation frequency
was reduced, emphasising potentially severe consequences of further
ongoing land-use change for pollination services.