Trophic level and specialization moderate effects of habitat loss and landscape diversity on cavity‐nesting bees, wasps and their parasitoids

Abstract

1. Habitat loss is a primary driver of biodiversity decline, but differences in species responses to habitat loss from local to landscape scales are poorly understood. 2. Trophic level, food and habitat specialization have been suggested to be important predictors of species responses to habitat loss, landscape diversity and landscape scale. 3. Using cavity-nesting communities of bees, wasps and their parasitoids on calcareous grasslands as a model system allowed us to compare responses of species differing regarding their trophic level, and degree of specialization on habitat and food. 4. We found that species from higher trophic levels experienced semi-natural habitat at larger spatial scales than those of lower trophic levels, but only, when they were generalists (abundance of bees, 150 m radius, vs. wasps feeding on herbivores, 450 m radius), not specialists (bees, 150 m, vs. bee parasitoids, 150 m). 5. Parasitoids, which are typically more specialized regarding their food resources (hosts), compared to predators such as predatory wasps, responded to habitat loss at the same spatial scales as their hosts, suggesting strong bottom-up effects of resource availability, that is, host availability driving parasitoid abundance. 6. Bees were mostly habitat specialists of calcareous grasslands and mainly driven by local habitat loss, whereas wasps as habitat generalists were mostly affected by landscape diversity. 7. Our study highlights the need to consider the different spatial scales contingent on trophic level and specialization of target species groups, maintaining or restoring both local habitat and landscape diversity, as this is needed for their successful conservation.