| dc.description.abstract | Aim: Temperature, food resources and top-down regulation by antagonists are considered as major drivers of insect diversity, but their relative importance is poorly
understood. Here, we used cavity-nesting communities of bees, wasps and their
antagonists to reveal the role of temperature, food resources, parasitism rate and
land use as drivers of species richness at different trophic levels along a broad
elevational gradient.
Location: Mt. Kilimanjaro, Tanzania.
Taxon: Cavity-nesting Hymenoptera (Hymenoptera: Apidae, Colletidae, Megachilidae,
Crabronidae, Sphecidae, Pompilidae, Vespidae).
Methods: We established trap nests on 25 study sites that were distributed over
similar large distances in terms of elevation along an elevational gradient from 866
to 1788 m a.s.l., including both natural and disturbed habitats. We quantified species
richness and abundance of bees, wasps and antagonists, parasitism rates and flower
or arthropod food resources. Data were analysed with generalized linear models
within a multi-model inference framework.
Results: Elevational species richness patterns changed with trophic level from
monotonically declining richness of bees to increasingly humped-shaped patterns
for caterpillar-hunting wasps, spider-hunting wasps and antagonists. Parasitism
rates generally declined with elevation but were higher for wasps than for bees.
Temperature was the most important predictor of both bee and wasp host richness patterns. Antagonist richness patterns were also well predicted by temperature, but in contrast to host richness patterns, additionally by resource abundance
and diversity. The conversion of natural habitats through anthropogenic land use,
which included biomass removal, agricultural inputs, vegetation structure and percentage of surrounding agricultural habitats, had no significant effects on bee and
wasp communities.
Main conclusions: Our study underpins the importance of temperature as a main
driver of diversity gradients in ectothermic organisms and reveals the increasingly
important role of food resources at higher trophic levels. Higher parasitism rates at higher trophic levels and at higher temperatures indicated that the relative importance of bottom-up and top-down drivers of species richness change across trophic
levels and may respond differently to future climate change | en_US |
