Climate and food resources shape species richness and trophic interactions of cavity‐nesting Hymenoptera

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.

Seasonal variation in the ecology of tropical cavity-nesting Hymenoptera on Mt. Kilimanjaro

“…Temperature, which has been shown to be one of the most important factors for driving species diversity patterns of multiple taxa at Mt. Kilimanjaro (Peters et al 2016), but also for cavity-nesting Hymenoptera (Mayr et al 2020), was positively correlated with the nest-building activity of spider-hunting wasps, while relative humidity decreased it. Spider abundances at Mt.…”

“…(Supplementary material, Fig. S1), which we identified as the upper limit of the distribution of cavity-nesting Hymenoptera in a previous study (Mayr et al 2020). Study sites covered five major ecosystem types found at the southern slopes of Mt.…”

“…3f), morphospecies were identified, and nest-building activity, ecological rates and life-history traits were recorded. For more information and pictures about the trap-nesting method see Mayr et al 2020. The nestbuilding activity was used as a proxy for the reproduction activity.…”

Just bird food? – On the value of invertebrate macroecology

“…Niche breadth surely impacts ecological macro-pattern, and insects will allow testing concepts and predictions over a large range of specializations. Several recent studies used the unique feeding habits of insects to investigate the more-individuals hypothesis and its inherent links among productivity, food availability, abundance, and richness along elevational gradients (Classen et al, 2015, Gebert et al, 2020, Mayr et al, 2020.…”

Spatiotemporal shifts in the role of floral traits in shaping tropical plant-pollinator interactions

“…A. Johnson, 2013;Pichler, Boreux, Klein, Schleuning, & Hartig, 2020). The second problem is that the role of individual floral traits and the related selection pressures can vary in space and time (Abrahamczyk, Kluge, Gareca, Reichle, & Kessler, 2011;Albrecht et al, 2018;González et al, 2009;Hawkins & Devries, 2009;Mayr et al, 2020;J. Mertens et al, 2020;Fig.…”