Profiling crop pollinators: life history traits predict habitat use and crop visitation by Mediterranean wild bees

Abstract

Wild pollinators, bees in particular, may greatly contribute to crop pollination and provide a safety net against declines in commercial pollinators. However, the identity, life history traits, and environmental sensitivities of main crop pollinator species.have received limited attention. These are crucial for predicting pollination services of different communities and for developing management practices that enhance crop pollinators. We sampled wild bees in three crop systems (almond, confection sunflower, and seed watermelon) in a mosaic Israeli Mediterranean landscape. Bees were sampled in field/orchard edges and interiors, and in seminatural scrub surrounding the fields/orchards. We also analyzed land cover at 50-2500 m radii around fields/orchards. We used this data to distinguish crop from non-crop pollinators based on a set of life history traits (nesting, lecty, sociality, body size) linked to habitat preference and crop visitation. Bee abundance and species richness decreased from the surrounding seminatural habitat to the field/orchard interior, especially across the seminatural habitat-field edge ecotone. Thus, although rich bee communities were found near fields, only small fractions crossed the ecotone and visited crop flowers in substantial numbers. The bee assemblage in agricultural fields/orchards and on crop flowers was dominated by ground-nesting bees of the tribe Halictini, which tend to nest within fields. Bees' habitat preferences were determined mainly by nesting guild, whereas crop visitation was determined mainly by sociality. Lecty and body size also affected both measures. The percentage of surrounding seminatural habitat at 250-2500 m radii had a positive effect on wild bee diversity in field edges, for all bee guilds, while at 50-100 m radii, only aboveground nesters were positively affected. In sum, we found that crop and non-crop pollinators are distinguished by behavioral and morphological traits. Hence, analysis of life-history traits of bee communities can help assess the pollination services they are likely to provide (when taking into account single-visit pollination efficiency). The ecotone between agricultural fields and surrounding habitats is a major barrier that filters many bee species, particularly with regard to their nesting requirements. Thus, greater attention should be given to management practices that encourage pollinators to live and nest, and not only forage, within fields.

Watermelon pollinators exhibit complementarity in both visitation rate and single‐visit pollination efficiency

“…The distance from components of semi‐natural habitat had further variable effects within the wild bee assemblage, with the smallest species (with the shortest flight ranges) being largely confined to field edges containing wild plants, while larger species being more common in field interiors, and unaffected by edge type. Notably, in a related study we found similar contrasts in edge–interior abundance patterns among the main visitors L. malachurum , L. politum and H. taeniolatus using combined net and pan trap sampling (Pisanty & Mandelik ). These contrasts likely reflect differences in foraging needs (Potts et al .…”

“…Furthermore, the increase in average body size in the field interior may be linked to longer flight distances from stable foraging resources (such as wild vegetation surrounding the field) covered by larger species (Greenleaf et al . ; Pisanty & Mandelik ). Although at the time of sampling there was little wild bloom in most field edges and sometimes even in the semi‐natural batha, patches of wild plants blooming outside the crop blooming season and year are important as a stable foraging resource for bees (Garibaldi et al .…”

“…The wild bee fauna in the region is diverse, consisting mostly of tiny‐ to medium‐sized, solitary to primitively eusocial bees (Pisanty & Mandelik ). Honeybees Apis mellifera Linnaeus 1758 are commonly managed for crop pollination and honey production, but feral honeybees are rare due to Varroa mites.…”

Fragmentation of nest and foraging habitat affects time budgets of solitary bees, their fitness and pollination services, depending on traits: Results from an individual-based model

“…In agricultural landscapes it is common that bees are most abundant in field edges [56, 57]. Field interiors often show low abundance of solitary bees, and bees foraging there may be soil-nesting bees provided locally with nests [58]. …”

“…When soil-nesting bees are limited to field edges they must fly farther distances from the nest and face more local competition with bees around the nest. In general, soil disturbance in crop fields is assumed to be too high for soil-nesting bees to survive [83–85], but recent studies suggest that it is possible [58, 86] for species that nest a meter below the surface. Agricultural practices that reduce the depth of mechanical 'action' and pesticide application will benefit the survival of soil-nesting bees within fields.…”