Restoration in intensive agricultural landscapes differentially supports more vulnerable species in pollinator communities

Background/Question/Methods

Agriculture now constitutes 40-50% of terrestrial land use and thus, restoration within agricultural landscapes, by affecting habitat suitability, matrix properties, and connectivity for vulnerable species, could have a major influence on biodiversity conservation. Some work, however, suggests that habitat management within intensive agricultural landscapes primarily boosts abundances of common, disturbance-adapted species, while providing few benefits for the vulnerable species that are the chief targets of conservation action.  These disturbance-adapted species are likely highly mobile with generalist habits, and thus able to survive even in intensive agricultural landscapes.  We studied composition of pollinator communities with maturation of native plant hedgerows over 7 years in a before-after-control-impact experiment in California’s intensively-farmed Central Valley, and analyzed how functional response traits (including floral specialization, habitat specialization, frequency, body size and sociality) of pollinator species interacted with hedgerow maturation.   If restoration chiefly benefits the common generalists that are able to survive in intensive agriculture, then we would expect to see changes in mean abundance of species between restored and control sites, but no increases in the abundances of the species that are most sensitive to disturbance, such as those with narrow larval and/or adult diet breadth.

Results/Conclusions

On five hedgerow and ten control sites, we found that hedgerows significantly enhanced abundance of native bee and syrphid fly species. Additionally, we found that hedgerows had a greater effect on the abundances of more specialized flower visitors (both bees and flies) and on species with more specialized habitat requirements (cavity-nesting as opposed to ground-nesting bees; aphid-feeding as opposed to bacteria and detritus feeding syrphid flies).  For syrphid flies only, hedgerows also had a greater effect on less common species.  Hedgerows also had a slightly greater, but significant effect on small-bodied bees and flies that are less mobile.  There was no interaction between hedgerow maturation and sociality (bees only). These results suggest that small-scale habitat restoration within intensive agricultural landscapes has the most positive effects on precisely the species whose traits may render them most vulnerable to habitat degradation, namely the more specialized, less mobile and/or less common species.