Understanding patterns of biodiversity change is crucial to conserving biodiversity. Across many taxa, one of the most common patterns of biodiversity change is that specialists on undisturbed habitat are being replaced by species that can tolerate human-disturbed environments. We investigated whether this pattern exists for forest specialist bee species in eastern North America, where deforestation and regrowth have reduced the average size and age of the available forest habitat. To determine how the richness of forest specialist and disturbance-associated bee species varies with forest age and area, we collected 8,886 bees of 79 species at 32 forests in New Jersey. Forests were chosen to vary orthogonally in age and area.
To examine the regional, long-term trends in the diversity of forest specialist and disturbance-associated bees, we used a dataset of 30,135 museum specimens of 454 species collected between 1872 and 2011 in eastern North America. Because sampling effort is uncontrolled in museum data, we used rarefaction to estimate rarefied richness within time periods of equal sample size.
Results/Conclusions
We used a previously published study by one of us (TH) to identify 35 species of forest specialist bees and 79 species of disturbance-associated bees. We found that, with increasing forest area in a landscape, the richness of disturbance-associated bees decreased (z=-2.94, p = 0.003), and the richness of forest specialist bees increased (z=2.60, p = 0.009). Forest age had no significant effect on the richness of either group of bees (p >= 0.11). Between 1872 and 2011, the rarefied richness of disturbance-associated bees in northeastern North America did not significantly change (p = 0.447), but the rarefied richness of forest specialist bees increased by 28% (p = 0.012). This increase in forest specialist bee diversity contrasts with the results of other studies of habitat specialists; we suspect that reforestation in eastern North America during the past 150 years drove this pattern. Our results suggest that, first, the loss of forest area from a landscape benefits disturbance-associated bee species but harms forest specialist bee species; second, young forests have high conservation value for forest specialist bee species, and third, forest regrowth has the potential to restore forest specialist bee biodiversity following deforestation.