Fruit quantity of invasive shrubs predicts the abundance of common native avian frugivores in central Pennsylvania


Jason M. Gleditsch, The Pennsylvania State University, Department of Biology, 208 Mueller Laboratory, University Park, PA 16802, USA.


Aim  Biological invasions pose one of the most severe threats to global biodiversity. Still, invasions can create positive ecological relationships and services, which can sometimes result in challenges for conservation efforts. A case in point is the invasion of alien plants that form mutualisms with native frugivorous birds. Here, we examined the correlation between honeysuckles (Lonicera spp.) and the bird communities in a landscape of central Pennsylvania during the fall months.

Location  State College area in central Pennsylvania, USA.

Methods  We conducted point counts to quantify the abundance of birds and fleshy-fruited plant species within a 187.5 km2 landscape that included forested, urban and agricultural lands. We also compared fruit-removal rates for a native fruiting plant under low and high Lonicera densities.

Results  The abundance of birds showed a strong positive association with Lonicera fruits, with the abundance of Turdus migratorius and Dumetella carolinensis showing the strongest correlations. We also found that fruit-removal rates were 30% larger for a native plant species in areas of high Lonicera density compared to a site with low density of Lonicera.

Main conclusions  Our results suggest that Lonicera may currently serve as a main axis for the organization of bird communities and the networks of frugivore–plant interactions in central Pennsylvania. Since populations of key bird frugivores may be currently depending on Lonicera resources, we argue that control measures should account for the negative effects that the loss of this fruit resource could have on populations of native consumers in highly invaded regions.