| Popis: |
Summary1. Seed dispersal by frugivores is the basis for regeneration of fleshy-fruited plants in forest ecosys-tems. Previous studies have reported a decrease in forest specialist frugivores due to logging andforest edges. Forest generalists appear less sensitive and may even increase at forest edges. Suchchanges in the abundance of frugivores may have consequences for consumer/resource ratios andcompetition in plant–frugivore networks.2. Optimal foraging theory predicts an increase in dietary specialization of animals at low consumer/resource ratios due to reduced competition. A decrease in forest specialists in logged forests shouldcause decreased consumer/resource ratios, increased dietary specialization and reduced redundancy,whereas an increased abundance of forest generalists at edges may compensate for a loss of specialists.3. In Europe’s last old-growth lowland forest (Bialowieza, Eastern Poland), we recorded fruit_removal by frugivores from fleshy-fruited plant species in the interior and at edges of logged andold-growth forests for 2 consecutive years.4. The abundance of forest generalists increased at forest edges, whereas specialists were unaffected.Conversely, logging resulted in a decrease in abundance of forest specialists but had no effect onthe abundance of generalists. Accordingly, consumer/resource ratios increased from interior to edgesand were reduced in the interior of logged forests compared with the interior of old-growth forests.As predicted by optimal foraging theory, a decrease in consumer/resource ratios coincided withincreased dietary specialization and a loss of redundancy in the interior of logged forests. Despitelow dietary specialization, redundancy was reduced at forest edges as forest generalists dominatedplant–frugivore interactions.5. Synthesis. We show that a shift in frugivore assemblages at forest edges and increased dietaryspecialization of frugivores in the interior of logged forests involved a loss of redundancy comparedwith continuous old-growth forests. This suggests that seed dispersal services in secondary foresthabitats depend on an impoverished subset of dispersal vectors and may suffer reduced adaptivepotential to changing environmental conditions. Thus, our study highlights the value of old-growthforests for the conservation of frugivore-mediated seed dispersal processes.Key-words: Bialowieza Forest, ecosystem services, functional niche, mutualistic networks, optimal_foraging, plant–animal interactions, resource specialization, seed dispersalIntroduction |
Plný text