Seed predation along an elevation in and out of species' native ranges

Background/Question/Methods

In montane forests plant species are predicted to move upslope to track changing temperatures and avoid extinction. This migration to new elevations will expose tree species to new suites of biotic interactions, which are known to play important roles in setting species distributions and abundances. Previously we quantified variation in seed predation from a comparative seed predation study of 23 species of tropical trees across a 2.5 km elevation gradient in the Peruvian Andes. The 23 species used in this experiment were from both lowland tropical forests and montane cloud forest. In the predation experiment seeds were placed both in and out of their species range. We calculated the elevation minimum, maximum, and midpoint of all species using GBIF records and data from permanents plots to test between two hypotheses. 1) Species placed outside their range escaped specialist predators and experienced less predation outside of their range (home range disadvantage). Or 2) species experienced less predation inside their range (home range advantage), possibly due to predator satiation or the development of chemical defenses against frequently encountered predators.

Results/Conclusions

Species show different patterns in their response to being placed in and out of their ranges. Twelve species are significantly depredated more in or out of their range. Of these 12 species, most experienced a home range advantage and are eaten less when they were placed inside their range. This suggests that seeds may be escaping predation through predator satiation or chemical defenses. However, there is no correlation between seed predation of a species and the abundance of closely related species in the area.