LB 32-312 - Increased herbivory on pepper trees (Schinus terebinthifolia) close to urban forest remnants and homogeneous predation pressure on caterpillars in the cityscape of a tropical city

Background/Question/Methods:

Plant–animal interactions are sensitive to changes in the urban landscape. For instance, Insect herbivory increases in urban environment, while the community of insect predator declines. In this study, we assessed how differences across the cityscape impacts leaf damage and predation pressure on herbivorous insects. Our hypothesis was that habitats with more impervious surface cover and less vegetation cover would create an enemy-free space allowing increased herbivory, while areas with higher habitat complexity and abundance of trees would support more natural enemies causing reduction in herbivory (the enemy hypothesis). We evaluate herbivory on leaf of the native Brazilian pepper tree (S. terebinthifolia) and we used dummy caterpillar models as indicators of predation pressure. We quantified impervious cover, abundance of trees around focal pepper trees and canopy volume among other variable that could affect herbivory.

Results/Conclusions:

We measure leaf damage in trees located in streets (n= 30), public square (n = 27) and native forest remants (n = 18). There was significant differences in herbivory across the cityscape (F(2, 74) = 6.78.; p < 0.002) and, contrarily to our prediction, pepper trees on the edge of native forest remnant showed increased leaf herbivory (post hocTukey HSD, p < 0.02). Predation on dummy caterpillars did not show differences among the different habitats sampled (F(2, 74) = 1.92; p = 0.15). A multiple regression model explained 38.6% of the variability in leaf damage and predicted herbivory well (F(3, 71) = 4.15; p = 0.009). The variables proportion of impervious surface (p = 0.018) and canopy volume ( p = 0.072) were the best predictors for herbivory. Our findings suggest that forest remnants possible harbour a greater diversity of herbivorous, which could explain increased herbivory. Although high plant diversity in urban forest remnant could result in a better top-down regulation of insect herbivory, the sampled trees and the dummy caterpillars were located on the edge of the forest fragments, which could have negatively impacted the presence of predators.