Relationships among Key deer, insect herbivores, and plant quality

Abstract

Deer can have severe effects on plant communities, which in turn can affect insect communities. We studied the effects of Key deer herbivory on the incidence of insect herbivores that occur within deer habitats in the lower Florida Keys, within the National Key Deer Refuge (NKDR). We analyzed plant chemistry (tannins, nitrogen) and surveyed for the occurrence of insects (above the browse tier) among plant species that were either deer-preferred or less-preferred. Results indicated higher levels of foliar tannins on islands with fewer Key deer and larger amounts of foliar nitrogen on islands with a high density of Key deer. Consequently, leaf miners were significantly more abundant on islands with high deer density, irrespective of deer-preference of plant species. On islands with a high deer density, incidence of leaves damaged by chewing insects was lower on preferred plant species but greater on less-preferred species than on islands with fewer deer. No apparent patterns were evident in the distribution of leaf gallers among plant species or islands with different deer density. Our results imply that plant nutrition levels-either preexisting or indirectly affected by deer deposition-are more important than plant defenses in determining the distribution of insect herbivores in the NKDR. Although high densities of the endangered Key deer have negative effects on some plant species in the NKDR, it seems Key deer might have an indirect positive influence on insect incidence primarily above the browse tier. Further research is warranted to enable fuller understanding of the interactions between Key deer and the insect community.

Herbivory on Handroanthus ochraceus (Bignoniaceae) along a successional gradient in a tropical dry forest

“…Thus, the unexpected herbivory increase in H. ochraceus individuals along the successional gradient is likely a consequence of their increased foliar nitrogen. Other studies have found a strong positive relationship between insect herbivory and leaf nitrogen content in different ecosystems, including SDTFs (Mattson 1980;Filip et al 1995;Cornelissen and Fernandes 2001;Boege 2004;Boege 2005;Stiling and Moon 2005;Barret and Stiling 2007). The inverse successional pattern of leaf nitrogen content observed for H. ochraceus is probably a consequence of the higher soil nutrient content (N, P, K-base saturation) observed in advanced compared to the early successional stages at the Mata Seca State Park (unpublished data).…”

Impact of deer on temperate forest vegetation and woody debris as protection of forest regeneration against browsing

“…Ungulate herbivory affects vegetation, from the plant organ to the landscape scale (Weisberg and Bugmann, 2003) with cascade mechanisms impacting bird and arthropod communities (Allombert et al, 2005;Barrett and Stiling, 2007;Gill and Fuller, 2007), ground flora (Kirby, 2001) and trees and shrubs (Gill and Beardall, 2001). This situation causes damage to economically important human activities (e.g., agriculture, forestry).…”

Ranking temperate woody species along a gradient of browsing by deer

“…Ungulate herbivory affects vegetation at all levels, from individual plant organs to landscape scales (Augustine and DeCalesta, 2003;Weisberg and Bugmann, 2003) with cascade mechanisms impacting trees and shrubs (Gill and Beardall, 2001), ground flora (Kirby, 2001) but also bird and arthropods communities (Allombert et al, 2005a,b;Barrett and Stiling, 2007). A recent pan-European enquiry highlights browsing as the third main threat to forests in Europe (Schuck and Requardt, 2008), after insect infestations and storms.…”