Effects of Amazonian forest fragmentation on the interaction between plants, insect herbivores, and their natural enemies

Abstract

Abstract:We evaluated the effects of forest fragmentation on herbivory on central Amazonian trees. Levels of herbivory were measured on leaves from a total of 1200 saplings from 337 species. There was a positive and significant effect of forest fragment area on herbivore damage, with plants from continuous forest having twice as much damage as plants in the smallest fragments studied (1 ha). Measurements of herbivory rates on two species, however, indicate that the effect can be species-specific. Forest area had a positive and linear effect on rates of herbivory in Henriettella caudata (Melastomataceae), whereas in Protium hebetatum (Burseraceae), rates of herbivory were greater in the 10-ha fragments than in the 1-ha fragments and in continuous forest. There is no evidence that the nutritional and defensive characteristics of the leaves of the species we studied changed as a result of forest fragmentation, at least not in a manner consistent with the observed herbivory patterns. Herbivore predation levels, measured with artificial caterpillars, also showed no significant relationship with forest area. Therefore, neither of these top-down and bottom-up forces could explain the observed patterns of herbivory. It is suggested, instead, that forest fragmentation may affect the dispersal of insect herbivores, and reduce their abundances on small forest isolates. Altered patterns of herbivory on tree saplings may have important consequences for forest structure and dynamics.

Arthropod responses to the experimental isolation of Amazonian forest fragments

“…Nevertheless, the community-wide level of herbivory increased positively and significantly with forest area, with plants from continuous forest suffering on average twice as much as damage as plants in the 1-ha fragments (FAVERI et al 2008). This occurred despite no significant changes in the species composition of the tree sapling community according to fragment size, or in the nutritional or defensive leaf traits of the species studied.…”

“…Similarly, the relationship between forest area and herbivore damage was found to be species specific in leaves of naturally occurring tree saplings (FAVERI et al 2008). Nevertheless, the community-wide level of herbivory increased positively and significantly with forest area, with plants from continuous forest suffering on average twice as much as damage as plants in the 1-ha fragments (FAVERI et al 2008).…”

Consequências ecológicas da fragmentação florestal na amazônia

“…entretanto, para plântulas, não se observou diferenças significativas na taxa de herbivoria entre fragmentos de diferentes tamanhos (Benitez-Malvido et al 1999). Já a taxa de infecção por patógenos em plântulas (Benitez-Malvido et al 1999), assim como a herbivoria em arvoretas (Fáveri et al 2008) aumentaram positivamente com o tamanho do fragmento. embora em relação à herbivoria este efeito tenha variado entre espécies de plantas (Fáveri et al 2008), houve uma clara tendência geral de menor taxa de danos para plantas em fragmentos menores.…”

“…Já a taxa de infecção por patógenos em plântulas (Benitez-Malvido et al 1999), assim como a herbivoria em arvoretas (Fáveri et al 2008) aumentaram positivamente com o tamanho do fragmento. embora em relação à herbivoria este efeito tenha variado entre espécies de plantas (Fáveri et al 2008), houve uma clara tendência geral de menor taxa de danos para plantas em fragmentos menores. uma possibilidade é que a fragmentação limite a dispersão de insetos herbívoros especialistas o que acarretaria numa menor abundância destes insetos em fragmentos pequenos e isolados (Fáveri et al 2008).…”

The Interplay Between Landscape Structure and Biotic Interactions

“…When applicable, earlier references are included as well was far lower in forest fragments, with just approximately 5% of the number of seeds being dispersed further than 10 m away from parent trees than in intact forests [107]. Leaf herbivory in the Amazon can also be reduced in isolated fragments, possibly because of lower immigration of insect herbivores [108]. Similar relationships were found in a landscape-scale fragmentation experiment of understory plants in a longleaf pine savanna that controlled for potential confounding effects of isolation, the ratio of edge to area, and edge proximity through its arrangement of landscape structure [64].…”