Host specificity of Lepidoptera in tropical and temperate forests

Abstract

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats 1 . A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15° S to 55° N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater fi diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.Ecological theory requires that organisms differ in their use of shared, limiting resources if they are to coexist. The role of resource specialization in fostering biodiversity is thus a central issue in ecology and evolutionary biology. A longstanding hypothesis predicts a direct relationship between ecological specialization and species richness in communities 2 . Specialization reduces interspecific competition and facilitates species coexistence by partitioning niche space 3,4 . Character divergence across generations in response to trophic interactions or competition 5 provides an evolutionary mechanism by which species richness and specialization can increase together 6 " 8 . Beginning with observations recounted by Darwin 9 and Wallace 10 , examples of ecological specialization in tropical organisms have fostered a widespread perception that specificity of interactions is a hallmark of the high-diversity tropics.Although biotic inventories often confirm the higher species richness of tropical communities than those at higher latitudes 1 , few studies have quantified increased ecological specialization along a latitudinal gradient 11 . Novotny et al. 12 recently challenged the notion that herbivorous insects are more specialized in the tropics by the use of a quantitative comparison of host specificity of herbivorous insects in tropical forests of Papua New Guinea and those in temperate forests of central Europe. They reported a similar host specificity among temperate and tropical herbivorous insects and concluded that the ...

Herbivore pressure increases toward the equator

“…Although we found that generalist and not specialist herbivores contributed to higher herbivore species richness at lower latitudes, we cannot draw any clear conclusions about possible patterns of herbivore specialization across the latitudinal gradient (3,5). Our study was not designed to exhaustively measure herbivore diet breadth.…”

“…As a result, species at lower latitudes are likely to have higher levels of specialization to lessen competition and greater defenses to reduce predation (2). For plant-herbivore interactions in particular, it is expected that at lower (tropical) latitudes, abundance and species richness of insect herbivores will be higher, and, therefore, lower latitudes will also have more specialized herbivores and plants will suffer greater biomass loss to herbivory (3)(4)(5). Consequently, this herbivore species latitudinal gradient is likely to impose stronger herbivore pressure on plants at lower latitudes (6)(7)(8).…”

Establishing the evidence base for maintaining biodiversity and ecosystem function in the oil palm landscapes of South East Asia

“…(a) Biological simplification The huge reduction in tree species diversity (table 2) will inevitably lead to a comparable reduction in the diversity of animals that use trees, especially the legions of herbivorous insects: plant biodiversity begets animal biodiversity [59][60][61]. Not only is diversity reduced at the taxonomic level, but clearly oil palm plantations are architecturally much simpler than forests, with fewer canopy layers, and less diverse elements of, for example, lianas, epiphytes and litter (table 2).…”

Genetic mapping of two components of reproductive isolation between two sibling species of moths, Ostrinia nubilalis and O. scapulalis

“…In particular, phytophagous insect species previously considered to be polyphagous are frequently found to be mixtures of genetically differentiated, specialist taxa, each feeding on a restricted range of host plants (Berlocher and Feder, 2002;Drès and Mallet, 2002;Dyer et al, 2007;Feder and Nosil, 2010;Matsubayashi et al, 2010). These specialized taxa display a recurrent pattern of host-plant associations, together with partial or complete reproductive isolation in sympatry.…”