Low host specificity of herbivorous insects in a tropical forest

Abstract

Two decades of research [1][2][3][4] have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity 1,4,5 . Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity 6 should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4-6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas 7,8 .Host specificity is difficult to measure, and the limitations of existing studies include sampling only certain taxonomic groups rather than entire guilds, or sampling limited numbers of host plant species and lineages. Studies are often of insufficient duration, producing samples too small for quantitative analysis, or insects are sampled destructively, which precludes feeding experiments and the study of immature stages. Further, previous studies 2 failed to consider the phylogenetic relationships of host plants by using measures of host specificity that relied on counts of higher plant taxa (for example, genera or families). This approach can be misleading when taxonomic ranks are not commensurate with plant lineages. We examined the impacts of sampling bias and phylogenetic effects on estimates of host specificity by analysing the largest available data set of its kind. The leaf-chewing insect community on 51 plant species was characterized by using a sample

Forest tree neighborhoods are structured more by negative conspecific density dependence than by interactions among closely related species

“…Functional traits associated with ecological performance are significantly more similar among closely related species than expected by chance (e.g., Swenson et al 2007, Lebrija-Trejos et al 2014. In addition, the probability that two plant species share a common pest species (e.g., pathogens, herbivores) and, hence, the strength of indirect interactions mediated by shared pests, also declines with evolutionary divergence time (Novotny et al 2002, Gilbert and Webb 2007, Liu et al 2012, Gilbert et al 2015. Finally, Darwin's prediction that closely related species are strong competitors has been confirmed experimentally for plants and microbes (Maherali and Klironomos 2007, Burns and Strauss 2011, Violle et al 2011.…”

An updated checklist of the Thysanoptera of Panama with comments on host associations

“…Rates of tropical forest habitat degradation and destruction are higher than in almost any other biome and we are in danger of losing the vast majority of species before we have documented them (Lawton and May 1995). In comparison with most temperate ecosystems, Panamanian tropical ecosystems are characterized by extraordinarily high but poorly inventoried insect diversity, and by an absence of basic biological and ecological information (Godfray et al 1999;Novotny et al 2002). Information on the Neotropical species of the insect Order Thysanoptera is widely scattered (Mound and Marullo 1996).…”

Biology and occurrence of Inga Busk species (Lepidoptera: Oecophoridae) on Cerrado host plants

“…This work provides the first set of ecological and biological information for the moth genus Inga. Although it is well recognized that most phytophagous insects tend to feed on more or less closely related host plants rather than on a random selection of plants from a local flora (Strong et al 1984, Novotny et al 2002, we have shown that in the cerrado Inga caterpillars feed on a wide variety of non-related host plant families including some isolated ones, such as Caryocaraceae and Proteaceae both of which are monotypic in this region. Our results are based on an extensive data set that showed a strong preference by I. ancorata for C. brasiliense, suggesting a change of host plant utilization by this species during its life cycle.…”