Low host specificity of herbivorous insects in a tropical forest. Nature

Department of Biology and Ecology, University of Ostrava, Ostrava, Moravskoslezský, Czech Republic
Nature (Impact Factor: 41.46). 05/2002; 416(6883):841-4. DOI: 10.1038/416841a
Source: PubMed

ABSTRACT Two decades of research 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. 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 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.

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Available from: Scott E. Miller, Sep 26, 2015
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    • "Recently, indices of species diversity have been applied to calculate how similar the parasite faunas of host species are (Novotny et al. 2002; Weiblen et al. 2006; Vinarski et al. 2007; Davies and Pedersen 2008; Poulin 2010), driving a new interest in the understanding of community similarity of host species, also known as faunal similarity. The Jaccard index is widely used to assess community similarity across geography and phylogeny, and for the case of parasites, a number of studies have shown that the similarity in species composition decreases exponentially with phylogenetic and geographic distance among the host species (Poulin 2003, 2010; Fellis and Esch 2005; Krasnov et al. 2005; Oliva and Gonz alez 2005; Poulin et al. 2011). "
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    ABSTRACT: Parasite host range can be influenced by physiological, behavioral and ecological factors. Combining data sets on host-parasite associations with phylogenetic information of the hosts and the parasites involved can generate evolutionary hypotheses about the selective forces shaping host range. Here, we analyzed associations between the nest-parasitic flies in the genus Philornis and their host birds on Trinidad. Four of ten Philornis species were only reared from one species of bird. Of the parasite species with more than one host bird species, P. falsificus was the least specific and P. deceptivus the most specific attacking only Passeriformes. Philornis flies in Trinidad thus include both specialists and generalists, with varying degrees of specificity within the generalists. We used three quantities to more formally compare the host range of Philornis flies: the number of bird species attacked by each species of Philornis, a phylogenetically-informed host specificity index (Poulin and Mouillot’s STD) and a branch-length based STD. We then assessed the phylogenetic signal of these measures of host range for twenty-nine bird species. None of these measures showed significant phylogenetic signal, suggesting that clades of Philornis did not differ significantly in their ability to exploit hosts. We also calculated two quantities of parasite species load for the birds – the parasite species richness, and a variant of the STD index based on nodes rather than on taxonomic levels – and assessed the signal of these measures on the bird phylogeny. We did not find significant phylogenetic signal for the parasite species load or the node-based STD index. Finally, we calculated the parasite associations for all bird pairs using the Jaccard index and regressed these similarity values against the number of nodes in the phylogeny separating bird pairs. This analysis showed that Philornis on Trinidad tend to feed on closely related bird species more often than expected by chance.
    Ecology and Evolution 08/2015; DOI:10.1002/ece3.1621/full · 2.32 Impact Factor
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    • "The lack of increase in specialism toward the poles matches the patterns reported for other interaction types, which we also show to form well-linked webs in our study region (Appendix 2). Comparisons between tropical and temperate latitudes offer no evidence of latitudinal differences in the specialism of antagonistic interactions of herbivores and plants (Beaver 1979; Fiedler 1998; Novotny et al. 2002, 2006; Lewinsohn and Roslin 2008), or suggest an increase in specialism toward the equator (Dyer et al. 2007). An increase in specialism toward the equator has been also found in mutualistic interactions of plants and pollinators (Olesen and Jordano 2002; Armbruster 2006; Dalsgaard et al. 2011; Trojelsgaard and Olesen 2013), but such latitudinal trends sometimes disappear once sampling bias (Ollerton and Cranmer 2002; V azquez and Stevens 2004) or differences in plant diversity (Ollerton et al. 2006) have been accounted for. "
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    ABSTRACT: How food webs are structured has major implications for their stability and dynamics. While poorly studied to date, arctic food webs are commonly assumed to be simple in structure, with few links per species. If this is the case, then different parts of the web may be weakly connected to each other, with populations and species united by only a low number of links. We provide the first highly resolved description of trophic link structure for a large part of a high-arctic food web. For this purpose, we apply a combination of recent techniques to describing the links between three predator guilds (insectivorous birds, spiders, and lepidopteran parasitoids) and their two dominant prey orders (Diptera and Lepidoptera). The resultant web shows a dense link structure and no compartmentalization or modularity across the three predator guilds. Thus, both individual predators and predator guilds tap heavily into the prey community of each other, offering versatile scope for indirect interactions across different parts of the web. The current description of a first but single arctic web may serve as a benchmark toward which to gauge future webs resolved by similar techniques. Targeting an unusual breadth of predator guilds, and relying on techniques with a high resolution, it suggests that species in this web are closely connected. Thus, our findings call for similar explorations of link structure across multiple guilds in both arctic and other webs. From an applied perspective, our description of an arctic web suggests new avenues for understanding how arctic food webs are built and function and of how they respond to current climate change. It suggests that to comprehend the community-level consequences of rapid arctic warming, we should turn from analyses of populations, population pairs, and isolated predator–prey interactions to considering the full set of interacting species.
    Ecology and Evolution 08/2015; 5(17):3842-3856. DOI:10.1002/ece3.1647 · 2.32 Impact Factor
    • "Especially plant diversity is supposed to drive species variety of herbivorous insects (Borer et al., 2012; Castagneyrol and Jactel, 2012; Haddad et al., 2001; Novotny et al., 2006; Santos et al., 2014; Siemann et al., 1998). This trend seems to exist in temperate forests contrary to tropical forests rich in tree species where herbivory and host specificity of arboreal and freeliving insects seems to be reduced (Basset, 1992; Jactel and Brockerhoff, 2007; Novotny et al., 2002). Trees do not only provide resources to herbivorous insects that directly feed on them, but they also feed insects, like ants, by the way of sap feeding insect producing honeydew (Blüthgen et al., 2000). "
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    ABSTRACT: Free until May 24 at: Ant communities are generally structured by territoriality, dominance and resource monopolization, but in Mediterranean hot grassland thermal tolerance plays a more important role. The main purposes of the present research were to investigate the hypothesis that in cooler Mediterranean forests resource monopolization structures the generalist ground-nesting ant community while foraging on trees, and to learn if tree heterogeneity plays any role in this structure. In Mediterranean forests in Israel, I visually recorded and trapped ants on the forest floor and those climbing on trees of five species. Ants of 27 species were detected, while the Chao2 index indicated an asymptotic richness estimation of 31 ± 8.1 species (mean ± S.D.). The numerically dominant species were Crematogaster lorteti and Tapinoma simrothi followed by Tapinoma israele and Crematogaster scutellaris. In more than 80% of the cases, specimens of only one ant species climbed at the same time on any individual tree, and no tree was occupied by more than three species. The C-score of climbing ants was statistically higher than simulated indexes when resources were individual trees, indicating that the ants strongly monopolized each tree. No difference was detected between observed and simulated C-scores when resources were tree species. The observed index of Pianka's niche overlap indicated no species specific interaction between trees and ants. In conclusion, this study confirms that ant mosaic structure may be formed by ground-nesting ants while foraging on trees. Tree species heterogeneity did not have a selective impact on the ants nor a central role in the ant community structure.
    Acta Oecologica 04/2015; 65:11-16. DOI:10.1016/j.actao.2015.03.002 · 1.62 Impact Factor
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