Variation of butterfly diet breadth in relation to host‐plant predictability: results from two faunas

Abstract

Host‐plant data for North American and Australian butterflies were used to test the hypothesis that larval diet breadth increases with decreasing resource predictability (where the latter was estimated by host‐plant growth‐form/duration). For each region in turn we compared the diet breadths of butterflies which utilise herbaceous host‐plants with those of species having woody hosts. For North America alone we also compared the diet breadths of species having annual hosts with those utilising perennial hosts, and the diets of species having herbaceous‐annual hosts with those using woody‐perennial hosts. Studies of diet breadth may be biased by the host taxonomic level which contributes most to the diet index used. For example, the results of analyses which employ indices based on numbers of families of hosts utilised may differ from those using indices based on counts of host species or genera. To investigate this potential problem we performed cross‐species analyses where diet breadth was defined in turn as the number of host species, genera, or families eaten. We found that using different taxonomic levels did give inconsistent results. To avoid this we employed phylogenetic diet breadth indices in comparative analyses of Independent Contrasts. The former incorporate information from the whole of the host‐plant phylogeny, whilst the comparative method eliminates any confounding effects of butterfly phylogeny. The results indicated that there is a phylogenetic component to butterfly diet breadth. They also largely differed from those of the cross‐species investigations, although there were similarities (i.e. results differed between regions and varied according to whether the whole fauna or just endemics were investigated). Our results suggested that in both regions, non‐endemics which feed on herbaceous plants have wider diet breadths than non‐endemics which utilise woody hosts. However, we found no consistent evidence that the diet breadths of endemics increase with decreasing resource predictability (as estimated here).

Reduced resistance of invasive varieties of the alien tree Sapium sebiferum to a generalist herbivore

“…2) and survived and gained weight by doing so, biochemical barriers to their consumption of Sapium foliage are weak or do not exist. Rather, Sapium may be a suitable food choice that is avoided because there is strong selection against host range expansion when new host plants may be toxic (Chew and Courtney 1991), temporally or spatially uncommon (Chew and Courtney 1991;Beccaloni and Symons 2000) or of limited use due to the influence of herbivore natural enemies (Camara 1997). If the process of host range expansion requires biochemical or nutritional acceptability as a prerequisite to behavioral adaptation, any costs of experimentation in the presence of other acceptable food sources may greatly delay the inclusion of new food items.…”

A trade-off between female lifespan and larval diet breadth at the interspecific level in Lepidoptera

“…In such studies it would be relatively easy to record each plant species' average abundance and also its ''apparency'' (sensu Feeny 1976, e.g. in terms of growth form/ duration (see Beccaloni and Symons 2000). Due to a paucity of data, we were unable to examine the role of plant abundance, but it is vital that future investigators do so, as the abundance of ''presently acceptable'' plants will influence the foraging decisions of herbivores (Levins and MacArthur 1969;Jaeinke 1978;Mayhew 1997).…”

“…more basal clades) among species for which ovigeny index data are available (see Table 1 in Jervis et al (2005a, b). Host plant use also is phylogenetically constrained, at least among butterflies (Beccaloni and Symons 2000;Ehrlich and Raven 1964). We therefore used Harvey and Pagel's (1991) method of independent contrasts, although we supplemented our analysis with traditional cross-species analyses that ignore phylogeny.…”

“…Since the models tested do not make assumptions concerning either plant taxonomy or phylogeny (i.e. female decisions and fitness returns are assumed to be independent of each of these factors), neither plant higher taxonomic grouping (family, genus) nor clade were taken into account in the main analyses (see Beccaloni and Symons (2000) for an investigation in which a plant-based phylogenetic index of diet breadth was used). However, we did undertake supplementary, curiosity-driven analyses in which diet breadth was measured as the number of plant genera exploited as larval food plants.…”

“…A life history approach, in which a correlation is sought between the degree of dietary specialisation and variation in other traits among insect herbivore species, has also been taken (Wasserman and Mitter 1978;Niemelä et al 1981;Gaston and Reavey 1989). Although a proper comparative analysis (sensu Harvey and Pagel 1991) has been used to study larval dietary specialisation (Beccaloni and Symons 2000), herbivore inter-trait correlations have hitherto not been investigated using such an approach in that context. Here, we use the method of independent contrasts to establish whether the degree of larval dietary specialisation among herbivorous Lepidoptera is related to two key life history traits: female adult lifespan and egg maturation strategy.…”