The relationship between diet breadth and geographic range size in the butterfly subfamily Nymphalinae--a study of global scale

The "oscillation hypothesis" has been proposed as a general explanation for the exceptional diversification of herbivorous insect species. The hypothesis states that speciation rates are elevated through repeated correlated changes--oscillations--in degree of host plant specificity and geographic range. The aim of this study is to test one of the predictions from the oscillation hypothesis: a positive correlation between diet breadth (number of host plants used) and geographic range size, using the globally distributed butterfly subfamily Nymphalinae. Data on diet breadth and global geographic range were collected for 182 Nymphalinae butterflies species and the size of the geographic range was measured using a GIS. We tested both diet breadth and geographic range size for phylogenetic signal to see if species are independent of each other with respect to these characters. As this test gave inconclusive results, data was analysed both using cross-species comparisons and taking phylogeny into account using generalised estimating equations as applied in the APE package in R. Irrespective of which method was used, we found a significant positive correlation between diet breadth and geographic range size. These results are consistent for two different measures of diet breadth and removal of outliers. We conclude that the global range sizes of Nymphalinae butterflies are correlated to diet breadth. That is, butterflies that feed on a large number of host plants tend to have larger geographic ranges than do butterflies that feed on fewer plants. These results lend support for an important step in the oscillation hypothesis of plant-driven diversification, in that it can provide the necessary fuel for future population fragmentation and speciation.     

Shifts in developmental diet breadth of Lymantria xylina (Lepidoptera: Lymantriidae)

The moth Lymantria xylina Swinhoe (1903) (Lepidoptera: Lymantriidae) is a major defoliator of hardwood and fruit trees in Taiwan. Although the plants identified as host plants of L. xylina usually refer to plants used as food or as shelter, most of the host plant identifications have not considered the role of these hosts on larval development. This study investigated various instars feeding on different plants to assess the developmental diet breath of L. xylina. Forty-seven plant species, belonging to 25 families were used in feeding trials. Various bioassays, including first instar survival and long-term feeding trials, indicated the most suitable host plants for the different developmental stages. Results of the first instar survival trial indicated that first instars could survive only on 13 of the tested plant species. In addition, first instars could only successfully grow to pupa on seven of these 13 test plants species. To assess the developmental diet breath shifts of this moth, 38 plant species (excluding those nine plant species that the first instars did not feed upon) were fed to third and fifth instars in long-term feeding trials. Survival to pupa was noted on 12 and 13 test plant species for the third and fifth instars, respectively. In short, we found that the larvae performed differently when fed on various host plants and that the host plant range increased with the larval stage. Therefore, it is necessary to adjust the host plant range of this moth and to consider host plant breadth together with the developmental stages of caterpillars.     

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

A prediction arising from several evolutionary diet breadth models is that, in insect herbivores whose adults practise adaptive host plant selection based on larval performance, female adult lifespan should be negatively correlated with larval diet breadth. In one category of models, female adult lifespan drives evolutionary changes in larval diet breadth; in the other category, larval diet breadth drives evolutionary changes in female adult lifespan. Applying the method of independent contrasts to a biologically and phylogenetically diverse array of Lepidoptera, we ask whether larval diet breadth—as measured by the number of larval food plant species reported in the literature—is negatively correlated with female adult lifespan at the interspecific level. We show that these two life history variables are indeed inversely related. Next, we relax the assumption, common to all of the models, that the female adult is the life stage responsible for the distribution of progeny among different host plants. By introducing into our data set three species whose females are incapable of flight (due to either aptery or brachyptery), and whose larvae are the dispersive stage, the negative correlation between female adult lifespan and larval diet breadth is lost, when using the independent contrasts method. We interpret this effect as supporting the models’ common prediction. Ours is the first reported evidence of a lifespan/diet breadth trade-off at the interspecific level among insects, and it confirms the findings of a previous study in which the degree of habitat specialisation among arthropods was inversely related to proxy measures of the degree of search time constraint. In one of our “diet breadth drives changes in lifespan” models, the females’ type of egg maturation strategy (as measured by the ovigeny index) is predicted to be positively correlated with larval diet breadth, and it mediates a female adult lifespan/larval diet breadth trade-off; however, we found no convincing support for such a role.     

The relationship between female body size and egg size in pipefishes

Comparing five species of pipefish, egg size was significantly larger in species with brood pouches (Syngnathus typhle, Syngnathus acus and Syngnathus rostellatus) than in species without brood pouches (Entelurus aequoreus and Nerophis ophidion). Egg size correlated positively with female body size in species with brood pouches, but was similar across female sizes in the species lacking pouches. These results may reflect differences in offspring competition as a consequence of variable offspring relatedness within a brood, due to the mating systems adopted by the different species and the presence or absence of a brood pouch.     

The relationship between body size and population size in bromeliad tank faunas

Relationships between body size and abundance in collections of animals from the tanks of 73 bromeliads belonging to five species were analysed. Unlike data in previously published studies on this relationship, these collections of species are not taxonomically restricted and represent complete communities over the macroscopic range of organisms. There is no overall tendency for there to be a positive or negative relationship between population abundance and body size of morphospecies. We can find no evidence that body size-abundance patterns are triangular in complete communities. However, there is weak evidence that the relationship in the aquatic subsets of those communities may have some underlying triangularity, with medium-sized species having the largest populations.     

The relationship between body size and population abundance in animals

On average, large-bodied species live at lower densities than small-bodied ones. Early studies suggested that population densities might scale so that the energy use of a population is independent of body size. However, recent work shows that, at the scale of local communities, this is rarely true and that the pattern varies among taxonomic or ecological subsets of those communities. Energetic considerations may only be relevant to the densities of more abundant species. In fact, within natural assemblages o f organisms, the underlying relationship is very variable; in subsets of those assemblages, ecological processes such as competition may structure abundance patterns.     

The non-linear relationship between body size and function in parrotfishes

Parrotfishes are a group of herbivores that play an important functional role in structuring benthic communities on coral reefs. Increasingly, these fish are being targeted by fishermen, and resultant declines in biomass and abundance may have severe consequences for the dynamics and regeneration of coral reefs. However, the impact of overfishing extends beyond declining fish stocks. It can also lead to demographic changes within species populations where mean body size is reduced. The effect of reduced mean body size on population dynamics is well described in literature but virtually no information exists on how this may influence important ecological functions. The study investigated how one important function, scraping (i.e., the capacity to remove algae and open up bare substratum for coral larval settlement), by three common species of parrotfishes (Scarus niger, Chlorurus sordidus, and Chlorurus strongylocephalus) on coral reefs at Zanzibar (Tanzania) was influenced by the size of individual fishes. There was a non-linear relationship between body size and scraping function for all species examined, and impact through scraping was also found to increase markedly when fish reached a size of 15–20 cm. Thus, coral reefs which have a high abundance and biomass of parrotfish may nonetheless be functionally impaired if dominated by small-sized individuals. Reductions in mean body size within parrotfish populations could, therefore, have functional impacts on coral reefs that previously have been overlooked.     

Bee foraging ranges and their relationship to body size

Bees are the most important pollinator taxon; therefore, understanding the scale at which they forage has important ecological implications and conservation applications. The foraging ranges for most bee species are unknown. Foraging distance information is critical for understanding the scale at which bee populations respond to the landscape, assessing the role of bee pollinators in affecting plant population structure, planning conservation strategies for plants, and designing bee habitat refugia that maintain pollination function for wild and crop plants. We used data from 96 records of 62 bee species to determine whether body size predicts foraging distance. We regressed maximum and typical foraging distances on body size and found highly significant and explanatory nonlinear relationships. We used a second data set to: (1) compare observed reports of foraging distance to the distances predicted by our regression equations and (2) assess the biases inherent to the different techniques that have been used to assess foraging distance. The equations we present can be used to predict foraging distances for many bee species, based on a simple measurement of body size. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The relationship of tooth size to body size in a population of rhesus monkeys (Macaca mulatta)

Tooth areas correlate significantly with long bone measurements in a skeletal population of rhesus monkeys from Cayo Santiago. Correlations are relatively large for the troop as a whole, as well as for males and females separately. Femur and humerus length measurements show the highest correlations with tooth size.     

Reproductive strategies of primates: The influence of body size and diet on litter size

The frequency of multiple births, life history parameters, body size, and diet characteristics were obtained from the literature for 70 primate species. The general pattern within the primate order is to have single infant litters, yet multiple births regularly occur in a number of species in specific phylogenetic groups. Primates which have large litters tend to be small, have short gestation periods and give birth to small infants, which are weaned quickly, and mature rapidly. Species in which multiple births are common also have short interbirth intervals and in the Callitrichidae have males which exhibit paternal care. In addition, they are commonly insectivorous. Although it is difficult to isolate the effects of diet on litter size, independent of body size, analyses suggest that after the influence of body size is statistically removed, as the proportion of insects in the diet increases, animals have larger litters. We suggest that by adopting a mixed diet of insects and fruit primates may be able to ensure access to a seasonally stable food resource that is not greatly restricted by the presence of toxins. This diet would allow a relatively high metabolism and facilitate large litters.     

The relationship between genome size, development rate, and body size in copepods

Freshwater cyclopoid copepods exhibit at least a fivefold range in somatic genome size and a mechanism, chromatin diminution, which could account for much of this interspecific variation. These attributes suggest that copepods are well suited to studies of genome size evolution. We tested the nucleotypic hypothesis of genome size evolution, which poses that variation in genome size is adaptive due to the bulk effects of both coding and noncoding DNA on cell size and division rates, and their correlates. We found a significant inverse correlation between genome size and developmental (growth) rate in five freshwater cyclopoid species at three temperatures. That is, species with smaller genomes developed faster. Species with smaller genomes had significantly smaller bodies at 22 °C, but not at cooler and warmer temperatures. Species with smaller genomes developed faster at all three temperatures, but had smaller bodies only at 22 °C. We propose a model of life history evolution that adds genome size and cell cycle dynamics to the suite of characters on which selection may act to mold life histories and to influence the distribution of traits among different habitats.     

Connectance and parasite diet breadth in flea-mammal webs

The number of links in webs of species interactions, which lies at the heart of the biodiversity-stability debate, has given rise to controversy during the last 20 yr. Studies exploring these web properties have mainly focused on symmetric webs where each species can potentially feed on any other species; asymmetric webs such as host-parasite webs, where one set of species feed on another set of species, have been overlooked. However, food webs are incomplete without parasites and the study of parasite-host sub-web properties deserves attention. Here, using a large database involving 33 regional interaction webs between mammals and their flea parasites, we found a negative relationship between species richness and host-parasite connectance. We suggest that some phylogenetic constraints on flea diet may explain our observed patterns because we found that parasite diet breadth, measured as host taxonomic diversity, was invariant along our host richness gradient. We found that the slope of the logarithmic relationship between the number of realized links and species richness is lower than slope values reported for food webs. We suggest that connectance may not respond to increasing species richness as rapidly in host-parasite webs as in predator-prey food webs due to stronger coevolutionary requirements.     

Components of male fitness in relation to body size in Epirrita autumnata (Lepidoptera, Geometridae)

Abstract. 1. The effect of body size on different components of male fitness was studied for Epirrita autumnata , a geometrid known for its eruptive population dynamics. Body size is the main determinant of female fecundity in this species.
2. Longevity of males was found to have a weak negative correlation with body size at low temperatures. No significant correlation was found at higher temperatures.
3. We found no correlation between male size and female fecundity or egg size which is consistent with the small size of spermatophores in this species.
4. Small and large males were equally successful when allowed to compete for females in laboratory conditions.
5. In one or two field collections, males found mating were larger than males found singly. Large males also had an advantage in finding of virgin females, offered experimentally. No size-assortative mating was recorded.
6. We conclude that size-dependent mate location ability is the factor accounting for most of the variance in male fitness in E.autumnata. The dependence of fitness on body size may well be equally strong in males and females.     

Ecological correlates of body size in gamasid mites parasitic on small mammals: abundance and niche breadth

We studied ecological correlates of body size (abundance and niche breadth) in gamasid mites parasitic on small mammals in 28 regions of the Palearctic. We predicted that smaller species would be characterized by higher abundance than larger species, all else (e.g. host species) being equal. We also predicted that host specificity of mites would decrease (that is, number of host species they use would increase) with an increase in their body size. We focused on mites collected from host bodies that include a) species that feed solely on host’s blood (obligate exclusive haematophages), b) species that feed on both host’s blood and small arthropods (obligate non‐exclusive haematophages), and c) facultative haematophages. We expected that the relationship between body size and abundance and/or host specificity would be more pronounced in obligate exclusively haematophagous mites than for obligate non‐exclusively and facultative haematophagous mites. Across all mite species across regions, mean abundance correlated negatively with body size. The same was true for obligate haematophagous species, but not for facultative haematophages. When mite communities on the same host in a location were considered, the negative body mass–abundance relationship was found in only 3 of 44 communities. Nevertheless, a meta‐analytic (across host species) estimate of the slope of this relationship appeared to be significantly negative. No significant relationship between mite body size and host specificity was found in the analyses across all mite species as well as in obligate exclusive or obligate non‐exclusive haematophages. However, the number of hosts used by facultative haematophagous mites decreased significantly with an increase in their body size. We explain the relationships between morphological (body size) and ecological (abundance and niche breadth) properties of ectoparasites by their interactions with hosts or physical environment.     

The relationship between ecological segregation and sexual body size dimorphism in large herbivores

Ecological segregation (sexual differences in diet or habitat use) in large herbivores has been intimately linked to sexual body size dimorphism, and may affect both performance and survival of the sexes. However, no one has tested comparatively whether segregation occurs at a higher frequency among more dimorphic species. To test this comparatively, data on sex-specific diet, habitat use and body size of 40 species of large herbivores were extracted from the literature. The frequency of ecological segregation was higher among more dimorphic herbivores; however, this was only significant for browsers. This provides the first evidence that segregation is more common among more dimorphic species. The comparative evidence supported the nutritional-needs hypothesis over the incisor breadth hypothesis, as there was no difference in frequency of segregation between seasons with high and low resource levels, and since segregation was also evident among browsers. Whether the absence of a correlation between ecological segregation and level of sexual body size dimorphism for intermediate feeders and grazers is due to biological differences relative to browsers or to the fact that the monomorphic species included in the analysis were all browsers is discussed. Received: 18 August 1999 / Accepted: 31 January 2000     

Habitat use, diet and body size of Heard Island weevils

Habitat use, diet and body-size variation are examined in weevils from Heard Island, with specific attention being given to the Ectemnorhinus viridis species complex. E. viridis shows marked altitudinal variation in body size and vestiture, but there are no consistent associations between body size and diet, nor are there consistent among-individual differences in conventional taxonomic characters. Thus, the status of E. viridis as a single, variable species is maintained. This species occurs from sea level to 600 m and it feeds on vascular plants and bryophytes. Canonopsis sericeus also feeds on bryophytes and vascular plants and occurs over a narrower altitudinal range. Palirhoeus eatoni is restricted to the surpralittoral zone where it feeds on marine algae and lichens. Bothrometopus brevis and B. gracilipes both feed on cryptogams, with the former species occurring from sea level to 450 m, and the latter from 50 to 550 m above sea level. In all species, males are smaller than females and there is a size cline such that populations from higher elevations are smaller than those at lower altitudes. This cline is the reverse of that found on the Prince Edward Islands which, unlike Heard Island, lie to the north of the Antarctic Polar Frontal Zone. This difference in body-size clines between weevils on the two island groups is ascribed to the shorter growing season on the colder Heard Island. The information presented here supports previous ideas regarding the evolution of the Ectemnorhinus-group of weevils on the South Indian Ocean Province Islands, although it suggests that subsequent tests of these hypotheses would profit from the inclusion of molecular systematic work.