Field sampling is biased against small-ranged species of high conservation value: a case study on the sphingid moths of East Africa

The range size of species co-occurring in local assemblages is a pivotal variable in assessments of a site’s conservation value. Assemblages featuring many small-ranged species are given more priority than assemblages consisting mainly of wide-ranging species. However, the assembly of relevant information can be challenging and local range size distributions of tropical invertebrates are rarely available for conservation planning. We present such data for sphingid moths in East Africa, a highly diverse region of high conservation value. We compare geographic range size distributions based on field samples with predictions from modelled range map data. Using this system as a case study, we provide evidence for a systematic sampling bias when inferring average local range sizes from field data. Unseen species (i.e., species present but missed in local sampling) are often those with small ranges (hence, of high conservation value). Using an elevational gradient, we illustrate how this bias can lead to false, counterintuitive assessments of environmental effects on local range size distributions. Furthermore, with particular reference to sphingid moths in the study region, we show that current protected areas appear unrelated to the spatial distribution of species richness or average geographic range sizes at a local scale. We discuss the need to treat field sampled data with caution and in concert with other data sources such as probabilistic models.     

Evolution, Ecology, and Multimodal Distributions of Body Size

The sizes of organisms are determined by their interactions with their environment and related ecological and evolutionary processes. Recent studies of body size distributions across communities show evidence for multimodality. The multiple modes were originally explained as a consequence of textural discontinuities in habitat structure. Because communities consist of species that are drawn from lineages, body size patterns within lineages will affect those that are expressed in communities. We used a cellular automation model to argue that multimodality in body sizes within lineages can arise from a few fundamental evolutionary mechanisms alone. We tested the hypothesis using body size data for 138 fish genera and found strong support for the idea that evolution structures body size distributions. The results suggest, first, that we should expect the distribution of body sizes within lineages to be multimodal and second, that a coherent theory of community body size distributions will need to combine both evolutionary and ecological perspectives. Received 28 January 2002; accepted 21 March 2002     

Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny,Functional Biogeography,and Environmental Gradients

To compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current‐day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and re‐colonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re‐expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).     

Range size heritability in Carnivora is driven by geographic constraints

Range size heritability refers to an intriguing pattern where closely related species occupy geographic ranges of similar extent. Its existence may indicate selection on traits emergent only at the species level, with interesting consequences for evolutionary processes. We explore whether range size heritability may be attributable to the fact that range size is largely driven by the size of geographic domains (i.e., continents, biomes, areas given by species' climatic tolerance) that tend to be similar in phylogenetically related species. Using a well-resolved phylogeny of Carnivora, we show that range sizes are indeed constrained by geographic domains and that the phylogenetic signal in range sizes diminishes if the domain sizes are accounted for. Moreover, more detailed delimitation of species' geographic domain leads to a weaker signal in range size heritability, indicating the importance of definition of the null model against which the pattern is tested. Our findings do not reject the hypothesis of range size heritability but rather unravel its underlying mechanisms. Additional analyses imply that evolutionary conservatism in niche breadth delimits the species' geographic domain, which in turn shapes the species' range size. Range size heritability patterns thus emerge as a consequence of this interplay between evolutionary and geographic constraints.     

Stream noise,habitat filtering,and the phenotypic and phylogenetic structure of Neotropical anuran assemblages

The structure of assemblages may be determined by interspecific interactions or environmental factors (e.g. competition and habitat filtering). Since communication between conspecific and heterospecific affects fitness of individuals, habitat characteristics that prevent communication could determine habitat use and co-occurrence of species. However, at present there are few studies, most with birds, testing the relationship between sensory ecology and community ecology. Abiotic noise on streams could impede the detection and decoding of auditory signals by receivers through a process named auditory masking. Therefore, we tested the role of abiotic noise on streams as a habitat characteristic influencing the phenotypic and phylogenetic structure of Neotropical anuran assemblages. We tested this hypothesis using data of male body size, call frequency, calling place (alongside and away from streams), and phylogenetic relationship of 110 and 38 anuran species at regional and local scale, respectively. After we found quantitative evidence suggesting that call frequency and body size are conserved phenotypic traits, we found that assemblages alongside streams exhibit both phenotypic and phylogenetic clustering, while assemblages away from streams exhibit both phenotypic and phylogenetic overdispersion. These results offer quantitative evidence suggesting a role of noise on streams promoting a process of habitat filtering and affecting the structure of anuran assemblages alongside streams both at Neotropical and local scale. This is the first study using modern phylogenetic comparative metrics for covering potential causes of phenotypic and phylogenetic structure of anuran assemblages, and one of the few testing a link between community ecology and the evolutionary biology of acoustic communication to understand the processes mediating species co-occurrence in vertebrates.     

The classification, evolution and biology of the Costa Rican species of Cryptophion (Hymenoptera: Ichneumonidae)

The six known Costa Rican species of the campoplegine ichneumonid genus Cryptophion Viereck are described and keyed. The distribution of species throughout Costa Rica is detailed based on data gathered by an intensive Malaise trap survey of the ichneumonids of the country. Five new species are recognized: C. espinozai. C. guillermoi, C. manueli. C. moragai and C. tickelli , and a sixth, C. inaequalipes (Cresson) redescribed. The monophyly of the genus is demonstrated and the phylogeny of the Costa Rican species reconstructed. Host relationships have been established for all species in Costa Rica; they develop as koinobiont endoparasitoids of first to third instar larvae of Sphingidae or Saturniidae. Analysis of the host relationships from a phylogenetic perspective suggested that the genus first evolved using macroglossine sphingid larvae feeding on rubiaceous understorey plants as hosts, and subsequently diversified to utilize sphingine sphingids and ceratocampine saturniids feeding on a variety of food-plants. Most species appear to be monophagous and oligophagy is apparently a derived feature of one sister-species pair, C. espinozai and C. manueli . In Santa Rosa National Park, Costa Rica, only a small proportion of the species of Saturniidae and Sphingidae present are used as hosts by Cryptophion species. No one host species is parasitized by more than one Cryptophion species. No species of Cryptophion is known to parasitize more than one host species feeding on any one plant species. The monophagous species C. inaequalipes is only known to develop in its sphingid host when that host is feeding on one of its two alternative food-plants.     

The geography of body size – challenges of the interspecific approach

Recent compilations of large-scale data bases on the geographical distributions and body sizes of animals, coupled with developments in spatial statistics, have led to renewed interest in the geographical distribution of animal body sizes and the interspecific version of Bergmann's rule. Standard practice seems to be an examination of mean body sizes within higher taxa on gridded maps, with little regard to species richness or phylogeny. However, because the frequency distribution of body sizes is typically highly skewed, average size within grid cells may differ significantly between species-rich and species-poor cells even when the median and modal sizes remain constant. Species richness influences body size patterns because species are not added to communities at random in relation to their size: areas of low diversity are characterized by a higher range of body sizes than is expected by chance. Finally, a consideration of phylogenetic structure within taxa is necessary to elucidate whether patterns in the geography of size result from turnover between or within intermediate taxonomic levels. We suggest that the highest and lowest quantiles of body size distribution be mapped in order to expose possible physiological or ecological limitations on body size.     

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.     

Primary productivity can affect mammalian body size frequency distributions

Frequency distributions of mammal body sizes in large‐scale assemblages have often been found to show a positive skew. In an attempt to explain this pattern, a model has been put forward which incorporates energetic constraints on fitness and thereby predicts optimal body sizes corresponding to the mode of the distribution. A key assumption of the model is that energy is unlimited. However, if energy is limited, the input of energy into a herbivorous mammal community should influence the shape of the frequency distribution. Thus, I propose that increases in primary productivity will decrease the variation of body size and increase the mean body size in a distribution. So, in low‐productivity environments we should see a predominance of small‐sized species, but with a great variation of body sizes due to limitations of resources (energy). I tested this hypothesis using the herbivorous mammal fauna (rodents, bats and marsupials) in seven biomes of Australia. Because herbivorous marsupials generally are fairly large‐bodied while rodents and bats are small‐sized and because marsupials also have a different mode of reproduction from placental mammals, the hypothesis was also tested on placental mammals and marsupials separately. There was no clear mode for the entire assemblage in any biome, but as primary productivity increased, the variation of body masses decreased and the mean body mass of the distribution increased. Body mass distributions of both placental mammals and marsupials displayed clear modes. Placental mammals also showed an increase in mean body mass. The variation in body mass of marsupials was highest for the intermediately productive biomes. Primary productivity does seem to have some effect on mammalian body mass in this case, but the results here need to be complemented with studies of other assemblages before any general conclusions can be drawn. It is also important to distinguish which taxa are affected in a heterogeneous assemblage like the Australian herbivorous mammal fauna.     

Interactions between hawkmoths and flowering plants in East Africa: polyphagy and evolutionary specialization in an ecological context

Hawkmoths (Lepidoptera, Sphingidae) are considered important pollinators in tropical regions, but the frequency and degree of reciprocal specialization of interactions between hawkmoths and flowers remain poorly understood. Detailed observations at two sites in Kenya over a two‐year period indicate that adult hawkmoths are routinely polyphagous and opportunistic, regardless of their proboscis length. About 700 individuals of 13 hawkmoth species were observed visiting a wide range of plant species at the study sites, including 25 taxa that appear to be specifically adapted for pollination by hawkmoths. We estimate that 277 plant species in Kenya (c. 4.61% of the total angiosperm flora) are adapted for pollination by hawkmoths. Floral tube lengths of these plants have a bimodal distribution, reflecting the existence of two hawkmoth guilds differing in tongue length. Hawkmoths exhibited strongly crepuscular foraging patterns with activity confined to a 20‐min period at dusk and, in some cases, a similar period just before dawn. Corolla tube length appears to act as a mechanical filter as the longest‐tubed plants were visited by the fewest hawkmoth species and these were exclusively from the long‐tongued guild. Tube length showed a strong positive relationship with nectar volume, even after phylogenetic correction, which implies that plants with long corolla tubes are under selection to offer relatively large amounts of nectar to entice visits by polyphagous long‐tongued hawkmoths. Our study shows that diffusely co‐evolved pollination systems involving long‐tongued hawkmoths are clearly asymmetrical, with plants exhibiting a high degree of floral specialization, while hawkmoths exhibit polyphagous behaviour. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 199–213.     

Latitudinal variation in the shape of the species body size distribution: an analysis using freshwater fishes

Many taxonomic and ecological assemblages of species exhibit a right-skewed body size-frequency distribution when characterized at a regional scale. Although this distribution has been frequently described, factors influencing geographic variation in the distribution are not well understood, nor are mechanisms responsible for distribution shape. In this study, variation in the species body size-frequency distributions of 344 regional communities of North American freshwater fishes is examined in relation to latitude, species richness, and taxonomic composition. Although the distribution of all species of North American fishes is right-skewed, a negative correlation exists between latitude and regional community size distribution skewness, with size distributions becoming left-skewed at high latitudes. This relationship is not an artifact of the confounding relationship between latitude and species richness in North American fishes. The negative correlation between latitude and regional community size distribution skewness is partially due to the geographic distribution of families of fishes and apparently enhanced by a nonrandom geographic distribution of species within families. These results are discussed in the context of previous explanations of factors responsible for the generation of species size-frequency distributions related to the fractal nature of the environment, energetics, and evolutionary patterns of body size in North American fishes.     

Cross-scale Habitat Structure Drives Fish Body Size Distributions on Coral Reefs

Despite a large number of studies focusing on the complexity of coral reef habitats and the characteristics of associated fish assemblages, the relationship between reef structure and fish assemblages remains unclear. The textural discontinuity hypothesis, which proposes that multi-modal body size distributions of organisms are driven by discontinuous habitat structure, provides a theoretical basis that may explain the influence of habitat availability on associated organisms. In this study we use fractal techniques to characterize patterns of cross-scale habitat complexity, and examine how this relates to body-depth abundance distributions of associated fish assemblages over corresponding spatial scales. Our study demonstrates that: (1) Reefs formed from different underlying substrata exhibit distinct patterns of cross-scale habitat complexity; (2) The availability of potential refuges at different scales correlates with patterns in fish body depth distributions, but habitat structure is more strongly related to the relative abundance of fish in the body depth modes, rather than to the number of modes; (3) As reefs change from coral- to algal-dominated states, the complexity of the underlying reef substratum may change, presenting a more homogenous environment to associated assemblages; (4) Individual fish body depth distributions may be multi-modal, however, these distributions are not static characteristics of the fish assemblage and may change to uni-modal forms in response to changing habitat condition. In light of predicted anthropogenic changes, there is a clear need to improve our understanding of the scale of ecological relationships to anticipate future changes and vulnerabilities.     

Why do European stoats Mustela erminea not follow Bergmann's rule?

Stoat Mustela erminea body size shows remarkably great variation over the species' European range. The pattern of this variation is opposite to that suggested by Bergmann's rule, i.e., stoats in central Europe are significantly larger than those in southern Sweden which, in turn are considerably larger than their conspecifics in northern Sweden. Neither winter temperature nor the length of snow cover shows any consistent correlation with stoat body size variation, and the larger body size of the southern populations could not be related to a widening of the stoat's feeding niche. A positive correlation was found between the frequency distribution, by size, of available prey and stoat body size in the different areas examined. This supports the hypothesis that body size variation in the stoat, especially females, is an adjustment to regional variations in the sizes of their available prey.     

Determinants of regional species richness: an empirical analysis of the number of hawkmoth species (Lepidoptera: Sphingidae) on the Malesian archipelago

Aims Major patterns and determinants of the species richness of Sphingidae in the Malesian archipelago were investigated, including a distinction of richness patterns between subfamilies and range‐size classes. Location Southeast Asia, Malesia. Methods Using a compilation of specimen‐label data bases, geographic information system (GIS)‐supported estimates of distributional ranges for all Sphingidae species of Southeast Asia were used to assess the species richness of islands. Range maps for all species and checklists for 114 islands can be found at http://www.sphingidae‐sea.biozentrum.uni‐wuerzburg.de . Potential determinants of the species richness of islands were tested with general linear models. Results The estimated species richness of islands in the region is determined by biogeographical association, seasonality, availability of rain forest and island size. Species–area relationships are linear on a semi‐logarithmic representation, but not on a double‐logarithmic scale. Species richness of all sphingid subfamilies is influenced by biogeography. The presence of large rain‐forest areas affects mainly Smerinthinae, whereas distance from continental Asia is conspicuously irrelevant for this group. Widespread rather than geographically restricted species shape the overall distribution patterns of species richness. The altitudinal range of islands does not significantly affect species‐richness patterns, but its potential effects on geographically restricted species are discussed. Main conclusions As well as being affected by climatic and vegetation parameters, sphingid species richness is strongly influenced by a historical, directional dispersal process from continental Southeast Asia to the Pacific islands. This process did not apply equally to species of different taxonomic groups or range sizes. Widespread species decline in species richness towards the south‐east, whereas geographically restricted species exhibit an inverse pattern of species richness, probably because speciation becomes more important in this group within the more isolated island groups.     

Size-specific interaction patterns and size matching in a plant�Cpollinator interaction web

Background and Aims

Many recent studies show that plant–pollinator interaction webs exhibit consistent structural features such as long-tailed distributions of the degree of generalization, nestedness of interactions and asymmetric interaction dependencies. Recognition of these shared features has led to a variety of mechanistic attempts at explanation. Here it is hypothesized that beside size thresholds and species abundances, the frequency distribution of sizes (nectar depths and proboscis lengths) will play a key role in determining observed interaction patterns.

Methods

To test the influence of size distributions, a new network parameter is introduced: the degree of size matching between nectar depth and proboscis length. The observed degree of size matching in a Spanish plant–pollinator web was compared with the expected degree based on joint probability distributions, integrating size thresholds and abundance, and taking the sampling method into account.

Key Results

Nectar depths and proboscis lengths both exhibited right-skewed frequency distributions across species and individuals. Species-based size matching was equally close for plants, independent of nectar depth, but differed significantly for pollinators of dissimilar proboscis length. The observed patterns were predicted well by a model considering size distributions across species. Observed size matching was closer when relative abundances of species were included, especially for flowers with openly accessible nectar and pollinators with long proboscises, but was predicted somewhat less successfully by the model that included abundances.

Conclusions

The results suggest that in addition to size thresholds and species abundances, size distributions are important for understanding interaction patterns in plant–pollinator webs. It is likely that the understanding will be improved further by characterizing for entire communities how nectar production of flowers and energetic requirements of pollinators covary with size, and how sampling methods influence the observed interaction patterns.Key words: Plant–pollinator community, flower morphology, generalization, nectar, pollination network, body size, size matching, specialization     

Reproductive assurance and the evolutionary ecology of self-pollination in Clarkia xantiana (Onagraceae)

The reproductive assurance hypothesis posits that selection favors self-pollination in flowering plants where mates and/or pollinators are scarce. A corollary is that self-pollinating populations are expected to be superior colonizers of mate- and pollinator-scarce environments. The California annual Clarkia xantiana includes outcrossing populations (ssp. xantiana) and autogamously self-pollinating populations (ssp. parviflora). Outcrossing is ancestral, and the subspecies have parapatric distributions with a narrow contact zone. We tested aspects of the reproductive assurance hypothesis by examining geographic and subspecies variation in the densities of mates and pollinators (native bees) and the density dependence of pollinator visitation and pollen receipt. Plant and flower densities, pollinator density, and pollinator visitation rates were lowest in the region of exclusively self-pollinating populations. Pollinator assemblages there lacked Clarkia-associated pollinator taxa that were common elsewhere. Self-pollinating populations in the contact zone generally had densities and visitation rates intermediate between allopatric self-pollinating populations and outcrossing populations. Visitation rate and pollen receipt increased significantly with plant density. These findings suggest that selection for reproductive assurance influenced the origin of self-pollination and/or that reproductive assurance influenced the geographic distribution of self-pollination. Geographic variation in pollinator assemblages may have generated variation in the value of reproductive assurance.     

Network robustness and structure depend on the phenological characteristics of plants and pollinators

Many structural patterns have been found to be important for the stability and robustness of mutualistic plant–pollinator networks. These structural patterns are impacted by a suite of variables, including species traits, species abundances, their spatial configuration, and their phylogenetic history. Here, we consider a specific trait: phenology, or the timing of life history events. We expect that timing and duration of activity of pollinators, or of flowering in plants, could greatly affect the species'' roles within networks in which they are embedded. Using plant–pollinator networks from 33 sites in southern British Columbia, Canada, we asked (a) how phenological species traits, specifically timing of first appearance in the network and duration of activity in a network, were related to species'' roles within a network, and (b) how those traits affected network robustness to phenologically biased species loss. We found that long duration of activity increased connection within modules for both pollinators and plants and among modules for plants. We also found that date of first appearance was positively related to interaction strength asymmetry in plants but negatively related to pollinators. Networks were generally more robust to the loss of pollinators than plants, and robustness increased if the models allow new interactions to form when old ones are lost, constrained by overlapping phenology of plants and pollinators. Robustness declined with the loss of late‐flowering plants, which tended to have higher interaction strength asymmetry. In addition, robustness declined with loss of early‐flying or long‐duration pollinators. These pollinators tended to be among‐module connectors. Our results point to networks being limited by early‐flying pollinators. If plants flower earlier due to climate change, plant fitness may decline as they will depend on early emerging pollinators, unless pollinators also emerge earlier.     

Effects of phylogeny,leaf traits,and the altitudinal distribution of host plants on herbivore assemblages on congeneric Acer species

Historical, niche-based, and stochastic processes have been proposed as the mechanisms that drive community assembly. In plant–herbivore systems, these processes can correspond to phylogeny, leaf traits, and the distribution of host plants, respectively. Although patterns of herbivore assemblages among plant species have been repeatedly examined, the effects of these factors among co-occurring congeneric host plant species have rarely been studied. Our aim was to reveal the process of community assembly for herbivores by investigating the effects of phylogeny, leaf traits, and the altitudinal distribution of closely related host plants of the genus Acer. We sampled leaf functional traits for 30 Acer species in Japan. Using a newly constructed phylogeny, we determined that three of the six measured leaf traits (leaf thickness, C/N ratio, and condensed tannin content) showed a phylogenetic signal. In a field study, we sampled herbivore communities on 14 Acer species within an elevation gradient and examined relationships between herbivore assemblages and host plants. We found that herbivore assemblages were significantly correlated with phylogeny, leaf traits, phylogenetic signals, and the altitudinal distribution of host plants. Our results indicate that the interaction between historical and current ecological processes shapes herbivore community assemblages.     

The interplay between natural and sexual selection in the evolution of sexual size dimorphism in Sceloporus lizards (Squamata: Phrynosomatidae)

Sexual size dimorphism (SSD) evolves because body size is usually related to reproductive success through different pathways in females and males. Female body size is strongly correlated with fecundity, while in males, body size is correlated with mating success. In many lizard species, males are larger than females, whereas in others, females are the larger sex, suggesting that selection on fecundity has been stronger than sexual selection on males. As placental development or egg retention requires more space within the abdominal cavity, it has been suggested that females of viviparous lizards have larger abdomens or body size than their oviparous relatives. Thus, it would be expected that females of viviparous species attain larger sizes than their oviparous relatives, generating more biased patterns of SSD. We test these predictions using lizards of the genus Sceloporus. After controlling for phylogenetic effects, our results confirm a strong relationship between female body size and fecundity, suggesting that selection for higher fecundity has had a main role in the evolution of female body size. However, oviparous and viviparous females exhibit similar sizes and allometric relationships. Even though there is a strong effect of body size on female fecundity, once phylogenetic effects are considered, we find that the slope of male on female body size is significantly larger than one, providing evidence of greater evolutionary divergence of male body size. These results suggest that the relative impact of sexual selection acting on males has been stronger than fecundity selection acting on females within Sceloporus lizards.