Climate tolerance and interspecific variation in geographic range size

The fact that climate influences the continental-scale distributions of species is one of the central tenets of ecology and biogeography. Equally elemental is that species exhibit enormous variation in geographic range size, with most occupying comparatively small areas. The degree to which climate can account for this variation remains unclear. Here, I test three alternative climate-based hypotheses for variation in range size using a large sample of tree and shrub species native to North America north of Mexico. I show that the lowest value of January average daily minimum temperature encompassed by a species' geographic range (T(MIN)), representing the 'climate extremes hypothesis', explains almost 80% of the variation in range size. Hypotheses based on seasonality and climate optima find substantially less support. The relationship between range size and T(MIN) does not change across the breadth of latitudes examined, and is general for conifers and hardwoods, and growth form (tree versus shrub). Differential freezing resistance gains support as the mechanism underlying interspecific variation in range size: using 35 species for which data were available, both T(MIN) and range size are shown to be strongly correlated with measures of freezing resistance.     

Survival dynamics of reef coral larvae with special consideration of larval size and the genus Acropora

Temporal dynamics of larval survival were examined in vitro in four broadcast-spawning reef coral species, Acropora hyacinthus, A. japonica, A. solitaryensis, and Goniastrea pectinata. Larval size was treated as an important characteristic that may relate to larval lifespan. Two patterns were observed in larval survival dynamics between the three Acropora species (mean initial larval size; 0.05-0.08 mm(3)) and G. pectinata (0.02 mm(3)), based on the timing of a sharp drop in larval survival rates (ca. > 50% reduction over a 1-2 week period). Consequently, the majority of larvae of the three Acropora species had a lifespan of less than 2-3 weeks, whereas those of G. pectinata were extended a further 2-3 weeks despite the smaller larval size. No significant relationship was detected between the initial larval size and larval lifespan in any of the four reef coral species. These results suggest that (1) larval dispersal of spawning Acropora species may be on a more local scale than that of G. pectinata and most other reef coral species previously reported, and (2) larval size is not a good estimator of larval lifespan in reef coral species.     

Constant relative age and size at sex change for sequentially hermaphroditic fish

A general problem in evolutionary biology is that quantitative tests of theory usually require a detailed knowledge of the underlying trade-offs, which can be very hard to measure. Consequently, tests of theory are often constrained to be qualitative and not quantitative. A solution to this problem can arise when life histories are viewed in a dimensionless way. Recently, dimensionless theory has been developed to predict the size and age at which individuals should change sex. This theory predicts that the size at sex change/maximum size (L50/L(max)), and the age at sex change/age at first breeding (tau/alpha) should both be invariant. We found support for these two predictions across 52 species of fish. Fish change sex when they are 80% of their maximum body size, and 2.5 times their age at maturity. This invariant result holds despite a 60 and 25 fold difference across species in maximum size and age at sex change. These results suggest that, despite ignoring many biological complexities, relatively simple evolutionary theory is able to explain quantitatively at what point sex change occurs across fish species. Furthermore, our results suggest some very broad generalities in how male fitness varies with size and age across fish species with different mating systems.     

Leaf size modifies support biomass distribution among stems, petioles and mid-ribs in temperate plants

The implications of extensive variation in leaf size for biomass distribution between physiological and support tissues and for overall leaf physiological activity are poorly understood. Here, we tested the hypotheses that increases in leaf size result in enhanced whole-plant support investments, especially in compound-leaved species, and that accumulation of support tissues reduces average leaf nitrogen (N) content per unit dry mass (N(M)), a proxy for photosynthetic capacity. Leaf biomass partitioning among the lamina, mid-rib and petiole, and whole-plant investments in leaf support (within-leaf and stem) were studied in 33 simple-leaved and 11 compound-leaved species. Support investments in mid-ribs and petioles increased with leaf size similarly in simple leaves and leaflets of compound leaves, but the overall support mass fraction within leaves was larger in compound-leaved species as a result of prominent rachises. Within-leaf and within-plant support mass investments were negatively correlated. Therefore, the total plant support fraction was independent of leaf size and lamina dissection. Because of the lower N(M) of support biomass, the difference in N(M) between the entire leaf and the photosynthetic lamina increased with leaf size. We conclude that whole-plant support costs are weakly size-dependent, but accumulation of support structures within the leaf decreases whole-leaf average N(M), potentially reducing the integrated photosynthetic activity of larger leaves.     

Range expansion as a response to increasing group size in the Yunnan snub-nosed monkey

The Yunnan snub-nosed monkey (Rhinopithecus bieti) is characterized by a larger home range and group size than other colobine species. We investigated variations in home range size of a free-ranging group of R. bieti from 1998 to 2007 in the Baimaxueshan National Nature Reserve in Yunnan, China. Group size increased from 160 to 450 over the 10 years. Results also showed a home range shift and yearly home range expansion, although this expansion was very limited. The study group covered a 33.78-km(2) area during the 10-year period, with some areas abandoned and others used repeatedly. The yearly home range increase stopped in 2004 and decreased thereafter. Despite increasing group size usually being coupled with larger yearly home range (>30 km(2)), the group confined itself within a relatively small and stable area (<18 km(2)) during 2005-2007, with a significant portion of their accessible home range discarded. Consequently, the study group showed the highest recorded population density among extant groups of R. bieti. Reasons why the group settled into a substantially smaller home range area remain unclear.     

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.     

Sexual size dimorphism within species increases with body size in insects

Studies examining interspecific differences in sexual size dimorphism (SSD) typically assume that the degree of sexual differences in body size is invariable within species. This work was conducted to assess validity of this assumption. As a result of a systematic literature survey, datasets for 158 insect species were retrieved. Each dataset contained adult or pupal weights of males and females for two or more different subsets, typically originating from different conditions during immature development. For each species, an analysis was conducted to examine dependence of SSD on body size, the latter variable being used as a proxy of environmental quality. A considerable variation in SSD was revealed at the intraspecific level in insects. The results suggest that environmental conditions may strongly affect the degree, though not the direction of SSD within species. In most species, female size appeared to be more sensitive to environmental conditions than male size: with conditions improving, there was a larger relative increase in female than male size. As a consequence, sexual differences in size were shown to increase with increasing body size in species with female-biased SSD (females were the larger sex in more than 80% of the species examined). The results were consistent across different insect orders and ecological subdivisions. Mechanisms leading to intraspecific variation in SSD are discussed. This study underlines the need to consider intraspecific variation in SSD in comparative studies.     

Dominant cold desert plants do not partition warm season precipitation by event size

We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C(4)) and Oryzopsis hymenoides (C(3)), and two shrubs, Ceratoides lanata (C(3)), and Gutierrezia sarothrae (C(3)). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C(3) plants, and a larger effect on the C(4) plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability.     

Life history and environmental variation interact to determine effective population to census size ratio

Successful recovery and sustainability of threatened and exploited species depends in part on retention and maintenance of genetic diversity. Theory indicates that genetic diversity is lost at a rate inversely proportional to the genetically effective population size (N(e)), which is roughly equal to one-half the adult census size (N) in many organisms. However, N(e) has been reported to be up to five orders of magnitude lower than N in species with life histories that result in type III survivorship (high fecundity, but heavy mortality in early life stages, e.g. bony fishes), prompting speculation that low values of N(e) may be a general feature of such organisms despite sometimes vast abundances. Here, we compared N(e) and the ratio N(e)/N across three ecologically similar fish species from the arid southwestern United States, all with type III life histories but with differing expectations of egg and larval survivorship that correlate with the degree of human-imposed habitat fragmentation. Our study indicates that type III life history may be necessary, but this alone is insufficient to account for extraordinarily low values of N(e)/N. Rather, life history interacts with environmentally imposed mortality to determine the rate and magnitude of change in genetic diversity in these desert fish species.     

Body size and sexual size dimorphism in calanoid copepods

Patterns of sexual size dimorphism and body size in calanoid copepods are examined. We hypothesize that favorable conditions for development will result in large body size and high sexual size dimorphism among populations of a given species and that differences in this allometric relationship among species is governed by the male's role in insemination. We confirm that there is a greater advantage to large female size, normally the larger sex, when compared to males, hence leading to selection for developmental patterns favoring high size dimorphism. Individuals from populations of four centropagid copepod species were measured; other sizes were obtained from published sources. In the four species we examined, the relationships between prosome length and both clutch size and the ability to produce multiple clutches with one insemination were determined. Results show a trend toward hyperallometry in all centropagid species examined: sexual size dimorphism increases with increasing size. Large females produce larger clutches and more additional clutches on one insemination. That hyperallometry is not observed in diaptomid copepods may result from the greater role the male plays in reproduction. Males are needed for each clutch produced, hence the selective pressure to be larger is greater than that in the centropagidae.     

Habitat patch size and mating system as determinants of social group size in coral-dwelling fishes

It is thought that the size and dispersion of habitat patches can determine the size and composition of animal social groups, however, this has rarely been tested. The relationship between group size, the mating system, and habitat patch size in six species of coral-dwelling gobies was examined. For all species, there was a positive correlation between coral colony size and social group size, however the strength of this relationship varied among species. Paragobiodon xanthosomus exhibited the strongest relationship and a manipulative field experiment confirmed that coral colony size limited group size in this species. For other species including Paragobiodon melanosomus and Eviota bifasciata, either a highly conservative mating system (P. melanosomus), or increased mobility (E. bifasciata) appeared to disrupt the relationship between habitat patch size and group size. There was no consistent relationship between the mating system exhibited and group size among the species investigated. These results demonstrate that habitat patch size, mobility, and mating systems can interact in complex ways to structure group size even among closely related species.     

Amphipod crustacean size spectra: new insights in the relationship between size and oxygen

Oxygen availability limits the maximum potential size attainable in benthic gammaridean amphipods from the suborder to the generic level, while also influencing size within species. In this paper we investigate the effect of oxygen on 15 size spectra worldwide, established by compiling maximum length data of more than 2000 amphipod species. We used TS95/5 as a proxy for maximum size and defined this as the threshold size between the 95% smallest and the 5% largest species at any given site. Our data show that beside TS95/5, minimum, mean and modal sizes, as well as all 10% increment threshold sizes (from TS10/90 to TS90/10) also vary significantly with oxygen concentration. Size distributions are very similar in shape from one geographical area to another, whatever the width of the spectrum, hence if overall numbers of species stay constant more small species should coexist at low than at high latitudes. No amphipod species were found in water with an oxygen content lower than the minimum requirement predicted (175 mmol O₂ kg⁻¹). Our data also show that minimum adult amphipod size is probably limited by the minimum possible egg size, whereas maximum size is set by the physico-chemic ceiling of oxygen availability.     

Worker size and seed size selection by harvester ants in a neotropical forest

The rules ants follow when selecting seeds are important both to theories of colony organization and to the shaping of their impact as harvesters. Two Costa Rican forests yielded the most diverse harvester ant assemblages yet studied (41 and 44±4 species). I assayed seed size preferences within and between species using milled barley. Seed size selection varied at a number of levels. First, species differed in seed size use: small species mainly carried off small seeds; large species retrieved a broad range of seed sizes. Within species, one-third of those tested yielded inter-colony differences in preferred seed sizes. Finally, workers of polymorphic species tested showed significant worker/seed size correlations. Species, colony, and worker level differences are common among harvester ants. Their significance to community organization and colony ergonomics however is hotly debated and requires a better understanding of the dynamics of food limitation. From the plant's perspective, small seeds will be harvested by a wider variety of ants than large seeds.     

A phylogenetic analysis of egg size,clutch size,spawning mode,adult body size,and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm³, scattered eggs = 0.18 mm³, pelagic eggs = 0.52 mm³) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.     

昆虫体型及性体型二型性的地理变异

体型是昆虫基本的形态特性,它会影响到昆虫几乎所有的生理和生活史特性。同种昆虫不同地理种群在体型上常表现出明显的渐变,导致这些渐变的环境因素包括温度、湿度、光照、寄主植物、种群密度等,并且多种环境因素也会对昆虫种群内个体体型产生影响。雌雄个体的体型存在差异,称性体型二型性。性体型二型性也显示了地理差异。这些差异形成的途径已经得到详细的分析,其形成机制导致多个假说的提出,这些假说又在多种昆虫中得到验证。本文从同一种昆虫不同种群间、同一种群内、雌雄虫个体间3个水平,对种内昆虫体型变异的方式,影响昆虫种群间体型变异和种群内昆虫体型的变异的环境因素,以及昆虫性体型二型性及其地理变异的现象等方面的研究进行了综述,并对未来的相关研究提供了建议。     

Competition and body size in plants: the between-species trade-off for maximum potential versus minimum reproductive threshold size

Aims According to traditional theory, superior competitive ability in plants generally requires relatively large plant body size. Yet even within the most crowded vegetation, most resident species are relatively small; species size distributions are right-skewed at virtually every scale. We examine a potential explanation for this paradox: small species coexist with and outnumber large species because they have greater 'reproductive economy', i.e. they are better equipped—and hence more likely—to produce offspring despite severe size suppression from intense competition.Methods Randomly placed plots within old-field vegetation were surveyed across the growing season. Within each plot, the largest (MAX) and smallest (MIN) reproductive individuals of each resident species were collected for above-ground dry mass measurement. We tested three hypotheses: (i) smaller resident species (with smaller MAX size) have generally smaller reproductive threshold sizes; (ii) smaller resident species have greater 'reproductive economy', i.e. a smaller MIN relative to MAX reproductive plant size; and (iii) MIN size predicts plot occupancy (species abundance within the community) better than MAX size.Important findings The results supported the first and third, but not the second hypothesis. However, we could not reject the hypothesis that smaller species have greater reproductive economy, as it was not possible to record data for the largest potential plant size for each species—since even the largest (MAX) plants collected from our sampled plots were subjected to competition from neighbours under these natural field conditions. Importantly, contrary to conventional competition theory, more successful species (in terms of greater plot occupancy) had smaller minimum not larger (or smaller) maximum reproductive sizes. These results suggest that a small reproductive threshold size, commonly associated with relatively small potential body size, is generally more effective in transmitting genes into future generations when selection from neighbourhood crowding/competition is intense—at least within natural old-field vegetation. Accordingly, we propose a simple conceptual model that represents the basis for a fundamental paradigm shift in the predicted selection effects of crowding/competition on plant body size evolution.     

Ecological correlates of body size and egg size in parasitic Ascothoracida and Rhizocephala (Crustacea)

In order to identify key factors in the evolution of life history traits in Ascothoracida and Rhizocephala (two groups of crustacean parastes of invertebrates), comparative analyses were performed using phylogenetically independent contrasts. Among 59 ascothoracidan species, latitude correlated positively with body size, whereas there was no relationship between water depth and body size. Body size also correlated strongly with egg size; however, once corrected for body size, egg size was not related to either latitude or water depth. Among 91 rhizocephalan species, neither latitude nor water depth correlated with body size. However, host species of larger sizes harboured larger species of rhizocephalan parasites. Egg size of rhizocephalans did not correlate with body size, and was not influenced by either latitude or water depth. The patterns observed in this study show both differences from an similarities to those reported for other groups of crustacean parasites, and suggest that adaptations to similar selective pressures are not always identical among distantly-related taxa.     

Body size, biomic specialization and range size of African large mammals

Aim The goal of this paper is to examine the relationships between body size, biomic specialization and range size in the African large mammals, which are defined as all the African species corresponding to the orders Primates, Carnivora, Proboscidea, Perissodactyla, Hyracoidea, Tubulidentata, Artiodactyla and Pholidota. Location The study used the large mammal assemblage from Africa. Methods The degree of biomic specialization of African large mammals is investigated using the biomic specialization index (BSI) for each mammal species, based on the number of biomes it inhabits. Range size for each species is measured as the latitudinal extent of the geographical distribution of the species. We have analysed our data using both conventional cross‐species analyses and phylogenetically independent contrasts. Results There is a polygonal relationship between species biomic specialization and body size. While small and large species are biomic specialists, medium‐sized species are distributed along the whole range of biomic specialization. The latitudinal extent–body size relationship is approximately triangular. Small‐bodied species may have either large or small ranges, whereas large‐bodied ones have only large ranges. A positive correlation between latitudinal extent and biomic specialization is evident, although their relationship is better described as triangular. Main conclusions We found a polygonal relationship between species biomic specialization and body size, which agrees with previous arguments that small‐bodied species have more limited dispersal and, therefore, they may come to occupy a lesser proportion of their potential inhabitable biomes. On the other hand, large‐bodied species are constrained to inhabit biomes with a high productivity. A polygonal relationship between species latitudinal extent and body size in African large mammals agrees with previous studies of the relationship between range size and body size in other continents. The independent study of the macroecological pattern in biomic specialization highlights different factors that influence the body size–range size relationship. Although body size is usually implicated as a correlate of both specialization and geographical range size in large mammals, much of the variation in these variables cannot be attributed to size differences but to biome specific factors such as productivity, area, history, etc.     

Maternal body size as a morphological constraint on egg size and fecundity in butterflies

It is a widespread notion that in arthropods female reproductive output is strongly affected by female size. In butterflies egg size scales positively with female size across species, suggesting a constraint imposed by maternal size. However, in intraspecific comparisons body size often explains only a minor part of the variation in progeny size. We here include representatives of various butterfly families to test the generality of this phenomenon across butterflies. Phenotypic correlations between egg and maternal body size were inconsistent across species: correlations were non-significant for Pararge aegeria and Lycaena tityrus, significantly positive for Papilio machaon, significantly negative for Araschnia levana, and contradictory for Pieris napi. Thus, there was no general pattern linking egg size to maternal size, e.g., caused by an allometric relationship. Consequently, there was at best limited evidence for maternal size acting as a morphological constraint on egg size within butterfly species. Realized fecundity depended on maternal size in P. napi and A. levana, but not in P. aegeria, suggesting that maternal size may affect egg number more strongly than egg size. Yet, variation in fecundity was primarily explained by variation in longevity as is expected for income breeders. Heritability estimates across species were rather similar for pupal mass (ranging between 0.14 and 0.19), but more variable for egg size (0.17–0.31).     

Sexual size dimorphism in anurans

Several hypotheses have been proposed to explain the direction and extent of sexual size dimorphism in anurans (in which males are usually smaller than females) as a result of sexual selection. Here, we present an analysis to test the hypothesis that sexual dimorphism in anurans is largely a function of differences between the sexes in life-history strategies. Morphological and demographic data for anurans were collected from the literature, and the mean size and age in each sex were calculated for 51 populations, across 30 species and eight genera. Comparisons across 14 Rana species, eight Bufo species and across the genera showed a highly significant relationship between size dimorphism, measured using the female-male size ratio, and mean female-male age difference. A comparison of a subset of 17 of these species for which phylogenetic information was available, using the method of independent contrasts, yielded a similar result. These results indicate that most of the variation in size dimorphism in the anura can be explained in terms of differences in the age structure between the sexes in breeding populations. If sexual selection has an effect on size dimorphism in anurans, it is likely to be only a secondary one.