Body Size Distribution Research Articles

Investigating the Dynamics of Elk Population Size and Body Mass in a Seasonal Environment Using a Mechanistic Integral Projection Model.

Environmentally mediated changes in body size often underlie population responses to environmental change, yet this is not a universal phenomenon. Understanding when phenotypic change underlies population responses to environmental change is important for obtaining insights and robust predictions of population dynamics in a changing world. We develop a dynamic integral projection model that mechanistically links environmental conditions to demographic rates and phenotypic traits (body size) via changes in resource availability and individual energetics. We apply the model to the northern Yellowstone elk population and explore population responses to changing patterns of seasonality, incorporating the interdependence of growth, demography, and density-dependent processes operating through population feedback on available resources. We found that small changes in body size distributions can have large impacts on population dynamics but need not cause population responses to environmental change. Environmental changes that altered demographic rates directly, via increasing or decreasing resource availability, led to large population impacts in the absence of substantial changes to body size distributions. In contrast, environmentally driven shifts in body size distributions could occur with little consequence for population dynamics when the effect of environmental change on resource availability was small and seasonally restricted and when strong density-dependent processes counteracted expected population responses. These findings highlight that a robust understanding of how associations between body size and demography influence population responses to environmental change will require knowledge of the shape of the relationship between phenotypic distributions and vital rates, the population status with regard to its carrying capacity, and importantly the nature of the environmentally driven change in body size and carrying capacity.

Connectivity, habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia

Abstract Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off‐channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry‐season flows that maintain perenniality and persistence of freshwater fishes. Fish assemblages were surveyed at 55 locations during the dry season over a 2‐year period with the goal of establishing the key landscape‐scale and local‐scale (i.e. habitat) drivers of fish species distribution. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

Recent warming reduces the reproductive advantage of large size and contributes to evolutionary downsizing in nature.

Body size is a key functional trait that is predicted to decline under warming. Warming is known to cause size declines via phenotypic plasticity, but evolutionary responses of body size to warming are poorly understood. To test for warming-induced evolutionary responses of body size and growth rates, we used populations of mosquitofish (Gambusia affinis) recently established (less than 100 years) from a common source across a strong thermal gradient (19–33°C) created by geothermal springs. Each spring is remarkably stable in temperature and is virtually closed to gene flow from other thermal environments. Field surveys show that with increasing site temperature, body size distributions become smaller and the reproductive advantage of larger body size decreases. After common rearing to reveal recently evolved trait differences, warmer-source populations expressed slowed juvenile growth rates and increased reproductive effort at small sizes. These results are consistent with an adaptive basis of the plastic temperature–size rule, and they suggest that temperature itself can drive the evolution of countergradient variation in growth rates. The rapid evolution of reduced juvenile growth rates and greater reproduction at a small size should contribute to substantial body downsizing in populations, with implications for population dynamics and for ecosystems in a warming world.

Transgressing Wallace's Line brings hyperdiverse weevils down to earth

Wallace's Line, located in the heart of the Indo‐Australian archipelago, has historically been hypothesized to strongly inhibit dispersal. Taxa crossing this barrier are confronted with different biota of Asian or Australian origin, respectively, but the extent to which these conditions have affected the evolution of the colonizing lineages remains largely unknown. We examined the potential correlations of body size, lifestyle and biogeographical distribution in the weevil genus Trigonopterus. These beetles are highly diverse both on foliage and in litter east of Wallace's Line but occur exclusively in leaf litter in the west. Based on a comprehensive, dated phylogeny of 303 species, we inferred nine crossing events of Wallace's Line, all from east to west. Five previously foliage‐dwelling lineages changed their lifestyle to leaf litter habitats after crossing this barrier. Our results indicate that dispersal is not more likely in edaphic lineages, but rather that abiotic and/or biotic factors may be responsible for the exclusive leaf litter habitat of Trigonopterus in Sundaland. This includes differences in climate, and the different predatory faunas of Australia‐New Guinea, Wallacea and Sundaland. A mimicry complex in New Guinea with Trigonopterus species as presumable model may be of relevance in this context.

First evidence of a palaeo-nursery area of the great white shark

Shark nurseries are essential habitats for shark survival. Notwithstanding the rich fossil record of the modern great white shark (Carcharodon carcharias, GWS), its use of nursery areas in the fossil record has never been assessed before. Here, we analysed the fossil record of the GWS from three South American Pliocene localities, assessed body size distributions and applied previously established criteria to identify palaeo-nurseries. We found that juveniles dominate the Coquimbo locality (Chile), whereas subadults and adults characterize Pisco (Peru) and Caldera (Chile), respectively. These results, summed to the paleontological and paleoenvironmental record of the region, suggest that Coquimbo represents the first nursery area for the GWS in the fossil record. Our findings demonstrate that one of the top predators in today’s oceans has used nursery areas for millions of years, highlighting their importance as essential habitats for shark survival in deep time.

The scaling of biomass variance across trophic levels in stream species communities: a macroecological approach

Much has been published about different aspects of body-size distribution resting on the assumptions of metabolic scaling, although a number of studies in aquatic ecosystems have questioned its generality. This study considers the effects of individual body-mass and biomass variability on scaling properties of multi-species communities (protists, meio- and macroinvertebrates), and their intrinsic variations in assemblage structure. We examine how size traits within communities are distributed on local and regional scales and assess the potential sources of variation affecting whole ecosystems. Our results, built upon seven river catchment communities including 1204 species, revealed micro-meiofauna-dominated biomass distributions driven by stochastic hydrophysical processes that induce a fractal fluctuation scaling, irrespective of trophic levels, shaping local and regional scaling relations. Fractal-scaling differences are largely generated by the frequency of high flow events that influence the biomass assemblage configurations, which are significantly better represented by the Power Fraction model compared to single statistical random models. We conclude that environmental random variability contributes to the decoupling of total biomass and body mass per site from assemblage size, resulting in scale-invariant body-size traits among assemblages and systems. Generally, these findings emphasize that ignoring small-sized species and, thus, the wide range of body sizes makes accurate ecological model predictions, impossible.

New specimen of Dinodontosaurus (Therapsida, Anomodontia) from west-central Argentina (Chañares Formation) and a reassessment of the Triassic Dinodontosaurus Assemblage Zone of southern South America

The Chañares Formation is known worldwide for its diverse tetrapod assemblage, including representatives of proterochampsid archosauromorphs, early offshoots of the crocodilian lineage, precursors of the dinosaurian lineage, and dicynodont and cynodont therapsids. The dicynodont Dinodontosaurus, originally described nearly 80 years ago, is the most common dicynodont therapsid in the assemblage. Here we present a new specimen of this taxon, focusing on the basicranium structure using 3D modeling and digital segmentation of the individual bones to provide a novel description of this region of the skull. Among the newly-recognized anatomical structures are a rod-like pila antotica in the prootic, the presence of a dorsal conical projection of the parasphenoid, and the anterior extension of the supraoccipital between the prootic and the parietal. The Chañares tetrapod assemblage was historically correlated with the Dinodontosaurus Assemblage Zone of Southern Brazil, originally due to the presence of this large dicynodont, as well as the cynodont Massetognathus, and more recently by absolute dates of the fossil-bearing strata. Both assemblages are similar in diversity and taxonomy, particularly in their non-mammalian therapsids; however their body-size distributions are very different. These differences in body-size are likely not reflecting a taphonomic bias but local variations in climate that promoted more open landscapes in southern Brazil in contrast to western Argentina, where more humid conditions prevailed during the early Late Triassic.

Associations of Nativity, Age at Migration, and Percent of Life in the U.S. with Midlife Body Mass Index and Waist Size in New York City Latinas.

Migration to the U.S. has been associated with increased body size and obesity risk in Latinas, but results for Caribbean immigrant women are limited and inconclusive. Emerging evidence also suggests that early-life environment associations with women’s midlife body mass index (BMI) may be different for larger and smaller women, but this has not been tested within migration life-course history. We examined the associations of nativity and migration timing with midlife body size in a sample of majority Caribbean Latinas and whether these associations varied across the body size distribution. We used interview data from 787 self-identified Latinas (ages 40–65 years) and assessed overall obesity using BMI (kg/m2) and central obesity based on waist circumference (WC, cm). We used linear and quantile regression to examine the association of migration history with BMI and WC and logistic regression for the probability of obesity. Foreign birthplace, later migration age, and lower percent of life in the U.S. were associated with lower BMI and WC means and lower odds of overall and central obesity. Quantile regression showed only inverse associations in the upper quantiles of BMI and WC. For example, relative to U.S.-born women, women living <50% of their lives in the U.S. had lower BMI in the 75th BMI percentile (β = −4.10, 95% CI: −6.75, −0.81), with minimal differences in the 25th (β = 0.04, 95% CI: −1.01, 0.96) and 50th BMI percentiles (β = −1.54, 95% CI: −2.90, 0.30). Our results support that migration to and increasing time in the U.S. are associated with greater body size in midlife Latina women, with stronger influences at higher body size distribution.

Patterns of fish use in urban estuaries: Engineering maintenance schedules to protect broader seascape habitat

Estuaries are experiencing high rates of modification because of urban development and on-going associated maintenance works which impacts their ecosystem functions and services. This research appraises the fish and crustacean community occupying urbanised estuaries, and whether necessary maintenance works (dredging, mangrove pruning) could be timed to better protect the ecosystem values. Using a range of sampling equipment we collected fish and crustacean assemblages from urban, semi-urban, and non-urban estuaries, in addition to water quality, tidal inundation, and marine plant densities to determine relationships among sites. Seasonal differences in body size distributions of socio-economically important species were also examined to infer timing of juvenile recruitment. Despite common assumptions that urbanised estuaries are degraded and provide little habitat value for coastal species, we found that the species composition of aquatic assemblages was similar between urban and non-urban sites, but differed according to tidal position (i.e. supralittoral vs. lower tidal). Seasonality in body size distributions differed among socio-economically important fisheries species, with some species showing juvenile recruitment during the wet season, dry season, or throughout the year. This study demonstrates that, regardless of urban vs. non-urban context, estuaries provide habitat for many aquatic animals, including socio-economically important fish species. Complexity associated with the dynamism of estuarine ecosystems and variability in constituent species’ life-history patterns makes management decisions regarding timing and delivery of urban waterway maintenance difficult. However, maintenance works that occur during Austral dry season (May to October) would provide the best protection for marine plants (non-flowering season for mangroves), while also reduces downstream movement of sediments and contaminants during wet season rainfall flow. Undertaking necessary maintenance works in the dry season provides grounds for wide scale seascape ecosystem optimism.

Advanced Cancer Imaging Applied in the Comparative Setting.

The potential for companion (pet) species with spontaneously arising tumors to act as surrogates for preclinical development of advanced cancer imaging technologies has become more apparent in the last decade. The utility of the companion model specifically centers around issues related to body size (including spatial target/normal anatomic characteristics), physical size and spatial distribution of metastasis, tumor heterogeneity, the presence of an intact syngeneic immune system and a syngeneic tumor microenvironment shaped by the natural evolution of the cancer. Companion species size allows the use of similar equipment, hardware setup, software, and scan protocols which provide the opportunity for standardization and harmonization of imaging operating procedures and quality assurance across imaging protocols, imaging hardware, and the imaged species. Murine models generally do not replicate the size and spatial distribution of human metastatic cancer and these factors strongly influence image resolution and dosimetry. The following review will discuss several aspects of comparative cancer imaging in more detail while providing several illustrative examples of investigational approaches performed or currently under exploration at our institutions. Topics addressed include a discussion on interested consortia; image quality assurance and harmonization; image-based biomarker development and validation; contrast agent and radionuclide tracer development; advanced imaging to assess and predict response to cytotoxic and immunomodulatory anticancer agents; imaging of the tumor microenvironment; development of novel theranostic approaches; cell trafficking assessment via non-invasive imaging; and intraoperative imaging to inform surgical oncology decision making. Taken in totality, these comparative opportunities predict that safety, diagnostic and efficacy data generated in companion species with naturally developing and progressing cancers would better recapitulate the human cancer condition than that of artificial models in small rodent systems and ultimately accelerate the integration of novel imaging technologies into clinical practice. It is our hope that the examples presented should serve to provide those involved in cancer investigations who are unfamiliar with available comparative methodologies an understanding of the potential utility of this approach.

Body size, sampling completeness, and extinction risk in the marine fossil record

AbstractLarger body size has long been assumed to correlate with greater risk of extinction, helping to shape body-size distributions across the tree of life, but a lack of comprehensive size data for fossil taxa has left this hypothesis untested for most higher taxa across the vast majority of evolutionary time. Here we assess the relationship between body size and extinction using a data set comprising the body sizes, stratigraphic ranges, and occurrence patterns of 9408 genera of fossil marine animals spanning eight Linnaean classes across the past 485 Myr. We find that preferential extinction of smaller-bodied genera within classes is substantially more common than expected due to chance and that there is little evidence for preferential extinction of larger-bodied genera. Using a capture–mark–recapture analysis, we find that this size bias of extinction persists even after accounting for a pervasive bias against the sampling of smaller-bodied genera within classes. The size bias in extinction also persists after including geographic range as an additional predictor of extinction, indicating that correlation between body size and geographic range does not provide a simple explanation for the association between size and extinction. Regardless of the underlying causes, the preferential extinction of smaller-bodied genera across many higher taxa and most of geologic time indicates that the selective loss of large-bodied animals is the exception, rather than the rule, in the evolution of marine animals.

Ecophysiological and life-history adaptations of Gammarus balcanicus (Schäferna, 1922) in a sinking-cave stream from Western Carpathians (Romania)

Freshwater gammarids are known to colonise occasionally sinking-cave streams, providing contrasting morphological, life-history and ecophysiological adaptations compared to their surface conspecifics. In this study, a subterranean and a surface population of the species Gammarus balcanicus was surveyed for one year in a sinking-cave stream from the Western Carpathians (Romania). The results showed that the cave-dwelling population comprised individuals that were significantly larger compared to their surface conspecifics, had larger body-size at sexual maturity and that the females produced fewer, but larger eggs, compared to the population situated outside the cave. The trophic position and the omnivory were significantly higher for the cave-dwelling compared to surface population and the elemental imbalance for C:P molar ratios lower, but similar for C:N. However, the subterranean population did not present troglomorphic characters or longer lifespan as known for other cave-surface paired crustaceans. This, together with the rather extensive hydrological connection of the habitats, suggests active gene-flow between populations and similar response to seasonality for body-size distributions, indicating that the observed ecophysiological and life-history differences are rather the consequence of phenotypic plasticity than the result of genetic adaptation.

Physiological constraints on body size distributions in Crocodyliformes.

At least 26 species of crocodylian populate the globe today, but this richness represents a minute fraction of the diversity and disparity of Crocodyliformes. Fossil forms are far more varied, spanning from erect, fully terrestrial species to flippered, fully marine species. To quantify the influence of a marine habitat on the directionality, rate, and variance of evolution of body size in Crocodyliformes and thereby identify underlying selective pressures, we compiled a database of body sizes for 264 fossil and modern species of crocodyliform covering terrestrial, semi-aquatic, and marine habitats. We find increases in body size coupled with increases in strength of selection and decreases in variance following invasions of marine habitats but not of semiaquatic habitats. A model combining constraints from thermoregulation and lung capacity provides a physiological explanation for the larger minimum and average sizes of marine species. It appears that constraints on maximum size are shared across Crocodyliformes, perhaps through factors such as the allometric scaling of feeding rate versus basal metabolism with body size. These findings suggest that broad-scale patterns of body size evolution and the shapes of body size distributions within higher taxa are often determined more by physiological constraints than by ecological interactions or environmental fluctuations.

Effects of gas pressurization on the interpretation of NMR hydrocarbon measurements in organic rich shales

The estimation of total hydrocarbons (HCs) in place is one of the most important economic challenges in unconventional resource plays. Nuclear magnetic resonance (NMR) has proven to be a valuable tool in directly quantifying both hydrocarbons and brines in the laboratory and the field. Some major applications of NMR interpretation include pore body size distributions, wettability, fluid types, and fluid properties. However, for tight formations, the effects of the factors on NMR relaxation data are intertwined. One purpose of this study is to review the interpretation of NMR response of HCs in a tight rock matrix through illustrated examples. When comparing NMR data between downhole wireline and laboratory measurement, three important elements need to be considered: 1) temperature differences, 2) system response differences, and 3) pressure (mainly due to the lost gasses.) The effect of temperature on HCs would be presented with experimental results for bulk fluids. Whereas, the effect of pressure is investigated by injecting gas back into rock matrix saturated with original fluids. The experiments were performed within an NMR transparent Daedalus ZrO2 pressure cell, which operates at pressures up to 10,000 psi. The results show that, at ambient temperature and pressure, NMR responds to a fraction of HCs, which is volatile enough to be observed as an NMR relaxation sequence. The invisible fraction of HCs to NMR sequence at ambient condition can be up to 20% of the total extractable HCs. Molecular relaxation is impacted by fluid viscosity, pore size, and surface affinity. In other words, the fluid with higher viscosity (either due to temperature or gas loss), presenting in smaller pore, or highly affected by the pore surface, will relax faster, and would be partially invisible to NMR, especially in the field. This is critical to the interpretation of NMR response for liquid rich source rocks, in which all of the above molecular relaxing restrictions can be found. Thus, engineers can underestimate movable HCs by using routine core analysis data.

Twenty-eight years of decline: Nesting population demographics and trajectory of the north-east Queensland endangered hawksbill turtle (Eretmochelys imbricata)

Globally, hawksbill turtles (Eretmochelys imbricata) are listed as Critically Endangered, the cause of which is largely attributed to excessive historical take by the tortoiseshell industry. Yet few long-term data analyses describing population trend or survivorship exist. Here we analyse a long-term dataset for a globally significant western Pacific E. imbricata nesting population on Milman Island, northern Great Barrier Reef. Three demographic indicators were used: (1) number of egg clutches laid, (2) nester abundance and survival, and (3) the body-size distribution of nesters (curved carapace length, CCL). Models were developed for a time series from the 1990–91 to 2016–17 nesting season that included 21 years of sampling, with predicted trends evaluated against samples from the 2017–18 nesting season. The number of clutches laid and nester abundance rate of decline varied over the study period, but the decline was markedly similar with a 58 and 57% overall reduction, respectively. Annual survival rate was high (0.972, 95% CI = 0.965 to 0.977), but was not estimated separately for all years. Models predicted that the current rate of decline would lead to nesting extirpation by 2036 (95% CI: 2026–2058) and 2032–2037 (95% CI: from 2020 to increasing), for the models of nester abundance and number of eggs laid, respectively; and aligned with the observed values for the test dataset (2017–18 season).The rate of decline of E. imbricata nesting at Milman Island highlights the urgency to understand and mitigate risks faced by this endangered population and more broadly across the western Pacific.

Evolutionary and ecophenotypic controls on bivalve body size distributions following the end-Permian mass extinction

Abstract Mass extinction events are characterized by major losses in faunal diversity and are associated with several other ecological effects, e.g., reductions in tiering, selective losses of ecological lifestyles, and body size reductions. The latter has received considerable attention and debate, as to whether the reduced size of post-extinction organisms is due to the selective extinction of large species, absence of large species as a stochastic effect of low-diversity faunas (the Gulliver absence effect), a size decrease within surviving genera and species (the Lilliput effect), or a combination of these factors. Here, we investigated both evolutionary and ecophenotypic controls on body size distributions following the end-Permian mass extinction event by investigating size changes in bivalves (Claraia, “Unionites”, and Neoschizodus) from the Werfen Formation (Dolomites, Italy) and the Bodvaszilas Sandstone Formation (Aggtelek Karst, Hungary). Our results show that the Early Triassic shell size increase of bivalve genera was driven by both evolutionary and ecophenotypic responses. First, genera Claraia and “Unionites” show significant increases in body size with the appearance of the new species C. clarai and “U”. canalensis, respectively, suggesting that evolution played a role on Early Triassic bivalve body size dynamics. Further, the same genera record significant within-species increases in average and maximum body size into the late Griesbachian and Dienerian stages (the Brobdingnag effect), indicating that within-species ecophenotypic changes were also involved on observed long-term body size trends. These increases are associated with invigorated ocean circulation, improved oxygenation of the seafloor, and probably increased food supply. We, therefore, hypothesize that both growth-limiting environmental conditions (deoxygenation and reduced primary productivity) and the extinction-induced absence of large species led to small-sized species dominating early Griesbachian benthic invertebrate communities.

Foliar N Application at Anthesis Stimulates Gene Expression of Grain Protein Fractions and Alters Protein Body Distribution in Winter Wheat (Triticum aestivum L.).

The major components of wheat storage proteins are gliadins and glutenins, and as they contribute differently to baking quality, a balanced mixture of these components is essential. The application of foliar nitrogen (N) at anthesis is a common practice to improve protein concentration and composition. The aim of this study was to investigate the effects of a foliar N application at anthesis on storage protein gene expression during grain development and on the distribution of protein concentration and protein body size within the grain. In this experiment, an additional N application at anthesis stimulated the expression of genes of the majority of storage proteins when the N supply was low. Furthermore, it led to higher protein concentrations in the subaleurone layers, while in the center of the lobes, the protein concentrations were decreased. These changes will affect the protein recovery in white flours, as proportionally more protein might be lost during milling processes.

Habitat loss and fragmentation increase realized predator–prey body size ratios

Abstract In the absence of predators, habitat fragmentation favours large body sizes to facilitate gap crossing. The size of primary consumers is, however, also shaped by top‐down effects as predators select prey of a certain size. Therefore, higher trophic levels should be taken into consideration when studying the effect of habitat loss and fragmentation on size distributions of herbivores. We built a model to study the effect of habitat loss and fragmentation within a tri‐trophic food chain. Body size is directly linked to movement capacity and metabolic processes and considered as a master trait under selection. We show that basal resources accumulate locally if a predator causes top‐down control of the herbivore. Due to this increasing spatiotemporal variability in resource availability, larger herbivores are selected than in scenarios without predator as they are able to move further. As predators cause herbivores to be intrinsically much larger than the optimal sizes selected by habitat fragmentation in the absence of predators, habitat fragmentation is no longer a significant driver of herbivore size. However, there is selection for increased predator size with habitat fragmentation as herbivores become less abundant, hence favouring gap‐crossing ability of the predator. Since herbivore and predator body size respond differently to habitat loss and fragmentation, realized predator–herbivore body size ratios increase along this fragmentation gradient. Our model demonstrates how feedbacks between the abundance, body size and mobility of predators and prey ultimately determine body size distributions in food webs. These new insights shed light on the impact of habitat destruction and fragmentation on overall food web structure. A free Plain Language Summary can be found within the Supporting Information of this article.

Influence of phylogenetic structure and climate gradients on geographical variation in the morphology of Mexican flycatcher forests assemblages (Aves: Tyrannidae).

Morphological variation is strongly related to variation in the ecological characteristics and evolutionary history of each taxon. To explore how geographical variation in morphology is related to different climatic gradients and phylogenetic structure, we analyzed the variation of morphological traits (body size, bill, and wing) of 64 species of tyrant flycatchers (Tyrannidae) distributed in Mexico. We measured these morphological traits in specimens from biological collections and related them to the climatic and topographic data of each collection locality. We performed the analyses separately at two levels: (1) the regional level and (2) the assemblage level, which was split into (assemblage I) lowland forests and (assemblage II) highland forests and other vegetation types. We also calculated the phylogenetic structure of flycatchers of each locality in order to explore the influence of climatic variables and the phylogenetic structure on the morphological variation of tyrant flycatchers, by means of linear mixed-effects models. We mapped the spatial variation of the relationship between morphological traits and environmental gradients, taking into account the phylogenetic structure. Important climatic variables explaining the morphological variation were those of temperature ranges (seasonality) and the results suggest that the phylogenetic clustering increases towards the highlands of Sierra Madre Oriental and Sierra Madre del Sur, and the lowlands of Balsas Depression. For the regional level, the spatial distribution of body size showed a pattern coincident with Bergmann’s rule, with increasing in size from south to north. In the tropical lowland forests assemblage, body size tend to increase in seasonally dry forests (western Mexico) and decrease in the humid ones (eastern Mexico). In the assemblage of highland forests and other types of vegetation, morphological trait values increased northeast to southwest. Phylogenetic structure helped to explain the variation of morphology at the assemblage level but not at the regional level. The patterns of trait variation in the lowland and highland assemblages suggest that parts of morphological variation are explained both by the climatic gradients and by the lineage relatedness of communities. Overall, our results suggest that morphological variation is best explained by a varied set of variables, and that regression models representing this variation, as well as integrating phylogenetic patterns at different community levels, provide a new understanding of the mechanisms underlying the links among biodiversity, its geographical setting, and environmental change.

A global analysis of cladoceran body size and its variation linking to habitat, distribution and taxonomy

AbstractBody size is a functional trait that influences the overall biology and ecology of an organism. Studying the shape of size–frequency distributions and size variability within different scales, approximates the influence of large-scale ecological and evolutionary processes on a species. In this study we examine the patterns of distribution and variability of body size among freshwater Cladocera across different taxonomic levels, geographic distribution and habitat association. Using extensive literature data, we show the global distribution of body size in freshwater Cladocera. Hierarchical models were used to assess the effect of different categorical variables on size variability. Our results show that almost all size–frequency distributions were skewed right in all categories. The hierarchical model showed that taxonomic affiliation contributes the most to size variability in our dataset, suggesting that size might be a conserved trait. Large genera (≥1mm) have larger estimated variability compared to smaller genera. In general, our observations on size–frequency distributions and size variability show a brief insight in the varying advantages of adaptive body size in this group of organisms in both biology (physiology) and ecology (competition and co-existence). Thus, body size is a trait important to the survival and continuing evolution of Cladocera.