Genetic similarity, breeding distribution range and sexual selection

Large populations with extensive breeding distributions may sustain greater genetic variability, thus producing a positive relationship between genetic variation and population size. Levels of genetic variability may also be affected by sexual selection, which could either reduce levels because a small fraction of males contribute to the following generation, or augment them by generating genetic variability through elevated rates of mutations. We investigated to what extent genetic variability, as estimated from band sharing coefficients for minisatellite markers, could be predicted by breeding distribution range, population size and intensity of sexual selection (as reflected by degree of polygyny and extra-pair paternity). Across a sample of 62 species of birds in the Western Palearctic, we found extensive interspecific variation in band sharing coefficients. High band sharing coefficients (implying low local genetic variability among individuals) were associated with restricted breeding distributions, a conclusion confirmed by analysis of statistically independent linear contrasts. Independently, species with large population sizes had small band sharing coefficients. Furthermore, bird species with a high richness of subspecies for their breeding distribution range had higher band sharing coefficients. Finally, bird species with high levels of polygyny and extra-pair paternity had small band sharing coefficients. These results suggest that breeding distribution range, population size and intensity of sexual selection are important predictors of levels of genetic variability in extant populations.     

Cover distributions of vascular plants in relation to soil chemistry and soil depth in a granite rock ecosystem

The variability in the cover distribution of vascular plants, accounted for by soil chemical properties and soil depth, on a granite slope with shallow autochtonous soil in southeast Sweden was evaluated using multivariate statistical regression and graphical methods. Soil acidity and soil depth were, to an often high degree, able to account for the variability in the distributions of the ca. 30 most frequent species, including Rumex acetosella, Vincetoxicum hirundinaria, Filipendula vulgaris, Satureja acinos, Geranium columbinum, Silene rupestris, and Arenaria serpyllifolia. The best expression of soil acidity was pH-KCl, though exchangeable Ca and Al were also important measures of the soil-plant relationships. The Ca:Al ratio was inferior in this respect. Also exchangeable or acid soluble phosphate was significantly related to the distribution of several species, whereas soil organic matter content was almost unrelated.     

Unimodal Tree Size Distributions Possibly Result from Relatively Strong Conservatism in Intermediate Size Classes

Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes.     

Investigations in commonness and rarity: a comparative analysis of co-occurring, congeneric Mexican trees

Population size distributions were examined for 12 species of trees co-occurring at Chamela Biological Station in Jalisco, Mexico. Species had been selected as congeneric pairs and trios similar in gross morphology and ecology in order better to identify correlates of relative abundance. Rarer species were found unanimously to have more irregular distributions of individuals among size classes than more common species when distributions were compared to a smooth, descending curve constructed from population mean stem diameters (an exponential distribution). Examination among species of patterns of deviation from these corresponding smooth distributions indicates that the most reasonably inferred cause for the observed pattern is consistent differences in degree of fluctuation in recruitment into adult size classes. These results thereby suggest a demographic difference between locally rarer and more common species that may be generally associated with observed differences in relative abundance and indicate a focus for management of rarity in forest trees.     

The impact of global climate change on tropical forest biodiversity in Amazonia

Aim To model long‐term trends in plant species distributions in response to predicted changes in global climate. Location Amazonia. Methods The impacts of expected global climate change on the potential and realized distributions of a representative sample of 69 individual Angiosperm species in Amazonia were simulated from 1990 to 2095. The climate trend followed the HADCM2GSa1 scenario, which assumes an annual 1% increase of atmospheric CO₂ content with effects mitigated by sulphate forcing. Potential distributions of species in one‐degree grid cells were modelled using a suitability index and rectilinear envelope based on bioclimate variables. Realized distributions were additionally limited by spatial contiguity with, and proximity to, known record sites. A size‐structured population model was simulated for each cell in the realized distributions to allow for lags in response to climate change, but dispersal was not included. Results In the resulting simulations, 43% of all species became non‐viable by 2095 because their potential distributions had changed drastically, but there was little change in the realized distributions of most species, owing to delays in population responses. Widely distributed species with high tolerance to environmental variation exhibited the least response to climate change, and species with narrow ranges and short generation times the greatest. Climate changed most in north‐east Amazonia while the best remaining conditions for lowland moist forest species were in western Amazonia. Main conclusions To maintain the greatest resilience of Amazonian biodiversity to climate change as modelled by HADCM2GSa1, highest priority should be given to strengthening and extending protected areas in western Amazonia that encompass lowland and montane forests.     

Patterns in the local assembly of Egyptian rodent faunas: Areography and species combinations

We implicate ecological processes in assembly patterns of Egyptian desert rodents using spatial variation of distribution and composition of local assemblages. We also compare our assemblages to prior analyses of North American and Australian small mammal communities in terms of species richness and representation of trophic groups.We studied patterns of occurrence of 29 rodent species among 335 collecting events in 308 sites using museum specimen records resulting from a country-wide survey. The studied taxa vary greatly in their natural histories and ecology. Fully 69% of studied species (20) were localized in 30 or fewer sites (9% of all sites). Site incidence was closely correlated with the geographic range size of species, while local abundance of a species showed little relationship to its geographic range. The species richness of local assemblages ranged from a lone species at 73 sites to 11 species at 3 sites. A total of 214 different combinations were recorded of which 164 (77%) were unique to a single site. G. gerbillus was both the most abundant and most ubiquitous species. Coexistence with other species was positively correlated with incidence and geographic range size. Body mass distribution was remarkably uniform for the fauna as a whole, and influenced the geographic distributions and abundance of individual species.Our sites have low species richness and substantial variability in species composition, which also characterize desert rodent communities elsewhere. Habitat requirements, exclusive distributions of sibling species, low primary productivity, and Egypt's location all influenced species assembly. The Egyptian and Australian deserts supported higher proportions of low richness assemblages compared to North America. As in North America, Egyptian sites were dominated by granivorous species.     

Canine tooth size variability in primates

I present an analysis of canine tooth size variability in male and female primates. The coefficient of variation (CV = SD X 100/mean) as an index of canine size variability proved to be dependent on mean canine size in males and, to a lower extent, in females. Therefore, variability tends to increase with increasing values of mean canine size. Using residuals from the regression of log SD on log mean canine size in male and female primates, I analysed the contribution of diet, habitat and mating system to canine size variability. Habitat and mating system are known to influence to a certain extent the degree of sexual dimorphism in canine size. Given the well-known relationship between sexual dimorphism and phenotypic variability, it was suggested that these factors might influence variability in canine size. Everything else being equal, males of polygynous species are characterized by more variable canine sizes than males of monogamous species. Habitat and diet did not contribute to the level of variability observed in either males or females. It is proposed that a high level of variability in canine size may be related to the likelihood that enlarged canines evolved as a result of male-male competition for mates in polygynous species.     

Planting densities and bird and rodent absence affect size distributions of four dicots in synthetic tallgrass communities

Variability in the size distributions of populations is usually studied in monocultures or in mixed plantings of two species. Variability of size distributions of populations in more complex communities has been neglected. The effects of seeding density (35 or 350 seeds/species/m²) and presence of small vertebrates on the variability of size distributions were studied for a total of 1,920 individuals of 4 species in replicated synthetic communities of 18 species in northern Illinois. End-of season height and above-ground biomass were measured for prairie perennials Dalea purpurea (purple prairie clover), Echinacea purpurea (purple coneflower), Desmanthus illinoensis (Illinois bundleflower) and Heliopsis helianthoides (early sunflower). Variability in biomass distribution of the four target species was twice as great at low than at high densities when small vertebrates were excluded. Our results suggest that inter- and intraspecific competition may affect all individuals more under high-density conditions, thereby reducing the variability in their biomass distributions within this community. This result, a consequence of plant-plant interaction, is obscured when small birds or mammals are present, presumably because either or both add variance that overwhelms the pattern.     

Latitudinal variation in the competition‐colonisation trade‐off reveals rate‐mediated mechanisms of coexistence

Theories of species coexistence often describe a trade‐off between colonising and competitive abilities. In sessile marine invertebrates, this trade‐off can manifest as trends in species distributions relative to the size of isolated patches of substrate. Based on their abilities to find available substrate and competitively exclude neighbours, good colonisers tend to dominate smaller patches, whereas better competitors tend to monopolise larger patches. In theory, species with equivalent colonising and competitive abilities should display similar distributions across patch sizes. We used patch size to observe this manifestation of the competition‐colonisation trade‐off over 20° of latitude. The trade‐off was more readily observed at lower latitudes and was proportional to the ‘ecological age’ of communities (i.e. the degree of resource acquisition and likelihood of species interactions). Results suggest that ecological age may mediate the prominence of stochastic or deterministic coexistence mechanisms and will depend on the rate of ecological processes.     

Mapping from heterogeneous biodiversity monitoring data sources

Field monitoring can vary from simple volunteer opportunistic observations to professional standardised monitoring surveys, leading to a trade-off between data quality and data collection costs. Such variability in data quality may result in biased predictions obtained from species distribution models (SDMs). We aimed to identify the limitations of different monitoring data sources for developing species distribution maps and to evaluate their potential for spatial data integration in a conservation context. Using Maxent, SDMs were generated from three different bird data sources in Catalonia, which differ in the degree of standardisation and available sample size. In addition, an alternative approach for modelling species distributions was applied, which combined the three data sources at a large spatial scale, but then downscaling to the required resolution. Finally, SDM predictions were used to identify species richness and high quality areas (hotspots) from different treatments. Models were evaluated by using high quality Atlas information. We show that both sample size and survey methodology used to collect the data are important in delivering robust information on species distributions. Models based on standardized monitoring provided higher accuracy with a lower sample size, especially when modelling common species. Accuracy of models from opportunistic observations substantially increased when modelling uncommon species, giving similar accuracy to a more standardized survey. Although downscaling data through a SDM approach appears to be a useful tool in cases of data shortage or low data quality and heterogeneity, it will tend to overestimate species distributions. In order to identify distributions of species, data with different quality may be appropriate. However, to identify biodiversity hotspots high quality information is needed.     

Stony endocarp dimension and shape variation in prunus section prunus

BACKGROUND AND AIMS: Identification of Prunus groups at subspecies or variety level is complicated by the wide range of variation and morphological transitional states. Knowledge of the degree of variability within and between species is a sine qua non for taxonomists. Here, a detailed study of endocarp dimension and shape variation for taxa of Prunus section Prunus is presented. METHODS: The sample size necessary to obtain an estimation of the population mean with a precision of 5 % was determined by iteration. Two cases were considered: (1) the population represents an individual; and (2) the population represents a species. The intra-individual and intraspecific variation of Prunus endocarps was studied by analysing the coefficients of variance for dimension and shape parameters. Morphological variation among taxa was assessed using univariate statistics. The influence of the time of sampling and the level of hydration on endocarp dimensions and shape was examined by means of pairwise t-tests. In total, 14 endocarp characters were examined for five Eurasian plum taxa. KEY RESULTS: All linear measurements and index values showed a low or normal variability on the individual and species level. In contrast, the parameter 'Vertical Asymmetry' had high coefficients of variance for one or more of the taxa studied. Of all dimension and shape parameters studied, only 'Triangle' differed significantly between mature endocarps of P. insititia sampled with a time difference of 1 month. The level of hydration affected endocarp dimensions and shape significantly. CONCLUSIONS: Index values and the parameters 'Perimeter', 'Area', 'Triangle', 'Ellipse', 'Circular' and 'Rectangular', based on sample sizes and coefficients of variance, were found to be most appropriate for further taxonomic analysis. However, use of one, single endocarp parameter is not satisfactory for discrimination between Eurasian plum taxa, mainly because of overlapping ranges. Before analysing dried endocarps, full hydration is recommended, as this restores the original dimensions and shape.     

Phenotypic variation in metamorphosis in four species of freshwater copepods

1. Physiological metamorphosis accompanied by an ecological habitat shift is a widespread life-history phenomenon, and both age and size at metamorphosis are highly variable in many organisms. In this study, age and size at metamorphosis (defined as the transition from the last naupliar to the first copepodite stage) were quantified for four species of freshwater copepods to determine the scale on which these two traits vary, if age and size at metamorphosis are equally variable, and if variation at metamorphosis is related to variation in newborn size. 2. Measurements of laboratory-reared and field-caught individuals show that age and size at metamorphosis, together with newborn size, vary among siblings, between families within a population, between populations of one species and between closely related species. 3. In all populations, age at metamorphosis was the most variable trait, a result observed in many other organisms. Most of the variation in age at metamorphosis could be explained by differences between families within a population, while differences among siblings from the same clutch accounted for most of the variation in size at metamorphosis. 4. Although newborn size was variable, differences in this trait could not fully account for variation observed at metamorphosis. Newborn size differed among populations, but most interpopularional differences disappeared by the rime metamorphosis was reached. In particular, size at metamorphosis appears to be tightly constrained in freshwater copepods. 5. Age and size at metamorphosis were not equally variable among species, either. Species-specific metamorphic envelopes (joint distributions of age and size at metamorphosis) result from differences in trait means, variances and covariances, and suggest very different larval growth trajectories among three of the species examined.     

Niche variability and its consequences for species distribution modeling

When species distribution models (SDMs) are used to predict how a species will respond to environmental change, an important assumption is that the environmental niche of the species is conserved over evolutionary time-scales. Empirical studies conducted at ecological time-scales, however, demonstrate that the niche of some species can vary in response to environmental change. We use habitat and locality data of five species of stream fishes collected across seasons to examine the effects of niche variability on the accuracy of projections from Maxent, a popular SDM. We then compare these predictions to those from an alternate method of creating SDM projections in which a transformation of the environmental data to similar scales is applied. The niche of each species varied to some degree in response to seasonal variation in environmental variables, with most species shifting habitat use in response to changes in canopy cover or flow rate. SDMs constructed from the original environmental data accurately predicted the occurrences of one species across all seasons and a subset of seasons for two other species. A similar result was found for SDMs constructed from the transformed environmental data. However, the transformed SDMs produced better models in ten of the 14 total SDMs, as judged by ratios of mean probability values at known presences to mean probability values at all other locations. Niche variability should be an important consideration when using SDMs to predict future distributions of species because of its prevalence among natural populations. The framework we present here may potentially improve these predictions by accounting for such variability.     

Updating bird species distribution at large spatial scales: applications of habitat modelling to data from long-term monitoring programs

Mapping of species distributions at large spatial scales has been often based on the representation of gathered observations in a general grid atlas framework. More recently, subsampling and subsequent interpolation or habitat spatial modelling techniques have been incorporated in these projects to allow more detailed species mapping. Here, we explore the usefulness of data from long-term monitoring (LTM) projects, primarily aimed at estimating trends in species abundance and collected at shorter time intervals (usually yearly) than atlas data, to develop predictive habitat models. We modelled habitat occupancy for 99 species using a bird LTM program and evaluated the predictive accuracy of these models using independent data from a contemporary and comprehensive breeding bird atlas project from the same region. Habitat models from LTM data using generalized linear modelling were significant for all the species and generally showed a high predictive power, albeit lower than that from atlas models. Sample size and species range size and niche breadth were the most important factors behind variability in model predictive accuracy, whereas the spatial distribution of sampling units at a given sample size had minor effects. Although predictive accuracy of habitat modelling was strongly species dependent, increases in sample size and, secondarily, a better spatial distribution of sampling units should lead to more powerful predictive distribution models. We suggest that data from LTM programs, now established in a large number of countries, has the potential for being a major source of good quality data suitable for the estimation and regularly update of distributions at large spatial scales for a number of species.     

Bird community composition patterns in urban parks of Madrid: The role of age, size and isolation

This study intends to assess the influence of fragment age, size and isolation (from the regional species pool) on bird community composition patterns in urban parks in Madrid, and the role of local and regional factors on community structure. Park age was a good indicator of habitat complexity. Park age and area accounted for 62% of the variability in species richness, but two measures of isolation from the regional species pool were not included as significant factors. Species composition in urban parks showed a high degree of nestedness, which was associated with park age and area, but not with two measures of isolation from the regional species pool. The degree of nestedness increased with park age; the distribution of species varying from nested in old and mature parks to random in young parks. The incidence (% of species occurrence in parks) in young parks was correlated with regional densities, whereas in mature and old parks the incidence was correlated with local densities. In this urban landscape, species composition appears to be regulated by local factors (particularly in mature and old parks), such that species accumulate in an orderly (not random) fashion in relation to park age and area. Regional influences seem to be more pronounced only in young parks, which are mainly colonized by species from the regional species pool.     

Relating belowground microbial composition to the taxonomic,phylogenetic, and functional trait distributions of trees in a tropical forest

The complexities of the relationships between plant and soil microbial communities remain unresolved. We determined the associations between plant aboveground and belowground (root) distributions and the communities of soil fungi and bacteria found across a diverse tropical forest plot. Soil microbial community composition was correlated with the taxonomic and phylogenetic structure of the aboveground plant assemblages even after controlling for differences in soil characteristics, but these relationships were stronger for fungi than for bacteria. In contrast to expectations, the species composition of roots in our soil core samples was a poor predictor of microbial community composition perhaps due to the patchy, ephemeral, and highly overlapping nature of fine root distributions. Our ability to predict soil microbial composition was not improved by incorporating information on plant functional traits suggesting that the most commonly measured plant traits are not particularly useful for predicting the plot‐level variability in belowground microbial communities.     

Group size variability in primates

The effects of mean troop size, diet, territoriality, and habitat upon temporal variability of group size in primates were investigated using variance functions relating mean group size and temporal variability. Two different types of variability were described: (1) within group variability where a single troop was followed over a given period of time; and (2) between group variability where the author(s) did not distinguish one troop from the other. In the second category, CV (SD/mean) as an index of temporal group size variability proved to be dependent on mean group size among the Cercopithecidae. Large groups are more unstable in size than small ones. In the Cebidae, variability was independent of mean group size and therefore large groups are as variable through time as small ones. Ecological factors showed no effects on the observed level of between group variability. Within group variability was found to be smaller than the level of between group variability in all species tested. The results are related to social organization and to the degree of feeding interference observed within and between troops. Future practical applications for our results are considered.     

Natural gene-expression variation in Down syndrome modulates the outcome of gene-dosage imbalance

Down syndrome (DS) is characterized by extensive phenotypic variability, with most traits occurring in only a fraction of affected individuals. Substantial gene-expression variation is present among unaffected individuals, and this variation has a strong genetic component. Since DS is caused by genomic-dosage imbalance, we hypothesize that gene-expression variation of human chromosome 21 (HSA21) genes in individuals with DS has an impact on the phenotypic variability among affected individuals. We studied gene-expression variation in 14 lymphoblastoid and 17 fibroblast cell lines from individuals with DS and an equal number of controls. Gene expression was assayed using quantitative real-time polymerase chain reaction on 100 and 106 HSA21 genes and 23 and 26 non-HSA21 genes in lymphoblastoid and fibroblast cell lines, respectively. Surprisingly, only 39% and 62% of HSA21 genes in lymphoblastoid and fibroblast cells, respectively, showed a statistically significant difference between DS and normal samples, although the average up-regulation of HSA21 genes was close to the expected 1.5-fold in both cell types. Gene-expression variation in DS and normal samples was evaluated using the Kolmogorov-Smirnov test. According to the degree of overlap in expression levels, we classified all genes into 3 groups: (A) nonoverlapping, (B) partially overlapping, and (C) extensively overlapping expression distributions between normal and DS samples. We hypothesize that, in each cell type, group A genes are the most dosage sensitive and are most likely involved in the constant DS traits, group B genes might be involved in variable DS traits, and group C genes are not dosage sensitive and are least likely to participate in DS pathological phenotypes. This study provides the first extensive data set on HSA21 gene-expression variation in DS and underscores its role in modulating the outcome of gene-dosage imbalance.     

From climate change predictions to actions – conserving vulnerable animal groups in hotspots at a regional scale

Current climate change is a major threat to biodiversity. Species unable to adapt or move will face local or global extinction and this is more likely to happen to species with narrow climatic and habitat requirements and limited dispersal abilities, such as amphibians and reptiles. Biodiversity losses are likely to be greatest in global biodiversity hotspots where climate change is fast, such as the Iberian Peninsula. Here we assess the impact of climate change on 37 endemic and nearly endemic herptiles of the Iberian Peninsula by predicting species distributions for three different times into the future (2020, 2050 and 2080) using an ensemble of bioclimatic models and different combinations of species dispersal ability, emission levels and global circulation models. Our results show that species with Atlantic affinities that occur mainly in the North‐western Iberian Peninsula have severely reduced future distributions. Up to 13 species may lose their entire potential distribution by 2080. Furthermore, our analysis indicates that the most critical period for the majority of these species will be the next decade. While there is considerable variability between the scenarios, we believe that our results provide a robust relative evaluation of climate change impacts among different species. Future evaluation of the vulnerability of individual species to climate change should account for their adaptive capacity to climate change, including factors such as physiological climate tolerance, geographical range size, local abundance, life cycle, behavioural and phenological adaptability, evolutionary potential and dispersal ability.