General Macroecological Pattern Research Articles

Blind spots in global soil biodiversity and ecosystem function research

Soils harbor a substantial fraction of the world’s biodiversity, contributing to many crucial ecosystem functions. It is thus essential to identify general macroecological patterns related to the distribution and functioning of soil organisms to support their conservation and consideration by governance. These macroecological analyses need to represent the diversity of environmental conditions that can be found worldwide. Here we identify and characterize existing environmental gaps in soil taxa and ecosystem functioning data across soil macroecological studies and 17,186 sampling sites across the globe. These data gaps include important spatial, environmental, taxonomic, and functional gaps, and an almost complete absence of temporally explicit data. We also identify the limitations of soil macroecological studies to explore general patterns in soil biodiversity-ecosystem functioning relationships, with only 0.3% of all sampling sites having both information about biodiversity and function, although with different taxonomic groups and functions at each site. Based on this information, we provide clear priorities to support and expand soil macroecological research.

Spatial and species‐level predictions of road mortality risk using trait data

AbstractAimCollisions between wildlife and vehicles are recognized as one of the major causes of mortality for many species. Empirical estimates of road mortality show that some species are more likely to be killed than others, but to what extent this variation can be explained and predicted using intrinsic species characteristics remains poorly understood. This study aims to identify general macroecological patterns associated with road mortality and generate spatial and species‐level predictions of risks.LocationBrazil.Time period2001–2014.Major taxaBirds and mammals.MethodsWe fitted trait‐based random forest regression models (controlling for survey characteristics) to explain 783 empirical road mortality rates from Brazil, representing 170 bird and 73 mammalian species. Fitted models were then used to make spatial and species‐level predictions of road mortality risk in Brazil, considering 1,775 birds and 623 mammals that occur within the continental boundaries of the country.ResultsSurvey frequency and geographical location were key predictors of observed rates, but mortality was also explained by the body size, reproductive speed and ecological specialization of the species. Spatial predictions revealed a high potential standardized (per kilometre of road) mortality risk in Amazonia for birds and mammals and, additionally, a high risk in Southern Brazil for mammals. Given the existing road network, these predictions mean that >8 million birds and >2 million mammals could be killed per year on Brazilian roads. Furthermore, predicted rates for all Brazilian endotherms uncovered potential vulnerability to road mortality of several understudied species that are currently listed as threatened by the International Union for Conservation of Nature.ConclusionWith a rapidly expanding global road network, there is an urgent need to develop improved approaches to assess and predict road‐related impacts. This study illustrates the potential of trait‐based models as assessment tools to gain a better understanding of the correlates of vulnerability to road mortality across species, and as predictive tools for difficult‐to‐sample or understudied species and areas.

Comparing macroecological patterns across continents: evolution of climatic niche breadth in varanid lizards

Macroecological analyses often test hypotheses at the global scale, or among more closely related species in a single region (e.g. continent). Here, we test several hypotheses about climatic niche widths among relatively closely related species that occur across multiple continents, and compare patterns within and across continents to see if they differ. We focus on the lizard genus Varanus (monitor lizards), which occurs in diverse environments in Africa, Asia, and Australia. We address three main questions. 1) How do climatic niche breadths of species on a given niche axis change based on the position of species along that niche axis? (E.g. are species that occur in more extreme environments more narrowly specialized for those conditions?) 2) Are there trade‐offs in niche breadths on temperature and precipitation axes among species, or are niche widths on different axes positively related? 3) Is variation in niche breadths among species explained primarily by within‐locality seasonal variation, or by differences in climatic conditions among localities across the species range? We generate a new time‐calibrated phylogeny for Varanus and test these hypotheses within and between continents using climatic data and phylogenetic methods. Our results show that patterns on each continent often parallel each other and global patterns. However, in many other cases, the strength of relationships can change dramatically among closely related species on different continents. Overall, we found that: 1) species in warmer environments have narrower temperature niche breadths, but there is no relationship between precipitation niche breadth and niche position; 2) temperature and precipitation niche breadths tend to be positively related among species, rather than showing trade‐offs; and 3) within‐locality seasonal variation explains most variation in climatic niche breadths. Some of these results are concordant with previous studies (in amphibians and North American lizards), and might represent general macroecological patterns.

Biogeographical variation in arthropod communities on coyote bush, Baccharis pilularis

Abstract A classic pattern in biogeography is the decline in species richness from lower to higher latitudes. Communities, however, can also vary with other geographical patterns, such as the abiotic gradients that occur from coastal to interior habitats. In this study, we surveyed arthropod communities and herbivore pressure on populations of a dominant shrub, Baccharis pilularis, across a 2000 km latitudinal transect to determine whether coastal versus interior location mediates arthropod responses to latitude. We found that arthropod species richness and abundance declined with increasing latitude. We also found significant coastal‐interior shifts in community composition and trophic structure. Specifically, predator and scavenger richness were two and three fold greater at coastal sites compared to interior sites, and were three‐ and six‐fold more abundant on the coast than in the interior. Herbivore pressure displayed a similar pattern, with greater abundance at lower latitudes and at coastal sites. Our results corroborate the general macroecological pattern that diversity declines with increasing latitude, and that coastal versus interior location can also shape community assemblages. We did not, however, find any interaction between latitude and location suggesting the effect of latitude on arthropod communities remains consistent inland compared to more constant coastal conditions.

Characterizing abundance–occupancy relationships: there is no artefact

ABSTRACTPositive abundance–occupancy relationships (AORs) are among the most general macroecological patterns: locally common species are regionally widespread, locally rare species are regionally restricted. In a recent contribution, Wilson (Global Ecology and Biogeography, 2011, 20, 193–202) made three claims: (1) that AORs are critically dependent on the method used to calculate average abundance; (2) averaging abundance over occupied sites tends to lead to a very high incidence of negative relationships; (3) this represents a statistical artefact that should be considered in studies of AORs. Here we show that this outcome arises in Wilson's simulations purely due to an arbitrary choice of occupancy models and parameter ranges. The resulting negative relationships are not statistical artefacts, but are easily interpreted in terms of spatial aggregation in abundant species. The fact that empirical evidence fails to support a high prevalence of negative AORs suggests, however, that such parameter combinations arise only rarely in nature. We conclude that simulations that are based on untested assumptions, and that produce patterns unsupported by empirical evidence, have limited use in characterizing AORs, and add little to understanding of the processes driving important relationships between local population size and regional occupancy.

Abundance–variance and abundance–occupancy relationships in a marine host–parasite system: The importance of taxonomy and ecology of transmission

Abundance–occupancy and abundance–variance relationships are two of the most general macroecological patterns capturing essential fundamentals of the structuring of species distributions and are widely documented for free-living animal and plant species populations at different spatial scales. However, empirical data for parasites have been gathered using appropriate sampling designs only recently. We performed analyses across species of the variation in infection parameters and patterns of aggregation of the most widespread parasites in the marine sparid fish Boops boops across seven localities of two marine biogeographical regions, the North East Atlantic and the Mediterranean. We used a large dataset of multiple population samples replicated over time for 20 parasite species and carried out assessments both intraspecifically and interspecifically, across taxonomic and ecological groupings. This taxonomically diverse complex of species representing five major metazoan higher taxa with differing transmission ecologies allowed us to assess the effect of taxonomic and ecological determinants on the abundance–occupancy and abundance–variance relationships in the model marine host–parasite system. The results revealed that: (i) a power function, relating spatial variance to mean abundance, represents a suitable model for the spatial distribution of the species; (ii) prevalence, abundance and the degree of spatial heterogeneity are true species characteristics and differ consistently between higher level taxonomic groupings; (iii) infection parameters and abundance–variance relationship are dependent on host specificity and regional distribution patterns of the parasites; and (iv) the observed infection parameters agree well with predictions from the epidemiological negative binomial abundance–occupancy model built on parameters of Taylor’s power law both within and across species.

Range contraction in large pelagic predators.

Large reductions in the abundance of exploited land predators have led to significant range contractions for those species. This pattern can be formalized as the range-abundance relationship, a general macroecological pattern that has important implications for the conservation of threatened species. Here we ask whether similar responses may have occurred in highly mobile pelagic predators, specifically 13 species of tuna and billfish. We analyzed two multidecadal global data sets on the spatial distribution of catches and fishing effort targeting these species and compared these with available abundance time series from stock assessments. We calculated the effort needed to reliably detect the presence of a species and then computed observed range sizes in each decade from 1960 to 2000. Results suggest significant range contractions in 9 of the 13 species considered here (between 2% and 46% loss of observed range) and significant range expansions in two species (11-29% increase). Species that have undergone the largest declines in abundance and are of particular conservation concern tended to show the largest range contractions. These include all three species of bluefin tuna and several marlin species. In contrast, skipjack tuna, which may have increased its abundance in the Pacific, has also expanded its range size. These results mirror patterns described for many land predators, despite considerable differences in habitat, mobility, and dispersal, and imply ecological extirpation of heavily exploited species across parts of their range.

Sometimes the obvious answer is the right one: a response to ‘Missing the rarest: is the positive interspecific abundance–distribution relationship a truly general macroecological pattern?’

In a recent Opinion piece, [Komonen et al. (2009)][1] suggested that, contrary to previous assertions, the positive interspecific relationship between abundance and distribution may not be a general macroecological pattern. The basis for this claim was their analysis of a single dataset on the

Rarity, Commonness, and the Contribution of Individual Species to Species Richness Patterns

Common species have a greater effect on observed geographical patterns of species richness than do rare ones. Here we present a theory of the relationship between individual species occurrence patterns and patterns in species richness, which allows purely geometrical and statistical causes to be distinguished from biological ones. Relationships between species occupancy and the correlation of species occurrence with overall species richness are driven by the frequency distribution of species richness among sites. Moreover, generally positive relationships are promoted by the fact that species occupancy distributions are mostly right skewed. However, biological processes can lead to deviations from the predicted pattern by changing the nestedness of a species' spatial distribution with regard to the distributions of other species in an assemblage. We have applied our theory to data for European birds at several spatial scales and have identified the species with significantly stronger or weaker correspondence with the overall richness pattern than that predicted by the null model. In sum, whereas the general macroecological pattern of a stronger influence of common species than of rare species on species richness is predicted by mathematical considerations, the theory can reveal biologically important deviations at the level of individual species.

Missing the rarest: is the positive interspecific abundance–distribution relationship a truly general macroecological pattern?

Lepidopterists have long acknowledged that many uncommon butterfly species can be extremely abundant in suitable locations. If this is generally true, it contradicts the general macroecological pattern of the positive interspecific relationship between abundance and distribution, i.e. locally abundant species are often geographically more widespread than locally rare species. Indeed, a negative abundance-distribution relationship has been documented for butterflies in Finland. Here we show, using the Finnish butterflies as an example, that a positive abundance-distribution relationship results if the geographically restricted species are missed, as may be the case in studies based on random or restricted sampling protocols, or in studies that are conducted over small spatial scales. In our case, the abundance-distribution relationship becomes negative when approximately 70 per cent of the species are included. This observation suggests that the abundance-distribution relationship may in fact not be linear over the entire range of distributions. This intriguing possibility combined with some taxonomic biases in the literature may undermine the generalization that for a given taxonomic assemblage there is a positive interspecific relationship between local abundance and regional distribution.

INTRASPECIFIC AGGREGATION DECREASES LOCAL SPECIES DIVERSITY OF ARTHROPODS

The aggregation model of species coexistence predicts that insect species diversity within a community is maintained by intraspecific aggregation among resource patches. An untested corollary of this prediction is that diversity within resource patches should decrease with increasing intraspecific aggregation. The recently derived species–aggregation relationship provides a general formulation of this prediction: as intraspecific aggregation increases within a geographic area, the species richness within samples of the area decreases. We tested this prediction by compiling and analyzing 76 data sets of arthropod species distribution and abundance. For each data set, we determined the mean amount of intra- and interspecific aggregation and three types of within-sample or local species diversity: species richness, evenness, and dominance. Using regression, we found a negative relationship between intraspecific aggregation and all three types of local diversity. Intraspecific aggregation explained a significant percentage of the variation in species diversity, typically between 20% and 60%. By comparison, interspecific aggregation usually explained <1% of the variation in species diversity. Our study provides empirical support for the species–aggregation relationship as a general macroecological pattern that emerges from intraspecific aggregation.

Macroecologia de mamíferos neotropicais com ocorrência no Cerrado

The macroecological approach has been used recently to analyze correlations between ecological variables in large taxonomic groups, at continental scales. A positive relationship between body weight and geographic range size has been described as a poligonal space envelope form, that can be explained by ecological and evolutionary constraints. However, these variables can be disturbed by spatial and phylogenetic autocorrelation effects. In this work, the relationship between body weight and geographic range size was analyzed for 80 species of Neotropical mammals present in the Brazilian cerrado. Spatial and taxonomic effects were tested using a linear trend surface analysis and an ANOVA (at level of order), combined in a generalized model. Around 61% of variation in geographic range size and 69% of variation in body weight in mammals of the cerrado can be explained simultaneously by spatial and taxonomic effects. The analysis of residuals of the generalized model showed that positive correlation between variables persist even after removing these effects. Thus, variation and covariation of traits in the mammals of the brazilian cerrado agree with the general macroecological pattern proposed for another taxonomic groups such as mammals, birds and snakes worldwilde.