Macroecological Studies Research Articles

An amniote life‐history database to perform comparative analyses with birds, mammals, and reptiles

Studying life‐history traits within and across taxonomic classifications has revealed many interesting and important patterns, but this approach to life history requires access to large compilations of data containing many different life‐history parameters. Currently, life‐history data for amniotes (birds, mammals, and reptiles) are split among a variety of publicly available databases, data tables embedded in individual papers and books, and species‐specific studies by experts. Using data from this wide range of sources is a challenge for conducting macroecological studies because of a lack of standardization in taxonomic classifications, parameter values, and even in which parameters are reported. In order to facilitate comparative analyses between amniote life‐history data, we created a database compiled from peer‐reviewed studies on individual species, macroecological studies of multiple species, existing life‐history databases, and other aggregated sources as well as published books and other compilations. First, we extracted and aggregated the raw data from the aforementioned sources. Next, we resolved spelling errors and other formatting inconsistencies in species names through a number of computational and manual methods. Once this was completed, subspecies‐level data and species‐level data were shared via a data‐sharing algorithm to accommodate the variety of species transformations (taxonomic promotions, demotions, merges, divergences, etc.) that have occurred over time. Finally, in species where multiple raw data points were identified for a given parameter, we report the median value. Here, we report a normalized and consolidated database of up to 29 life‐history parameters, containing at least one life‐history parameter for 21 322 species of birds, mammals, and reptiles.

Analyze causal relations between climatic and biotic velocities using circular statistics so as to inform biodiversity conservation

Directional (or circular) biodiversity data are characterized by a series of values within the range 0 –360 . This constrained range implies that conventional statistical methods suitable for the analysis of linear data do not apply to directional data. Circular statistics, which have been well developed over the past several decades (Upton and Fingleton 1989; Jammalamadaka and SenGupta 2001), are an ideal tool to analyze directional data. However, in climate change-related biodiversity studies, circular statistics have been rarely employed, even though some previous macroecological studies began to use this powerful technique (Cunningham et al. 2015; Du et al. 2015). Velocity is a vector containing both magnitude and direction components. Both components should be analyzed so as to provide a holistic understanding on the general relations between climatic and biotic velocities. Here climatic velocity is defined as the change speed of climate over time, while biotic velocity is defined as the shift speed of species’ range over time (Loaire et al. 2009; Chen 2015; Comte and Grenouillet 2015). The magnitudinous relation between climatic and biotic velocities can be analyzed using conventional regression techniques, while the directional relation between these velocities may be analyzed by circular statistics. In a recent study, Comte and Grenouillet (2015) found that there were either nonsignificant or significant associations between climatic and biotic velocities for the distribution of freshwater fish in French streams. However, from Figs. 3 and 5 in their paper, only the magnitude component of these velocities was analyzed actually. The directional relations were not analyzed and interpreted at all. Here, I recommend applying circular–

Spatial autocorrelation potentially indicates the degree of changes in the predictive power of environmental factors for plant diversity

In the literature of ecological indicators, more attention has yet to be paid to the potential effects of spatial autocorrelation (SAC) on the prediction of plant community structure. At a selected foredune ridge in a temperate coast of South Korea, this research developed two regression models: (1) a non-spatial ordinary least squares (OLS) in which the fine-scale (ca. 10m) variability of diversity was predicted by soil and topographic parameters and (2) a spatial model in which spatial filters extracted by spatial eigenvector mapping were incorporated as additional predictors into the original OLS. After such incorporation, a reduction apparently occurred in the predictive power of the environmental variables, especially those with an inherently high amount of SAC. For example, Mg2+ was the most significant predictor for species diversity in OLS, but it became insignificant in spatial regression. This indicates that, during the incorporation of SAC, the predictive importance of Mg2+ was replaced by that of spatial filters. In other words, because the SAC of Mg2+ was inherently strong (global Moran's I=0.68, p<0.001), this soil attribute became redundant when the spatial filters were added to the non-spatial OLS. These discussions corroborate the general idea of this paper that SAC potentially indicates the degree of shifts in the predictive power of environmental factors for plant diversity. In sum, we suggest that environmental variables, which are highly structured over space, should be the target of special attention and care in future modeling attempts aiming to predict the spatial patterns of plant species diversity in coastal dunes. This fine-scale approach can also be applied to macroecological studies along a variety of ecological systems, spanning latitudinal or disturbance gradients.

High speciation rate at temperate latitudes explains unusual diversity gradients in a clade of ectomycorrhizal fungi.

Understanding the patterns of biodiversity through time and space is a challenging task. However, phylogeny-based macroevolutionary models allow us to account and measure many of the processes responsible for diversity buildup, namely speciation and extinction. The general latitudinal diversity gradient (LDG) is a well-recognized pattern describing a decline in species richness from the equator polewards. Recent macroecological studies in ectomycorrhizal (EM) fungi have shown that their LDG is shifted, peaking at temperate rather than tropical latitudes. Here we investigate this phenomenon from a macroevolutionary perspective, focusing on a well-sampled group of edible EM mushrooms from the genus Amanita-the Caesar's mushrooms, which follow similar diversity patterns. Our approach consisted in applying a suite of models including (1) nontrait-dependent time-varying diversification (Bayesian analysis of macroevolutionary mixtures [BAMM]), (2) continuous trait-dependent diversification (quantitative-state speciation and extinction [QuaSSE]), and (3) diversity-dependent diversification. In short, results give strong support for high speciation rates at temperate latitudes (BAMM and QuaSSE). We also find some evidence for different diversity-dependence thresholds in "temperate" and "tropical" subclades, and little differences in diversity due to extinction. We conclude that our analyses on the Caesar's mushrooms give further evidence of a temperate-peaking LDG in EM fungi, highlighting the importance and the implications of macroevolutionary processes in explaining diversity gradients in microorganisms.

The macroecology of phylogenetically structured hummingbird–plant networks

AbstractAimTo investigate the association between hummingbird–plant network structure and species richness, phylogenetic signal on species' interaction pattern, insularity and historical and current climate.LocationFifty‐four communities along a c. 10,000 km latitudinal gradient across the Americas (39° N–32° S), ranging from sea level to c. 3700 m a.s.l., located on the mainland and on islands and covering a wide range of climate regimes.MethodsWe measured the level of specialization and modularity in mutualistic plant–hummingbird interaction networks. Using an ordinary least squares multimodel approach, we examined the influence of species richness, phylogenetic signal, insularity and current and historical climate conditions on network structure (null‐model‐corrected specialization and modularity).ResultsPhylogenetically related species, especially plants, showed a tendency to interact with a similar array of mutualistic partners. The spatial variation in network structure exhibited a constant association with species phylogeny (R2 = 0.18–0.19); however, network structure showed the strongest association with species richness and environmental factors (R2 = 0.20–0.44 and R2 = 0.32–0.45, respectively). Specifically, higher levels of specialization and modularity were associated with species‐rich communities and communities in which closely related hummingbirds visited distinct sets of flowering species. On the mainland, specialization was also associated with warmer temperatures and greater historical temperature stability.Main conclusionsOur results confirm the results of previous macroecological studies of interaction networks which have highlighted the importance of species richness and the environment in determining network structure. Additionally, for the first time, we report an association between network structure and species phylogenetic signal at a macroecological scale, indicating that high specialization and modularity are associated with high interspecific competition among closely related hummingbirds, subdividing the floral niche. This suggests a tighter co‐evolutionary association between hummingbirds and their plants than in previously studied plant–bird mutualistic systems.

Geospatial data of freshwater habitats for macroecological studies: an example with freshwater fishes

Global data sets are essential in macroecological studies. File formats of the few available data sets of freshwater ecosystems, however, are either incompatible with most macroecological software packages, incomplete, or of coarse spatial resolutions. We integrated more than 460 million geographical coordinates for freshwater habitats in the FRWater data set, partitioned into seven different habitats (lentic, wetlands, reservoirs, small rivers, large rivers, small ditches, large ditches, small channels, large channels, small drains and large drains) in ModestR (http://www.ipez.es/ModestR). A comprehensive collection of geospatial rasters was assembled, one for each of the seven freshwater habitats, with the area in km2 occupied by each habitat presented in cells of 5 arc-minute resolution. The utility of FRWater was evaluated using hierarchical partitioning via the identification of the contribution of the seven different freshwater habitats to both species richness and rarity. To this end, we used a data set of 836,123 geographical records of the 16,216 species of freshwater fishes recognized as valid by systematists at the end of 2014. Areas in North America and Europe are the most detailed in the FRWater data set, evidencing the higher quality of data sources in those regions. The number of geographical coordinates is much lower for Africa, Asia, Australia, and South America where many water bodies remain unmapped. In light of the variation in information quality at continental levels, we performed and present comparative analyses for Europe versus South America at local (5ʹ × 5ʹ grid cells) and regional (5° × 5° grid cells) scales. The relative contribution of small rivers to both species richness and rarity was highest under almost all analyses, followed by lentic habitats and large rivers. The areas of different habitats moreover explained a relatively high proportion of the observed variance in geographic rarity. Our findings corroborate previous findings that the greater contribution of small rivers to species richness is probably due to these habitats promoting geographical rarity. Hence, species richness is favored by the isolation resultant from, and the refuges associated with, small river basins and via the diversification processes promoted by such isolation.

5‐ and 10‐km mesh datasets of agricultural land use based on governmental statistics for 1970–2005

AbstractLand use data serve as an essential part of large‐scale ecological research, such as landscape ecology and macroecological studies. For agricultural fields in Japan, existing time series statistical records can be used to convert map data according to a map of municipality units. In this data paper, we determined the areas of agricultural land use in Japan from 1970 to 2005, excluding small islands, at spatial resolutions of 5‐ and 10‐km mesh grid units, which are often referred to as the Five‐fold Mesh and Japanese Second‐order Mesh, respectively. The elements considered included total farmland, paddy fields, dry farmland, and orchards. In 2005, we included abandoned agricultural areas because the related data were available in the agricultural statistical records. The source data came from the Census for Agriculture, Forestry and Fisheries conducted by the Ministry of Agriculture, Forestry and Fisheries, Japan. The Datum was the Japanese Geodetic Datum 2000 (JGD2000). All of the datasets have open data licenses under the rules of the Creative Commons CC‐BY 4.0 International (https://creativecommons.org/licenses/by/4.0/legalcode).

Species richness patterns of waterbirds wintering in the gulf of Gabès in relation to habitat and anthropogenic features

Identifying factors affecting waterbird diversity is a major topic in avian ecology, as well as for conservation purposes. In this work, we investigated the relevance of habitat features and human presence in predicting the diversity of waterbirds wintering in the gulf of Gabès, an important but poorly known wintering area of palearctic waterbirds. This includes two major sources of bias in macroecological studies, namely species imperfect detection and spatial non-independence among sampled communities. Our results showed that species richness overall varied among sites according to habitat quality and tidal area use by humans. In particular, large intertidal areas, characterized by high numbers of tidal channels, elevated amounts of mud and organic materials in the sediment and important coverage of seagrass, hosted a greater diversity of waterbirds with different ecological requirements than did the small and relatively homogeneous sandy beaches. Moreover, we found that intertidal area use by humans for clam harvesting was associated with high diversity of waterbirds, particularly shorebirds, suggesting positive effects of clam harvesting on shorebirds. Further investigations of habitat selection processes and foraging behaviors are however needed to more profoundly understand the role of traditional human activities in the intertidal areas of the gulf of Gabès in shaping wintering waterbird communities.

The integration of Artificial Night-Time Lights in landscape ecology: A remote sensing approach

High-biodiversity landscapes around the globe are under immense pressure due to the expansion of human activities. To ensure effective monitoring and management of such landscapes, it is necessary to integrate landscape composition and the associated socio-economic processes in the conservation schemes. Artificial Night-Time Light (ANTL) pollution is a recent but striking environmental alteration due to human interventions. It is a major threat for species and communities which co-evolved with invariant natural light patterns over geological times. In spite of its potential key role in re-shaping natural systems, ANTL is seldom considered in macroecology. Remote sensing provides a unique set of tools to integrate ANTL in macroecological studies. In this work, we used remote sensing data of night-time lights along with Enhanced Vegetation Index (EVI) to study the effects and extent of ANTL in the night-time landscape (nightscape) of two protected areas in Italy. Our results showed that a considerable number of semi-natural vegetated patches suffer from ANTL pollution with varying magnitude. We observed a decline in highly suitable patches for biodiversity while the remaining patches were found concentrated in the innermost part of the parks. By simulating an exponential decrease in ANTL we showed that a moderate reduction in ANTL pollution would result in regaining a substantial amount of highly suitable patches for biodiversity. The decline in homogeneous dark patches in vegetated landscapes has negative impacts on biodiversity as well as on the ecosystem services it provides. Therefore, it is high time that the scientific community and the policy-makers increase their efforts to monitor and mitigate the ecological impacts of ANTL on ecosystems. The integration of light pollution in landscape ecology could combine remote sensing with other aspects of light pollution like indirect propagation and spectral composition.

Aragonite bias, and lack of bias, in the fossil record: lithological, environmental, and ecological controls

AbstractMacroevolutionary and macroecological studies must account for biases in the fossil record, especially when questions concern the relative abundance and diversity of taxa that differ in preservation and sampling potential. Using Cenozoic marine mollusks from a temperate setting (New Zealand), we find that much of the long-term temporal variation in gastropod versus bivalve occurrences is correlated with the stage-level sampling probabilities of aragonitic versus calcitic taxa. Average sampling probabilities are higher for calcitic species, but this contrast is time-varying in a predictable way, being concentrated in stages with widespread carbonate deposition.To understand these results fully, we link them with analyses at the level of individual point occurrences. Doing so reveals that aragonite bias is effectively absent in terrigenous clastic sediments. In limestones, by contrast, calcitic species have at least twice the odds of sampling as aragonitic species. This result is most pronounced during times of widespread carbonate deposition, where the difference in the per-collection odds of sampling species is a factor of eight. During carbonate-rich intervals, calcitic taxa also have higher odds of sampling in clastics. At first glance this result may suggest simple preservational bias against aragonite. However, comparing relative odds of aragonitic versus calcitic sampling with absolute sampling rates shows that the positive calcite bias during carbonate-rich times reflects higher than average occurrence rates for calcitic taxa (rather than lower rates for aragonitic taxa) and that the negative aragonite bias in limestones reflects lower than average occurrence rates for aragonitic taxa (rather than higher rates for calcitic taxa).Our results therefore indicate a time-varying interplay of two main factors: (1) taphonomic loss of aragonitic species in carbonate sediments, with no substantial bias in terrigenous clastics; and (2) an ecological preference of calcitic taxa for environments characteristic of periods with pervasive carbonate deposition, irrespective of lithology per se.

Potassium: a neglected nutrient in global change

AbstractAimPotassium (K) is the second most abundant nutrient in plant photosynthetic tissues after nitrogen (N). Thousands of physiological and metabolic studies in recent decades have established the fundamental role of K in plant function, especially in water‐use efficiency and economy, and yet macroecological studies have mostly overlooked this nutrient.MethodsWe have reviewed available studies on the content, stoichiometry and roles of K in the soil–plant system and in terrestrial ecosystems. We have also reviewed the impacts of global change drivers on K content, stoichiometry and roles.ConclusionsThe current literature indicates that K, at a global level, is as limiting as N and phosphorus (P) for plant productivity in terrestrial ecosystems. Some degree of K limitation has been seen in up to 70% of all studied terrestrial ecosystems. However, in some areas atmospheric K deposition from human activities is greater than that from natural sources. We are far from understanding the K fluxes between the atmosphere and land, and the role of anthropogenic activities in these fluxes. The increasing aridity expected in wide areas of the world makes K more critical through its role in water‐use efficiency. N deposition exerts a strong impact on the ecosystem K cycle, decreasing K availability and increasing K limitation. Plant invasive success is enhanced by higher soil K availability, especially in environments without strong abiotic stresses. The impacts of other drivers of global change, such as increasing atmospheric CO2 or changes in land use, remain to be elucidated. Current models of the responses of ecosystems and carbon storage to projected global climatic and atmospheric changes are now starting to consider N and P, but they should also consider K, mostly in arid and semi‐arid ecosystems.

On the relationship between species age and geographical range in reef fishes: are widespread species older than they seem?

AbstractAimIn order to better understand processes of speciation, range‐size transformation and extinction, macroecological studies seek to identify the evolutionary dynamics of species geographical ranges. This requires accurate estimates of range size and species age. Species ages are attainable through recent success with techniques to estimate phylogenetic divergence time. Conceptual synthesis of the inherent problems with these techniques has been limited. Our aim is to address the effects of estimation of phylogenetic divergence time on the relationship between species age and geographical range.InnovationCommonly, estimates of divergence time from the nodes of a time‐calibrated phylogeny are used as indicators of ages of extant species. However, this method can sometimes produce misleading age estimates, specifically in the presence of extinction and ancestral persistence. An example of this is illustrated using a comprehensive genetic dataset of genera with near‐complete sampling of species from four of the major coral reef fish families. We present a method to minimize the impacts of extinction and ancestral persistence on divergence time estimation. The method focuses on recent divergences and involves pairing minimum divergence time estimates (as indicators of species ages) with the minimum geographical range area between two sister‐species, for all sister‐species pairs.Main conclusionsWhen applied to coral reef fishes, this method revealed trends in the relationship between species age and geographical range. The difference in the trend recovered from excluding potential biases associated with ancestral persistence suggests that ancestral persistence may be prevalent among coral reef fishes, with successive peripheral speciation affecting area–age relationships. The method may reveal the occurrence of successive peripheral speciation events across a broad range of taxa.

Macroecological trends in nestedness and modularity of seed‐dispersal networks: human impact matters

AbstractAimWe aim to characterize the macroecological patterns in the structure of mutualistic seed‐dispersal networks. Tropical areas hold more species than temperate ones. This difference in species number may favour ecological processes that minimize interspecific competition in species‐rich areas. There is theoretical evidence that both modularity (i.e. the presence of semi‐independent groups of highly interacting species) and nestedness (i.e. specialists interact with a subset of the species interacting with generalists) reduce the effects of competition. Thus, we expect high degrees of modularity or nestedness at low latitudes in seed‐dispersal networks. Moreover, we test whether climate, topography and human impact influence network structure.LocationThirty‐four qualitative and 21 weighted seed‐dispersal interaction networks located world‐wide.MethodsWe related the degree of modularity and nestedness of seed‐dispersal interaction networks with latitude. To disentangle the macroecological drivers of network structure, we also associated modularity/nestedness with species richness, altitudinal range, human impact and an array of climate predictors: precipitation, temperature, precipitation/temperature seasonality and historical climate‐change velocity and anomaly.ResultsBinary networks showed stronger macroecological patterns than weighted networks. Latitude was unrelated to the structure of seed‐dispersal networks, but more nested assemblages were species rich and were located in areas with a high degree of human impact, high temperature seasonality, low precipitation, and, especially on the mainland, high stability in precipitation. Modular networks were species rich and found in areas with low human impact. For both nestedness and modularity, the effects of species richness and human impact were especially strong and consistent.Main conclusionsAs for previous macroecological studies of mutualistic networks, we found that the structure of seed‐dispersal assemblages was related to current and historical climate. The largest influences on nestedness and modularity, however, were the number of competing species and the degree of human impact. This suggests that human disturbance, not just climate, is an important factor determining the structure of a seed‐dispersal network.

Can we derive macroecological patterns from primary Global Biodiversity Information Facility data?

AbstractAimTo determine whether the method used to build distributional maps from raw data influences the representation of two principal macroecological patterns: the latitudinal gradient in species richness and the latitudinal variation in range sizes (Rapoport's rule).LocationWorld‐wide.MethodsAll available distribution data from the Global Biodiversity Information Facility (GBIF) for those fish species that are members of orders of fishes with only marine representatives in each order were extracted and cleaned so as to compare four different procedures: point‐to‐grid (GBIF maps), range maps applying an α‐shape [GBIF‐extent of occurrence (EOO) maps], the MaxEnt method of species distribution modelling (GBIF‐MaxEnt maps) and the MaxEnt method but restricted to the area delimited by the α‐shape (GBIF‐MaxEnt‐restricted maps).ResultsThe location of hotspots and the latitudinal gradient in species richness or range sizes are relatively similar in the four procedures. GBIF‐EOO maps and most GBIF‐MaxEnt‐maps provide overestimations of species richness when compared with those present in a priori well‐surveyed cells. GBIF‐EOO maps seem to provide more reasonable world macroecological patterns. MaxEnt can erroneously predict the presence of species in environmentally similar cells of another hemisphere or in other regions that lie outside the range of the species. Limiting this overpredictive capacity, as in the case of GBIF‐MaxEnt‐restricted maps, seems to mimic the frequency of observations derived from a simple point‐to‐grid procedure, with the utility of this procedure consequently being limited.Main conclusionsIn studies of macroecological patterns at a global scale, the simple α‐shape method seems to be a more parsimonious option for extrapolating species distributions from primary data than are distribution models performed indiscriminately and automatically with MaxEnt. GBIF data may be used in macroecological patterns if original data are cleaned, autocorrelation is corrected and species richness figures do not constitute obvious underestimations. Efforts therefore should focus on improving the number and quality of records that can serve as the source of primary data in macroecological studies.

Environmental heterogeneity predicts species richness of freshwater mollusks in sub-Saharan Africa

Species diversity and how it is structured on a continental scale is influenced by stochastic, ecological, and evolutionary driving forces, but hypotheses on determining factors have been mainly examined for terrestrial and marine organisms. The extant diversity of African freshwater mollusks is in general well assessed to facilitate conservation strategies and because of the medical importance of several taxa as intermediate hosts for tropical parasites. This historical accumulation of knowledge has, however, not resulted in substantial macroecological studies on the spatial distribution of freshwater mollusks. Here, we use continental distribution data and a recently developed method of random and cohesive allocation of species distribution ranges to test the relative importance of various factors in shaping species richness of Bivalvia and Gastropoda. We show that the mid-domain effect, that is, a hump-shaped richness gradient in a geographically bounded system despite the absence of environmental gradients, plays a minor role in determining species richness of freshwater mollusks in sub-Saharan Africa. The western branch of the East African Rift System was included as dispersal barrier in richness models, but these simulation results did not fit observed diversity patterns significantly better than models where this effect was not included, which suggests that the rift has played a more complex role in generating diversity patterns. Present-day precipitation and temperature explain richness patterns better than Eemian climatic condition. Therefore, the availability of water and energy for primary productivity during the past does not influence current species richness patterns much, and observed diversity patterns appear to be in equilibrium with contemporary climate. The availability of surface waters was the best predictor of bivalve and gastropod richness. Our data indicate that habitat diversity causes the observed species–area relationship, and hence, that environmental heterogeneity is a principal driver of freshwater mollusk richness on a continental scale.

Current and future latitudinal gradients in stream macroinvertebrate richness across North America

Freshwater ecosystems are highly vulnerable to warming climates. However, macroecological studies of climate-change effects on aquatic biodiversity are rare because of a lack of standardized large-scale surveys, e.g., along large latitudinal gradients. Our goal was to assess the overall richness pattern and projected differences in present and future patterns of the stream insect orders Ephemeroptera (E), Plecoptera (P), Trichoptera (T), and combined EPT along an extensive latitudinal gradient across North America (30 to 70°N). We applied Bioclimatic Envelope Models (BEMs) to project present-day and future climatically suitable areas for EPTs on a spatial resolution of 10 arc-min (20 km × 20 km) across North America. To overcome issues related to spatially biased sampling, we assessed climatically suitable areas (CSAs) for each genus and modeled potential generic richness/grid cell, rather than assessing observed generic richness patterns directly. Projected present-day generic richness was greatest between 40 and 48°N latitude, with peaks at 44, 45, and 47°N for the E, P, and T orders, respectively. Our models projected that CSAs would shift an average 4.2 to 5.2°, 4.4 to 5.3° and 3.4 to 4.1°N latitude by 2080 for E, P, and T genera, respectively. Overall, the present-day projected generic EPT richness is highest in the warm and cool temperate zones and shows a unimodal richness pattern that is projected to shift northward under climate-change conditions. A similar northward shift of richness patterns might also apply to other aquatic insects with relatively narrow thermal sensitivity and terrestrial, winged adults, e.g., freshwater Diptera or many aquatic Coleoptera. This large-scale application of genus-by-genus models gives a first approximation of the likely consequences of climate-change effects on freshwater biota across North America.

Dispersal is linked to habitat use in 59 species of water beetles (Coleoptera: Adephaga) on Madagascar

Lentic habitats (standing water, such as ponds and lakes) differ from lotic habitats (running water; streams and rivers) in their spatiotemporal persistence, with lentic habitats being more ephemeral in evolutionary time. This habitat instability is thought to select for dispersal, and several phylogenetic and macroecological studies have suggested that high rates of dispersal are more characteristic of lentic than lotic species. We tested this hypothesis using a comparative population genetic and phylogeographic approach based on mitochondrial DNA for 59 aquatic beetle species, sampled across Madagascar. Species were classified as lotic (n = 25), lentic (n = 25), or lotolentic (associated with both running and standing water; n = 9). Hierarchical population genetic structure (AMOVA), nucleotide diversity (π), and geographic structure were compared among habitat types. Lotic species had significantly greater population structure (ФST = 0.55, hierarchical AMOVA) than lentic (ФST = 0.13) and lotolentic (ФST = 0.19) species using phylogenetic generalized least squares (PGLS) to correct for phylogeny. Body size was independent of habitat preference, and did not explain any of the intraspecific variation. A greater proportion of lotic species were endemic to Madagascar and lotic species had more pronounced geographic structure in their haplotype networks. The results indicate that dispersal is consistently lower among lotic species, independent of phylogenetic relatedness. This has macroevolutionary and biogeographical consequences for the freshwater fauna of this tropical biodiversity hotspot where remaining natural habitats are becoming increasingly isolated from one another.

Perspectives on the use of lakes and ponds as model systems for macroecological research

Macroecology studies large-scale patterns aiming to identify the effects of general ecological processes. Although lakes (and ponds) are particularly suited for macroecological research due to their discrete nature and non geographically-structured variability, the development of this discipline in lentic habitats is comparatively much smaller than for terrestrial environments. This is despite the interest of limnologists for large-scale phenomena, which results in the high level of development of some disciplines such as predictive limnology. Here we discuss how current state-of-the-art in macroecology may benefit from research in lentic habitats at five topics. First, by including an island biogeography analytical framework to incorporate the effects of lake origin and history on lentic biodiversity. Second, by studying local and regional effects on the latitudinal gradients of species richness. Third, by considering lakes and ponds altogether for the study of beta diversity and metacommunity structure, which is already common ground in limnological research. Fourth, by relating species traits with ecosystem structure and functioning; here we consider in particular the potential effects of body size-determined dispersal and competitive exclusion processes on lake-wide trophic organization. And fifth, by incorporating current research in functional (i.e. trait) and phylogenetic diversity to the study of community structure. We finally conclude that lentic habitats can be particularly important for the development of the most functional aspects of macroecology, due to the relative ease of studying the different biotic and abiotic components of the system separately, compared to most terrestrial systems. This can allow teasing apart many of the confounding factors that are characteristic of macroecological research, thus helping the development of future theoretical syntheses.

GlUV: a global UV‐B radiation data set for macroecological studies

Summary Macroecology has prospered in recent years due in part to the wide array of climatic data, such as those provided by the WorldClim and CliMond data sets, which has become available for research. However, important environmental variables have still been missing, including spatial data sets on UV‐B radiation, an increasingly recognized driver of ecological processes. We developed a set of global UV‐B surfaces (glUV) suitable to match common spatial scales in macroecology. Our data set is based on remotely sensed records from NASA's Ozone Monitoring Instrument (Aura‐OMI). Following a similar approach as for the WorldClim and CliMond data sets, we processed daily UV‐B measurements acquired over a period of eight years into monthly mean UV‐B data and six ecologically meaningful UV‐B variables with a 15‐arc minute resolution. These bioclimatic variables represent Annual Mean UV‐B, UV‐B Seasonality, Mean UV‐B of Highest Month, Mean UV‐B of Lowest Month, Sum of Monthly Mean UV‐B during Highest Quarter and Sum of Monthly Mean UV‐B during Lowest Quarter. We correlated our data sets with selected variables of existing bioclimatic surfaces for land and with Terra–MODIS Sea Surface Temperature for ocean regions to test for relations to known gradients and patterns. UV‐B surfaces showed a distinct seasonal variance at a global scale, while the intensity of UV‐B radiation decreased towards higher latitudes and was modified by topographic and climatic heterogeneity. UV‐B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe. UV‐B surfaces were otherwise widely independent of existing bioclimatic surfaces. Our data set provides new climatological information relevant for macroecological analyses. As UV‐B is a known driver of numerous biological patterns and processes, our data set offers the potential to generate a better understanding of these dynamics in macroecology, biogeography, global change research and beyond. The glUV data set containing monthly mean UV‐B data and six derived UV‐B surfaces is freely available for download at: http://www.ufz.de/gluv.

Tree-grass ratios in savannas – challenging paradigms

news and update ISSN 1948-6596 commentary Tree–grass ratios in savannas: challenging paradigms One of the greatest challenges for plant ecologists is to ascertain which factors allow trees and grasses to co-exist in savannas (Moustakas et al. 2010; Figure 1). Two major hypotheses that ad- dress this issue have been proposed (Figure 2). The resource-based hypothesis states that grasses and trees have different root depths, and thus occupy different competitive niches (Scholes and Archer 1997). More recently, various versions of the disturbance hypothesis have been formulated, which postulate that disturbances such as fires and herbivory are major factors restricting the growth of trees (Higgins et al. 2000, Sankaran et al. 2005). In both hypotheses, rainfall is thought to benefit trees. Higher rainfall should cause deeper water infiltration, thereby benefitting the deeper- lying roots of trees and allowing them to grow faster and outcompete grasses by shading. Distur- bances that reduce woody cover, such as fires, would explain lower woody cover in relatively high-rainfall areas. Recently, these ideas have been the focus of a number of macroecological studies, which have found some support for the positive influ- ence of rainfall, and the negative influence of dis- turbances, on woody cover. In their seminal pa- per, Sankaran et al. (2005) showed that, for 854 sites across Africa, maximum woody cover in- creased with precipitation at sites with lower lev- els of precipitation (< 650 mm/year), but showed no relationship with precipitation at higher rainfall levels. They thus suggested that arid and semi-arid savannas are ‘stable’: here, even in the absence of disturbances, trees and grasses would continue to coexist. In contrast, in higher rainfall (mesic) sa- vannas, tree–grass coexistence would be facili- tated by disturbances such as fire and herbivory; in the absence of disturbances, high-rainfall sa- vannas would be expected to become forests. Other continental studies have corroborated these findings (Bucini and Hanan 2007, Sankaran et al. 2008, Staver et al. 2011). These studies have contributed to the idea that, at continental scale, rainfall, with the mediating effect of disturbances, plays a pivotal role in the tree–grass ratio of sa- vannas. However, two studies that were recently published have challenged various aspects of these two hypotheses. February et al. (2013) set up experimental plots to assess the effect of rain- fall manipulation on tree growth in a nutrient- poor mesic and a nutrient-rich semi-arid savanna Figure 1. What de- termines tree–grass ratios in tropical savannas? (Photo- graph taken at Weenen Game Re- serve, South Africa). frontiers of biogeography 5.3, 2013 — © 2013 the authors; journal compilation © 2013 The International Biogeography Society