Spatial Variation In Species Richness Research Articles

Evolutionary factors and habitat filtering affect the pattern of Gerbillinae diversity

Abstract How ecological and evolutionary factors affect small mammal diversity in arid regions remains largely unknown. Here, we combined the largest phylogeny and occurrence dataset of Gerbillinae desert rodents to explore the underlying factors shaping present-day distribution patterns. In particular, we analyzed the relative contributions of ecological and evolutionary factors on their species diversity using a variety of models. Additionally, we inferred the ancestral range and possible dispersal scenarios and estimated the diversification rate of Gerbilliane. We found that Gerbillinae likely originated in the Horn of Africa in the Middle Miocene and then dispersed and diversified across arid regions in northern and southern Africa and western and central Asia, forming their current distribution pattern. Multiple ecological and evolutionary factors jointly determine the spatial pattern of Gerbillinae diversity, but evolutionary factors (evolutionary time and speciation rate) and habitat filtering were the most important in explaining the spatial variation in species richness. Our study enhances the understanding of the diversity patterns of small mammals in arid regions and highlights the importance of including evolutionary factors when interpreting the mechanisms underlying large-scale species diversity patterns.

Chromosomal evolution, environmental heterogeneity, and migration drive spatial patterns of species richness in Calochortus (Liliaceae)

We used nuclear genomic data and statistical models to evaluate the ecological and evolutionary processes shaping spatial variation in species richness in Calochortus (Liliaceae, 74 spp.). Calochortus occupies diverse habitats in the western United States and Mexico and has a center of diversity in the California Floristic Province, marked by multiple orogenies, winter rainfall, and highly divergent climates and substrates (including serpentine). We used sequences of 294 low-copy nuclear loci to produce a time-calibrated phylogeny, estimate historical biogeography, and test hypotheses regarding drivers of present-day spatial patterns in species number. Speciation and species coexistence require reproductive isolation and ecological divergence, so we examined the roles of chromosome number, environmental heterogeneity, and migration in shaping local species richness. Six major clades-inhabiting different geographic/climatic areas, and often marked by different base chromosome numbers (n = 6 to 10)-began diverging from each other ~10.3 Mya. As predicted, local species number increased significantly with local heterogeneity in chromosome number, elevation, soil characteristics, and serpentine presence. Species richness is greatest in the Transverse/Peninsular Ranges where clades with different chromosome numbers overlap, topographic complexity provides diverse conditions over short distances, and several physiographic provinces meet allowing immigration by several clades. Recently diverged sister-species pairs generally have peri-patric distributions, and maximum geographic overlap between species increases over the first million years since divergence, suggesting that chromosomal evolution, genetic divergence leading to gametic isolation or hybrid inviability/sterility, and/or ecological divergence over small spatial scales may permit species co-occurrence.

Environmental DNA compliments traditional sampling for monitoring fish communities in a Texas estuary

AbstractObjectiveEnvironmental DNA (eDNA) metabarcoding has become an important method for inventorying and monitoring biota in aquatic systems. The Texas Parks and Wildlife Department conducts regular fishery‐independent sampling of biotic communities using traditional sampling gears, such as gill nets and bag seines, in all of the major estuaries of adjacent to the Gulf of Mexico in Texas. Previous studies have shown that eDNA approaches can complement traditional sampling methods.MethodsWe compared fish community structure data in the Cedar Lakes estuary system obtained with traditional sampling gears with data obtained using eDNA sampling using a small sequence of mitochondrial 12S ribosomal RNA gene and a validated taxonomic reference file.ResultFor spring and fall of 2022, eDNA metabarcoding detected a larger number of species than either bag seines or gill nets. Species richness detected via eDNA in two seasons in a single year was comparable with the species richness of agency’s historical record based on traditional gears for Cedar Lakes.ConclusionSeasonal and spatial variation in species richness was similar between traditional and eDNA sampling; however, eDNA metabarcoding allowed detection of several species that would be difficult or impossible to capture with either bag seines or gill nets. We observed two limitations of eDNA metabarcoding. Read depth was not a good index of relative abundance, which limits our ability to infer relative biomass using single samples. Secondly, we observed detection bias in our eDNA results. Specifically, eDNA failed to detect two species of elasmobranchs present when water sampling was performed and eDNA also performed poorly compared to traditional sampling gears for some species of bony fishes. Despite these limitations, eDNA metabarcoding proved to be an efficient and cost‐effective alternative and compliment to traditional fisheries sampling gears for fishery‐independent monitoring of community structure and composition in estuaries of the Gulf of Mexico.

Effects of secondary forest succession on the richness and composition of frog species in humid tropical forest

ABSTRACT Our aim was to evaluate whether the richness and composition of anurans responded to the time of forest regeneration via secondary succession. We sampled the anuran community in a mosaic of areas at three different stages of secondary succession in the Atlantic Forest, southern Brazil. The anurans were collected from nine lentic ponds and from their margins up to a 50 m radius. The late secondary forest sheltered the higher species richness, followed by the primary forest. The spatial variation in species richness was related to the forest succession stage and predominance of arboreal vegetation on the pond edge. The species composition changed throughout the succession stages, regardless of the distance among areas. Along the gradient of forest succession, environmental changes have driven species distribution, limiting the occurrence of forest species and favoring the colonization of areas at the early succession stage by opportunist species. We could observe that the secondary forest succession was a determining factor in the anuran community structure, and with the advancement of the secondary succession, both richness and composition were partly restored. Thus, the conservation of secondary forests might be an efficient strategy to preserve the biodiversity in areas of the Atlantic Forest.

Time-lagged effects of habitat fragmentation on terrestrial mammals in Madagascar.

Biodiversity is severely threatened by habitat destruction. As a consequence of habitat destruction, the remaining habitat becomes more fragmented. This results in time-lagged population extirpations in remaining fragments when these are too small to support populations in the long term. If these time-lagged effects are ignored, the long-term impacts of habitat loss and fragmentation will be underestimated. We quantified the magnitude of time-lagged effects of habitat fragmentation for 157 nonvolant terrestrial mammal species in Madagascar, one of the biodiversity hotspots with the highest rates of habitat loss and fragmentation. We refined species' geographic ranges based on habitat preferences and elevation limits and then estimated which habitat fragments were too small to support a population for at least 100 years given stochastic population fluctuations. We also evaluated whether time-lagged effects would change the threat status of species according to the International Union for the Conservation of Nature (IUCN) Red List assessment framework. We used allometric relationships to obtain the population parameters required to simulate the population dynamics of each species, and we quantified the consequences of uncertainty in these parameter estimates by repeating the analyses with a range of plausible parameter values. Based on the median outcomes, we found that for 34 species (22% of the 157 species) at least 10% of their current habitat contained unviable populations. Eight species (5%) had a higher threat status when accounting for time-lagged effects. Based on 0.95-quantile values, following a precautionary principle, for 108 species (69%) at least 10% of their habitat contained unviable populations, and 51 species (32%) had a higher threat status. Our results highlight the need to preserve continuous habitat and improve connectivity between habitat fragments. Moreover, our findings may help to identify species for which time-lagged effects are most severe and which may thus benefit the most from conservation actions.

Is species richness mediated by functional and genetic divergence? A global analysis in birds.

Unravelling why species richness shows such dramatic spatial variation is an ongoing challenge. Common to many theories is that increasing species richness (e.g. with latitude) requires a compensatory trade-off on an axis of species' ecology. Spatial variation in species richness may also affect genetic diversity if large numbers of coexisting, related species result in smaller population sizes.Here, we test whether increasing species richness results in differential occupation of morphospace by the constituent species, or decreases species' genetic diversity. We test for two potential mechanisms of morphological accommodation: denser packing in ecomorphological space, and expansion of the space. We then test whether species differ in their nucleotide diversity depending on allopatry or sympatry with relatives, indicative of potential genetic consequences of coexistence that would reduce genetic diversity in sympatry. We ask these questions in a spatially explicit framework, using a global database of avian functional trait measurements in combination with >120,000 sequences downloaded from GenBank.We find that higher species richness within families is not systematically correlated with either packing in morphological space or overdispersion but, at the Class level, we find a general positive relationship between packing and species richness, but that points sampled in the tropics have comparatively greater packing than temperate ones relative to their species richness. We find limited evidence that geographical co-occurrence with closely related species or tropical distributions decreases nucleotide diversity of nuclear genes; however, this requires further analysis.Our results suggest that avian families can accumulate species regionally with minimal tradeoffs or cost, implying that external biotic factors do not limit species richness. Read the free Plain Language Summary for this article on the Journal blog.

Geographic context is a key driver of spatial variation of bird species richness during migration

AbstractAimDetermine whether primary productivity or location (distance to the coast) is more important to migrating bird habitat selection.LocationYucatan Peninsula, Mexico.Time periodAugust–December and February–May 2009–2016.TaxaMigratory birds.MethodsUsing eBird data, we modelled spatial variation in species richness as a function of primary productivity and distance to the coast and how the relationships vary with time during spring and autumn migration. We compared the standardized regression coefficients of linear models with a Poisson error distribution.ResultsWe found that three primary productivity indices [normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), heterogeneity] performed similarly in predicting species richness. However, species richness was more strongly associated with distance to the coast. In autumn, richness was higher closer to the coast through most of the season and then shifted inland late in autumn. Richness was also higher in more productive habitats. In spring, richness was higher inland early in the season but then increased closer to the coast. Species richness was relatively similar across the primary productivity gradient, even declining slightly with increasing NDVI.Main conclusionsWe did not find convincing evidence for a strong relationship between species richness and primary productivity. Instead, migration constrains birds such that they concentrate in coastal environments. In autumn, migrants may favour habitats that are both coastal and productive, such as those that occur along the Caribbean coast. In spring, migrants may also use the less productive Gulf of Mexico coast, possibly due to high arthropod production occurring during an otherwise dry time of year.

Altitude and temperature drive anuran community assembly in a Neotropical mountain region

AbstractUnderstanding the spatial variation in species richness and the mechanisms that limit species range sizes along geographical gradients belong to the central research issues in macroecology. Here, we aim to test the topographic and climatic effects on anuran species richness and community composition in mountainous regions in the Brazilian Atlantic Forest biome. We used Individual‐Based Rarefaction Curve (interpolation and extrapolation), Generalized Additive Model (GAM), Midpoint method and Principal Coordinates Analysis (PCoA) to analyze the topographic and climatic effects on anuran community composition, richness, and range sizes in a global biodiversity hotspot. Our results showed that altitude and annual mean temperature and temperature seasonality were the main drivers of species altitudinal range sizes and community assembly in mountainous regions. In conclusion, Anuran community richness peaked at intermediate altitudes following thus a hump‐shaped pattern and corroborated the Rapoport's altitudinal rule as range sizes increased with altitude in mountainous regions from the Atlantic Forest biome. This study revealed new insights into the patterns and drivers of Neotropical anuran communities.Abstract in Portuguese is available with online material.

Testing the causal mechanism of the peninsular effect in passerine birds from South Korea.

The peninsular effect is a geographical phenomenon that explains patterns of species richness. Given that spatial variation in species richness along a peninsular may be driven by multiple processes, we aimed to identify the sources of latitudinal patterns in passerine species richness and test hypotheses regarding (1) recent deterministic processes (climate, primary productivity, forest area, and habitat diversity), (2) anthropogenic processes (habitat fragmentation), and (3) stochastic processes (migration influence) in the Korean peninsula. We used the distribution data of 147 passerine species from 2006 to 2012. Single regression between passerine species richness and latitude supported the existence of the peninsular effect. Mean temperature increased with decreasing latitude, as did habitat diversity but leaf area index and forest area decline. However, mean temperature and forest area only influenced passerine species richness. Although habitat diversity influenced passerine species richness, it was counter to the expectations associated with peninsular effect. The number of habitat patches decreased as latitude increased but it had no effect on passerine species richness. Ratio of migrant species richness showed no significant relationship with leaf area index, forest area, and habitat diversity. However, the ratio of migrant species richness increased with decreasing mean temperature and that contributed to the increase in passerine species. Overall, our finding indicate that the observed species richness pattern in peninsulas with the tip pointing south (in the northern hemisphere) counter to the global latitudinal gradient. These results were caused by the peninsular effect associated with complex mechanism that interact with climate, habitat area, and migrant species inflow.

From town to town: Predicting the taxonomic, functional and phylogenetic diversity of birds using NDVI

Biodiversity mapping in urban areas is imperative for their conservation. Remote sensors produce environmental information, such as the Normalized Difference Vegetation Index (NDVI), an indicator of vegetation cover in urban areas. NDVI can be used to predict the taxonomic, functional and phylogenetic bird diversity in urban areas. Moreover, a predictive model constructed in one city can be used to predict the bird diversity in other cities. The objectives of this study were: 1) to construct and evaluate predictive models between NDVI and taxonomic, functional and phylogenetic diversity of birds in Mar del Plata city, Argentina; and 2) to extrapolate these models to two other cities in the region: Balcarce and Miramar. Generalized additive models were applied to relate bird diversity variations to NDVI. In Mar del Plata, the taxonomic and functional diversity increased with increasing NDVI values, and the predictive models explained 64–81% of the taxonomic and functional diversity variation. The models correctly predicted taxonomic and functional diversity values in additional transects not included in the models, although they had a low predictive power of phylogenetic diversity. The models constructed in Mar del Plata adequately predicted the spatial variation of species diversity (Shannon index) in Balcarce and Miramar, the spatial variation of species richness in Balcarce, and the variation of functional diversity in Miramar. Our analysis revealed that a predictive model of bird diversity based on NDVI patterns created in one city can also depict the expected species diversity in other cities, being a time-saving and cost-effective method to create a tool for urban biodiversity conservation.

The Importance of Including Soil Properties When Disentangling the Drivers of Species Richness: The Case of the Alpine Genus Saxifraga L. in China

Despite the numerous studies on the large-scale patterns of species richness, the spatial variation and determinants of species richness for alpine plant are still an outstanding question and critical to future biodiversity conservation. The genus Saxifraga is a typical alpine plant group with high species richness in the Himalaya-Hengduan mountain regions, China. We performed simple regression models and variance partitioning to assess the importance of different factors, especially soil-related ones, in driving Saxifraga richness patterns. The results showed that environmental energy, habitat heterogeneity, and soil heterogeneity together dominated the spatial variation of species richness. The coarse fragments volume of soil, elevation range, and soil heterogeneity, are positively related to Saxifraga richness. Soil slightly outperforms habitat heterogeneity in predicting the spatial variation of Saxifraga species richness with an explanatory power of 39.3% and 36.6%, respectively. Environmental energy, such as the maximum temperature of the warmest quarter, is negatively correlated with species richness and explains 44.8% of spatial variation of Saxifraga richness. Multiple regression models, including three variables, each representing energy, soil, and habitat heterogeneity, can only explain 53.1% variation of species richness. Variance partitioning outscored 26% of the shared effects of the three variables, while the independent effect of each variable is less than 10%. These results indicated the energy, soil, and habitat heterogeneity together are primary determinants of the spatial variation of Saxifraga species richness. However, there are probably other hidden factors predicting species richness variation due to the low explanatory power of the multiple regression models. Our study emphasizes the significance of soil properties in determining species richness patterns in China, especially for the alpine plant groups. The negative association of species richness with temperature suggests a potential threat of alpine biodiversity loss in HHM from future warming.

Environmental filters determine the distribution of tree species in a threatened biodiversity hotspot in western Mexico

Background: Analyzing interactions between vegetation and environmental factors at regional scales provide information for the understanding of species assemblages.
 Hypotheses: Environmental restrictions at higher elevations produce a decreasing species richness pattern along an elevational gradient and the climatic variables related to temperature and precipitation are the main filters of species distribution.
 Objectives: (1) To identify the different assemblages of tree species occurring in a biodiversity hotspot; (2) to analyze the pattern of tree species richness along an elevational gradient; and (3) to analyze the environmental filters that determine the species distribution.
 Study site: Serranías Meridionales of Jalisco in western Mexico.
 Period of study: 2016-2018.
 Methods: Thirty-three rectangular 0.1 ha plots were established for vegetation and environmental characterization. Cluster and canonical correspondence analyses were conducted to analyze tree species composition. We defined three groups of variables (climatic, relief and soil) to evaluate the influence of environmental filters. We used generalized linear models to assess the contribution of each group to the spatial variation in species richness.
 Results: A total of 63 tree species were recorded. The cluster analysis defined eight groups within three forest types. The species richness showed a hump-shaped pattern along the elevational gradient and the climatic and soil variables explained a considerable amount of variation in the species richness.
 Conclusions: The tree species richness in the Serranías Meridionales de Jalisco is dominated by a striking number of Pinus and Quercus species. This biodiversity hotspot is an important site for the understanding of tree ecological diversification in Mexico.

Epiphytic bryophyte diversity and range distributions along an elevational gradient in Marojejy, Madagascar

AbstractDescribing spatial variation in species richness and understanding its links to ecological mechanisms are complementary approaches for explaining geographical patterns of richness. The study of elevational gradients holds enormous potential for understanding the factors underlying global diversity. This paper investigates the pattern of species richness and range‐size distribution of epiphytic bryophytes along an elevational gradient in Marojejy National Park, northeast Madagascar. The main objectives are to describe bryophyte species composition and endemism in Marojejy National Park, to describe the species richness and distribution patterns of epiphytic bryophytes along an elevational gradient from 250 m to 2050 m and to evaluate the explanatory value of environmental variables for the observed patterns. Bryophyte samples were collected following a nested design with four hierarchical levels: elevational belts, plots, quadrats, and microplots. In total, 254 epiphytic bryophyte species were recorded, comprising 157 liverworts and 97 mosses. Twenty‐three of these are endemic to Madagascar. Species richness exhibits a hump‐shaped pattern along the elevational gradient, peaking at 1,250 m. Eighty‐seven percent of the total recorded species have a range distribution lower than 1,000 m, at which point 36% are restricted to these single elevations. Our results suggest that mean temperature, relative humidity, and vapor pressure deficit play important roles in shaping the richness pattern observed in this study. While the liverwort richness pattern did not correlate to vapor pressure deficit and responded only weakly to relative humidity, the richness pattern shown by mosses correlates well with mean temperature, relative humidity, and vapor pressure deficit.

The geography of biodiversity change in marine and terrestrial assemblages.

Human activities are fundamentally altering biodiversity. Projections of declines at the global scale are contrasted by highly variable trends at local scales, suggesting that biodiversity change may be spatially structured. Here, we examined spatial variation in species richness and composition change using more than 50,000 biodiversity time series from 239 studies and found clear geographic variation in biodiversity change. Rapid compositional change is prevalent, with marine biomes exceeding and terrestrial biomes trailing the overall trend. Assemblage richness is not changing on average, although locations exhibiting increasing and decreasing trends of up to about 20% per year were found in some marine studies. At local scales, widespread compositional reorganization is most often decoupled from richness change, and biodiversity change is strongest and most variable in the oceans.

Spatial variation in phylogenetic diversity of communities of Atlantic Forest harvestmen (Opiliones, Arachnida)

Abstract The study of diversity has become increasingly sophisticated, including the use of measures of phylogenetic diversity. We calculate the spatial variation in species richness, taxonomic beta diversity, and alpha and beta phylogenetic diversity (PDα and PDβ, respectively) of Atlantic Forest harvestman communities using a data set containing 556 species from 68 sites, distributed in 12 Brazilian states. We compare the congruence of phylogenetic and taxonomic diversity patterns, and also compare PDα with null model expectations, to check for phylogenetic clustering or overdispersion in communities. Species richness and PDα are correlated, peaking in southern and south‐eastern coastal sites and decreasing towards the interior and towards the north‐east. PDα in north‐eastern sites was higher than expected, while a clustered phylogenetic pattern characterised most other sites. Communities in the southern and south‐eastern regions were dominated by species from the large family Gonyleptidae, presenting a high richness and a low PDα. As the dominance of Gonyleptidae decreased towards the north, where local communities have fewer species, but a higher PDα, they contain representatives of other families. The beta diversity was more sensitive to the compositional changes involving closely related Gonyleptidae species, while PDβ is more influenced by deeper phylogenetic compositional changes, between more distant lineages. Phylogenetic diversity may be of special importance to assess the conservation value of distantly related lineages. These species‐poor groups are less likely to influence taxonomic‐based diversity analyses, but their importance for conservation arises from their phylogenetic distinctiveness, captured by PDα and PDβ measures.

Modelling the spatial pattern of biodiversity utilizing the high-resolution tree cover data at large scale: Case study in Yunnan province, Southwest China

Explicit biodiversity level at large spatial scale is often indicated by species richness. The spatial variability of species richness has been postulated to be related with influencing factors such as climate, habitat and human activities using many geostastical methods. Understanding the relationship between species richness and its influencing factors is of critical importance for its conservation. As tree cover data with high resolution can reflect the terrestrial habitat with environment, its efficiency for modelling spatial pattern of biodiversity was investigated in this study. The spatial distribution of tree cover and its influencing factors in Yunnan province, and the relationship between tree cover and species richness of mammals and birds were analyzed by linear regression method and Geographically Weighted Regression (GWR) model. The results showed that tree cover in this study region exhibited a substantially spatial heterogeneity, which was affected by human activities, topography and climate. Linear regression analysis showed that tree cover was significantly correlated with the species richness of mammals and birds. The explanatory power (local R2) of GWR model between tree cover and species richness of mammals and birds showed great spatial variability. The predicted spatial distribution of species richness of mammals and birds was consistent with the actual observed values. Our study revealed that the GWR model provides local details of spatial variation in species richness of mammals and birds. These results will be helpful to understand the impact of tree cover on variation of species richness of mammals and birds under global change and will be of theoretical significance for better conservation and management of biodiversity.

Spatial phylogenetics reveals evolutionary constraints on the assembly of a large regional flora.

We used spatial phylogenetics to analyze the assembly of the Wisconsin flora, linking processes of dispersal and niche evolution to spatial patterns of floristic and phylogenetic diversity and testing whether phylogenetic niche conservatism can account for these patterns. We used digitized records and a new molecular phylogeny for 93% of vascular plants in Wisconsin to estimate spatial variation in species richness and phylogenetic α and β diversity in a native flora shaped mainly by postglacial dispersal and response to environmental gradients. We developed distribution models for all species and used these to infer fine-scale variation in potential diversity, phylogenetic distance, and interspecific range overlaps. We identified 11 bioregions based on floristic composition, mapped areas of neo- and paleo-endemism to establish new conservation priorities and predict how community-assembly patterns should shift with climatic change. Spatial phylogenetic turnover most strongly reflects differences in temperature and spatial distance. For all vascular plants, assemblages shift from phylogenetically clustered to overdispersed northward, contrary to most other studies. This pattern is lost for angiosperms alone, illustrating the importance of phylogenetic scale. Species ranges and assemblage composition appear driven primarily by phylogenetic niche conservatism. Closely related species are ecologically similar and occupy similar territories. The average level and geographic structure of plant phylogenetic diversity within Wisconsin are expected to greatly decline over the next half century, while potential species richness will increase throughout the state. Our methods can be applied to allochthonous communities throughout the world.

Forecasted homogenization of high Arctic vegetation communities under climate change

AbstractAimClimate change results in increasing temperature and modified precipitation regimes in the High Arctic. Models can help anticipate the consequences on future biotic dynamics, e.g. vegetation. In rugged terrain, forecasts should consider fine‐scale spatial variability in environmental conditions that are proximally linked to plant performance. Here, we forecasted Arctic plant community response to future climate change using high‐resolution environmental variables.LocationZackenberg in the High Arctic of Greenland.MethodsUsing a combination of remote‐sensing data and field measurements, we interpolated soil moisture and temperature at 1 m resolution together with spatial data on snow cover and solar radiation. We calibrated stacked species distribution models (S‐SDMs) with data from 200 vegetation plots. To explore the sensitivity of Arctic communities to climate change, we forecasted these models under simulated increases in temperature and changes (positive or negative) in snow cover and soil moisture, corresponding to more winter and/or summer precipitation and higher frequencies of summer droughts.ResultsS‐SDMs associated with high‐resolution environmental variables were able to reproduce the spatial variation in species richness and plant community structure along a mountain slope in Zackenberg. Model forecasts under climate change revealed that most species reacted to a combination of changes in soil moisture and temperature, and changes in these two variables resulted in an extensive restructuring of the distributions of species assemblages. In most scenarios, a gradual homogenization of communities was forecasted due to shrub expansion.Main conclusionsIncreasing temperatures and altered soil moisture were predicted to turn the currently highly heterogeneous tundra landscape at Zackenberg into homogenous dwarf‐shrub tundra. Such homogenization of vegetation communities may have profound ramifications for species, interaction webs, and ecosystem processes via modifications to the surface albedo, energy and water balance, as well as snow accumulation and permafrost.

PHYLOGENETIC DIVERSITY AS A KEY TO UNDERSTAND MECHANISMS OF NEW WORLD MARSUPIALS DIVERSIFICATION (DIDELPHIMORPHIA: DIDELPHIDAE)

Phylogenetic diversity is a measure that can provide information about the history of diversification of a lineage and the events that shaped contemporary communities, as macroevolutionary processes leave marks on the relationships of the lineages. However, this approach has been applied primarily in studies on local scales, and rarely has been employed to analyze regional or continental patterns. Here we mapped spatial patterns that could identify regions of intense diversification or dispersion of the New World marsupials (order Didelphimorphia) by analyzing the spatial variation of species richness and phylogenetic diversity (PD). Based on the phylogeny and occurrences of the Didelphimorphia species we calculated three diversity measures, and applied a model selection by information criteria approach to identify the relative importance of four environmental determinants: potential evapotranspiration, productivity, topography, and the number of ecoregions. Species richness and PD are highly correlated, and both are associated to productivity, topography, and number of ecoregions, while relative PD (rPD) is associated to potential evapotranspiration and topography. Productivity showed a clear positive relation with species richness and PD, consistent with the productive energy, but rPD was affected by potential evapotranspiration, which points to a role of environmental energy in the process of diversification. This study is pioneer in testing and confirming effects of the productive and environmental energy on species diversification as other studies analyzing the same questions neither could isolate the effects of the two energy measurements due to their collinearity, nor did make any distinction between energy hypotheses. Physical geography and ecological differences among habitats can shape biogeographical patterns and drive speciation in continental faunas, leaving marks on their phylogenetic register. Comparing patterns among other autochthonous taxa whose evolutionary history and geographic range is congruent to the Didelphimorphia could provide interesting clues about the processes that shaped the diversification of Neotropical fauna.

The more-individuals hypothesis revisited: the role of community abundance in species richness regulation and the productivity-diversity relationship.

Species richness increases with energy availability, yet there is little consensus as to the exact processes driving this species-energy relationship. The most straightforward explanation is the more-individuals hypothesis (MIH). It states that higher energy availability promotes a higher total number of individuals in a community, which consequently increases species richness by allowing for a greater number of species with viable populations. Empirical support for the MIH is mixed, partially due to the lack of proper formalisation of the MIH and consequent confusion as to its exact predictions. Here, we review the evidence of the MIH and evaluate the reliability of various predictions that have been tested. There is only limited evidence that spatial variation in species richness is driven by variation in the total number of individuals. There are also problems with measures of energy availability, with scale-dependence, and with the direction of causality, as the total number of individuals may sometimes itself be driven by the number of species. However, even in such a case the total number of individuals may be involved in diversity regulation. We propose a formal theory that encompasses these processes, clarifying how the different factors affecting diversity dynamics can be disentangled.