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Open Access Publications from the University of California

Frontiers of Biogeography

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Frontiers of Biogeography (FoB) is the scientific journal of the International Biogeography Society (IBS,, a not-for-profit organization dedicated to promotion of and public understanding of the biogeographical sciences.  IBS launched FoB to provide an independent forum for biogeographical science, with the academic standards expected of a journal operated by and for an academic society.

Issue cover
A caddisfly larva, belonging to the Hydrobiosidae family (Atopsyche sp.), sampled in a small stream in the “la Hotte" Biosphere Reserve, Haiti. Whereas, the area is well known for its high species richness and high endemism of many taxa (e.g. reptiles, amphibians), the ecology of aquatic invertebrates communities is generally poorly documented. In this issue, Cinéas & Dolédec look for the main environmental factors constraining aquatic insect species richness, distribution and endemism in the Caribbean islands. Photo by C. Cinéas.


Research Articles

Which is the richest of them all? Comparing area-adjusted plant diversities of Mediterranean- and tropical-climate regions

Mediterranean- and tropical-climate regions harbour the richest regional-scale floras globally. Until recently, however, comparisons of their diversities have been hindered by a lack of comprehensive inventories of tropical floras. Using taxonomically verified floras, we analyse area-adjusted plant diversities of five Mediterranean- and 35 tropical-climate regions to determine which are the most species-rich regions on Earth. On average, the Neotropics and tropical Southeast Asia support the most diverse floras globally. However, the area-adjusted diversities of the richest floras in these tropical regions are matched by those of two Mediterranean-climate floras, namely the Cape (second richest) and Mediterranean Basin (sixth richest). Except for Madagascar and Burundi, the Afrotropical regions were substantially less diverse than other tropical floras and half of the Afrotropical floras were poorer than the least diverse Mediterranean-climate region, namely Central Chile. We evaluate the likely ecological and evolutionary drivers of these plant diversity patterns in terms of three hypotheses that are apposite for global scale comparisons, namely water-energy dynamics, biome stability, and ecological heterogeneity. Water-energy dynamics appear to have little influence in explaining these diversity patterns: nodes of high global plant diversity are associated with climates that support year-round plant production (tropical climates) and those where the growing season is constrained by a winter rainfall regime (Mediterranean-type climates). Moreover, while the Afrotropics have higher primary production than the Neotropics and Southeast Asian tropics, they have markedly lower plant diversity. Instead, these patterns appear to be consistent with the hypothesis that the synergy of historical biome stability (reducing extinction rates) and high ecological heterogeneity (promoting speciation rates) better explain global patterns of regional-scale plant diversity.

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The macroecology of community energy use in terrestrial vertebrates

Energy is a fundamental macroecological property as it governs all ecological processes and interactions. Understanding variation in community energy use and its correlations is crucial to knowing how communities function across the globe. As an organism’s metabolic rate equates to its rate of energy flow, individual rates can predict community-level functioning. Here, daily rates of community energy flow are calculated for 118 bat, 109 bird, and 196 non-volant small mammal inventories from around the world. These were scaled up from individual metabolic rates that were obtained for the 416 bat, 1880 bird, and 562 small mammal species present in the samples. While controlling for spatial autocorrelation, rates were contrasted and compared to various ecological, environmental, geographic, and anthropogenic variables, using a method of sequential regression that renders the variables orthogonal to each other, thus addressing the issue of collinearity. In all groups, there is a strong positive correlation between community energy use and community mass, with biomass being the primary determinant of community energy flow. More surprisingly, there are strong biogeographic differences within and between groups. Bat communities have consistently higher rates of energy flow in the Neotropics, while small mammal communities have higher rates relative to mass in Holarctic realms. Investigations of individual-level patterns reveal that these differences are a direct result of contrasting patterns of abundance, average individual mass, and metabolic rates. These results indicate that community energy use is strongly linked to differences in ecology and evolutionary history within and among groups.

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Invasive risk assessment and expansion of the realized niche of the Oriental Garden Lizard Calotes versicolor species complex (Daudin, 1802)

Correlative species distribution modelling (SDM) can be a useful tool to quantify a species’ realized niche and to predict its potential distribution for non-native ranges. The agamid lizard Calotes versicolor s.l. belongs to the most widely distributed reptile taxa worldwide. In the past, C. versicolor s.l. has been introduced to several countries, including regions in the Oriental, the Neotropical and the Afrotropical realms, where strong negative impact on the local fauna is assumed. Due to the complicated taxonomy and the existence of several cryptic species, which are covered by this taxon, we used C. versicolor sensu lato and its four subtaxa (C. versicolor sensu stricto, C. irawadi, C. vultuosus, C. farooqi) as target species to (1) compute correlative SDMs for C. versicolor s.l. and its subtaxa and project them across the globe to highlight climatically suitable areas of risk for future invasion and (2) based on the ecological niche concept, we investigate if the species complex expanded its realized climatic niche during the invasion process. We use two different SDM approaches, namely n-dimensional hypervolumes and Maxent. N-dimensional hypervolumes are a non-hierarchically ranked approach, which is a useful tool to investigate the expansion in the realized niche, while Maxent, a hierarchically ranked model, is used to focus on potentially suitable areas for future invasion. We calculated two final models for C. versicolor s.l., one based on records from the native range and one based on records from the native and invaded range, as well as one model for each subtaxon. Our results show a geographic expansion into novel climatic conditions as well as an expansion in the realized niche. Our results reveal that C. versicolor s.l. is currently inhabiting 13% of its potential range but could find suitable climatic conditions on a global surface area between 14,025,100 km2 and 53,142,600 km2. Our predictions reveal large areas of highly suitable climatic conditions for the Oriental, Australian, Afrotropical and Neotropical realms, whereas only small regions of the Palearctic and Nearctic realms provide moderately suitable conditions. Further, some localities, especially those with a high amount of human traffic like ports or airports, might act as multiplicators and might therefore be a stepping stone into further areas.

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Species richness and composition of Caribbean aquatic entomofauna: role of climate, island area, and distance to mainland

From a literature review, we constructed a database comprising >1000 freshwater insect species (especially Odonata, Coleoptera, Trichoptera, Ephemeroptera; OCTE) in 26 Geographical Caribbean Units (GCU) and quantified local filtering (climate heterogeneity, annual rainfall, annual temperature), geography (area, distance from the mainland) and emergence age as a proxy for island ontogeny. We investigated the relative role of these variables on the species richness, endemism and composition of the units using island species-area relationship (ISAR), generalised linear modelling (GLM) and nonmetric multidimensional scaling (NMDS). In addition, we analysed the spatial patterns of species richness and composition using Moran’s I index. ISAR generally demonstrated one or two thresholds and continuous or discontinuous responses according to OCTE groups. A small island effect could be detected for Trichoptera and Ephemeroptera richness, whereas Odonata and Coleoptera only demonstrated differences in slope between smaller and larger GCUs. Area, climate heterogeneity, maximal rainfall and distance from mainland were major drivers of species composition in GCUs, whereas local climate variables were of main importance for the endemism rate. Due to the potential complexity of the Caribbean island ontogeny, middle-stage islands had an expected higher freshwater invertebrate richness than younger ones but an unexpected lower richness compared to older islands. Finally, the degree of colonization of islands was linked to the dispersal ability of species, with Odonata and Coleoptera having larger distribution ranges than Trichoptera and Ephemeroptera, which were more restricted by their comparatively narrow ecological niches. The high endemism (>60%) found in the Caribbean freshwaters calls for more conservation effort in managing these highly threatened freshwater environments.

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Biogeographic and β-diversity patterns for southern Africa’s native freshwater fishes: a synthesis

Freshwater habitats are some of the most imperilled ecosystems in the world as they harbour numerous species threatened with extinction. In tropical Africa, acute deficiency of scientific data on the distribution patterns of freshwater biodiversity hampers successful conservation interventions. The number of newly described and resurrected freshwater fish species in southern Africa has increased considerably since the last bioregionalization effort, nearly three decades ago.  Here, we utilize an updated matrix of catchment-scale native freshwater fish distributions to re-evaluate earlier biogeographic zonation patterns and examine the relative contribution of beta diversity to observed spatial distribution patterns in the subregion. Cluster analysis applied to an incidence data matrix of 259 native freshwater fish species from 17 drainage basins resulted in three major biogeographic zones, which generally corresponded to patterns shown in earlier studies. However, our analysis further revealed a split of the Eastern zone into two sub-clusters -- Northeast and Southeast. We decomposed the overall beta diversity (βSOR), of southern Africa’s native freshwater fishes into its nestedness (βSNE) and turnover (βSIM) components. In all three zones, the proportion of the nestedness resultant component (βratio) was less than 0.5, implying that the compositional variation in overall beta diversity was mainly driven by species turnover. The dominance of the turnover component to overall β-diversity suggests that conservation initiatives targeting multiple sites across broad spatial scales are likely to provide better outcomes for southern Africa’s native ichthyofauna than a few large, protected areas. We discuss the relative contribution of environmental heterogeneity and dispersal limitation on observed bioregionalization and β-diversity patterns of native freshwater fishes in southern Africa. Incomplete knowledge of the taxonomic diversity of southern Africa’s ichthyofauna affects the mapping of distribution patterns, stressing the need for increased sampling efforts, especially in high diversity drainages that border the Congo basin.

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Can sea snakes slither through seascape structure? Comparative phylogeography and population genetics of Hydrophis group sea snakes in Australia and Southeast Asia

Pleistocene sea level changes substantially shaped the biogeography of northern Australia and the Indo-Malayan Archipelago (IMA). For co-distributed species, their phylogeographic and population genetic patterns are expected to be concomitant with geological transformations of the Pleistocene. However, species-specific ecologies and life history traits may also be influential in generating patterns which depart from simple expectations arising from biogeographic features. Thus, comparative population genetic studies, which use taxa that reduces variation in taxonomy and geography, may refine our understanding of how biogeographic elements shape the populations of co-occurring species. Here, we sampled two sea snake species, Hydrophis curtus and H. elegans, throughout their known ranges in the IMA and northern Australia. These sea snakes have similar life history strategies and ecologies as well as overlapping distributions across the Torres Strait, a well-known biogeographic feature. We analysed two mitochondrial DNA (mtDNA) fragments and 10 microsatellite loci using traditional population genetic approaches and used Bayesian clustering methods to examine species- specific phylogenetic relationships, genetic diversities, and population genetic structures. For both species, we found a consistent lack of significant genetic variation among sampling sites across the Gulf of Carpentaria (GOC) and the Great Barrier Reef (GBR). Similarly, Bayesian clustering showed no to weak genetic partitioning across the historical Torres Strait land bridge. Both species sampled in Australia displayed population expansion signatures in tests using mtDNA and microsatellite markers. We conclude that the phylogeographic and population genetic patterns of these sea snake species do not align with the Torres Strait land bridge. This lack of population genetic structure departs from previous findings on Aipysurus sea snakes and may be linked to the association of Hydrophis species to soft sediment habitats typically found across northern Australia. These divergent patterns between the sea snake groups present the importance of considering taxon-specific attributes in formulating conservation strategies.

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Do genetically informed distribution models improve range predictions in past climates? A case study with balsam poplar

Species distribution models (SDMs) are one of the most widely used approaches to predict changes in habitat suitability in response to climate change. However, as typically implemented, SDMs treat species as genetically uniform throughout their ranges and thereby ignore potentially important genetic differences between populations. While numerous studies have used SDMs to model genetically based subgroupings within species, the ability of such models to be transferred to new times has rarely been evaluated. Here, we used standard and genetically informed distribution models (gSDMs) to predict the future and past range of balsam poplar (Populus balsamifera L.). We then assessed model transferability of standard SDMs and gSDMs using balsam poplar fossil pollen and macrofossil occurrences. In general, standard and gSDMs performed similarly through time, with both predicting a northward expanding range from refugia as glaciers receded over the past 22 ky BP and declining suitable area in future climates. Both standard and gSDMs showed moderate abilities to distinguish balsam poplar fossils from pseudo-absences but tended to predict lower suitability at fossil sites during the Pleistocene-Holocene transition. Although gSDMs applied to balsam poplar did not prove more transferable than standard SDMs, they provided numerous unique insights, such as the change in suitable area of genetic clusters through time and potential refugial locations. We argue more research is needed to determine which species may benefit most from the gSDM approach and to test gSDMs with temporally or spatially independent occurrences, as is often recommended for standard SDMs.

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