Species-rich Biome Research Articles

How diverse are the mountain karst forests of Mexico?

Tropical forests on karstic relief (tropical karst forest) are among the most species-rich biomes. These forests play pivotal roles as global climate regulators and for human wellbeing. Their long-term conservation could be central to global climate mitigation and biodiversity conservation. In Mexico, karst landscapes occupy 20% of the total land surface and are distributed mainly in the southeast of the country, along the eastern slope, and in the Yucatan Peninsula. Within each of these areas, the following types of karst occur: coastal karst, plain karst, hill karst, and mountain karst (low, medium, high). Mountain karst cover 2.07% of Mexico's land surface and are covered by tropical rainforests, montane cloud forests, and tropical deciduous forests. These are probably one of the most diverse biomes in Mexico. However, the mountain karst forests of Mexico have received little attention, and very little is known about their diversity. Here, we evaluated the vascular plant species richness within the mountain karst forests of Mexico. We assembled the first, largest, and most comprehensive datasets of Mexican mountain karst forest species, from different public databases (CONABIO, GBIF, IBdata-UNAM), which included a critical review of all data. We compiled a list of the families, genera, and species present within the mountain karst forests of Mexico. Taxa that best characterize these forests were identified based on their spatial correlation with this biome. We explored biodiversity patterns, identifying areas with the highest species richness, endemism centers, and areas of relatively low sampling intensity. We found that within the mountain karst forests of Mexico there are representatives of 11,771 vascular plant species (253 families and 2,254 genera), ca. 50% of the Mexican flora. We identified 372 species endemic to these forests. According to preliminary IUCN red list criteria, 2,477 species are under some category of conservation risk, of which 456 (3.8%) are endangered. Most of the Mexican mountain karst forests have been extensively explored and six allopatric, species-rich areas were identified. Compared to other regions in the world, the mountain karst forests of Mexico are one of the most diverse biomes. They contain more species than some entire montane systems in Mexico such as Sierra Madre Oriental, and Sierra Madre del Sur. Also, the mountain karst forests of Mexico are most diverse than similar forests of South America and Asia, even if considering the effect of different sampling areas. The fact that mountain karst forests are embedded in areas of high biotic diversity, probably contributes to their great floristic diversity. Thus, the mountain karst forests of Mexico are an important source of diversity and shelters a large percentage of the Mexican flora.

Comparative richness patterns of range sizes and life forms of Apocynaceae along forest–savanna transitions in Brazil

Abstract Brazilian moist forests and savannas are some of the most species-rich biomes in the Neotropics. In the transition zones between these regions, ecotones often accumulate even higher taxonomic diversity. However, whether these ecotonal communities consist of overlapping species widespread from the neighbouring biomes or a specific set of locally adapted species still needs to be clarified. Regional differences in species richness may be influenced by factors such as species' environmental tolerances, life forms, or species’ range sizes. To investigate the species richness found in ecotones, we used the ‘milk-weed’ family (Apocynaceae), which comprises both widespread and narrowly distributed trees, lianas, and shrubs, as a model to evaluate if (i) their observed richness in ecotones is promoted by widespread species or by locally adapted species; (ii) trees, lianas, and shrubs show different richness patterns in savannas, ecotones, and forests; and (iii) species found in ecotones have broader environmental tolerances than other species in the family. We used a taxonomically curated georeferenced dataset to compare the range sizes of 643 species of Apocynaceae from 73 genera listed for Brazil, comprising 298 species with a liana life form and 345 trees, herbs, or shrubs. We recorded 335 predominantly forest species, 56 savanna species, and 152 ecotone species, for which we quantified species richness, areas of occurrence, precipitation, and temperature ranges and tested for differences in range sizes and environmental tolerances between habits and ecoregions. Our results indicate that (i) Apocynaceae species occurring in ecotones have wider geographical ranges than species not occurring in ecotones; (ii) lianas showed higher area-weighted richness in ecotones than other life forms; and (iii) species found in ecotones had broader environmental tolerances than species restricted to moist forests or savannas. These results indicate that the species richness found in ecotones between savannas and moist forests in Brazil is not necessarily a consequence of higher endemism and local adaptation but may also be a result of overlapping ranges of widespread species typically associated with neighbouring biomes. Together, our findings add to our understanding of ecotones and biomes as continuous, gradual biogeographical transitions instead of sharply defined ecological units.

Taxonomic notes and key to the West Palearctic Antocha (Antocha) Osten Sacken, 1860 (Diptera, Limoniidae) with description of a new species from Morocco.

The Mediterranean Region of the West Palearctic is one of the most species-rich biomes in the world, hosting a high level of endemism and relict species with important conservation value. The North Africa Atlas Mountains (spanning Morocco, Algeria and Tunisia) belong to a poorly-investigated region of the Mediterranean area, with overlooked aquatic biodiversity; hence, a number of species still remain to be discovered. The subgenus Antocha (Antocha) Osten Sacken, 1860 is recorded for the first time from Africa, with a description of A. (A.) staryi Keresztes & Mabrouki sp. nov. from hilly regions of the Middle Atlas region, Morocco. The unique design of the male terminalia differentiates well the newly-discovered species from its closely-related and range-restricted A. (A.) phoenicia Thomas and Dia, 1982. This is in contrast with the high intraspecific and geographically poorly-defined variability of the widespread A. (A.) vitripennis (Meigen, 1830), for which morphological variability of male genital structures is discussed.Illustrations of male genital parts, distribution data and key to the species from the West Palearctic area are also provided.

The emergence of the tropical rainforest biome in the Cretaceous

Abstract. Modern tropical rainforests (TRFs) are one of the most ecologically important and species-rich biomes on the planet. However, the origin of modern TRFs is still debated, especially due to the incongruence between the fossil record and molecular data. Here, we test whether Campanian assemblages from northeastern Africa could represent fossil TRF vegetation. In so doing, we compare the investigated assemblages with other assemblages known to represent temperate forests, subtropical forests, and TRF in terms of leaf physiognomy, species richness, and taxonomic composition. We conclude based on fossil leaves that modern-looking TRFs already existed since 80 Ma during the Campanian in northeastern Africa in an area corresponding to 10 % of the modern Amazonian or 25 % of the Congolese TRF. The apparent conflict between the fossil record and phylogenetic evidence is due to the nearly complete absence of published tropical floras for the Cretaceous.

Surge in global metal mining threatens vulnerable ecosystems

Mining activities induce profound changes to societies and the environment they inhabit. With global extraction of metal ores doubling over the past two decades, pressures related to mining have dramatically increased. In this paper, we explore where growing global metal extraction has particularly taken effect. Using fine-grain data, we investigate the spatial and temporal distribution of mining of nine metal ores (bauxite, copper, gold, iron, lead, manganese, nickel, silver and zinc) across approximately 3,000 sites of extraction worldwide between 2000 and 2019. To approach the related environmental implications, we intersect mining sites with terrestrial biomes, protected areas, and watersheds categorised by water availability. We find that 79% of global metal ore extraction in 2019 originated from five of the six most species-rich biomes, with mining volumes doubling since 2000 in tropical moist forest ecosystems. We also find that half of global metal ore extraction took place at 20 km or less from protected territories. Further, 90% of all considered extraction sites correspond to below-average relative water availability, with particularly copper and gold mining occurring in areas with significant water scarcity. Our study has far-reaching implications for future global and local policy and resource management responses to mitigate the negative effects of the expected expansion of metal mining.

C4 grass functional traits are correlated with biotic and abiotic gradients in an African savanna

Savanna is a species-rich biome, that includes many modern mammal lineages and C4 grass (Poaceae) species. The greater productivity and grazing pressure associated with savannas is likely attributable to the foliar traits of the grasses they support. Thus, it is important to understand the complex relationships between the abiotic environment, foliar attributes and the floristic composition of savanna grasses, and the supported grazer densities. We sampled 37 grass communities in the Kruger National Park (South Africa) across three soil types and along a rainfall gradient and found that these communities lack strong phylogenetic structure. We then measured specific leaf area and leaf tensile strength for 384 individuals representing 66 species and found that both traits were strongly phylogenetically structured and associated with both rainfall and soil type. Finally, we found that grazer densities in the Park are correlated with the foliar traits of the associated grass communities, but the resolution of our data do not allow for a thorough analysis of this association. Our results demonstrate the complex interactions between climate, soils and grazer densities relative to C4 grass functional traits.

A new and unusual species of Hericium (Basidiomycota: Russulales, Hericiaceae) from the Dja Biosphere Reserve, Cameroon

Tropical rainforests form the most species-rich biome on the earth. The Dja Biosphere Reserve (DBR) in Cameroon is a biodiverse tropical forest characterized in part by upland monodominant stands of the ectomycorrhizal (ECM) Gilbertiodendron dewevrei and ECM Uapaca spp. scattered along river banks. This mostly primary Guineo-Congolian evergreen forest harbors natural populations of large megafauna and numerous plant and fungal species. Studies have indicated that some ECM fungal groups of the large order Russulales are abundant in certain localities in the tropics, including the DBR. However, currently, other predominantly wood-decaying families of Russulales are poorly represented in Africa. For example, only three records of the saprotrophic genus Hericium (Russulales, Hericiaceae) are known from the African continent. Here, we describe a new species of Hericium recently collected from the DBR. Morphological characteristics and molecular phylogenetic analyses support placement of the Cameroonian collection in Hericium and its recognition as a new species within a larger H. coralloides species complex. The new species, H. bembedjaense, differs from H. coralloides in its smaller basidiospores (2.6–3.0 × 1.7–2.2 μm compared to 3.5–5.0 × 2.8–4.2 μm) and longer basidia (up to 27.0 μm compared to 15.0 μm). It differs from all other described Hericium species in the production of pleurocystidia. This is the first species of Hericiaceae known from sub-Saharan lowland tropical evergreen forests. This study highlights the need to increase fungal sampling in species-rich tropical forests such as those of the Congo Basin.

Charcoal identification in a species-rich environment: The example of Dibamba, Cameroon

Identification of archaeological or soil charcoal in a species-rich biome, such as the Central African rainforest, is challenging because of the large number of woody taxa with similar and overlapping wood anatomical features. Valid environmental or archaeological interpretations can only derive from reliable and transparent identifications that allow comparison of and referencing between different charcoal assemblages. The identification of 30 archaeological charcoal types from the site Dibamba in southern Cameroon serves as a starting point for a discussion on classification and naming. These 30 types are fully documented and illustrated in the Supplementary Online Material (SOM). The discussion underlines the basics of “good practice” of charcoal identification in a speciesrich tropical environment. The value of differential diagnosis is stressed, as is the importance of leaving identification levels on higher taxonomic level if necessary. We argue that the level of identification must be reflected in the name of the charcoal type. Names of charcoal types are written in small capitals to clearly distinguish them from botanical taxa with which they are not necessarily identical. The Dibamba charcoal assemblage offers the first and so far unique possibility to directly comprehend human impact on the structure and composition of West Central African rainforest over the last 3000 years. The paleoenvironmental significance of the results presented here will be subject of a forthcoming publication.

ATLANTIC BATS: a data set of bat communities from the Atlantic Forests of South America.

Bats are the second most diverse mammal order and they provide vital ecosystem functions (e.g., pollination, seed dispersal, and nutrient flux in caves) and services (e.g., crop pest suppression). Bats are also important vectors of infectious diseases, harboring more than 100 different virus types. In the present study, we compiled information on bat communities from the Atlantic Forests of South America, a species-rich biome that is highly threatened by habitat loss and fragmentation. The ATLANTIC BATS data set comprises 135 quantitative studies carried out in 205 sites, which cover most vegetation types of the tropical and subtropical Atlantic Forest: dense ombrophilous forest, mixed ombrophilous forest, semideciduous forest, deciduous forest, savanna, steppe, and open ombrophilous forest. The data set includes information on more than 90,000 captures of 98 bat species of eight families. Species richness averaged 12.1 per site, with a median value of 10 species (ranging from 1 to 53 species). Six species occurred in more than 50% of the communities: Artibeus lituratus, Carollia perspicillata, Sturnira lilium, Artibeus fimbriatus, Glossophaga soricina, and Platyrrhinus lineatus. The number of captures divided by sampling effort, a proxy for abundance, varied from 0.000001 to 0.77 individuals·h-1 ·m-2 (0.04 ± 0.007 individuals·h-1 ·m-2 ). Our data set reveals a hyper-dominance of eight species that together that comprise 80% of all captures: Platyrrhinus lineatus (2.3%), Molossus molossus (2.8%), Artibeus obscurus (3.4%), Artibeus planirostris (5.2%), Artibeus fimbriatus (7%), Sturnira lilium (14.5%), Carollia perspicillata (15.6%), and Artibeus lituratus (29.2%).

Nesting ecology of the oil-collecting bee Centris (Melacentris) conspersa Mocsáry and its potential association with the cleptoparasite Cyphomelissa diabolica Friese (Apidae: Centridini, Ericrocidini)

The genus Centris is by far the most diverse group of oil-collecting bees worldwide. In spite of its broad distributional range through Americas, data on the biology of several species remain unknown. We aimed to study the nesting ecology of Centris (Melacentris) conspersa in two islands in the Atlantic Forest domain, Southeastern Brazil. In both areas, nests were constructed in sloping, shaded areas of clayey soil. Two specimens emerged around one year after the brood cells were collected at the nesting site, indicating that this species is likely to be univoltine. Four females of the cuckoo bee Cyphomelissa diabolica were recorded flying over nest entrances of C. conspersa, what may be the first putative host record for this cleptoparasitic genus. Also, the mutillid Hoplomutilla spinosa was also registered at the nest aggregation. The pollen analysis of the residual content of 32 brood cells revealed a narrow spectrum of plants visited, with only six pollen types from five botanical families. Stigmaphyllon arenicola (Malpighiaceae) was the lone floral oil source identified, and Senna multijuga (Fabaceae) pollen grains were found dominant (63.5 to 100%) in all samples analyzed. Despite occurring in a plant species-rich biome as the Atlantic Forest, C. conspersa can be classified as an oligolectic bee species concerning both pollen and oil collection.

Spectral niche segregation and community organization in a tropical cricket assemblage

In species-rich biomes such as tropical rainforests, the efficiency of intraspecific acoustic communication will strongly depend on the degree of signal overlap. Signal interference deteriorates detection, recognition, and localization of conspecific signals. Thus, the communication space should be partitioned sufficiently to reduce masking interference and to promote intraspecific communication. Here, we studied the community organization of a tropical cricket assemblage with respect to its multidimensional niche axes, such as song frequencies, space (horizontal and vertical), and time, affecting acoustic communication. We used the null model approach to test whether observed community patterns differed from those expected by chance. The assemblage clearly showed partitioning in the spectral domain of calling frequencies of their songs. Furthermore, the range of song frequencies occupied by species is positively correlated with the distance to the average calling frequency of its adjacent neighbors. Thus, species tended to use a greater range of frequency channels for intraspecific communication if the frequency space is available. Our results support the idea that competition for the acoustic communication channel may have resulted in niche segregation along the frequency axes. Concerning the spatiotemporal organization at the community level the spatial (horizontal) distribution appeared to be randomly structured, whereas we found a significant vertical stratification between species. At a temporal scale, the assemblage aggregated their calling activity with an observed niche overlap significantly greater than expected by chance. However, combining the spatial and temporal distribution resulted in low co-occurrence of pairwise species association, consequently reducing chances for masking events.

Recent assembly of the Cerrado, a neotropical plant diversity hotspot, by in situ evolution of adaptations to fire

The relative importance of local ecological and larger-scale historical processes in causing differences in species richness across the globe remains keenly debated. To gain insight into these questions, we investigated the assembly of plant diversity in the Cerrado in South America, the world's most species-rich tropical savanna. Time-calibrated phylogenies suggest that Cerrado lineages started to diversify less than 10 Mya, with most lineages diversifying at 4 Mya or less, coinciding with the rise to dominance of flammable C4 grasses and expansion of the savanna biome worldwide. These plant phylogenies show that Cerrado lineages are strongly associated with adaptations to fire and have sister groups in largely fire-free nearby wet forest, seasonally dry forest, subtropical grassland, or wetland vegetation. These findings imply that the Cerrado formed in situ via recent and frequent adaptive shifts to resist fire, rather than via dispersal of lineages already adapted to fire. The location of the Cerrado surrounded by a diverse array of species-rich biomes, and the apparently modest adaptive barrier posed by fire, are likely to have contributed to its striking species richness. These findings add to growing evidence that the origins and historical assembly of species-rich biomes have been idiosyncratic, driven in large part by unique features of regional- and continental-scale geohistory and that different historical processes can lead to similar levels of modern species richness.

A PHYLOGENETIC PERSPECTIVE ON ELEVATIONAL SPECIES RICHNESS PATTERNS IN MIDDLE AMERICAN TREEFROGS: WHY SO FEW SPECIES IN LOWLAND TROPICAL RAINFORESTS?

Differences in species richness at different elevations are widespread and important for conservation, but the causes of these patterns remain poorly understood. Here, we use a phylogenetic perspective to address the evolutionary and biogeographic processes that underlie elevational diversity patterns within a region. We focus on a diverse but well-studied fauna of tropical amphibians, the hylid frogs of Middle America. Middle American treefrogs show a "hump-shaped" pattern of species richness (common in many organisms and regions), with the highest regional diversity at intermediate elevations. We reconstructed phylogenetic relationships among 138 species by combining new and published sequence data from 10 genes and then used this phylogeny to infer evolutionary rates and patterns. The high species richness of intermediate elevations seems to result from two factors. First, a tendency for montane clades to have higher rates of diversification. Second, the early colonization of montane regions, leaving less time for speciation to build up species richness in lowland regions (including tropical rainforests) that have been colonized more recently. This "time-for-speciation" effect may explain many diversity patterns and has important implications for conservation. The results also imply that local-scale environmental factors alone may be insufficient to explain the high species richness of lowland tropical rainforests, and that diversification rates are lower in earth's most species-rich biome.

Insights into the historical construction of species‐rich biomes from dated plant phylogenies, neutral ecological theory and phylogenetic community structure

Analytical methods are now available that can date all nodes in a molecular phylogenetic tree with one calibration, and which correct for variable rates of DNA substitution in different lineages. Although these techniques are approximate, they offer a new tool to investigate the historical construction of species-rich biomes. Dated phylogenies of globally distributed plant families often indicate that dispersal, even across oceans, rather than plate tectonics, has generated their wide distributions. By contrast, there are indications that animal lineages have undergone less long distance dispersal. Dating the origin of biome-specific plant groups offers a means of estimating the age of the biomes they characterize. However, rather than a simple emphasis on biome age, we stress the importance of studies that seek to unravel the processes that have led to the accumulation of large numbers of species in some biomes. The synthesis of biological inventory, systematics and evolutionary biology offered by the frameworks of neutral ecological theory and phylogenetic community structure offers a promising route for future work.

Introduction and synthesis: plant phylogeny and the origin of major biomes

Phylogenetic trees based upon DNA sequence data, when calibrated with a dimension of time, allow inference of: (i) the pattern of accumulation of lineages through time; (ii) the time of origin of monophyletic groups; (iii) when lineages arrived in different geographical areas; (iv) the time of origin of biome-specific morphologies. This gives a powerful new view of the history of biomes that in many cases is not provided by the incomplete plant fossil record. Dated plant phylogenies for angiosperm families such as Leguminoaceae (Fabaceae), Melastomataceae sensu stricto, Annonaceae and Rhamnaceae indicate that long-distance, transoceanic dispersal has played an important role in shaping their distributions, and that this can obscure any effect of tectonic history, previously assumed to have been the major cause of their biogeographic patterns. Dispersal from other continents has also been important in the assembly of the Amazonian rainforest flora and the Australian flora. Comparison of dated biogeographic patterns of plants and animals suggests that recent long-distance dispersal might be more prevalent in plants, which has major implications for community assembly and coevolution. Dated plant phylogenies also reveal the role of past environmental changes on the evolution of lineages in species-rich biomes, and show that recent Plio-Pleistocene diversification has contributed substantially to their current species richness. Because of the critical role of fossils and morphological characters in assigning ages to nodes in phylogenetic trees, future studies must include careful morphological consideration of fossils and their extant relatives in a phylogenetic context. Ideal study systems will be based upon DNA sequence data from multiple loci and multiple fossil calibrations. This allows cross-validation both of age estimates from different loci, and from different fossil calibrations. For a more complete view of biome history, future studies should emphasize full taxon sampling in ecologically important groups, and should focus on geographical areas for which few species-level phylogenies are available, such as tropical Africa and Asia. These studies are urgent because understanding the history of biomes can both inform conservation decisions, and help predict the effects of future environmental changes at a time when biodiversity is being impacted on an unprecedented scale.