Frontiers of Biogeography

An undescribed, species of Tricholoma growing in soil in a mixed podocarp and southern beech forest. This species is one of 18 in the genus Tricholoma found in New Zealand that are yet to be formally described. In this issue’s article by Cunningham et al., mushroom-forming fungi, along with lichenized and plant associated fungi, were predicted to experience the greatest increase in new species descriptions. Photo by David Hera.

The world’s “100 worst invasive species” were listed in 2000. The list is taxonomically diverse, often cited (typically for single-species studies), and its species are frequently reported in global biodiversity data bases. We acted on the principle that these notorious species should be well-reported to help answer two questions about global biogeography of invasive species (i.e., not just their invaded ranges): (1) “how are data distributed globally?” and (2) “what predicts diversity?” We collected location data for each of the 100 species from multiple data bases; 95 had sufficient data for analyses. For question (1), we mapped global species richness and cumulative occurrences since 2000 in (0.5 degree)2 grids. For question (2) we compared alternative regression models representing non-exclusive hypotheses for geography (i.e., spatial autocorrelation), sampling effort, climate, and anthropocentric effects. Reported locations of the invasive species were spatially-biased, leaving large gaps on multiple continents. Accordingly, species richness was best explained by both anthropocentric effects not often used in biogeographic models (Government Effectiveness, Voice & Accountability, human population size) and typical natural factors (climate, geography; R2 = 0.87). Cumulative occurrence was strongly related to anthropocentric effects (R2 = 0.62). We extract five lessons for invasive species biogeography; foremost are the importance of anthropocentric measures for understanding invasive species diversity patterns and large lacunae in their known global distributions. Despite those knowledge gaps, advanced models here predict well the biogeography of the world’s worst invasive species for much of the world.

Global estimates of the number of species of Fungi have ranged from 1.5 to 13.2 million, but have been based more on opinion and simple ratios than quantitative assessment. We analysed trends in the rate of description of fungal species over four centuries, noted the use of molecular methods in species delimitation, and used a statistical model designed for such data to predict future trends. A total of 144,035 fungal species were analysed, along with smaller species groups extracted from the core dataset that approximated biological and ecological traits. The groups explored included fungi of medical significance (728 spp), those associated with the marine environment (972 spp), rust and smut fungi (9,125 spp), arthropod ectoparasites of class Laboulbeniomycetes (2,376 spp), mushroom-forming fungi of class Agaricomycetes (37,717 spp), the budding yeasts of subphylum Saccharomycotina (1,165 spp), the class Dothideomycetes (30,912 spp), and lichenized fungi of classes Lecanoromycetes and Arthoniomycetes (12,154 spp). There was an acceleration in overall fungal description rates within the last two decades accompanied by the increased use of genetic data in new species descriptions. Mushroom-forming, lichenized, and plant-associated fungi were predicted to experience the greatest increase in new species. Increased description rates are supported by an increase in the number of authors describing species. However, the number of species described per author in a year has been declining since 1875. Because less than 10% of currently accepted fungal species have molecular data associated with corresponding type specimens, genetic data should not be used to discriminate new species without associated phenotypic information. An additional 68,750 species (48%) were predicted to be described this century, making Fungi the least well-described Kingdom assessed to date.

Globally, large mammals are in decline. Biological traits including low population densities and longer generation times make them particularly susceptible. Their losses can have wide-ranging ecological consequences, including dramatic reductions in total heterotrophic energy use. To determine the key drivers of variation in energy use, we calculated daily rates of energy flow across the globe for 241 ecological communities, encompassing 441 large mammal species, using camera trap inventories. These were scaled up from individual metabolic rates and compared with various climate, anthropogenic, geographic, and species richness variables using three analytical methods: model selection, spatial autoregression, and a multiple regression method that completely removes multicollinearity known as least-squares orthogonalization. Community energy use is significantly lower in the Neotropics and Australasia than in the Afrotropics and Eurasia. This pattern mirrors the spatial distribution of megafaunal extinction intensity during the Late Pleistocene. Rates not being greatly reduced in the Nearctic is a notable exception to this pattern, and is likely due to the high abundances of certain species not present in the other highly-impacted realms. There are also strong negative correlations between community per-gram rates of energy flow and species richness, indicating that megafauna persist mainly in more speciose communities. The strong geographic differences that dominate energy use patterns indicate that past mammal extinctions are the ultimate cause of modern energetic variation in large mammal communities. If so, then ongoing losses of large mammals will greatly impact community and ecosystem functioning.

The Gesneriaceae consists of around 150 genera and c. 3750 species with a predominantly tropical and subtropical distribution across all continents. Although previous studies have proposed an American origin of Gesneriaceae, the biogeographic history of this pantropical plant family is still unclear, particularly in the Old World. To address this, we assembled the most comprehensively sampled matrix of Gesneriaceae with 143 Gesneriaceae genera and 355 species, including key samples from Sri Lanka analysed here for the first time. We generated molecular phylogenies based on four plastid gene regions (ndhF, matK, rps16 and trnL-F), obtained fossil-calibrated trees, and reconstructed ancestral areas and dispersal routes using Bayesian methods. Our results confirm the origin for the family in the Early Palaeocene (67. Ma) in the region of present day Central America & Andean South America, and that diversity in the Old World originated from a longdistance dispersal event from South America around 59 Ma, most likely to the Indian plate, which was an island at the time. This lineage then dispersed to Malesia and later East Asia, which would ultimately become a major centre of diversity and source of many dispersals to other regions. Our results thus highlight the Indian plate as a likely key player in the early diversification of Old World Gesneriaceae, even though it is now more diverse elsewhere, and hence offer novel insights into this plant family’s dispersal routes and areas of diversification in the Old World.

A contributing element of the exceptional plant biodiversity of the Arizona-New Mexico sky islands is the numerous southern taxa at their northern extent, yet the local distribution and drivers of subtropical plant richness have not been delineated. We assess the proportion of subtropical richness (PSR) in sky islands as the ratio of subtropical taxa to total species richness. We (1) identified 284 subtropical vascular plant species at or near their northern range in 24 sky islands, (2) calculated PSR for each sky island, (3) quantified spatial patterns of PSR and subtropical beta diversity, (4) determined regional hotspots of PSR, and (5) analyzed independent eight variables as potential drivers of PSR and subtropical species turnover. Sky islands with the highest PSR occur in the southwestern portion of the region close to the international border. Four predictor variables (ordered by significance) strongly correlate with PSR: minimum winter temperature, monsoon season precipitation, area, and latitude. The primary subtropical hotspot occurs mostly within Santa Cruz County (southeastern Arizona), representing the largest regional concentration of rare subtropical taxa. We determined three primary clusters of species cooccurrence with a strong longitudinal trend driving subtropical beta diversity. Nearly half of subtropical taxa are regionally rare or vulnerable, illustrating the potential value of assessing regional peripheral plant taxa to discern hotspots of ecological significance. The sky islands of Santa Cruz County represent a unique botanical hotspot with exceptional subtropical richness and rarity. Understanding regional drivers of subtropical influences helps forecast potential responses to global change, while strengthening conservation strategies that minimize future losses of biodiversity.

The dynamic nature of intrinsic (e.g., reproductive system, hybridization) and extrinsic factors (e.g., physical barriers to gene flow) across space and time generate complex biological processes that influence contemporary patterns of genetic diversity, highlighting the need for interdisciplinary studies. Using the widespread, mixed-mating annual Triodanis perfoliata, previous work demonstrated the important roles of breeding system, isolation by distance, and isolation by resistance in shaping patterns of population genetic diversity. Here we significantly build on this first step by incorporating paleoclimatic data, historical admixture, and estimating species divergence times across 18 populations of T. perfoliata spanning the contiguous US. This current study provides novel insights into factors driving patterns of intraspecific diversification that were not explained using only contemporary climate models. Specifically, these new analyses highlight the early Holocene (11.7 - 8.326 ka) and the Marine Isotope Stage M2 (ca. 3.3 Ma), as important time periods for explaining patterns of contemporary population genetic diversity, the latter of which appears to be an important time period for intraspecific divergence of T. perfoliata. In addition, we explored the influence of historical intrinsic factors, via admixture to explain patterns of population isolation and connectivity. The inclusion of an admixture analysis provided clarity through evidence of historical gene flow between populations that would have experienced suitable habitat connectivity in past climates. Our study illustrates the importance of incorporating historic, as well as contemporary data, into phylogeographic studies to generate a comprehensive understanding of patterns of population diversity, and the processes important in driving these patterns.

Understanding the distribution of species is a primary requirement to understand their behaviour, conservation, and phylogeography. Over the last decades, the number of species described on the Korean Peninsula has significantly increased, but surveys around the boundaries of the Peninsula are still needed to refine the range of these species. Further surveys, supported by ecological niche models, are especially needed in areas where the environment is similar and connected. We conducted surveys in the continuous landscapes of the Republic of Korea, the Democratic People’s Republic of Korea, and the People’s Republic of China to determine the distribution of the gold-spotted pond frog, Pelophylax chosenicus (Okada, 1931). The surveys were conducted between 2015 and 2021 through the use of visual and call encounters. We supported our surveys with molecular analyses by sequencing the mitochondrial 16S rRNA, 12S rRNA, and Cytb gene fragments to confirm the species identity of the northernmost population in China. As a result, we found the species to be widespread in low-elevation wetlands along the eastern coast of the Yellow Sea, with two isolated populations in the southeast of the Korean Peninsula, and the northernmost population in the vicinity of Dandong in the People’s Republic of China. We then determined the importance of landscape types for the species, especially rice paddies, and used ecological niche models to define suitable habitats across the region. As this species is listed as threatened in the Republic of Korea, knowing its exact distribution will be important for conservation practices.