Frontiers of Biogeography

Chytridiomycosis, a disease caused by the emerging fungus Batrachochytrium dendrobatidis (Bd), has been implicated in the decline of over 500 amphibian species. Population declines could have important genetic consequences, including reduced genetic diversity. We contrasted genetic diversity among both long-Bd-exposed and unexposed populations of the south-east Australian alpine tree frog (Litoria verreauxii alpina) across its range. At the population level, we found no significant differences in genetic diversity between Bd-exposed and unexposed populations. Encouragingly, even Bd-infected remnant populations that are now highly isolated maintain genetic diversity comparable to populations in which Bd is absent. Spatial genetic structure among populations followed an isolation-by-distance pattern, suggesting restricted movement among remnant populations. At the individual level, greater heterozygosity was associated with reduced probability of infection. Loss of genetic diversity in remnant populations that survived chytridiomycosis epidemics does not appear to be a threat to L. v. alpina. We suggest several factors underpinning maintenance of genetic diversity: (1) remnant populations have remained large enough to avoid losses of genetic diversity; (2) many individuals in the population are able to breed once before succumbing to disease; and (3) juveniles in the terrestrial environment have low exposure to Bd, providing an annual ‘reservoir’ of genetic diversity. The association between individual heterozygosity and infection status suggests that, while other work has shown all breeding adults are typically killed by Bd, males with greater heterozygosity may survive longer and obtain fitness benefits through extended breeding opportunities. Our results highlight the critical role of life history in mitigating the impacts of Bd infection for some amphibian species, but we infer that increased isolation as a result of disease-induced population extirpations will enhance population differentiation and thus biogeographic structure.

The islands of Southeast Asia comprise one of the most geologically and biogeographically complex areas in the world and are a centre of exceptional floristic diversity, harbouring 45,000 species of flowering plants. Cyrtandra, with over 800 species of herbs and shrubs, is the largest genus in the family Gesneriaceae and is one of the most emblematic and species-rich genera of the Malesian rainforest understorey. The high number of species and tendency to narrow endemism make Cyrtandra an ideal genus for examining biogeographic patterns. We sampled 128 Cyrtandra taxa from key localities across Southeast Asia to evaluate the geo-temporal patterns and evolutionary dynamics of this clade. One nuclear and four chloroplast regions were used for phylogenetic reconstruction, molecular dating, and ancestral range estimation. Results from the dating analysis suggest that the great diversity of Cyrtandra seen in the Malesian region results from a recent radiation, with most speciation taking place in the last five million years. Borneo was recovered as the most likely ancestral range of the genus, with the current distribution of species resulting from a west to east migration across Malesia that corresponds with island emergence and mountain building. Lastly, our investigation into the biogeographic history of the genus indicates high levels of floristic exchange between the islands on the Sunda shelf and the important role of the Philippines as a stepping stone to Wallacea and New Guinea. These patterns underlie much of the plant diversity in the region and form an emerging paradigm in Southeast Asian plant biogeography.

Field ecologists and macroecologists often compete for the same grants and academic positions, with the former producing primary data that the latter generally use for model parameterization. Primary data are usually cited only in the supplementary materials, thereby not counting formally as citations, creating a system where field ecologists are routinely under-acknowledged and possibly disadvantaged in the race for funding and positions. Here, we explored how the performance of authors producing novel ecological data would change if all the citations to their work would be accounted for by bibliometric indicators. We collected the track record of >2300 authors from Google Scholar and citation data from 600 papers published in 40 ecology journals, including field-based, conservation, general ecology, and macroecology studies. Then we parameterized a simulation that mimics the current publishing system for ecologists and assessed author rankings based on number of citations, H-Index, Impact Factor, and number of publications under a scenario where supplementary citations count. We found weak evidence for field ecologists being lower ranked than macroecologists or general ecologists, with publication rate being the main predictor of author performance. Current ranking dynamics were largely unaffected by supplementary citations as they are 10 times less than the number of main text citations. This is further exacerbated by the common practice of citing datasets assembled by previous research or data papers instead of the original articles. While accounting for supplementary citations does not appear to offer a solution, researcher performance evaluations should include criteria that better capture authors’ contribution of new, publicly available data. This could encourage field ecologists to collect and store new data in a systematic manner, thereby mitigating the data patchiness and bias in macroecology studies, and further accelerating the advancement of ecology and related areas of biogeography.

Phylogenetic constraints on ecophysiological adaptations and specific resource requirements are likely to explain why some taxonomic/functional groups exhibit different richness patterns along climatic gradients. We used interpolated species elevational distribution data and climatic data to describe gymnosperm species richness variation along elevational and climatic gradients in the Himalayas. We compared the climatic and elevational distributions of gymnosperms to those previously found for bryophytes, ferns, and angiosperm tree lineages to understand the respective drivers of species richness. We divided our study location into three regions: Eastern; Central; and Western Himalayas, in each calculating gymnosperm species richness per 100-m band elevational interval by determining the sum of species with overlapping elevational distributions. Using linear regression, we analyzed the relationship between species’ elevational mid-point and species’ elevational range size to test the Rapoport’s rule for gymnosperms in the Himalayas. Generalized linear models were used to test if potential evapotranspiration, growing degree days, and the number of rainy days could predict the observed patterns of gymnosperm species richness. We used the non-linear least squares method to examine if species richness optima differed among the four taxa. We found supporting evidence for the elevational Rapoport’s rule in the distribution of gymnosperms, and we found a unimodal pattern in gymnosperm species richness with elevation, with the highest species richness observed at ca. 3000 m. We also found a unimodal pattern of gymnosperm species richness along both the potential evapotranspiration and growing degree day gradients, while the relationship between species richness and the number of rainy days per year was non-significant. Gymnosperm species richness peaked at higher elevations than for any other plant functional group. Our results are consistent with the view that differences in response of contrasting plant taxonomic groups with elevation can be explained by differences in energy requirements and competitive interactions.

Biogeography has its origins in European colonialism. The legacies of colonial relations are evident in the distribution of practicing biogeographers, the direction of flow of biogeographical data, and the language used when describing and interpreting our studies. Biogeographers can address these legacies through increasing access to research data and publication outlets, improved recognition of collaborative relationships, and critically reflecting upon how our assumptions and perspectives might perpetuate colonial attitudes. Achieving these goals will improve not only inclusivity and equity within our field but also increase the diversity of insights and validity of our findings. If biogeography is to be a truly global science then decolonisation is a collective responsibility.

Recent work in island biogeography has shown that back-colonization (‘boomerang’ events) from islands to continents have occurred more frequently than previously understoodWe report possibly the earliest inference of this pattern, by John Ball and Joseph Dalton Hooker in a book published in 1878.

The spread of chytridiomycosis is causing the decline and extinction of many amphibian species worldwide. In a paper in this issue of Frontiers of Biogeography, Banks and colleagues show that the populations of south-east Australian alpine tree frog (Litoria verreauxii alpina) surviving the infection hold similar genetic diversity as unaffected ones, and that individuals with greater heterozygosity present reduced probability of infection. Photo credit: David Hunter.