Frontiers of Biogeography (FoB) is the scientific magazine of the International Biogeography Society (IBS, www.biogeography.org), 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.
Volume 9, Issue 3, 2017
Climatic variables determining Rhododendron sister taxa distributions and distributional overlaps in the Himalayas
Endemic species in mountains are vulnerable to rapid climate change. We elucidated distributional overlaps and related climatic variables for two endemic sister taxa of Rhododendron and a generalist with respect to current and future climate conditions. Our research questions are: (i) Which climate factors separate the distributions of Rhododendron cowanianum, R. lepidotum and R. lowndesii? (ii) How large is the geographic overlap in current and future distributions? (iii) Is it likely that the species are able to track their niches in the future? To answer these questions, we performed species distribution modelling on binomial Rhododendron occurrences accompanied by random pseudo-absences and absences constrained by other Rhododendron taxa. We used Generalized Linear Modelling to select variables, and modelled the distribution of each species using Random Forest algorithms, predicting their potential distribution in current and future climates. We also examined range differences to identify the variables segregating the distribution of these sister taxa, and estimated current and future distributional overlap between and within species. Precipitation variables explained R. lowndesii distribution, whereas temperature variables explained distributions of the other two species. We found that sister taxa have similar climate niche and hence high overlap in geographic distribution in current climate (46–68%) and potentially in future climate (53–77%). Under future climate conditions, the potential distribution area of R. lepidotum and R. cowanianum is predicted to be at a higher elevation, while the prediction for R. lowndesii is similar to its current geography. Our models suggest that there are more potential distribution areas for these narrowly distributed endemic species than are currently occupied, which illustrates that it is rather uncertain whether the Rhododendron species will be able to track the geographical location of their niches in the future.
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Opinions, Perspectives & Reviews
To conciliate the individualistic and holistic paradigms dominating community ecology, I analysed the main factors driving the distribution of xerophytic shrub communities at different scales. I found that the patchy distribution of xerophytic shrubs in southwestern Portugal mainly responds to both local (i.e., soil organic matter) and regional (i.e., climate) factors, confirming the importance of processes acting at different scales. I propose a conceptual model including the ecological dynamics of these communities supported by the analyses of both kinds of drivers and changes in functional diversity. The ecological dynamics between the communities dominated by Stauracanthus genistoides and Ulex australis throughout their co-occurrence area were significantly consistent, despite the factors driving this successional gradient changing regionally. An integrative approach for linking species diversification and distribution assessed the role of edaphic and climatic requirements in the current parapatric distribution of the three species of the genus Stauracanthus.
Assemblage-level studies of mean trait variation are common in macroecology. However, how phylogenetic relationships among species affect trait-based macroecological patterns is still unresolved. I used an approach based on variation partitioning analysis using environmental and phylogenetic lineage variation as predictors to investigate whether variation in mean trait values among Neotropical sigmodontine rodent communities is best explained by macroecological adaptation, biogeographical history, or joint effects of both – the latter resulting in phylogenetic niche conservatism (PNC) at the metacommunity scale. Metacommunity PNC best explained mean variation in body size and skull/mandible shape across assemblages, and the pattern of metacommunity PNC suggests that influence of environmental factors on mean trait variation relies heavily on spatial biogeographical clade sorting. This suggests that biogeographical lineage distribution should be taken into account in analyses seeking to correlate environmental variables with mean trait variation.
News & Update
A number of concerns persist regarding (i) how functional spaces should be quantified, (ii) how phylogenetic richness should be calculated, (iii) and how functional beta diversity should be calculated. Because all current methods have their shortcomings we think that analytical choices are as much a matter of knowing the limitations of the data and knowing the working hypothesis. Only then can one follow their personal choice, weighing up the shortcomings of different methods that, at the end of the day, usually produce qualitatively similar results.
A review of Global Climate Change and Terrestrial Invertebrates (2017).
Flowering branch of Stauracanthus genistoides near Espichel Cape (Portugal). See Chozas’ article in this issue of Frontiers of Biogeography for a synopsis of the evolution and biogeography of this species and the ecological dynamics of the xerophytic shrub communities where it grows. Picture by Sergio Chozas (see also http://flora-on.pt/#1Stauracanthus+genistoides).