Rafaël Govaerts

Three keys to the radiation of angiosperms into freezing environments

Early flowering plants are thought to have been woody species restricted to warm habitats. This lineage has since radiated into almost every climate, with manifold growth forms. As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species’ traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile, but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold.

A GLOBAL ASSESSMENT OF DISTRIBUTION, DIVERSITY, ENDEMISM, AND TAXONOMIC EFFORT IN THE RUBIACEAE 1

Abstract Analyses of distribution, diversity, endemism, and taxonomic effort for Rubiaceae are reported, based on queries from a World Rubiaceae Checklist database. Rubiaceae are widespread and occur in all major regions of the world except the Antarctic Continent, but are predominantly a group in the tropics with greatest diversity in low- to mid-altitude humid forests. A count of Rubiaceae species and genera is given (13,143 spp./611 genera), which confirms that this is the fourth largest angiosperm family. Psychotria L. is the largest genus in the Rubiaceae (1834 spp.) and the third largest angiosperm genus. Most genera (72%) have fewer than 10 species and 211 are monotypic. Calculation of relative species diversity and percentage endemism enables areas of high diversity and endemism to be enumerated, and identifies areas where further field collecting and taxonomic research are required. Endemism is generally high in Rubiaceae, which supports data from recent studies showing that many species have restricted distributions. Given the assumed ecologic sensitivity of Rubiaceae, in combination with a range of other factors including restricted distribution, we suggest that species in this family are particularly vulnerable to extinction. The rate at which new species are being described is inadequate; more resources are required before the diversity of Rubiaceae is satisfactorily enumerated.

Measuring the fate of plant diversity: towards a foundation for future monitoring and opportunities for urgent action

Vascular plants are often considered to be among the better known large groups of organisms, but gaps in the available baseline data are extensive, and recent estimates of total known (described) seed plant species range from 200 000 to 422 000. Of these, global assessments of conservation status using International Union for the Conservation of Nature (IUCN) categories and criteria are available for only approximately 10 000 species. In response to recommendations from the Conference of the Parties to the Convention on Biological Diversity to develop biodiversity indicators based on changes in the status of threatened species, and trends in the abundance and distribution of selected species, we examine how existing data, in combination with limited new data collection, can be used to maximum effect. We argue that future work should produce Red List Indices based on a representative subset of plant species so that the limited resources currently available are directed towards redressing taxonomic and geographical biases apparent in existing datasets. Sampling the data held in the worlds major herbaria, in combination with Geographical Information Systems techniques, can produce preliminary conservation assessments and help to direct selective survey work using existing field networks to verify distributions and gather population data. Such data can also be used to backcast threats and potential distributions through time. We outline an approach that could result in: (i) preliminary assessments of the conservation status of tens of thousands of species not previously assessed, (ii) significant enhancements in the coverage and representation of plant species on the IUCN Red List, and (iii) repeat and/or retrospective assessments for a significant proportion of these. This would result in more robust Sampled Red List Indices that can be defended as more representative of plant diversity as a whole; and eventually, comprehensive assessments at species level for one or more major families of angiosperms. The combined results would allow scientifically defensible generalizations about the current status of plant diversity by 2010 as well as tentative comments on trends. Together with other efforts already underway, this approach would establish a firmer basis for ongoing monitoring of the status of plant diversity beyond 2010 and a basis for comparison with the trend data available for vertebrates.

How many species of seed plants are there?: a response

My recent article in which I estimated that there are about 420,000 seed plant species in the world (Govaerts, 2001) has provoked many comments in discussion and correspondence. Two replies have been published in this journal, both suggesting that my figure is considerably too high. That by Thorne (2002) gave an estimate of 260,000, while that by Scotland & Wortley (2003) was only 223,000-little more than half the figure I or Bramwell (2002) had proposed. It is of interest to compare the respective methods of calculation and try to establish why there should be such disparity. I am not convinced that my own estimate is so far from the truth. Thorne (2002) reached his figure by adding together figures given in Mabberley (1997), a method similar to that used by some other authors on this subject. This of course calls into question the accuracy of the figures given by Mabberley. A major problem is caused by large genera. According to my figures, it appears that if genera are arranged in order of size, the 20% including the larger genera will contain some 80% of the species. Thus if there are 13,000 genera of seed plants, the 10,400 smaller genera, which are by and large the ones with the most recent revisions and most reliable data, will include only a small proportion of the total number of species. On the other hand, the other 2,600 genera will include by far the greater part of the total number of species, and it is exactly these genera for which reliable data are difficult to obtain. Figures quoted for these larger genera are apt to vary greatly. Table 1 gives, for example, the variation between the first edition of Mabberleys book (1987) and the second edition (1997). In other genera, Mabberleys estimate has stayed the same even though many new speies were described in the ten years between the two

Alpha e-taxonomy: responses from the systematics community to the biodiversity crisis

SummaryThe crisis facing the conservation of biodiversity is reflected in a parallel crisis in alpha taxonomy. On one hand, there is an acute need from government and non-government organisations for large-scale and relatively stable species inventories on which to build major biodiversity information systems. On the other, molecular information will have an increasingly important impact on the evidential basis for delimiting species and is likely to result in greater scientific debate and controversy on their circumscription. This paper argues that alpha-taxonomy built on the Internet (alpha e-taxonomy) can provide a key component of the solution. Two main themes are considered: (1) the potential of e-taxonomic revisions for engaging both the specialist taxonomic community and a wider public in gathering taxonomic knowledge and deepening understanding of it, and (2) why alpha-species will continue to play an essential role in the conventional definition of species and what kinds of methodological development this implies for descriptive species taxonomy. The challenges and requirements for sustaining e-taxonomic revisions in the long-term are discussed, with particular reference to models being developed by five initiatives with botanical exemplar websites: CATE (Creating a Taxonomic E-Science), Solanaceae Source, GrassBase and EDIT (European Distributed Institute of Taxonomy) exemplar groups and scratchpads. These projects give a clear indication of the crucially important role of the national and regional taxonomic organisations and their networks in providing both leadership and a fruitful and beneficial human and technical environment for taxonomists, both amateur and professional, to contribute their expertise towards a collective global enterprise.

Erratum: Three keys to the radiation of angiosperms into freezing environments (Nature (2014) 506 (89-92) (Doi:10.1038/nature12872))

This corrects the article DOI: 10.1038/nature12872

Do Global Diversity Patterns of Vertebrates Reflect Those of Monocots

Few studies of global diversity gradients in plants exist, largely because the data are not available for all species involved. Instead, most global studies have focussed on vertebrates, as these taxa have historically been associated with the most complete data. Here, we address this shortfall by first investigating global diversity gradients in monocots, a morphologically and functionally diverse clade representing a quarter of flowering plant diversity, and then assessing congruence between monocot and vertebrate diversity patterns. To do this, we create a new dataset that merges biome-level associations for all monocot genera with country-level associations for almost all ∼70,000 species. We then assess the evidence for direct versus indirect effects of this plant diversity on vertebrate diversity using a combination of linear regression and structural equation modelling (SEM). Finally, we also calculate overlap of diversity hotspots for monocots and each vertebrate taxon. Monocots follow a latitudinal gradient although with pockets of extra-tropical diversity, mirroring patterns in vertebrates. Monocot diversity is positively associated with vertebrate diversity, but the strength of correlation varies depending on the clades being compared. Monocot diversity explains marginal amounts of variance (<10%) after environmental factors have been accounted for. However, correlations remain among model residuals, and SEMs apparently reveal some direct effects of monocot richness. Our results suggest that collinear responses to environmental gradients are behind much of the congruence observed, but that there is some evidence for direct effects of producer diversity on consumer diversity. Much remains to be done before broad-scale diversity gradients among taxa are fully explained. Our dataset of monocot distributions will aid in this endeavour.

Late Quaternary climate stability and the origins and future of global grass endemism.

Background and Aims Earth’s climate is dynamic, with strong glacial–interglacial cycles through the Late Quaternary. These climate changes have had major consequences for the distributions of species through time, and may have produced historical legacies in modern ecological patterns. Unstable regions are expected to contain few endemic species, many species with strong dispersal abilities, and to be susceptible to the establishment of exotic species from relatively stable regions. We test these hypotheses with a global dataset of grass species distributions. Methods We described global patterns of endemism, variation in the potential for rapid population spread, and exotic establishment in grasses. We then examined relationships of these response variables to a suite of predictor variables describing the mean, seasonality and spatial pattern of current climate and the temperature change velocity from the Last Glacial Maximum to the present. Key Results Grass endemism is strongly concentrated in regions with historically stable climates. It also depends on the spatial pattern of current climate, with many endemic species in areas with regionally unusual climates. There was no association between the proportion of annual species (representing potential population spread rates) and climate change velocity. Rather, the proportion of annual species depended very strongly on current temperature. Among relatively stable regions (<10 m year−1), increasing velocity decreased the proportion of species that were exotic, but this pattern reversed for higher-velocity regions (>10 m year−1). Exotic species were most likely to originate from relatively stable regions with climates similar to those found in their exotic range. Conclusions Long-term climate stability has important influences on global endemism patterns, largely confirming previous work from other groups. Less well recognized is its role in generating patterns of exotic species establishment. This result provides an important historical context for the conjecture that climate change in the near future may promote species invasions.

Corrigendum: Three keys to the radiation of angiosperms into freezing environments

This corrects the article DOI: 10.1038/nature12872

Indian Ocean Mapouria species transferred toPsychotria (Rubiaceae–Psychotrieae)

Mapouria Aubl. is a synonym of Psychotria L. In Madagascar and the Comoros there are 67 species of Mapouria that fall within the circumscription of Psychotria and correspondingly 64 species (67 taxa) require transfer to Psychotria. Thirty-seven new combinations and 30 new names are proposed; five lectotypes are designated.