Hans Peter Linder

We review the complicated nomenclatural history of the Clanwilliam cedar. Much of this centres around the application of the name Widdringtonia wallichii Endl. ex Carrière. We are unable to identify any original material of this name and designate a neotype to fix its application as it appears to have been originally intended and as it is currently understood. We also confirm that the correct name for the Clanwilliam cedar is W. cedarbergensis J.A.Marsh.

The Cretaceous–Palaeogene (K-Pg) extinction of the non-avian dinosaurs (66 Ma) led to a 25 million year gap of megaherbivores (>1000 kg) before the evolution of megaherbivorous mammals in the Late Eocene (40 Ma). The botanical consequences of this ‘Palaeocene megaherbivore gap’ (PMHG) remain poorly explored. We hypothesize that the absence of megaherbivores should result in changes in the diversification and trait evolution of associated plant lineages. We used phylogenetic time- and trait-dependent diversification models with palms (Arecaceae) and show that the PMHG was characterized by speciation slowdowns, decreased evolution of armature and increased evolution of megafaunal (≥4 cm) fruits. This suggests that the absence of browsing by megaherbivores during the PMHG may have led to a loss of defence traits, but the absence of megaherbivorous seed dispersers did not lead to a loss of megafaunal fruits. Instead, increases in PMHG fruit sizes may be explained by simultaneously rising temperatures, rainforest expansion, and the subsequent radiation of seed-dispersing birds and mammals. We show that the profound impact of the PMHG on plant diversification can be detected even with the overwriting of adaptations by the subsequent Late Eocene opening up of megaherbivore-associated ecological opportunities. Our study provides a quantitative, comparative framework to assess diversification and adaptation during one of the most enigmatic periods in angiosperm history.

Understanding how and why rates of evolutionary diversification vary is a key issue in evolutionary biology, ecology, and biogeography. Evolutionary rates are the net result of interacting processes summarized under concepts such as adaptive radiation and evolutionary stasis. Here, we review the central concepts in the evolutionary diversification literature and synthesize these into a simple, general framework for studying rates of diversification and quantifying their underlying dynamics, which can be applied across clades and regions, and across spatial and temporal scales. Our framework describes the diversification rate (d) as a function of the abiotic environment (a), the biotic environment (b), and clade‐specific phenotypes or traits (c); thus,d ~ a,b,c. We refer to the four components (a–d) and their interactions collectively as the “Evolutionary Arena.” We outline analytical approaches to this framework and present a case study on conifers, for which we parameterize the general model. We also discuss three conceptual examples: theLupinusradiation in the Andes in the context of emerging ecological opportunity and fluctuating connectivity due to climatic oscillations; oceanic island radiations in the context of island formation and erosion; and biotically driven radiations of the Mediterranean orchid genusOphrys. The results of the conifer case study are consistent with the long‐standing scenario that low competition and high rates of niche evolution promote diversification. The conceptual examples illustrate how using the synthetic Evolutionary Arena framework helps to identify and structure future directions for research on evolutionary radiations. In this way, the Evolutionary Arena framework promotes a more general understanding of variation in evolutionary rates by making quantitative results comparable between case studies, thereby allowing new syntheses of evolutionary and ecological processes to emerge.

With the realization that much of the biological diversity on Earth has been generated by discrete evolutionary radiations, there has been a rapid increase in research into the biotic (key innovations) and abiotic (key environments) circumstances in which such radiations took place. Here we focus on the potential importance of population genetic structure and trait genetic architecture in explaining radiations. We propose a verbal model describing the stages of an evolutionary radiation: first invading a suitable adaptive zone and expanding both spatially and ecologically through this zone; secondly, diverging genetically into numerous distinct populations; and, finally, speciating. There are numerous examples of the first stage; the difficulty, however, is explaining how genetic diversification can take place from the establishment of a, presumably, genetically depauperate population in a new adaptive zone. We explore the potential roles of epigenetics and transposable elements (TEs), of neutral process such as genetic drift in combination with trait genetic architecture, of gene flow limitation through isolation by distance (IBD), isolation by ecology and isolation by colonization, the possible role of intra‐specific competition, and that of admixture and hybridization in increasing the genetic diversity of the founding populations. We show that many of the predictions of this model are corroborated. Most radiations occur in complex adaptive zones, which facilitate the establishment of many small populations exposed to genetic drift and divergent selection. We also show that many radiations (especially those resulting from long‐distance dispersal) were established by polyploid lineages, and that many radiating lineages have small genome sizes. However, there are several other predictions which are not (yet) possible to test: that epigenetics has played a role in radiations, that radiations occur more frequently in clades with small gene flow distances, or that the ancestors of radiations had large fundamental niches. At least some of these may be testable in the future as more genome and epigenome data become available. The implication of this model is that many radiations may be hard polytomies because the genetic divergence leading to speciation happens within a very short time, and that the divergence history may be further obscured by hybridization. Furthermore, it suggests that only lineages with the appropriate genetic architecture will be able to radiate, and that such a radiation will happen in a meta‐population environment. Understanding the genetic architecture of a lineage may be an essential part of accounting for why some lineages radiate, and some do not.

Summary: Plants use roots to access soil resources, so differences in root traits and their ecological consequences could be a mechanism of species coexistence and niche divergence. Current views of the evolution of root diversity are informed by large‐scale evolutionary analyses based on taxonomically coarse sampling and led to the ‘root trait phylogenetic conservatism hypothesis’. Here we test this hypothesised conservatism among closely related species, and whether root variation plays an ecological role. We collected root architectural traits for the species‐rich Cape rushes (Restionaceae) in the field and from herbaria. We used machine learning to interpolate missing data. Using model‐based clustering we classified root syndromes. We modelled the proportion of the syndromes along environmental gradients using assemblages and environmental data of 735 plots. We fitted trait evolutionary models to test for the conservatism hypothesis. We recognised five root syndromes. Responses to environmental gradients are syndrome specific and thus these represent ecomorphs. Trait evolutionary models reveal an evolutionary lability in these ecomorphs. This could present the mechanistic underpinning of the taxonomic radiation of this group which has been linked to repeated habitat shifts. Our results challenge the perspective of strong phylogenetic conservatism and root trait evolution may more generally drive diversification.

Aim: Local richness is a result of both regional richness and local site‐specific factors. We quantify the effects of different regional (dispersal, environmental filtering) and local (habitat selection) community assembly processes in the Cape reeds (Restionaceae) of the Cape flora and test if community assembly processes vary spatially.Location: Southern Africa, Cape Floristic Region.Taxon: Angiosperms, African Restionaceae (restios).Methods: We calculate local probabilistic species pools, based on local species richness, dispersal rates and environmental filtering at a 4 km² resolution. We then compare the relative contribution of the processes shaping the species pool spatially. Finally, we correlate observed species richness (based on 916 circular, 10 m diameter relevés) with the local species pools to test the explanatory power of additional local edaphic variables that could act as filters at very small scales.Results: There is substantial spatial variation in the local probabilistic species pools. Within the central part of the Cape, the local pools are mostly influenced by environmental filtering, while along the periphery dispersal limitation dominates. Observed species richness is lower than the predicted species pool size, which forms an upper boundary of the potential species richness for a local site. Local, site‐specific edaphic factors help to explain the remaining differences between local species pool size and α‐richness.Main conclusion: The analytical framework for inferring local probabilistic species pools provides a powerful tool for including the influence of regional species richness on variations in relevé α‐richness. This allows us to disentangle the various processes that operate at different spatial scales, and ultimately determine local restio species richness in the Cape Floristic Region.

Aim: I test whether species range size variation is driven by the age of the species, their intrinsic traits, environment or by historical‐geographical patterns (e.g. the location of climatic or environmental refugia).Location: Greater Cape Floristic Region (GCFR) of South Africa.Taxon: Angiosperms, Restionaceae (restios).Methods: I determined the area of occupancy and extent of occurrence of all restios in the GCFR, and derive a list of “single‐site endemics” (SSE). I inferred a rate‐corrected and dated phylogeny which includes 98% of the species. I explored the correlates of range size variation with phylogenetically corrected regressions, focussing on likely candidate traits (dispersal and fire survival modes), habitats (soil drainage, elevation), climatic variables (rainfall and temperature) and history (age of species). I calculated the species richness, community mean range sizes and numbers of SSE for 49 sites and 938 10 m diameter circular relevés across the GCFR, and sought correlates of these, specifically testing for historical‐geographical patterns in relationship to the distance from the centre of the region.Results: Narrow‐range restios are correlated with higher elevations, rainfall and rainfall seasonality; are found more likely in marshes and seepages; and are more likely killed by fire and have to re‐establish from seed after fire. Wide‐ranging species are found in areas with lower rainfall, at lower elevations, in well‐drained habitats, and resprout after fire. Community mean ranges sizes are larger towards the eastern part of the GCFR; and relevé data show that sandstones, shale, laterite and granites are associated with wider distribution ranges, as are soils with pebbles or sandy soils without rocks, and limestones with smaller community mean ranges than other bedrock types. The number of SSE is largely correlated with species richness, except that SSE are more likely at higher elevations.Main Conclusion: Range size variation in the restios is largely driven by history (expressed as the distance from the Kogelberg region), suggesting that the Kogelberg region may have been most climatically stable during the Neogene and Pleistocene. The second‐most important driver is the environment (i.e. rock type, elevation, rainfall), generally with spatially restricted habitats hosting range‐restricted species.

Aim: Fragmented distributions should show immigration and diversification dynamics consistent with the predictions of island biogeography theory. We test whether this applies to the fragmented Cape fynbos vegetation.Location: Southern Africa, Cape Floristic Region (CFR).Taxon: Angiosperms, Restionaceae (restios).Methods: We used a large occurrence dataset and environmental layers to characterize an existing regionalization and the intervals between the regions ecologically and spatially. We extended the available phylogeny for restios and inferred their historical biogeography using models implemented in BioGeoBEARS. We then measured the relative contribution of immigration and in situ speciation to the species richness of each region within the CFR. We used standard statistical methods to test the predictions of the island biogeography theory.Results: The area and environmental heterogeneity of the seven regions of the CFR are positively correlated with in situ speciation rate. Furthermore, more isolated areas, and areas colonized more recently, have proportionally higher immigration rates, and more central and older areas proportionally higher in situ speciation rates.Main conclusions: The variation in immigration and diversification dynamics among the regions within the CFR is extensive and consistent with the archipelago model of island biography theory. This dynamic may contribute significantly to the diversity of the Cape flora. Such a model could be generally useful for understanding the generation and maintenance of diversity in biodiversity hotspots, and may even scale up to explain continental biodiversity.

Understanding how and why rates of evolutionary diversification vary is a key issue in evolutionary biology, ecology, and biogeography, and the metaphorical concepts of adaptive radiation and evolutionary stasis describe two opposing aspects causing variation in diversification rates. Here we review the central concepts in the evolutionary diversification literature and synthesize these into a simple, general framework for studying rates of diversification and quantifying their underlying dynamics, which can be applied across clades and regions and across spatial and temporal scales. Our framework describes the diversification rate ( d ) as a function of the abiotic environment ( a ), the biotic environment ( b ) and clade-specific phenotypes or traits ( c ); thus d ∼ a,b,c . We refer to the four components ( a – d ) and their interactions collectively as the ‘Evolutionary Arena’. We outline analytical approaches to this framework and present a case study on conifers, for which we parameterise the general model. We also discuss three conceptual examples: the Lupinus radiation in the Andes in the context of emerging ecological opportunity and fluctuating connectivity due to climatic oscillations; oceanic island radiations in the context of island formation and erosion; and biotically driven radiations of the Mediterranean orchid genus Ophrys . The results of the conifer case study are consistent with the long-standing scenario that low competition and high rates of niche evolution promote diversification. The conceptual examples illustrate how using the synthetic Evolutionary Arena framework helps to identify and structure future directions for research on evolutionary radiations. In this way, the Evolutionary Arena framework promotes a more general understanding of variation in evolutionary rates by making quantitative results comparable between case studies, thereby allowing new syntheses of evolutionary and ecological processes to emerge.

Scientific publishing has seen many changes in its ~350 years of existence. Nonetheless, the changes currently underway may be among the most radical. The five major biogeography journals (Diversity and Distributions, Ecography, Frontiers of Biogeography, Global Ecology and Biogeography, and Journal of Biogeography) are indicative of the major undercurrents in publishing today: two are society owned, three are owned by a private publisher; two are open access, three are reader-pays; four are published by a for-profit publisher, one is not; two are double-blind review, three are the traditional single blind. Despite these differences, we serve as editors-in-chief for these journals for one common reason: to make sure there is a healthy publishing ecosystem available to communicate biogeographical research. With that goal in mind, here, we provide a brief potted history of scientific publishing to contextualize the modern publishing environment. We consider what current trends may mean for the future of scientific publishing. And we highlight a suite of factors that we recommend be considered when choosing a venue in which to publish your research. We particularly wish to emphasize one point: while editors-in-chief may guide journals, and editors and reviewers shape the science that is published, all journals depend ultimately on the manuscripts that authors choose to submit. For this reason, authors have great power over the future of the publishing landscape. To ensure a healthy landscape, we feel it is critical that all authors—but especially we senior and mid-career authors—are educated about today's complex world of publication and make informed choices about where to submit, which signals to publishers the criteria that our community values. Authors’ choices now have potential to shape a sustainable publishing environment that better serves the current and future generations of biogeographers.