Edaphic specialization onto bare, rocky outcrops as a factor in the evolution of desert angiosperms.

Understanding the processes that enable organisms to shift into more arid environments as they emerge is critical for gauging resilience to climate change, yet these forces remain poorly known. In a comprehensive clade-based study, we investigate recent shifts into North American deserts in the rock daisies (tribe Perityleae), a diverse tribe of desert sunflowers (Compositae). We sample rock daisies across two separate contact zones between tropical deciduous forest and desert biomes in western North America and infer a time-calibrated phylogeny based on target capture sequence data. We infer biome shifts using Bayesian inference with paleobiome-informed models and find evidence for seven independent shifts into desert habitats since the onset of aridification in the late Miocene. The earliest shift occurred out of tropical deciduous forests and led to an extensive radiation throughout North American deserts that accounts for the majority of extant desert rock daisies. Estimates of life history and micro-habitat in the rock daisies reveal a correlation between a suffrutescent perennial life history and edaphic endemism onto rocky outcrops, an ecological specialization that evolved prior to establishment and diversification in deserts. That the insular radiation of desert rock daisies stemmed from ancestors preadapted for dry conditions as edaphic endemics in otherwise densely vegetated tropical deciduous forests in northwest Mexico underscores the crucial role of exaptation and dispersal for shifts into arid environments.

The "evil tribe" spreads across the land: A dated molecular phylogeny provides insight into dispersal, expansion, and biogeographic relationships within one of the largest tribes of the sunflower family (Vernonieae: Compositae).

PREMISE: With over 1500 species, the globally distributed Vernonieae is one of the most successful members of the largest family of flowering plants, the Compositae. However, due to its morphological complexity and limited geographic representation in previous studies, subtribal and biogeographic relationships are unclear. Here, new DNA sequence data spanning the geographic range of the tribe provides a taxonomically robust time-calibrated phylogeny, estimates migration pathways and timing of important biogeographic events, and allows inference of environmental factors that have contributed to the success of the Vernonieae worldwide. METHODS: Phylogenetic relationships were estimated for 368 taxa representing all Vernonieae subtribes. Molecular clock and ancestral range estimation analyses provide a framework for inference of the biogeographic history of the tribe. RESULTS: Relationships among the subtribes were established and correct placement determined for problematic taxa, along with the first model-based assessment of the biogeographic history of the tribe. The Vernonieae were estimated to have evolved ~50 mya. Africa was the first center of diversity, from which a single dispersal event established the monophyletic New World lineage. Long-distance dispersal from Africa and Brazil established the tribe on five continents and Oceania. CONCLUSIONS: The New World lineage is monophyletic, but Old World taxa are not. New subtribal taxonomies are needed. Moquinieae are nested in Vernonieae. Long-distance dispersal from Africa beginning 45 mya was key to establishing the tribe's near-global distribution. Migration corridors created by volcanic mountain chains and iron-rich soils in Africa and the Americas promoted radiation and range expansion.

Both temperature fluctuations and East Asian monsoons have driven plant diversification in the karst ecosystems from southern China.

Karst ecosystems in southern China are species-rich and have high levels of endemism, yet little is known regarding the evolutionary processes responsible for the origin and diversification of karst biodiversity. The genus Primulina (Gesneriaceae) comprises ca. 170 species endemic to southern China with high levels of ecological (edaphic) specialization, providing an exceptional model to study the plant diversification in karsts. We used molecular data from nine chloroplast and 11 nuclear regions and macroevolutionary analyses to assess the origin and cause of species diversification due to palaeoenvironmental changes and edaphic specialization in Primulina. We found that speciation was positively associated with changes in past temperatures and East Asian monsoons through the evolutionary history of Primulina. Climatic change around the mid-Miocene triggered an early burst followed by a slowdown of diversification rate towards the present with the climate cooling. We detected different speciation rates among edaphic types, and transitions among soil types were infrequently and did not impact the overall speciation rate. Our findings suggest that both global temperature changes and East Asian monsoons have played crucial roles in floristic diversification within the karst ecosystems in southern China, such that speciation was higher when climate was warmer and wetter. This is the first study to directly demonstrate that past monsoon activity is positively correlated with speciation rate in East Asia. This case study could motivate further investigations to assess the impacts of past environmental changes on the origin and diversification of biodiversity in global karst ecosystems, most of which are under threat.

Competitive avoidance not edaphic specialization drives vertical niche partitioning among sister species of ectomycorrhizal fungi.

Soil depth partitioning is thought to promote the diversity of ectomycorrhizal (EM) fungal communities, but little is known about whether it is controlled by abiotic or biotic factors. In three bioassay experiments, we tested the role of vertical soil heterogeneity in determining the distributions and competitive outcomes of the EM sister species Rhizopogon vinicolor and Rhizopogon vesiculosus. We planted Pseudotsuga menziesii seedlings into soils that were either a homogenized mix of upper and lower depths or vertically stratified combinations mimicking natural field conditions. We found that both species colonized the upper or lower soil depths in the absence of competition, suggesting that their distributions were not limited by abiotic edaphic factors. In competition within homogeneous soils, R. vesiculosus completely excluded colonization by R. vinicolor, but R. vinicolor was able to persist when soils were stratified. The amount of colonization by R. vinicolor in the stratified soils was also significantly correlated with the number of multilocus genotypes present. Taken together, our findings suggest that the differential vertical distributions of R. vinicolor and R. vesiculosus in natural settings are probably attributable to competition rather than edaphic specialization, but that soil heterogeneity may play a key role in promoting EM fungal diversity.

Large herbivores promote habitat specialization and beta diversity of African savanna trees.

Edaphic variation in plant community composition is widespread, yet its underlying mechanisms are rarely understood and often assumed to be physiological. In East African savannas, Acacia tree species segregate sharply across soils of differing parent material: the ant-defended whistling thorn, A. drepanolobium (ACDR), is monodominant on cracking clay vertisols that are nutrient rich but physically stressful, whereas poorly defended species such as A. brevispica (ACBR) dominate on nutrient-poor but otherwise less-stressful sandy loams. Using a series of field experiments, we show that large-mammal herbivory interacts with soil properties to maintain this pattern. In the absence of large herbivores, transplanted saplings of both species established on both soil types. Browsers strongly suppressed survival and growth of ACDR saplings on sandy soil, where resource limitation constrained defensive investment. On clay soil, ACBR saplings established regardless of herbivory regime, but elephants prevented recruitment to maturity, apparently because trees could not tolerate the combination of biotic and abiotic stressors. Hence, each tree species was filtered out of one habitat by browsing in conjunction with different edaphic factors and at different ontogenetic stages. Browser abundance was greater on sandy soil, where trees were less defended, consistent with predicted feedbacks between plant community assembly and herbivore distributions. By exploring two inversely related axes of soil "quality" (abiotic stress and nutrient content), our study extends the range of mechanisms by which herbivores are known to promote edaphic specialization, illustrates how the high cost of a protection mutualism can constrain the realized niche of host trees, and shows that large-scale properties of savanna ecosystems are shaped by species interactions in cryptic ways that mimic simple abiotic determinism. These results suggest that ongoing declines in large-herbivore populations may relax spatial heterogeneity in plant assemblages and reduce the beta diversity of communities.

Macroevolutionary patterns of glucosinolate defense and tests of defense-escalation and resource availability hypotheses.

We explored macroevolutionary patterns of plant chemical defense in Streptanthus (Brassicaceae), tested for evolutionary escalation of defense, as predicted by Ehrlich and Raven's plant-herbivore coevolutionary arms-race hypothesis, and tested whether species inhabiting low-resource or harsh environments invest more in defense, as predicted by the resource availability hypothesis (RAH). We conducted phylogenetically explicit analyses using glucosinolate profiles, soil nutrient analyses, and microhabitat bareness estimates across 30 species of Streptanthus inhabiting varied environments and soils. We found weak to moderate phylogenetic signal in glucosinolate classes and no signal in total glucosinolate production; a trend toward evolutionary de-escalation in the numbers and diversity of glucosinolates, accompanied by an evolutionary increase in the proportion of aliphatic glucosinolates; some support for the RAH relative to soil macronutrients, but not relative to serpentine soil use; and that the number of glucosinolates increases with microhabitat bareness, which is associated with increased herbivory and drought. Weak phylogenetic signal in chemical defense has been observed in other plant systems. A more holistic approach incorporating other forms of defense might be necessary to confidently reject escalation of defense. That defense increases with microhabitat bareness supports the hypothesis that habitat bareness is an underappreciated selective force on plants in harsh environments.

Taxonomic, biological and geographical traits of species in a coastal dune flora in the southeastern Cape Floristic Region: regional and global comparisons.

In Mediterranean-Climate Ecosystems (MCEs), Holocene coastal dunes comprise small, fragmented and dynamic features which have nutritionally imbalanced and excessively drained, droughty, sandy soils. These characteristics, along with summer drought and salt-laden winds, pose many challenges for plant colonization and persistence. Consequently, MCE dune floras are likely to be distinctive with a high proportion of habitat specialists and strong convergence in growth form mixes. Very little research has compared the species traits of dune floras within and across MCEs. This paper contributes to filling that gap. Here, we analyze the taxonomic, biological and geographical traits for all 402 species in a flora from a dune landscape (Cape St Francis) in the southeastern Cape Floristic Region (CFR) and compare patterns with the trait profiles of other dune floras at a regional (CFR) and global (MCE) scale. Within the CFR, the southeastern (all-year-rainfall) flora at Cape St Francis had a similar trait profile to western (winter-rainfall) dune floras, except for having a lower representation of species belonging to CFR-endemic clades, and higher number of species associated with tropical lineages. The St Francis flora, in common with other CFR and MCE floras, was dominated by members of the Asteraceae, Fabaceae and Poaceae. Some 40% of the St Francis flora was endemic to the CFR, typical of the high rate of MCE-level endemism elsewhere in the CFR, and in other MCEs. About 30% of the flora was confined to calcareous sand, a value typical for many other MCE sites. The St Francis flora, as well as other CFR dune floras, differs from those of other MCEs by having many species associated with shrubby lineages, and by the relatively high incidence of species associated with tropical lineages. The growth form profile of the St Francis and other CFR floras shows strongest similarity with that of Australian MCE dunes in that in both regions, evergreen hemicryptophytes and shrubs share dominance, and annuals are floristically and ecologically subordinate. The least similar of MCEs to the St Francis trait profile is the Mediterranean Basin where annuals are the most frequent growth form while shrubs are subordinate. California and Chile dune floras appear to occupy an intermediate position, in terms of growth form mix, between the Cape and Australia on the one hand, where dune floras have retained features typical of nutrient-poor soils, and the Mediterranean Basin, where dwarf, deciduous shrubs and annuals dominate the life form spectrum. All MCE dunes are threatened by alien plants, infrastructure development, tourism demands and rising sea levels. The high incidence of species of conservation concern in CFR dune floras underestimates the exponentially increasing threats to their habitats, which are already historically at a much-reduced extent. All remaining coastal dune habitat in the CFR, and probably in other MCEs, should be conserved in their entirety.

Woody species distribution across a savanna-dry forest soil gradient in the Brazilian Cerrado / Distribuição de espécies arbóreas em gradiente de solo savana-floresta seca no Cerrado brasileiro

Although richness and distribution of woody species in the Cerrado physiognomies have been extensively studied, the shifts of woody species from savanna physiognomies to dry forests have not yet been addressed. Here, we investigate the effect of soil physical-chemical traits on the woody species turnover between adjacent cerrado stricto sensu and dry forest physiognomies. Woody species were surveyed, and soil and topographic variables measured, in 30 10×40 m plots systematically distributed, with 15 plots in each physiognomy. We found a spatially structured distribution of woody species, and differences of soil traits between cerrado stricto sensu and dry forest areas, mainly related to the aluminum saturation, base saturation, and available phosphorus. Aluminum saturation increased toward the savanna area, while base saturation increased toward the dry forest. Most woody species predominated in one physiognomy, such as Callisthene major in the cerrado stricto sensu and Anadenanthera colubrina in the dry forest. Only 20% of the species were widely distributed across both physiognomies or, not often, restricted to the intermediary values of the soil gradient. General results indicate that contrasting soil traits between cerrado stricto sensu and dry forest produce a strongly spatially organized and sharp transition in terms of species distribution between these physiognomies.

Embora a distribuição e a riqueza em espécies arbóreas nas fitofisionomias do Cerrado venham sendo bastante estudadas, a transição entre savanas e florestas deciduais ainda não foi abordada. Investigamos o efeito de características físico-químicas do solo sobre a distribuição de espécies arbóreas em região de contato entre cerrado sentido restrito e floresta estacional decidual (FED). As espécies arbóreas foram amostradas sistematicamente, e variáveis de topografia e características do solo foram medidas em 30 parcelas de 10×40 m, sendo 15 parcelas em cada fisionomia. A distribuição das espécies arbóreas foi espacialmente estruturada, e as características do solo diferiram entre as áreas de cerrado sentido restrito e FED, principalmente relacionadas à saturação de alumínio, saturação de bases e teores de fósforo. A saturação de alumínio aumentou em direção ao cerrado sentido restrito, enquanto a saturação de bases aumentou em direção à FED. A maioria das espécies arbóreas predominou em uma das fisionomias, como Callisthene major em cerrado sentido restrito e Anadenanthera colubrina em FED. Apenas 20% das espécies foram amplamente distribuídas em ambas as fisionomias ou, em poucos casos, restritas aos valores intermediários do gradiente de solo. Os resultados indicam um forte contraste de características do solo entre o cerrado sentido restrito e a FED, assim como uma transição acentuada e espacialmente organizada quanto à distribuição de espécies arbóreas.

Woody species distribution across a savanna-dry forest soil gradient in the Brazilian Cerrado

Abstract Although richness and distribution of woody species in the Cerrado physiognomies have been extensively studied, the shifts of woody species from savanna physiognomies to dry forests have not yet been addressed. Here, we investigate the effect of soil physical-chemical traits on the woody species turnover between adjacent cerrado stricto sensu and dry forest physiognomies. Woody species were surveyed, and soil and topographic variables measured, in 30 10×40 m plots systematically distributed, with 15 plots in each physiognomy. We found a spatially structured distribution of woody species, and differences of soil traits between cerrado stricto sensu and dry forest areas, mainly related to the aluminum saturation, base saturation, and available phosphorus. Aluminum saturation increased toward the savanna area, while base saturation increased toward the dry forest. Most woody species predominated in one physiognomy, such as Callisthene major in the cerrado stricto sensu and Anadenanthera colubrina in the dry forest. Only 20% of the species were widely distributed across both physiognomies or, not often, restricted to the intermediary values of the soil gradient. General results indicate that contrasting soil traits between cerrado stricto sensu and dry forest produce a strongly spatially organized and sharp transition in terms of species distribution between these physiognomies.

Resumo Embora a distribuição e a riqueza em espécies arbóreas nas fitofisionomias do Cerrado venham sendo bastante estudadas, a transição entre savanas e florestas deciduais ainda não foi abordada. Investigamos o efeito de características físico-químicas do solo sobre a distribuição de espécies arbóreas em região de contato entre cerrado sentido restrito e floresta estacional decidual (FED). As espécies arbóreas foram amostradas sistematicamente, e variáveis de topografia e características do solo foram medidas em 30 parcelas de 10×40 m, sendo 15 parcelas em cada fisionomia. A distribuição das espécies arbóreas foi espacialmente estruturada, e as características do solo diferiram entre as áreas de cerrado sentido restrito e FED, principalmente relacionadas à saturação de alumínio, saturação de bases e teores de fósforo. A saturação de alumínio aumentou em direção ao cerrado sentido restrito, enquanto a saturação de bases aumentou em direção à FED. A maioria das espécies arbóreas predominou em uma das fisionomias, como Callisthene major em cerrado sentido restrito e Anadenanthera colubrina em FED. Apenas 20% das espécies foram amplamente distribuídas em ambas as fisionomias ou, em poucos casos, restritas aos valores intermediários do gradiente de solo. Os resultados indicam um forte contraste de características do solo entre o cerrado sentido restrito e a FED, assim como uma transição acentuada e espacialmente organizada quanto à distribuição de espécies arbóreas.

Woody species distribution across a savanna-dry forest soil gradient in the Brazilian Cerrado / Distribuição de espécies arbóreas em gradiente de solo savana-floresta seca no Cerrado brasileiro

Abstract Although richness and distribution of woody species in the Cerrado physiognomies have been extensively studied, the shifts of woody species from savanna physiognomies to dry forests have not yet been addressed. Here, we investigate the effect of soil physical-chemical traits on the woody species turnover between adjacent cerrado stricto sensu and dry forest physiognomies. Woody species were surveyed, and soil and topographic variables measured, in 30 10×40 m plots systematically distributed, with 15 plots in each physiognomy. We found a spatially structured distribution of woody species, and differences of soil traits between cerrado stricto sensu and dry forest areas, mainly related to the aluminum saturation, base saturation, and available phosphorus. Aluminum saturation increased toward the savanna area, while base saturation increased toward the dry forest. Most woody species predominated in one physiognomy, such as Callisthene major in the cerrado stricto sensu and Anadenanthera colubrina in the dry forest. Only 20% of the species were widely distributed across both physiognomies or, not often, restricted to the intermediary values of the soil gradient. General results indicate that contrasting soil traits between cerrado stricto sensu and dry forest produce a strongly spatially organized and sharp transition in terms of species distribution between these physiognomies.

Resumo Embora a distribuição e a riqueza em espécies arbóreas nas fitofisionomias do Cerrado venham sendo bastante estudadas, a transição entre savanas e florestas deciduais ainda não foi abordada. Investigamos o efeito de características físico-químicas do solo sobre a distribuição de espécies arbóreas em região de contato entre cerrado sentido restrito e floresta estacional decidual (FED). As espécies arbóreas foram amostradas sistematicamente, e variáveis de topografia e características do solo foram medidas em 30 parcelas de 10×40 m, sendo 15 parcelas em cada fisionomia. A distribuição das espécies arbóreas foi espacialmente estruturada, e as características do solo diferiram entre as áreas de cerrado sentido restrito e FED, principalmente relacionadas à saturação de alumínio, saturação de bases e teores de fósforo. A saturação de alumínio aumentou em direção ao cerrado sentido restrito, enquanto a saturação de bases aumentou em direção à FED. A maioria das espécies arbóreas predominou em uma das fisionomias, como Callisthene major em cerrado sentido restrito e Anadenanthera colubrina em FED. Apenas 20% das espécies foram amplamente distribuídas em ambas as fisionomias ou, em poucos casos, restritas aos valores intermediários do gradiente de solo. Os resultados indicam um forte contraste de características do solo entre o cerrado sentido restrito e a FED, assim como uma transição acentuada e espacialmente organizada quanto à distribuição de espécies arbóreas.