Caught in the Act: Incipient Speciation at the Southern limit of Viburnum in the Central Andes.

A fundamental objective of evolutionary biology is to understand the origin of independently evolving species. Phylogenetic studies of species radiations rarely are able to document ongoing speciation; instead, modes of speciation, entailing geographic separation and/or ecological differentiation, are posited retrospectively. The Oreinotinus clade of Viburnum has radiated recently from north to south through the cloud forests of Mexico and Central America to the Central Andes. Our analyses support a hypothesis of incipient speciation in Oreinotinus at the southern edge of its geographic range, from central Peru to northern Argentina. Although several species and infraspecific taxa of have been recognized in this area, multiple lines of evidence and analytical approaches (including analyses of phylogenetic relationships, genetic structure, leaf morphology, and climatic envelopes) favor the recognition of just a single species, V. seemenii. We show that what has previously been recognized as V. seemenii f. minor has recently occupied the drier Tucuman-Bolivian forest region from Samaipata in Bolivia to Salta in northern Argentina. Plants in these populations form a well-supported clade with a distinctive genetic signature and they have evolved smaller, narrower leaves. We interpret this as the beginning of a within-species divergence process that has elsewhere in the neotropics resulted repeatedly in Viburnum species with a particular set of leaf ecomorphs. Specifically, the southern populations are in the process of evolving the small, glabrous, and entire leaf ecomorph that has evolved in four other montane areas of endemism. As predicted based on our studies of leaf ecomorphs in Chiapas, Mexico, these southern populations experience generally drier conditions, with large diurnal temperature fluctuations. In a central portion of the range of V. seemenii, characterized by wetter climatic conditions, we also document what may be the initial differentiation of the leaf ecomorph with larger, pubescent, and toothy leaves. The emergence of these ecomorphs thus appears to be driven by adaptation to subtly different climatic conditions in separate geographic regions, as opposed to parapatric differentiation along elevational gradients as suggested by Viburnum species distributions in other parts of the neotropics.

Ecological quality as a coffee quality enhancer. A review.

As both coffee quality and sustainability become increasingly important, there is growing interest in understanding how ecological quality affects coffee quality. Here we analyze, for the first time, the state of evidence that ecological quality, in terms of biodiversity and ecosystem functions, impacts the quality of Coffea arabica and C. canephora, based on 78 studies. The following ecosystem functions were included: pollination; weed, disease, and pest control; water and soil fertility regulation. Biodiversity was described by the presence, percentage, and diversity of shade trees. Coffee quality was described by the green bean physical characteristics, biochemical compounds, and organoleptic characteristics. The presence and diversity of shade trees positively impacted bean size and weight and reduced the percentage of rejected beans, but these observations were not consistent over different altitudes. In fact, little is known about the diversity of shade trees and their influence on biochemical compounds. All biochemical compounds varied with the presence of shade, percentage of shade, and elevation. Coffee beans from more diverse tree shade plantations obtained higher scores for final total organoleptic quality than simplified tree shade and unshaded plantations. Decreasing ecological quality diminished ecosystem functions such as pollination, which in turn negatively affected bean quality. Shade affected pests and diseases in different ways, but weeds were reduced. High soil quality positively affected coffee quality. Shade improved the water use efficiency, such that coffee plants were not water stressed and coffee quality was improved. While knowledge on the influence of shade trees on overall coffee quality remains scarce, there is evidence that agroecosystem simplification is negatively correlated with coffee quality. Given global concerns about biodiversity and habitat loss, we recommend that the overall definition of coffee quality include measures of ecological quality, although these aspects are not always detectable in certain coffee quality characteristics or the final cup.

Elevational gradients in ß-diversity reflect variation in the strength of local community assembly mechanisms across spatial scales.

Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (ß-diversity) across elevations. Recent studies have suggested that ß-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic ß-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of ß-diversity to null-model expectations. ß-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in ß-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in ß-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in ß-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in ß-diversity. In contrast to the hypothesis that variation in species pools alone drives ß-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in ß-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.