Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Eleocharis reznicekii (Cyperaceae), a new species from the Mexican High Plateau

Eleocharis reznicekii (Cyperaceae, subg. Eleocharis, series Eleocharis), is described and illustrated. It is morphologically intermediate between E. densa and two species of Eleocharis subseries Eleocharis (E. macrostachya and E. palustris). The new species differs in a combination of characters including conspicuously compressed culms (3 to over 5 times wider than thick) and stylopodium sessile on a thin annular base. Eleocharis reznicekii differs additionally from E. densa by having relatively lax spikelets, mostly bifid styles, and achenes almost smooth at 30x. From E. macrostachya and E. palustris it is distinguished in its oblong to linear-oblong spikelets, the proximal floral scale clasping only 1/3 to slightly more than 1/2 of the culm, and the proximal plus 1-2(3) subproximal scales without a flower. Eleocharis reznicekii is known only from the state of Durango, in the Mexican high plateau and piedmont of the Sierra Madre Occidental.Se describe e ilustra Eleocharis reznicekii (Cyperaceae, subg. Eleocharis, serie Eleocharis), especie con características morfológicas intermedias entre las de Eleocharis densa y las de dos especies de la subserie Eleocharis (E. macrostachya y E. palustris). Se distingue por tener tallos conspicuamente comprimidos (3-5 veces más anchos que gruesos en fresco) y estilopodio sésil sobre una base anular fina. De E. densa se distingue además por tener espiguillas menos densas, estilos en su mayoría bífidos y aquenio casi liso a 30x, más redondeado hacia el ápice. De E. macrostachya y E. palustris lo hace por su hábito más robusto, espiguillas oblongas a linear-oblongas, gluma proximal envolviendo únicamente 1/3 a poco más de 1/2 de la base de la espiga, y por tener la gluma proximal y 1 a 2(3) glumas subproximales sin flor. Hasta ahora, E. reznicekii se conoce solamente del estado de Durango, en el Altiplano Mexicano y piedemonte de la Sierra Madre Occidenta