The geographic mosaic of plant chemistry and its effects on community and population genetic diversity In 1802 naturalist

In 1802 naturalist Alexander von Humboldt, his botanist companion Aim e Bonpland, and the Ecuadorian Carlos Mont ufar attempted to ascend the 6263-m high Chimborazo volcano in Ecuador, which was then thought to be the highestmountain in the world. The small group of explorers onlymade it to 5875 m, higher than any European before them, but they came back with an outstanding collection of botanical specimens and unusually detailed data on plant community composition. Von Humboldt compiled these data in his famous 1805 map depicting the ‘distribution of plants in equinoctial America, according to elevation above the level of the sea’ (Fig. 1; von Humboldt & Bonpland, 2009). This work established that plant communities assembled according to physical properties of the habitat, such as precipitation, mean annual temperature and soil conditions, and this built the basis for many fields of modern biology, for example, biogeography, and more recently, modeling of ecosystem changes as a result of global warming. Elevational and latitudinal gradients became an important subject and tool of research in ecophysiology, community and population ecology (Lomolino & Brown, 2004). With the changes in the physical properties of a habitat, interactions among organisms change as well. Thus natural selection on a population of organisms is a function of the interactions with other species and the environmental context in which these interactions are played out, both of which are likely to vary with geographic location. A resulting mosaic of geographically differential natural selection with co-evolutionary hotspots and trait remixing was hypothesized as a major driver of population-genetic structure and speciation (Thompson, 1999). Almost 210 years after the attempt to reach the summit of Chimborazo by von Humboldt, Bonpland and Mont ufar, and only 130 km northeast, at the Yanayacu Biological Station on the Eastern slope of the Andean Antisana volcano, Glassmire et al. (in this issue of New Phytologist, pp. 208–219) studied a midcanopy shrub, Piper kelleyi Tepe (Piperaceae) (Fig. 2a), which is endemic to the eastern slope of the Andes within a narrow range of between 1400 and 2400 m in altitude (Tepe et al., 2014). Instead of studying communities along altitude gradients per se, they studied the interaction of variation on the population level with that on the community level and with it the increasingly appreciated interaction between ecological and evolutionary processes. Glassmire et al. report results of their study on the secondary metabolite variation among subpopulations of P. kelleyi and the effects of the phenotypic variation on herbivore and parasitoid community composition and population-genetic structure (Fig. 2). Community composition of a group of specialist lepidopteran herbivores in the Eois (Geometridae: Larentiinae) genus, as well as their parasitoid wasp community, varied with the concentrations of three prenylated bencoic acid derivatives that had previously been shown to negatively affect herbivores, fungi and bacteria (Jeffrey et al., 2014). While the relative chemical composition of plants varied widely and with elevation, higher concentrations of chromene, prenylated benzoic acid and dimeric chromane supported lower diversity of the