Diversity patterns of selected Andean plant groups correspond to topography and habitat dynamics, not orogeny.

Jens Mutke,Rana Jacobs,Maximilian Weigend,Katharina Meyers,Tilo Henning

doi:10.3389/fgene.2014.00351

Abstract

The tropical Andes are a hotspot of biodiversity, but detailed altitudinal and latitudinal distribution patterns of species are poorly understood. We compare the distribution and diversity patterns of four Andean plant groups on the basis of georeferenced specimen data: the genus Nasa (Loasaceae), the two South American sections of Ribes (sect. Parilla and sect. Andina, Grossulariaceae), and the American clade of Urtica (Urticaceae). In the tropical Andes, these often grow together, especially in (naturally or anthropogenically) disturbed or secondary vegetation at middle to upper elevations. The climatic niches of the tropical groups studied here are relatively similar in temperature and temperature seasonality, but do differ in moisture seasonality. The Amotape–Huancabamba Zone (AHZ) between 3 and 8° S shows a clear diversity peak of overall species richness as well as for narrowly endemic species across the groups studied. For Nasa, we also show a particular diversity of growth forms in the AHZ. This can be interpreted as proxy for a high diversity of ecological niches based on high spatial habitat heterogeneity in this zone. Latitudinal ranges are generally larger toward the margins of overall range of the group. Species number and number of endemic species of our taxa peak at elevations of 2,500–3,500 m in the tropical Andes. Altitudinal diversity patterns correspond well with the altitudinal distribution of slope inclination. We hypothesize that the likelihood and frequency of landslides at steeper slopes translate into temporal habitat heterogeneity. The frequency of landslides may be causally connected to diversification especially for the numerous early colonizing taxa, such as Urtica and annual species of Nasa. In contrast to earlier hypotheses, uplift history is not reflected in the pattern here retrieved, since the AHZ is the area of the most recent Andean uplift. Similarly, a barrier effect of the low-lying Huancabamba depression is not retrieved in our data.

Highlights

ANDEAN DIVERSITY GRADIENTS The northern and central Andes have been identified as globally outstanding centers of plant diversity across life forms and phylogenetic groups (Gentry, 1982; Myers et al, 2000; Barthlott et al, 2005; Mutke et al, 2011)
Plant endemism in Peru peaks at 1,500–3,000 m across life forms, a figure based on the overall predominance of epiphytes, terrestrial herbs, and shrubs amongst endemic taxa (Van Der Werff and Consiglio, 2004)
“Density” of endemic species in their study was even found to be more than 10 times higher at 2,000–3,500 m than in the Amazonian lowlands (0–500 m, Van Der Werff and Consiglio, 2004) – this was computed based on a linear species-area relationship, which is at least problematic

Summary

Introduction

ANDEAN DIVERSITY GRADIENTS The northern and central Andes have been identified as globally outstanding centers of plant diversity across life forms and phylogenetic groups (Gentry, 1982; Myers et al, 2000; Barthlott et al, 2005; Mutke et al, 2011). A widely cited study by Terborgh (1977) shows a monotonic decrease of bird species richness with elevation in the Peruvian Andes. In the Peruvian flora, epiphytic orchids show highest species richness at lower and mid elevations up to 2,000 m above sea level (m a.s.l.). Overall diversity of tree taxa and of the entire flora across taxonomic groups and life forms peaks at low elevations (

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