Latitudinal Variation in Plant Functional Types

Abstract

Relationships between species richness, diversity and latitudinal gradients present “the oldest problem in ecology and biogeography” (Hawkins 2008). Overall biotic richness increases toward equatorial regions, but underlying explanations for this trend are inconclusive. One reason is that comparative studies of latitudinal variation at global scale are limited by a pervasive lack of uniformity in purpose and scale of data collection and analysis. This chapter explores patterns of functional diversity along latitudinal gradients across all major biomes using a global database in which all data were collected using a uniform survey protocol (VegClass). Plant functional attributes are considered at two levels: individual traits (plant functional elements or PFEs) and whole-plant syndromes or Plant Functional Types (PFTs). Together with species richness, the data reveal departures from a commonly assumed latitudinal trend that are manifested by as yet unexplained mid-latitudinal peaks. Spatial patterning between PFTs and functional traits and certain environmental factors (mainly climate and substrate) across multiple scales exhibit non-linear relationships that are generally consistent with known responses of plant functional characteristics. Other key factors that may contribute to latitudinal variation in PFTs are briefly reviewed including nutrient stoichiometry, differences in continental gene pools and land use history.