Environmental causes for plant biodiversity gradients

Abstract

One of the most pervasive patterns observed in biodiversity studies is the tendency for species richness to decline towards the poles. One possible explanation is that high levels of environmental energy promote higher species richness nearer the equator. Energy input may set a limit to the number of species that can coexist in an area or alternatively may influence evolutionary rates. Within flowering plants (angiosperms), families exposed to a high energy load tend to be both more species rich and possess faster evolutionary rates, although there is no evidence that one drives the other. Specific environmental effects are likely to vary among lineages, reflecting the interaction between biological traits and environmental conditions in which they are found. One example of this is demonstrated by the high species richness of the iris family (Iridaceae) in the Cape of South Africa, a likely product of biological traits associated with reproductive isolation and the steep ecological and climatic gradients of the region. Within any set of conditions some lineages will tend to be favoured over others; however, the identity of these lineages will fluctuate with a changing environment, explaining the highly labile nature of diversification rates observed among major lineages of flowering plants.

Phylogenetic diversity as a window into the evolutionary and biogeographic histories of present-day richness gradients for mammals

“…To date, results have been mixed, for example, Cardillo et al [72,73] and Ricklefs [74] reported faster rates of diversification at lower latitude in birds, but Wiens et al [75] [77,78]. Area by far explains the most variation in diversification models for plants [79][80][81], but significant additional variation in rates is explained by environmental energy [80,82].…”

Introduction and synthesis: plant phylogeny and the origin of major biomes

“…The amount of energy input into a system may limit the number of species that coexist in an area or influence evolutionary rates. Davies et al (2004) demonstrate that angiosperm families that are exposed to a high-energy load tend to be both more species rich and possess faster evolutionary rates, although it is not known whether one drives the other. They also highlight the case of Iridaceae, which demonstrates that the effects of the environment can vary among lineages.…”

“…The final paper (Davies et al 2004) takes a different approach and asks why some biomes contain more species. There may be contemporary ecological explanations for this phenomenon in that different biomes may allow differing numbers of species to coexist.…”

“…However, why did more species evolve (or less become extinct) in different biomes? Davies et al (2004) take a global perspective to try to determine some of the causes of these patterns. One pattern that has been observed is that species richness tends to decline towards the poles.…”

“…One pattern that has been observed is that species richness tends to decline towards the poles. Davies et al (2004) investigate the possibility that high levels of environmental energy promote higher species richness nearer the Equator. The amount of energy input into a system may limit the number of species that coexist in an area or influence evolutionary rates.…”