Showing papers by "Andy Hector published in 2006"

Conventional functional classification schemes underestimate the relationship with ecosystem functioning

Abstract: Studies linking the functional diversity of a biota to ecosystem functioning typically employ a priori classifications of species into hypothetically complementary groups. However, multiple alternate classifications exist in which the number of functional groups, the number of species per functional group, and the grouping of species differ from the a priori scheme. Without assessing the relative precision, or ability of an a priori scheme to accurately predict ecosystem functioning relative to its many alternatives, the validity and utility of analyses based on a single a priori classification scheme remains unclear. We examine the precision of a priori classifications used in 10 experimental grassland systems in Europe and the United States that have found evidence for a significant role of functional plant diversity in governing ecosystem function. The predictive precision of the a priori classifications employed in these studies was seldom significantly higher than the precision of random classifications. Post-hoc classification schemes that performed well in predicting ecosystem function resembled each other more with regard to species composition than average classifications, but there was still considerable variability in the manner in which these classification schemes grouped species. These results suggest that we need a more nuanced understanding of how the diversity of functional traits of species in an assemblage affects ecosystem functioning.

Overyielding and stable species coexistence.

Abstract: The concept of overyielding originated in plant sciences in the 1950s and 1960s and was widely used in the following decades to assess whether mixtures of plants performed better than expected when compared with monocultures. Overyielding has re-emerged in the last few years as an important method in the analysis of biodiversity experiments (Hector, 1998; Loreau, 1998; Loreau et al., 2001, 2002; Hooper et al., 2005) and other new research areas (Bernasconi et al., 2003). Biodiversity experiments manipulate community diversity (while holding other factors constant) to investigate impacts on ecosystem functioning. Previously, use of the overyielding concept has been limited mainly to the analysis of community ecology experiments on species interactions and in agricultural research, particularly intercropping. However, there has been relatively little work that assesses the overyielding concept in the context of community ecology theory. Loreau (2004) used the classical Lotka–Volterra competition model to investigate overyielding and functional redundancy of species in the context of theory on the stable coexistence of species (Fig. 1). In this issue, Beckage & Gross (pp. 140–148) also use Lotka–Volterra competition models to assess the frequency and degree of overyielding of theoretical communities.

Seed size variability: from carob to carats

Abstract: The seeds of various plants were used as weights because their mass reputedly varies so little. Carob (Ceratonia siliqua), which has given its name to the carat, is particularly famous in this regard. But are carob seeds unusually constant in weight and, if not, how did the myth arise? The variability of seeds sampled from a collection of carob trees (CV=23%) was close to the average of 63 species reviewed from the literature (CV=25%). However, in a perception experiment observers could discriminate differences in carob seed weight of around 5% by eye demonstrating the potential for humans to greatly reduce natural variation. Interestingly, the variability of pre-metrication carat weight standards is also around 5% suggesting that human rather than natural selection gave rise to the carob myth.