Showing papers by "Andy Hector published in 2009"

Competition for light causes plant biodiversity loss after eutrophication

Abstract: Human activities have increased the availability of nutrients in terrestrial and aquatic ecosystems. In grasslands, this eutrophication causes loss of plant species diversity, but the mechanism of this loss has been difficult to determine. Using experimental grassland plant communities, we found that addition of light to the grassland understory prevented the loss of biodiversity caused by eutrophication. There was no detectable role for competition for soil resources in diversity loss. Thus, competition for light is a major mechanism of plant diversity loss after eutrophication and explains the particular threat of eutrophication to plant diversity. Our conclusions have implications for grassland management and conservation policy and underscore the need to control nutrient enrichment if plant diversity is to be preserved.

Biodiversity, Ecosystem Functioning, and Human Wellbeing: An Ecological and Economic Perspective

Abstract: In an age of accelerating biodiversity loss, this timely and critical volume summarizes recent advances in biodiversity-ecosystem functioning research and explores the economics of biodiversity and ecosystem services. The book starts by summarizing the development of the basic science and provides a meta-analysis that quantitatively tests several biodiversity and ecosystem functioning hypotheses. It then describes the natural science foundations of biodiversity and ecosystem functioning research including: quantifying functional diversity, the development of the field into a predictive science, the effects of stability and complexity, methods to quantify mechanisms by which diversity affects functioning, the importance of trophic structure, microbial ecology, and spatial dynamics. Finally, the book takes research on biodiversity and ecosystem functioning further than it has ever gone into the human dimension, describing the most pressing environmental challenges that face humanity and the effects of diversity on: climate change mitigation, restoration of degraded habitats, managed ecosystems, pollination, disease, and biological invasions.However, what makes this volume truly unique are the chapters that consider the economic perspective. These include a synthesis of the economics of ecosystem services and biodiversity, and the options open to policy-makers to address the failure of markets to account for the loss of ecosystem services; an examination of the challenges of valuing ecosystem services and, hence, to understanding the human consequences of decisions that neglect these services; and an examination of the ways in which economists are currently incorporating biodiversity and ecosystem functioning research into decision models for the conservation and management of biodiversity. A final section describes new advances in ecoinformatics that will help transform this field into a globally predictive science, and summarizes the advancements and future directions of the field. The ultimate conclusion is that biodiversity is an essential element of any strategy for sustainable development.

Belowground nitrogen partitioning in experimental grassland plant communities of varying species richness.

Abstract: Partitioning of soil nitrogen (N) by niche separation among species may be an important mechanism explaining species coexistence and positive biodiversity-productivity relationships in terrestrial plant communities. However, there is little experimental evidence for such partitioning, in particular, as assessed across a gradient of species richness. In experimental communities of one, three, and six temperate grassland species in the field, we tested whether increasing species richness (1) decreases niche breadths of individual species, (2) decreases niche overlap among species, and (3) increases niche breadth of whole communities. Six N sources consisting of three different chemical forms of 15N-labeled N (15NO3(-), 15NH4+, 13C2-15N-glycine) injected at two soil depths (3 and 12 cm) were applied to each community. The chemical form and the soil depth of N characterize the niches for which niche breadth (Levins' B) and overlap (proportional similarity) were measured. After 48 hours, aboveground plant material was harvested to measure 15N enrichment. As expected, niche breadth of single species and niche overlap among species decreased with increased species richness, but community niche breadth did not increase. The decrease in niche breadth and niche overlap mostly occurred among subordinate species or pairs of subordinate and dominant species, rather than among dominant species. Species in the six-species mixtures mostly preferred NO3(-) from shallow soil. This may be partly explained by the presence of legumes in all six-species mixtures which allowed "N sparing" (i.e., increased availability of soil N since legumes rely more on atmospheric N2 than on soil N). Niche separation with respect to N uptake from different chemical forms and soil depths did not contribute much to facilitating the coexistence of dominant species, nor do our results suggest it as a major driver of positive diversity-ecosystem functioning relationships. However, partitioning of N may be important for the persistence of subordinate species.

A Linear Model Method for Biodiversity–Ecosystem Functioning Experiments

Abstract: Experiments that manipulate species richness and measure ecosystem functioning attempt to separate the effects of species richness (the number of species) from those of species identity. We introduce an experimental design that ensures that each species is selected the same number of times at each level of species richness. In combination with a linear model analysis, this approach is able to unambiguously partition the variance due to different species identities and the variance due to nonlinear species richness, a proxy measure for interactions among species. Our design and analysis provide several advantages over methods that are currently used. First, the linear model method has the potential to directly estimate the role of various ecological mechanisms (e.g., competition, facilitation) rather than the consequences of those mechanisms (e.g., the "complementarity effect"). Second, unlike other methods that are currently used, this one is able to estimate the impact of diversity when the contribution of individual species in a mixture is unknown.

The analysis of biodiversity experiments: from pattern toward mechanism

Abstract: Meta-analysis of the first generation of biodiversity experiments has revealed that there is a general positive relationship between diversity and ecosystem processes that is consistent across trophic groups and ecosystem types. However, the mechanisms generating these general patterns are still under debate. While there are unresolved conceptual issues about the nature of diversity and complementarity, the debate is partly due to the difficulty of performing a full-factorial analysis of the functional effects of all species in a diverse community. However, there are now several different analytical approaches that can address mechanisms even when full factorial analysis is not possible. This chapter presents an overview and users' guide to these methods. This chapter concludes that the current toolbox of methods allows investigation of the mechanisms for most, if not all, biodiversity and ecosystem functioning experiments conducted to date that manipulate species within a single trophic level (e.g. plant biodiversity experiments). Methods that can address mechanisms in multitrophic studies are a key need for future research.

Effects of biodiversity on the functioning of ecosystems: a summary of 164 experimental manipulations of species richness

Abstract: Over the past decade, accelerating rates of species extinction have prompted an increasing number of studies to reduce the number of species experimentally in a variety of ecosystems and examine how this aspect of diversity alters the efficiency by which communities capture biologically essential resources and convert them into new tissue. Here we summarize the results of 164 experiments (reported in 84 publications) that have manipulated the richness of primary producers, herbivores, detritivores, or predators in a variety of terrestrial and aquatic ecosystems and examined how this impacts (1) the standing stock abundance or biomass of the focal trophic group, (2) the abundance or biomass of that trophic group's primary resource(s), and/or (3) the extent to which that trophic group depletes its resource(s). Our summary includes studies that have focused on the top-down effects of diversity, whereby researchers have examined how the richness of trophic group t impacts the consumption of a shared resource, and also studies that have focused on the bottom-up effects of diversity, whereby researchers have examined how the richness of trophic group t impacts consumption of t by the next highest trophic level. The first portion of the data set provides information about the source of data and relevant aspects of the experimental design, including the spatial and temporal scales at which the work was performed. The second portion gives the magnitude of each response variable, the standard deviation, and the level of replication at each level of species richness manipulated. The third portion of the data set summarizes the magnitude of diversity effects in two ways. First, log ratios are used to compare the response variable in the most diverse polyculture to either the mean of all monocultures or the species having the highest/lowest value in monoculture. Second, data from each level of species richness are fit to three nonlinear functions (log, power, and hyperbolic) to assess which best characterizes the shape of diversity effects. The final portion of the data set summarizes any information that helps parse diversity effects into that attributable to species richness vs. that attributable to changes in species composition across levels of richness. The complete data sets corresponding to abstracts published in the Data Papers section of the journal are published electronically in Ecological Archives at 〈http://esapubs.org/archive〉. (The accession number for each Data Paper is given directly beneath the title.)

Introduction: The ecological and social implications of changing biodiversity. An overview of a decade of biodiversity and ecosystem functioning research

Abstract: Conventional approaches to ecology often lack the necessary integration to make a compelling case for the critical importance of biodiversity to ecosystem functioning and human wellbeing. This linear approach does not prepare one for understanding and applying ecology in the context of the modern world. A different, rather unconventional approach is needed for understanding ecology and environmental biology, one that asks the question that is rarely asked — What is the significance of biodiversity to human wellbeing? That is what this book asks.

Darwin's "Principle of divergence" and the link between biodiversity and ecosystem functioning

Abstract: The effect of biodiversity loss on ecosystem functioning is a relatively new research topic in ecology. The motivation for this research comes largely from current forecasts of ongoing loss of biodiversity. However, the intellectual link between biodiversity and ecosystem processes was first inferred by Darwin based on his Principle of Divergence. In the notes for his Big Species Book Darwin explicitly states that communities composed of organisms developed under “many and widely differing forms” should have higher rates of productivity and decomposition. Darwin also cites supporting evidence in the form of the Hortus Gramineus Woburnensis: a grass garden at Woburn Abbey in the South of England that contains early experiments on the relationship between organisms and their environment.

Charles Darwin and the importance of biodiversity for ecosystem functioning

Abstract: The link between biodiversity and ecosystem functioning is a relatively new research area motivated by forecasts of ongoing biodiversity loss. However, the intellectual link between biodiversity and ecosystem processes was first inferred by Darwin based on his "Principle of Divergence". In the notes for his "Big Species Book" Darwin explicitly states that communities composed of organisms developed under "many and widely differing forms" should have higher rates of productivity and decomposition. Darwin also cites supporting evidence in the form of the Hortus Gramineus Woburnensis: a grass garden at Woburn Abbey in the South of England that arguably contains the earliest known ecological experiments.