Andy Hector

Bio: Andy Hector is an academic researcher from University of Oxford. The author has contributed to research in topics: Biodiversity & Species richness. The author has an hindex of 74, co-authored 183 publications receiving 36456 citations. Previous affiliations of Andy Hector include University of Zurich & Natural Environment Research Council.

Quantifying effects of biodiversity on ecosystem functioning across times and places.

Abstract: Biodiversity loss decreases ecosystem functioning at the local scales at which species interact, but it remains unclear how biodiversity loss affects ecosystem functioning at the larger scales of space and time that are most relevant to biodiversity conservation and policy. Theory predicts that additional insurance effects of biodiversity on ecosystem functioning could emerge across time and space if species respond asynchronously to environmental variation and if species become increasingly dominant when and where they are most productive. Even if only a few dominant species maintain ecosystem functioning within a particular time and place, ecosystem functioning may be enhanced by many different species across many times and places (β-diversity). Here, we develop and apply a new approach to estimate these previously unquantified insurance effects of biodiversity on ecosystem functioning that arise due to species turnover across times and places. In a long-term (18-year) grassland plant diversity experiment, we find that total insurance effects are positive in sign and substantial in magnitude, amounting to 19% of the net biodiversity effect, mostly due to temporal insurance effects. Species loss can therefore reduce ecosystem functioning both locally and by eliminating species that would otherwise enhance ecosystem functioning across temporally fluctuating and spatially heterogeneous environments.

Phylogenetic classification of the world's tropical forests

Abstract: Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.

Coexistence, niches and biodiversity effects on ecosystem functioning.

Abstract: General principles from coexistence theory are often invoked to explain how and why mixtures of species outperform monocultures. However, the complementarity and selection effects commonly measured in biodiversity experiments do not precisely quantify the niche and relative fitness differences that govern species coexistence. Given this lack of direct correspondence, how can we know whether species-rich mixtures are stable and that the benefits of diversity will therefore persist? We develop a resource-based included-niche model in which plant species have asymmetric access to a nested set of belowground resource pools. We use the model to show that positive complementarity effects arise from stabilising niche differences, but do not necessarily lead to stable coexistence and hence can be transient. In addition, these transient complementarity effects occur in the model when there is no complementary resource use among species. Including a trade-off between uptake rates and the size of the resource pool stabilised interactions and led to persistent complementarity coupled with weak or negative selection effects, consistent with results from the longest-running field biodiversity experiments. We suggest that future progress requires a greater mechanistic understanding of the links between ecosystem functions and their underlying biological processes.

Globally, functional traits are weak predictors of juvenile tree growth, and we do not know why

Abstract: Additional co-authors: Herve Jactel, Xuefei Li, Kaoru Kitajima, Julia Koricheva, Cristina Martinez-Garza, Christian Messier, Alain Paquette, Christopher Philipson, Daniel Piotto, Lourens Poorter, Juan M. Posada, Catherine Potvin, Kalle Rainio, Sabrina E. Russo, Mariacarmen Ruiz-Jaen, Michael Scherer-Lorenzen, Campbell O. Webb, S. Joseph Wright, Rakan A. Zahawi, and Andy Hector

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.

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Human biochemical genetics

Abstract: So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

A safe operating space for humanity

Abstract: Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockstrom and colleagues.

Planetary boundaries: Guiding human development on a changing planet

Abstract: The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge

Abstract: Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the re- lationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are struc- tured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain.