8
Biodiversity and Ecosystem
Processes: Theory, Achievements
and Future Directions
JOHN H. LAWTON
NERC Centre for Population Biology, Imperial College, Silwood Park, Ascot SLS 7PY, UK
Abstract
Field and laboratory experiments with model plant communities show clear evidence of a reduction in ecosystem processes (productivity and nutrient cycling)
with declining plant species richness within anyone site. Across different sites,
however, relationships can be more complex, so that mixing between- and withinsite effects is confusing. A robust body of emerging theory underpins and explains
these empirical results. I start by reviewing the theory, before briefly summarising
the empirical data. The paper then describes preliminary new results from the European-wide BIODEPTH experiment to illustrate the key points. The challenges,
now are: (i) To understand better the mechanism(s) underpinning these responses.
(ii) To distinguish between the role of biodiversity in maintaining ecosystem processes under constant, or benign environmental conditions, and under extreme environmental perturbations (the 'insurance hypothesis'). (iii) To start to consider
the role of animal and microbial diversity for ecosystem processes.
1 Introduction
Ecologists have made great strides over the last decade in understanding the relationship between biodiversity (here used in the narrow sense of species richness)
and ecosystem processes (for example primary production, or nutrient cycling). In
a characterif>tically pioneering book, Ehrlich and Ehrlich (1981) were among the
Key words. animals, between and within site effects, biomass, insurance hypothesis, microorganisms, niche complementarity, nutrient cycling, overyielding, plants, positive species
interactions, primary production, redundancy, sampling hypothesis, soil fauna, species-richness
119
Biodiversity and Ecosystem
Processes: Theory, Achievements
and Future Directions
JOHN H. LAWTON
NERC Centre for Population Biology, Imperial College, Silwood Park, Ascot SLS 7PY, UK
Abstract
Field and laboratory experiments with model plant communities show clear evidence of a reduction in ecosystem processes (productivity and nutrient cycling)
with declining plant species richness within anyone site. Across different sites,
however, relationships can be more complex, so that mixing between- and withinsite effects is confusing. A robust body of emerging theory underpins and explains
these empirical results. I start by reviewing the theory, before briefly summarising
the empirical data. The paper then describes preliminary new results from the European-wide BIODEPTH experiment to illustrate the key points. The challenges,
now are: (i) To understand better the mechanism(s) underpinning these responses.
(ii) To distinguish between the role of biodiversity in maintaining ecosystem processes under constant, or benign environmental conditions, and under extreme environmental perturbations (the 'insurance hypothesis'). (iii) To start to consider
the role of animal and microbial diversity for ecosystem processes.
1 Introduction
Ecologists have made great strides over the last decade in understanding the relationship between biodiversity (here used in the narrow sense of species richness)
and ecosystem processes (for example primary production, or nutrient cycling). In
a characterif>tically pioneering book, Ehrlich and Ehrlich (1981) were among the
Key words. animals, between and within site effects, biomass, insurance hypothesis, microorganisms, niche complementarity, nutrient cycling, overyielding, plants, positive species
interactions, primary production, redundancy, sampling hypothesis, soil fauna, species-richness
119