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.

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

The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.

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Biodiversity loss and its impact on humanity

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.

Humans integrate visual and haptic information in a statistically optimal fashion.

The ecological consequences of biodiversity loss have aroused considerable interest and controversy during the past decade. Major advances have been made in describing the relationship between species diversity and ecosystem processes, in identifying functionally important species, and in revealing underlying mechanisms. There is, however, uncertainty as to how results obtained in recent experiments scale up to landscape and regional levels and generalize across ecosystem types and processes. Larger numbers of species are probably needed to reduce temporal variability in ecosystem processes in changing environments. A major future challenge is to determine how biodiversity dynamics, ecosystem processes, and abiotic factors interact.

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Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges

This article defines social resilience as the ability of groups or communities to cope with external stresses and disturbances as a result of social, political and environmental change. This definition highlights social resilience in relation to the concept of ecological resilience which is a characteristic of ecosystems to maintain themselves in the face of disturbance. There is a clear link between social and ecological resilience, particularly for social groups or communities that are dependent on ecological and environmental resources for their livelihoods. But it is not clear whether resilient ecosystems enable resilient communities in such situations. This article examines whether resilience is a useful characteristic for describing the social and economic situation of social groups and explores potential links between social resilience and ecological resilience. The origins of this interdisciplinary study in human ecology, ecological economics and rural sociology are reviewed, and a study of the impacts of ecological change on a resource- dependent community in contemporary coastal Vietnam in terms of the resilience of its institu- tions is outlined. I Introduction The concept of resilience is widely used in ecology but its meaning and measurement are contested. This article argues that it is important to learn from this debate and to explore social resilience, both as an analogy of how societies work, drawing on the ecological concept, and through exploring the direct relationship between the two phenomena of social and ecological resilience. Social resilience is an important component of the circumstances under which individuals and social groups adapt to environmental change. Ecological and social resilience may be linked through the dependence on ecosystems of communities and their economic activities. The question is, then, whether societies dependent on resources and ecosystems are themselves less resilient. In addition, this analysis allows consideration of whether institutions

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Social and Ecological Resilience: Are They Related?

COMMUNITIES of species and their associated biological, chemical and physical processes, collectively known as ecosystems, drive the Earth's biogeochemical processes1,2. Currently most ecosystems are experiencing loss of biodiversity associated with the activities of human expansion3–5, raising the issue of whether the biogeochemical functioning of ecosystems will be impaired by this loss of species6–8. Current ecological knowledge supports a wide range of views on the subject9–13, but empirical tests are few9,14–16. Here we provide evidence from direct experimental manipulation of diversity by over an order of magnitude, using multi-trophic level communities and simultaneous measures of several ecosystem processes, that reduced biodiversity may indeed alter the performance of ecosystems.

Declining biodiversity can alter the performance of ecosystems

We examined experimentally the association between species diversity and ecosystem processes in a series of terrestrial mesocosms. We developed and maintained 14 mesocosms whose biota were assembled from a single pool of plant and animal species and whose environmental conditions were identically controlled. Each community contained four trophic levels: primary producers (annual herbs), consumers (herbivorous molluscs and phloem sucking insects), secondary consumers (parasitoids) and decomposers (earthworms, Collembola and microbes). All mesocosms received the same diurnal pattern of light, temperature, relative humidity and water. The initial volume of soil, soil structure, composition, nutrient content and inocula of both soil microbes and nematodes were also identical among replicates. The only experimentally manipulated factor was the number of plant and animal species within each trophic level. High, medium and low diversity communities had nine, 15 or 31 plant and animal species, respectively. We measured five ecosystem processes as response variables in these mesocosms over the course of 206 days: (i) community respiration; (ii) productivity; (iii) decomposition; (iv) nutrient retention; and (v) water retention. The manipulation of diversity produced communities that differed significantly in their ecosystem processes. Our results provide the first evidence (obtained by a direct manipulation of diversity under controlled environmental conditions) that ecosystem processes may be affected by loss of diversity.

Empirical Evidence that Declining Species Diversity May Alter the Performance of Terrestrial Ecosystems

This paper reports on aspects of the design and philosophy of the Ecotron, an integrated series of 16 controlled environmental chambers at the NERC Centre for Population Biology. The Ecotron serves as an experimental means for analysing population and community dynamics and ecosystem processes under controlled physical conditions. Within the chambers, terrestrial experimental communities are assembled into foodwebs of desired complexity from a pool of species selected for their preadaptations to the physical conditions of the Ecotron. These species include decomposers (earthworms, snails, microarthropods and microbes), primary producers (16 species of plants), primary consumers (four species of herbivorous arthropods), and secondary consumers (four species of parasitoids). The design of the Ecotron is unique in several aspects with respect to its blend of biology and technology. It supports small, dynamic communities of up to 30 plant and metazoan species, thereby making it among the more biologically complex controlled environmental systems currently in use. Its architecture permits replication and variation of spatial scale in experimental design. Its artificial climate simulates natural environmental conditions within chambers allowing experimental control over light, water, temperature, humidity, and in the near future CO $_{2}$ and UV-B radiation. Sensors monitor both macro- and micro-environmental conditions of a number of physical factors within the chambers. Preliminary experiments show the Ecotron to be an excellent facility for long-term population and community-level experiments. We discuss the results of one of these early experiments and briefly consider ongoing and future experiments.

The Ecotron: A Controlled Environmental Facility for the Investigation of Population and Ecosystem Processes

To predict changes in the range and density of plant species as a consequence of elevated atmospheric CO2, it is essential to characterize the effect of elevated CO2 on key components of plant life history stages such as rate of establishment and maturation of individuals, reproductive output and offspring fitness. We measured vegetative response, phenology, reproductive output and seed quality of four annual C3 plant species, grown from seed to senescence under ambient and elevated (ambient+200 ppm) CO2 and ambient and reduced (33% shade) light. Few previous studies have included all stages of a plant's life as well as characteristics of the next generation. Elevated CO2 had no effect on the vegetative attributes of Cardamine hirsuta, Spergula arvensis or Poa annua whereas Senecio vulgaris produced longer leaves and greater biomass. Both Senecio and Poa had faster maturation times. The vegetative response of Senecio was not translated into increased seed output, although seed mass and carbon∶nitrogen ratios were significantly increased. By contrast, Poa showed no vegetative response to elevated CO2, but had significantly increased seed production. Thus we found no evidence for a simple translation from vegetative response to elevated CO2 into reproductive response. There was also no consistent light-mediated response to elevated CO2 among the four species. However, the effect of reduced light (33% shade) on vegetative and reproductive output was consistent across the four species and significantly stronger than the effect of elevated CO2. On the basis of this glasshouse study, we predict that Poa would be most likely of the four species to show significant increases in population size and migration potential, as a result of increased reproductive output, under elevated atmospheric CO2. However, this response may be relatively small compared with variation in growth and reproduction as a result of environmental heterogeneity in resources such as light.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.1999.00544.x

The effects of elevated CO2 and light environment on growth and reproductive performance of four annual species

/pdf/biodiversity-in-model-ecosystems-4ioge9g3di.pdf

Richard M. Woodfin

Papers

Declining biodiversity can alter the performance of ecosystems

Empirical Evidence that Declining Species Diversity May Alter the Performance of Terrestrial Ecosystems

The Ecotron: A Controlled Environmental Facility for the Investigation of Population and Ecosystem Processes

The effects of elevated CO2 and light environment on growth and reproductive performance of four annual species

Biodiversity in model ecosystems