Effects of biodiversity on ecosystem functioning: a consensus of current knowledge AbstractHumans 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 relationship 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 structured, 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.Based on our review of the scientific literature, we are certain of the following conclusions:1)Species' functional characteristics strongly influence ecosystem properties. Functional characteristics operate in a variety of contexts, including effects of dominant species, keystone species, ecological engineers, and interactions among species (e.g., competition, facilitation, mutualism, disease, and predation). Relative abundance alone is not always a good predictor of the ecosystem-level importance of a species, as even relatively rare species (e.g., a keystone predator) can strongly influence pathways of energy and material flows.2)Alteration of biota in ecosystems via species invasions and extinctions caused by human activities has altered ecosystem goods and services in many well-documented cases. Many of these changes are difficult, expensive, or impossible to reverse or fix with technological solutions.3)The effects of species loss or changes in composition, and the mechanisms by which the effects manifest themselves, can differ among ecosystem properties, ecosystem types, and pathways of potential community change.4)Some ecosystem properties are initially insensitive to species loss because (a...

We explore the issues relevant to those types of ecosystems containing new combinations of species that arise through human action, environmental change, and the impacts of the deliberate and inadvertent introduction of species from other regions. Novel ecosystems (also termed 'emerging ecosystems') result when species occur in combinations and relative abundances that have not occurred previously within a given biome. Key characteristics are novelty, in the form of new species combinations and the potential for changes in ecosystem functioning, and human agency, in that these ecosystems are the result of deliberate or inadvertent human action. As more of the Earth becomes transformed by human actions, novel ecosystems increase in importance, but are relatively little studied. Either the degradation or invasion of native or 'wild' ecosystems or the abandonment of intensively managed systems can result in the formation of these novel systems. Important considerations are whether these new systems are persistent and what values they may have. It is likely that it may be very difficult or costly to return such systems to their previous state, and hence consideration needs to be given to developing appropriate management goals and approaches.

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As the rate and extent of environmental change increases, traditional perspectives on ecosystem management and restoration are being juxtaposed with approaches that focus on the altered settings now being encountered or anticipated. We suggest that a combination of traditional and emerging frameworks is necessary to achieve the multiple goals of ecosystem management, including biodiversity conservation and provision of other ecosystem services such as food and fiber production, recreation, and spiritual enrichment.An effective approach entails a move away from partitioning the environment into dichotomous categories (eg natural/unnatural, production/conservation, intact/degraded). Instead, landscapes are increasingly characterized by a complex mosaic of ecosystems or "patches" in varying states of modification, each of which delivers various combinations of services and presents assorted management challenges and opportunities. These patches interact and affect broader-scale processes (such as water flows and animal migrations), necessitating the urgent development of a conservation and restoration strategy that recognizes these rapid spatial changes.Here, we focus on an emerging framework that differentiates patches according to the degree of change from a historical state (resulting from altered abiotic factors and biotic compositions), the likely extent to which such changes are reversible, and the effect of altered patches on other patches within the landscape (WebPanel 1). This framework, derived from recent research on novel ecosystems (Hobbs et al. 2009, helps to identify the relative values of ecosystems in different conditions and the management options available in each case. As seen from a landscape perspective, this framework provides a comprehensive approach to decision making and management, including much-needed prioritization of resource allocations.n Managing the whole landscape Recent analyses have highlighted the need for management and restoration efforts to go beyond site-focused interventions and to consider landscape and regional scales (Mentz et al. 2013). Ecosystem managers increas- REVIEWS REVIEWS REVIEWSManaging the whole landscape: historical, hybrid, and novel ecosystems The reality confronting ecosystem managers today is one of heterogeneous, rapidly transforming landscapes, particularly in the areas more affected by urban and agricultural development. A landscape management framework that incorporates all systems, across the spectrum of degrees of alteration, provides a fuller set of options for how and when to intervene, uses limited resources more effectively, and increases the chances of achieving management goals. That many ecosystems have departed so substantially from their historical trajectory that they defy conventional restoration is not in dispute. Acknowledging novel ecosystems need not constitute a threat to existing policy and management approaches. Rather, the development of an integrated approach to management interventions can provide options that are in tune with ...

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