The Princeton Guide to Ecology

Ecosystem services are provided by biological processes and structures as well as by the geophysical environment. Biodiversity is a measure of the variation in life forms and is the result of many biological and geological processes and constraints. To understand what species do in ecosystems, particular attention must be paid to the traits of these species, such as their optimal temperature for growth, their ability to avoid predators, or their nutrient uptake capacity. It is the distribution of traits relevant for particular ecosystem services, so-called trait spectra, that determines the performance of the biological community as a whole. The variation in particular traits within the community, such as the range of temperature tolerances, is a measure of the response capacity, i.e., the overall ability of the community, species, and individuals to respond to changes in environmental factors, such as temperature changes. Greater response capacity reduces variability in ecosystem services under environmental variability. This is particularly important for systems that are susceptible to critical transitions. Landscape patterns and processes provide a regional source of trait variability for local communities and thus maintain response capacity.

abiotic environment. The chemical, geological, and physical part of the ecosystem.

critical transitions. A change of the dominating feedback processes in an ecosystem, with implications for ecosystem structure and functioning. Systems undergoing a critical transition may be profoundly different before and after the transition.

response capacity. The ability of a local community to respond to changes in environmental drivers.

trait spectra. The abundance-weighted distribution of particular traits in the community.

Ecosystem services are sustained by an interaction between abiotic and biological processes. Thus, biological processes such as primary production account for only a part of ecosystem services. Water provisioning depends on biological processes as well as physical ones, such as those that drive the climate system. Similarly, it may be the presence of a particular striking feature, such as a blue whale or the Grand Canyon, that delivers a service, largely independent of any current biological processes (although historic biological processes were required to produce the blue whale and the Grand Canyon to begin with). The abiotic environment, such as the geomorphology of the landscape or the climate and the hydrosphere, largely sets the constraints within which biological communities develop. The abiotic environment is, however, by no means unaffected by the biological system. Water flow, for example, is determined by the climate and hydrology, but trees may play a large role in channeling water back to the atmosphere, thereby potentially affecting groundwater levels and even large-scale climate patterns (figure 1).

The role of particular species in the ecosystem processes is determined by functional and morphological characteristics, i.e., traits. Functionally similar species may be involved in sustaining particular ecosystem processes either directly (e.g., provisioning services) or indirectly (e.g., support or regulating services). The attributes (traits) of particular species and the effects of environmental variables on the species as

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