Living organisms, including humans, and non-living elements of the environment interact in often complex ways. The study of these interactions—ecology—was founded as an academic subject (oecology) in 1866 by Ernst Häckel. By 1914 The Journal of Ecology had been established. Charles Elton in 1927 described ecology as ‘scientific natural history’; modern definitions would include: the study of the structure and function of nature; the study of interactions between organisms (biotic) and their non-living (abiotic) environment; the science of the relations of organisms to their total environment, and the interrelationships of organisms inter-specifically and between themselves within a species (Fraser-Darling, 1963; Odum, 1975; Park, 1980). Since the early 1970s ‘ecology’ has also come to mean a viewpoint—typically a concern for the environment—as much as the discipline (O’Riordan, 1976). The science of ecology should guide environmental management, environmentalism and environmental ethics.
People’s behaviour and culture are partly a consequence of physical surroundings and partly human genetics (just how much of each is debated). Humans either adapt to, or seek to modify, their environment to achieve security and well-being. In making modifications people create a ‘human environment’ (Treshow, 1976). Human ecology developed in the early twentieth century to facilitate the study of people and their environment, expanding in the 1960s and 1970s, and then dying back (Sargeant, 1974; Richerson and McEvoy, 1976). A field that currently seems to be expanding, and which can be very useful for environmental management, is political ecology. Political ecologists seek to build foundations for sustainable relations between society and the environment (Atkinson, 1991b;
Blaikie, 1985) (see chapter 13).
The global complex of living and dead organisms forms a relatively thin layer, the biosphere. The term ‘ecosphere’ is used to signify the biosphere interacting with the non-living environment, biological activity being capable of affecting physical conditions even at the global scale. The global ecosphere can be divided into various climates, the pattern of which has changed in the past (a world map of climate for, say, 20,000 years ago would be very different from today’s) and will doubtless do so in the future. Climate might be affected by one or more of many factors, e.g.:
♦ Variation in incoming solar energy due to fluctuations in the Sun’s output or possibly dust in space.
♦ Variation in the Earth’s orbit around or change in its rotation about its axis.
♦ Variation in the composition of the atmosphere or in the quantity of dust, gases or water vapour present (biological activity may alter atmospheric composition).
♦ Altered distribution of continents, changes in oceanic currents or of sea-level that may expose or submerge continental shelves.
♦ Formation and removal of topographic barriers.
Environmental managers must not assume climate is fixed and stable—even if there is no significant threat of change through pollution (Figure 7.3).
The ecosystem
The biosphere is composed of many interacting ecosystems (ecological systems), the boundaries between which are often indistinct, taking the form of transition zones (ecotones) where organisms from adjoining zones may be present (it is possible for organisms to be restricted to an ecotone only). Large land ecosystems or biomes (synonymous with biotic areas) can be recognized. These are areas with a prevailing regional climax vegetation and its associated animal life, in effect regional-scale ecosystems. Biomes usually reflect climate but are also likely to be shaped by the incidence of fire, drainage, soil characteristics, grazing, trampling, etc. (e.g. desert biomes or grassland biomes). The biome concept seeks to extend the ideas of community among vegetation and animal populations to cover the patterns of life within both (Watts, 1971:186). The term ‘ecosystem’ was coined by Tansley in 1935, and has become the basic functional unit of ecology (Tansley, 1935; Park, 1990:107).
It is an assemblage of organisms living and interacting in association under certain environmental conditions, with, according to Miller (1991:112), six major features:
interdependence, diversity, resilience, adaptability, unpredictability and limits. An ecosystem boundary can be defined at organism, population, or community level, the crucial thing being that biotic processes are sustainable within that boundary. It is possible to have different physical and functional boundaries to an ecosystem. No two ecosystems are exactly the same, but one may recognize general rules and similarities. There are two ways of viewing ecosystems: (1) as populations—the community (biotic) approach, in which research can be conducted by individuals;
(2) as processes—the functional approach (energy flow studies), best investigated by a multidisciplinary team.
Ecosystems can be subdivided, according to local physical conditions, into habitats (places where an organism or group of organisms live) populated by characteristic assemblages of organisms (e.g. a lake ecosystem may be composed of gravel bottom habitats rock bottom habitats, and mud bottom habitats). Biomes and habitats may be subdivided into communities, which may consist of several populations of different species that live and interact together in a particular place.
In a stable ecosystem each species is assumed to have found a position, primarily in relation to its functional needs: food, shelter, etc. This position, or niche, is where a given organism can operate most effectively. Some organisms have very specialized demands and so occupy very restricted niches (e.g. the water-filled hollow of a particular bromeliad plant, itself with a restricted niche), others can exist in a wide range of niches. A species may be using only a portion of its potential niche; or alteration of a single parameter affecting competition with other organisms may suddenly open, restrict or deny a niche for an organism.
The ecosystem concept
The ecosystem concept may be applied to natural or human-modified conditions.
The latter include urban ecosystems and agroecosystems, although these are not true, discrete units in terms of energy flows, function and so on. Ecosystem FIGURE 7.3 A glacier calving into the sea, Cumberland Bay, South Georgia. Evidence shows considerable change in extent of glaciers on this island over the last 10,000 years. Climate is not static.
management is the application of the ecosystem concept (Golley, 1993). Slocombe (1993) was optimistic that the ecosystem concept might offer a route to integrating environmental management and development planning that would lead to sustainable development (the value of the ecosystem approach is discussed in chapter 9).
Biodiversity Ecological diversity refers to the range of biological communities that interact with each other in a given environment. Biodiversity (biological diversity) refers to species diversity plus genetic diversity within those species. Loss of biological diversity occurs when species extinctions exceed the rate of species creation. Extinction is a natural process, sometimes sudden, perhaps catastrophic, otherwise an ongoing, gradual process. However, humans have greatly accelerated the rate of extinctions.
Loss of biodiversity is one of the most serious problems facing environmental managers.
Biogeochemical and biogeophysical cycles Within the biosphere, cyclic processes move and renew supplies of energy, water, chemical elements and air. These cycles affect the physical environment and organisms, and some are affected by life forms. Although upset by occasional catastrophic events (e.g. volcanic eruptions, planetesimal strikes), biogeochemical and biogeophysical cycles are assumed to reach a state of dynamic stability.
Nevertheless, environmental managers must not assume an unchanging natural environment, and human activity is affecting global cycles and might trigger serious runaway problems (i.e which are difficult to solve).
There are cycles which are crucial for the nutrition of organisms: the maintenance of atmospheric gas mix and maintaining global temperature within acceptable limits, including water, oxygen, carbon dioxide, nitrogen, phosphorus, sulphur (there are over 30 known biogeochemical cycles). Some involve gases and have a turnover of as little as a few days; some involve sediments, and are so slow (with turnovers of perhaps millions of years) that the material is non-renewable as far as humans are concerned. Biogeochemical and biogeophysical cycles are not fully understood, for example, there is much to learn about the cycling of carbon.
Without better insight, accurate modelling and prediction of global change is very difficult.
Biogeochemical and biogeophysical cycles can be classified as: (1) natural, (2) upset by humans and (3) recycling (managed by man and sustainable) (Chadwick and Goodman, 1975:4). Many of the first group have already been converted to the second and the threat of this grows; conversion of these to the third group is an important goal for environmental managers.