Gwybodaeth Modiwlau

To explore the nature of components and processes within the ecosystem.

The ecosystem is the basic unit of study in ecology and many important relationships between organisms, both plants and animals, and with their abiotic environment are best explored at this level. Initially, an holistic approach is adopted with an analysis of a simple ecosystem, the arctic tundra, to show how our knowledge of this system has evolved and to describe the basic relationships that exist between its various components. It is necessary, however, to place the concept of the ecosystem within the context of the ecological hierarchy which considers ecological organisation from the individual level up to the biosphere. The main themes introduced in these initial lectures provide the structure for the remainder of the course.

In the first group of lectures, the powering of ecosystems is analysed with specific reference to systems based on sunlight and green plants and those based on dead organic matter. In particular, emphasis is placed on the transfer of energy between different trophic levels. The transfer of energy through organic matter, however, inevitably involves the transfer of materials, mainly nutrients but also, for example, pollutants, between the components of ecosystems. The cycling of nutrients within systems is analysed with an emphasis on the key role of soils in this process. The complex interactions between vegetation and soils have a marked influence on this function.

Soil type is but one of many factors that affect the distribution of plants and animals in space. The range of abiotic factors are reviewed at the start of the next group of lectures. In the remainder, biotic factors, especially predation and competition are discussed. Predation is one factor that limits population numbers from infinite exponential growth. Similarly, competition for resources has an equally important effect. In addition, a study of resource utilisation by species helps us to understand their position within ecological systems, generally defined as the niche. Within its distribution, however, a species will often show specific adaptation to particular situations; examples of such ecotypic variation will be discussed.

Some aspects of the ecology of individual plant and animal species, however, can best be understood from a study of their autecology. Individual plant and animal species will be used to illustrate the concept of autecology.

The final theme discussed in this course is the change in ecosystems over time, the phenomenon generally known as succession. Whether these successions are predictable and what drives the changes has long been a contentious issue. Examples of successions and the competing theories will be reviewed.