The study of biological diversity or biodiversity is the central theme of biology and ecology is the science that studies the interactions between organisms (biodiversity) and their environment. Ecology is studied at different spatial scales, ranging from a single species influenced by one environmental factor, to regional and global perspectives. Ecological interactions can be studied at all level of biodiversity, and the course will reflect this by considering the ecology of populations, species (in terms of life histories) and communities. At its most fundamental level ecology is concerned with the processes that determine the rates of births, deaths, immigration and emigration of organisms. Associated factors of importance are the rate of development to adult and the length of reproductive life. Any factor that affects the birth or death rate, movement, development or longevity of a species will have an impact on the size of a population. These factors are broadly defined as abiotic (e.g. weather) or biotic (e.g. competition for a resource), and can affect species in both density dependent and independent ways. The course will also reflect the fact that plants and animals differ in their ecological interactions. The module will provide an understanding of the variety and complexity of ecological systems, and of the rules that are thought to govern and constrain that complexity. The study of ecology has become increasingly important and popular in recent years, reflecting the widespread concern over issues such as climate warming, invasions, biodiversity, pollution and biodiversity conservation.