Ecology and Environment — Scientific Principles

Scientific Principles

Organise ecology by scale. An organism responds to conditions such as temperature and water availability. A population consists of individuals of a species in a relevant area; births, deaths, immigration and emigration alter its size. A community includes interacting populations, while an ecosystem also includes the physical environment and exchanges of energy and matter.

Population growth depends on conditions. Exponential growth assumes an effectively unconstrained rate over the period considered. Logistic growth incorporates a carrying capacity, so growth slows as the population approaches the level the environment can support under those conditions. Carrying capacity is not a permanent number independent of resources or disturbance.

Interactions include competition, predation, parasitism, mutualism and commensalism. Classify an interaction by its effects on the participants, rather than by whether they happen to occupy the same place. An orchid growing on a mango tree illustrates support benefiting the orchid without the host necessarily being harmed.

Ecosystem productivity is a rate. Gross primary productivity measures production through photosynthesis; subtract producers' respiration to obtain net primary productivity. Standing biomass is a stock at a time, so it cannot be substituted directly for a production rate.

Energy flows through trophic relationships and is dissipated, while nutrients cycle. Biodiversity spans genetic, species and ecosystem levels; conservation in natural habitats and conservation outside them address different needs.