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Levels of organization and study

Levels of organization and study

Ecosystems regenerate after a disturbance such as fire, forming mosaics of different age groups structured across alandscape. Pictured are different seral stages in forested ecosystems starting from pioneers colonizing a disturbed site and maturing in successional stages leading to old-growth forests.

Because ecology deals with ever changing ecosystems, both time and space must be taken into account when describing ecological phenomena. In regards to time, it can take thousands of years for ecological processes to mature. The life-span of a tree, for example, can pass through different successional or seral stages leading to mature old-growth forests. The ecological process is extended even further through time as trees topple over and decay.

Ecosystems are also classified at different spatial scales. The area of an ecosystem can vary greatly from very tiny to vast. For instance, several generations of an aphid population and their predators might exist on a single leaf. And inside each of those aphids diverse communities of bacteria exist. The scale of study must at times be quite large, when studying the life of the tree in the forest where bacteria and aphids live. To understand tree growth, for example, soil type, moisture content, slope of the land, forest canopy closure, and other local site variables must all be examined. And to understand the ecology of the forest, complex global factors such as climate must be taken into account.

Long-term ecological studies provide important track records to better understand ecosystems over space and time. The International Long Term Ecological Network manages and exchanges scientific information among research sites. The longest experiment in existence is the Park Grass Experiment that started in 1856.Another example includes the Hubbard Brook study in operation since 1960. Ecology is also complicated by the fact that small scale patterns do not necessarily explain large scale phenomena, otherwise captured in the expression 'the sum is greater than the parts'. These emergent phenomena operate at different environmental scales of influence, ranging from molecular to planetary scales, and require different sets of scientific explanation.

To structure the study of ecology into a manageable framework of understanding, the biological world is conceptually organized as a nested hierarchy of organization, ranging in scale from genes, to cells, to tissues, to organs, to organisms, to species and up to the level of the biosphere. Ecosystems are primarily researched at (but not restricted to) three key levels of organization, including (1) organisms, (2) populations, and (3) communities. Ecologists study ecosystems by sampling a certain number of individuals that are representative of a population. Ecosystems consist of communities interacting with each other and the environment. In ecology, communities are created by the interaction of the populations of different species in an area.