ECOSYSTEMS vary in size. They can be as small as a puddle or as large as the Earth itself. Any group of living and nonliving things interacting with each other can be considered as an ecosystem.Within each ecosystem there are habitats which may also vary in size. A habitat is the place where population lives. A population is a group of living organisms living in the same place at the same time. All of the populations interact and form a community. The community of living things interacts with the nonliving world around it to form the ecosystem.

1. Energy Flow – passage of energy through the components of the ecosystem

> Autotrophs – convert light energy into chemical energy

> Heterotrophs – obtain chemical energy from food

> Decomposers - feed on all levels

2. Chemical Cycling – circular movements of materials within the ecosystem

> ecosystems are more or less self-contained in terms of materials

> chemical components are cycled between abiotic components

(air, water, soil) and biotic components of the ecosystem.

This figure with plants, zebra, lion and so forth illustrates the 2 main ideas on how ecosystem function: ecosystems have energy flows and ecosystem cycles materials. These 2 processes are linked but they are not quite the same.

> The transformation of energy in an ecosystem begin first with the input of energy from the sun. Energy from the sun is captures by the process of PhotosynthesisPhotosynthesis. Carbon Dioxide is combined with Hydrogen to produce carbohydrates. Energy is stored in the high energy bonds of adenosine triphosphate or ATP.

Diversity>the varierty of different organisms in a community is its biodiversity. Two components:

species richness (how many ?)relative abundance of species

>ecologists consider both richness and relative abundance in measuring biodiversity.Prevalent form of vegetation

>applies mainly to terrestrial situations>determine to a large part what other organisms will live there

Response to disturbance>some communities are stable (e.g. cedar and hemlock forests may last 1000’s years);

when disturbed, such communities rebound to original state very slowly.>other communities are constantly changing and unless disturbed by fire, for example,

succession would lead to different species composition (e.g. grasslands require periodic fires to remove competitors and allow grasses to dominate). Therefore disturbance plays a

vital role in determining community structure and composition.Trophic structure

>feeding relationships among various species making up a community.>determines pasage of energy and nutrients from plants and other primary producers to

herbivores to carnivores.

Competition may occur when a shared resource is limited

Predation leads to diverse adaptations in predators and prey

Predation can maintain stability in a community

Symbiotic relationships help structure communities.

Disturbance is a dominant feature of most communities