Ecosystems and Ecological Communities

What sustains life on Earth?

The Sun helps sustain life on Earth by lighting and warming the planet, supporting photosynthesis, powering the cycling of matter, and driving the climate and weather systems that distribute heat and fresh water over the Earth’s surface. Without the sun’s energy, the temperature would approach absolute zero (–– 273 ⁰C) and all water would be frozen, even in the ocean. The sun’s energy is captured by photosynthetic organisms which use it to make the food molecules required by almost all forms of life. Without the sun, almost all life would cease.

Mini Glossary

Ecology: Ecology is a study of interactions of organisms with each other and with physical environment. In effect, it is a study of connections in nature.

Species: Organisms can be classified into species. A species is a group of organisms that resemble one another in appearance, behavior, chemistry, and genetic makeup that can reproduce sexually among themselves but that cannot produce fertile offspring when mated with other organisms. Species differ in how they produce offspring.

A keystone species is one that has a critical role to play in the maintenance of specific ecosystems. The relationship between sea urchins, sea otters, and kelps suggests that sea otters are a keystone species (see community effect).

Population: A population is group of individuals of the same species living in the same area or interbreeding and sharing genetic information.

Ecological Community is an assemblage of all the interacting populations of different species of organisms in an area. Some species play minor roles, while others play major roles, but all are part of the community.

Habitat is place of organism’s residence, where it can be found, such as under a log.