A. Ecology is the study of the interactions of organisms with each other and their environment

1. population = all the individuals of a species that live together in one place at one time

2. habitat = the location where a population lives

3. community = the sum of all the populations living together in a habitat

4. abiotic factors = the physical aspects of a habitat (soil, water, climate)

5. biotic factors = the living aspects of a habitat

6. ecosystem = (community + habitat) or (abiotic + biotic factors)

B. Ecosystems support diverse communities

1. biodiversity = the number of species living in an ecosystem

2. examples of ecosystem inhabitants in a pine forest

3. ecosystem boundaries are often unclear

C. Ecosystems change over time

1. primary succession = the development of an ecosystem where there had been no previous growth

2. secondary succession = the development of an ecosystem after previous growth was disrupted

3. example: Glacier Bay, Alaska, USA

• receding glaciers reveal bare rock
• pioneer species, able to take advantage of newly exposed rock, succeed where other species cannot
• lichen, mosses and Dryas arrive by seeds or spores carried by wind
• Dryas grows in clumps close to the ground,eventually outcompeting other species; its roots break up rocks and develop soil
• after about 10 years, alders are able to survive in soil created and improved by Dryas
• alder roots have nitrogen-fixing bacteria, enriching the soil
• willows and cottonwoods take advantage of enriched soil and outcompete Dryas, by growing taller and depriving them of light
• after about 80 years, Sitka spruce trees invade, grow taller than other trees, and outcompete them by depriving them of light, replacing the willows, cottonwood and alders
• eventually hemlock trees, which tolerate shade, grow up under the spruce trees, producing a stable spruce/hemlock forest