Understanding Ecology: Pyramids, Populations, and Limiting Factors in Biology

1. Pyramids, Populations, and Limiting Factors Applied Biology 1

2. Ecology Pyramids • Shows how energy, numbers, or biomass decreases through a food chain. • Each level is called a trophic level.

3. Trophic levels

4. 10% Rule • 90% is lost as you move from one trophic level to another. 10% is available for next level = 10% rule.

5. Pyramids - #, biomass, energy Biomass = organic matter (carbon) If there are 10,000 units of grass, how many herbivores are there?

6. Populations • A group of organisms belonging to the same species living in the same area. • Examples: a group of foxes or an acre of corn

7. Populations • Interact with each other. • Evolution occurs from changes in populations, not changes in an individual.

8. Limiting Factors • Factors that limit the size of a population. Allows the population to increase in size or can reduce their numbers.

9. Density-dependent factors • Limits how large a population can grow. The larger the population the more important these factors are in limiting growth.

10. Examples • Food and water supply – Large populations require more of this. Limited supplies results in competition.

11. Examples • Living space – The growth of plants is affected by competition for space. Crowded conditions means less access to sunlight so less photosynthesis and less growth.

12. Examples • Predation – Less prey animals means less food for predators, so the level of predation decreases.

13. Examples • Disease – spread of disease is faster in a dense population than in a sparse one.

14. Density-independent factors • Mostly abiotic factors such as natural disasters, weather changes, pollutants from human activity. • All population sizes are affected – both large and small.

15. Examples • Forests fires, volcanic eruptions, hurricanes, flooding, oil spills, global warming…