The Web of Life

1. The Web of Life This part of the course we will study ecology. Ecology is the interaction of organisms with other organisms and the environment.

2. How do organisms interact with each other? • Eat each other. • Some organisms get their energy directly from the sun. • Other organisms get their energy indirectly from the sun.

3. Food Chains • Food chains show a pathway of energy and tells what eats what. • Producers, use light energy to make their own food. • Consumers, organisms unable to make their own food. • Decomposers, break down the bodies of dead plants and animals • Community, the producers, decomposers, and consumers that interact with each other in one area.

4. An Example of a Food Chain

6. Food Webs, when all the food chains in the community are connected to each other a food web is formed.

7. Food Energy Pyramids • Food chains can also be presented as a food energy pyramid. • The producers are at the bottom of the pyramid. • The primary consumers come next. • The secondary consumers are next and so on.

8. Food Energy Pyramid

9. Energy in the Web of Life • All organisms activities require energy. • Energy in food is chemical energy. What are other forms of energy? • Photosynthesis, plants absorb light energy and convert it to chemical energy. • Animals eat plants to get their energy. • The conversion of chemical energy is not efficient. Energy is lost as heat. Eventually all energy is lost as heat.

10. Biological Populations • A population is a group of interbreeding individuals of the type in a given area at a given time.

11. Four rates determine the size of a population • Mortality, death rate • Natality, birth rate • Immigration, when one or more organisms move into an area • Emigration, when organisms leave the area.

12. The Environment • The Environment is everything that surrounds and affects the organism • There are two main components • Biotic, living and abiotic, non living

13. Limiting Factors • Why don’t populations reach very high numbers? • Biotic and abiotic factors affect population size. • Limiting factors are things that prevent a population from growing any larger. For example, 10 rabbits may live in a habitat that has enough water, cover and space to support 20 rabbits, but if there is only enough food for ten rabbits, the population will not grow any larger. In this example, food is the limiting factor.

14. Limiting Factors • Space, Climate, Water, Food are all limiting factors. • What can the environment do to populations?

15. Carrying Capacity • Carrying capacity: The maximum number of individuals of a species that an area can support.

16. Population Density may Fluctuate • Population density = Number of individuals / Space D = N/S Rate of Change = change in numbers / change in time Homeostasis, is the tendency of a population to stay the same in size

17. Dispersal • Dispersal, tendency of a population to spread out into a new area. • Dispersal may be passive, like dandelions. • What can limit the dispersal of populations physical barriers, large bodies of water, ecological barriers

18. Geographic Range“Where an organism lives” • What’s wrong with these two pictures

19. The Human Population • Natality exceeds mortality. • Human can live almost anywhere in the World. There are few barriers for the human population. • Demand for space is great. • Not all people have equal access to food. • Some countries in Africa have experienced a famine for the past two decades.

21. Famine in Africa Farming Deforestation

22. Calories • One calorie is the amount of heat energy needed to raise the temperature of 1 gram of water 1 degree Celsius. • Teenage males need 2,100 – 3,900 Kcal. • Teenage females need 1,200 – 3,000 Kcal. depending of their activities.