1. The study of interactions between organisms & their environment.
Ecology
The study of interactions between organisms & their environment.

2. Ecosystems
An ecosystem is an interaction among populations of all the organisms in a community with the non-living parts of their environment.

3. Species, Population, & Community
A species is a group of organisms that interbreed & produce fertile offspring.
A population is a group of organisms all of the same species, which interbreed and live in the same place at the same time.
A biological community is all the organisms in a given area.

4. Limiting Factors
Anything that limits the number of individuals that can live in an ecosystem is a limiting factor.

5. Examples of Limiting Factors:
Food
Water
Climate
Disease
Shelter
Predators

6. Population Density
Population density is measured by the # of organisms that can live & be supported in a defined space.
Density-dependent factors are triggered by overcrowding. Examples are: competition (food, water, shelter, space), predation, parasitism, & disease.
Density-independent factors occur regardless of how large the population & it reduces the size of the population in the area in which they occur. Examples are: weather changes, human activity (pollution), & natural disasters (fire).

7. Biotic Factors
The living components of an ecosystem are called biotic factors.

8. Examples of Biotic Factors:
Animals
Plants
Fungi
Bacteria
Protists

9. Abiotic Factors
The non-living components of an ecosystem are called abiotic factors.

10. Examples of Abiotic Factors:
Water
Nitrogen
Oxygen
Salinity pH
Soil nutrients & composition
Temperature
Sunlight
Precipitation

11. Stable Ecosystem
A stable ecosystem is one where the population numbers, supply of resources, & energy fluctuates at a predictable rate.

12. What keeps an ecosystem stable?
Competition is the relationship that occurs when two or more organisms need the same resource at the same time.
Predation is an interaction between species.
Predator – the animal that preys on others
Prey – the animal hunted and killed for food
Symbiotic Relationships exists between organisms of two different species that live together in direct contact.

13. Examples of Symbiotic Relationships
Parasitism – one organism (parasite) benefits at the expense of the other organism (host)
Mutualism – Both organisms benefit.
Commensalism – one species benefits and the other is neither harmed nor benefited

14. Remember: The Sun is the ultimate energy source.
The flow of energy can be described in food chains, food webs, & pyramids.
Each level in the transfer of energy through an ecosystem is called a trophic level.
1st level – producers (green plants or autotrophs)
2nd level – primary consumers (herbivores or heterotrophs)
3rd or higher – consumers (carnivores or omnivores)
Decomposer – returns nutrients to soil, water, or air for 1st level