1. Section 13.2: Biotic and Abiotic Factors
Biology

2. Objectives Define and give an example of biotic and abiotic factors.
Outline the importance in biodiversity in the health of an ecosystem.
What is a keystone species and how does it affect its ecosystem? Give an example.

3. Ecosystems Include living and nonliving components
Biotic Factors: living things, such as plants and animals, that each play a particular role in the ecosystem
Abiotic Factors: Nonliving things, such as moisture, temperature, wind, sunlight, and soil, which determine what living things can survive in a particular environment

4. Caribbean Sea Ecosystem
Observation: More fish in coral reefs near marshes than out to sea
Biotic Factors: Fish, mangrove trees, other plants within marsh
Abiotic Factors: Oxygenation in mud, salinity of ocean, tidal changes
The mangrove trees protect newly hatched fish, who when they mature swim to the reefs
The ability of the mangrove tree to survive is greatly affected by the ocean, and the fishes survival is dependent upon the mangrove tree’s survival

5. Example What is our ecosystem? Biotic Factors? Abiotic Factors?
How could each of these things affect the overall health of our ecosystem?

6. Ecosystems Are Always Changing
Ecosystems can look similar from one year to the next, but they are actually quite dynamic
The amount of precipitation can change the dominant plant species, which can change the communities composition (the number of plants is similar, but the species is different)
This can change the animals that get their food from this area
As these cyclic changes occur, an ecosystem falls into balance, which is called an approximate equilibrium
What changes occur in our ecosystem, and what is our approximate equilibrium?

7. One Factor Can Affect Change
The change of a biotic or abiotic factor can affect all of the organisms in an ecosystem
Changes that can affect an ecosystem:
Biodiversity
Keystone Species

8. Biodiversity
Biodiversity: Assortment, or variety, of living things in an ecosystem
Rainforest: high level of biodiversity, which accounts for more than 50% of the plant and animal species on the planet
Amount of biodiversity depends on many factors, including moisture and temperature

9. Keystone Species
Complex ecosystems are dependent on very few important parts of the web, that when disturbed can have a significant effect on the health of the ecosystem
A species that has an unusually large effect on its ecosystem
Example: Beavers

10. Beavers Beavers fell trees to construct dams
Change free-flowing streams into ponds, wetlands & meadows
Changes to the ecosystem:
Wider variety of fish in still water of pond
Attraction of birds that eat the above fish
Insects are attracted to the pond, which brings insect eating birds as well
Waterfowl nest near the pond, which brings in prey animals that eat the eggs
Beavers can greatly change their environment, and the loss of them can severely impact the ecosystem

12. Sea Otters
Sea Otters are also a keystone species, because they eat sea urchins
Sea urchins, if allowed to populate the ocean without a predator, eat all of the available kelp
The loss of kelp means less food for crabs, snails, and geese
It also means that species of fish that hide in the kelp from predators are heavily eaten and their numbers drop dramatically, further upsetting the ecosystem

14. Outputs
We live in the Sonoran Desert. Name three biotic and abiotic factors.
Compare with your neighbor and write down one biotic and abiotic factor that you did not have.
Hummingbirds are a keystone species in the Sonoran Desert. Give 3 reasons why you think this is.