1. QOTD
What is a fluctuation?

2. Fluctuations and changes
Mr. Dunnum

3. What are fluctuations?
The rise and fall in populations

4. What causes fluctuations and changes?
Population fluctuations in nature can result from changing environment
We call this extrinsic environmental factors
Alternatively, population fluctuations can result from things such as high growth rate coupled with time delay allowing population to exceed carrying capacity
We call this intrinsic demographic factors

5. However…..
Under extreme conditions populations could in theory behave chaotically, even in a constant environment!
Both time delays and high population growth rate tend to destabilize populations, leading to greater fluctuations

6. Example
Population growth rate depends on ecological conditions--e.g., two grain beetle species

7. Population Growth
Stabilize
Destabilized
Density-dependent population growth tends to stabilize population size
Changes in populations can result from changes in food, temperatures, light levels, chemistry, and a variety of other factors that influence birth and death rates

8. Wrap up Population fluctuations the norm in nature
In many cases populations vary in response to extrinsic environmental factors such as changing food, temperatures, light, chemicals, etc., that affect reproduction and survival
In other cases, however, intrinsic dynamics including time-delays can cause fluctuations, including limit cycles and chaos--even though the environment is constant (e.g., r, K do not change!)