QOTD What is a fluctuation?

Fluctuations and changes Mr. Dunnum

What are fluctuations? The rise and fall in populations

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

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

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

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

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!)