Understanding Population Dynamics: Limiting Factors OBJ: Differentiate between density-dependent and density-independent regulation of populations. Essential Vocab: Carrying capacity

THINK ABOUT IT What determines the carrying capacity of an environment for a particular species? In its native Asia, populations of hydrilla increase in size until they reach carrying capacity, and then population growth stops. But here in the United States, hydrilla grows out of control. Why does a species that is “well-behaved” in one environment grow out of control in another?

Limiting Factors What factors determine carrying capacity? Acting separately or together, limiting factors (density-dependent or density-independent) determine the carrying capacity of an environment for a species.

Limiting Factors A limiting factor is a factor that controls the growth of a population. There are several kinds of limiting factors.

Density-Dependent Limiting Factors Density will limit a population Population density refers to how crowded and area is. High density? Low density? Predict: Why would being crowded start to cause death and a realization of carrying capacity?

Density-Dependent Limiting Factors What limiting factors depend on population density? Limiting factors: Competition (example to follow) Predation (example to follow) Herbivory Parasitism Disease Stress from overcrowding Why are these factors called density-DEPENDENT?

Competition When population density is high? -Individuals compete for food, water, space, sunlight, and other essentials. Consequences? -Some individuals obtain enough to survive and reproduce. -Some may obtain just enough to live, but not enough to enable them to raise offspring. -Some may starve to death or die from lack of shelter. Competition can lower birthrates, increase death rates, or both.

Population Trends:Compare Moose & Wolf predator/prey relationship

Predator-Prey Relationships 1. More moose? Easy prey=more for wolves to eat and their population grows 2. Too many wolves? Kill more moose than are born, moose population falls. 3. Moose population drops? Wolves begin to starve= increase death rate, wolf population also falls. 4. Other Density Dependent limiting factors?

Density-Independent Limiting Factors What limiting factors do not typically depend on population density? Limiting factors: Unusual weather such as- Hurricanes Droughts (example to follow) Floods Other Natural disasters such as- Wildfires Why are these factors called density-INDEPENDENT?

Density-Independent Limiting Factors Population may “crash.” After the crash, the population may build up again quickly, or it may stay low for some time.