Population Density and Spatial Distribution Population density is the number of individuals per unit area. High population density injures all individuals within the population because they compete severely for necessary resources. Dispersal: Movement of individuals from densely populated locations to new areas. Emigration: Movement from an area. Immigration: Movement into an area.

7.2 A Population Growth Curve Biotic potential is the biological ability to produce offspring of a species. Generally, biotic potential is much above replacement level. There is a natural tendency for increase.

7.2 A Population Growth Curve Population growth follows a pattern consisting of a lag phase, an exponential growth phase, a deceleration phase, and a stable equilibrium phase. Lag Phase: This is the first portion of the curve; slow population growth.

7.2 A Population Growth Curve Exponential Growth Phase (Log Phase): More organisms are reproducing, causing accelerated growth; this continues as long as birth rate exceeds death rate. Deceleration Phase: The population growth rate slows as the death rate and birthrate come to equal one another. Stable Equilibrium Phase: The death rate and birth rate become equal and the population stops growing.

7.2 A Population Growth Curve A typical population growth curve

7.3 Factors That Limit Population Size Factors that prevent unlimited population growth are known as limiting factors. Different limiting factors that act on a population are collectively known as environmental resistance. Extrinsic limiting factors are those that come from outside the population. Predators Loss of food source Lack of sunlight Accidents of nature

7.3 Factors That Limit Population Size Intrinsic limiting factors are those factors that originate within the population and exercise control over it. Behavioral changes amongst the population cause lower birthrates and higher death rates. Density-dependent limiting factors are those that become more effective as the density of the population increases. Density-independent limiting factors are population-controlling influences that are not related to the density of the population.