How do communities change over time? Population Growth How do communities change over time?

Characteristics of Populations Geographic distribution- describes the area inhabited by a population Distribution density- the number of individuals per unit area Growth rate- increase/decrease per unit time Age Structure-how many people of different ages make up a given population

Population Growth Number of births (birth rate) Number of deaths (death rate) Movement into a population (immigration) and movement out of a population (emigration) Examples: ↑ birth rate + ↓ death rate= ↑ pop. growth ↑ birth rate + ↑ death rate = ↔ pop. Growth ↑ immigration = ↑ pop. Growth ↑ emigration = ↓ pop. Growth Immigration = emigration = ↔ pop. growth

Population growth Populations will grow until they reach their biotic potential, unless they are limited by factors in the environment This type of growth is known as a J-curve

Exponential Growth Occurs when the individuals in a population reproduce at a constant rate Under ideal conditions with unlimited resources

Fill It In … Define “exponential growth”:

Population growth Limiting factors, such as availability of food, water, and space establish a carrying capacity for populations This type of growth is known as a S-curve.

Logistic Growth Occurs when a population’s growth slows or stops following a period of exponential growth As resources become less available, the growth of a population slows or stops

Fill It In … List limiting factors for a population of dandelions:

Population growth Carrying capacity is defined as the number of individuals an environment can support.

Population growth Limiting factors in the environment help to maintain ecosystem stability by allowing populations to fluctuate around the carrying capacity. This is called dynamic equilibrium.

Population growth Density dependent factors have a greater effect on a population when there is a higher population density (the number of individuals in a given space). For example, competition, predation, and the spread of infectious diseases are density-dependent factors.

Population growth Density independent factors influence the size of a population regardless of its density. For example, natural disasters such as forest fires are density independent factors.

Age Structure

Check Yourself! What kind of curve illustrates exponential growth? What determines the carrying capacity of the environment? List 3 examples of limiting factors.

Population growth Succession is the idea that communities will replace other communities in a predictable, orderly way; this happens because every community alters the physical factors of the environment. Ex. As trees grow, they produce shade.

Check Yourself! What kind of curve illustrates exponential growth? J-CURVE What determines the carrying capacity of the environment? List 3 examples of limiting factors.

Check Yourself! What kind of curve illustrates exponential growth? J-CURVE What determines the carrying capacity of the environment? LIMITING FACTORS List 3 examples of limiting factors.

Check Yourself! What kind of curve illustrates exponential growth? J-CURVE What determines the carrying capacity of the environment? LIMITING FACTORS List 3 examples of limiting factors. FOOD, WATER, AND SPACE