Warm-up What can cause the population numbers of a species to change?

Population Growth

Vocabulary Terms Population Density Immigration Emigration Exponential Growth Logistic Growth Carrying Capacity Limiting Factor Density-Dependent Factor Predator-Prey Relationships Density-Independent Relationships

Characteristics of a Population Three main characteristics: – Geographic distribution, density, growth rate Population density: number of individuals per unit area

Population Growth Three things affect population size: births, deaths, immigration/emigration Natural population numbers generally stay stable In order to grow, birth rate must exceed death rate

Population Growth Immigration: movement of individuals into an area – Increase in population numbers Emigration: movement of individuals out of an area – Decrease in population numbers – Can lead to genetic diversity of a species

Exponential Growth Exponential Growth: occurs when individuals in a population reproduce at a constant rate – With ideal conditions (unlimited room/resources), all populations will undergo exponential growth Exponential growth will appear as a J shaped graph Population will eventually use the resources when undergoing exponential growth

Logistic Growth Logistic Growth: occurs when a population growth slows or stops – Always follows a period of exponential growth – Shows up as a S shaped graph – Population numbers level off Carrying Capacity – Maximum number of organisms an environment can sustain

Limiting Factors A factor that causes population growth to decrease – Competition, predation, parasitism/disease, drought, human disturbances

Density-Dependent Factors Density-Dependent Factors depend on population size – Only come into play when population numbers reach a certain size Competition: competition for resources such as food, water, space, sunlight, etc. Predation: most common mechanism of population control – Seen in the mouse/owl lab

Density-Dependent Factors Parasitism/disease: limit growth of a population – Similar to predators, except the end result is generally weakening of the host rather than death

Density-Independent Factors Density-Independent Factors affect population regardless of how many organisms there are – Generally involve things like weather, natural disasters, and human activities

Activity Answer the following questions in full and complete sentences: – What factors might cause the carrying capacity of a population to change? – Give an example of a density-independent limiting factor that has affected a human population. Describe how this factor changed the human population. – How is the carrying capacity of a city’s roads similar to the carrying capacity of an ecosystem?