Populations

Important Vocabulary 1. Birth rate: number of births in a population in one year 2. Death rate: number of deaths in a population in one year 3. Immigration: number of individuals that move into a population 4. Emigration: number of individuals that move out of a population Slide # 2

Populations and Their Growth 1.Growth Rate: the change in a population’s size 2.A population’s size can increase (positive), decrease in size (negative) or remain the same size (constant) 3.Logistic growth: “J” shaped curve 4.Exponential growth: “S” shaped curve Slide # 3 5. Carrying capacity: largest number of individuals the environment can support.

Positive Population Growth 1. Occurs when birth rate is higher than the death rate 2. Usually occurs when conditions are ideal; will increase until something stops it Human Population Growth Curve Slide # 4

Negative Population Growth 1.Occurs when birth rate is lower than death rate a.Ex. Overgrazing and drought left this area with out enough resources to sustain all of the wildlife. b.individuals die and the population decreases. Slide # 5

Steady State -No population growth Steady State Population Growth of Rabbits Years # of Rabbit 1. Occurs when birth and death rates are about equal Slide # 6

Population Boom and Population Bust The human population experienced a boom (baby boom) after world war II. Slide # 7 Boom Bust Boom: Birth rate is higher than death rate Bust: Birth rate is lower than death rate

Limiting Factors: Limit Population Growth Slide # 8 1.Limiting factors: help stabilize population numbers when the population reaches carrying capacity for that ecosystem a.Density independent: factors that affect all members of the population equally if population is dense or not.  Natural disasters: floods, wildfires, tornadoes, pollution, habitat destruction b.Density dependent: factors that affect crowded populations  EX: competition, predation, crowding and stress, parasitism, and disease

Density Independent Limiting Factors Slide # 9

Slide # 10 1.Competition for limited resources is the most important limiting factor that affects carrying capacity. 2.Predation a.Most species serve as food for others b.These evolved relationships are important for the health & survival of predator and prey populations. Removes weak & unhealthy individuals Density Dependent Limiting Factors Competition Predation

Density Dependent Limiting Factors 3. Crowding and stress a.Most animals have a built-in need for a certain amount of space & end up fighting among themselves if they become overcrowded b.Increase in stress can reduce their resistance to disease, reduce mating, or cause low birth weight. c.Individuals who are stressed may neglect, kill, or even eat their offspring. As the tiger’s territory is shrinking due to habitat destruction, they fight and end up suffering from stress related problems. Slide # 11

Lyme disease – bacterial disease transmitted by ticks; characterized by a bulls eye shaped rash. Density Dependent Limiting Factors 4. Parasitism & Disease a.The more crowded the population, the easier it is for disease and parasites to spread. Slide # 12