POPULATION BIOLOGY Review: Population is a group of 1 species living in the same place at the same time. A species is defined by reproduction (with each other, producing fertile offspring) WHAT LIMITS A POPULATIONS GROWTH? Answer: Limiting Factors 1. Density Dependent – increases as the population increases. EXAMPLES OF DENSITY DEPENDENT DISEASE SPREADS FASTER MAD COW DISEASE COMPETITION FOR FOOD COMPETITION FOR WATER PARASITES SPREAD EASIER EXAMPLES OF DENSITY DEPENDENT Diseases, competition, parasites, lack of food All of these things increase pressure on the population as the population gets bigger. WHAT LIMITS A POPULATIONS GROWTH? Answer: Limiting Factors 1. Density Dependent 2. Density Independent – affects the population regardless of the population size. EXAMPLES OF DENSITY INDEPENDENT STORMS FLOODS DROUGHT POLLUTION HABITAT DESTRUCTION EXAMPLES OF DENSITY INDEPENDENT Storms, floods, drought, habitat destruction, natural disasters, pollution All of these things affect a population of 10 individuals or 10 million individuals. The size does not matter! CARRYING CAPACITY Definition: Number of organisms in the population (remember: just 1 species) that the environment can support. Populations may be over or under the CARRYING CAPACITY. If a population is under the Carrying Capacity, Then the population will increase (more births and survival because there are enough resources like food, water, space) If a population is over the Carrying Capacity, Then the population will decrease (more deaths because of lack of food, water, space,…) POPULATION GROWTH CURVE POSSIBILITIES J-Curve Exponential Growth Starts small Rapid increase POPULATION GROWTH CURVE POSSIBILITIES S- Curve Population growth adjusts to amount of resources. POPULATION GROWTH CURVE POSSIBILITIES Fluctuating Curve Population oscillates above and under carrying capacity. Ex. Lynx and snowshoe hare ORGANISM INTERACTIONS THAT AFFECT POPULATION SIZE Predator- Prey – prey pop. Goes up, then predator pop. Goes up, prey goes down, then predator pop. Goes down. Competition - btwn organisms for food, space, light, water, mates,… ORGANISM INTERACTIONS THAT AFFECT POPULATION SIZE Crowding and Stress Stress symptoms in a population: Aggression Decrease in parental care Decrease in fertility Decreased resistance to disease All of these things can lead to population decline! HUMANS ARE ANIMALS TOO! We are not exempt from limiting factors like Natural disasters, disease, lack of food, water or space, overcrowding, and competition. HUMANS ARE ANIMALS TOO! Humans have been able to exceed their carrying capacity by overcoming some limiting factors. Ex. Medicine for diseases Eliminating competition (wars, hunting,…) Increasing food production Every second: 4-5 babies are born somewhere on Earth. Also in every second, 2 people die. Net growth: 2.5 people every second. 9,000 people every hour. 214,000 people per day. HUMAN POPULATION Vocabulary Alert! Demography: study of human populations Population Growth Rate= birth rate – death rate In the U.S.: birth rates are down, but death rates are down as well. People are having fewer children but life expectancy increases every year. Vocabulary Alert! Age Structure: number of individuals at each age group. Histogram (or Population Pyramid): a graph of the age structure of a population (usually a country) EXAMPLES OF HISTOGRAMS HISTOGRAMS CAN HELP DEMOGRAPHERS PREDICT WHAT THE POPULATION WILL LOOK LIKE IN THE FUTURE. If a pyramid shape – the population will grow. If a rectangle shape – the population is steady. If an inverted pyramid – the population will shrink. Vocabulary Alert! Mobility – movement of animals that affects population size and structure. Immigration – movement of individuals INTO a population. Emigration –individuals EXIT a population.