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POPULATIONS POPULATIONS All living things require a balance to be attained in order to survive. This homeostasis in nature includes cellular respiration and photosynthesis, predation and prey, the water cycle, the carbon and nitrogen cycles, and even populations! POPULATIONS Population can be defined as all the members of one species that occupy a certain area during a certain time. Ex. The population of sharks in the Pacific Ocean DID YOU KNOW??? As of May 22nd, 2009, Earth’s population is estimated to be 6,781,521,494! By 2040, the population of Earth is estimated to reach ~ 9 billion people! POPULATION GROWTH PATTERNS Changes in population size occur when individuals are added or removed from a population. There are four factors that affect the size of a population: POPULATION GROWTH PATTERNS Increases are the result natality (birth-rate) increases as well as immigration increases. Natality is the number of offspring of a species born in one year. Immigration refers to the number of individuals of a species moving into an existing population. POPULATION GROWTH PATTERNS Decreases are the result mortality (death-rate) increases as well as emigration increases. Mortality is the number of individuals of a species that die in one year. Emigration refers to the number of individuals of a species moving out of an existing population. POPULATION GROWTH PATTERNS The four factors can be expressed mathematically: Population Growth = (births + immigration) – (deaths + emigration) CARRYING CAPACITY The maximum size of a population that an ecosystem can sustain is called its carrying capacity. It is determined by the availability of resources, like food and water. Carrying capacity can be affected by the following things: CARRYING CAPACITY 1. Amount of Available Water and Energy If the population grows too large, it will eventually crash when resources run out. Ex. The availability of frogs limits the population of garter snakes CARRYING CAPACITY 2. Predation If the population grows too large, predation will increase, reducing the size of the population of the prey. CARRYING CAPACITY 3. Competition If resources become more scarce, members of a population must fight for their survival. This competition reduces the population by weaning out the weak or vulnerable members. CARRYING CAPACITY 3. Competition Male lions have been known to kill the cubs of another lion to reduce the threat of competition. http://www.youtube.com/watch?v=NvoyMq84G O0 TYPES OF COMPETITION Intraspecific Competition – competition among members of the same species Interspecific Competition – competition between members of different species CARRYING CAPACITY 4. Space If a population grows too large, space will run out. Competition for space will reduce the population. Ex. Moose require a large area to forage. CARRYING CAPACITY 5. Density-Dependent Factors These can be anything that affects the population due to its size Ex. a food shortage CARRYING CAPACITY 6. Density-Independent Factors These can be anything that affects the population regardless of its size Ex. a flood