Populations Objective: A4 - Analyze how populations & communities respond to abiotic & biotic factors and recognize that long-term survival of a species is dependent on changing resources that are limited Review: Population - a group of organisms, all of the same species living in a specific area. Density - # of organisms 3 important characteristics of a population are: distribution density growth rate

the number of individuals per unit area 1 Population density – the number of individuals per unit area 3 factors that can affect population: - number of births - number of deaths - number of individuals that enter or leave the population Immigration – movement of individuals into an area Emigration – movement of individuals out of an area

Population Growth Population Growth of Houseflies 2 Population Growth of Houseflies 1 million 500,000 100 One year Population size ● J-shaped growth curve — illustrates exponential population growth

Population Growth of Houseflies 1 million 500,000 100 One year Population size 3 Exponential growth – occurs when the individuals in a population reproduce at a constant rate (as a population gets larger, it also grows at a faster rate) No limits on growth Under ideal conditions with unlimited resources Could not occur indefinitely in nature

Logistic growth – occurs when a population’s growth slows or stops 4 Logistic growth – occurs when a population’s growth slows or stops - as resources become less available, following a period of exponential growth Exponential Limits on growth A S-shaped curve illustrates logistic growth

Carrying capacity 5 Carrying capacity – largest number of individuals of a population that a given environment can support

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Limiting factor – a factor that causes population growth to decrease 7 Limiting factor – a factor that causes population growth to decrease Any biotic or abiotic factor that restricts the existence, numbers, reproduction, or distribution of organisms Examples Lack of food Overcrowding Competition for resources

Characteristics of Population Growth 8 Characteristics of Population Growth Exponential growth Carrying capacity J curve S curve Population Time DISEASE SPACE PREDATORS FOOD

2 kinds of limiting factors: 9 2 kinds of limiting factors: Density-dependent limiting factor Exp. competition, predation, parasitism, disease Density-independent limiting factor Exp. Unusual weather, natural disasters, seasonal cycles, certain human activities biotic abiotic

Resources Glenco Interactive Chalkboard 2003 Prentice Hall Biology 2004 www.mun.ca/biology/scarr/Logistic_growth.htm