POPULATIONS

3 Characteristics of populations Geographic (Spatial) Distribution Density Growth Rate

Geographic (SPATIAL) Distribution Dispersion – the pattern of spacing of a population within an area 3 types Uniform Clumped Random

Uniform Distribution Population is spread out evenly

Clumped Distribution Populations gather in clumps

Random Distribution Populations spread out randomly, forming clumps in some areas and uniformity in others

Density The number of organisms per unit area Low density vs. High density

Growth Rate How fast does a given population grow? 2 main types Exponential Growth Logistic Growth

Exponential Growth Occurs when the individuals in a population reproduce at a constant rate The increase is slow at first. This is called the Lag Phase. Over time the population becomes larger. This is called the exponential growth phase. Under ideal conditions with unlimited resources, a population will grow exponentially

What does it look like? A.K.A. J- curve Lag Phase

Logistics When a population’s growth slows or stops following a period of exponential growth Limited by availability of resources Population growth may slow down when: The death rate increases The birthrate decreases When resources (food, shelter, optimal temperature) are not available When the carrying capacity is reached. Carrying Capacity – the maximum number of organisms that can be supported by a given environment

What does it look like? Carrying capacity A.K.A. S-curve

Factors that affect the population size Number of Births Number of Deaths Number of Individuals that enter or leave a population

Limiting Factors Factors that cause population growth to decrease Can be Density Dependent – depends on the # of organisms Can be Density Independent – does not depend on the # of organisms

DDF: Competition Crowded populations compete for food, shelter, water, sunlight The more individuals in a given area, the sooner they will use up the available resources Occurs between same species and also members of different species Both species are under pressure to change (evolution) to occupy the separate niches No two species can occupy the same niche, this is called competitive exclusion

DDF: Predation There are always more prey than predators When this balance shifts, then competition for prey will result Starvation may also be the result if prey is not available

DDF: Parasitism and Disease Parasites range in size from microscopic, disease causing bacteria to tapeworm 30 cm or more in length They take nourishment at the expense of their hosts, often weakening them and causing disease and death

Density Independent Factors Unusual weather (storms or hurricanes) Natural Disasters (earthquakes, volcanic eruptions) Seasonal Cycles (Extreme hot or cold weather) Human Activities (Damming rivers, clear-cutting forests, industrialization, hunting, fishing)