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Population Ecology Chapter 5, Section 3 Population Dynamics Population: all the individuals of a species that live together in an area Demography: the statistical study of populations, make predictions about how a population will change Population Dynamics Three Key Features of Populations •Size •Density •Dispersion Three Key Features of Populations 1. Size: number of individuals in an area Three Key Features of Populations Four Variables: (Births+ Immigrants) − (Deaths + Emigrants) = Population Change Factors That Affect Future Population Growth Immigration Natality + + Population Emigration - Mortality Three Key Features of Populations 2. Dispersion: describes their spacing relative to each other • clumped • even or uniform • random clumped even (uniform) random *Species tend to cluster where resources are available *Groups have a better chance of finding clumped resources *Protects some animals from predators *Packs allow some to get prey *Temporary groups for mating and caring for young Three Key Features of Populations 2. Density: measurement of population per unit area or unit volume Formula: Dp= N S Pop. Density = # of individuals ÷ unit of space Populations CANNOT grow indefinitely… Biotic potential – capacity for population growth under ideal conditions Intrinsic rate of increase (r) – the rate at which a population would grow with UNLIMITED resources Factors that affect population growth Limiting factors = ENVIRONMENTAL RESISTANCEthe combination of all factors that act to limit the growth of a population Ex: Amount of water Amount of food Temperature Together, biotic potential and environmental resistance determine the CARRYING CAPACITY! Environmental Resistance Density-dependent factors- Biotic factors in the environment that have an increasing effect as population size increases Predation Parasitism Infectious disease Competition for resources Environmental Resistance Density-independent factors- Abiotic factors in the environment that affect populations regardless of their density Ex. temperature storms habitat destruction drought Other factors that affect population growth Carrying Capacity = K = the maximum population size that can be supported by the available resources There can only be as many organisms as the environmental resources can support Logistic growth = “S” A sheep population on the island of Tasmania between 1800 and 1925 - After sheep were introduced in 1800, their population grew exponentially, thanks to an ample food supply. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity. Carrying Capacity N u m J-shaped curve (exponential growth) Carrying Capacity (k) b S-shaped curve (logistic growth) e r Time r-selected versus k-selected species 2 Life History Patterns 1. R Strategists short life span small body size reproduce quickly have many young little parental care Ex: cockroaches, weeds, bacteria 2 Life History Patterns 2. K Strategists long life span large body size reproduce slowly have few young provides parental care Ex: humans, elephants 4 General Patterns of Variation 1. Stable – pop fluctuates slightly around carrying capacity 2. Irruptive - many short-lived, rapidly reproducing organisms – high peak, then crash 3. Cyclic - predator-prey 4. Irregular – no recurring patterns Population Cycles for the Snowshoe Hare and Canada Lynx