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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.
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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 + + - Population Mortality Natality - Emigration
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 Pop. Density = # of individuals ÷ unit of space S
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 RESISTANCE-the 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.
Nu m b e r J-shaped curve (exponential growth) Carrying Capacity Carrying Capacity (k) S-shaped curve (logistic growth) Time
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
