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POPULATIONS
SC STANDARD B-6. 2: Students will demonstrate an understanding of the way populations are affected by density-dependent factors & density-independent factors.
How do Populations Grow?
3 important characteristics of a population are its :
geographic distribution density growth rate
Hooker’s Manzanita
found in maritime chaparrel (threatened habitat due to development)
Central California (Monterrey County)
Franklin’s Bumble Bee
Most restricted geographic distribution of any known bee
Between Pacific coast & Sierra Nevada in Oregon & northern California
Density
population density: the # of individuals per unit area
Density is one of the main characteristics that describes a natural population.
Growth Rate
3 factors affect population growth:
1. # of births 2. # of deaths 3. # of
individuals that immigrate or emmigrate
Immigration: movement of individuals into an area
Emmigration: movement of individuals out of an area
EXPONENTIAL GROWTH
growth pattern in which the individuals in a population reproduce at a constant rate
Under ideal conditions with unlimited resources, a population will grow exponentially
LOGISITIC GROWTH
growth pattern in which a population’s growth rate slows or stops following a period of exponential growth
carrying capacity: largest # of individuals of a population that a given environment can support
Limiting Factors to Growth
In respect to populations a limiting factor is anything that causes population growth to decrease.
Limiting factors are either:
Density-Dependent
Density-Independent
Density-Dependent Limiting Factors limiting factor
that depends on population size
become limiting only when population density reaches a certain level
Include: 1. competition 2. predation 3. parasitism &
disease
1. Competition
When populations become crowded members of same or different species compete for food, shelter, mates, space, sunlight
2. Predation
Predator-Prey relationships mechanism of population control
3. Parasitism & Disease
Parasites take nourishment from their host host weakens does not usually die
Density-Independent Factors
affect all the populations in similar ways, regardless of #’s Forest fires Floods Seasonal cycles Human
interference (clear-cutting, damming river)
Human Population Growth
Population of humans on Earth increases with time
Patterns of Population Growth Birth rates,
death rates, & the age structure of a population help predict why some countries have high growth rates while other countries grow slowly.
The Demographic Transition
the change in a population from high birth & death rates to low birth & death rates