Notes: Population Growth and Regulation

Notes: Population Growth and Regulation
How Populations Grow
Factors the determine how much a population will change
1. births
2. deaths
3. migration
Stable populations occur when as many individuals join (birth or immigration) as
leave (death or emigration)
Population change = (birth - deaths) + (immigrants - emigrants)
Biotic Potential: maximum rate at which a population could grow given optimal
conditions (food, water, space)
Factors that influence biotic potential:
age of reproduction
frequence of reproduction
number of offspring produced
reproductive life span
average death rate under ideal conditions
Environmental Resistance: Decreases the birth rate, or increases death rate,
related to environmental conditions, such as food & space.
Density Independent Factors: weather and other natural disasters
Density Dependent Factors: food, space, water, parasitism, competition
Growth rate (r) = birth rate (b) - death
rate (d)
Population growth = rN
(r = growth rate, N = original population
J-shaped curve showing exponential growth
of a population
S-shaped curve shows how a population
becomes limitied by environmental factors
This population has not yet reached its
carrying capacity.
Carrying Capacity: the maximum size of a
population that an area can support
Boom and Bust Cycles
Rapid population growth followed by a massive die-off
Populations that are influenced by seasonal weather patterns, such as cold and
Predator-Prey Cycles
Most populations fluctuate in cycles. The prey population rises, causing the predator
population to also rise. Predators then overfeed on prey, causing the prey population
to drop, Once the prey population drops, the predator population drops due to lack of
food. The cycle repeats indefinitely.
Resources limit the size of populations as individuals compete
Interspecific competition: occurs between members of different species
Intraspecific competition: occurs beweeen members of the same species
Scramble competition: free-for-all, plants disperse seeds and as they grow they
choke out other seedlings
Contest competition: social interaction in animals that leads to the gaining of
Contest competition: social behaviors, territoriality
Dominance heirarchies: pecking orders within members of a species, dominant
individuals get more resources or mating priveleges
Simulation of Predator Prey Interactions
Population Patterns in Space and Time
Survivorship curve
Early loss
Constant loss
Late Loss