Chapter 10: Populations Dynamics Flashcards
Populations show different patterns of _______ over time
population growth
Population Dynamics
refers to the ways in which population sizes change over time
Exponential Growth
When rate of growth increases or decreases in proportion to the current number of individuals
How long can populations increase exponentially?
when conditions are favorable, a population can increase exponentially for a limited time, but it can’t continue indefinitely
What can lead to exponential growth?
dispersal
How does exponential growth work via dispersal?
new regions are colonized by long-distance events. Local populations then increase and expand by short-distance dispersal events
Logistic Growth
some populations reach a relatively stable population size, or equilibrium, that changes little over time
-numbers of individuals increase rapidly at first, then stabilize as the population reaches carrying capacity
Carrying capacity
max population size that can supported by the environment. Population size fluctuates around this number
Population Fluctuations
in some populations, numbers increase or decrease erratically from an overall mean
-also many occur as deviations from a population growth pattern (such as exponential or logistic)
Population Outbreak
number of individuals in a population explodes at certain times
What organism does population outbreak occur most often in?
insects. Mountain Pine Beetles altered ecosystems by killing millions of trees in BC
Factors that can cause population fluctuations?
nutrient supplies, temperature, and predator abundance
What is an important factor of disease outbreaks?
population fluctuations
Why does population fluctuations affect disease outbreaks?
high densities of species can increase contact. Harboring the spread of disease
Population Cycles
alternating periods of high and low abundance occur at regular intervals
Causes of Population Cycles
-internal factors (hormonal, behavioral changes in response to crowding)
-External factors (weather, food supplies, predators)
-The factors may vary with location and species
Delayed Density Dependance
may be a factor in population cycles
When does delayed density dependance occur?
when the number of individuals born in a given time period is influenced by population density or other conditions that were present several time periods ago
What can stop population cycles?
key changes in environmental factors
Fluctuations in population size can increase
risk of extinction
Why does fluctuation in population size increase risk of extinction?
-a population that fluctuates grows slower than one that does not vary
-when variable environmental conditions result in large fluctuations in growth rate, the risk of extinction increases
-small populations are at greatest risk
Effective Population Size
number of individuals that can contribute offspring to the next generation
Extinction Vortex
small population sizes leads to further declines in population size, eventually resulting in extinction
Factors that place small populations at risk of extinction
genetic drift and inbreeding depression
Inbreeding
mating between related individuals that increases the frequency of homozygotes, including harmful alleles
Genetic drift
chance events influence which alleles are passed on to the next generation. alleles can be lost or become fixed
Demographic Stochasticity
chance events affect survival and reproduction of individuals
-more likely in small populations
Allee Effects
growth rate decreases as population decreases
-at low densities, individuals have difficulty finding mates
-cause the population growth rates to drop, which causes population size to decrease even further in a downward spiral towards extinction
Environmental Stochasticity
erratic or unpredictable changes in the environment
Natural Catastrophes
(floods, fires, etc.) can eliminate or greatly reduce even large populations and play a role in extinctions
Bottom-Up Control
increased nutrient inputs caused eutrophication and increased phytoplankton biomass, decreased oxygen, fish die-off, etc.
Top-Down Control
top predators control the abundance of populations
