Flashcards in Ch. 11 Population Dynamics Deck (57)
Excessive richness of nutrients in a lake or other body of water
Populations can change in size as a result of four processes:
Birth, death, immigration, and emigration
The ways in which populations change in abundance over time
Populations exhibit a wide range of growth patterns, including..
- exponential growth
- logistic growth
- regular cycles
Exponential growth usually happens when..
- when conditions are favorable
- when a species reaches a new geographic area
- some populations reach a stable size that changes little over time
- fluctuate by a small amount around what appears to be carrying capacity
- assumed to be constant
- the population size for which birth and death rates are equal
Logistic growth example
- when sheep were first introduced to Tasmania, the population increased rapidly
- later, population numbers fluctuated above and below a maximum sustainable population size
Birth and death rates vary over time, thus we expect..
Carrying capacity to fluctuate
An equilibrium with their environmental resources
Near exponential growth when..
Resources are unlimited
Growth slows as species approaches carrying capacity of environment
___ factors reduce population growth rates.
Density-dependent factor examples
- food abundance
- parasite load
- intraspecific competition
Rise and fall in population size over time
Population outbreak (bloom)
Populations may explode, causing a bloom
Some populations have alternating periods of high and low abundance at regular interval
Internal factors that may drive population cycles in rodents:
Hormonal or behavioral changes in response to crowding
External factors that may drive population cycles in rodents:
Weather, food supplies, or predators
Example of top-down regulation in lemmings
Used field observations and mathematical models to argue that their 4-year cycle is driven by predators
Example of bottom-up regulation in lemmings
In other studies, predator removal had no effect on population cycles
These cycles were driven by food supply
Effects of population density often have a ___ or delay.
What may this lag be due to?
Need time to reproduce
Delayed density dependence
- delays in effect that density has on population size
Example of delayed density dependence
When a predator reproduces more slowly than its prey
__ can cause fluctuations in population size.
Stable limit cycle
Pattern when the population fluctuates indefinitely about the carrying capacity
Many factors can drive populations to extinction:
- predictable factors
- fluctuation in population growth rate and population size
- chance events
If you fluctuate to zero ->