# Lecture 10: Populations: Growth potential, limits, & dynamics Flashcards

Density independent factors

- Factors affecting population growth that are unrelated to population size
- ex: natural disasters

Negative density dependent factors

Factors negatively affecting population growth that have increasing strength with increasing population size

why would a population become self-limiting

a variety of consequences associated with too many individuals

Logistic growth curve

- s-shaped curve of density-dependent population growth
- Formalizes the relationship between increasing population size and decreasing growth rate, as the carrying capacity is approached

Inflection point

- Separates early accelerating phase from the later decelerating phase
- located in the middle of the graoh

carrying capacity

- The maximum number of organisms the environment can support
- the point where growth falls to zero in the logistic growth curve.

where on the density-dependent curve is r > 0

- before / to the left of the inflection point
- early growth is exponential

where on the curve is r approaching 0

- after / to the right of the inflection point
- as it reaches carrying capacity

where on the curve is r = 0

at the carrying capacity

density dependence in plants

- slow growth
- smaller size at higher density -> reduced survival and fecundity

Self thinning

- Negative effects of high density cause some individuals to die, allowing remaining plants to increase in average size
- Consistent negative relationship established between plant density and average plant size

Positive density dependence

Increasing population size has a positive

influence of growth rate (up to a point!)

Causes of positive density dependence

- Larger populations are more genetically diverse
- Allee effect

define the Allee effect

Beneficial social interactions at larger group sizes increases individual fitness

lemming population cycle

- Rapid population growth leads to depletion of resources.
- Triggers group migration behavior to locate new resources.
- Obstacles are overcome by a collective behavior/mass action.
- Population crashes (but not all die) and a new cycle begins