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

Question 1

Density independent factors

Answer 1

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

Question 2

Negative density dependent factors

Answer 2

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

Question 3

why would a population become self-limiting

Answer 3

a variety of consequences associated with too many individuals

Question 4

Logistic growth curve

Answer 4

• 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

Question 5

Inflection point

Answer 5

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

Question 6

carrying capacity

Answer 6

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

Question 7

where on the density-dependent curve is r > 0

Answer 7

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

Question 8

where on the curve is r approaching 0

Answer 8

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

Question 9

where on the curve is r = 0

Answer 9

at the carrying capacity

Question 10

density dependence in plants

Answer 10

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

Question 11

Self thinning

Answer 11

• 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

Question 12

Positive density dependence

Answer 12

Increasing population size has a positive
influence of growth rate (up to a point!)

Question 13

Causes of positive density dependence

Answer 13

• Larger populations are more genetically diverse
• Allee effect

Question 14

define the Allee effect

Answer 14

Beneficial social interactions at larger group sizes increases individual fitness

Question 15

lemming population cycle

Answer 15

• 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

Question 16

why does the lemming population cycle happen

Answer 16

Migratory behavior boosts reproductive output (increases fitness) in period before they fall off the cliff bc they mate along the way

Question 17

why may a population fluctuate

Answer 17

• Near carrying capacity, birth and death rates follow environmental fluctuations.
• Biology of the organism may favor instability in population size

Question 18

if fluctuations are the norm in population growth, then what varies between populations

Answer 18

the magnitude and frequency of the fluctuations

Question 19

biology favoring intrinsic population stability

Answer 19

• Large body size.
• Homeostasis (ability to resist external environmental fluctuations).
• Long life.
• Significant overlap of generations.

Question 20

biology favoring intrinsic fluctuations/instability

Answer 20

• Minute size and no homeostasis.
• Very short lived.
• High turnover - high mortality rate, so organisms at any time are mostly those from last reproductive event

Question 21

Periodic population cycling

Answer 21

Repeated, regular fluctuations in population size

Question 22

Overshooting

Answer 22

More individuals are produced than can be sustained at adulthood

Question 23

Die-off

Answer 23

• caused by strong effects of overpopulation
• defined as a population decline that drives the population well below carrying capacity
• population crash following density dependent effects

Question 24

what generates the overshoot and the subsequent die-off

Answer 24

momentum from birth and death rates

Question 25

what drives increased oscillations around the carrying capacity

Answer 25

Increasing time delay in population response to carrying capacity

Question 26

how are oscillations amplified and when do they stop

Answer 26

• amplified by an increased time delay
• stops when the population growth responds to the approach of the carrying capacity

Question 27

how can the Allee effect be in reverse?

Answer 27

Populations that experience the allee effect also suffer sudden collapse once population size declines below the critical minimum