Lecture 8

Question 1

Abundance

Answer 1

• Can change over time and space
• Fluctuating abundance could reflect changes in environmental factors (nutrient supplies, temperature, or predator abundance)

Question 2

Types of Patterns of Population Growth

Answer 2

• 1. exponential growth
• 2. logistic growth
• 3. Fluctuations
• 4. regular cycles

Question 3

Patterns of Population Growth

Answer 3

• These four patterns are not mutually exclusive
• A single population can experience each of them at different times

Question 4

Exponential Growth

Answer 4

• Population increases by a constant proportion at each point in time

Question 5

Exponential Growth When Conditions are Favourable

Answer 5

• a population can increase exponentially for a limited time
• When a species reaches a new area, the population may grow exponentially until density-dependent factors regulate its numbers

Question 6

Logistic Growth

Answer 6

• Populations first increase and then fluctuate by a small amount around carrying capacity
• Limited by space or food
• Used broadly to indicate any population that increases initially, then levels off at the carrying capacity

Question 7

Population Fluctuation

Answer 7

• Numbers rise and fall over time
• Fluctuations can be deviations from a growth pattern or erratic

Question 8

Population Outbreak

Answer 8

• the number of individuals increases rapidly

Question 9

Long Term Data Sets

Answer 9

• can help solve applied problems
• An outbreak of a new disease in 1993 in New Mexico was caused by a new strain of hantavirus, carried by the deer mouse

Question 10

Delayed Density Dependence

Answer 10

• Delays in the effect that density has on population size
• Commonly, the number of individuals born in a given time period is influenced by population densities that were present several time periods ago
• can cause populations to fluctuate in size

Question 11

Population Extinction

Answer 11

• Becoming very common because of various land pressures
• The risk of extinction increases greatly in small populations

Question 12

What Can Affect a Population’s Risk of Extinction

Answer 12

1. Fluctuations in growth rate
2. Population size
3. Chance events

Question 13

The Geometric Growth Equation

Answer 13

• can include random variation in the finite rate of increase
• Random variation in environmental conditions can cause λ to change from year to year
  (good years and bad years for growth)
• Fluctuations increase the risk of extinction

Question 14

Chance Events

Answer 14

1. Genetic
2. Demographic
3. Environmental Events

Question 15

Genetic Chance Event

Answer 15

• Genetic drift
• Allele frequencies can change at random from one generation to the next and genetic variation is reduced
• Much lower genetic diversity by chance in small populations

Question 16

Genetic Drift Definition

Answer 16

• chance events influence which alleles are passed on to the next generation

Question 17

Demographic Chance Event

Answer 17

• Chance events affect the survival and reproduction of individuals
• birth and death rates are constant, but the actual fates of individuals differ
• The environment is stable, but you have bad luck

Question 18

Environmental Chance Event

Answer 18

• Unpredictable changes in the environment that can cause extinction of small populations
• Change in average birth or death rates from year to year because of random changes in environmental conditions (environment changes)
• Can play a role in the extinction of small populations

Question 19

Allee Effects

Answer 19

• At low densities, individuals have difficulty finding mates, so the growth rate decreases as population density decreases
• Can reduce small population size even further

Question 20

Natural Catastrophes

Answer 20

• floods, fires, etc
• Eliminate or greatly reduce even large populations and play a role in extinctions
  (Ex. heath hens)

Question 21

Extinction Vortex

Answer 21

• see notes

Question 22

Types of Events in the Black Sea Ecosystem

Answer 22

• 1. Bottom-up Control
• 2. Top-down Control
• both can be very important for regulating populations

Question 23

Bottom-up Control

Answer 23

• increased nutrient inputs
• caused eutrophication
• increased phytoplankton biomass
• decreased oxygen
• fish die-offs

Question 24

Top-down Control

Answer 24

• top predators control the abundance of populations.
• Overfishing of predators is an example of top-down

Question 25

Population Cycles

Answer 25

• Have alternating periods of high and low abundance at regular intervals
• Different factors may drive population cycles in rodents
• Some population cycles may stop if certain environmental factors change