Population Dynamics

Question 1

Abundance

Answer 1

Can change over time and space
Understanding what drives fluctuations
Fluctuating abundance could reflect changes in environmental factors such as nutrient supplies, temperature, or predator abundance

Question 2

Patterns of Population Growth

Answer 2

Populations exhibit a wide range of growth patterns, including:
exponential growth
logistic growth
Fluctuations
regular cycles
These four patterns are not mutually exclusive
A single population can experience each of them at different times

Question 3

Exponential Growth

Answer 3

Population increases by a constant proportion at each point in time
When conditions are favourable:
a population can increase exponentially for a limited time
When a species reaches a new area, exponential growth can occur if conditions are favourable
The population may grow exponentially until density-dependent factors regulate its numbers

Question 4

Logistic Growth

Answer 4

Populations first increase and then fluctuate by a small amount around carrying capacity
Limited by space or food
Over time, populations level off when they reach their maximum carrying capacity
Plots of real populations rarely match the logistic curve exactly
Used broadly to indicate any population that increases initially, then levels off at the carrying capacity

Question 5

Population Fluctuations

Answer 5

Numbers rise and fall over time
Fluctuations can be deviations from a growth pattern
Ex. The Tasmanian Sheep Population
Or erratic
In Lake Erie phytoplankton populations

Question 6

Population Outbreak

Answer 6

the number of individuals increases rapidly

Question 7

Long term data sets

Answer 7

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 8

Population Cycles

Answer 8

Have alternating periods of high and low abundance at regular intervals
Populations of small rodents, such as lemmings and voles, typically reach a peak every 3-5 years
Weasels are often the main predators of lemmings
Different factors may drive population cycles in rodents
For collared lemmings in Greenland, field studies and modelling indicated that the 4- year cycle is driven by predators, such as the stoat
In other studies, predator removal had no effect on population cycles. Factors driving population cycles may vary by place/species.
Some population cycles may stop if certain environmental factors change

Question 9

Delayed density dependence

Answer 9

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
Delayed density dependence can cause populations to fluctuate in size

Question 10

Population extinction

Answer 10

Becoming very common because of various land pressures
The risk of extinction increases greatly in small populations
What can affect a Population’s Risk of Extinction:
1. Fluctuations in growth rate
2. Population size
3. Chance events

Question 11

The geometric growth equation

Answer 11

This 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
The degree of fluctuation is important

Question 12

Chance Events: Genetic

Answer 12

Genetic drift: chance events influence which alleles are passed on to the next generation
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 13

Chance Events: Demographic

Answer 13

Chance events affect the survival and reproduction of individuals
Ex; a population of ten individuals, a rock slife wipes out 6
40% survival rate may be much lower than the average rate for that species
birth and death rates are constant, but the actual fates of individuals differ
The environment is stable, but you have bad luck

Question 14

Chance Events: Environmental Events

Answer 14

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
The environment actually changes
Can play a role in the extinction of small populations

Question 15

Allee Effects

Answer 15

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 16

Natural Catastrophes

Answer 16

floods, fires, etc
Eliminate or greatly reduce even large populations and play a role in extinctions
Ex. heath hens were reduced to one population of 50 on Martha’s Vineyard when a series of bad weather, fires, diseases, and predators drove the population to extinction

Question 17

Extinction vortex

Answer 17

CHECK DIAGRAM ON LECTURE 8 NOTES

Question 18

Events in the Black Sea Ecosystem

Answer 18

both can be very important for regulating populations
Illustrate 2 types of causation in ecological communities
1. Bottom-up Control
increased nutrient inputs
caused eutrophication
increased phytoplankton biomass
decreased oxygen
fish die-offs
2. Top-down Control
top predators control the abundance of populations.
Overfishing of predators is an example of top-down