Ecology Quiz 5

Question 1

Population

Answer 1

A population consists of all the individuals of a single species living within a specific geographic distribution (or range)

Question 2

Individual

genet
ramet

Answer 2

An individual can be defined as the product of a single fertilization

The aspen grove would then be a single genetic individual, or genet
If members of a genet are independent physiologically, each member is called a ramet

Question 3

Population size (N):

Population density:

Absolute population size:

Relative population size:

Answer 3

Population size (N): the total number of individuals

Population density: the number of individuals within a specific area or volume

Absolute population size: Actual population abundance - abundance is the relative representation of a species in a particular ecosystem

Relative population size: Number of individuals in one time period or place relative to the number in another - Estimates based on data presumed to be correlated with absolute population size

Question 4

How do ecologists measure population size and density?

Answer 4

Census: count all of the individuals within the habitat
Often not logistically or economically feasible, especially when studying large habitats

Sampling: scientists usually study populations by sampling a representative portion of each habitat
Use this data to make inferences about the habitat as a whole

Question 5

Methods for estimating abundance

Answer 5

1. Area-based counts: individuals in a given area or volume are counted
2. Distance methods: distance of individuals from a line or point are converted into estimates of abundance
3. Mark–recapture studies are used for mobile organisms

Question 6

1. Area-based counts:

Answer 6

Area-based counts: individuals in a given area or volume are counted

Used most often to estimate abundance of sessile organisms such as plants.

Quadrats: Sampling areas of specific size; must be a good representation of the entire area and are chosen at random or placed on a grid

Individuals are counted in several quadrats; counts are averaged to estimate population size.

Question 7

2. Distance methods:

Answer 7

Distance methods: distance of individuals from a line or point are converted into estimates of abundance

Line transects: observer travels along a randomly placed line, counts individuals and determines distance from the line

A detection function converts distance measurements into an estimate of the absolute population size

Question 8

3. Mark–recapture studies are used for

Answer 8

Mark–recapture studies are used for mobile organisms

A subset of individuals (sample) is captured and marked or tagged, then released

At a later date, individuals are captured again, and the ratio of marked to unmarked individuals is used to estimate population size

To estimate total population size (N): M / N = R /C

Question 9

Dispersal:

Answer 9

Movement of individuals into (immigration) or out of (emigration) an existing population

Question 10

Dispersion:

Uniform:

Random:

Clumped:

Answer 10

Dispersion: Spatial arrangement of individuals in a population.

Uniform:
Individuals in the population are more evenly spaced than would be expected by chance
Territorial birds such as penguins tend to have uniform distribution
Competition for root space and soil water in desert plants

Random:
Individuals in the population are distributed randomly
Rare
Environment is uniform and resources available

Clumped:
Individuals in the population are distributed in a clumped manner
Most common because
Environment and resources are patchy
Safety in numbers (herds)

Question 11

Metapopulations:

Fragmentation

Patches

Rescue effect:

Answer 11

Metapopulations are a network of distinct populations that may exchange members i.e. individuals move in and out of populations

Larger populations in prime habitat may act as a source to smaller sink populations is less than ideal habitat

Habitat fragmentation can result in a metapopulation

Patches can become smaller and more isolated
colonization rate may decrease
extinction rates increase

Rescue effect: High rates of immigration from a nearby patch that protects a small population from extinction.

Question 12

Geographic Range:

Answer 12

Geographic Range = region over which a species is found
Geographic range includes areas a species occupies during all life stages
Geographic ranges vary in size
Geographic ranges within a species’ range, not all habitat is suitable, so distributions are patchy
Patchy distribution of populations may be due to abiotic factors
Some species have very specific habitat requirements, others tolerate a broader range

Question 13

Population Dynamics Concepts:

Answer 13

1. Population size can change from one time period to the next.
2. Population dynamics refers to the ways in which populations change in abundance over time and space.
   Fluctuations in environmental conditions and biotic/abiotic interactions
   Populations don’t say the same

Question 14

Population growth models

Exponential growth

Logistic growth
Carrying capacity (K)

Answer 14

Exponential growth (J-shaped pattern):
When conditions are favorable, a population can increase exponentially for a limited time, but it can’t continue indefinitely bc it has to stop bc they can’t grow forever bc there are not unlimited resources - Dispersal into new habitat can lead to exponential growth

Logistic growth (S-shaped pattern): build off of J with exponential phase but resources become limited you get to K
Population increases rapidly, then stabilizes at the carrying capacity
Carrying capacity (K) maximum population size that can be supported indefinitely by the environment - determined by resources available in that system
“Logistic growth” is used broadly to indicate any population that increases initially, then levels off at the carrying capacity. - fluctuations around logistic curve through time bc of environmental conditions or abiotic

Question 15

Population sizes fluctuate
erratically
Population outbreak:

Answer 15

Fluctuations may occur as deviations from a population growth pattern, such as exponential or logistic growth

​​In some populations, numbers increase or decrease erratically from an overall mean - Rapid changes in a wide range of environmental factors, including nutrient supplies, temperature, and predator abundance.

Population outbreak: Number of individuals in a population explodes at certain times, e.g Mnemiopsis.
Often occurs in insects.

Question 16

What causes population fluctuations?

Answer 16

1. Carrying capacity (K) can fluctuate over time (maximum population size that can be supported indefinitely by the environment). - adjust or fluctuation of carrying capacity
2. Population cycles - relative constant changes in size through time
   Internal factors, such as hormonal or behavioral changes in response to crowding.
   External factors, such as climate, food supplies, predators - predator prey cycles
   Factors that drive population cycles may vary with location and species
3. Delays in density effects on population size: delayed meaning predator prey interactions - boom in prey and delayed boom in predator - more predators than less prey at higher levels so constant cycles, Also caused by how much food available at a given time
   Delayed density dependence caused the adult population to fluctuate; the negative effects of high adult densities were not realized until a later time.
4. Environmental variation
   stochasticity = unpredictable changes in the environment. When a factor is unpredictable, it is described as stochastic.
   Natural catastrophes, such as floods, fires, severe windstorms, can eliminate or greatly reduce populations.
   Often impacts the entire population, density-independent. - doesn’t matter how large or small population is

Question 17

1. Carrying capacity (K) can fluctuate over time

Answer 17

(maximum population size that can be supported indefinitely by the environment). - adjust or fluctuation of carrying capacity

Question 18

2. Population cycles

Answer 18

• relative constant changes in size through time
  Internal factors, such as hormonal or behavioral changes in response to crowding.
  External factors, such as climate, food supplies, predators - predator prey cycles
  Factors that drive population cycles may vary with location and species

Question 19

3. Delays in density effects on population size:

Answer 19

delayed meaning predator prey interactions - boom in prey and delayed boom in predator - more predators than less prey at higher levels so constant cycles, Also caused by how much food available at a given time
Delayed density dependence caused the adult population to fluctuate; the negative effects of high adult densities were not realized until a later time.

Question 20

4. Environmental variation

Answer 20

stochasticity = unpredictable changes in the environment. When a factor is unpredictable, it is described as stochastic.
Natural catastrophes, such as floods, fires, severe windstorms, can eliminate or greatly reduce populations.
Often impacts the entire population, density-independent. - doesn’t matter how large or small population is

Question 21

Population extinction

Answer 21

Fluctuations in population size can increase risk of extinction. Small populations are at greatest risk.
A population that fluctuates in size grows slower than one that does not vary.
When variable environmental conditions result in large fluctuations in growth rate, the risk of extinction increases.
Effective population size: Number of individuals that can contribute offspring to the next generation.
Reduction of effective population size can result in an extinction vortex: Small population size leads to further declines in population size, eventually resulting in extinction.

Question 22

Population extinction
Vulnerable to the effects of genetic drift(random chance):

Answer 22

1. Loss of genetic variability.
2. Genetic drift can cause harmful alleles to occur at high frequencies.
3. Small populations show a high frequency of inbreeding (mating between related individuals).

Question 23

Demographic stochasticity:

Answer 23

Chance events affect survival and reproduction of individuals.
Example: In a population of ten individuals, a storm wipes out six. The 40% survival rate may be much lower than the average rate for that species

Question 24

Allee effects:

Answer 24

Allee effects: Growth rate decreases as population density decreases.
At low densities, individuals may have difficulty finding mates.
Allee effects can cause the population growth rate to drop, which causes population size to decrease even further in a downward spiral toward extinction.