Ch. 11 Population Dynamics

Question 1

Eutrophication

Answer 1

Excessive richness of nutrients in a lake or other body of water

Question 2

Populations can change in size as a result of four processes:

Answer 2

Birth, death, immigration, and emigration

Question 3

Population dynamics

Answer 3

The ways in which populations change in abundance over time

Question 4

Populations exhibit a wide range of growth patterns, including..

Answer 4

• exponential growth
• logistic growth
• fluctuations
• regular cycles

Question 5

Exponential growth usually happens when..

Answer 5

• when conditions are favorable

- when a species reaches a new geographic area

Question 6

Logistic curve

Answer 6

• some populations reach a stable size that changes little over time
• fluctuate by a small amount around what appears to be carrying capacity

Question 7

Logistic equation

K

Answer 7

• assumed to be constant

- the population size for which birth and death rates are equal

Question 8

Logistic growth example

Answer 8

• when sheep were first introduced to Tasmania, the population increased rapidly
• later, population numbers fluctuated above and below a maximum sustainable population size

Question 9

Birth and death rates vary over time, thus we expect..

Answer 9

Carrying capacity to fluctuate

Question 10

Carrying capacity

Answer 10

An equilibrium with their environmental resources

Question 11

Logistic growth

Near exponential growth when..

Answer 11

Resources are unlimited

Question 12

Environmental resistance

Answer 12

Growth slows as species approaches carrying capacity of environment

Question 13

___ factors reduce population growth rates.

Answer 13

Density-dependent

Question 14

Density-dependent factor examples

Answer 14

• predation
• food abundance
• parasite load
• intraspecific competition

Question 15

Population fluctuation

Answer 15

Rise and fall in population size over time

Question 16

Population outbreak (bloom)

Answer 16

Populations may explode, causing a bloom

Question 17

Population cycles

Answer 17

Some populations have alternating periods of high and low abundance at regular interval

Question 18

Internal factors that may drive population cycles in rodents:

Answer 18

Hormonal or behavioral changes in response to crowding

Question 19

External factors that may drive population cycles in rodents:

Answer 19

Weather, food supplies, or predators

Question 20

Example of top-down regulation in lemmings

Answer 20

Used field observations and mathematical models to argue that their 4-year cycle is driven by predators

Question 21

Example of bottom-up regulation in lemmings

Answer 21

In other studies, predator removal had no effect on population cycles

These cycles were driven by food supply

Question 22

Effects of population density often have a ___ or delay.

Answer 22

Lag time

Question 23

What may this lag be due to?

Answer 23

Need time to reproduce

Question 24

Delayed density dependence

Answer 24

• delays in effect that density has on population size

Question 25

Example of delayed density dependence

Answer 25

When a predator reproduces more slowly than its prey

Question 26

__ can cause fluctuations in population size.

Answer 26

Time lags

Question 27

Stable limit cycle

Answer 27

Pattern when the population fluctuates indefinitely about the carrying capacity

Question 28

Many factors can drive populations to extinction:

Answer 28

- predictable factors - fluctuation in population growth rate and population size - chance events

Question 29

If you fluctuate to zero ->

Answer 29

Extinction

Question 30

Fluctuations increase risk of ___.

Answer 30

Extinction

Question 31

When variable environmental conditions result in ___ in populations growth rate, extinction risk of population increases.

Answer 31

Large fluctuations

Question 32

___ populations are at greatest risk.

Answer 32

Small

Question 33

Implications for natural populations:

Answer 33

The larger the population size, the less likely a population will go extinct due to fluctuations

Question 34

___ events can influence fluctuations in population growth rates over time.

Answer 34

Chance

Question 35

Genetic drift

Answer 35

- chance events influence which alleles are passed on to next generation - allele frequencies can change at random from one generation to next in small populations

Question 36

___ can reduce genetic variation of small populations, but has little effect on large populations.

Answer 36

Drift

Question 37

Small populations are vulnerable to the effects of genetic drift for three reasons:

Answer 37

- reduced genetic variability reduces ability of a population to respond to environmental change - harmful alleles to occur at high frequencies - high frequency of inbreeding -> further reduces genetic variation

Question 38

___ tends to increase the frequency of homozygotes.

Answer 38

Inbreeding

Question 39

Demographic stochasticity

Answer 39

"Chance" events related to survival and reproduction of individuals

Question 40

When population size is large, there is little risk of extinction from demographic stochasticity because of laws of ___.

Answer 40

Probability

Question 41

Allee effects

Answer 41

Population growth rate decreases as population density decreases - individuals have difficulty finding mates or are less stimulated to breed at low population densities

Question 42

Environmental stochasticity

Answer 42

Unpredictable changes in environment that can cause extinction of small populations

Question 43

Environmental stochasticity example

Answer 43

Yellowstone grizzly bear population is at risk of extinction from random environmental variation of the number of females drops to 30-40

Question 44

Demographic stochasticity vs. environmental stochasticity

Answer 44

Demographic stochasticity -> population-level birth and death rates are constant within a given year, but actual fates of individuals differ Environmental stochasticity -> changes in average birth or death rates that occur from year to year because of random changes in environmental conditions Both are more problematic for small populations

Question 45

Natural catastrophes

Answer 45

Floods, fires, severe windstorms, or outbreaks of disease or natural enemies

Question 46

For many species, areas of suitable habitat exist as a series of favorable sites that are ___ from one another.

Answer 46

Spatially isolated

Question 47

Metapopulations

Answer 47

Set of spatially isolated populations linked by dispersal of individuals or gametes Characterized by repeated extinctions and colonizations of small individual populations

Question 48

Populations of some species are prone to extinction for two reasons:

Answer 48

- landscapes they live in are patchy | - environmental conditions often change in a rapid and unpredictable manner

Question 49

Sinks

Answer 49

Populations that receive more immigrants than the number of emigrants they produce

Question 50

For a metapopulation to persist for a long time, the extinction/colonization ratio must be..

Answer 50

Less than 1

Question 51

Habitat fragmentation

Answer 51

Large tracts of habitat are often converted to spatially isolated habitat fragments by human activities

Question 52

As patches get smaller and more isolated, colonization ___ and extinction rate ___.

Answer 52

Decreases; increases

Question 53

Isolation by distance

Answer 53

Patches located far from occupied patches are less likely to be colonized than those near occupied patches

Question 54

Patch area effect

Answer 54

- large patches tend to have larger population sizes | - small patches may be harder to find, and have higher extinction rates

Question 55

Rescue effect

Answer 55

High rates of immigration that protects a population from extinction

Question 56

Black Sea Bottom-up control

Answer 56

- increased nutrients inputs caused eutrophication and increased phytoplankton biomass, decreases oxygen, fish die-offs, etc - prior to nutrient enrichment, phytoplankton were limited by nutrient supply

Question 57

Black Sea Top-down control

Answer 57

- top predators Mnemiopsis and Beroe control abundance of populations - overfishing was also a factor in the Black Sea