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Ecology > Ch. 11 Population Dynamics > Flashcards

Ch. 11 Population Dynamics Flashcards

1
Q

Eutrophication

A

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

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2
Q

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

A

Birth, death, immigration, and emigration

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3
Q

Population dynamics

A

The ways in which populations change in abundance over time

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4
Q

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

A
  • exponential growth
  • logistic growth
  • fluctuations
  • regular cycles
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5
Q

Exponential growth usually happens when..

A
  • when conditions are favorable

- when a species reaches a new geographic area

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6
Q

Logistic curve

A
  • some populations reach a stable size that changes little over time
  • fluctuate by a small amount around what appears to be carrying capacity
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7
Q

Logistic equation

K

A
  • assumed to be constant

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

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8
Q

Logistic growth example

A
  • when sheep were first introduced to Tasmania, the population increased rapidly
  • later, population numbers fluctuated above and below a maximum sustainable population size
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9
Q

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

A

Carrying capacity to fluctuate

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10
Q

Carrying capacity

A

An equilibrium with their environmental resources

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11
Q

Logistic growth

Near exponential growth when..

A

Resources are unlimited

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12
Q

Environmental resistance

A

Growth slows as species approaches carrying capacity of environment

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13
Q

___ factors reduce population growth rates.

A

Density-dependent

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14
Q

Density-dependent factor examples

A
  • predation
  • food abundance
  • parasite load
  • intraspecific competition
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15
Q

Population fluctuation

A

Rise and fall in population size over time

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16
Q

Population outbreak (bloom)

A

Populations may explode, causing a bloom

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17
Q

Population cycles

A

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

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18
Q

Internal factors that may drive population cycles in rodents:

A

Hormonal or behavioral changes in response to crowding

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19
Q

External factors that may drive population cycles in rodents:

A

Weather, food supplies, or predators

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20
Q

Example of top-down regulation in lemmings

A

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

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21
Q

Example of bottom-up regulation in lemmings

A

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

These cycles were driven by food supply

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22
Q

Effects of population density often have a ___ or delay.

A

Lag time

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23
Q

What may this lag be due to?

A

Need time to reproduce

24
Q

Delayed density dependence

A
  • delays in effect that density has on population size
25
Q

Example of delayed density dependence

A

When a predator reproduces more slowly than its prey

26
Q

__ can cause fluctuations in population size.

A

Time lags

27
Q

Stable limit cycle

A

Pattern when the population fluctuates indefinitely about the carrying capacity

28
Q

Many factors can drive populations to extinction:

A
  • predictable factors
  • fluctuation in population growth rate and population size
  • chance events
29
Q

If you fluctuate to zero ->

A

Extinction

30
Q

Fluctuations increase risk of ___.

A

Extinction

31
Q

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

A

Large fluctuations

32
Q

___ populations are at greatest risk.

A

Small

33
Q

Implications for natural populations:

A

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

34
Q

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

A

Chance

35
Q

Genetic drift

A
  • 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
36
Q

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

A

Drift

37
Q

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

A
  • 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
38
Q

___ tends to increase the frequency of homozygotes.

A

Inbreeding

39
Q

Demographic stochasticity

A

“Chance” events related to survival and reproduction of individuals

40
Q

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

A

Probability

41
Q

Allee effects

A

Population growth rate decreases as population density decreases

  • individuals have difficulty finding mates or are less stimulated to breed at low population densities
42
Q

Environmental stochasticity

A

Unpredictable changes in environment that can cause extinction of small populations

43
Q

Environmental stochasticity example

A

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

44
Q

Demographic stochasticity vs. environmental stochasticity

A

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

45
Q

Natural catastrophes

A

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

46
Q

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

A

Spatially isolated

47
Q

Metapopulations

A

Set of spatially isolated populations linked by dispersal of individuals or gametes

Characterized by repeated extinctions and colonizations of small individual populations

48
Q

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

A
  • landscapes they live in are patchy

- environmental conditions often change in a rapid and unpredictable manner

49
Q

Sinks

A

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

50
Q

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

A

Less than 1

51
Q

Habitat fragmentation

A

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

52
Q

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

A

Decreases; increases

53
Q

Isolation by distance

A

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

54
Q

Patch area effect

A
  • large patches tend to have larger population sizes

- small patches may be harder to find, and have higher extinction rates

55
Q

Rescue effect

A

High rates of immigration that protects a population from extinction

56
Q

Black Sea

Bottom-up control

A
  • 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
57
Q

Black Sea

Top-down control

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

Ecology (12 decks)

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