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BIOL 370 > Problems with small populations (class 15) > Flashcards

Problems with small populations (class 15) Flashcards

1
Q

“No population lasts forever”- Name 3 reasons why every population eventually goes extinct.

A
  • changing climate
  • succession
  • disease
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2
Q

What is conservation biology concerned with in this section?

A

Whether populations go extinct sooner rather than later, and whether other populations of the same species will continue elsewhere

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3
Q

What is “the key to conserving species”?

A

Protecting populations, as endangered species often consist of a few populations

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4
Q

What is the ideal goal of a conservation plan?

A
  • to protect as many individuals as possible within the greatest possible area of high-quality protected habitat
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5
Q

What does MVP stand for?

A

Minimum viable population

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6
Q

What is MVP?

A

The number of individuals necessary to ensure the long-term survival of a species (through both average and harsh years)

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7
Q

Numerically, how is MVP defined?

A

The smallest isolated population having a 99% chance of remaining extant (surviving) for 1000 years despite the foreseeable effects changes/catastrophies

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8
Q

For vertebrates, what does the MVP value average around?

A

between 3000-5000 individuals

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9
Q

A greater length of persistence requires what?

A

Greater population size

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10
Q

Graph about bighorn sheep- survival time vs initial population size. What is the number of individuals that last 50 years?

A

Populations with more than 100 individuals lasted about 50 years.
Populations with less than 50 animals often went extinct within 50 years

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11
Q

Channel island bird populations- How many breeding pairs were needs for a 90% chance of surviving 80 years?

A

Over 100 breeding pairs needed for 90% chance of survival for 80 years

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12
Q

What is MDA?

A

Minimum dynamic area. The area of suitable habitat necessary for maintaining the minimum viable population

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13
Q

How can MDA be estimated?

A

can be estimated by studying the home range size of individuals and colonies of endangered species

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14
Q

What is the MDA or small mammals vs large carnivores?

A

100-1000 km2 for small mammals.

10,000 km2 needed for large carnivores

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15
Q

Why does genetic variability occur?

A

Occurs as a result of individuals having different alleles (dif. forms of same gene)

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16
Q

What does a population’s genetic variability affect?

A

It affects the population’s ability to adapt to a changing environment

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17
Q

Population declines in small populations result in what?

A

Lower genetic diversity

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18
Q

True or false:

species with low genetic diversity have small populations

A

FALSE. Species with low genetic diversity do not necessarily have small populations

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19
Q

In small populations, why might allele frequencies change significantly in one generation?

A

CHANCE! Based on which individuals survive to sexual maturity and mate

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20
Q

The random process of allele frequency change is called…?

A

Genetic drift

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21
Q

What is the risk of an allele that occurs at a low frequency in a population?

A

That it has a significant chance of being lost in each generation

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22
Q

What does maintenance of genetic diversity depend on?

A

The effective population size

(Ne)= the number of breeding individuals in a population

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23
Q

What does this equation show: H= 1-1/ (2Ne) ?

A

The proportion of original heterozygosity remaining after each generation (H), with (Ne) being effective pop size

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24
Q

What 2 processes increase genetic variability of a population?

A

1) regular mutation of genes

2) migration of even a few individuals from distant populations

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25
Q

What is an average mutation rate?

A

Between 1/10,000 and 1/one million

26
Q

Is mutation enough to counterbalance effects of drift in populations of less than 100 individuals?

A

No

27
Q

What is the percentage of mutation rate per gene per generation to counteract effects of drift?

A

1% per gene per generation

28
Q

Is migration or mutation better at counteracting drift?

A

Migration, even low frequency of migration among populations helps. Migration of 1-2 individuals per gen. in pop of 100 can minimize loss of genetic diversity

29
Q

What number of migrants in a generation with pop of 100 fully negates the effects of drift?

A

4-10 migrants (high migration is good)

30
Q

Rare and endangered species often have _____ _____ populations

A

Small and isolated

31
Q

Give an example of a rare species in Australia with little genetic variation

A

Wollemi pine, species consists of 40 plants in 2 nearby populations, lacks genetic variation completely

32
Q

How big should a population be? What’s a rule to show this?

A

50/500 rule. 50 reproductive individuals needed to avoid short-term inbreeding depression. 500 needed to generate adequate mutation to balance loss of alleles through drift

33
Q

What is the 50/500 rule best used for?

A

Urgent conservation efforts. Larger population numbers needed for long-term health of populations and species

34
Q

What are the 3 consequences of reduced genetic variability?

A

1) inbreeding depression
2) outbreeding depression
3) loss of evolutionary flexibility

35
Q

What is inbreeding depression?

A

condition that occurs when an individual recieves identical copies of a defective allele from both parents.

36
Q

What is inbreeding depression characterized by?

A

Higher mortality of offspring, fewer offspring, or offspring that are weak, sterile, or have low mating success

37
Q

What populations are prone to inbreeding?

A

Small captive populations in zoos, or small isolated populations in the wild

38
Q

In a study of 51 bird species, what is the consequence of small population sizes?

A

Hatching failure due to inbreeding depression in the wild

39
Q

What is outbreeding depression?

A

When an individual mates with an individual of a different related species. (can also happen from mating between dif subspecies or divergent populations of the same species)

40
Q

What can outbreeding depression result in?

A

Weakness, sterility, or lack of adaptability to the environment

41
Q

Give an example of outbreeding.

A

horse and donkey = sterile mule

- could also be captive bred individuals with wild individuals (weaken the gene pool)

42
Q

What have studies found about outbreeding depression?

A

Many studies have failed to demonstrate it

43
Q

What is hybrid vigor? (related to outbreeding)

A

Often, many hybrid individuals are more vigorous than their parents

44
Q

Explain the loss of evolutionary flexibility

A

loss of genetic variability limits ability to respond to new conditions and long-term changes in the environment

45
Q

rare alleles and unusual combos of alleles that are harmless may turn out to be what…?

A

They may be uniquely suited for a future set of environmental conditions, and give an advantage later to the individuals that have them

46
Q

What are 3 ways an environment could change that a unique allele could be an advantage?

A

pollution, climate change, new diseases

47
Q

What are the 4 factors that determine effective population size?

A

1) unequal sex ratio
2) variation in reproductive output
3) population fluctuations and bottlenecks
4) managing for genetic variation

48
Q

What is effective population size?

A

Mature individuals that can mate

- it is lower than total pop. size b/c many individuals do not mate

49
Q

Effective pop size-

Describe unequal sex ratio.

A

As the sex ratio of breeding individuals becomes less equal, Ne goes down.

Can also occur when a few individuals of one sex make up a disproportionate amount of genetic material in the next gen (elephant seals- one dominant male)

50
Q

What is the problem with climate change for the sex ratio?

A

Climate change skews the sex ratio of species with temperature dependent sex-determination (ex. fish)

51
Q

Effective pop. size-

Describe variation in reproductive output

A

Occurs in species where a number of offspring varies substantially among individuals. Ex. large plants produce more seeds than small plants

52
Q

Effective pop. size-

Describe population fluctuation and bottlenecks

A

Ne is largely determined by years in which the population has the smallest number of breeding individuals

53
Q

Effective pop size-

define population bottleneck

A

Occurs when a population is greatly reduced in size and loses rare alleles if no individuals possessing those alleles survive and reproduce

54
Q

Effective pop size-

Define founder effect

A

special type of bottleneck that occurs when a few individuals leave one population to establish a new one.
New pop has less genetic variabiliy

55
Q

Give one example of a bottleneck population

A

Ngorongoro Crater lions were reduced from 9 females and 1 male at one point

56
Q

Name a less prevalent factor that affects the persistence of small populations

A
  • stochasticty (random variation)

- can be environmental or demographic (variation of birth and death rates among years)

57
Q

Define the allee effect

A

The interaction between population size, density, growth rate, and behaviour.

58
Q

Why are many small populations demographically unstable? And give an example.

A

because social interactions can be disrupted once population density falls below a certain level (ex. Bears live in widely dispersed pop and can have a hard time finding a mate if density is too low)

59
Q

What is an extinction vortex?

A

tendency of a small population to spiral towards extinction

60
Q

What are the factors that can cause an extinction vortex?

A

The smaller a population becomes, the more vulnerable it is to further demographic variation, environmental variation, and genetic factors that tend to lower reproduction

61
Q

To what extent does each factor of an extinction vortex increase vulnerability?

A

Each factor increases vulnerability to the other 2, they build on each other

62
Q

How can extinction vortices be handled?

A

Only addressing the original cause of pop. decline may not be enough to recover the pop.. Need to do more than this.

BIOL 370 (9 decks)

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