2-24 - 2-27, problems of small populations

Question 1

Problems of Small Populations

Answer 1

Habitat destruction usually leads to fragmentation into many smaller units  smaller population sizes
So what happens to such populations?
* Natural variation in population size 
small population more vulnerable
due to ”random” fluctuations
Not just total population, but number of breeding individuals, and sex ratio
e.g. Northern White Rhinoceros: only 2 females left
(But not my colony of the African tick Argas brumpti: 4 females left, all males died, but after 4 years laid
eggs!)

Question 2

Heath Hen = eastern race of the Prairie Chicken

Answer 2

Greater vulnerability to climatic events  local extirpation
Open grasslands and scrub (“heaths”) – often fire-
maintained
PreColumbian Native Americans maintained some
open places for hunting – widespread in Northeast
Eventually restricted to one population on Martha’s ,
Vineyard (large island off southeast coast of MA)
Enough space but small population + bad winters
+ fire  extinction in 1932

Question 3

Miami Blue Butterfly

Answer 3

Race in Florida Keys extirpated by hurricane in
1992. Thought to be last population, but rediscovered on mainland in 1999. Close call.

Question 4

Allee effect

Answer 4

population of social species so low that individuals have a hard time finding mates, foraging, or defending themselves
reproduction and survival decline as population size decreases. Might think
relaxation of competition would counteract and may in some cases.

Question 5

reasons for the allee effect

Answer 5

1. Hard to locate mates
2. Success depends on group cooperation
3. Plants that pollinators cannot find if sparse

Question 6

species examples that show the Allee effect

Answer 6

North Atlantic Right Whale (Hard to locate mates)
Bachman’s Warbler (Hard to locate mates)
wolf packs (Success depends on group cooperation)
red hot poker (Plants that pollinators cannot find if sparse)

Question 7

Duffy experiment

Answer 7

Red Hot Poker plants pollinated by
birds and insects
Differently sized plots of flowers
Caged some flowers adjacent to
uncaged ones to exclude birds but
allow insects
Significant decrease in seed set of
uncaged flowers, presumably due to
failure of birds to locate plants in the
smaller populations  Allee effect
Apparently insect pollinators find
flowers at all plant population levels,
so don’t demonstrate Allee effect.
But provide a good control.

Question 8

Genetic vulnerability

Answer 8

inbreeding, lack of heterozygosity
Emergence of recessive lethal or maladaptive alleles in homozygotes
Can happen due to inbreeding or genetic drift
E.g. Florida pumas

Question 9

Florida Panther population

Answer 9

Hunting decimated the population badly
During the 1970s, only about 20-30 Florida panthers remained in the wild

Question 10

ideal population postulate according to conservationists, aka effective population size

Answer 10

number of individuals is
constant, all are breeders, and sex ratio is equal

Question 11

Heterozygote advantage

Answer 11

different alleles = more ways to confront environmental challenges

Question 12

n sub e is equal to the actual n only if…

Answer 12

sexes are equal in number and all breed, and the population is constant in size

Question 13

effective population size

Answer 13

n sub e

Question 14

if sex ratio is unequal…

Answer 14

lower heterozygosity and therefore n sub e is lower

Question 15

example of a lower n sub e

Answer 15

99 females and 1 male –> n sub e = 3.96 (not 100)

Question 16

if population levels fluctuate, they can go through a….

Answer 16

population bottleneck (n sub e is lower than actual n)

Question 17

How does sex ratio affect effective population size? (formula)

Answer 17

Ne = (4NmNf) / (Nm + Nf)
N(f) = # of females
N(m) = # of males

Question 18

Elephant Seals

Answer 18

One bull typically has a harem of 40 females
and gets almost all of the copulations
That would give Ne = &laquo_space;N
But turns out that bulls don’t usually maintain
their dominance for more than one season,
so average sex ratio is about 5 females: 1 male

Question 19

Extinction Vortex

Answer 19

Positive feedback cycle in a negative direction

Question 20

Hardy Weinberg formula

Answer 20

(A1 + A2)^2 = A1A1 + 2A1A2 + A2A2

Question 21

inbreeding coefficient

Answer 21

F = (H(expected) – H(observed)) / H(expected)

Question 22

Sampling by transects or quadrats importance

Answer 22

important to get a random sample,
and also to get a sufficient number

Question 23

Mark-recapture technique formula and problems

Answer 23

If population is mixed completely:
Marked1/Unknown = Marked2/All caught2
Problems: poor mixing, territories, heterogeneous environment