Population Cycles

Question 1

define group selection?

Answer 1

operates between groups of organisms rather than between individuals
–> adaptation that benefit the group rather than individual

Question 2

“suicidal lemmings” is an example of what?

Answer 2

group selection

Question 3

lemmings are considered ______ herbivores in tundra areas

why?

Answer 3

keystone

consume more vegetation than caribou or muskoxen.
primary prey for many Arctic predators
Active summer & winter & breed year round

Question 4

Describe what factors allow lemmings to be so reproductively efficient

Answer 4

high reproductive capacity (4-6 young per litter)
gestation 3 weeks, weaned at 3 weeks mature at 4 weeks
generation time is 7 weeks!
Breed all year

Question 5

list species that show long-term fluctuations

Answer 5

lynx
arctic fox
snowshoe hare
muskrat
mink

Question 6

What two species are considered keystone herbivores?

Answer 6

snowshoe hare

lemming

Question 7

snowshoe hares represent __ % of vertebrate biomass and __% of the average energy flow in boreal forest of SW Yukon

how does this compare to moose and bears?

Answer 7

48% vertebrate biomass
41% avg energy flow

M/B = 13.6% biomass
2.6% energy flow

Question 8

what % of tested pop are cyclic? What type of animals were these mainly?

Answer 8

~30%

mainly mammal and fish

Question 9

T/F The incidence of cycles increases with latitude.

All animals?

Answer 9

Y but only in mammals

Question 10

Is there a latitudinal gradient in cycle periods?

Answer 10

nope

Question 11

why are cyclic patterns mores a northern phenomenon in mammals/

Answer 11

fgreater dependancy on select prey mammals

Specialized to be able to survive within the arctic and smaller organisms are not

Question 12

Why incidence of cycles increase with latitude only in mammals?

Answer 12

fish, birds and insects can migrate

Question 13

define population cycle

Answer 13

a pattern of periodic fluctuations in population size with rather constant period
*not seasonal - but regular, multi-annual cycles! Predictable

Question 14

List the 5 features of population cycles

Answer 14

periodic
regular
large amplitude
northern distribution 
synchronous

Question 15

define delayed density dependence

Answer 15

time lag until negative feedback mechanisms bring the pop back down

Question 16

T/F reproductive rate is highest at peak densities

Answer 16

F

lowest @ peak

Question 17

T/F most aggressive at peak

Answer 17

T

Question 18

T/F animals largest during peak phase

Answer 18

T

Question 19

What is an intrinsic and extrinsic hypothesis?

Answer 19

I - assume pop are self-regulated

E- biotic or abiotic influences

Question 20

What are the 5 main hypotheses? Are they intrinsic or extrinsic?

Answer 20

Density-dependent selection (Chitty) I
Social stress E
Abiotic E
Veg-herb interactions E
Pred/Prey interactions E

Question 21

what is the Chitty hypotheses?

Answer 21

selection favours different genotypes at different densities
–> behavioural and genetic factors

Question 22

general geographic distribution of specialists and generalists

Answer 22

specialist - north

generalists - south

Question 23

are generalists or specialists driving cycles?

Answer 23

specialists

Question 24

what is a functional response

how many are there?

Answer 24

relationship between food and consumption

3

Question 25

functional response is a specialist?

Answer 25

type 2

efficient even at low prey densities

Question 26

functional response in a generalist?

Answer 26

type 3

may switch to alternative source

Question 27

why cycles in the N?

Answer 27

simple food web - specialist predators tightly coupled to prey
long winters - food supply not replenished
delayed density dependence is stronger in long winter

Question 28

T/F lemming populations are increasing in Arctic

why?

Answer 28

F
need deep snow for insulation and protection
seeing lower reproduction and higher juvenile mortality
–> exposed to predators earlier in summer

Question 29

2 hyp for whats driving the lynx - hare cycle

Answer 29

hares used up food when pop densities are high –> starve –> decline in lynx population
(bottom up)

lynx reach high density in response to increase in hare density. high density, eat all hares –> hares crash
(top-down)

Question 30

Which hyp for lynx-hare cycle is a trophic cascade

Answer 30

bottom up regulation

hyp 1

Question 31

why hyp is correct?

Answer 31

hare pop are limited by both food and predation!! not exclusive!

Question 32

effects of predators on prey may one of which two mechanisms?

Answer 32

density-mediated (pred reduce prey)

trait-mediated (pred affect prey phenotype
–> N.A. favours certain trails

Question 33

list 2 non-consumptive predator effects

Answer 33

1. altered foraging patters (behaviour)

2. chronic stress under risk of predation (physiology)

Question 34

ecological communities are increasingly occupied by _____

Answer 34

generalists

Question 35

T/F lynx are not facultative specialists

Answer 35

F