Struggle for Existence pt. 6

Question 1

How are age differences treated in age structured populations?

Answer 1

Population is divided into a convenient number of different age classes, each of which has different, AGE SPECIFIC, prospects of death and reproduction.

Question 2

Age structured models only account for….

Answer 2

females, as they are the only propulsive force of a population

Question 3

First age class is denoted by subscript…

Answer 3

0

• N_0 = # newborns
• N_1 = # of one year olds

Question 4

age structure of a population

Answer 4

set of N_x values for a population

Question 5

Ix

Answer 5

survivorship at age x (probability that an individual is still alive at age x), thus values range from 0 to 1.

Question 6

What is the Ix value for the last age class in a life table?

Answer 6

0

Question 7

senescence

Answer 7

generalized breakdown of organisms

Question 8

Hypothetically, what does it mean if the probability of dying is constant across all ages? What does the graph look like?

Answer 8

External sources cause death rather than intrinsic biological characteristics. The graph would mimic exponential decay.

Question 9

Type I Survivorship

Answer 9

convex curve; low early mortality

Question 10

Type II Survivorship

Answer 10

Exponential decay but on a logarithmic scale, a linear downwards slope.

Question 11

Type III Survivorship

Answer 11

Concave curve; a lot of early death.

Question 12

bx

Answer 12

average number of daughters produced by a female in her xth year of life

Question 13

Why is b0 typically 0?

Answer 13

Newborns need to pass through a period of resource acquisition and growth after birth before they are capable of reproducing themselves.

Question 14

First age of reproduction

Answer 14

waiting period before reproduction can begin

Question 15

Why are age-structured models are not density dependent?

Answer 15

Because fecundity and survivorship are both treated as constants.

Question 16

Why do we need to consider survivorship when calculating how many daughters a female will have?

Answer 16

Fecundity and survivorship interact. A female will have more daughters the longer she lives but the older she is the less likely it is that she will be alive. You must down-weight the extra births with the lesser probability of being alive at x age.

Question 17

net reproductive rate/replacement rate

Answer 17

sum of ( survivorship probability x the average number of births) for all age classes.
Ro = ∑Ixbx
(still a step function)

Question 18

How are Ro and lamda different?

Answer 18

Their time scale. Lamda is the amount of growth that occurs over one unit of time (like a year) while Ro is the amount of growth that occurs over one generation

Question 19

How is generation time calculated?

Answer 19

T = ∑x Ixbx/ Ro

- sum of age multiplied by Ro all over Ro

Question 20

Stable age distribution

Answer 20

proportion of the population in each class stabilizes. Value of lamda also stabilizes.

Question 21

Examples of life history characteristics

Answer 21

lifespan, first age of reproduction, number and timing of offspring

Question 22

Constraints and tradeoffs

Answer 22

size-number tradeoff
- many small offspring/seeds or few large offspring/seed

early vs late reproduction
- organisms that reproduce earlier do not have as long a period as resource accumulation

cost of reproduction

• offspring require energy and nutrients
• parental care

Question 23

reproductive value

Answer 23

expected number of daughters to be produced by a female of age x, now and for the rest of her lifetime (all previous births do not matter). Denoted by Vx

Question 24

Why is the graph of reproductive value often bell curve shaped?

Answer 24

Newborn must go through resource acquisition stage before she can begin reproducing and she encounters some risk of dying during that period.

Question 25

What do you expect in a species that forms lasting pair bonds?

Answer 25

strong selection for males to prefer female mates with high reproductive values. Produces tendency for traits associated with the onset of reproductive age to become associated with sexual attractiveness.

Question 26

semelparity

Answer 26

Big bang reproduction. Accumulate resources for their whole life, reproduce and then die.

Question 27

iteroparity

Answer 27

reproduce numerous times in life

Question 28

What are iteoparous plants called?

Answer 28

usually called perennials

Question 29

What are semelparous plants called?

Answer 29

Monocarpic (making fruit once)

• annuals if they only live one season
• biennials if they grow vegetatively in first year then flower and die in second

Question 30

Monocarpic perennials

Answer 30

plants that live for more than two years before flowering and dying . Resource accumulation stage is long

Question 31

What kind of plants are common in desert conditions?

Answer 31

Annuals are common in deserts because they are small and fast growing. They can grow and flower in the brief, wet season and produce seeds that spend dry season dormant.

• seeds germinate only after heavy rains that leach out germination inhibitors from seed coat
• Don’t really need water conservation strategy because all active growth is during period of non desert conditions.

Question 32

Name classes of plants where annuals are prominent. Why are they prominent?

Answer 32

Plants that take advantage of brief windows of time (milder conditions)

• desert plants
• weeds

annual strategy selected for by humans to maximize seed output (ancestors were likely perennials)
- crop plants: rice, maize, wheat

Question 33

What are weeds adapted for?

Answer 33

Growing in transient habitats that have been disturbed (either by animals burrowing or human activity like agriculture). Soil disturbance allows a brief period for small annual plants to occupy an uncrowded bare site before taller perennials outcompete them.
- seeds germinate when struck by sunlight

Question 34

What’s another name for weeds?

Answer 34

Fugitive species

Question 35

Characteristic of desert annuals and weeds?

Answer 35

Have long lasting seed banks in the ground. Large proportion of the population is underground at any one time.

Question 36

Century plants

Answer 36

ex. agaves

grow for decades without flowering

Question 37

Why do plants bloom in synch?

Answer 37

Might use same cues to induce flowering. Would suck if you bloomed before everyone else and there were no pollinators.

Question 38

Examples of synchronized blooming/growth

Answer 38

• Frasera speciosa (monument plant)

- some bamboos

Question 39

Why synchronicity?

Answer 39

• predator satiation

- ability to attract pollination as a whole group is greater

Question 40

mast crops

Answer 40

synchronization of seed production in regular iteroparous perennials (nut-bearing trees like oaks) (predator satiation)

Question 41

Semelparous animals

Answer 41

• salmon

- antechinus

Question 42

R-strategist/ R selected species

Answer 42

• high fecundity
• poor competitors
• low survival
• short generation times
• small but numerous seeds
• good dispersal ability

ex. fugitive annual weeds
These adaptations are good in low-density situations

Question 43

K-strategist

Answer 43

• low fecundity
• good competitors
• high survival rate
• longer generations (slower growing)
• few, large seeds
• poor dispersal ability

These adaptations are good in high-density, competitive situations (carrying capacity)

Question 44

J.P. Grime

Answer 44

advocated for three categories “CSR trichotomy”

• competitive species (slow k strategists)
• stress tolerators (grow in hostile environments that remain uncrowded)
• Ruderal species (fugitive weedy species)

Question 45

Deterministic models

Answer 45

parameters that determine births and deaths are constants (determined by starting conditions)

Question 46

What are stochastic models and why have they replaced deterministic models?

Answer 46

Accounts for random variation in parameters in Nx, bx, and Ix that could result in chance extinction (other than just relying on average values).