Lecture 3

Question 1

Describe a Life History Model

Answer 1

A Mathematical or graphical model that proposes comprehensive theories based on ecological and evolutionary principles by pulling together many observations and data on life history traits

Question 2

How does the old Life History Model differ from the new one?

Answer 2

Older models were more deductive starting with fundamental ecological and evolutionary principles. Newer models rely on an inductive approach using trait databases and computer strategies to find and distill general patterns

Question 3

Describe the history of the r and K selection model. Who proposed it? When? On what ideas/postulates was it based

Answer 3

It was proposed by Robert MacArthur and students in 1960. It relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. Based on demographic and logistic growth equation

Question 4

What is the logistic model equation? What are the different components? dD/dt=rN (K-N/K)

Answer 4

dD/dt=rN (K-N/K)

• dD/dt Change in Population size over change in time
• R intrinsic rate of change of the population/maximum rate of growth
• N is the Population Size
• K is the carrying capacity

Question 5

In the r and K model, natural selection is thought to act on which parts of the equation at low population density?

Answer 5

R would be acted on becasue the population is small

Question 6

In the r and K model, natural selection is thought to act on which parts at a high population density?

Answer 6

The rate of growth would be effected

Question 7

Describe a “K strategy” and the environment in which each is expected to be found.

Answer 7

Mainly stays arround carrying capacity. These species tend to take care of their young

Question 8

Describe an “r strategy” and the environment in which each is expected to be found

Answer 8

This strategy is associated with organisms that have a high reproductive rate, but provide little or no parental care to their offspring
- unstable environments

Question 9

What are the problems with the r and K model?

Answer 9

• May not have a biological/ genetic trade-off between maximizing R and maximizing K
• Model is qualitative; it doesn’t tend to generate testable quantitative predictions.
• Mature habitats are no longer thought to be stable climax communities

Question 10

Who proposed the CSR model?

Answer 10

Rick Grimes

Question 11

The CSR model was related and built from the R and K model, How do they relate?

Answer 11

K-Selected = Competitors
R-Selected = Ruderals
He proposed Stress-Tolerators

Question 12

Describe CSR competitive apex

Answer 12

Perennial Herbs, shrubs, or trees with small seeds and rapid potential growth rate. They are often abundant in leaf litter with a short leaf longevity )from large amounts of resources). They would flower near the time of max productivity. They also had a long lifespan

Question 13

Describe CSR Ruderal apex

Answer 13

Grow as annuals with large seed production and rapid potential growth rate. Not plentiful in leaf litter with a short leaf longevity. Flowers at the end of a favorable period and has a brief period of production at time of maximum productivity. Short lifespan

Question 14

Describe CSR Stress-Tolerators Apex

Answer 14

Lichenous, potential herbs. They have a small seed production and slow potential growth rate. They were little in leaf litter with long leaf longevity )from lack of resources_. There is no flowering pattern. Typically evergreen with a long life span

Question 15

What are the problems with Grime’s triangle model? Why is it not used by contemporary ecologists?

Answer 15

• Predictions are qualitative and relative
• Difficult to test with the scientific method
• Model categories apply only to some species/traits but not others.

Question 16

Describe the reproductive value model

Answer 16

Fitness is maximized when the reproductive effort at each age past maturity, is balanced to maximize present and potential future reproduction, weighted by the reproductive value at each age

Question 17

Define Reproductive Effort

Answer 17

The amount of resources put towards reproduction at any age is the reproductive effort at that age

Question 18

What are the problems of the reproductive value model?

Answer 18

• Difficult to measure reproductive effort. The fraction of resources used for reproduction is unclear due to unknowns in plant development and biochemistry processes.
• Organs serve multiple functions. Classifying them to present of future reproduction is difficult
• Model is based on ratios. Many strategies could have similar results of distribution with sampled at a single time point

Question 19

What is a trait-based meta-analysis? How is this approach fundamentally different from the model approach being used in the 1960 and 70’s?

Answer 19

Bottom-up model that looks for patterns in data. Previous top down models started with principles the predicted traits

Question 20

What are the strengths and challenges of a meta-analysis approach to describing life history?

Answer 20

• Uses large databases for research, allows testing of existing hypotheses and new hypotheses from patterns on the data. Unified theory for life history may go beyond case studies

Question 21

Define Bet-Hedging, how does it improve fitness?

Answer 21

Equalizing fitness across time, maintaining reduced fitness in favorable years to avoid having low fitness in poor years

Question 22

Define Seed Bank

Answer 22

Group of dormant seeds stored in the soil

Question 23

Define Recruitment

Answer 23

Germination of seeds to become actively growing members of the population

Question 24

Explain the pros and cons of seed dormancy from an evolutionary fitness perspective.

Answer 24

• Buffering populations from environmental stochasticity
• Seed dormancy would be opposed if there was no environmental variation
• Only germinated plants can reproduce

Question 25

Describe the three bet hedging strategies used by plants

Answer 25

• Maternal plants hold back resources to even out reproduction across years
• Seeds remain dormant in a seed bank to save recruitment for favorable years
• Disperse widely in hopes a seed finds a good habitat (Dandelions)

Question 26

Why can’t annuals use all three bet-hedging strategies?

Answer 26

They only get one chance to reproduce so they can’t do strategy 1. So they put more effort into strategy 2. They do lots of the 3rd bet hedging

Question 27

Define Seed Pool

Answer 27

Collection of dormant seeds

Question 28

What are the inputs and outputs of the seed pool?

Answer 28

Input: Seed Rain
Output: Seedlings, Decay and senescence, predation

Question 29

Define Seed Rain

Answer 29

All the seeds produced and released from maternal plants in a population

Question 30

Explain how seed pool dynamics can promote plant community diversity within a habitat

Answer 30

Variation in stimuli required to germinate in seedlings helps maintain species diversity in a community.

Question 31

Define Masting. Pros? Cons?

Answer 31

• Masting: Regular periodic large reproductive bouts separated by periods of very low production
• Pros: Maximize Variation
• Cons: Reduce reproductive success and fitness

Question 32

Name two adaptive hypothesis for selection to maintain masting.

Answer 32

Adaptation to granivores and wind pollination

Question 33

Name one non-adaptive hypothesis for selection to maintain masting.

Answer 33

Response to year-to-year environmental stochasticity. (resource numbers are low and it takes a set number of years to prepare for reproduction)

Question 34

Describe the types of biotic and abiotic factors that can affect selection on phenology

Answer 34

• Abiotic: temperature, moisture, light
  = Biotic: Pollinator availability, seed disperser, herbivores

Question 35

Define “coevolution” and describe an example of coevolution with Ranunculus phenology

Answer 35

The reciprocal selective pressure leading to evolution of both species
Ex.) Snowpack affects light availability and temperature stimuli

Question 36

Describe an example of leaf-out phenology

Answer 36

The flowers growing and sprouting before the trees do in a forest

Question 37

Explain two adaptive hypotheses for natural selection for delayed leaf-out

Answer 37

• Trees may have more risk of late from bc being higher up where ground layers are more protected by the trees
• Earlier leaf out phenology and flowering in understory because they get lots of light before leaves grow on the trees.