Lecture 3 Flashcards
Describe a Life History Model
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
How does the old Life History Model differ from the new one?
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
Describe the history of the r and K selection model. Who proposed it? When? On what ideas/postulates was it based
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
What is the logistic model equation? What are the different components? dD/dt=rN (K-N/K)
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
In the r and K model, natural selection is thought to act on which parts of the equation at low population density?
R would be acted on becasue the population is small
In the r and K model, natural selection is thought to act on which parts at a high population density?
The rate of growth would be effected
Describe a “K strategy” and the environment in which each is expected to be found.
Mainly stays arround carrying capacity. These species tend to take care of their young
Describe an “r strategy” and the environment in which each is expected to be found
This strategy is associated with organisms that have a high reproductive rate, but provide little or no parental care to their offspring
- unstable environments
What are the problems with the r and K model?
- 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
Who proposed the CSR model?
Rick Grimes
The CSR model was related and built from the R and K model, How do they relate?
K-Selected = Competitors
R-Selected = Ruderals
He proposed Stress-Tolerators
Describe CSR competitive apex
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
Describe CSR Ruderal apex
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
Describe CSR Stress-Tolerators Apex
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
What are the problems with Grime’s triangle model? Why is it not used by contemporary ecologists?
- Predictions are qualitative and relative
- Difficult to test with the scientific method
- Model categories apply only to some species/traits but not others.
Describe the reproductive value model
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
Define Reproductive Effort
The amount of resources put towards reproduction at any age is the reproductive effort at that age
What are the problems of the reproductive value model?
- 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
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?
Bottom-up model that looks for patterns in data. Previous top down models started with principles the predicted traits
What are the strengths and challenges of a meta-analysis approach to describing life history?
- 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
Define Bet-Hedging, how does it improve fitness?
Equalizing fitness across time, maintaining reduced fitness in favorable years to avoid having low fitness in poor years
Define Seed Bank
Group of dormant seeds stored in the soil
Define Recruitment
Germination of seeds to become actively growing members of the population
Explain the pros and cons of seed dormancy from an evolutionary fitness perspective.
- Buffering populations from environmental stochasticity
- Seed dormancy would be opposed if there was no environmental variation
- Only germinated plants can reproduce
