Biology Lecture 18
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How do strong climates effect population growth models?
It causes them to jump around
What does the logistic model of poppulations assume?
- 1. Birth/death and density affect growth
- 2. All individuals genetically the same
- 3. All individuals equal in terms of birth and death - age doesn't matter
This is not realistic
Age structure alters population growth (How is this shown)
Age pyramids show the age structure they sumarize the population growth rates.
What is a disadvantage of an age pyramid?
They can not be used for calculations you have to use a life table for that
What do life tables summarize? and what type of life tables are they?
- Mortality and survival rates = static life table
- Survival and fecundity = cohort life table
What is included in a static life table?
Construced by a snapshot of the whole population across different generations
What is included in a chohort life table?
Constructed by looking at one generation through all times - can only be done for a small population
Static life tables curves show?
- Survivorship with age
- There are 3 different types.
What are disadvantages of static life tables?
They don't show if population is increasing because you don't know the reproductin rate.
What is N1 in a cohort life table equation?
the initial population
What is Lx in a cohort life table equation?
What is x in a cohort life table?
Age of the population
What is Mx in a Cohort Life table?
Done out in the field - number of average seeds or eggs - seed per individual
What is LxMx in a cohort life table?
survivorship corrective fecundity
What is Ro in a Cohort Life table and how do you find it?
The average number of offspring per individual, you multiply Lx and Mx
How do you interperet Ro?
Ro > 1
Ro = 1
Ro < 1
This is wheter a female is replacing herself or not
- 1. population is increasing
- 2. population is steady
- 3. population is decreasing
What do populations generally do relating to survival and reproduction? What happens if they do not follow the norm?
- produce about 1 offspring per individual in the population
- If less than 1 the population will go extinct
- If more than 1 the population there will be uncontrolled growth
How does reproduction and death balance out? (2 ways)
- High egg production low survivorship
- Low reproduction high survivorship
What does semelparous mean?
One big bang reproduction
What does Iteroparous mean?
What are is the best strategy for reproduction why doesn't this happen?
- Long lived, multiple reproductions, many offspring per episode, high survival of offspring (high investment / parental care), early age of first reproduction.
- if one trait is maximized another suffers there are tradeoffs
what is the tradeoff between mortality and fecundity?
As fecundity rises so does mortality they are positively correlated.
What are elements of R - selected environments?
- Fast growing
- Small, numerous seeds
- Single reproduction
- Short-life span
- Good dispersers
- Poor competitors
- Disturbed habitats
What are elements of a K - selected environments?
- Slow growing
- Few, large seeds
- Long-live span
- Poor dispersers
- Good competitors
- Stable, old habitats
How did the human population grow?
Steadily till the industrial revolution then it started to grow exponentially
When is Death > Birth?
When the population growth goes down
What is different about human population?
- Individual natural selection
- Human population growth is often affected by unpredictable factors
- Political, ethical, religious, sociological, economic issues are important
Why did industrialized countries growth rate slow?
Declined due to women entering professions, delaying reproduction, having fewer children.
Problems with human growth rate are?
- Disagreement on K, the carrying capacity
- Most economies growth oriented, and depend on expanding population ( especially care of elderly )
- Population size also depends on immigration/emigration
- Limits on population size - has many negative connotations
- There is no easy answer
Whats the norm for understanding human population growth?
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