Question

1) Charles Darwin's argument for natural selection can be presented in a variety of ways. In class we discussed four postulates for natural selection (note: a reasonable statement or assumed truth used in developing mathematical or logical reasoning). Identify and briefly describe the four postulates of natural selection.

2) In many animal societies there is a pattern of limited dispersal where members of a group stay together and other members of the group leave (disperse) and join up with different groups. What is likely the difference between the members of the group that stay versus those that leave, and what are the fitness benefits of this arrangement (a complete response will indicate who benefits and why)?

3) Explain what is meant by the principle of allocation, and how might we expect this principle to constrain life histories. Give at least one specific restriction on a life history trait that is result of the principle of allocation.

4) When using the mark-recapture method to estimate a population size, we make a variety of assumptions. Describe at least two assumptions that are violated in following example, and how those violations are like to affect the estimate of population size. Also identify at least one assumption that appears to have been satisfied.

A population of butterflies inhabiting a fieldworker is sampled: captured individuals are marked by brushing a Sharpie pen across the wing, but sometimes the wing is damaged as a result of this marking technique. After the sample is marked, the butterflies are releases and a researcher observes a few of the marked individuals flying away from the field and into a nearby wooded area. When the population is resampled the next day, one of the collectors is seen specifically targeting butterflies that had been previously captured and marked.

Answer 1

Answer to the first question is given here;

Darwin's four postulates of natural selection:

i.Variation:There exists variations in traits among organisms.Darwin states that in a given species ,a particular trait varies among the individual organisms.For example, beaks of birds vary in sizes, moths are colored in differently,birds have different patterns on wings etc,

ii.Heritability: These variations are inherited by the offspring. Organisms acquire traits from both their parents and hence the variations are passed on from parents to offspring.Darwin at that time was unaware of the underlying reason, but now we know that the variations in traits are due to genetic variations (different alleles of a gene) which are inherited by the offspring from parents

iii.Struggle for existence:Because organisms are capable of over-reproducing in an environment with limited resources, there is a strong competition among them to gain access to resources and reproduce.This was termed s struggle for existence.

iv.Survival of the fittest:During the struggle for existence, organisms with variations that enable them to adapt to the environment( favorable variations) survive and reproduce more than do individuals with less favorable variations:'survival of the fittest'.These variations are passed on the next generation thus resulting in evolutionary change by natural selection.For example, during long periods of drought years, plant species producing small seeds are less frequent than plant species producing large seeds, and birds with large beaks are better able to exploit large seeds than birds with small beaks.Hence birds with large birds were able to reproduce more and pass on the variation to their offspring resulting in evolutionary change by natural selection among the bird population.