1. List the different life history attributes of r and k – selected species. Which type of species moves in earlier in succession and why?
r – selected
-High growth rate
-Short generation time
-Small body size
-Little parental care
-Population size can fluctuate by several order of magnitude
-Quick recover and colonization
K - selected
-Low growth rate
-Long generation time
-Large body size
-Advanced parental care
-Population size generally fluctuates by less than one order of magnitude
-Slow recover and colonization
r – selected species will generally move in before K – selected species in early succession because of their high growth rate and quick generation time. They are able to reproduce quickly and colonize the area. r – selected species are eventually outcompeted and replaced by more competitive K – selected species.
2. What is the Allee effect?
With the Allee effect, the probability of finding a mate increases as population density increases. Larger groups may also be able to better detect predators and warn others, thus, decreasing predation. Larger populations also contain greater genetic diversity and less inbreeding, causing harmful mutations to appear less frequently. Small populations exhibit the opposite characteristics.
3. Draw a graph depicting three types of natural selection (hint: stabilizing, directional and disruptive selection.)
Answer: lecture 12, slide 19
What maintains genetic variation in populations?
Mutation- change in genetic code or DNA.
Migration- change of individuals among discrete pop'ns may introduce novel gene combinations. Most important with small pop'ns or if gene conveys strong advantage. Assumes variation in genetic make-up of discrete pop'ns.
Environmental Variation- selection favors different genotypes at different times (wet v. dry years), or different locations (sandy v. stony soils.)
Sex- recombination and division of genes through sexual reproduction (meiosis)
Trade-offs- energy expended on one character trait cannot simultaneously be expanded on another trait, therefore, perfect strategies cannot evolve.
What is the Hardy Weinberg Equilibrium?
Answer: If you have a large population that freely interbreeds and has a lot of offspring, random mating will not cause a change in gene frequencies, the gene frequencies will stay the same that provided:
- Large population
- Random mating
- No Migration
- Negligible mutation (back and forth at same rate)
- No selection