BIO220 Lecture 17 Flashcards
How harvesting affects populations
define: continuous traits
= quantitative traits
= phenotypes that vary continuously, determined by many genes, and are affected by the environment
define: Mendelian traits
= discrete qualitative traits
= controlled by 1 gene, no environmental influence
Rule of thumb/equation for quantitative traits
P = G + E + GE
Mendelian traits allow us to infer many things. What are they?
infer phenotype from genotype
How do we understand the evolution of continuous traits?
use statistical descriptions
How do we calculate the strength of selection (s)?
current mean - past mean
how do we interpret s?
neg: selecting down (smaller size, etc.)
pos: selecting up (bigger size, etc.)
TRUNCATION SELECTION
strong form of directional selection
- individuals with phenotype above threshold die, and those below live
how to measure intensity of truncation selection?
s = z* - z
z* = mean of population after selection z = mean of population before selection
How do we track the evolution of quantitative traits, given that environment also plays a huge part?
- measure environmental factors and account for it statistically
- track genetic changes explicitly
what are 2 things that have experienced harvest-induced evolution?
- Atlantic cod
2. Sheep (trophy hunting)
At the _____ Fishery, Atlantic __ and __ were declining
Gulf of St. Lawrence Fishery;
abundance;
size
avg size of cod was reduced by…
15-25 cm
If cod had density dependent population growth, low density should promote…
- faster population growth
- larger sizes of individuals
fish grow best under what temp?
warmer temperatures promote better fish growth
what was the observed data regarding fish growth & temperature?
colder temperatures = higher densities of fish
warmer temp = lower densities of fish
“natural” selection favoured __ sized fish due to ___
smaller or same;
fishing
ecological forces select for __ sized fish due to ____
larger;
temperature & density-dependence
Taking into account both ecological & evolutionary forces, what is happening to cod size?
No net change in fish size;
the 2 forces oppose each other
What does R^2 mean?
How well the model explains the data
e.g. R^2 = 0.6
60% of the variation in the data can be explained by the model
female size positively correlates with…
fecundity
what are the implications for a recovering fishery (ecological vs. selection forces)?
- female fish will be small
- small fish = less fecundity
- less offspring produced
- slow recovery of population size
Economic pressures usually lead to ___ harvesting than ____.
more;
MSY
