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Lecture 1

BIOL208 Lecture Notes - Lecture 1: Medium Ground Finch, Darwin'S Finches, Genetic Drift

Biology (Biological Sciences)
Course Code
Saewan Koh

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Ecology happens at different scales*
Spatial scale, ex. individual organism- population level (Age, sex, genetic composition of
population)- community ecology (interactions between different organisms)- ecosystem
(movement of energy and materials)- biosphere (global ecology)
Temporal scale ex. response of a animal eating another animal (quick response), seasonal
changes, longer time scale: evolutionary relationship between plant and animal
Importance of Ecology
Food, plants, spread of disease. Study of organisms in the environment (not necessarily
Foundation of many bio fields for the world to keep functioning and how we exist in the world.
Ecology and the Scientific Method
Information: Observation, experiment, modeling, published studies
Hypothesis (hypothesis suported: conduct additional tests of the hypo using an original
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Test of Hypothesis: Observation, Experimenting, Modeling (DATA: Gathering, Management,
Display, Summary Stats, Stat Analysis, Accept/Reject Hypothesis)
Evolutionary mechanisms and fitness
Evolution and natural selection
Genetic drift
Constraints on Evolution
Darwin: Galapagos- organisms that looked very similar but were not the same* pieced together
why the populations where different
1859 Published The Origin of Species outlined that overtime, organisms in a certain environment
can change from their original form to a new form: descent with modification or evolution.
Malthus: Essay on the Principles of Population. Why can't we grow infinitely? *Influenced
Some individuals have traits that help them survive during more challenging situations: they are
more likely to reproduce and survive
Mendel: Looking at plants where parents had characteristics which were passed to the offspring.
There was some distinct unit that was being passed: alleles-dominant or recessive. Link between
genotype and phenotype at the same time that Darwin was working on his ideas.
Natural Selection
Many offspring are produced, not all survive (limited resources)
Traits vary among individuals within a population and may be heritable*
Some heritable traits give individuals and advantage (some individuals have higher fitness: the
relative genetic contribution of individuals to future generations. Organisms with higher fitness
become more prominent in a population so traits become more common overtime
Individuals do not evolve!! Natural selection is the mechanism..
Advantageous traits become more common
Classic Example
Darwin Finches: Galapalos,
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Medium ground finch: exhibit a lot of variation on bill size.. There is an average where most of
the population lies, yet there are a lot of animals with larger bills. Size of bill has to do with what
you're able to eat, different bill sizes have different ability to find seeds.
Huge drought: seeds were scarce.. Affected certain seeds more than others. The distribution of
seeds available changed. The seeds that were left were relatively hard: change in resource
available. At the same time, the population of birds also declined. However, there was higher
survival of birds with larger bills, which would eat the harder seeds available.
In future generations, there was a shift... more birds with big beaks were available and
In order for natural selection to work, a trait has to be heritable*
h2= VG/Vp
Vg- Genetic variation
Vp- phenotypic variation
Vp= Vg + Ve
Ve- environmental effects
Therefore h^2= Vg/(Vg+Ve)
What happens to h^2 if
Vg increases? increasing the heritability of the trait as a whole. If genetic variation increases it is
most likely that the trait will be heritable
Ve increases? decreases the heritability of the trait: the more the trait is influenced by
environment, the less heritable
VE= 0? all heritable, the environment has no effect
Vg= 0? undefined. It's all environmental, nothing to do with genes. No heritability
Stabilizing Selection
It's not good to be an extreme. Fitness is higher when you're average.
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