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The interaction between evolution and ecology
I. WHAT IS EVOLUTION?
A. Evolution is change, and biological evolution can be defined as changes in any attribute of a
population over time.
1. A more specific definition is that evolution represents a change in the allele frequency at a
locus ( i.e. a gene) in a population that persists among generations.
II. Redefinition of terms and concepts.
1. Species ≡ a natural population or group of (potentially) interbreeding natural populations that
produces fertile offspring and is reproductively isolated from other groups.
2. Population ≡ a group of individuals of a single species that interact and interbreed in a
particular area (locale).
3. Gene pool ≡ the total sum of genes available for reproduction in a given population at a given
time.
a. The number of alleles in a population is 2NG.
4. Allele frequency – if a gene has two alleles, A1 and A2, then the frequency of A1 is
(# copies of A1)/(# copies of A1 + A2).
a. Old definition of evolution – descent with modification, inherited change in population.
b. New definition – If allele frequencies describe composition of gene pool, then evolution is
the change in allele frequencies.
5. Fitness.
a. Old Darwinian def. – The ability to survive and reproduce in a particular environment.
b. New definition – A measure of the expected relative contribution of an individual to the
gene pool of the next generation.
III. Allele and genotype frequencies.
1. If we know the numbers of all the genotypes, we can easily calculate p and q.
2. But, we cannot do the reverse. Given a p and a q, we cannot determine the number of different
genotype frequencies.
IV. Hardy-Weinberg equilibrium. (p + q)2 = p2 + 2pq + q2
1. Can be used to calculate the frequencies of alleles in the gene pool if the genotype frequencies
are known
2. And the genotype frequencies can be determined if the allele frequencies are known.
V. Conditions of Hardy-Weinberg equilibrium.
1. Assumptions made;
a. Random mating.
b. Population is large.
c. No differential survival or reproduction.
d. No net mutations
e. No migrations into or out of the population.
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