Positive
Frequency-Dependent Selection
A plant species occurs in two
flower color forms (morphs), red
and blue.
Pollinator insect species are attracted preferentially to
the rarer, standout morph, therefore, each morph has
higher fitness when rare (e.g., Wblue 
2
while f(blue)
0 and Wred 1
while f(red) 1) [top].
[Bottom] Optimal population fitness occurs when both morphs
are maintained at intermediate frequency: any deviation is
corrected back towards the equilibrium. Positive
frequency-dependent selection stabilizes and maintains intra-population
variation.
Compare dynamics with negative
frequency-dependent
selection.
[note to self: curves are backwards, swap 4.11
& 4.12 ?]