What's the difference biological fitness and reproductive success in the biological terminology?
$\begingroup$ There is the term "evolution" in you title who is not found in the post. But this term is used in an unclear way. did you "evolution, fitness and reproductive success" or do you think that "evolution fitness" is a concept by itself? $\endgroup$– Remi.bApr 15, 2016 at 14:53
The concepts are very similar but there are a few differences.
Firstly, fitness is usually applied to alleles or genotypes, reproductive success to individuals.
Secondly (and partially as a consequence of this), fitness is an average or idealised/expected property across a population; but actual reproductive success per individual is stochastic. Individuals possessing an allele with a relative fitness of "2" will on average have twice as many offpsring as their competitors, all else being equal, but individual reproductive success will vary as a consequence of other factors such as predation, parasitism, starvation etc.
Finally, absolute fitness relates to the proportional representation of a genotype in a population. Reproductive success relates to offspring per individual. For example, in a growing population a genotype could be simultaneously declining in proportion while it is increasing in absolute number, if other genotypes are increasing in number more rapidly.