  We identify the genetic signature of a selective sweep in a population
described by a birth-and-death process with density dependent competition. We
study the limit behaviour for large K, where K scales the population size. We
focus on two loci: one under selection and one neutral. We distinguish a soft
sweep occurring after an environmental change, from a hard sweep occurring
after a mutation, and express the neutral proportion variation as a function of
the ecological parameters, recombination probability r\_K, and K. We show that
for a hard sweep, two recombination regimes appear according to the order of
r\_K log K.
