Population regulation and density‐dependent demography in the Trinidadian guppy

Classic theory for density-dependent selection for delayed maturation
requires that a population be regulated through some combination of adult
fecundity and/or juvenile survival. We tested whether those demographic
conditions were met in four experimental populations of Trinidadian
guppies in which delayed maturation of males evolved when the densities of
those populations became high. We used monthly mark-recapture data to
examine population dynamics and demography in these populations. Three of
the four populations displayed clear evidence of regulation. In all four
populations, monthly adult survival rates were independent of biomass
density or actually increased with increased biomass density. Juvenile
recruitment, which is a combination of adult fecundity and juvenile
survival, decreased as biomass density increased in all four populations.
Demography showed marked seasonality, with greater survival and higher
recruitment in the dry season than the wet season. Population regulation
via juvenile recruitment supports the hypothesis that density-dependent
selection was responsible for the evolution of delayed maturity in males.
This body of work represents one of the few complete tests of
density-dependent selection theory.