Data from: Density dependence and population regulation in marine fish: a large-scale, long-term field manipulation

Do small-scale experiments showing spatial density dependence in marine
fishes scale-up to temporal density dependence and regulation of
relatively large local populations? If so, what are the causative
mechanisms and their implications? We conducted an 8-year multi-generation
study of population dynamics of bicolor damselfish (Stegastes partitus)
inhabiting four large coral reefs in the Bahamas. After a 4-year baseline
period, it was clear that two populations naturally received very few
settlement-stage larvae, so recruitment of recently settled fish was
artificially enhanced at one low-settlement reef and reduced at one
high-settlement reef to ensure a broad range of population sizes over
which to test for regulation. Over all 8 years, populations on the two
naturally high-settlement reefs experienced temporal density dependence in
multiple per capita demographic rates mortality, survival to adulthood,
and fecundity. These local populations also displayed components of
regulation persistence, boundedness, and return tendency. Reefs supporting
regulated populations were structurally complex, providing sufficient prey
refuges that ensured high survival at low densities. In contrast,
populations at low-settlement reefs experienced either density-independent
or slightly inversely density-dependent demographic rates, even though
recruitment was artificially augmented to high levels at one reef. There
was no evidence of regulation at these reefs, and indeed, one local
population suffered temporary extirpation. Here, habitat complexity was
relatively low, increasing the risk of predation, especially at low
population densities when fish would have to travel longer distances when
finding mates or home sites inhabited by conspecifics. Among all
demographic parameters, density dependence in individual growth (an
indicator of within-species competition for food) was least correlated
with the presence or absence of local population regulation. We conclude
that, for systems like these, the environmental context of a local
population -- especially predation risk and the distribution and abundance
of spatial refuges -- is more important than the magnitude of larval
supply alone in determining the existence of regulating density
dependence. At the broader metapopulation scale, density dependence in
both survival and fecundity exogenously caused by predation may provide
regulation for the entire stock, even when endogenous within-species
competition (assumed to be important in most fisheries models) is weak.