Novel parasite invasion leads to rapid demographic compensation and recovery in an experimental population of guppies
Description
The global movement of pathogens is altering populations and communities through a variety of direct and indirect ecological pathways. The direct effect of a pathogen on a host is reduced survival, which can lead to decreased population densities. However, theory also suggests that increased mortality can lead to no change or even increases in the density of the host. This paradoxical result can occur in a regulated population when the pathogen's negative effect on survival is countered by increased reproduction at the lower density. Here we analyze data from a long-term capture-mark-recapture experiment of Trinidadian guppies (Poecilia reticulata) that was recently infected with a nematode parasite (Camallanus cotti). By comparing the newly infected population with a control population that was not infected we show that decreases in the density of the infected guppy population were transient. The guppy population compensated for the decreased survival by a density-dependent increase in recruitment of new individuals into the population, without any change in the underlying recruitment function. Increased recruitment was related to an increase in the somatic growth of uninfected fish. Twenty months into the new invasion, the population had fully recovered to pre-invasion densities even though the prevalence of infection of fish in the population remained high (72%). These results show that density-mediated indirect effects of novel parasites can be positive, not negative, which makes it difficult to extrapolate to how pathogens will affect species interactions in communities. We discuss possible hypotheses for the rapid recovery.
Notes
Individual Data
individual_id = curated identifier code (each individual is associated to an number)
stream = which stream the individual is from
sampling = which month of the study is the observation.
sex = If the individual is male (M) or female (F)
weight = Individual weight when captured in g.
parasite = 0 if no parasite observed. 1 if parasite observed.
survival = 0 if individual was not observed in subsequent capture periods. 1 if individual was observed in subsequent capture periods.
F.dens.hat = density of female guppies in the stream (individuals / square meter)
Note: Missing values are noted by NA symbols and occur when an individual fish is not captured on one sampling occassion, but is later observed.
Population Summaries
stream = which stream the summary is from
sampling = which month of the study is the observation.
year = year of the study
month = calendar month
| M.dens.hat, | M.dens.lcl, | M.dens.ucl = mean, lower 95% confidence interval, upper 95% confidence interval of male density |
(individuals / square meter)
F.dens.hat, F.dens.lcl, F.dens.ucl=mean, lower 95% confidence interval, upper 95% confidence interval of female density (individuals / square meter)
M.bio.dens.hat = mean grams of male fish per meter square
F.bio.dens.hat = mean grams of female fish per meter square
M.phi, M.phi.lcl, M.phi.ucl = mean, lower 95% confidence interval, upper 95% confidence interval of male survival
F.phi, F.phi.lcl, F.phi.ucl = mean, lower 95% confidence interval, upper 95% confidence interval of female survival
F.rec.dens.hat, F.rec.dens.lcl, F.rec.dens.ucl=mean, lower 95% confidence interval, upper 95% confidence interval of female recruit density (individuals / square meter)
prop.para = proportion of population observed with parasites
Lab Data
ID = Numeric indentifier of an individual
Sex = If the individual is male (M) or female (F)
Initial.Length = standard length at the begining of the experiment (mm)
num.embryos = number of embryos being carried at the end of the experiment
embryo.wet.wt = mass in mg of embryos
stage = developmental stage of embryos (0-50)
num.regressors = number of undeveloped eggs.
num.worms = number of parasites in gut
embryo.dry.et = dry mass of all embryos (g)
para.load = wet mass of parasites in gut (g)