Abstract
Much has been written about fishery‐induced evolution (FIE) in exploited species, but relatively little attention has been paid to the consequences for one of the most important parameters in evolutionary biology—effective population size (N e). We use a combination of simulations of Atlantic cod populations experiencing harvest, artificial manipulation of cod life tables, and analytical methods to explore how adding harvest to natural mortality affects N e, census size (N), and the ratio N e/N. We show that harvest‐mediated reductions in N e are due entirely to reductions in recruitment, because increasing adult mortality actually increases the N e/N ratio. This means that proportional reductions in abundance caused by harvest represent an upper limit to the proportional reductions in N e, and that in some cases N e can even increase with increased harvest. This result is a quite general consequence of increased adult mortality and does not depend on harvest selectivity or FIE, although both of these influence the results in a quantitative way. In scenarios that allowed evolution, N e recovered quickly after harvest ended and remained higher than in the preharvest population for well over a century, which indicates that evolution can help provide a long‐term buffer against loss of genetic variability.
Highlights
In recent decades, humans have created a global experiment by subjecting natural populations to harvest at rates that equal or exceed the rate of natural mortality (Darimont et al 2009)
Species with low rates of natural mortality as adults generally mature at older ages, because investing limited energy into growth rather than early maturity means that they will be larger when they reach maturity, and they can expect to reap the benefits of higher fecundity for many years because mortality is low
Adding harvest on top of natural mortality roughly doubled the total adult mortality experienced by the population
Summary
In recent decades, humans have created a global experiment by subjecting natural populations to harvest at rates that equal or exceed the rate of natural mortality (Darimont et al 2009). Marty et al (2015) simulated both neutral and adaptive genes and estimated Ne from neutral genes by tracking the rate of change in allele frequency over time (the temporal method; Waples 1989) They took samples every 20 years and converted this time interval into elapsed generations based on calculations of generation length (T) from the simulated demographies. We use a method for calculating Ne (AgeNe; Waples et al 2011) that is designed for use with iteroparous, age-structured species and which can estimate effective size for individual cohorts We consider both Ne and the ratio Ne/N (with N defined as the number of mature adults) because the latter allows us to disentangle the effects of changes in vital rates that affect the Ne/N ratio from effects on abundance, which can reduce Ne even if Ne/N is not reduced. To explore generality of our results, we supplement the simulations with analytical results and artificial manipulation of another life table for Atlantic cod
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
