Persistence of a reef fish metapopulation via network connectivity: Theory and data

Allison G. Dedrick, Stanford University, CA, Katrina A. Catalano and Malin L. Pinsky, Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ, Michelle R. Stuart, Rutgers University, New Brunswick, NJ, J. Wilson White, Department of Fisheries and Wildlife, Oregon State University, Newport, OR, Humberto R. Montes Jr., Visayas State University, Baybay, Philippines

Background/Question/Methods
Determining metapopulation persistence requires understanding both demographic rates and patch connectivity. Persistence is well understood in theory but has proved challenging to test empirically for species with high connectivity that precludes classic colonization/extinction dynamics. Here, we assessed persistence for a yellowtail anemonefish (Amphiprion clarkii) metapopulation using seven years of mark-recapture, genetic parentage, and census data across 19 subpopulations along 30 km of coastline. From these data, we calculated growth, survival, lifetime egg production, dispersal, and the influence of density dependence, as well as uncertainty in each rate. We assessed self-persistence of each patch as well as network-persistence of all patches together using spatial population dynamics theory.

Results/Conclusions
We found stable population sizes through time and sufficient lifetime production of surviving offspring to achieve replacement (1.7 offspring per adult). However, offspring dispersal patterns made the metapopulation unlikely to persist in isolation and instead reliant on immigrants from outside habitats. After accounting for dispersal, the patch closest to self-persistence only retained 0.09 surviving adults per adult in the previous generation. At a network scale, the metapopulation only achieved 20% of the growth rate required for persistence when considering offspring produced within the metapopulation. To persist in isolation, the metapopulation would need five-fold higher fecundity or to retain essentially all recruits produced. This assessment of persistence in a marine metapopulation shows that stable abundance alone does not indicate persistence, emphasizing the necessity of assessing both demographic and connectivity processes to understand metapopulation dynamics.