Populations with selection-decelerated growth may increase, or decline, or first increase and then decline in numbers
The simplest form of selection-decelerated growth refers to cases where natural selection is decelerating the population dynamic growth rate at a constant pace. So far, this form of dynamics has been identified as the best population dynamic model for 77 populations of North American birds, 13 populations of British birds, 27 populations of Danish birds, and 24 populations of birds and mammals in the Global Population Dynamic Database.
Decelerating natural selection is expected when the level of interference competition is sufficiently large in the population, with the figure illustrating the three qualitatively difference cases where a population is either increasing, or increasing and then declining, or declining in numbers.
We do not expect the long-term dynamics of any animal population to be constantly decelerating. It is more that constant deceleration is a fair approximation in cases where we are unable to identify a change in the rate of deceleration over time. In declining populations, selection by density dependent interactive competition should eventually disappear, slowing down the deceleration of the growth rate, and eventually turn deceleration into acceleration.
- Sauer, J.R., D.K. Niven, J.E. Hines, D.J. Ziolkowski, K.L. Pardieck, J.E. Fallon and W.A. Link 2017. The North American Breeding Bird Survey, Results and analysis 1996 -- 2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, Maryland, Available at www.mbr-pwrc.usgs.gov/bbs/bbs.html.
- Witting, L. 2021. Selection-regulated population dynamic in birds and mammals. Preprint at bioRxiv https://dx.doi.org/10.1101/2021.11.27.470201.