Idea paper: Controlling trait adaptation to decrease population densities for conservation and management

Ecologists and evolutionary biologists have revealed that adaptive microevolution (i.e., allele frequency changes through time) and behavioral changes occur rapidly enough to affect contemporary ecological dynamics, and we can consider rapid adaptation for better conservation and management of wild populations. However, previous studies tended to focus on adaptation that increases population densities (e.g., evolutionary rescue), and did not pay attention to adaptation that decreases population densities (e.g., evolutionary suicide). Here, we demonstrate that controlling trait adaptation may be potentially important for decreasing population densities. One possibility is introducing “selfish” genotypes to populations. If the genotypes increase their reproductive success at the expense of population growth (e.g., cheaters in subsocial ants or coercive males in damselflies), we can decrease population densities (intraspecific adaptation load). The other possible option is diverting trait values of animals from the value that maximizes population growth (ecological trap). For example, we may be able to change behavior of a deer population by hunting so that they will not approach the best habitat with ample resources (landscape of fear). Then, we can consider the optimal allocation of our effort to directly decrease their population densities and control their trait values. However, we should carefully conduct controlling trait adaptation because it may result in unintended outcomes through modified genetic compositions and behaviors, such as increasing genetic variation of the focal population that enhances adaptation to changing environments by introducing selfish genotypes or a transient increase of population densities by modified behaviors.