Predation can select for later and more synchronous arrival times in migrating species

Abstract

For migratory species, the timing of arrival at breeding grounds is an important determinant of fitness. Too early arrival at the breeding ground is associated with various costs, and we focus on one understudied cost: that migrants can experience a higher risk of predation if arriving earlier than the bulk of the breeding population. We show, using both a semi-analytic and simulation model, that predation can select for later arrival. This is because of safety in numbers: predation risk becomes diluted if many other individuals, either con-or heterospecific, are already residing in the area. Predation risk dilution can also select for more synchronous arrival because deviating from the current population-wide norm to earlier or later dates leads to higher predation risk or to failures in territory acquisition, respectively. The fact that selection for high arrival synchrony can in some cases be more important than selection for a specific date (early or late) within the season is an example of an 'evolutionary priority effect': whichever strategy -in this case a particular arrival time -becomes established in a population can remain stable over long periods of time; there are many possible equilibria (multiple stable states) which the population can remain at. Mixed arrival strategies are also possible under some circumstances.

Modelling migration in birds: competition's role in maintaining individual variation

“…These additions tend to lessen the strength of competition to arrive early. Harts et al [69] investigated the effect of predation risk upon migrants, which favoured uniform arrival dates.…”

Effects of food abundance and early clutch predation on reproductive timing in a high Arctic shorebird exposed to advancements in arthropod abundance

“…Schmidt et al (2015) suggested that clutch predation may prevent phenological shifts in response to climate change. More recently, Harts et al (2016) suggested that a higher predation risk on early arriving individuals may select for later arrival times of migratory birds. Indeed, birds may not only adjust their phenology to stay in pace with the timing of their prey, but also to escape their predators (Both et al 2009).…”

Maladaptive migration behaviour in hybrids links to predator‐mediated ecological selection

“…By deviating from the norm, migrants that leave the streams multiple times during the winter season would thus form a small fraction of the potential prey in the lake habitat. Hence, the per capita risk for individuals that visit the lake habitat during winter would be high and such individuals would not be able to benefit from a predator dilution effect (Harts, Kristensen, & Kokko, 2016). We view the above as candidate mechanisms behind the elevated risk of predation for individuals with high migration frequency, and thereby particularly so for hybrids.…”