The timing of life history events in the presence of soft disturbances

Abstract

We study a model for the evolutionarily stable strategy (ESS) used by biological populations for choosing the time of life-history events, such as migration and breeding. In our model we accounted for both intra-species competition (early individuals have a competitive advantage) and a disturbance which strikes at a random time, killing a fraction 1 − p of the population. Disturbances include spells of bad weather, such as freezing or heavily raining days. It has been shown in [23], that when p = 0, then the ESS is a mixed strategy, where individuals wait for a certain time and afterwards start arriving (or breeding) every day. We remove the constraint p = 0 and show that if 0 < p < 1 then the ESS still implies a mixed choice of times, but strong competition may lead to a massive arrival at the earliest time possible of a fraction of the population, while the rest will arrive throughout the whole period during which the disturbance may occur. More precisely, given p, there is a threshold for the competition parameter a, above which massive arrivals occur and below which there is a behaviour as in [23]. We study the behaviour of the ESS and of the average fitness of the population, depending on the parameters involved. We also discuss how the population may be affected by climate change, in two respects: first, how the ESS should change under the new climate and whether this change implies an increase of the average fitness; second, which is the impact of the new climate on a population that still follows the old strategy. We show that, at least under some conditions, extreme weather events imply a temporary decrease of the average fitness (thus an increasing mortality). If the population adapts to the new climate, the survivors may have a larger fitness. * The first two authors contributed equally to this work.

Barn swallows long-distance migration occurs between significantly temperature-correlated areas

“…Early arrival affords a number of social advantages including access to the best breeding territories, as well as advantages in the mate choice process and in sperm competition 46 – 48 . On the other hand, too early arrival relative to the current ecological conditions as determined for example by temperature, which is the main driver of spring phenological events at temperate and boreal latitudes, can entail major fitness costs in terms of survival or physiological state via an effect on food availability 21 , 39 . Information on future temperatures at destination may thus allow migratory barn swallows to optimize the resolution of the trade-off between the benefits and costs of arriving early.…”

“…On the other hand, migratory animals that periodically move over large distances, alternating between breeding and non-breeding areas, have no direct clue as to the conditions that they will experience along their migration journey and at destination, weeks to months later. Migrants are therefore considered to be particularly susceptible to environmental uncertainty and thus, for example, to the negative effects of human-driven, rapid climate change, including advancement of spring phenology at temperate latitudes 3 , 15 – 18 and increased frequency of extreme meteorological events 16 , 19 – 21 . The fitness advantages of appropriate timing of life-history events, however, is expected to select for the ability to capitalize on any environmental cue that allows to buffer the negative effects of environmental unpredictability on individual performance.…”

An evolution model with uncountably many alleles

“…In the first case the process is usually a birth-death process and one can focus either on the equilibrium when time grows, or on the trajectories. For instance the asymptotic distribution of fitnesses is studied by [15,3,4] in an evolution scheme where a random number of least fit individuals die at each generation, while [6,18] study the effect of random/deterministic events on this distribution; [2] and [7] study the convergence of the evolutionary process as the population size goes to infinity. The population is assumed to have a constant size in classical models such as the Wright-Fisher and the Moran models, but even with this assumptions there are still many theoretical challenges and applications (see for instance [10,21,22]).…”

Weathering The Storm: The Implications Of Wave Exposure On The Distribution, Phenotype And Growth Of A Temperate Reef Fish

“…In heterogeneous environments, particularly with unpredictable disturbance, individuals increase their reproductive fitness by reproducing on different schedules (Post et al 2001). Furthermore, in species where early arrival coincides with competitive advantage, offspring have an increased chance of survival if parents alter reproduction in response to changing environmental conditions (Post et al 2001b, Bertacchi et al 2016. Additionally, species breed earlier when conspecific densities are high (Svensson et al 1995, Dunn andWinkler 1999) suggesting high triplefin densities at sheltered sites may also influence reproductive timing.…”