Environmental change effects on life history traits and population dynamics of anadromous fishes

Abstract

Migration, the recurring movement of individuals between a breeding and a non-breeding habitat, is a widespread phenomenon in the animal kingdom. Since the life cycle of migratory species involves two habitats, they are particularly vulnerable to environmental change, which may affect either of these habitats as well as the travel between them. In this study, we investigate the consequences of environmental change affecting older life history stages for the population dynamics and the individual life history of a migratory population. In particular, we use a theoretical approach to study how increased energetic cost of the breeding travel and reduced survival and food availability in the non-breeding habitat affect an anadromous fish population. These unfavorable conditions have impacts at individual and population level.First, when conditions deteriorate individuals in the breeding habitat have a higher growth rate as a consequence of reductions in spawning that reduce competition. Second, population abundance decreases, and its dynamics change from stable to oscillations with a period of four years. The oscillations are caused by the density-dependent feedback between individuals within a cohort through the food abundance in the breeding habitat, which results in alternation of a strong and a weak cohort. Our results explain how environmental change, by affecting older life history stages, has multiple consequences for other life stages and for the entire population. We discuss these results in the context of empirical data and highlight the need for mechanistic understanding of the interactions between life history and population dynamics in response to environmental change.

Individual energy dynamics reveal nonlinear interaction of stressors threatening migratory fish populations

“…Moreover, the body size at the habitat switch in this population is negatively correlated with the individual density in the freshwater habitat (Jutila et al., 2006); therefore large body sizes at the habitat switch are reached when population abundance is low in this habitat. This is the consequence of relaxed density dependence enabling a high body growth rate (Chaparro‐Pedraza & de Roos, 2019; Walters et al., 2013). Since threatened anadromous populations have relatively low population abundance, this suggests that its individuals are more likely to reach a larger body size at the habitat switch and therefore to experience lower predation mortality once in the ocean.…”

“…We use the model formulated by Chaparro‐Pedraza and de Roos (2019) to describe the dynamics of anadromous populations based on individual energetic dynamics. Here we provide a synopsis of the model.…”