Population and evolutionary dynamics in spatially structured seasonally varying environments

Abstract

Increasingly imperative objectives in ecology are to understand and forecast population dynamic and evolutionary responses to seasonal environmental variation and change. Such population and evolutionary dynamics result from immediate and lagged responses of all key life-history traits, and resulting demographic rates that affect population growth rate, to seasonal environmental conditions and population density. However, existing population dynamic and eco-evolutionary theory and models have not yet fully encompassed within-individual and among-individual variation, covariation, structure and heterogeneity, and ongoing evolution, in a critical life-history trait that allows individuals to respond to seasonal environmental conditions: seasonal migration. Meanwhile, empirical studies aided by new animal-tracking technologies are increasingly demonstrating substantial within-population variation in the occurrence and form of migration versus year-round residence, generating diverse forms of 'partial migration' spanning diverse species, habitats and spatial scales. Such partially migratory systems form a continuum between the extreme scenarios of full migration and full year-round residence, and are commonplace in nature. Here, we first review basic scenarios of partial migration and associated models designed to identify conditions that facilitate the maintenance of migratory polymorphism. We highlight that such models have been fundamental to the development of partial migration theory, but are spatially and demographically simplistic compared to the rich bodies of population dynamic theory and models that consider spatially structured populations with dispersal but no migration, or consider populations experiencing strong seasonality and full obligate migration. Second, to provide an overarching conceptual framework for spatio-temporal population dynamics, we define a 'partially migratory meta-population' system as a spatially structured set of locations that can be occupied by different sets of resident and migrant individuals in different seasons, and where locations that can support reproduction can also be linked by dispersal. We outline key forms of within-individual and among-individual variation and structure in migration that could arise within such systems and interact with variation in individual survival, reproduction and dispersal to create complex population dynamics and evolutionary responses across locations, seasons, years and generations. Third, we review approaches by which population dynamic and eco-evolutionary models could be developed to test hypotheses regarding the dynamics and persistence of partially migratory meta-populations given diverse forms of seasonal environmental variation and change, and to forecast system-specific dynamics. To demonstrate one such approach, we use an evolutionary individual-based model to illustrate that multiple forms of partial migration can readily co-exist in a simple spatially structured landscape. Finally, we summarise recent empirical studies that demon...

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

“…Migratory species are found across all major taxonomic groups (Dingle & Drake, 2007), an increasing number of which are recognized as partial migrants (Chapman, Brönmark, Nilsson, & Hansson, 2011b;Meller et al, 2016;Reid et al, 2018), wherein migratory and non-migratory individuals exist within the same population of a species (Chapman, Brönmark, Nilsson, & Hansson, 2011a;Lundberg, 1988). Previously underrepresented in migration literature (Chapman et al, 2011a;Sekercioglu, 2010), partial migration has seen an increase in published studies only in recent years (Meller et al, 2016)-at least in part owing the greater empirical research enabled by advances in tracking technologies (Chapman et al, 2011a(Chapman et al, , 2011bReid et al, 2018). The emergence of rigorous study on this topic represents an opportunity to address unanswered questions surrounding the evolution and maintenance of partial migration (and behavioural polymorphisms in general), the ecological consequences of different migratory patterns and the evolution of migration itself (Chapman et al, 2011b;Sekercioglu, 2010).…”

Bet-hedging across generations can affect the evolution of variance-sensitive strategies within generations

“…In contrast to the many decision events involved in foraging, certain important key decisions in the life of organisms are made only once or a few times, and can offer similar variance sensitive scenarios of choosing between 'safe but low gain' versus 'high risk / high gain' options. For example, decisions related to seasonal migration, including timing, choice of route, choice of destination, or even whether to migrate at all (Hebblewhite and Merrill 2009;Bauer et al 2011;Grist et al 2017;Reid et al 2018), which are likely to include strong bet-hedging elements if there are correlations in the payoffs among related individuals that all choose the risky strategy. Therefore, ongoing rapid changes in the spatial scale of synchrony in resource availability or environmental variation as a consequence of anthropogenic climate change, habitat change or habitat destruction can all have dramatic effects on population viability (Shuter et al 2011;Koenig and Liebhold 2016;Walter et al 2017).…”

The physiology of movement

“…Maximising body condition does, however, not maximise fitness as individuals also have to deal with unpredictable environmental changes at larger spatiotemporal scales. Organisms therefore need to disperse and expose themselves to costs largely exceeding those experienced during routine movements [7,8]. Movement is thus a fundamental behaviour in life history and the result of a continuous decision making process in terms of how, when and where to displace [1,9].…”