Nutritional conditions during key periods of development, when the architecture and modus operandi of the body become established, are of profound importance in determining the subsequent life-history trajectory of an organism. If developing individuals experience a period of nutritional deficit, they can subsequently show accelerated growth should conditions improve, apparently compensating for the initial setback. However, recent research suggests that, although compensatory growth can bring quick benefits, it is also associated with a surprising variety of costs that are often not evident until much later in adult life. Clearly, the nature of these costs, the timescale over which they are incurred and the mechanisms underlying them will play a crucial role in determining compensatory strategies. Nonetheless, such effects remain poorly understood and largely neglected by ecologists and evolutionary biologists.

Compensation for a bad start: grow now, pay later?

Individual-based modeling is a new, exciting discipline that allows ecologists to explore, using computer simulations, how properties of populations and ecosystems might evolve from the characteristics and behaviors of individual organisms. Individual-based Modeling and Ecology, written by Volker Grimm and Steven F. Railsback, gives an excellent introduction and overview of this field. It should be read by everyone interested in individual-based modeling, and especially by anyone contemplating developing, or being involved with a group developing, an individualbased model.

http://www.gbv.de/dms/weimar/toc/396272002_toc.pdf

Individual-based modeling and ecology

 – Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3–5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour.

https://onlinelibrary.wiley.com/doi/pdf/10.1034/j.1600-0633.2003.00010.x

Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

Animal personality traits such as boldness, activity and aggressiveness have been described for many animal species. However, why some individuals are consistently bolder or more active than others, for example, is currently obscure. Given that life-history tradeoffs are common and known to promote inter-individual differences in behavior, we suggest that consistent individual differences in animal personality traits can be favored when those traits contribute to consistent individual differences in productivity (growth and/or fecundity). A survey of empirical studies indicates that boldness, activity and/or aggressiveness are positively related to food intake rates, productivity and other life-history traits in a wide range of taxa. Our conceptual framework sets the stage for a closer look at relationships between personality traits and life-history traits in animals.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(08)00159-6.pdf

Are animal personality traits linked to life-history productivity?

The shy-bold continuum is a fundamental axis of behavioral variation in humans and at least some other species, but its taxonomic distribution and evolutionary implications are unknown. Models of optimal risk, density- or frequency-dependent selection, and phenotypic plasticity can provide a theoretical framework for understanding shyness and boldness as a product of natural selection. We sketch this framework and review the few empirical studies of shyness and boldness in natural populations. The study of shyness and boldness adds an interesting new dimension to behavioral ecology by focusing on the nature of continuous behavioral variation that exists within the familiar categories of age, sex and size.

http://behav.zoology.unibe.ch/sysuif/uploads/files/esh/pdf_online/ws/Wilson_TREE1994.pdf

Shyness and boldness in humans and other animals.

Summary The great diversity of life-history patterns in the salmonids has stimulated many theoretical studies However, virtually all studies are based on ultimate considerations, in which predictions are made by comparing the expected reproductive success of diAerent developmental or life-history pathways and choosing the one (or ones) with the highest fitness Such models are post hoc because they attribute fitness to individuals at the completion of the particular phase of the life cycle and do not attempt to characterize the mechanisms that animals use to achieve the life-history pattern We describe a model, based on proximate considerations, for salmonid life histories, focused on Atlantic salmon Salmo salar L The model involves identification of the times at which developmental conversions are initiated or inhibited and the connection between physiological states and the thresholds for such conversions Developmental paths are based on the comparison of the current physiological status of the fish (and its change of state) with a genetic threshold The state of the fish and rate of change of state are determined by environmental opportunity, but the threshold is genetic This approach therefore immediately generates a genotype‐environment interaction We use expected reproductive success to determine the fitness of individuals with diAerent genetically determined thresholds Instead of finding an optimal life history, our theory generates fitness surfaces for diAerent life histories, so that variation is inherent in this approach We describe and explain the structure of the model and present evidence on which this structure is based, thus providing a framework within which one can understand how ecology relates to the physiological mechanisms leading to the developmental changes of smolt metamorphosis and maturation

Modelling the proximate basis of salmonid life-history variation, with application to Atlantic salmon, Salmo salar L.

The activity patterns of animals, whether diurnal, crepuscular or nocturnal, are usually fixed endogenous rhythms, entrained by environmental Zeitgebers. Here we demonstrate that juvenile Atlantic salmon, Salmo salar, switch between diurnal and nocturnal foraging solely in response to environmental temperature, and independently of photoperiod and season. Above 10 degrees C juvenile Atlantic salmon fed predominantly during daylight, spending the night exposed in the water column but relatively quiescent. As temperature dropped below 10 degrees C they became increasingly nocturnal, hiding in refuges by day but emerging to feed at night. It has previously been shown that parallel physiological changes take place in the retinae of several species of salmonids: the quantity and composition of the visual pigments change so as to make the fish more dark adapted at low temperatures. As the fish were found to be far less aggressive by night than by day at all temperatures, the switch to nocturnal activity was also accompanied by a change in social structure. We suggest that this temperature-dependent strategy maximizes feeding efficiency in summer but reduces predation risk in winter.

Temperature-Dependent Switch between Diurnal and Nocturnal Foraging in Salmon

Developmental rate, fecundity and egg size in Atlantic salmon, Salmo salar L.

Dominance relationships between pairs of Atlantic salmon parr of known size were assessed at various times during their first year of life. In tests conducted between first feeding and early July, the larger of two fish was dominant in only 54% of pairs, regardless of the magnitude of the size difference between the fish. In September, there was a stronger association between size and status, especially in pairs with a large size differential, where the dominant was larger in 72% of cases. In groups of parr tested in April of the following year, there was no relationship between size and status, the larger of two fish being dominant in 48% of cases, regardless of the magnitude of the size differential. This result suggests that status in early social interactions may depend on behavioural properties rather than size and that the larger size of dominant fish reported in a number of salmonids might be a consequence and not a cause of high status.

Social dominance and body size in Atlantic salmon parr, Salmo solar L.

Evaluation de l'hypothese selon laquelle le temps mis pour atteindre la smoltification est dependant du potentiel alimentaire et de la croissance et que ces parametres sont eux meme dependant de la temperature et de la photoperiode (puisque les saumons ne se nourrissent que le jour).L'age moyen de smoltification est fortement correle avec la latitude lorsque l'on considere separement les populations de l'Est et de l'Ouest de l'Atlantique

John E. Thorpe

Papers

Modelling the proximate basis of salmonid life-history variation, with application to Atlantic salmon, Salmo salar L.

Temperature-Dependent Switch between Diurnal and Nocturnal Foraging in Salmon

Developmental rate, fecundity and egg size in Atlantic salmon, Salmo salar L.

Social dominance and body size in Atlantic salmon parr, Salmo solar L.

Determinants of geographical variation in the age of seaward-migrating salmon, Salmo salar