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Spatial and temporal synchrony in abundance or survival trends can be indicative of whether populations are affected by common environmental drivers. In Atlantic salmon (Salmo salar), return rates to natal rivers have generally been assumed to be affected primarily by shared oceanic conditions, leading to spatially synchronous trends in mortality. Here, we investigated the existence of parallel trends in salmon sea survival, using data on migrating smolts and returning adults from seven Canadian populations presumed to share feeding grounds. We analysed sea survival, using a Bayesian change-point model capable of detecting nonstationarity in time series data. Our results indicate that while salmon have experienced broadly comparable patterns in survival, finer-scale temporal shifts are not synchronous among populations. Our findings are not consistent with the hypothesis that salmon populations consistently share the same mortality-related stressors in the marine environment. Although populations may have shared greater synchrony in survival patterns in the past, this synchrony may be breaking down. It may be prudent to direct greater attention to smaller-scale regional and population-level correlates of survival. Le synchronisme spatial et temporel des tendances d'abondance ou de survie peut indiquer si differentes populations sont influencees par les memes facteurs environnementaux. Il est generalement presume que, chez les saumons atlantiques (Salmo salar), les taux de retour aux rivieres natales sont principalement influences par des conditions oceaniques communes, ce qui mene a des tendances de mortalite synchrones dans l'espace. Nous examinons l'existence de tendances paralleles de survie en mer des saumons en utilisant des donnees sur les saumoneaux migrants et les adultes retournant dans leur riviere natale de sept populations canadiennes presumees avoir les memes aires d'alimentation. Nous analysons la survie en mer en utilisant un modele bayesien de points de changement pouvant detecter la presence de non-stationnarite dans les donnees de series chronologiques. Nos resultats indiquent que, bien que les saumons presentent des motifs de survie generalement semblables, des changements temporels a echelle plus fine ne sont pas synchrones d'une population a l'autre. Nos resultats ne concordant pas avec l'hypothese voulant que les populations de saumons aient toujours en commun les memes facteurs de stress relies a la mortalite dans le milieu marin. Si les motifs de survie des populations peuvent avoir presente un plus grand synchronisme par le passe, ce synchronisme pourrait etre en train de s'effriter. Il peut etre prudent d'accorder plus d'attention aux correlats de la survie a des echelles regionales ou populationnelles plus fines. [Traduit par la Redaction], 1. Introduction The viability of a species depends on the resistance and resilience of its constituent populations to natural and human-induced environmental change. Reduced viability reflects reductions in the abundance [...]

Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a variation cascade that propagated across the food web, including fish, zooplankton and phytoplankton species. In fisheries that removed a large amount of top-predatory and cannibalistic fish, the biomass oscillations started to decrease after fishing was started. In fisheries that mainly targeted large planktivorous fish, the biomass oscillations did not dampen but slightly increased over time. Removing species with specific ecological functions might alter the food web dynamics and potentially affect the ecological resilience of aquatic ecosystems. Les etudes de cascades trophiques reposent souvent sur des chaines alimentaires lineaires plutot que sur des reseaux trophiques complexes, ainsi que sur des mesures de la biomasse moyenne, plutot que des variations de la biomasse. Nous etudions la propagation de cascades trophiques a travers un reseau trophique complexe en integrant une mesure de la variation de la biomasse en plus de la moyenne de cette derniere. Nous tentons de determiner si differentes strategies de peche induisent des cascades trophiques et si ces dernieres different les unes des autres. Nous utilisons un modele de reseau trophique allometrique (RTA) pour etudier de maniere mecaniste les modifications induites par la peche de la dynamique du reseau trophique. Differentes strategies de peche ne declenchent pas de cascades trophiques reciproques traditionnelles, telles que mesurees par la biomasse moyenne. La peche declenche plutot une cascade de variations qui se propage dans tout le reseau trophique, incluant des especes de poissons, de zooplancton et de phytoplancton. Dans les peches qui prelevent une grande quantite de poissons cannibales et predateurs de niveau superieur, les oscillations de la biomasse commencent a diminuer apres le debut de la peche. Dans les peches qui ciblent principalement de grands poissons planctonivores, les oscillations de la biomasse ne s'attenuent pas, mais augmentent plutot legerement au fil du temps. Le retrait d'especes ayant des fonctions ecologiques precises pourrait modifier la dynamique des reseaux trophiques et avoir une incidence sur la resilience ecologique des ecosystemes aquatiques. [Traduit par la Redaction], Introduction The widespread importance of trophic cascades ('indirect species interactions that originate with predators and spread downward through food webs' sensu Ripple et al. 2016) has become increasingly recognized since [...]

Animals with different life‐history types vary in their stress‐coping styles, which can affect their fitness and survival in changing environments. We studied how chronic exposure to manganese sulfate (MnSO4), a common aquatic pollutant, affects life‐history traits, physiology, and behavior of zebrafish (Danio rerio) with two life‐history types: fast (previously selected for fast juvenile growth, early maturation, and small adult body size) and slow life histories (selected for slow juvenile growth, late maturation, and large adult body size). We found that MnSO4 had negative effects on growth and condition factors, but the magnitude of these effects depended on the life‐history type. Individuals with fast life histories were more susceptible to MnSO4 than fish with slow life histories as they had lower growth rate, condition factor and feeding probability in high MnSO4 concentrations. Our results demonstrate that MnSO4 can impair fish performance, and life‐history variation can modulate the stress‐coping ability of individuals. Animals with different life‐history types vary in their stress‐coping styles, which can affect their fitness and survival in changing environments. We found that MnSO4 had negative effects on growth and condition factors, but the magnitude of these effects depended on the life‐history type. Individuals with fast life histories were more susceptible to MnSO4 than fish with slow life histories as they had lower growth rate, condition factor and feeding probability in high MnSO4 concentrations. [ABSTRACT FROM AUTHOR]

Key life‐history data, such as growth and age, are necessary to effectively manage and conserve threatened freshwater mussel species. Traditionally growth and age studies require large yet destructive sample sizes covering all age classes. Such methods pose a risk to populations of conservation concern, and therefore, alternative methods that need only limited sample sizes are necessitated to prevent further threats to such populations. We applied retrospective shell growth at age reconstructions to 98 critically endangered freshwater pearl mussel (FPM) individuals from 34 populations across Finland and Sweden, enabling the use of extremely small sample sizes (n = 1–6 per population). We compared the performance of six different growth models with the reconstructed size‐at‐age data across FPM juvenile (<20 years old) and adult life stages. The growth reconstruction model showed reasonable skill in reconstructing FPM growth patterns. The von Bertalanffy model showed to be a good general descriptor of growth for FPM, but it systematically underestimated the asymptotic size. The power law model was the most accurate in estimating juvenile growth (lowest deviances from the size‐at‐age data). FPM showed great variability in longevity (Amax = 54–254 years) and growth constant k (0.018–0.057 year−1). Our results show that reasonable estimates of growth can be attained even when sample sizes are extremely limited. The results can be further applied to gain knowledge on the population's age structure, size at maturation, and recovery potential. The methodology is applicable to other freshwater mussel species of conservation concern. [ABSTRACT FROM AUTHOR]

Many generalist predators, including fish, insects and mammals, temporarily focus on their search behaviour and can switch between prey species. Flexible and rapid behavioural plasticity enables a predator to forage optimally, as guided by search image formation and prey switching in response to changing prey abundances.More than half a century of studies have used Holling type III functional response to model the impact of this feeding behaviour on population dynamics, yet a mechanistic understanding for the pathway between individual behaviour and feeding rates remains poorly understood.To understand this common feeding behaviour, we developed three mechanistic models using first‐principles to provide direct derivations for the relationship between observed individual behaviour and feeding rates.The derived models yield three novel, generalised functional responses for predators characterised by prey switching and mutually exclusive feeding (i.e. feeding is limited to one prey species at a time). We show how these functional responses act as Holling type III response, and how they can be used to predict predators' diet compositions.Our results demonstrate that several behavioural forms of prey switching, as displayed in a wide range of predator species, consistently produce type III conforming functional responses. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Many considerably declined fish populations have not fully recovered despite reductions in fishing pressure. One of the possible causes of impaired recovery is the (demographic) Allee effect. To investigate whether low‐abundance recruitment dynamics can switch between compensation and depensation, the latter implying the presence of the Allee effect, we analysed the stock–recruitment time series of 17 depleted cod‐type and flatfish populations using a Bayesian change point model. The recruitment dynamics were represented with the sigmoidal Beverton–Holt and the Saila–Lorda stock–recruitment models, allowing the parameters of the models to shift at a priori unknown change points. Our synthesis study questions the common assumption that recruitment is stationary and compensatory and the high amount of scatteredness often present in stock–recruitment data is only due to random variation. When a moderate amount of such variation was assumed, stock–recruitment dynamics were best explained by a non‐stationary model for 53% of the populations, which suggests that these populations exhibit temporal changes in the stock–recruitment relationship. For four populations, we found shifts between compensation and depensation, suggesting the presence of temporary Allee effects. However, the evidence of Allee effects was highly dependent on the priors of the stock–recruitment model parameters and the amount of random variation assumed. Nonetheless, detection of changes in low‐abundance recruitment is essential in stock assessment since such changes affect the renewal ability of the population and, ultimately, its sustainable harvest limits. [ABSTRACT FROM AUTHOR]

Competition for shared resources is commonly assumed to restrict population‐level niche width of coexisting species. However, the identity and abundance of coexisting species, the prevailing environmental conditions, and the individual body size may shape the effects of interspecific interactions on species' niche width.Here we study the effects of interspecific and intraspecific interactions, lake area and altitude, and fish body size on the trophic niche width and resource use of a generalist predator, the littoral‐dwelling large, sparsely rakered morph of European whitefish (Coregonus lavaretus; hereafter LSR whitefish). We use stable isotope, diet and survey fishing data from 14 subarctic lakes along an environmental gradient in northern Norway.The isotopic niche width of LSR whitefish showed a humped‐shaped relationship with increasing relative abundance of sympatric competitors, suggesting widest population niche at intermediate intensity of interspecific interactions. The isotopic niche width of LSR whitefish tended to decrease with increasing altitude, suggesting reduced niche in colder, less productive lakes.LSR whitefish typically shifted to a higher trophic position and increased reliance on littoral food resources with increasing body size, although between‐lake differences in ontogenetic niche shifts were evident. In most lakes, LSR whitefish relied less on littoral food resources than coexisting fishes and the niche overlap between sympatric competitors was most evident among relatively large individuals (>250 mm). Individual niche variation was highest among >200 mm long LSR whitefish, which likely have escaped the predation window of sympatric predators.We demonstrate that intermediate intensity of interspecific interactions may broaden species' niche width, whereas strong competition for limited resources and high predation risk may suppress niche width in less productive environments. Acknowledging potential humped‐shaped relationships between population niche width and interspecific interactions can help us understand species' responses to environmental disturbance (e.g. climate change and species invasions) as well as the driving forces of niche specialization. [ABSTRACT FROM AUTHOR]

Can the advantage of risk-managing life-history strategies become a disadvantage under human-induced evolution? Organisms have adapted to the variability and uncertainty of environmental conditions with a vast diversity of life-history strategies. One such evolved strategy is multiple-batch spawning, a spawning strategy common to long-lived fishes that 'hedge their bets' by distributing the risk to their offspring on a temporal and spatial scale. The fitness benefits of this spawning strategy increase with female body size, the very trait that size-selective fishing targets. By applying an empirically and theoretically motivated eco-evolutionary mechanistic model that was parameterized for Atlantic cod ( Gadus morhua ), we explored how fishing intensity may alter the life-history traits and fitness of fishes that are multiple-batch spawners. Our main findings are twofold; first, the risk-spreading strategy of multiple-batch spawning is not effective against fisheries selection, because the fisheries selection favours smaller fish with a lower risk-spreading effect; and second, the ecological recovery in population size does not secure evolutionary recovery in the population size structure. The beneficial risk-spreading mechanism of the batch spawning strategy highlights the importance of recovery in the size structure of overfished stocks, from which a full recovery in the population size can follow.