Dylan J. Fraser

Concordia University Montreal · Department of Biology

Salmonids are of immense socio‐economic importance in much of the world, but are threatened by climate change. This has generated a substantial literature documenting effects of climate variation on salmonid productivity in freshwater ecosystems, but there has been no global quantitative synthesis across studies. We conducted a systematic review an...

We uncover a largely unnoticed and unaddressed problem in conservation research: arguments built within studies are sometimes defective in more fundamental and specific ways than appreciated, because they misrelate values and empirical matters. We call this the unraveled rope problem because just as strands of rope must be properly and intricately...

Sustainable harvesting of wild populations relies on evidence‐based knowledge to predict harvesting outcomes for species and the ecosystems they inhabit. Although harvesting may elicit compensatory density‐dependence, it is generally size‐selective, which induces additional pressures that are challenging to forecast. Furthermore, responses to harve...

The broad scale distribution of population-specific genetic diversity (GDP) across taxa remains understudied relative to species diversity gradients, despite its relevance for systematic conservation planning. We used nuclear DNA data collected from 3678 vertebrate populations across the Americas to assess the role of environmental and spatial vari...

Effective population size (N e ) is a particularly useful metric for conservation as it affects genetic drift, inbreeding and adaptive potential within populations. Current guidelines recommend a minimum N e of 50 and 500 to avoid short-term inbreeding and to preserve long-term adaptive potential, respectively. However, the extent to which wild pop...

Although efforts to estimate Ne, Nc, and their ratio in wild populations are expanding, few empirical studies investigate interannual changes in these parameters. Hence, we do not know how representative many estimates may be. Answering this question requires studies of long-term population dynamics. We non-lethally sampled N=5400 brook trout (Salv...

Effective population size ( N e ) is a particularly useful metric for conservation as it affects genetic drift, inbreeding and adaptive potential within populations. Current guidelines recommend a minimum N e of 50 and 500 to avoid short‐term inbreeding and to preserve long‐term adaptive potential respectively. However, the extent to which wild pop...

Understanding recruitment, the process by which individuals are added to a population or to a fishery, is critical for understanding population dynamics and facilitating sustainable fisheries management. Important variation in recruitment dynamics is observed among populations, wherein some populations exhibit asymptotic productivity and others exh...

The eradication of invasive species and associated side effects that influence the reestablishment of biological communities is a major challenge for conservation management of invaded ecosystems. We present a before-and-after-disturbance whole lake manipulation study from a high-elevation mountain lake in which we applied a 2-pronged approach to e...

Predicting the persistence of species under climate change is an increasingly important objective in ecological research and management. However, biotic and abiotic heterogeneity can drive asynchrony in population responses at small spatial scales, complicating species‐level assessments. For widely distributed species consisting of many fragmented...

Climate change is increasing global atmospheric temperatures, which can reduce abundance and cause range shifts in species that are sensitive to warming. However, fine‐scale thermal heterogeneity can drive highly variable local responses to climate change, especially in freshwater environments that differ in groundwater inputs and geomorphology. We...

Invasion of non-native fishes threatens freshwater biodiversity worldwide. Yet, detailed estimates of population demography for invasive species, such as population size and body size, are rarely integrated in evaluating aquatic community responses. Our study capitalised on detailed brook trout population demographic data collected for a replicated...

Analyses of functional trait variation across ecological communities offer valuable insights into the factors that influence and predict trait composition, deepening our understanding of community structure. These analyses also shed light on patterns of trait dispersion, including underdispersion and overdispersion, which are often linked to the me...

Sustainable management of exploited populations benefits from integrating demographic and genetic considerations into assessments, as both play a role in determining harvest yields and population persistence. This is especially important in populations subject to size‐selective harvest, because size selective harvesting has the potential to result...

Natural resources in northern regions are often data-limited because they are difficult and expensive to access. Indigenous ecological knowledge (IEK) can provide information similar to, different from, or complementary to Western scientific data (WSD). We evaluated the general hypothesis that congruence in outcomes of IEK and WSD for population mo...

Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole-genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule p...

Relative to species diversity gradients, the broad scale distribution of population-specific genetic diversity (PGD) across taxa remains understudied. We used nuclear DNA data collected from 6285 vertebrate populations across the Americas to assess the role environmental variables play in structuring the spatial/latitudinal distribution of PGD, a k...

Local support is critical to the success and longevity of fishery management initiatives. Previous research suggests that how resource users perceive ecological changes, explain them, and cope with them, influences local support. The objectives of this study were twofold. First, we collated local fishers' knowledge to characterize the long-term soc...

Analysing the geographical distribution of evolutionary linages can reveal the potential locations of past refugia and colonisation routes and thus can improve understanding of current patterns of genetic variation and adaptive potential. We analysed 94 full mitogenome sequences to assess phylogeographic relationships amongst ten Arctic char (Salve...

Density dependence is a strong regulator of animal populations, operating primarily through intraspecific competition for a limiting resource. Because food is generally limited in natural environments, it is typically assumed that increasing animal density leads to reduced individual fitness through food depletion or monopolization. However, recent...

Beaulieu J, Trépanier-Leroux D, Fischer JM, Olson MH, Thibodeau S, Humphries S, Fraser DJ, Derry AM. 2021. Rotenone for exotic trout eradication: nontarget impacts on aquatic communities in a mountain lake. Lake Reserv Manage. XX:XXX–XXX. Rotenone is widely used in lake and reservoir management for the eradication of exotic fish. However, nontarget...

Rotenone is widely used in lake and reservoir management for the eradication of exotic fish. However, nontarget effects of rotenone on freshwater organisms such as zooplankton and macroinvertebrates are of concern because of the ecological importance of these organisms in aquatic food webs as a resource base for fish, especially when rotenone is ap...

Introduction Road networks and human density are major factors contributing to isolation of wildlife populations causing reduced genetic diversity. Terrestrial mammals are particularly sensitive to roads and human populations. However, there are limited assessments of the impacts of road networks and human density on population‐specific nuclear gen...

The biodiversity hotspot approach is commonly used to identify key regions of conservation priority based on species richness and uniqueness. Like other countries, Canada uses below species-level conservation units, called Designatable Units (DUs), for assessing extinction risk on a case-by-case basis. Researchers have yet to investigate conservati...

Phenotypic reaction norms are often shaped and constrained by selection and are important for allowing organisms to respond to environmental change. However, selection cannot constrain reaction norms for environmental conditions that populations have not experienced. Consequently, cryptic neutral genetic variation for the reaction norm can accumula...

The Restricted Movement Paradigm (RMP) asserts that stream fishes are sedentary, living much of their lives within a single reach. To test the RMP, we implanted eyed Atlantic salmon eggs (Salmo salar L.) into a total of 19 artificial redds, in seven salmon-free streams, in six years, and estimated summer fry dispersal through electrofishing surveys...

Investigating whether changes within fish populations may result from harvesting requires a comprehensive approach, especially in more data‐sparse northern regions. Our study took a three‐pronged approach to investigate walleye population change by combining Indigenous knowledge (IK), phenotypic traits, and genomics. We thank Larson et al. (2020) f...

Organism abundance is a critical parameter in ecology, but its estimation is often challenging. Approaches utilizing eDNA to indirectly estimate abundance have recently generated substantial interest. However, preliminary correlations observed between eDNA concentration and abundance in nature are typically moderate in strength with significant une...

The extent and rate of harvest‐induced genetic changes in natural populations may impact population productivity, recovery and persistence. While there is substantial evidence for phenotypic changes in harvested fishes, knowledge of genetic change in the wild remains limited, as phenotypic and genetic data are seldom considered in tandem, and the n...

Large-scale reintroduction programs for landlocked Atlantic salmon Salmo salar are ongoing in Lakes Ontario and Champlain. Commonly, these programs involve stocking hatchery reared juveniles into streams and thus, quantifying the in situ habitat use of stocked fish can help support these efforts. To examine habitat use, we stocked young-of-the-year...

Elevating winter water temperatures is a common practice when rearing salmonids for supplementation or reintroduction. Doing so elevates developmental rates, producing larger juveniles with greater smolt-to-adult survival, but does not guarantee improved adult returns to stocked tributaries. To test whether more natural developmental conditions imp...

Understanding the complex variation in patterns of density‐dependent individual growth and survival across populations is critical to adaptive fisheries management, but the extent to which this variation is caused by biological or methodological differences is unclear. Consequently, we conducted a correlational meta‐analysis of published literature...

Motivation: Theory describing biodiversity gradients has focused on species richness with less conceptual synthesis outlining expectations for intraspecific diversity gradients, that is, broad-scale population richness and genetic diversity. Consequently, there is a need for a diversity–gradient synthesis that complements species richness with popu...

Reintroduction programs are increasingly implemented to regenerate self-sustaining salmon populations. The extent to which returning adults successfully produce surviving offspring is useful for informing reintroduction efforts but is often unknown, as is the genetic makeup of those offspring. We investigated the patterns of reproductive success (R...

Millions of wild animals in captivity are reared on diets that differ in their uptake and composition from natural conditions. Few studies have investigated whether such novel diets elicit unintentional domestication selection in captive rearing and supplementation programs. In highly fecund salmonid fishes, natural and captive mortality is highest...

Organism abundance is a critical parameter in ecology, but its estimation is often challenging. Approaches utilizing eDNA to indirectly estimate abundance have recently generated substantial interest. However, preliminary correlations observed between eDNA concentration and abundance in nature are typically moderate in strength with significant une...

Little empirical work in nature has quantified how wild populations with varying effective population sizes and genetic diversity perform when exposed to a gradient of ecologically important environmental conditions. To achieve this, juvenile brook trout from 12 isolated populations or closed metapopulations that differ substantially in population...

The Arctic will be especially affected by climate change, resulting in altered seasonal timing. Anadromous Arctic char (Salvelinus alpinus) is strongly influenced by sea surface temperature (SST) delimiting time periods available for foraging in the sea. Recent studies of salmonid species have shown variation at phenology‐related loci associated wi...

Important variation in the shape and strength of density‐dependent growth and mortality is observed across animal populations. Understanding this population variation is critical for predicting density‐dependent relationships in natural populations, but comparisons amongst studies are challenging as studies differ in methodologies and in local envi...

The extent and rate of harvest-induced genetic changes in natural populations may impact population productivity, recovery and persistence. While there is substantial evidence for phenotypic changes in harvested fishes, knowledge of genetic change in the wild remains limited, as phenotypic and genetic data are seldom considered in tandem, and the n...

Evolutionary biologist tend to approach the study of the natural world within a framework of adaptation, inspired perhaps by the power of natural selection to produce fitness advantages that drive population persistence and biological diversity. In contrast, evolution has rarely been studied through the lens of adaptation’s complement, maladaptatio...

Although hybridization can be used as a tool for genetic rescue, it can also generate outbreeding depression and reduce local adaptation. Improved understanding of these processes is required to better inform conservation decisions for threatened populations. Few studies, however, investigate how multiple factors influence hybridization effects. We...

Evolutionary biologists have long trained their sights on adaptation, focusing on the power of natural selection to produce relative fitness advantages while often ignoring changes in absolute fitness. Ecologists generally have taken a different tack, focusing on changes in abundance and ranges that reflect absolute fitness while often ignoring rel...

The use of eDNA to detect the presence/absence of rare or invasive species is well documented and its use in biodiversity monitoring is expanding. Preliminary laboratory research has also shown a positive correlation between the concentration of species‐specific eDNA particles and the density/biomass of a species in a given environment. However, th...

Evolutionary approaches are gaining popularity in conservation science, with diverse strategies applied in efforts to support adaptive population outcomes. Yet conservation strategies differ in the type of adaptive outcomes they promote as conservation goals. For instance, strategies based on genetic or demographic rescue implicitly target adaptive...

Population genetic data from nuclear DNA has yet to be synthesized to allow broad scale comparisons of intraspecific diversity versus species diversity. The MacroPopGen database collates and geo-references vertebrate population genetic data across the Americas from 1,308 nuclear microsatellite DNA studies, 897 species, and 9,090 genetically distinc...

By impeding migration and degrading habitat downstream, dam construction has caused population declines in many migratory fish populations. As part of the landlocked Atlantic salmon (Salmo salar) restoration program in Lake Champlain, the Willsboro Dam was removed from the Boquet River, NY in 2015 providing an opportunity to study the effects of da...

Non-anadromous Atlantic salmon (Salmo salar) exhibit a combination of variation in life history, habitat, and species co-existence matched by few vertebrates. Distributed in eastern North America and northern Europe, habitat ranges from hundreds of metres of river to Europe’s largest lakes. As juveniles, those with access to a lake usually migrate...

Effective remediation of heavy metal pollution in aquatic systems is desired in many regions, but it requires integrative assessments of sediments, water, and biota that can serve as robust biomonitors. We assessed the effects of a 5-year metal contamination remediation along the Xiangjiang River, China, by comparing concentrations of trace metals...

Understanding the extent to which captivity generates maladaptation in wild species can inform species recovery programs and elucidate wild population responses to novel environmental change. Although rarely quantified, effective population size (N e ) and genetic diversity should influence the magnitude of plastic and genetic changes manifested in...

We tested if there was a difference in mass-specific excretion rate between two genetically size-divergent brook trout (Salvelinus fontinalis) populations that can be accounted for by genetic/maternal factors. We conducted laboratory-based common garden experimentation using F1 generation fish, with five to seven families per population at two ages...

Comparing the ratio of effective number of breeders (Nb) to adult population size (N) among closely related coexisting species can provide insights into the role of life history on Nb/N ratios and inform conservation programs towards limiting the loss of evolutionary potential in natural populations. We estimated Nb and N in two coexisting salmonid...

We applied essential fatty acids as a biomarker to experimentally test the effects of a fish-mediated trophic cascade on calanoid copepod nutritional state and functional traits in north-temperate freshwater ponds. A whole-pond experiment was conducted where young-of-the-year brook trout (Salvelinus fontinalis) were introduced into three natural, f...

Partial barriers to migration can affect migratory fish population dynamics and be influenced by many biotic, abiotic, and anthropogenic factors, including nutritional deficiencies. We investigated how such variables (including a thiamine deficiency) impact fine-scale movement of landlocked Atlantic salmon, by treating returning spawners with thiam...

Experimental over harvest aims to expose how compensatory mechanisms (i.e. recruitment and growth) respond to decreased density.

Evolutionarily-informed approaches in conservation typically focus on fostering adaptive responses to human modified environments. Goals guiding such approaches are generally aimed either at maintaining optimal traits (i.e. conservation for an adaptive state) or increasing adaptive potential (i.e. conservation for an adaptive process). When viewed...

Is a key theory of evolutionary and conservation biology-that loss of genetic diversity can be predicted from population size-on shaky ground? In the face of increasing human-induced species depletion and habitat fragmentation, this question and the study of genetic diversity in small populations are paramount to understanding the limits of species...

A reduction in population size due to habitat fragmentation can alter the relative roles of different evolutionary mechanisms in phenotypic trait differentiation. While deter-ministic (selection) and stochastic (genetic drift) mechanisms are expected to affect trait evolution, genetic drift may be more important than selection in small populations....

Multidisciplinary approaches to conservation have become increasingly important in northern regions. Because many First Nations communities have relied on freshwater fish populations for essential food over millennia, community members often possess traditional ecological knowledge (TEK). We consulted Cree First Nation fishers to collate TEK for on...

Technological and methodological advances have facilitated the use of genetic data to infer census population size (Nc) in natural populations, particularly where traditional mark-and-recapture is challenging. The effective number of breeders (Nb) describes how many adults effectively contribute to a cohort and is often correlated with Nc. Predicti...

Radio‐tag signals from fixed‐position antennas are most often used to indicate presence or absence of individuals, or to estimate individual activity levels from signal strength variation within an antenna's detection zone. The potential of such systems to provide more precise information on tag location and movement has not been explored in great...

Dispersal from nesting sites and habitat selection are essential for the fitness of young individuals and shape the distribution, growth, and persistence of populations. These processes are important to consider when releasing young, hatchery-origin fishes into the wild to restore extirpated or depleted populations. By manipulating the density of r...

As climate warming threatens the persistence of many species and populations, it is important to forecast their responses to warming thermal regimes. Climate warming often traps populations in smaller habitat fragments, not only changing biotic parameters, but potentially decreasing adaptive potential by decreasing genetic variability. We examined...

The study of population differentiation in the context of ecological speciation is commonly assessed using populations with obvious discreteness. Fewer studies have examined diversifying populations with occasional adaptive variation and minor reproductive isolation, so factors impeding or facilitating the progress of early stage differentiation ar...

Supplemental genetic data of lake trout in Mistassini Lake. (PDF)

Effective population size (Ne) and gene flow Mistassini lake trout. (PDF)

A full lifecycle understanding of how different captive rearing strategies affect wild fitness is needed for many species of conservation concern. Over the lifecycle of endangered Atlantic salmon, we measured the effects on wild fitness of two widely applied conservation captive rearing strategies. One strategy releases juveniles before the onset o...

Adult census population size (N) and effective number of breeders (Nb) are highly relevant for designing effective conservation strategies. Both parameters are often challenging to quantify, however, making it of interest to determine whether one parameter can be generalized from the other. Yet, the spatiotemporal relationship between N and Nb has...

It is widely thought that small populations should have less additive genetic variance and respond less efficiently to natural selection than large populations. Across taxa, we meta-analytically quantified the relationship between adult census population size (N) and additive genetic variance (proxy: h2) and found no reduction in h2 with decreasing...

It is widely thought that small populations should have less additive genetic variance and respond less efficiently to natural selection than large populations. Across taxa, we meta-analytically quantified the relationship between adult census population size (N) and additive genetic variance (proxy: h (2)) and found no reduction in h (2) with decr...

Most salmon supplementation programs capture and spawn wild adults and release large numbers of their captive-reared juveniles. A rarely adopted alternative is smolt-to-adult supplementation (SAS), wherein migrating smolts are captured, captive-reared until maturation and subsequently released in freshwater. Where marine return rates are low, SAS c...

How population size influences quantitative genetic variation and differentiation among natural, fragmented populations remains unresolved. Small, isolated populations might occupy poor quality habitats and lose genetic variation more rapidly due to genetic drift than large populations. Genetic drift might furthermore overcome selection as populati...

Alternative reproductive phenotypes represent adaptive life-history responses to local environments. Hybridization with domesticated conspecifics exposed to selection against one of the phenotypes could affect the plasticity and incidence of alternative reproductive phenotypes within wild populations, potentially influencing individual fitness and...

The potential influence of population size on the magnitude of phenotypic plasticity, a key factor in adaptation to environmental change, has rarely been studied. Conventionally, small populations might exhibit consistently lower plasticity than large populations if small population habitats are generally poor in quality and if genetic diversity un...

Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to in...

Appendix S6. Summary of studies incorporated in a meta-analysis on survival of domestic-wild hybrids and wild salmonids in natural settings.

Landlocked Atlantic salmon (Salmo salar) were extirpated from Lake Champlain in the early 1800s. Management actions, including sea lamprey control and stocking yearling smolts, provide for a popular salmon fishery in the lake. However, spawning runs of salmon to rivers (i.e., river-runs) have remained low. In 2010, we initiated a long-term adaptive...

Current conservation practices exclude human-generated hybrid populations from protection, as genetic effects of hybridization on wild populations are thought to be long-lasting and potentially irreversible. Some theory, however, predicts otherwise. We transplanted combinations of wild, hatchery and hybridized populations of a fish species to new e...

Maintaining population diversity is critical for species survival. Recent research has documented multiple genetically- and morphologically-distinct fish populations in many large, north temperate lakes. Little is known about lake trout (Salvelinus namaycush) in Mistassini Lake, QC. We aimed to characterize the population structure by using morphol...

In a world undergoing severe anthropogenically induced environmental change, determining characteristics that predict the capacity of fish populations to persist in novel environmental conditions represents an understudied, yet crucial, area of research for conservationists and fisheries management. In the absence of data measuring adaptation withi...

The potential influence of population size on the magnitude of phenotypic plasticity, a key factor in adaptation to environmental change, is uncertain for salmonids. Conventionally, small populations might exhibit consistently lower plasticity than large populations if small population habitats are generally poor in quality and if genetic diversity...

Current conservation practices exclude human-generated hybridized populations from protection, as the genetic effects of hybridization in the wild have been observed to be long-lasting based on neutral genetic markers and are considered potentially irreversible. Theory, however, predicts otherwise for genes under selection. We transplanted combinat...

Small populations are predicted to perform poorly relative to large populations when experiencing environmental change. To explore this prediction in nature, data from reciprocal transplant, common garden, and translocation studies were compared meta-analytically. We contrasted changes in performance resulting from transplantation to new environmen...

The relationship between habitat variability and population size in fragmented habitats is poorly understood, yet might have important evolutionary consequences. For instance, fragmentation could (1) shift habitat characteristics, and by extension, selective regimes, in a consistent direction as populations and the fragments they occupy are reduced...

Human activities are breaking down barriers to interpopulation hybridization with results that range from populations that resist introgression to populations at serious risk of genetic extinction, particularly between wild and hatchery fish because of the routine stocking of lakes and streams containing wild populations. We investigated whether sp...

Phenotypic plasticity underlies much of the variation in life-history expression in fishes. An understanding of potential constraints on life-history plasticity thus may be critical for assessing the resiliency of populations or species to environmental change. Here, several evolutionary hypotheses are formulated for why a depleted lineage of Canad...