Density-dependent processes in the life history of fishes: evidence from laboratory populations of zebrafish Danio rerio

Population regulation is fundamental to the long-term persistence of populations and their responses to harvesting, habitat modification, and exposure to toxic chemicals. In fish and other organisms with complex life histories, regulation may involve density dependence in different life-stages and vital rates. We studied density dependence in body growth and mortality through the life-cycle of laboratory populations of zebrafish Danio rerio. When feed input was held constant at population-level (leading to resource limitation), body growth was strongly density-dependent in the late juvenile and adult phases of the life-cycle. Density dependence in mortality was strong during the early juvenile phase but declined thereafter and virtually ceased prior to maturation. Provision of feed in proportion to individual requirements (easing resource limitation) removed density dependence in growth and substantially reduced density dependence in mortality, thus indicating that 'bottom-up' effects act on growth as well as mortality, but most strongly on growth. Both growth and mortality played an important role in population regulation, with density-dependent growth having the greater impact on population biomass while mortality had the greatest impact on numbers. We demonstrate a clear ontogenic pattern of change in density-dependent processes within populations of a very small (maximum length 5 mm) fish, maintained in constant homogeneous laboratory conditions. The patterns are consistent with those distilled from studies on wild fish populations, indicating the presence of broad ontogenic patterns in density-dependent processes that are invariant to maximum body size and hold in homogeneous laboratory, as well as complex natural environments.     

A review and evaluation of study design considerations for site-specifically assessing the health of fish populations

Since there are not any well developed procedures for site-specifically evaluating the health of fish populations, most field surveillance programs have been restricted to collecting information on chemistry, toxicity, bioaccumulation, biochemical alterations orin situ benthic community structure. Identification of the mechanism and significance of contaminant effects on fish populations depends on the ability to identify changes and to distinguish changes in survival, food availability or food conversion efficiency, from coincidental changes associated with alterations in habitat or natural variability. Preliminary identification of the characteristics of adult fish can be used to cost-effectively focus financial resources on the alterations which are of relevance to interpretation of impacts and identification of causal factors. Proper interpretation requires that appropriate attention be given to monitoring level and strategy, selection of species and timing of sampling, sample size requirements and choice of reference site.     

Measuring the immune system of the three‐spined stickleback – investigating natural variation by quantifying immune expression in the laboratory and the wild

Current understanding of the immune system comes primarily from laboratory‐based studies. There has been substantial interest in examining how it functions in the wild, but studies have been limited by a lack of appropriate assays and study species. The three‐spined stickleback (Gasterosteus aculeatus L.) provides an ideal system in which to advance the study of wild immunology, but requires the development of suitable immune assays. We demonstrate that meaningful variation in the immune response of stickleback can be measured using real‐time PCR to quantify the expression of eight genes, representing the innate response and Th1‐, Th2‐ and Treg‐type adaptive responses. Assays are validated by comparing the immune expression profiles of wild and laboratory‐raised stickleback, and by examining variation across populations on North Uist, Scotland. We also compare the immune response potential of laboratory‐raised individuals from two Icelandic populations by stimulating cells in culture. Immune profiles of wild fish differed from laboratory‐raised fish from the same parental population, with immune expression patterns in the wild converging relative to those in the laboratory. Innate measures differed between wild populations, whilst the adaptive response was associated with variation in age, relative size of fish, reproductive status and S. solidus infection levels. Laboratory‐raised individuals from different populations showed markedly different innate immune response potential. The ability to combine studies in the laboratory and in the wild underlines the potential of this toolkit to advance our understanding of the ecological and evolutionary relevance of immune system variation in a natural setting.     

Behavioral and respiratory responses to stressors in multiple populations of three-spined sticklebacks that differ in predation pressure

Individual animals of the same species inhabiting environments which differ in the frequency and magnitude of stressors often exhibit different physiological and behavioral responses to stressors. Here, we compare the respiratory response to confinement stress, and behavioral responses to ecologically relevant challenges among sticklebacks from 11 different populations varying in predation pressure. We found that sticklebacks from high predation populations breathed faster in response to confinement stress and were, on an average, more behaviorally responsive to a pike behind glass compared with sticklebacks from low predation populations. These patterns differ from the results of studies on other species, highlighting the need for a conceptual framework to understand the proximate and ultimate factors shaping variable responses to stressors over developmental and evolutionary time. Moreover, physiological and behavioral responses were integrated with each other, both at the individual and population levels. In general, fish that were more aggressive and bold in the presence of a predator breathed faster, independent of body size. These results are consistent with the growing body of evidence that individuals differ in a suite of physiological and behavioral mechanisms for coping with challenges in the environment.     

A conceptual framework for the study of modular responses to local environmental heterogeneity within the plant crown and a review of related concepts

Plants respond to local heterogeneity in abiotic and biotic conditions by changing module-level morphology, growth, and reproductive patterns. This paper presents a conceptual framework for the study of modular responses in plant crowns, clarifies the points that should be considered for scaling up from modular responses to the consequences at the whole-plant level, characterizes the interspecific differences in modular response patterns, and discusses their ecological significance. The modular response was defined as either autonomous or interactive, depending on whether the response of a module to its local condition is independent from the conditions of other modules. For evaluation of the autonomy of the modular response, the importance of considering positional relationships and organizational levels of modules was then proposed as these internally affect the modular response pattern, and their interspecific differences were characterized using several concepts. The identification of an autonomous modular unit is essential for scaling up module-level studies to the whole plant. For understanding the ecological significance of the modular response, further interspecific comparisons and assessments of the scale and the predictability of environmental heterogeneity are required. The conceptual framework will be useful for such purposes.     

Predation risk and inter-population variation in antipredator behaviour in the three-spined stickleback, Gasterosteus aculeatus L.

Predation risk from fish and bird predators was assessed at seven Scottish Gasterosteus aculeatus L. sites. Samples of adult male and female sticklebacks and fry from each site were tested with either a model heron or a live pike to measure anti-predator responses. Principal Component Analyses were then used to describe the responses, the first factor to emerge from each multivariate analysis providing an index of overall level of response toward the predator. Significant sexual and inter-population differences in behaviour are described. Sticklebacks from populations at high risk from either predatory fish or birds showed higher fright response scores than fish from low risk sites. In general, adult male sticklebacks are bolder than adult females during interactions with predators.     

Fish population structuring in the North Sea: understanding processes and mechanisms from studies of the movements of adults

Few fish species form single, panmictic populations throughout their geographic range, most form subpopulations or 'stocks' with differing levels of interconnectivity. Different patterns of interconnectivity between subpopulations will give rise to different responses to exploitation and management, but they will also have different capacities to generate the genetic and phenotypic differences often used to discriminate between stocks. Consequently, knowledge of ontogenetic and seasonal patterns in the distribution, movement and behaviour of individuals is crucial to identifying population substructure. This paper considers the evidence gathered about movements and behaviour of adult fishes from mark-recapture and electronic tagging studies for a number of fish species in the North Sea and elsewhere in U.K. waters in an attempt to understand population structure and the processes that may give rise to it.     

Detecting and managing fisheries-induced evolution

Exploitation of fish populations can induce evolutionary responses in life histories. For example, fisheries targeting large individuals are expected to select for early maturation at smaller sizes, leading to reduced fecundity and thus also reduced fisheries yield. These predicted phenotypic shifts have been observed in several fish stocks, but disentangling the environmental and genetic causes behind them has proved difficult. Here, we review recent studies investigating phenotypic shifts in exploited populations and strategies for minimizing fisheries-induced evolution. Responses to selective harvesting will depend on species-specific life-history traits, and on community-level and environmental processes. Therefore, the detection of fisheries-induced evolution and successful fish stock management requires routine population monitoring, and a good understanding of genetics, relevant ecological processes and changing environmental conditions.     

Illuminating geographical patterns in species' range shifts

Species' range shifts in response to ongoing climate change have been widely documented, but although complex spatial patterns in species' responses are expected to be common, comprehensive comparisons of species' ranges over time have undergone little investigation. Here, we outline a modeling framework based on historical and current species distribution records for disentangling different drivers (i.e. climatic vs. nonclimatic) and assessing distinct facets (i.e. colonization, extirpation, persistence, and lags) of species' range shifts. We used extensive monitoring data for stream fish assemblages throughout France to assess range shifts for 32 fish species between an initial period (1980–1992) and a contemporary one (2003–2009). Our results provide strong evidence that the responses of individual species varied considerably and exhibited complex mosaics of spatial rearrangements. By dissociating range shifts in climatically suitable and unsuitable habitats, we demonstrated that patterns in climate‐driven colonization and extirpation were less marked than those attributed to nonclimatic drivers, although this situation could rapidly shift in the near future. We also found evidence that range shifts could be related to some species' traits and that the traits involved varied depending on the facet of range shift considered. The persistence of populations in climatically unsuitable areas was greater for short‐lived species, whereas the extent of the lag behind climate change was greater for long‐lived, restricted‐range, and low‐elevation species. We further demonstrated that nonclimatic extirpations were primarily related to the size of the species' range, whereas climate‐driven extirpations were better explained by thermal tolerance. Thus, the proposed framework demonstrated its potential for markedly improving our understanding of the key processes involved in range shifting and also offers a template for informing management decisions. Conservation strategies would greatly benefit from identifying both the geographical patterns and the species' traits associated with complex modifications of species' distributions in response to global changes.     

Environmental monitoring through protist next‐generation sequencing metabarcoding: assessing the impact of fish farming on benthic foraminifera communities

The measurement of species diversity represents a powerful tool for assessing the impacts of human activities on marine ecosystems. Traditionally, the impact of fish farming on the coastal environment is evaluated by monitoring the dynamics of macrobenthic infaunal populations. However, taxonomic sorting and morphology‐based identification of the macrobenthos demand highly trained specialists and are extremely time‐consuming and costly, making it unsuitable for large‐scale biomonitoring efforts involving numerous samples. Here, we propose to alleviate this laborious task by developing protist metabarcoding tools based on next‐generation sequencing (NGS) of environmental DNA and RNA extracted from sediment samples. In this study, we analysed the response of benthic foraminiferal communities to the variation of environmental gradients associated with salmon farms in Scotland. We investigated the foraminiferal diversity based on ribosomal minibarcode sequences generated by the Illumina NGS technology. We compared the molecular data with morphospecies counts and with environmental gradients, including distance to cages and redox used as a proxy for sediment oxygenation. Our study revealed high variations between foraminiferal communities collected in the vicinity of fish farms and at distant locations. We found evidence for species richness decrease in impacted sites, especially visible in the RNA data. We also detected some candidate bioindicator foraminiferal species. Based on this proof‐of‐concept study, we conclude that NGS metabarcoding using foraminifera and other protists has potential to become a new tool for surveying the impact of aquaculture and other industrial activities in the marine environment.     

Relationship Patterns between Ichthyoplankton and Zooplankton: A Conceptual Model

Selected cases of plankton studies were analyzed to illustrate the main types of relationships between the zooplankton and the ichthyoplankton abundance observed in the pelagic realm. Such relationships may exhibit a positive, a negative, or a random pattern. In the conceptual model here proposed, short-term oscillations among these patterns were attributed to small-scale biological processes, such as competition, predation, and intraguild predation, acting in conjunction with water turbulence. A negative relationship between zooplankton and ichthyoplankton abundance may be caused both by predation on fish eggs and larvae, and by detrimental competition and intraguild predation interactions for fish larvae. In contrast, positive relationships emerge from the absence or low abundance of major predators on the ichthyoplankton, and from food availability for fish larvae and competing species. The random pattern may appear as a gradual transitional stage between the negative and positive patterns, or be promoted by strong water turbulence – which generates random movements of individuals. The size of zooplankters greatly influences these small-scale phenomena. Hence, their role in the trophic web, the success in competition interactions and vulnerability to water turbulence depends on their size. Intra- and interspecific competition may be reduced by variability in body size within or among fish larvae populations. Owing to a strong interaction among phenomena at different scales, these small-scale processes are also influenced by larger scale features, such as seasonal changes in zooplankton biomass, water currents, or spawning periods of fish. At the space level, some theoretical studies have emphasized the role of water currents as a vector for fish larvae to reach the nursery grounds (migration triangle hypothesis), or to allow them to remain within their own population’s distributional area (member/vagrant hypothesis). At the temporal level, the match/mismatch theory insists in a synchrony between reproductive strategies of fish and cyclical changes in abundance and size spectrum of potential prey items for their larvae. In any case, a coincidence between favorable abiotic and biotic features during the whole life-cycle of fish would assure a success in survival of larvae and their subsequent recruitment to adult population.     

Overview of Fish Consumption Rates in the United States

Contaminants that accumulate in fish may pose health risks and have raised concerns among consumers. Contaminated finfish and shellfish are possible routes of human exposure to toxic chemicals. Fish advisories are established to protect local populations from the consumption of contaminated commercial and non-commercially caught fish. Children, women of childbearing age, and subsistence fishermen or other highly exposed individuals who for socioeconomic or cultural reasons consume more fish than the general population are among the populations of concern from the ingestion of contaminated fish. Estimating exposure to a toxic chemical among fish-consuming populations requires knowledge about intake rates of fish and shellfish. Data on fish consumption rates come from various sources, including national, state, and local government studies. Although these data have their limitations, they serve as a source for deriving fish consumption rates that may be used by exposure assessors. Data on specific populations of concern are critical. Studies presented here show that ethnicity, age, and geographical region play an important role in fishing behavior and consumption. Results from studies on Native American populations show that this ethnic group eats fish at a higher rate than recreational anglers. This article summarizes data on fish consumption for various populations and provides a framework for evaluating data from these studies for exposure assessment applications.     

A new approach to species distributional indicators for the Marine Strategy Framework Directive (MSFD)

We propose alternative fish-populations spatial indicators for use in the Marine Strategy Framework Directive (MSFD). Following Commission Decision 2010/477, we have applied two different spatial indicators to three fish populations with “slow type” life-history traits, i.e. slow growing like Helicolenus dactylopterus, or large bodied like Merluccius merluccius and Lophius budegassa. We tested their efficiency separately and combined. One of these indicators, the presence/absence of the population in sampling squares, had already been applied during the initial assessment of the MSFD in Spain. Another indicator, the geographical spread, is proposed here as a new monitoring tool for the MSFD in Spanish waters. The results demonstrate for the three populations analyzed that neither indicator was sufficient alone to describe the population spatial pattern or its evolution. Thus, the approach to implementing the MSFD indicated in Commission Decision 2010/477 is not sufficient to provide integrated information about the spatial behavior of the fish populations analyzed. Although numerical targets or threshold values cannot be set, directional targets could be proposed, based on the results of both indicators, if evaluation of them is extended to more species and more geographical areas. The analysis could be extended to other “slow type” populations within the fish community and also to different ecoregions. We propose an approach including the estimation of two different indicators to monitoring both the area occupied and the geographical spread of fish populations within communities, interpreting them together to generate a more complete picture of the spatial patterns of those populations. In spite of the difficulties in fixing numerical targets or thresholds, or in distinguishing between environmentally and human driven changes in the population spatial distributions, this approach helps to summarize fish spatial behavior. It improves information from the indicators applied alone and reduces the requirement for a large number of maps (except for some particular event or population). The proposed indicators can be readily used by managers and politicians.     

A cytokinetic model for heterogeneous mammalian cell populations. III. Tritiated thymidine studies: Correlations among multiple kinetic parameters in human tumors

A computer model for the simulation of radioautographic studies in growing mammalian cell populations was used to study multiple tritiated thymidine (³HTdR) associated parameters in model populations whose properties are comparable to those found in human tumors. Several different DNA synthesis rate patterns are distinguishable, designated type I, intermediate, and type II. Correlations among percent labelled mitosis (PLM) curves, interphase cell labelling patterns, and continuous ³HTdR labelling studies suggest a type I pattern in human breast cancer, an intermediate pattern in human melanoma, and a type II pattern in human adult leukemia. Detailed simulation studies were carried out in human adult acute leukemia and human melanoma. It was possible to fit all available kinetic data in leukemia and melanoma, both with respect to low threshold data, and with respect to radioautographic labelling intensity, provided that simulated experimental conditions and simulated radioautographic conditions corresponded to those actually employed. Kinetic differences between leukemia and melanoma were demonstrated which are in keeping with the natural histories and clinical drug response behavior of these two malignancies.     

Rapid morphological divergence of a stream fish in response to changes in water flow

Recent evidence indicates that evolution can occur on a contemporary time scale. However, the precise timing and patterns of phenotypic change are not well known. Reservoir construction severely alters selective regimes in aquatic habitats due to abrupt cessation of water flow. We examined the spatial and temporal patterns of evolution of a widespread North American stream fish (Pimephales vigilax) in response to stream impoundment. Gross morphological changes occurred in P. vigilax populations following dam construction in each of seven different rivers. Significant changes in body depth, head shape and fin placement were observed relative to fish populations that occupied the rivers prior to dam construction. These changes occurred over a very small number of generations and independent populations exhibited common responses to similar selective pressures. The magnitude of change was observed to be greatest in the first 15 generations post-impoundment, followed by continued but more gradual change thereafter. This pattern suggests early directional selection facilitated by phenotypic plasticity in the first 10–20 years, followed by potential stabilizing selection as populations reached a new adaptive peak (or variation became exhausted). This study provides evidence for rapid, apparently adaptive, phenotypic divergence of natural populations due to major environmental perturbations in a changing world.     

Spotted Wing Drosophila Prefer Low Hanging Fruit: Insights into Foraging Behavior and Management Strategies

Spotted wing drosophila, Drosophila suzukii, is an invasive insect that attacks ripe, small fruit such as raspberries, blackberries and blueberries. Little is known about its foraging ecology and current trapping methods and monitoring systems are ineffective at commercial scales. In semi-field studies, we evaluated adult alightment and ovipositional preference within and among raspberry plants using sentinel Tangletrap-coated and clean raspberry fruit, respectively, positioned within the exterior and interior plant canopy at four different heights (60, 85, 110 and 135 cm from the base) and conducted in field cages using sexually mature adults. Alightment of adults on Tangle-trap-coated fruit indicated a preference for fruit positioned at lower heights and/or interior locations based on significantly greater numbers being captured on sentinel sticky-coated berries at the two lowest heights. Oviposition in clean raspberry fruit also yielded a similar pattern. In mark-release-recapture studies conducted in the field, spotted wing drosophila prefer sentinel sticky fruit positioned on exterior rows as they alighted on these berries in significantly greater numbers than fruit at in the central portion of the plot. Likewise, in field trials with wild fly populations, infestations were significantly greater in edge rows compared with interior rows. Collectively, our results suggest that monitoring and behaviorally based management strategies may be more effective if they target adults foraging in the lower canopy of small fruit plants located on the crop perimeter.     

Are local weather,NDVI and NAO consistent determinants of red deer weight across three contrasting European countries?

There are multiple paths via which environmental variation can impact herbivore ecology and this makes the identification of drivers challenging. Researchers have used diverse approaches to describe the association between environmental variation and ecology, including local weather, large-scale patterns of climate, and satellite imagery reflecting plant productivity and phenology. However, it is unclear to what extent it is possible to find a single measure that captures climatic effects over broad spatial scales. There may, in fact, be no a priori reason to expect populations of the same species living in different areas to respond in the same way to climate as their population may experience limiting factors at different times of the year, and the forms of regulation may differ among populations. Here, we examine whether the same environmental indices [seasonal Real Bioclimatic Index (RBI), seasonal Normalized Difference Vegetation Index (NDVI) and winter North Atlantic Oscillation (NAO)] influence body size in different populations of a large ungulate living in Mediterranean Spain, Western Scotland and Norway. We found substantial differences in the pattern of weight change over time in adult female red deer among study areas as well as different environmental drivers associated with variation in weight. The lack of general patterns for a given species at a continental scale suggest that detailed knowledge regarding the way climate affects local populations is often necessary to successfully predict climate impact. We caution against extrapolation of results from localized climate–population studies to broad spatial scales.     

A scalar analysis of landscape connectivity

Landscape connectivity is critical to the maintenance of spatially-structured populations and consists of both a structural component, which describes the shape, size and location of landscape features; and a biological component, which consists of both the response of individuals to landscape features, and the patterns of gene flow that result from those individual responses. Traditional studies of landscape connectivity have attempted to discern individual behavioral responses to landscape features, but this methodology is intractable for many species. This paper is an attempt to relate the components of landscape connectivity through the explicit treatment of their spatial and temporal scales. Traditional measures of structural and biological components of connectivity are reviewed and more recently developed methods for the analysis of scale for each are introduced. I then present a framework for the comparison of scalar phenomena based on Watt's unit pattern, describe the potential outcomes of the comparison and discuss the implications of each. Several testable hypotheses emerge from the analysis that may serve as a useful framework for the investigation of landscape connectivity in the future .     

A holistic approach to ecosystem health assessment using fish population characteristics

The status of a fish population is a reflection of the overall condition of the aquatic environment in which that population resides. As such, fish population characteristics can be used as indicators of environmental health. Simple and inexpensive methods to follow fish population responses to environmental degradation are lacking. This paper outlines a protocol whereby environmental impacts on fish populations are classified by five patterns based on characteristics such as mean age, fecundity and condition factor. The patterns summarize population changes and describe responses to exploitation, recruitment failure, the presence of multiple stressors, food limitation and niche shifts. Classification is best based on the selection, and appropriate sampling, of a comparable reference population. Population characteristics can be used to examine ecosystems exposed to stressors for evidence of long-term damage, and when used with biochemical indicators, can be a powerful tool for ecosystem health assessment. The five responses are illustrated using published data on a number of species challenged by increased predation pressure, acidification, eutrophication, mine waste and reservoir impoundment. Application of this scheme will aid in directing and focusing research efforts on crucial aspects impacted by changing conditions.