Being there and getting there: balancing the costs of migration against the benefits of changing habitat for North Sea plaice

To improve survival and reproductive success, many fish species have evolved migratory life‐histories, showing ontogenetic and/or seasonal changes in habitat use. Individuals move between different areas, each of which is 'best' for a particular activity, such as feeding, growing or spawning. The benefits of moving to a different habitat, however, have to be balanced against the costs of migration, so any behaviour that reduces the cost of movement would be expected to expand the migratory range and thereby increase the range of habitats that can be exploited.
Previous tracking experiments in the southern North Sea have shown that plaice selectively exploit the tidal streams to aid their spawning migration. Here we examine whether this behaviour is primarily (1) an energy‐saving strategy, or (2) a transport mechanism by which fish that are unable to navigate over long distances can be carried reliably between feeding and spawning grounds. Because selective tidal stream transport requires that fish remain stationary on the sea‐bed during the 'non‐transporting' tide, energetic calculations predict that this behaviour is beneficial only when the current speed exceeds a critical, size‐dependent, value. We have used detailed information about migratory behaviour from individual fish to calculate the metabolic costs and the likely reproductive benefits of different migratory strategies. Our results show that plaice use selective tidal stream transport only in areas where the tidal streams are suitably fast, indicating that this behaviour is primarily an energy saving strategy.     

Growing large in a low grade environment: size dependent foraging gain and niche shifts to cannibalism in Arctic char

Arctic char ( Salvelinus alpinus ) living in allopatry in lakes often show a distinct size dimorphism where the large char prey upon small char. We studied the relationship between size scaling of energy intake, total metabolic costs and levels of storage energy related to the niche shift from invertebrate feeding to cannibalism in an alpine Arctic char population. Gill-net samples consisted of two distinct size modes, small invertebrate feeding char (92–172 mm total length) and large cannibalistic char (265–606 mm total length). Food consumption was estimated for a one year period using a radioactive tracer (¹³⁷Cs). The energy intake followed a hump-shaped relationship with fish size for invertebrate feeding char and increased monotonically with size for cannibalistic char. Total metabolic costs increased exponentially with size for both groups. Char feeding in the invertebrate niche had a maximum net energy gain at 140 mm total length with an upper size limit for positive net energy gain at 180 mm. For cannibals the relationship between size and net energy gain formed a hump shaped function with maximum net energy gain at 400 mm and a lower size limit for positive net energy gain at 230 mm. The size at maturation for both small and large char was close to the size for maximum energy gain in their respective niches. Immature individuals close to the upper size limit for positive net energy gain in the invertebrate niche had low levels of storage lipids but tended to have high mass specific growth rates. This may imply a reallocation from reversible (stored) energy to structural (length) growth as a strategy to transform into the size-range where the cannibalistic niche successfully could be exploited.     

Trophic niche width,offspring condition and immunity in a raptor species

Strategies developed by organisms to maximize foraging efficiency have a strong influence on fitness. The way in which the range of food resources is exploited has served to classify species, populations and individuals from more specialist (narrow trophic niche) to more generalist (broad trophic niche). Recent studies have provided evidence that many of the considered generalist species/populations are actually composed of different specialist individuals (individual specialization). Even the existence of generalism as an adaptive strategy has been questioned. In this study, we investigated the relationship between trophic niche width, individual quality and offspring viability in a population of common kestrel Falco tinnunculus during 4 years. We showed that the diet of kestrels varied significantly among years and that individuals of better quality fed their offspring with a higher diversity of prey species and a higher amount of food. Moreover, body condition and immune response of nestlings were positively correlated with diversity of prey delivered by parents. Our study suggests that generalism has the potential to increase fitness and that broadening the trophic niche may be an adaptive strategy in unpredictable environments.     

Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

The objectives of this work were to examine the past, current and potential influence of global climate change on the spatial distribution of some commercially exploited fish and to evaluate a recently proposed new ecological niche model (ENM) called nonparametric probabilistic ecological niche model (NPPEN). This new technique is based on a modified version of the test called Multiple Response Permutation Procedure (MRPP) using the generalized Mahalanobis distance. The technique was applied in the extratropical regions of the North Atlantic Ocean on eight commercially exploited fish species using three environmental parameters (sea surface temperature, bathymetry and sea surface salinity). The numerical procedure and the model allowed a better characterization of the niche (sensu Hutchinson) and an improved modelling of the spatial distribution of the species. Furthermore, the technique appeared to be robust to incomplete or bimodal training sets. Despite some potential limitations related to the choice of the climatic scenarios (A2 and B2), the type of physical model (ECHAM 4) and the absence of consideration of biotic interactions, modelled changes in species distribution explained some current observed shifts in dominance that occurred in the North Atlantic sector, and particularly in the North Sea. Although projected changes suggest a poleward movement of species, our results indicate that some species may not be able to track their climatic envelope and that climate change may have a prominent influence on fish distribution during this century. The phenomenon is likely to trigger locally major changes in the dominance of species with likely implications for socio‐economical systems. In this way, ENMs might provide a new management tool against which changes in the resource might be better anticipated.     

Overlapping niches between two co-occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus

Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length–weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.     

Predator biomass and vegetation influence the coastal distribution of threespine stickleback morphotypes

Intraspecific niche differentiation can contribute to population persistence in changing environments. Following declines in large predatory fish, eutrophication, and climate change, there has been a major increase in the abundance of threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea. Two morphotype groups with different levels of body armor—completely plated and incompletely plated—are common in coastal Baltic Sea habitats. The morphotypes are similar in shape, size, and other morphological characteristics and live as one apparently intermixed population. Variation in resource use between the groups could indicate a degree of niche segregation that could aid population persistence in the face of further environmental change. To assess whether morphotypes exhibit niche segregation associated with resource and/or habitat exploitation and predator avoidance, we conducted a field survey of stickleback morphotypes, and biotic and abiotic ecosystem structure, in two habitat types within shallow coastal bays in the Baltic Sea: deeper central waters and shallow near‐shore waters. In the deeper waters, the proportion of completely plated stickleback was greater in habitats with greater biomass of two piscivorous fish: perch (Perca fluviatilis) and pike (Esox lucius). In the shallow waters, the proportion of completely plated stickleback was greater in habitats with greater coverage of habitat‐forming vegetation. Our results suggest niche segregation between morphotypes, which may contribute to the continued success of stickleback in coastal Baltic Sea habitats.     

大型年长鱼类对海洋生态系统生物资源养护的作用

随着人口增长和渔业资源需求的上升,人类沿着食物网营养级自上向下捕捞渔业资源的趋势仍在持续,导致海洋生物多样性丧失及其生态功能与服务价值迅速下降。由捕捞活动造成的渔业诱导进化进一步导致鱼类资源小型化已受到国内外学者的广泛关注。从大型年长鱼类这一独特视角出发,综述了大型年长鱼类在种群繁衍过程中的作用,其具备巨大的繁殖能量输出、丰富的亲本繁殖经验以及强大的年龄组繁殖力贡献,更有利于种群的延续;大型年长鱼类对于初次性成熟亲鱼生殖洄游具有一定的引领作用,并在季节性集群繁殖过程中占据主导地位,可通过抑制小个体同类繁殖维护种群结构的稳定;大型年长鱼类在生态系统中更是占据了较高营养级和广阔的生态位宽度,面对生态环境的改变,具有更强的适应调控能力;大型年长鱼类在种群基因交流过程中亦起到十分关键的作用。保护大型年长鱼类更有利于鱼类种群的快速恢复,这为生物资源养护和渔业管理政策制定方面提供了一定的参考。     

Auto-adaptive Alpha Allocation: A Strategy to Mitigate Risk on Study Assumptions

In some clinical development programs, there are potential biomarkers with promising but uncertain predictive effect, while the probability of success in the overall population cannot be readily dismissed. It is risky to focus only on the overall population, or just the biomarker subpopulation. In 2009, Chen and Beckman proposed a Bayesian decision framework to optimize the type I error rate (alpha) allocation in a Phase III clinical study with possible predictive subset effect. The utilization of internal data in this framework is of particular interest because it provides an opportunity to mitigate the potential risk of misspecified study assumptions using an auto-adaptive strategy. In this paper, we examine this auto-adaptive strategy in detail through extensive numerical case studies and provide guidance on the appropriate use of partial current trial (internal) data in this data-driven optimization framework. We show that internal data can be used to inform the alpha allocation to hypothesis testing in the overall population and the subgroup. The resulting adaptive testing strategy is robust with respect to the uncertainty in the predictive subgroup effect and biomarker prevalence.     

Spotting the right location— imaging approaches to resolve the intracellular localization of invasive pathogens

Background

A common strategy of microbial pathogens is to invade host cells during infection. The invading microbes explore different intracellular compartments to find their preferred niche.

Scope of Review

Imaging has been instrumental to unravel paradigms of pathogen entry, to identify their exact intracellular location, and to understand the underlying mechanisms for the formation of pathogen-containing niches. Here, we provide an overview of imaging techniques that have been applied to monitor the intracellular lifestyle of pathogens, focusing mainly on bacteria that either remain in vacuolar-bound compartments or rupture the endocytic vacuole to escape into the host's cellular cytoplasm.

Major Conclusions

We will depict common molecular and cellular paradigms that are preferentially exploited by pathogens. A combination of electron microscopy, fluorescence microscopy, and time-lapse microscopy has been the driving force to reveal underlying cell biological processes. Furthermore, the development of highly sensitive and specific fluorescent sensor molecules has allowed for the identification of functional aspects of niche formation by intracellular pathogens.

General Significance

Currently, we are beginning to understand the sophistication of the invasion strategies used by bacterial pathogens during the infection process- innovative imaging has been a key ingredient for this.This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.     

Population dynamics of two small pelagic fish in the central-south area off Chile: delayed density-dependence and biological interaction

It is widely believed that environmental variability is the main cause for fluctuations in commercially exploited small pelagic fish populations around the world. Nevertheless, density-dependent factors also can drive population dynamics. In this paper, we analyzed thirteen years of a relative abundance index of two clupeoids fish populations coexisting in the central-south area off Chile, namely the common sardine, Strangomera bentincki, and anchovy, Engraulis ringens. We applied the classical diagnostic tools of time series analysis to the observed time-series. Also, the realized per capita population growth rate was studied with the aim of detecting the feedback structure that is characterizing the population dynamics of the two species. The analysis suggests that population fluctuations of the two species have an important density-dependent component, displaying first-order (direct density-dependent) and second-order (delayed density-dependent) simultaneously. The density-dependent component explained 70.5 and 55.6 % of the realized per capita population growth rate of common sardine and anchovy, respectively. The deterministic skeleton model showed an asymptotic convergence to equilibrium density. In presence of a stochastic environment, fluctuations were reproduced for the species showing a component of fluctuation with a period of 4 year. The intrinsic dynamics of each species is typical of interacting species resulting from trophic interactions. It is postulated that the second-order dynamics of S. bentincki and E. ringens in central-south Chile, may be the result from interactions with a specialist predator (the fishing fleet), interacting with exogenous environmental factors.     

Diel changes in resource use and diet overlap in temperate stream fishes

Interspecific variation in diel-scale temporal niches is common in natural communities. Such variation changes population dynamics via effects on the growth and reproduction of individuals. Also at the community level, theory predicts that animals can reduce competition for shared resources by changing diel activity in certain situations. However, the role of diel activity at the community-level has not been examined sufficiently. In this study, to examine whether the diel-scale temporal niche act as a competition-mitigating mechanism for stream fishes at the community level, we surveyed diel changes in microhabitat use and foraging, and the pattern of interspecific diet overlap in the middle reaches of a temperate stream where various fish species that seemed to be either nocturnal or diurnal coexisted. Our results suggest that the fishes forage during both daytime and night, but change their foraging mode at different times of the day, so that the foraging habits of these fish species cannot be divided simply into nocturnal and diurnal. Furthermore, fishes appeared to aggregate in the vicinity of common food resources during time zones with high availability of the resources, and therefore, inter-guild diet overlap was high during certain time zones. On the other hand, when inter-guild diet overlap was low, each fish species used foods or microhabitats that did not any have the potential to be used by species of another guild. Therefore, we conclude that variation in diel niche use is influenced by variation in the fundamental niche and food supply or availability rather than by competitive interaction between fishes in the stream fish community.     

Infectious disease in fish: global risk of viral hemorrhagic septicemia virus

As the global human population continues to increase and become more industrialized, the need for safe, secure, and sustainable protein production is critical. One sector of particular importance is seafood production, where capture fishery and aquaculture industries provide 15–20% of the global protein supply. However, fish production can be severely affected by diseases. Notably, viral hemorrhagic septicemia, caused by the viral hemorrhagic septicemia virus (VHSv; Rhabdoviridae), may be one of the most devastating viral diseases of fishes worldwide. We explored the ecology and epidemiology of VHSv using an ecological niche modeling approach to identify vulnerable disease-free regions. Results showed an impressive ecological plasticity of VHSv. The virus was found in >?140 fish species in marine and freshwater ecosystems, with high diversity of lineages in Eurasia. Sub-genotypes from marine and fresh waters were ecologically similar, suggesting broad ecological niches, rather than rapid evolutive adaptation to novel environments. Ecological niche models predicted that VHSv may have favorable physical (e.g., temperature, runoff), chemical (e.g., salinity, pH, phosphate), and biotic (i.e., chlorophyll) conditions for establishing into areas with important fish industries that, so far, are believed to be disease-free (i.e., freshwater and marine ecosystems of Africa, Latin America, Australia, and inland China). The model and our review suggest fish species from the Perciformes, Salmoniformes, and Gadiformes orders are likely to be infected with VHSv in novel regions as the virus expands its range to areas predicted to be at risk. In conclusion, VHSv remains an emerging disease threat to global food security and aquatic biodiversity.     

Periodic Lotka-Volterra competition equations

The Lotka-Volterra competition equations with periodic coefficients derived from the MacArthur-Levins theory of a one-dimensional resource niche are studied when the parameters are allowed to oscillate periodically in time. Specifically, niche positions and widths, resource availability and resource consumption rates are allowed small amplitude periodicities around a specified mean value. Two opposite cases are studied both analytically and numerically. First only resource consumption rates are allowed to oscillate while niche dimensions and resource availability are held constant. The resulting oscillations in population densities and the strength of the system stability as they depend upon crucial relative phase and amplitude differences between the species' consumption rates are studied. This leads to a clear notion of "temporal niche" and of the effects that such oscillations can have on competitive coexistence. Secondly, all system parameters are allowed to oscillate, although the oscillatory consumption rates are assumed identical for both species. The effects on the population density oscillations and their averages are studied and the "best" choice of the common, periodic resource consumption rate for these two "identical" species competing for similar (even identical) niches is considered.     

Identifying climatic niche shifts using coarse‐grained occurrence data: a test with non‐native freshwater fish

Aim We tested whether coarse‐grained occurrence data can be used to detect climatic niche shifts between native and non‐native ranges for a set of widely introduced freshwater fishes. Location World‐wide. Methods We used a global database of freshwater fish occurrences at the river basin scale to identify native and non‐native ranges for 18 of the most widely introduced fish species. We also examined climatic conditions within each river basin using fine‐grained climate data. We combined this information to test whether climatic niche shifts have occurred between native and non‐native ranges. We defined climatic niche shifts as instances where the ranges of a climatic variable within native and non‐native basins exhibit zero overlap. Results We detected at least one climatic niche shift for each of the 18 studied species. However, we did not detect common patterns in the thermal preference or biogeographic origin of the non‐native fish, hence suggesting a species‐specific response. Main conclusions Coarse‐grained occurrence data can be used to detect climatic niche shifts. They also enable the identification of the species experiencing niche shifts, although the mechanisms responsible for these shifts (e.g. local adaptation, dispersal limitation or physiological constraints) have yet to be determined. Furthermore, the coarse‐grained approach, which highlights regions where climatic niche shifts have occurred, can be used to select specific river basins for more detailed, fine‐grained studies.     

Proposed methods and endpoints for defining and assessing adverse environmental impact (AEI) on fish communities/populations in Tennessee River reservoirs

Two multimetric indices have been developed to help address fish community (reservoir fish assemblage index [RFAI]) and individual population quality (sport fishing index [SFI]) in Tennessee River reservoirs. The RFAI, with characteristics similar to the index of biotic integrity (IBI) used in stream fish community determinations, was developed to monitor the existing condition of resident fish communities. The index, which incorporates standardized electrofishing of littoral areas and experimental gill netting for limnetic bottom-dwelling species, has been used to determine residential fish community response to various anthropogenic impacts in southeastern reservoirs. The SFI is a multimetric index designed to address the quality of the fishery for individual resident sport fish species in a particular lake or reservoir[4]. The SFI incorporates measures of fish population aspects and angler catch and pressure estimates. This paper proposes 70% of the maximum RFAI score and 10% above the average SFI score for individual species as "screening" endpoints for balanced indigenous populations (BIP) or adverse environmental impact (AEI). Endpoints for these indices indicate: (1) communities/populations are obviously balanced indigenous populations (BIP) indicating no adverse environmental impact (AEI), or are "screened out"; (2) communities/populations are considered to be potentially impacted; and (3) where the resident fish community/population should be considered adversely impacted. Suggestions are also made concerning how examination of individual metric scores can help determine the source or cause of the impact.     

Analysis of the Trojan Y chromosome model for eradication of invasive species in a dendritic riverine system

The use of Trojan Y chromosomes has been proposed as a genetic strategy for the eradication of invasive species. The strategy is particularly relevant to invasive fish species that have XY sex determination system and are amenable to sex-reversal. In this paper we study the dynamics of an invasive fish population occupying a dendritic domain in which Trojan individuals bearing multiple Y chromosomes have been released as a means of eradication. We demonstrate the existence of a bounded absorbing set that represents extinction of the invasive species irrespective of the dendritic configuration. The method of analysis used to obtain global estimates could be applied to other population problems and other geometries.     

Generalist niche, specialist strategy: the diet of an Australian percichthyid

Dietary analysis revealed that an impoundment population of Australian bass Macquaria novemaculeata holds a generalist niche, but one arising from persistent individual specialization and interindividual variation. This 'individual specialist' strategy appeared adaptive, but the strength of individual specialization was largely independent of variation in diet composition, except during blooms of Daphnia sp. Diet composition and dietary overlap showed only moderate ontogenetic variation, and niche breadth showed no relationship with ontogeny. Macquaria novemaculeata showed an asymmetric predator and prey size distribution, consistent with many aquatic predators, with positive relationships between fish size and average, maximum and minimum prey size. There was no asymmetry in the relative size-based niche breadths of individuals, however, which indicates that the niche is a fixed 'window' of relative prey sizes. The difference in the dietary niche and prey-size relationships of M. novemaculeata at the population and individual levels highlights the necessity of assessing the niche at both these levels.     

Beyond ecological opportunity: Prey diversity rather than abundance shapes predator niche variation

1. Ecological opportunity (i.e. the diversity of available resources) has a pivotal role in shaping niche variation and trophic specialisation of animals. However, ecological opportunity can be described with regard to both diversity and abundance of resources. The degree to which these two components contribute to niche variation remains unexplored.
2. To address this, we used an extensive dataset on fish diet and benthic invertebrate diversity and density from 73 sampling events in three Norwegian rivers in order to explore realised trophic niches and the response of dietary niche variation along gradients of resource diversity (potential trophic niches), resource density (as a proxy of resource abundance) and fish density (as a proxy of inter‐ and intra‐specific competition) in a freshwater top predator (the brown trout, Salmo trutta L.).
3. Linear models indicated that individual and population niche variation increased with increasing ecological opportunity in terms of prey diversity. However, no simple cause‐and‐effect associations between niche indices and prey abundance were found. Our multiple regression analyses indicated that the abundance of certain resources (e.g. Chironomidae) can interact with prey diversity to determine individual and population realised trophic niches. Niche variation (within‐individual component and inter‐individual diet variation) decreased with increasing inter‐ and intra‐specific competition.
4. This study extends prevailing trophic ecology theory by identifying diversity, rather than density, of available prey resources as a primary driver of niche variation in fish of temperate riverine systems with no extensive resource limitation. The study also shows that ecological opportunity may mask the direction of the effect (compression or expansion) of competition on niche variation when food resources are diverse.
5. Our study provides novel empirical insight to the driving forces behind niche variation and reveals that diversity, rather than density, of available prey resources may be a primary driver of niche variation in freshwater fish. Our study supports the view that a broader potential trophic niche promotes broader realised trophic niche variation by individuals, which leads to individual niche diversification by opening access to alternatives resources, resulting in a concomitant rise in the realised trophic niche width of the population.

     

Range size, dispersal and niche breadth in the herbaceous flora of central England

1 It has been suggested that rare species differ from related common species in a variety of traits, including (among others) niche breadth and dispersal ability. We set out to test these ideas in the flora of central England.
2 We used two measures of range: number of hectads in Britain (national range) and number of 1 km² in a 3000-km² area of central England (local range). In each case we regressed phylogenetically independent contrasts in geographical range against contrasts in range of germination temperature (one aspect of fundamental niche breadth), terminal velocity of dispersule (a measure of wind dispersal capacity), seed weight and specialism index (a measure of the diversity of habitats exploited in central England). Seed weights and germination temperature were known for 263 species, specialism index for 261 and terminal velocity for 178.
3 Specialism index explained by far the largest part of the variance in local and national range. Seed weight, terminal velocity and germination temperature each explained only 2–4% of the variation in local range, and none of the variation in national range.
4 Most previous attempts to relate niche breadth and dispersal ability to range have concerned animals. There is little convincing published evidence for plants, and in the British herbaceous seed plants studied here the best predictor of range was diversity of habitats exploited. This pattern was independent of phylogeny.