A perspective on power generation impacts and compensation in fish populations

Renewed interest in the topic of compensation in fish populations has been stimulated by new EPA 316(b) regulations relating to entrainment and impingement looming on the horizon. The purpose of this paper is to revisit the topic of population compensation for fish populations in the context of assessing power generation impacts. I define compensation as the net population-level outcome of changes in growth, survival, and reproduction at the individual fish level that offsets decreases or increases in population density. Potential mechanisms of compensation have been well document in laboratory and field experiments. The process underlying all these mechanisms is that changes in population density can change per capita availability of essential resources such as food and space. The state of science in this area is constrained both retrospectively and prospectively by five technical stumbling blocks. Technological advances have improved our ability to bound the phenotypic plasticity of a species and to assess the potential effects of power generation impacts through a combination of monitoring, special studies, and simulation modeling. Four generalizations concerning compensation are mentioned. Progress has been made over the past three decades, but this topic remains scientifically challenging and politically controversial.     

Life history evolution: successes, limitations, and prospects

Life history theory tries to explain how evolution designs organisms to achieve reproductive success. The design is a solution to an ecological problem posed by the environment and subject to constraints intrinsic to the organism. Work on life histories has expanded the role of phenotypes in evolutionary theory, extending the range of predictions from genetic patterns to whole-organism traits directly connected to fitness. Among the questions answered are the following: Why are organisms small or large? Why do they mature early or late? Why do they have few or many offspring? Why do they have a short or a long life? Why must they grow old and die? The classical approach to life histories was optimization; it has had some convincing empirical success. Recently non-equilibrium approaches involving frequency-dependence, density-dependence, evolutionary game theory, adaptive dynamics, and explicit population dynamics have supplanted optimization as the preferred approach. They have not yet had as much empirical success, but there are logical reasons to prefer them, and they may soon extend the impact of life history theory into population dynamics and interspecific interactions in coevolving communities.     

Population viability analysis of white sturgeon and other riverine fishes

Many utilities face conflicts between two goals: generating cost-efficient hydropower and protecting riverine fishes. Research to develop ecological simulation tools that can evaluate alternative mitigation strategies in terms of their benefits to fish populations is vital to informed decision-making. In this paper, we describe our approach to population viability analysis of riverine fishes in general and Snake River white sturgeon in particular. We are finding that the individual-based modeling approach used in previous in-stream flow applications is well suited to addressing questions about the viability of species of concern for several reasons. Chief among these are: (1) the ability to represent the effects of individual variation in life history characteristics on predicted population viability; (2) the flexibility needed to quantify the ecological benefits of alternative flow management options by representing spatial and temporal variation in flow and temperature; and (3) the flexibility needed to quantify the ecological benefits of non-flow related manipulations (i.e., passage, screening, and hatchery supplementation).     

From IBM to IPM: Using individual-based models to design the spatial arrangement of traps and crops in integrated pest management strategies

The development of alternative pest-control strategies based on the spatial design of cropping systems requires a thorough understanding of the spatial links between the pest and its environment. Mechanistic models, especially individual-based models (IBMs), are powerful tools for integrating key behaviours, such as habitat selection and dispersal, with spatial heterogeneity. In this paper, we used an IBM calibrated and evaluated from real data to represent the spatial dynamics of the banana weevil in relation to the cropping system. We considered crop fragmentation and mass trapping as tools for suppressing pest numbers. Our simulation results showed that manipulating crop residues in the area surrounding each pheromone trap greatly improved trap efficiency. For an intensive banana plantation in fallow, traps were most effective when situated at the transition zone between banana area and fallow so as to maximize the trapping of weevils escaping the fallow. The model also showed that weevil numbers decreased when fragmentation of banana plantations was reduced.     

Establishment of facultative sexuals

The existence of sex is one of the major unsolved problems in biology. We use computer simulations to model conditions in which sex may first become established. We develop an individual-based population model and show that a hypothetical facultative sex gene can fix, provided that the initial cost is low. It is demonstrated that the equilibrium fitness in the population increases with increasing population size and decreasing mutation rate. The probability of the establishment of the sex gene is found not to be directly related to the fitness difference between the asexual and sexual populations. This change in fitness on changing the parameters of the model is investigated.     

Morphological distinctness despite large-scale phenotypic plasticity��analysis of wild and pond-bred juveniles of allopatric populations of Tropheus moorii

Cichlids are an excellent model to study explosive speciation and adaptive radiation. Their evolutionary success has been attributed to their ability to undergo rapid morphological changes related to diet, and their particular breeding biology. Relatively minor changes in morphology allow for exploitation of novel food resources. The importance of phenotypic plasticity and genetically based differences for diversification was long recognized, but their relationship and relative magnitude remained unclear. We compared morphology of individuals of four wild populations of the Lake Tanganyika cichlid Tropheus moorii with their pond-raised F(1) offspring. The magnitude of morphological change via phenotypic plasticity between wild and pond-bred F(1) fish exceeds pairwise population differences by a factor of 2.4 (mean Mahalanobis distances). The genetic and environmental effects responsible for among population differentiation in the wild could still be recognized in the pond-bred F(1) fish. All four pond populations showed the same trends in morphological change, mainly in mouth orientation, size and orientation of fins, and thickness of the caudal peduncle. As between population differentiation was lower in the wild than differentiation between pond-raised versus wild fish, we suggest the narrow ecological niche and intense interspecific competition in rock habitats is responsible for consistent shape similarity, even among long-term isolated populations.     

Extreme longevity in a deep-sea vestimentiferan tubeworm and its implications for the evolution of life history strategies

The deep sea is home to many species that have longer life spans than their shallow-water counterparts. This trend is primarily related to the decline in metabolic rates with temperature as depth increases. However, at bathyal depths, the cold-seep vestimentiferan tubeworm species Lamellibrachia luymesi and Seepiophila jonesi reach extremely old ages beyond what is predicted by the simple scaling of life span with body size and temperature. Here, we use individual-based models based on in situ growth rates to show that another species of cold-seep tubeworm found in the Gulf of Mexico, Escarpia laminata, also has an extraordinarily long life span, regularly achieving ages of 100–200 years with some individuals older than 300 years. The distribution of results from individual simulations as well as whole population simulations involving mortality and recruitment rates support these age estimates. The low 0.67% mortality rate measurements from collected populations of E. laminata are similar to mortality rates in L. luymesi and S. jonesi and play a role in evolution of the long life span of cold-seep tubeworms. These results support longevity theory, which states that in the absence of extrinsic mortality threats, natural selection will select for individuals that senesce slower and reproduce continually into their old age.     

Assessment of 316(b) impacts on Ohio River fish populations

Cooling water intake systems have the potential to adversely impact aquatic organisms though entrainment and impingement (impacts referenced under 316(b) of the Clean Water Act), yet the loss of individual fish does not necessarily mean that a population will suffer a significant decrease in number. The results of utility sponsored studies on Ohio River fish populations provide strong evidence of positive changes in the fishery due to water quality improvements. Despite these improvements, a simulation is needed to determine if a reduction in 316(b) fish losses would result in higher or similar fish population levels. Electrofishing data collected at seven power plant locations from 1981 to 1998 will be used for the population assessments. Potential 316(b) impacts on Ohio River fish populations will be modeled using site specific 316(b) data and a Leslie matrix model. The theoretical maximum population for various fish species, with and without 316(b) impacts, will be compared and the probabilistic risk that fish populations will fall below the threshold for species survival will be assessed. Historically, EPA has allowed 316(b) to be implemented on a case-by-case basis, however, the utilities believe that the first step in assessing potential adverse environmental impacts is to assess the condition of the affected fish populations.     

Surplus production,compensation, and impact assessments of power plants

For over 60 years, fishery scientists have been using the argument that nature creates surplus, and that the surplus can be used as justification to impose anthropogenic sources of mortality (power plants, fishing, pollution, etc.) on fish populations; otherwise, it is wasted. Surplus production is closely tied to the concept of compensation, a form of density-dependent mortality in which the mortality rate of a cohort is directly related to abundance of that cohort. Scientific arguments have been put forth in assessments of power plant impacts that compensation can at least partially offset impacts imposed by power plants. Although we cannot dismiss the existence of surplus production outright, since in some years environmental conditions are such that a surplus in reproductive effort may occur, we should be assessing the reproductive effort of fish populations in the context of the ecosystem in which they reside. In terms of addressing the risks of power plant mortality, we may be at a point in collection and analyses of biological data, coupled with a greater flexibility in managing power plant technology, to modulate the risks of power plant mortality on fish populations on a more-or-less real-time basis by taking into account environmental influences. For these reasons, assessments of power plant impacts should include analyses of predation forgone and production forgone.     

Phenotypic assortment by body shape in wild-caught fish shoals

Phenotypic variation plays a critical role in determining the structural organisation and ecological function of wild populations. Animal groups are often structured according to factors such as species, sex, body size and parasite load, but it is unclear whether body shape also influences patterns of social organisation, and thus contributes to population phenotypic structure. Here, we use geometric morphometric analyses to determine whether wild-caught shoals of a freshwater fish, the western rainbowfish (Melanotaenia australis), are structured according to body size and shape. Using randomisation analyses, we show that the level of variation in size and shape observed in natural group assemblages is lower than that expected under a null model of random shoal composition. In addition, we found evidence of further phenotypic structuring along an upstream-downstream environmental gradient. The putative benefits of morphological assortment include a reduction in predation risk (due to prey oddity and predator confusion effects) and increased hydrodynamic or foraging efficiency. We suggest that morphological variation is a neglected component of population social organisation that can affect population processes, such as patterns of gene flow, and ecological interactions, such as predator-prey dynamics.     

Non-migratory breeding by isolated green sea turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) in the Indian Ocean: biological and conservation implications

Green sea turtles (Chelonia mydas) are renowned for their long-distance migrations but have less fame for short-distance migrations or non-migratory behavior. We present satellite telemetric evidence from Cocos (Keeling) Islands, Indian Ocean for the first predominantly non-migratory green sea turtle (C. mydas) population. The mean migration distance from the nesting beach to the foraging grounds was 35.5 km with a maximum mean transit time of 3.4 days. The behavior of this population has major implications for our general understanding of green turtle behavior and their life cycle and for conservation. Firstly, these results indicate a level of juvenile or adult non-breeding homing behavior from the open ocean to foraging grounds adjacent to their natal nesting beach. Secondly, a non-migratory breeding phase reduces the consumption of reproductive energy utilized, potentially resulting in higher fecundity for this population. Thirdly, the close proximity of the nesting and foraging habitats allows for uniformity in management and conservation strategies rarely possible for wide-ranging green turtle populations.     

Why are reproductively parasitic fish males so small?—influence of tactic-specific selection

Despite the wide prevalence of alternative reproductive tactics, little attention has been paid to why reproductively parasitic males are so small. In this study, we tackled this issue in a shell-brooding fish Lamprologus callipterus. Sneaky ‘dwarf males’ of this fish remain much smaller than bourgeois conspecifics throughout their life and employ a unique parasitic tactic, i.e. entering into a gastropod shell where a female is spawning, passing through the space between the female and shell wall and staying behind her to ejaculate throughout the spawning event. Here, we tested the prediction that they remain small to get past her through the shell spaces by interpopulation comparison. We showed, across populations, a negative allometry for sexual size dimorphism, an exponential increase of female size with an increase in shell size and a negative correlation between the magnitude of sexual size dimorphism and shell size. These results suggest that the inner spaces strongly regulate dwarf male size. We conclude that the small bodies of dwarf males arise from adaptation to their unique reproductive behaviour.     

Differential survival rates in a declining and an invasive farmland gastropod species

Individual marking by using transponders represents a promising tool to further investigate causes of population trends of farmland invertebrates and the dynamics of farmland biodiversity. Once common in agricultural fields the slug Arion rufus is now restricted to forests, whereas the closely related and similar Arion lusitanicus recently built up high populations. Here, it was tested whether (1) transponder tagging combined with artificial shelters for recapturing is a suitable approach for quantifying adult survival of farmland gastropods under real field conditions, (2) whether captive bred and wild A. lusitanicus differ in survival, and (3) whether in agricultural fields the declining slug A. rufus shows reduced survival rates compared to the invasive slug A. lusitanicus. One hundred and thirty transponder-tagged slugs were released and individual-based mark-recapture models were performed. Individual marking by using transponders proved to be a successful method for quantifying survival rates of the slugs. The favoured model showed no differences in survival or encounter rates between captive bred and wild A. lusitanicus. A. rufus showed significantly reduced survival rates compared to A. lusitanicus coinciding with their population trends in farmland areas. This might be due to differential susceptibility to habitat degradation, differential predation rates or promotion of the invasive competitor species. A further decrease of A. rufus in agricultural landscapes is expected.     

Effects of paternal phenotype and environmental variability on age and size at maturity in a male dimorphic mite

Investigating how the environment affects age and size at maturity of individuals is crucial to understanding how changes in the environment affect population dynamics through the biology of a species. Paternal phenotype, maternal, and offspring environment may crucially influence these traits, but to my knowledge, their combined effects have not yet been tested. Here, I found that in bulb mites (Rhizoglyphus robini), maternal nutrition, offspring nutrition, and paternal phenotype (males are fighters, able to kill other mites, or benign scramblers) interactively affected offspring age and size at maturity. The largest effect occurred when both maternal and offspring nutrition was poor: in that case offspring from fighter sires required a significantly longer development time than offspring from scrambler sires. Investigating parental effects on the relationship between age and size at maturity revealed no paternal effects, and only for females was its shape influenced by maternal nutrition. Overall, this reaction norm was nonlinear. These non-genetic intergenerational effects may play a complex, yet unexplored role in influencing population fluctuations—possibly explaining why results from field studies often do not match theoretical predictions on maternal effects on population dynamics.     

Morphological change and phenotypic plasticity in native and non-native pumpkinseed sunfish in response to competition

Non-indigenous species are oftentimes exposed to ecosystems with unfamiliar species, and organisms that exhibit a high degree of phenotypic plasticity may be better able to contend with the novel competitors that they may encounter during range expansion. In this study, differences in morphological plasticity were investigated using young-of-year pumpkinseed sunfish (Lepomis gibbosus) from native North American and non-native European populations. Two Canadian populations, isolated from bluegill sunfish (L. macrochirus) since the last glaciation, and two Spanish populations, isolated from bluegill since their introduction in Europe, were reared in a common environment using artificial enclosures. Fish were subjected to allopatric (without bluegill) or sympatric (with bluegill) conditions, and differences in plasticity were tested through a MANOVA of discriminant function scores. All pumpkinseed populations exhibited dietary shifts towards more benthivorous prey when held with bluegill. Differences between North American and European populations were observed in body dimensions, gill raker length and pelvic fin position. Sympatric treatments induced an increase in body width and a decrease in caudal peduncle length in native fish; non-native fish exhibited longer caudal peduncle lengths when held in sympatry with bluegill. Overall, phenotypic plasticity influenced morphological divergence less than genetic factors, regardless of population. Contrary to predictions, pumpkinseeds from Europe exhibited lower levels of phenotypic plasticity than Canadian populations, suggesting that European pumpkinseeds are more canalized than their North American counterparts.     

Climatic influences on the breeding biology of the agile frog (<Emphasis Type="Italic">Rana dalmatina</Emphasis>)

Severe population declines of amphibians have been shown to be attributed to climate change. Nevertheless, the various mechanisms through which climate can influence population dynamics of amphibians remain to be assessed, notably to disentangle the relative synergetic or antagonistic influences of temperature and precipitations on specific life history stages. We investigated the impact of rainfall and temperature on the egg-clutch abundance in a population of agile frog (Rana dalmatina) during 29 years (1987–2016) on 14 breeding sites located in Brenne Natural Park, France. Specifically, we examined the influence of environmental conditions occurring during five temporal windows of the year cycle corresponding to specific life history stages. Overall, our results suggest that the year-to-year fluctuations of egg-clutch abundances in Brenne Natural Park were partly dependent on local climatic conditions (rainfall and temperature). Climate seemed to influence breeding frogs during the autumn-winter period preceding reproduction. Spring and summer conditions did not influence reproduction. Additionally, we failed to detect effects of climatic conditions on newly metamorphosed individuals. Other factors such as density dependence and inter-specific interactions with introduced predators are likely to play a significant role in reproduction dynamics of the studied frog populations.     

Linkages between fishery habitat quality,stressors, and fishery populations

Increasing human population densities and development along the coasts of the United States pose a threat to fish populations through alteration of their habitats due to modification of upland watersheds, increased inputs of nutrient and domestic and agricultural chemicals, and direct habitat replacement or destruction. Injuries to these habitats will in turn affect populations of marine and estuarine organisms. To effectively evaluate the impacts of human activities on essential fish habitat we propose a framework to assess the linkages between fishery habitat alteration and modification and fishery production and community structure in coastal environments. Inherent natural variability makes it difficult to detect changes to the population or community. Therefore, we target structural and functional components of fish habitat as assessment endpoints, rather than the fish populations that utilize those habitats.     

Diverse migration strategies in hoopoes (<Emphasis Type="Italic">Upupa epops</Emphasis>) lead to weak spatial but strong temporal connectivity

The annual cycle of migrating birds is shaped by their seasonal movements between breeding and non-breeding sites. Studying how migratory populations are linked throughout the annual cycle—migratory connectivity, is crucial to understanding the population dynamics of migrating bird species. This requires the consideration not only of spatial scales as has been the main focus to date but also of temporal scales: only when both aspects are taken into account, the degree of migratory connectivity can be properly defined. We investigated the migration behaviour of hoopoes (Upupa epops) from four breeding populations across Europe and characterised migration routes to and from the breeding grounds, location of non-breeding sites and the timing of key migration events. Migration behaviour was found to vary both within and amongst populations, and even though the spatial migratory connectivity amongst the populations was weak, temporal connectivity was strong with differences in timing amongst populations, but consistent timing within populations. The combination of diverse migration routes within populations and co-occurrence on the non-breeding grounds between populations might promote exchange between breeding populations. As a result, it might make hoopoes and other migrating bird species with similar strategies more resilient to future habitat or climatic changes and stabilise population trends.     

Incorporation of changes in habitat quantity and quality into density-dependent population models

The use of dynamic age-structured models is becoming more prevalent in environmental assessments. We review these models and discuss the application of density-dependent population models with varying intrinsic rate of increase (r) and carrying capacity (K). Application of these models is described in terms of the model selection process, evaluation of r and K and how they are influenced by habitat suitability, the calculation of habitat suitability indices, and the selection of competition type (scramble vs contest). A short example is given. We conclude that these models offer valuable insight into the understanding of population responses to environmental impacts and mitigation.     

The mechanisms of lift enhancement in insect flight

Recent studies have revealed a diverse array of fluid dynamic phenomena that enhance lift production during flapping insect flight. Physical and analytical models of oscillating wings have demonstrated that a prominent vortex attached to the wings leading edge augments lift production throughout the translational parts of the stroke cycle, whereas aerodynamic circulation due to wing rotation, and possibly momentum transfer due to a recovery of wake energy, may increase lift at the end of each half stroke. Compared to the predictions derived from conventional steady-state aerodynamic theory, these unsteady aerodynamic mechanisms may account for the majority of total lift produced by a flying insect. In addition to contributing to the lift required to keep the insect aloft, manipulation of the translational and rotational aerodynamic mechanisms may provide a potent means by which a flying animal can modulate direction and magnitude of flight forces for manoeuvring flight control and steering behaviour. The attainment of flight, including the ability to control aerodynamic forces by the neuromuscular system, is a classic paradigm of the remarkable adaptability that flying insects have for utilising the principles of unsteady fluid dynamics. Applying these principles to biology broadens our understanding of how the diverse patterns of wing motion displayed by the different insect species have been developed throughout their long evolutionary history.