Body size adaptions under climate change: Zooplankton community more important than temperature or food abundance in model of a zooplanktivorous fish

One of the most well-studied biogeographic patterns is increasing body size with latitude, and recent body size declines in marine and terrestrial organisms have received growing attention. Spatial and temporal variation in temperature is the generally invoked driver but food abundance and quality are also emphasized. However, the underlying mechanisms are not clear and the actual cause is likely to differ both within and among species. Here, we focused our attention on drivers of body size in planktivorous fish that forage through vision. This group of organisms plays a central role in marine ecosystems by linking the energy flow from lower to higher trophic levels. Using a model that incorporates explicit mechanisms for vision-based feeding and physiology, we investigated the influence on optimal body size of several biotic (prey size, prey energy content, and prey biomass concentration) and abiotic (temperature, latitude, and water clarity) factors known to affect foraging rates and bioenergetics. We found prey accessibility to be the most influential factor for body size, determined primarily by prey size but also by water clarity, imposing visual constraints on prey encounters and thereby limiting feeding rates. Hence, for planktivores that forage through vision, an altered composition of the prey field could have important implications for body size and for the energy available for reproduction and other fitness-related tasks. Understanding the complicated effects of climate change on zooplankton communities is thus crucial for predicting impacts on planktivorous fish, as well as consequences for energy flows and body sizes in marine systems.publishedVersio

Parent-offspring conflict over reproductive timing: ecological dynamics far away and at other times may explain spawning variability in Pacific herring

Timing of reproduction may be of crucial importance for fitness, particularly in environments that vary seasonally in food availability or predation risk. However, for animals with spatially separated feeding and breeding habitats, optimal reproductive timing may differ between parents and their offspring, leading to parent-offspring conflict. We assume that offspring have highest survival and fitness if they are spawned around a fixed date, and use state-dependent life-history theory to explore whether variation in conditions affecting only parents (food availability and survival) may influence optimal timing of reproduction. We apply the model to Pacific herring (Clupea palasii) in Puget Sound, USA, where 20 subpopulations spawn at different times of the year. Our model suggests that relatively small differences in adult food availability can lead to altered prioritization in the trade-off between maternal fecundity and what from the offspring’s perspective is the best time to be spawned. Our model also shows that observed among-population variability in reproductive timing may result from adults using different feeding grounds with divergent food dynamics, or from individual variation in condition caused by stochasticity at a single feeding ground. Identifying drivers of reproductive timing may improve predictions of recruitment, population dynamics, and responses to environmental change.publishedVersio

Quantitative genetics of breeding coloration in sand lizards; genic capture unlikely to maintain additive genetic variance

Sexual selection on fitness-determining traits should theoretically erode genetic variance and lead to low heritability. However, many sexually selected traits maintain significant phenotypic and additive genetic variance, with explanations for this “lek paradox” including genic capture due to condition-dependence, and breaks on directional selection due to environmental sources of variance including maternal effects. Here we investigate genetic and environmental sources of variance in the intrasexually selected green badge of the sand lizard (Lacerta agilis). The badge functions as a cue to male fighting ability in this species, and male–male interactions determine mate acquisition. Using animal models on a pedigree including three generations of males measured over an extensive 9-year field study, we partition phenotypic variance in both badge size and body condition into additive genetic, maternal, and permanent environmental effects experienced by an individual over its lifespan. Heritability of badge size was 0.33 with a significant estimate of underlying additive genetic variance. Body condition was strongly environmentally determined in this species and did not show either significant additive genetic variance or heritability. Neither badge size nor body condition was responsive to maternal effects. We propose that the lack of additive genetic variance and heritability of body condition makes it unlikely that genic capture mechanisms maintain additive genetic variance for badge size. That said, genic capture was originally proposed for male traits under female choice, not agonistic selection. If developmental pathways generating variance in body condition, and/or the covarying secondary sex trait, differ between inter- and intrasexual selection, or the rate at which their additive genetic variance or covariance is depleted, future work may show whether genic capture is largely restricted to intersexual selection processes.publishedVersio

Degrees of change: between and within population variation in thermal reaction norms of phenology in a viviparous lizard

As the earth warms, populations will be faced with novel environments to which they may not be adapted. In the short term, populations can be buffered against the negative effects, or maximize the beneficial effects, of such environmental change via phenotypic plasticity and, in the longer term, via adaptive evolution. However, the extent and direction of these population-level responses will be dependent on the degree to which responses vary among the individuals within them (i.e., within population variation in plasticity), which is, itself, likely to vary among populations. Despite this, we have estimates of among-individual variation in plastic responses across multiple populations for only a few systems. This lack of data limits our ability to predict the consequences of environmental change for population and species persistence accurately. Here, we utilized a 16-yr data set from climatically distinct populations of the viviparous skink Niveoscincus ocellatus tracking over 1,200 litters from more than 600 females from each population to examine inter- and intrapopulation variability in the response of parturition date to environmental temperature. We found that these populations share a common population-mean reaction norm but differ in the degree to which reaction norms vary among individuals. These results suggest that even where populations share a common mean-level response, we cannot assume that they will be affected similarly by altered environmental conditions. If we are to assess how changing climates will impact species and populations accurately, we require estimates of how plastic responses vary both among and within populations.publishedVersio

Panel-based Assessment of Ecosystem Condition of the North Sea Shelf Ecosystem

The System for Assessment of Ecological Condition, coordinated by the Norwegian Environment Agency, is intended to form the foundation for evidence-based assessments of the ecological condition of Norwegian terrestrial and marine ecosystems not covered by the EU Water Framework Directive. The reference condition is defined as “intact ecosystems”, i.e., a condition that is largely unimpacted by modern industrial anthropogenic activities. An ecosystem in good ecological condition does not deviate substantially from this reference condition in structure, functions or productivity. This report describes the first operational assessment of the ecological condition of the marine shelf ecosystem in the Norwegian sector of the North Sea and Skagerrak. The assessment method employed is the Panel-based Assessment of Ecosystem Condition (PAEC1) and the current assessment has considered to what extent the North Sea and Skagerrak shelf ecosystem deviates from the reference condition2 by evaluating change trajectories.Panel-based Assessment of Ecosystem Condition of the North Sea Shelf EcosystempublishedVersio

Panel-based Assessment of Ecosystem Condition of the North Sea Shelf Ecosystem - Appendices

publishedVersio

Planktivorous fish and environmental change: using mechanistic modelling to explore the underpinnings and general validity of expected responses

The living conditions of marine and terrestrial organisms are currently changing at a rapid pace due to human activities. To predict how this will affect them, and hence to develop appropriate management and conservation strategies, we need to identify the fundamental drivers of their ecology and hence the mechanisms that underlie observed spatial and temporal patterns. Present-day climate change is associated with three universal ecological responses: shifts in distribution, shifts in phenology, and declining body size. In this PhD thesis I use mechanistic modelling to investigate the underpinnings and general validity of these three expectations for planktivorous fishes. This work resulted in several unintuitive findings that can improve our understanding and prediction of environmental influences on planktivorous fishes. The first paper shows that seasonality in the resource environments of both parents and their offspring is important for spawning time phenology, but that the relative importance of high offspring fitness (match between birth and conditions that maximize offspring survival) depends on resource dynamics at the feeding grounds of adults. Thus, to better understand and predict changes in phenology and their consequences in marine systems, I advocate for incorporation of both the parental and offspring perspective, for considering changes at different locations, and for modelling optimal annual routines, which describe how annual periodicity affects optimal activity schedules within the annual cycle. Latitudinal variation in body size and recent body size declines in response to climate change are typically linked to gradients and changes in temperature and food abundance.In the second paper, we show that for planktivores that forage through vision, factors that affect the accessibility of prey, particularly the size of prey but also water clarity, are much more important for their optimal body size and energetics. This suggests that inferences based on temperature and prey abundance, or biomass, are likely to have limited predictive ability, and future work should prioritize research to improve predictions of body size shifts in this group. The third paper explores how accounting for increasing light seasonality with latitude affects predictions of poleward shifts and redistributions of visual foragers under global warming. We illustrate that shifts from lower to higher latitudes may be constrained by the long and dark winters at higher latitudes, and by increased predation risk. Contrary to the common expectation, our findings also suggest that ocean warming could lead to shifts towards the equator, and that the optimal direction of shift may vary between the seasons and among individuals of different body sizes. In the paper, we discuss the implications of our findings for predicting warming-driven redistributions in visual foragers

Planktivorous fish and environmental change: using mechanistic modelling to explore the underpinnings and general validity of expected responses

The living conditions of marine and terrestrial organisms are currently changing at a rapid pace due to human activities. To predict how this will affect them, and hence to develop appropriate management and conservation strategies, we need to identify the fundamental drivers of their ecology and hence the mechanisms that underlie observed spatial and temporal patterns. Present-day climate change is associated with three universal ecological responses: shifts in distribution, shifts in phenology, and declining body size. In this PhD thesis I use mechanistic modelling to investigate the underpinnings and general validity of these three expectations for planktivorous fishes. This work resulted in several unintuitive findings that can improve our understanding and prediction of environmental influences on planktivorous fishes. The first paper shows that seasonality in the resource environments of both parents and their offspring is important for spawning time phenology, but that the relative importance of high offspring fitness (match between birth and conditions that maximize offspring survival) depends on resource dynamics at the feeding grounds of adults. Thus, to better understand and predict changes in phenology and their consequences in marine systems, I advocate for incorporation of both the parental and offspring perspective, for considering changes at different locations, and for modelling optimal annual routines, which describe how annual periodicity affects optimal activity schedules within the annual cycle. Latitudinal variation in body size and recent body size declines in response to climate change are typically linked to gradients and changes in temperature and food abundance.In the second paper, we show that for planktivores that forage through vision, factors that affect the accessibility of prey, particularly the size of prey but also water clarity, are much more important for their optimal body size and energetics. This suggests that inferences based on temperature and prey abundance, or biomass, are likely to have limited predictive ability, and future work should prioritize research to improve predictions of body size shifts in this group. The third paper explores how accounting for increasing light seasonality with latitude affects predictions of poleward shifts and redistributions of visual foragers under global warming. We illustrate that shifts from lower to higher latitudes may be constrained by the long and dark winters at higher latitudes, and by increased predation risk. Contrary to the common expectation, our findings also suggest that ocean warming could lead to shifts towards the equator, and that the optimal direction of shift may vary between the seasons and among individuals of different body sizes. In the paper, we discuss the implications of our findings for predicting warming-driven redistributions in visual foragers

Body size adaptions under climate change: Zooplankton community more important than temperature or food abundance in model of a zooplanktivorous fish

One of the most well-studied biogeographic patterns is increasing body size with latitude, and recent body size declines in marine and terrestrial organisms have received growing attention. Spatial and temporal variation in temperature is the generally invoked driver but food abundance and quality are also emphasized. However, the underlying mechanisms are not clear and the actual cause is likely to differ both within and among species. Here, we focused our attention on drivers of body size in planktivorous fish that forage through vision. This group of organisms plays a central role in marine ecosystems by linking the energy flow from lower to higher trophic levels. Using a model that incorporates explicit mechanisms for vision-based feeding and physiology, we investigated the influence on optimal body size of several biotic (prey size, prey energy content, and prey biomass concentration) and abiotic (temperature, latitude, and water clarity) factors known to affect foraging rates and bioenergetics. We found prey accessibility to be the most influential factor for body size, determined primarily by prey size but also by water clarity, imposing visual constraints on prey encounters and thereby limiting feeding rates. Hence, for planktivores that forage through vision, an altered composition of the prey field could have important implications for body size and for the energy available for reproduction and other fitness-related tasks. Understanding the complicated effects of climate change on zooplankton communities is thus crucial for predicting impacts on planktivorous fish, as well as consequences for energy flows and body sizes in marine systems

Poleward distribution of mesopelagic fishes is constrained by seasonality in light

Aim Mesopelagic fishes have a near-global distribution in the upper 1,000 m from tropical to sub-Arctic oceans across temperature regimes. Yet, their abundance decreases poleward and viable populations seem excluded from high latitudes. Why? Location North Atlantic between 50–85°N, with implications for high-latitude oceans globally. Time period Present-day. Major taxa studied Diel vertically migrating (DVM) mesopelagic fishes. Methods We use a mechanistic, state-dependent life-history model to characterize DVM mesopelagic fishes. This model links light-dependent encounters and temperature-dependent physiology, allowing optimal DVM strategies to emerge. We run the model along a latitudinal gradient with increasing seasonality in light and track individual fitness-related measures, that is, survival and surplus energy, through the annual cycle to make predictions about population consequences. Results Mesopelagic fishes thrive in the oceans’ twilight zone, and many are dependent on periods of darkness for safe foraging near the surface, before migrating back to depth during daytime. When daylight lasts for 24 hr during the Arctic summer, these fish are trapped in deep waters void of prey because it is never safe to forage in the shallow waters where zooplankton prey are found. Hence, they are left with two poor options, starvation at depth or depredation while foraging. Our model predicts surplus energy, vital for reproduction and growth, to halve from 50–85°N and annual survival to drop by two-thirds over a narrow range of 10° of latitude around the Arctic Circle. Thus, low recruitment and high predation mortality during summer make polar waters population sinks for mesopelagic fishes because of the extreme seasonality in light. Main conclusions At high latitudes, foraging mesopelagic fishes are exposed to sunlight in upper waters also at night. This makes them easy prey for visual predators, which limits their poleward distribution. Our findings highlight the importance to think beyond temperature to explain high-latitude range limits