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Schroder A.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | van Leeuwen A.,Princeton University | Cameron T.C.,University of Essex
Trends in Ecology and Evolution | Year: 2014

Experimental and theoretical studies show that mortality imposed on a population can counter-intuitively increase the density of a specific life-history stage or total population density. Understanding positive population-level effects of mortality is advancing, illuminating implications for population, community, and applied ecology. Reconciling theory and data, we found that the mathematical models used to study mortality effects vary in the effects predicted and mechanisms proposed. Experiments predominantly demonstrate stage-specific density increases in response to mortality. We argue that the empirical evidence supports theory based on stage-structured population models but not on unstructured models. We conclude that stage-specific positive mortality effects are likely to be common in nature and that accounting for within-population individual variation is essential for developing ecological theory. © 2014 Elsevier Ltd.

Wolf M.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Weissing F.J.,University of Groningen
Trends in Ecology and Evolution | Year: 2012

Personality differences are a widespread phenomenon throughout the animal kingdom. Past research has focused on the characterization of such differences and a quest for their proximate and ultimate causation. However, the consequences of these differences for ecology and evolution received much less attention. Here, we strive to fill this gap by providing a comprehensive inventory of the potential implications of personality differences, ranging from population growth and persistence to species interactions and community dynamics, and covering issues such as social evolution, the speed of evolution, evolvability, and speciation. The emerging picture strongly suggests that personality differences matter for ecological and evolutionary processes (and their interaction) and, thus, should be considered a key dimension of ecologically and evolutionarily relevant intraspecific variation. © 2012 Elsevier Ltd.

Mehner T.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Kasprzak P.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Journal of Animal Ecology | Year: 2011

Field studies on diel vertical migration (DVM) usually report uniform behaviour with population-wide ascents and descents during crepuscular periods. This contrasts partial seasonal migrations of many animal populations, where individuals choose either the resident or the migrant strategy depending on population density, feeding opportunity and predation risk in the resident and migrant habitats. We tested whether DVM of freshwater zooplanktivorous fish (Coregonus spp.) resembles partial migrations. Twenty-eight hydroacoustic surveys were performed in the deep Lake Stechlin (Germany) between 2000 and 2010, with samplings encompassing all months between March and December. Zooplankton samples were simultaneously taken in epilimnetic and hypolimnetic layers. Fish obtained from depth-stratified samplings by a midwater trawl were used to test for individual differences between residents and migrants. We show for the first time that DVMs of freshwater fish resemble patterns of partial migrations often found in seasonal environments. Across all samplings, 7-33% of fish did not ascend at dusk, but exhibited the resident strategy. The proportion or residents increased at low zooplankton feeding rates in the daytime habitat and during months when the temperature difference between daytime and night-time habitats was minor. Slightly larger size and higher caloric density of migrants over residents in one of the coexisting Coregonus species suggested that individual differences contributed to the migration strategy performed. However, these results were based on one sample only, and extrapolation to the entire data set is not possible. 5.Our results are indirect evidence that the balance between migrants and residents may primarily depend on the trade-off between feeding gains and metabolic and predation costs of migration. However, the results also suggest that the global fitness consequences for the resident and migrant strategies may not be identical, rendering the importance of individual traits in the 'decision to migrate' likely. © 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.

Mehner T.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Limnology and Oceanography | Year: 2010

I tested relationships between fish predator and prey densities or size across 66 lakes of the European temperate zone, covering mean depths between 1 and 22 m and a phytoplankton biomass range between 1 and 270 mg m-3 chlorophyll a. I hypothesized that in lakes of comparable phytoplankton biomass or depth, prey fish densities and size were lower at high predator densities or size than in systems with lower piscivory. Accordingly, I also expected a stronger trophic cascade from predatory fish to phytoplankton biomass in high-piscivory systems. None of the hypotheses were confirmed. Prey abundances and biomasses were consistently higher in high-piscivory than in low-piscivory lakes, if the effects of trophic state or lake depth on fish densities were accounted for. Chlorophyll a concentrations in lakes of similar depth did not differ between high and low piscivory, suggesting no difference in the strength of the trophic cascade. The overall size of prey was slightly higher in lakes with larger predators. The weak top-down influence of predatory fish on lower trophic levels may be attributable to the fact that the numerically dominant predator, perch, has to recruit through smaller ontogenetic stages, which dominate the prey community in most of the lakes. The availability of size refuges for prey and the overall omnivory of predators may contribute to the weak evidence for a trophic cascade. © 2010, by the American Society of Limnology and Oceanography, Inc.

Wolf M.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | McNamara J.M.,University of Bristol
American Naturalist | Year: 2012

Personality differences can be found in a wide range of species across the animal kingdom, but why natural selection gave rise to such differences remains an open question. Frequency-dependent selection is a potent mechanism explaining variation; it does not explain, however, the other two key features associated with personalities, consistency and correlations. Using the hawk-dove game and a frequency-dependent foraging game as examples, we here show that this changes fundamentally whenever one takes into account the physiological architecture underlying behavior (e.g., metabolism). We find that the inclusion of physiology changes the evolutionary predictions concerning consistency and correlations: while selection gives rise to inconsistent individuals and stochastically fluctuating behavioral correlations in scenarios that neglect physiology, we find high levels of behavioral consistency and tight and stable trait correlations in scenarios that incorporate physiology. The coevolution of behavioral and physiological traits also gives rise to adaptive physiological differences that are systematically associated with behavioral differences. As well as providing a framework for understanding behavioral consistency and behavioral correlations, our work thus also provides an explanation for systematic physiological differences within populations, a phenomenon that appears to exist in a wide range of species but that, up to now, has been poorly understood. © 2012 by The University of Chicago.

Radinger J.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Wolter C.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Fish and Fisheries | Year: 2014

Quantifying fish dispersal and identifying its general predictors is key for understanding temporal patterns in population dynamics, emigration and immigration, meta-community dynamics, many ecological processes and predicting recovery time or population responses to environmental changes. This is the first comprehensive quantitative meta-analysis of heterogeneous freshwater fish movement, aiming to determine mobile and stationary shares of fish communities, their dispersal distances and key predictors of dispersal patterns. By reviewing and analysing 160 empirical data sets from 71 studies covering 62 fishes in streams, it goes beyond previous studies of salmonids' heterogeneous movement. Based on fitted leptokurtic dispersal kernels, the movement distances of (i) a stationary component (σstat) and (ii) a mobile component (σmob) as well as the (iii) share of each component (p) were calculated. The median movement distance of the stationary and mobile component of a fish population was 36.4 and 361.7 m, respectively. The share of the stationary individuals was high (median = 66.6%), but unrelated to movement distance. Single and multiple linear regressions as well as mixed-effects models revealed movement distances positively related to fish length, aspect ratio of the caudal fin, stream size and duration of the study. Furthermore, movement distance differed between taxonomic families. The quantitative parameters of heterogeneous fish movement provided are prerequisite to estimate time lags in fish response to river rehabilitation, temporal patterns in species dispersal, and minimum effective size of potential founder populations for species conservation and stock recovery based on minimum numbers of specimen to disperse. © 2013 John Wiley & Sons Ltd.

Kalinkat G.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Journal of Animal Ecology | Year: 2014

The consumption rate of the crab Panopeus herbstii feeding on the mussel Brachidontes exustus depends on predator and prey body size as well as the predator individual activity level. Photo credit: Kathryn Levasseur. Toscano, B.J. & Griffen,B.D. (2014) Trait-mediated functional responses: predator behavioural type mediates prey consumption. Journal of Animal Ecology, 83, 1469-1477. While the concept of consistent behavioural differences among individuals of the same population has gained a lot of scientific attention over the last decade, its implementation into a community context with a focus on species-level interactions is still in its infancy. In their study on the effects of animal personalities on predator-prey functional responses of mussel-eating crabs, Toscano & Griffen (2014) introduce a promising avenue for future research synthesizing concepts and ideas from animal behaviour and food web ecology. More precisely, by showing that the interplay of animal personalities and predator and prey body sizes significantly alters the outcome of predator-prey interactions, this study provides important evidence that the concept of animal personalities needs greater consideration if we want to refine and improve current models of predator-prey interactions and the impact of individual-level variation on quantitative food-web dynamics. © 2014 The Author.

Sukhodolov A.N.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Water Resources Research | Year: 2012

The effects of channel curvature on turbulent flow in meander bends have been the main focus of extensive experimental and theoretical research hitherto. This paper is motivated by growing evidence that riffle-pool morphology in bends can also have strong implications for the flow structure. Flow in a bend of a lowland river with a shallow riffle and a deep pool is examined in this study by using the results of field measurements. In the study, reach flow is quasi-uniform in the riffle. In the pool, two layers compose the vertical structure of flow with a quasi-uniform flow near the riverbed. The upper layer is affected by lateral advection of fluid with low momentum from the inner bank that results in reduced tangential velocities, submergence of velocity maximum, and almost zero shear stress. Bed shear stress is estimated from the local profiles of turbulent shear stress and is shown to comply with values computed with the modified length scale. The maximum bed shear stress is situated in the riffle while theoretical considerations based on the effect of curvature suggest the pool as the most probable location of the maximum. This fact supports the hypothesis that the effects of riffle-pool morphology are dominant for the study reach. The study contributes to the clarification of up-scaling results from laboratory experiments to natural rivers by providing a detailed analysis of turbulence profiles. It shows that parameters of turbulence profiles, scaled with the proper velocity and length scales, are similar to those reported by previous experimental studies for open-channel flow. © 2012 by the American Geophysical Union.

Grossart H.-P.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Environmental Microbiology Reports | Year: 2010

In recent years, microbial ecology has developed from a peripheral discipline into a central field of microbiology. This change in state and perception is mainly driven by a rapid development of methods applied in the manifold fields related to microbial ecology. In biogeochemistry, for example, the use of high-resolution techniques such as FT-ICR-MS (Fourier transform ion cyclotron mass spectroscopy) has uncovered an enormous diversity and complexity of natural organic matter produced or degraded microbially either in dissolved or particulate forms. On the other hand, the introduction of highthroughput sequencing methods, such as 454 pyrosequencing, in combination with advances in bioinformatics allows for studying the bacterial diversity in natural samples circumventing cultivation dependent approaches. These new molecular tools enable in depth studies on single-cell genomes, distinct populations or even metacommunities. In combination with metatranscriptome and proteome studies it is for the first time possible to simultaneously unravel the structure and function of complex communities in situ. These techniquederived findings have, on the one hand, dramatically increased our knowledge on the vast diversity and complexity of bacterial habitats and, on the other hand, on phylogentic diversity and physiological responses of natural bacterial communities to their environment. However, until now microbial ecology is lacking an ecologically relevant species definition and useful tools for the identification of ecologically coherent taxa. Studies on intra- and interspecies interactions even with higher organisms demonstrate that bacteria can rapidly adapt to temporal and spatial changes in their environment. Aquatic bacteria have optimized and dramatically expanded their living space by efficient exploitation of organic matter point sources such as particles/aggregates and higher organisms. Although it is evident that particles/aggregates and organisms such as phytoplankton are 'hotspots' for microbial growth and transformation processes, it has not affected sampling strategies of aquatic microbial ecologists, who often focus solely on the free-living bacterial fractions and a priori exclude higher organisms by nonrepresentative water sampling. Therefore, aquatic microbial ecologists have largely overlooked the fact that many aquatic bacteria may possess a complex lifestyle and frequently alternate between a free-living and a surface-associated stage. Here, I propose that modern concepts in aquatic microbial ecology should take into account the high chemical diversity and spatio-temporal variability of the bacterial environment. Interactions of aquatic bacteria with surfaces including living organisms are the key to understanding their physiological adaptations and population dynamics, as well as their contribution to biogeochemical cycles. New sampling strategies and theoretical concepts are needed in aquatic microbial ecology to access the whole spectrum of bacterial lifestyles and their ecological and evolutionary consequences. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Mehner T.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Freshwater Biology | Year: 2012

Diel vertical migrations (DVM) are typical for many cold-water fish species such as Pacific salmons (Oncorhynchus spp.) and coregonids (Coregonus spp.) inhabiting deep lakes. A comprehensive recent overview of DVM in freshwater fish has not been available, however. The main proximate trigger of DVM in freshwater fish is the diel change in light intensity, with declining illumination at dusk triggering the ascent and the increase at dawn triggering the descent. Additional proximate cues are hydrostatic pressure and water temperature, which may guide fish into particular water layers at night. Ultimate causes of DVM encompass bioenergetics efficiency, feeding opportunities and predator avoidance. None of these factors alone can explain the DVM in all cases. Multi-factorial hypotheses, such as the 'antipredation window' combined with the thermal niche hypothesis, are more likely to explain DVM. It is suggested that planktivorous fish move within a layer sufficiently well illuminated to capture zooplankton, but too dark for predators to feed upon the migrating fish. In complete darkness, fish seek layers with a temperature that optimises bioenergetics efficiency. The strength of each factor may differ from lake to lake, and hence system-specific individual analyses are needed. Mechanistic details that are still poorly explored are the costs of buoyancy regulation and migration, the critical light thresholds for feeding of planktivorous and piscivorous fish, and predator assessment by (and size-dependent predation risk of) the prey fish. A comprehensive understanding of the adaptive value of DVM can be attained only if the behaviour of individual fish within migrating populations is explicitly taken into account. Size, condition and reproductive value differ between individuals, suggesting that migrating populations should split into migrants and non-migrants for whom the balance between mortality risk and growth rate can differ. There is increasing evidence for this type of partial DVM within populations. Whereas patterns of DVM are well documented, the evolution of DVM is still only poorly understood. Because experimental approaches at realistic natural scales remain difficult, a combination of comprehensive data sets with modelling is likely to resolve the relative importance of different proximate and ultimate causes behind DVM in fish. © 2012 Blackwell Publishing Ltd.

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