Facing different predators: adaptiveness of behavioral and morphological traits under predation

Predation is thought to be one of the main structuring forces in animal communities. However, selective predation is often measured on isolated traits in response to a single predatory species, but only rarely are selective forces on several traits quantified or even compared between different predators naturally occurring in the same system. In the present study, we therefore measured behavioral and morphological traits in young-of-the-year Eurasian perch Perca fluviatilis and compared their selective values in response to the 2 most common predators, adult perch and pike Esox lucius. Using mixed effects models and model averaging to analyze our data, we quantified and compared the selectivity of the 2 predators on the different morphological and behavioral traits. We found that selection on the behavioral traits was higher than on morphological traits and perch predators preyed overall more selectively than pike predators. Pike tended to positively select shallow bodied and nonvigilant individuals (i.e. individuals not performing predator inspection). In contrast, perch predators selected mainly for bolder juvenile perch (i.e. individuals spending more time in the open, more active), which was most important. Our results are to the best of our knowledge the first that analyzed behavioral and morphological adaptations of juvenile perch facing 2 different predation strategies. We found that relative specific predation intensity for the divergent traits differed between the predators, providing some additional ideas why juvenile perch display such a high degree of phenotypic plasticity

Plasticity and consistency of behavioural responses to predation risk in laboratory environments

The individual animal is currently a major focus of behavioural research and an increasing number of studies raise the question of how between-individual behavioural consistency and behavioural plasticity interact. Applying the reaction norm concept on groups, our study addresses both of these aspects in one framework and within an animal's natural social environment. Risk-taking behaviour in 1-year-old perchPerca fluviatiliswas assayed in aquarium experiments before and after the fish were subjected to the presence or absence of a piscivorous predator for 3weeks. To analyse the inter-individual behavioural variation across the repeated measurements, we dissected the behavioural change across the predator treatment into individual constant and plastic components using hierarchical mixed-effects models. During the predator treatment, juvenile perch increased in boldness and decreased in vigilance, the magnitude of these behavioural changes was influenced by group composition. However, the behavioural changes were not influenced by the presence of a predator, indicating the difficulties in generating realistic long-term predation pressure in the laboratory. Individuals differed in the relative increase in boldness across the predator treatment and, thus, varied in the shape of their reaction norms. In accordance, the best linear unbiased predictors, extracted from the random effects of separate linear mixed-effects models for the data before and after the predator treatment were only weakly correlated. Hence, between-individual variation seems to change under laboratory conditions and therewith not necessarily represents the initially present ‘natural’ variation, giving important implications for the conduction and interpretation of behavioural experiments

Teaching laboratory for large cohorts of undergraduates : private and social information in fish

A challenge in the Bachelor's studies in Biology is to strike a balance between reducing the teaching of practical scientific experiments to what is feasible in a short time, and teaching “real” science in undergraduate laboratories for high numbers of participants. We describe a laboratory in behavioral biology, with the primary focus on the student learning. However, also the underlying scientific question and the results of the experiment, namely the behavior of the three‐spined stickleback (Gasterosteus aculeatus) in a trade‐off situation during foraging, is without a doubt timely and sufficient for scientific studies on this subject, and this through the experiments conducted and data collected by the students. The students rated this laboratory well and learned at the end that social information is certainly important, but that self‐learning can be more important, and this not only in small fish, but also for the students themselves.Publisher PDFPeer reviewe

Does social context affect boldness in juveniles?

Differences in boldness are common between populations or between related species and are discussed as part of individual coping style, personality, or behavioral syndrome. Boldness has been found to be dependent on experience, social, and environmental contexts. The major aim of the present study was to establish an experimental environment that would allow analyzing the risk-taking behavior of 2 competing invasive goby species. Neogobius melanostomus was more active in the absence of a predator Sander lucioperca than N. fluviatilis and clearly spent more time swimming and feeding than N. fluviatilis. In addition, N. melanostomus was always faster than N. fluviatilis both when leaving the shelter and reaching offered food. Based on the different behaviors recorded, species-specific boldness scores were established using a principal component analysis. Although there was no overall difference in boldness scores between the 2 species, both competitive conditions and the effect of the predator played significant roles as factors influencing boldness. Neogobius melanostomus was more affected by the presence/absence of the predator than the social circumstances. Neogobius fluviatilis, on the other hand, was more active and bolder in competitive situations. However, when alone, N. fluviatilis was rather inactive and displayed altogether shy behavior, independent of the presence/absence of the predator. Thus, the study confirms the prediction that there are differences in behavior and behavioral plasticity, and therein predator-avoidance strategies, between ecologically similar species of goby living in sympatry. We argue that these differences may be related to differential habitat use of both invasive species that presently dominate the fish community in the Lower Rhine

Competition fluctuates across years and seasons in a 6-species-fish community: empirical evidence from the field

Competition not only occurs between species, but (probably more importantly) also among individuals within species, especially, for species occurring in high densities and when resources are limiting. Fluctuating densities and dietary overlap may account for massive ecological and evolutionary changes in fish communities. We sampled a mixed juvenile (0+ stages, being younger than 1 year of age) fish community at the Lower Rhine over three consecutive years, including native and newly established species (similar to 64,000 captured individuals and similar to 4200 dissected fish). Our aim was to develop a new approach in which data on density, individual consumption rates, and diet overlaps (both intra- and interspecific) solely originating from the natural environment, were used and combined to estimate species-specific competitive strengths within and between seasons and species. The juvenile fish community at the food-limited Rhine was dominated by invasive gobies. Species-specific consumption rates decreased depending on the dietary overlap with other juveniles. Two invasive gobies (Neogobius melanostomus and N. fluviatilis) showed the greatest competitive abilities, followed by a third invasive Gobiid species (Ponticola kessleri) and the native Aspius aspius, a species utilizing an exclusive food source. Both other native species (Perca fluviatilis and Sander lucioperca) had the lowest estimates of food-related competitive strength, indicating that these species are forced into a juvenile competitive bottleneck by the invasive gobies, before they finally can develop into successful predators on gobies later in life. Our new analytical approach to measure dietary competitive strength among individuals provides a powerful tool to empirically study eco-evolutionary feedback dynamics in the field

Data from: A new mechanistic approach for the further development of a population with established size bimodality

Usually, the origin of a within-cohort bimodal size distribution is assumed to be caused by initial size differences or by one discrete period of accelerated growth for one part of the population. The aim of this study was to determine if more continuous pathways exist allowing shifts from the small to the large fraction within a bimodal age-cohort. Therefore, a Eurasian perch population, which had already developed a bimodal size-distribution and had differential resource use of the two size-cohorts, was examined. Results revealed that formation of a bimodal size-distribution can be a continuous process. Perch from the small size-cohort were able to grow into the large size-cohort by feeding on macroinvertebrates not used by their conspecifics. The diet shifts were accompanied by morphological shape changes. Intra-specific competition seemed to trigger the development towards an increasing number of large individuals. A stage-structured matrix model confirmed these assumptions. The fact that bimodality can be a continuous process is important to consider for the understanding of ecological processes and links within ecosystems