Matúš Maciak

Ostracism of an Albino Individual by a Group of Pigmented Catfish

Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in the wild; this trait is associated with easy detection by predators, non-native or damaged environments, and exclusively aphotic environments in total darkness. The social aspect of albinism is reported only for human beings, and the effect is distinguishable in time and space when social benefits, are used to a limited the extent. Thus far, the social consequences of albinism for animals remain unknown. We used socially established groups of the pigmented catfish, (Silurus glanis), to observe space and temporal distance detachment of albino specimens in laboratory conditions. The albino fish were separated at larger distances from the group than pigmented individuals with the same social status determined by familiarity, and this asymmetry also varied in time. Albinism-related ostracism results in a solitary existence, usually followed by enhanced predation risk. The motivation for an individual’s exclusion from a group appears to be the avoidance of the predation risk that increases not only for an odd individual but also for conspecifics within a group. Our findings indicate a role for albinism in behavioural processes related to sociality in a group of conspecifics.

Familiarity, prior residency, resource availability and body mass as predictors of the movement activity of the European catfish

When animals compete for resources, their competitive abilities and behavioural strategies can be expressed as changes in movement activity. Stress is an important predictor of activity, and the variability of this predictor reflects the impact of environmental and social factors, while the effects of stress are further influenced through individual behavioural syndromes. We examined the effects of social (familiar vs. unfamiliar and resident vs. intruder) and environmental (resource availability) factors and individual characteristics (body mass) on the movement activity of juvenile European catfish Silurus glanis (L.). Familiarity and prior residency decreased the movement activity of these catfish, whereas resource unavailability significantly increased the movement activity of intruders to a level 1.5 times greater than that of the residents. The occurrence of an interaction involving an individual whose body mass was higher than that of individuals from the opposite group predicted a low level of movement activity of this individual. These results suggest that familiarity, prior residency, and high body mass decrease stress from the limited availability of resources.

Testing Shape Constraints in Lasso Regularized Joinpoint Regression

Joinpoint regression models are very popular in some practical areas mainly due to a very simple interpretation which they offer. In some situations, moreover, it turns out to be also useful to require some additional qualitative properties for the final model to be satisfied. Especially properties related to the monotonicity of the fit are of the main interest in this paper. We propose a LASSO regularized approach to estimate these types of models where the optional shape constraints can be implemented in a straightforward way as a set of linear inequalities and they are considered simultaneously within the estimation process itself. As the main result we derive a testing approach which can be effectively used to statistically verify the validity of the imposed shape restrictions in piecewise linear continuous models. We also investigate some finite sample properties via a simulation study.

Diel movement of brown trout, Salmo trutta, is reduced in dense populations with high site fidelity

Abstract The movement of individuals within preferred areas is reduced by a high availability of food and information about its distribution, while high number of competitors promotes increased movement. Experienced animals use information about social and physical environment to improve resources exploitation, tended to maintain positions within the preferred areas and reuse the environment that is often referred to as site fidelity. In this study, radio‐telemetry was used to observe the movements of 98 adult brown trout, Salmo trutta, in oligotrophic streams with different population densities; to determine subpopulation site fidelity, 5,195 conspecifics from 14 subpopulations were individually tagged during spring and autumn. During a 7‐year‐long field study, we tested the hypothesis that brown trout individuals from subpopulations with high site fidelity would display lower movement. The hypothesis was supported, and reduced movement was further related to high subpopulation density in association with high slope indicating the physical environment‐influenced movement. The probability of contact between individuals increased with subpopulation site fidelity and subpopulation density. No influence of food abundance on brown trout movement was found. Furthermore, increased body size predicted higher movement (and vice versa). The least movement occurred during the day and during the full moons. Our study tended to show that individuals reused preferred areas and needed less movement to exploit available resources.

Discontinuities in robust nonparametric regression with α-mixing dependence

ABSTRACT The main idea of the paper is to introduce a robust regression estimation method under an α-mixing dependence assumption, staying free of any parametric model restrictions while also allowing for some sudden changes in the unknown regression function. The sudden changes in the model may correspond to discontinuity points (jumps) or higher order breaks (jumps in corresponding derivatives) as well. We firstly derive some important statistical properties for local polynomial M-smoother estimates and we will propose a statistical test to decide whether some given point of interest is significantly important for a change to occur or not. As the asymptotic distribution of the test statistic depends on quantities which are left unknown we also introduce a bootstrap algorithm which can be used to mimic the target distribution of interest. All necessary proofs are provided together with some experimental results from a simulation study and a real data example.