Das Projekt zielt auf die quantitative Erfassung zeitlicher und räumlicher Verteilungsmuster von Fischen im Litoral und deren zugrundeliegende Steuermechanismen. Im Mittelpunkt der Arbeit stehen die beiden benthischen Arten Trüsche und Bachschmerle, deren Abundanzen und Verteilungsmuster durch die Anzahl an Tag-Versteckmöglichkeiten im ufernächsten Flachwasserbereich bestimmt wird. Diese strenge Substratbindung führt zur Ausbildung hierarchischer Gruppenstrukturen mit dominanten und subordinaten Tieren. Die laufenden Untersuchungen zeigen weiter, dass die Ausprägung solcher hierarchischer Strukturen innerhalb einer Art kein zeitlich festes Gefüge darstellt sondern die einzelnen Gruppen in Abhängig des tagesperiodischen Aktivitätsniveaus zerfallen bzw. neu gebildet werden. Ein Schwerpunkt des laufenden Forschungsprojektes ist die detaillierte Analyse der Bildung und Auflösung solcher Gruppenstrukturen mit hierarchischer Ordnung sein. Das kausal-mechanistische Verständnis der Gruppenformation, d.h. wann es für ein Individuum von Vorteil ist, sich einer Gruppe "anzuschließen" oder sich "abzuspalten" und die zugrundeliegenden Mechanismen dieses dynamischen Verhaltens sind dabei Forschungsschwerpunkte des Projektes.The ongoing research in this project deals with mechanisms that regulate the temporal and spatial distribution patterns and habitat use of fish species in the littoral zone of large lakes. We focus our work on the mechanisms of inter- and intraspecific competition for littoral resources that are i) limited in availability due to the small area contribution of the littoral zone to the entire lake area (in Lake Constance 12%) and ii) seasonally limited in its availability for the fish due to seasonal water level fluctuations, a typical phenomenon in many large lakes systems around the world.p We centre our present experimental work on the two model species juvenile burbot Lota lota L. and stone loach Barbatula barbatula (L) as the two most abundant representatives of the benthic community in the littoral zone of Lake Constance. We already showed that the availability of adequate daytime shelter (substratum interstitial) in the uppermost eulittoral zone is the most important habitat resource which determines the abundance and distribution of the two benthic species in a certain littoral area. The strong relationship of the two species to the availability of daytime shelter induces a strong hierarchical order in this community with respect to shelter use with clearly defined dominant and subordinate individuals. Our studies furthermore showed that this social hierarchy in the littoral benthic community severely affects not only the behaviour of the individual fish but also the somatic growth rate and therefore long-term fitness with dominant specimen growing significantly better compared to subordinates. These substratum respectively hierarchy induced differences in growth rates especially in juvenile burbot, however, results in a complex migration behaviour in this species. Because the successful competition for a certain "optimal" substratum interstice as daytime shelter significantly enhances somatic growth rate but the availability of large interstices isrestricted, these primarily dominant species outgrow first from the spectrum of available daytime interstices in the littoral zone. This leads to the apparent paradoxon, that the most dominant specimen of a cohort, which are most successful to compete for their preferred daytime shelter, experience a higher level of intraspecific competition for daytime shelter which leads to comparatively early start the obligate profundal migration of this species already within their first year while the previously subordinate and slower growing littoral remainders stay in littoral habitats until their second summer.pOur experiments however also clearly show, that the strong hierarchical order within the benthic community is only part of a complex social structure within this community and is distinct mainly during daytime when the availability of adequate shelter is important for the individual specimen. Our experiments give strong hints, that the observed hierarchical order during daytime, which is established by the largest and most aggressive dominant conspecifics within the community, is strongly modified during night, when the fish leave shelter to forage. Then, the community is restructured in smaller sub-units (so called "cliques") which are composed also by dominant and subordinate individuals. However, these individuals now seem to form a foraging unit with a combined foraging strategy with much less conspecifics aggressiveness as observed during daytime sheltering. During dawn, these foraging units however, seem to break down again and the daytime hierarchical structure is established again.pUp to now, we have a profound understanding of the mechanisms of habitat use and group hierarchy formation in the two benthic species juvenile burbot and stone loach during their daytime sheltering phase. Based on these data and the technical equipment we have developed for studying the behaviour of nocturnal bottom dwelling fish species, we now plan to focus on their nocturnal foraging phase. We are specifically interested in the temporal constitution and reconstitution of hierarchical orders and social structures in the diel cycle and its underlying mechanisms.
