Universität zu Köln

Gertzen, Svenja (2016). The ecological niche of invasive gobies at the Lower Rhine in intra- and interspecific competitive and predatory nteractions. PhD thesis, Universität zu Köln.

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Abstract

Biological invasions represent a fascinating process with potentially severe consequences, as the displacement of native species. Therefore, determining the impact on natives and the whole ecosystem is inevitable to protect the endemic biodiversity. At the Lower Rhine a special situation has arisen from three congeneric fish species of the family Gobiidae establishing populations with high densities in a strongly anthropogenic altered habitat, which is additionally limited in dietary resources. Mechanisms of niche separation for the three goby species could be shown on a spatial and temporal axis. Although high dietary overlaps were obtained between the three goby species, ontogenetic dietary shifts in combination with habitat shifts reduced levels of competition. Fine-tuned niche differentiation was also displayed in reproductive traits by temporal separation of spawning onset and intensity, as well as in drifting patterns. Drifting strategy differed within the three species not only to their temporal occurrence in the drift, but also regarding the sizes of drifting individuals. These mechanisms of niche partitioning were suggested to allow for the co-existence of the three Gobiidae and to enforce the impact on native species. The system seemed to have reached its capacities, as already decreasing densities of bighead goby and high levels of dietary competition indicate. Competitive and predatory interactions emerged between the single goby species, as well as with the native fish community. A temporal scaled bottom-up top-down system could be obtained for invasive gobies and two native Percidae. Native piscivores were forced into a dietary juvenile competitive bottleneck, while later on preying on gobies. Adaptation to this novel prey has just started, thus up to now detrimental effects of the competitive interactions prevail. Additionally, population development of the three invasive species is still in progress, revealing a highly dynamic system, where the next years will determine the outcome of this invasion.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Gertzen, Svenja Svenja.Gertzen@gmx.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-69306
Date:	February 2016
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Natural sciences and mathematics Life sciences
Uncontrolled Keywords:	Keywords Language invasion, niche differentiation, reproduction, dispersal, competition, predation English
Date of oral exam:	13 April 2016
Referee:	Name Academic Title Borcherding, Jost PD Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/6930