Dr. Franz Hölker

IGB, Dept.4,
Biology and Ecology of Fishes 
12587 Berlin, Müggelseedamm 310

Fields of Interests:

fish ecology, modelling, ecophysiology, trophic interactions, chemical communication

as part of research topic no. 3.3:
Ecological factors in speciation of fishes

Tel: (030) 64 181 665
Fax: (030) 64 181 750

hoelker@igb-berlin.de

Populations have to be considered as groups of distinct individuals, which have to be analysed and modelled separately. Following these principles will help to find generalities in the organization of aquatic food webs and freshwater fish ecology. In addressing this topic, I combine comparative field studies, experiments and ecological modelling as well as behavioural observations and ecological monitoring.

(1) Changes in structure and function of the fish community in a mesotrophic lake after enhancement of piscivorous fish biomass (food web manipulation)

(DFG, together with T. Mehner, IGB, Berlin, in co-operation with H. Dörner and T. Schulze). We analyse the behavioural and numerical response of planktivorous fish to the introduction of a new predator. The data will be used to evaluate the stability and resilience of food webs under mesotrophic conditions. The role of indirect effects, especially piscivore-mediated effects through trait changes in fish (behaviour and phenotype) are analysed by using an individual-based model. By this the relative proportions of the resulting density-mediated and trait-mediated indirect effects on the consumption of littoral and pelagic resources by the consumer population can be evaluated

(2) A spatially explicit bioenergetics individual-based fish model to investigate emergent properties at the individual and at the population level

(IGB, in co-operation with B. Breckling, University of Bremen). Demographic equivalence (and thus exchangeability) of individuals is commonly used in population models where individual members of populations can be aggregated into a single-state variable representing population size. This contradicts the basic biological fact that an individual is unique. Processes that operate at the individual level can determine properties at the population level. Such new properties, which emerge at one level of a system as a consequence of interactions within the system and which are not a property of lower level units, play an important role in advancing our understanding in ecology and evolution. By tracking in a computer-simulation all individuals of a population, spatially explicit IBMs consider local interactions between an individual and its surrounding environment. This modelling approach is used as a virtual laboratory for testing the validity or possible consequences of ecological theories and to answer questions about the impact of environmental heterogeneity on individual fish and populations.

(3) From chemical communication to biogeochemistry: Adaptive behaviour of chironomid larvae in response to chemical stimuli from fish

(IGB, in co-operation with P.Stief, Institute of Biological Sciences, University of Aarhus, Denmark). Many antipredator tactics have costs associated with them. Therefore, they might be expected to be used only when the organism has an accurate assessment of predation risk and thus of the benefit of the defence. Such antipredator adaptations can be mediated solely by a chemical cue (kairomone) from the predator. In this study we analyse fish kairomone-mediated behaviour of chironomid larvae and its effects on benthic oxygen and nutrient dynamics

(4) Sympatric speciation along ecological gradients

(IGB, in co-operation with J. Ohlberger und G. Staaks). The goal of this project is to identify the mechanisms of the newly discovered sympatric speciation in the species-pair Coregonus albula and Coregonus fontanae by means of ecophysiological parameters. The analysis of the physiological optima and the functional response depending on the factors temperature, light and prey density sheds light on the question, which functional characteristics and adaptations enable both species to populate their respective realized niche with greatest ecological fitness maintaining them as separate species.

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Mehner, T., Freyhof, J. & Hölker, F.: 2007-2010, Budget: approx. 100 000.- €. The impact of climate variability on recruitment, life history, and physiology of sympatric pairs of ciscoes (Teleostei: Coregonus spp.) in lakes. AQUASHIFT, German Research Foundation.

Hölker, F. & Staaks, G.: 2005-2008, Budget: approx. 90 000.- €. Evolution in the depth: Sympatric speciation along ecological gradients? Winner of the IGB Idea Contest, Leibniz-Institute of Freshwater Ecology and Inland Fisheries.

Mehner, T. & Hölker, F.: 2001-2004, Budget: 255 061.88.- €. Changes in structure and function of the fish community in a mesotrophic lake after enhancement of piscivorous fish biomass (food web manipulation). German Research Foundation (ME 1686/4-1 + 4-2).

Hölker, F.: 1997, Budget: approx. 5 000.- €. Guest scientist and keynote speaker at the International Symposium on the Biology and Management of Ruffe, Ann Arbor, Michigan, USA, selected by solicitation of proposals by Minnesota and Michigan Sea Grant College Programs.

Hölker, F. & Breckling, B.: 1996, Budget: approx. 25 400.- €. Development of an individual-based model for roach (Rutilus rutilus). Federal Ministry of Education and Research, Germany (Ökosystemforschung in Bereich der Bonhöveder Seenkette).

Dipl. Biol. Jan Ohlberger: Swimming energetics of fishes, mechanisms of sympatric speciation

Dipl. Biol. Torsten Schulze: Piscivores in Lake Vätersee

Irina König: Nutrition physiology of Coregonus albula and C. fontanae

Technician Karena Kuntze: Physiological laboratory

International Master of Science study programme on Fishery Science and Aquaculture, Faculty of Agriculture and Horticulture, Humboldt University, Berlin, Germany.
Lecture: Bioenergetics of fishes (in English, WS 2000/01, WS 2002/03, WS 2004/2005).
Part of the lecture: Introduction in fishery science and aquaculture (in English, SS 2002, SS 2003, SS 2004, SS 2005).

Institute of Hydrobiology and Fishery Science, University of Hamburg, Germany
Lecture: From experiments to modelling: How to plan and to carry out a master thesis in aquatic ecology (SS 2004, SS 2006).
Advanced training for teachers (biology, environmental issues, and health)
· Lecture: Ecosystem of the River Elbe (SS 1996)
· Excursion: Ecological excursions on the River Elbe (SS 1997)
Teaching assistant:
· Introduction to fishery biology (WS 1993/94)
· Methods of fishery science (WS 1995/96, WS 1996/97)
· Practical course: Introduction to the objects of hydrobiology (SS 1995)

Institute of Biochemistry and Biology, University of Potsdam, Germany
Lecture: Ecology and diversity of fishes (SS 2004, SS 2006 together with Jörg Freyhof)

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Publications in peer-reviewed journals and books

[32] Stief, P. & Hölker, F. (2006): Trait-mediated indirect effects of predatory fish on oxygen dynamics and microbial mineralization in aquatic sediments. Ecology, in press.

[31] Hölker, F. (2006): Effects of body size and temperature on respiration of common bream compared to sympatric roach. Animal Biology, 56: 23-37.

[30] Schulze, T., Baade, U., Dörner, H., Eckmann, R., Haertel-Borer, S.S., Hölker, F. & Mehner, T. (2006): Interactions of residential piscivores with an introduced new predator type in a mesotrophic lake. Canadian Journal of Fisheries and Aquatic Sciences, in press.

[29] Ohlberger, J., Staaks, G. & Hölker F. (2006): Swimming efficiency and the influence of morphology on swimming costs. Journal of Comparative Physiology B, 176: 17-25.

[28] Dörner, H., Schulze, T., Mehner, T. & Hölker, F. (2006): Increasing water temperature induced no increase in mortality in small perch marked with coded wire tags (CWT). Journal of Fish Biology, in press.

[27] Schulze, T., Dörner, H., Hölker, F. & Mehner, T. (2006): Determinants of habitat use in large roach. Journal of Fish Biology, in press.

[26] Irmler, U., Hölker, F., Pfeiffer, H.-W., Nellen, W. & Reuter, H. (2006): Biocoenotical interactions between different ecotopes. Ecological Studies, in press.

[25] Hölker, F. & Stief P. (2005): Adaptive behaviour of chironomid larvae (Chironomus riparius) in response to chemical stimuli from predators and resource density. Behavioral Ecology and Sociobiology, 58: 256-263.

[24] Hölker, F. & Breckling, B. (2005): A spatial explicit bioenergetics individual-based model of roach (Rutilus rutilus) to investigate emergent properties at the organismal and at the population level. Ecological Modelling, 186: 406-426.

[23] Hölker, F. & Mehner, T. (2005): Simulation of trait-mediated and density-mediated indirect effects of piscivorous predators on a lake food web. Basic and Applied Ecology, 6: 289-300.

[22] Mehner, T., Ihlau, J., Dörner, H. & Hölker, F. (2005): Can feeding of fish on terrestrial insects subsidize the nutrient pool of lakes? Limnology and Oceanography, 50: 2022-2031.

[21] Mehner, T., Hölker, F. & Kasprzak, P. (2005): Spatial and temporal heterogeneity of trophic variables in a deep lake as reflected by repeated singular samplings. Oikos, 108: 401-409.

[20] Breckling, B., Müller, F. Reuter, H., Hölker, F. & Fränzle, O. (2005): Emergent properties in individual-based ecological models - introducing case studies in an ecosystem research context. Ecological Modelling, 186: 376-388.

[19] Reuter, H., Hölker, F., Middelhoff, U., Jopp, F., Eschenbach, C. & Breckling, B. (2005): The concepts of emergent and collective properties in individual-based models - Summary and outlook of the Bornhöved case studies. Ecological Modelling, 186: 489-501.

[18] Ohlberger, J., Staaks, G., van Dijk, P.L.M. & Hölker F. (2005): Modelling energetic costs of fish swimming. Journal of Experimental Zoology 303A: 657-664.

[17] Haertel-Borer, S.S., Zak, D., Eckmann, R., Baade, U. & Hölker, F. (2005): Population density of the crayfish, Orconectes limosus, in relation to fish and macorinvertebrate densities in a small mesotrophic lake - implications for the lake's food web. International Review of Hydrobiology, 90:523-533.

[16] Knopf, K. & Hölker F. (2005): First report of Philometra obturans (Nematoda) and Ergasilus japonicus (Copepoda) in Germany. Acta Parasitologica 50: 261-262.

[15] van Dijk, P.L.M., Hardewig, I. & Hölker, F. (2005): Energy reserves during food deprivation and compensatory growth in juvenile roach: the importance of season and temperature. Journal of Fish Biology 66: 167-181.

[14] Hölker, F., Volkmann, S., Wolter, C., van Dijk, P.L.M., & Hardewig, I. (2004): Colonization of the freshwater environment by a marine invader: How to cope with warm summer temperatures. Evolutionary Ecology Research, 6: 1123-1144.

[13] Hölker, F. & Haertel, S.S. (2004): Application of a bioenergetics model to roach. Journal of Applied Ichthyology, 20: 548-550.

[12] Schulze, T., Baade, U., Dörner, H., Eckmann, R., Haertel, S.S., Hölker, F. & Mehner, T. (2004): Impact of zander stocking on the food composition of perch and pike in a mesotrophic lake. In Percis III (Barry, T.P. & J.A. Malison, Eds.), University of Wisconsin Sea Grant Institute, Madison, WI, p. 102-103.

[11] Hölker, F. (2003): The metabolic rate of roach in relation to body size and temperature. Journal of Fish Biology 62: 565-579.

[10] Hölker, F., Haertel, S.S., Steiner, S. & Mehner, T. (2002): Effects of piscivore-mediated habitat use on growth, diet and zooplankton consumption of roach: an individual-based modelling approach. Freshwater Biology 47: 2345-2358.

[9] Hölker, F., Breckling, B. & Steinberg, C.E.W. (2002): Introduction to the contributions. In: Scales, hierarchies and emergent properties in ecological models (Hölker, F. ed.). Theorie in der Ökologie, Peter Lang, Frankfurt/M., p. 1-6.

[8] Hölker, F. & Breckling, B. (2002): Concepts of scales, hierarchies and emergent properties in ecological models. In: Scales, hierarchies and emergent properties in ecological models (Hölker, F. ed.). Theorie in der Ökologie, Peter Lang, Frankfurt/M., p. 7-27.

[7] Hölker, F. & Breckling, B. (2002): Influence of activity in a heterogeneous environment on the dynamics of fish growth: an individual-based model of roach. Journal of Fish Biology 60: 1170-1189.

[6] Hölker, F. & Breckling, B. (2001): An individual-based approach to depict the influence of the feeding strategy on the population structure of roach (Rutilus rutilus L.). Limnologica 31: 69-79.

[5] Hölker F. (2000) Bioenergetik dominanter Fischarten (Abramis brama (Linnaeus, 1758) und Rutilus rutilus (Linnaeus, 1758)) in einem eutrophen See Schleswig-Holsteins - Ökophysiologie und Individuen-basierte Modellierung. EcoSys (Suppl.) 32: 1-117.

[4] Hölker, F. & Thiel, R. (1998). Biology of ruffe (Gymnocephalus cernuus (L.)) - A review of selected aspects from European literature. Journal of Great Lakes Research 24: 186-204.

[3] Hölker, F. & Breckling, B. (1998): Object orientation in fish modeling - simulation of roach activity (Rutilus rutilus) in Lake Belau, Germany. In: Breckling, B. & Islo, H. (eds.), Object oriented modelling and simulation. Association of Simula Users, p. 41-52.

[2] Hölker, F. & Temming, A. (1996). Gastric evacuation in ruffe (Gymnocephalus cernuus (L.) and the estimation of food consumption from stomach content data of two 24-h fisheries in the Elbe Estuary. Archive of Fishery and Marine Research 44: 47-67.

[1] Hölker, F. & Hammer, C. (1994). Growth and food of ruffe Gymnocephalus cernuus (L.) in the lower Elbe River. Archive of Fishery and Marine Research 42: 47-61.

Non peer-reviewed articles and reports

[13] Dörner, H., Eckmann, R., Haertel-Bohrer, S.S., Hölker, F., Schulze, T. & Mehner, T. (2005): Habitatnutzung und Aktivität einer planktivoren Fischgemeinschaft in Reaktion auf das Auftreten eines neuen Räubertyps. Erweiterte Zusammenfassung Jahrestagung DGL, 2004, 336-339.

[12] Knopf, K., Krieger A. & Hölker F. (2005): Parasite community and parasite-induced mortality of over-wintering young-of-the-year roach (Rutilus rutilus). Berichte des IGB, 22: 154-163.

[11] Schulze, T., Baade, U., Dörner, H., Eckmann, R., Haertel, S.S., Hölker, F. & Mehner, T. (2004): Die Auswirkung eines Zanderbesatzes auf Barsch und Hecht in einem mesotrophen See. Erweiterte Zusammenfassung Jahrestagung DGL, 2003, 352-356.

[10] Dörner, H., Diekmann, H. & Hölker, F. (2003): Limnoökologie in Europa, Bericht vom dritten Symposium für Europäische Forschung an Binnengewässern. Fischer & Teichwirt, 54: 425-428.

[9] Hölker, F., Haertel, S.S., Steiner, S. & Mehner, T. (2003): Effects of predator-mediated habitat use habitat use on diet and growth of roach. Berichte des IGB, 17: 59-68.

[8] Breckling, B., Reuter, H., Jopp, F., Hölker, F., Middelhoff, U. & Eschenbach, C. (2002). Simula meets Ecology II: Object oriented model applications. ASU Newsletter, 27: 1-37.

[7] Pecher, W.T., Mokhtari-Derakshan, F., Hölker, F. & Böckler, W. (1998). Erste Befunde zur Helminthenfauna ausgewählter Süßwasserfische aus Schleswig-Holstein (Norddeutschland). Mitt. Österr. Ges. Tropenmed. Parasitol., 20: 117-122.

[6] Opitz, S., Barkmann, S., Bertram, C., Dienemann, P., Gessner, M., Hölker, F., Löhlein, B., Müller, U., Newzella, R., Schieferstein, B., Zimmermann, H. & Pöpperl, R. (1997). Ein quantitatives Nahrungsnetz-Modell für das Litoral des Belauer Sees (Schleswig-Holstein). Erweiterte Zusammenfassung Jahrestagung DGL, 1996, 186-190.

[5] Hölker F., Nellen W. & Thiel R. (1997). Der Kaulbarsch - als blinder Passagier in Nordamerika. Fischer & Teichwirt 48: 147-150.

[4] Bertram, C., Hölker, F., Moeschke, R., Pfeiffer, H.W. & Nellen, W. (1996): Abschlußbericht TV 6.6: Nekton (PZÖ-TVB 11), 134 pp.

[3] Hölker, F. & Temming, A. (1995). Zur Nahrungsbiologie des Kaulbarsches (Gymnocephalus cernuus L.), in der Unterelbe. Erweiterte Zusammenfassung Jahrestagung DGL, 1994, 657-661.

[2] Nellen, W., Thiel, R., Hölker, F. & Breckling, P. (1994). Überlegungen zu fischereilichen Perspektiven der Elbe. Fischer & Teichwirt 44: 265-267.

[1] Bertram, C., Hölker, F., Moeschke, R. & Nellen, W. (1994). Nekton. Int. Mitt. Ökosystemforschung im Bereich der Bornhöveder Seenkette 1: 239-252.

Editorial

Hölker, F., ed. (2002): Scales, hierarchies and emergent properties in ecological models. Theorie in der Ökologie, Peter Lang, Frankfurt/M.

Organisation of conferences

Session: Verhaltensstudien in der aquatischen Ökologie: Beitrag zum Verständnis von Populationsdynamik und Nahrungsnetzen. Jahrestagung der Deutschen Gesellschaft für Limnologie, Potsdam, September 2004.

Session: Emergent ecosystem properties: from individual properties to community dynamics, Jahrestagung der Gesellschaft für Ökologie, Halle, September 2003.

8^th conference of individual-based and structural-functional models in ecology, Helenenau bei Berlin, Juli 2000.

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