title: Model-based analysis of causes for habitat segregation inIdoteaspecies (Crustacea, Isopoda).
abstract: On the shore of the rocky island of Helgoland (North Sea) two closely related isopod species,Idotea balthicaPallas, 1772, andIdotea granulosaRathke, 1843, share a similar fundamental niche but inhabit well-separated habitats.Idotea balthicainhabits floating algae at the sea surface and accumulations of decaying algae on the seafloor, whereasI. granulosaprimarily occurs in intertidal macroalgal belts. In laboratory experiments on individually reared isopodsI. balthicaoutperformedI. granulosawith regard to growth, reproduction, and mortality in both a fully inundated habitat and in a tidal habitat with 5 h of daily emergence. We hypothesized that habitat segregation in the two isopod species is driven by one or multiple types of biotic interactions: (1) no interaction, (2) cannibalism, (3) intraguild predation, and (4) terrestrial predation. In order to evaluate how habitat segregation can be explained by each of these interaction types we employed a size-structured population model to account for the body-size-dependent predation. Net population growth rates were fitted to the simulations as a measure of population fitness. Experimental results served as database for parameter and process identification. As predation rates were unknown, we performed a sensitivity analysis for these. We found that below 5 h of daily tidal emergence either cannibalism or terrestrial predation sufficed to explain habitat segregation. Intraguild predation, in contrast, advantagedI. balthicain any case. From linear extrapolation of the effects occurring under conditions of 5 h of daily tidal emergence, we predict that contrasting physiological responses inI. balthicaandI. granulosawould cause segregation even without any interaction if emergence lasted long enough.
authors.affiliation: Institute of Land Use Systems, Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Straße 84, 15374 Müncheberg, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Strer
authors.affiliation: DHI-WASY, Max-Planck-Str 6, 28857 Syke, Germany ; Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Hammrich
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Gutow
authors.affiliation: Institut für Geoökologie, Technische Universität Braunschweig, 38106 Brunswick, Germany ; Environmental Systems Analysis, Faculty of Life Sciences, Rhein-Waal University of Applied Sciences, 47533 Kleve, Germany.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Moenickes
keywords: Competition; Idotea balthica; Idotea granulosa; Intraguild predation; Physiologically structured population model (PSPM); Tidal influence on habitat segregation