A Review of Ecological Models for Brown Trout: Towards a New Demogenetic Model

Ecology of Freshwater Fish 2011: 20: 167–198 Ó 2011 John Wiley & Sons A/S Printed in Malaysia Æ All rights reserved ECOLOGY OF FRESHWATER FISH Review A review of ecological models for brown trout: towards a new demogenetic model Beátrice M. Frank1, John J. Piccolo2, Philippe V. Baret1 1Earth and Life Institute, Universite´ catholique de Louvain, Louvain-la-Neuve, Belgium 2Biology Department, Karlstad University, Karlstad, Sweden Accepted for publication January 20, 2011 Abstract – Ecological models for stream fish range in scale from individual fish to entire populations. They have been used to assess habitat quality and to predict the demographic and genetic responses to management or disturbance. In this paper, we conduct the first comprehensive review and synthesis of the vast body of modelling literature on the brown trout, Salmo trutta L., with the aim of developing the framework for a demogenetic model, i.e., a model integrating both population dynamics and genetics. We use a bibliometric literature review to identify two main categories of models: population ecology (including population dynamics and population genetics) and population distribution (including habitat–hydraulic and spatial distribution). We assess how these models have previously been applied to stream fish, particularly brown trout, and how recent models have begun to integrate them to address two key management and conservation questions: (i) How can we predict fish population responses to management intervention? and (ii) How is the genetic structure of fish populations influenced by landscape characteristics? Because salmonid populations tend to show watershed scale variation in both demographic and genetic traits, we propose that models combining demographic, genetic and spatial data are promising tools for improving their management and conservation. We conclude with a framework for an individual-based, spatially explicit demogenetic model that we will apply to stream-dwelling brown trout populations in the near future. Key words: brown trout; demogenetics; ecological model; population dynamics; population genetics population-level responses such as demographic Introduction (Elliott 1994) and genetic variations (Wright 1969). Over the past three decades, ecological models have Later developments included functions to predict increasingly been applied in the management and spatial patterns of either fish occurrence (e.g., Stanfield conservation of freshwater fish populations (e.g., & Gibson 2006) or genetic diversity (e.g., Dillane Larkin 1978; Barnard et al. 1995; Whipple et al. et al. 2008). Most recently, individual-based simula- 2000; Filipe et al. 2004; Einum et al. 2008). These tion techniques have been developed to explicitly models have been used to predict abundance and include individual variation, as well as demographic population growth rate (Lebreton 2006), population and environmental stochasticity, into ecological mod- subdivision and gene flow (Pearse & Crandall 2004), els (e.g., Strand & Niehaus 2007; Landguth & habitat quality (Anderson et al. 2006) and large-scale Cushman 2010; Schumaker 2011). distribution (Ahmadi Nedushan et al. 2006). Thus, The rapid expansion in ecological modelling paral- ecological models are increasingly being used to guide lels technological advances in field methods (i.e., management decisions, especially for threatened and individual tagging and tracking), computing, and exploited species. Models for stream fish have ranged genetic analyses. Stream ecologists are now poised in scale from individuals to populations; early models to model and to better understand how the interaction focused on physical habitat (Bovee 1982) and on of demographic and genetic factors influences the Correspondence: B. M. Frank, Earth and Life Institute, Universite´ catholique de Louvain, Croix du Sud 2, Box 14, B-1348 Louvain-la-Neuve, Belgium. E-mail: [email protected] doi: 10.1111/j.1600-0633.2011.00491.x 167 Frank et al. distribution and abundance of fish. This is a daunting and molecular genetic techniques have contributed to task, however, because of the difficulty of assimilating improving the basic genetic information available on the broad knowledge base that has developed, some- population structure, both at large (Bernatchez 2001) what independently, in a number of subdisciplines and at small spatial scales (Hansen et al. 2001; (e.g., demography, genetics, physical habitat simula- Sonstebo et al. 2007b). Recent advances in fish tions, etc.). In this paper, we assemble and synthesise marking techniques, spatial analyses and molecular for the first time the vast body of ecological modelling genetics have allowed the establishment of long-term literature on stream fish, focusing on the brown trout, data sets of demography and population genetic Salmo trutta L. Our goal is to demonstrate how these structure based on sampling of individual fish (e.g., previously independent models have begun to be Hansen et al. 2002; Lobon-Cervia & Rincon 2004; integrated, and how further integration will allow Fraser et al. 2007; Haugen et al. 2008). Although ecologists to better address important questions for the advances have been achieved in both population management and conservation of freshwater fish. dynamics and population genetics models, compre- The brown trout is a species particularly well-suited hensive models that integrate these two characteristics for serving as a model organism for both management of salmonid populations are still in their infancy and conservation. Its quantitative ecology, from indi- (Palsboll et al. 2007). Because brown trout tend to vidual habitat selection to population dynamics, is as show both demographic variation and genetic diversity well known as that of any stream fish (e.g., Elliott at the watershed scale, models that link population 1994; but see numerous others). It is also one of the dynamics and genetics (i.e., demogenetics) across vertebrate species presenting the highest degree of spatial scales hold great promise in providing insights intraspecific biological diversity including strong into their management and conservation. genetic and phenotypic variation among populations In this review, we show how ecological models (Laikre 1999; Bernatchez 2001). This genetic vari- have previously been applied to stream fish popula- ability among brown trout populations is attributable tions, particularly brown trout, and how the most to several factors, including the effects of recent advanced models might be integrated to develop a new glaciations, the physical characteristics of the hydro- demogenetic model. First, we conduct a bibliometric graphic systems and local differentiation without review of the literature on ecological models for barriers owing to territorial behaviour and strong brown trout, and we identify and summarise two homing instinct (i.e., individuals return to spawn in the categories and four types of models that have been stream in which they were born) (Laikre 1999; developed over the past 30 years. Then, we demon- Antunes et al. 2006). These factors result in limited strate how some of these models have already begun gene flow among populations, producing partially to be integrated, and how they might be used to isolated random mating units both within and among address two key questions relevant to the conservation watersheds (Ferguson 1989). This often leads to and management of stream fish: (i) How can we adaptation to local environmental conditions, changes predict fish population responses to management in genetic structure and the development of unique intervention? and (ii) How is the genetic structure of demographic traits like morphology, feeding prefer- fish populations influenced by landscape characteris- ences and life history strategies (Laikre 1999; Klemet- tics? We conclude with a framework for a new sen et al. 2003; Ferguson 2006). The importance of demogenetic model for brown trout populations that this intraspecific diversity for fisheries management will further integrate existing theory through the use of has long been recognised (e.g., Ricker 1972; Spangler an individual-based, spatially explicit platform. et al. 1981; Taylor 1991), and most recently Schindler et al. (2010) identified its crucial role in providing Methods ecosystem services. Human activities, including environmental degradation (pollution, altered flow, frag- We developed a bibliometric approach to identify the mentation of habitat), fishing and fish stocking (Laikre main topics addressed by scientific publications of 1999; Cowx & Gerdeaux 2004; Dudgeon et al. 2006), ecological models for brown trout. We followed two have resulted in a loss of intraspecific diversity of steps: the selection of publications, and the construc- brown trout, and many remaining native stocks are tion of the corresponding directed network of citations. now faced with a medium-term risk of extinction (e.g., In the first step, we used the ISI Web of Knowl- Laikre 1999; Caudron et al. 2010). edgeSM search engine to identify key publications, the In recent years, considerable attention has been paid references they cited and those that cited them to the ecology of brown trout. Population dynamics of (Table 1). We selected 68 publications (from 2003 to a number of populations were reviewed (e.g., Roussel 2008), among which 59 articles, seven proceedings & Bardonnet 2002; Klemetsen et al. 2003; Lobon- papers, one editorial material and one review, and their Cervia 2005, 2007; Northcote & Lobon-Cervia 2008), 2964 citations (from

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