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  • 1.
    Liess, Antonia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rowe, Owen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pete, R.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Uszko, Wojciech
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Francoeur, S. N.
    Terrestrial runoff may reduce microbenthic net community productivity by increasing turbidity: a Mediterranean coastal lagoon mesocosm experiment2015In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 753, no 1, p. 205-218Article in journal (Refereed)
    Abstract [en]

    Terrestrial runoff into aquatic ecosystems may have both stimulatory and inhibitory effects, due to nutrient subsidies and increased light attenuation. To disentangle the effects of runoff on microbenthos, we added soil to coastal mesocosms and manipulated substrate depth. To test if fish interacted with runoff effects, we manipulated fish presence. Soil decreased microphytobenthic chlorophyll-a per area and per carbon (C) unit, increased microbenthic phosphorous (P), and reduced microbenthic nitrogen (N) content. Depth had a strong effect on the microbenthos, with shallow substrates exhibiting greater microbenthic net ecosystem production, gross primary production, and community respiration than deep substrates. Over time, micobenthic algae compensated for deeper substrate depth through increased chlorophyll-a synthesis, but despite algal shade compensation, the soil treatment still appeared to reduce the depth where microbenthos switched from net autotrophy to net heterotrophy. Fish interacted with soil in affecting microbenthic nutrient composition. Fish presence reduced microbenthic C/P ratios only in the no soil treatment, probably since soil nutrients masked the positive effects of fish excreta on microbenthos. Soil reduced microbenthic N/P ratios only in the absence of fish. Our study demonstrates the importance of light for the composition and productivity of microbenthos but finds little evidence for positive runoff subsidy effects.

  • 2.
    Liess, Antonia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Laboratoire Ecosystémes Marins Côtiers, UMR5119 CNRS, Université Montpellier2, IRD, IFREMER, Paris, France.
    Rowe, Owen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Francoeur, S. N.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lange, K.
    Schroeder, A.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lefèbure, Robert
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mathisen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial runoff boosts phytoplankton in a Mediterranean coastal lagoon, but these effects do not propagate to higher trophic levels2016In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 766, no 1, p. 275-291Article in journal (Refereed)
    Abstract [en]

    Heavy rainfall events causing significant terrestrial runoff into coastal marine ecosystems are predicted to become more frequent with climate change in the Mediterranean. To simulate the effects of soil runoff on the pelagic food web of an oligotrophic Mediterranean coastal lagoon, we crossed soil extract addition (increasing nutrient availability and turbidity) and fish presence in a full factorial design to coastal mesocosms containing a natural pelagic community. Soil extract addition increased both bacteria and phytoplankton biomass. Diatoms however profited most from soil extract addition, especially in the absence of fish. In contrast zooplankton and fish did not profit from soil extract addition. Furthermore, our data indicate that nutrients (instead of light or carbon) limited basal production. Presumed changes in carbon availability are relatively unimportant to primary and secondary production in strongly nutrient limited systems like the Thau Lagoon. We conclude that in shallow Mediterranean coastal ecosystems, heavy rainfall events causing soil runoff will (1) increase the relative abundance of phytoplankton in relation to bacteria and zooplankton, especially in the absence of fish (2) not lead to higher biomass of zooplankton and fish, possibly due to the brevity of the phytoplankton bloom and the slow biomass response of higher trophic levels.

  • 3.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Science and Mathematics Education.
    Achieving sustainability in an unpredictable global world?: The Swedish National Curriculum in the tension field between internationalization and sustainability2023In: NOFA9: Book of abstracts, 2023, p. 114-115Conference paper (Refereed)
    Abstract [en]

    Education is frequently put forward as a key to achieve societal change towards sustainability. National curricula present guidelines for educational practice stating what knowledge and skills students need to be prepared for future challenges. The curriculum is a canvas painted with imaginaries of a desired future. The description of knowledge, the use of concepts, and the emphasis put on different sections defineeducational practice.

    Here, I critically analyze the sustainability discourse in the Swedish national curriculum using Carol Bacchi’s WPR- approach keeping the following questions in mind: How is sustainability described in the curriculum? What are the challenges? What knowledge and skills are needed? So far, results show that sustainability imaginaries differ between sections. The first general section describes the purpose of education asl laying the foundation for democratic values, lifelong learning, and respect for thee nvironment and human rights. Accordingly, teachers’ shall on the one hand prepare students to become competitive in face of internationalization and a competitive mobile labor market, and on the other hand to take collective action to solve complex environmental issues. A sustainability imaginary composed of competing individuals that take collective action or an oxymoron?

    Both, competition and collective action, call for creativity, curiosity, self-confidence, communicative and social skills, as well as dynamic thinking and an understanding of the relativity of knowledge. The second subject-specific section describes education content and knowledge requirements with a focus on individual assessment. In their planning, teachers refer to this section more frequently than to the general section. Therefore, it is astonishing that collective action is touched upon only marginally here.

    Finally, although education for sustainability is presented as the key to collective action for societa lchange towards sustainability, the subject-specific section is dominated by sustainability imaginaries that emphasize individuals’ competitiveness rather than collective action.

  • 4.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Science and Mathematics Education.
    Building sustainable futures though research and education: foundational ES/ESE imagery diversity in peer-reviewed educational research literature2023In: ECER 2023: Programme, 2023, article id 30 SES 03 BConference paper (Refereed)
    Abstract [en]

    In Western countries, citizens spend a significant part of their life embedded in an educational system. Educational systems present facts and structures explicitly by WHAT is taught and assessed, and implicitly by HOW it is taught and assessed. Hence, education affects citizens’ perceptions of societal values in terms of both knowledge and behavior. Consequently, education can be expected to have homogenizing effects on citizens. Depending on WHAT and HOW we teach and assess, diversity in knowledge, values, and attitudes can either be acknowledged and embraced, or silenced and rejected.

    In times of sustainability crisis, education has been identified as a key component to solve environmental and sustainability challenges. Education for Sustainability (ES) andEnvironmental and Sustainability Education (ESE) acknowledge educational systems’ potential to prepare citizens, and aim at fostering responsible citizens that act for sustainable futures (Eilks et al., 2019; Niebert, 2018). To pursue sustainability - the mitigation of environmental impact to ensure the prevailing of a viable and livable planet Earth for all living organisms (human and non-human) - demands radical societal change in Western countries. Economies and lifestyles must be adjusted (Niebert, 2019, and this in ways that decenter us humans to make room for more relational approaches to planet earth and its inhabitants (UNESCO, 2021). For this adjustment of economies and lifestyles, citizens must perceive change and diverse views as valued in society. Educational systems must ensure not to reproduce, but to reconstruct, societies to enable transformation (Wals, 2022). Students and teachers must be invited to contribute to the diversity of solutions as knowledge producers rather than being presented with homogenizing one-fits-all solutions.

    I intend to stimulate awareness of and attentiveness to diverse views on sustainability in educational research. My focus concerns the diversity of applications and understandings of the concepts, ESand ESE, in peer reviewed educational research literature. A diversity with spatial, temporal, and cultural dimensions, and a concept with economical, ecological, and social dimensions. In Western countries, tensions between the economic dimension, and the ecological and societal dimensions have far-reaching consequences, not least on which views are amplified and which may be muffled. While economic forces ask for effectivization, ecological and social dimensions demand a slowdown of economy. A slowing down necessary to discover and explore alternative paths in a complex world. A complexity that must not be simplified for the sake of effectivization, but that should be embraced to explore diverse routes to sustainable futures (UNESCO 2021). Hence, I explore how the economically-dependent research machinery (cf., Savat & Thompson, 2015) affects the pace of ES/ESE research, and thereby our openness for true change in the worst-case causing diversity loss in ES/ ESE discourse. An unintended loss of alternative views that could cloud our judgement of how to act towards sustainability.

    With my critical analysis of the ES/ESE discourse in the peer-reviewed literature, I intend to further stimulate discussions regarding educational systems’ purpose and ability to prepare students for our journey towards sustainability.  A matured discourse that has and still tends to evolve around dichotomies like instrumental - emancipatory (e.g., Wals, 2011), alternatively qualification – citizenship (e.g. (Bauer, 2003; Hansen & Phelan, 2019; Willbergh, 2015). Human-centered dichotomies questioned by researchers that take more critical posthuman perspectives on ES/ESE (e.g. Lysgaard 2019). Recently, the diversity of perspectives on ES/ESE has taken a leap. This development led me to ask the following questions:

    • What strands of ES/ESE discourse are represented in western peer-reviewed educational research literature?
    • How does ES/ESE research utilize these diverse views, are there tensions or co-actions?

    Method: To answer my research questions, I apply a critical discourse analytical perspective on sustainability problems’ representations in research literature concerning ES. My analytical methodology is inspired by Carol Bacchi’s (2009) “What is the problem represented to be?” (WPR)-approach, an approach developed for policy texts, but equally applicable to other text types dealing with problem identification and solution proposals. The WPR-approach is inspired by Foucault, and aims to make visible the unsaid, the presupposed, the assumed, the silenced, the historical and cultural influences, the taken-for granted, and unintended effects (Bacchi, 2010). To keep the study feasible, I chose to limit data collection culturally to the Western countries and to the last 10 -15 years. Even with this scope, the volume of publications dealing with ES/ESE is still immense. Therefore, I use a 3-step selection method to limit the number of publications for analysis: (1) database literature search followed by machine language learning assisted relevance check using ASReview (van de Schoot et al., 2021), (2) citation network analysis using the bibliometric tool Bibliometrix (Aria & Cuccurullo,2017) to analyze co-author, co-citation, and term-co-occurrence networks, and (3) argumentative zoning (Teufel, 1999). Steps 2 & 3 allow me to identify clusters to draw random samples for the critical discourse analysis on publications’ introduction and discussion sections. This methodology enables me to identify and validate clusters representing the ES/ESE discourse. To identify differences in discourse within and between co-author/co-citation clusters, I use term-co-occurrence to compare the use of ES/ESE specific terms. Overlap between term-co-occurrence clusters and co-author/citation clusters indicate similarity in term use. Non-overlapping discourse clusters, then, represent different ES/ESE constructs indicating a potential for homogenization within isolated clusters. Argumentative zoning uses machine language learning to label text sections according to whether the argument made is neutral, affirmative, or contradictory. This method can confirm clusters’ distinctions and relations. Publications assigned to the same cluster should be either found in affirmative or neutral zones, while publications assigned to different cluster should be in contradictory or neutral zones, if cited in a different cluster.

    Expected Outcomes: I expect the analysis to reveal diverse strands of ES/ESE imageries represented by different clusters. Here, the WPR-approach enables me not only to depict imageries that are in the spotlight, but also to lighten up those imageries’ twilight zones that are constituted of the usually unintendedly taken-for-granted or silenced imageries. My aim is to show the diverse applications and understandings of the concept sustainability that frame Western ES/ESE research. Research that will have implications for what and how sustainability issues are presented in our schools and universities, because it is this research that informs national and international education policies. As educational researchers, we provide society not only with knowledge but we are societies’ critical friends. Being a researcher means taking responsibility for society, and demands a self-reflective practice to be aware of your own assumptions, biases, and what we take for granted. I see my analysis of ES/ESE imageries in Western educational research as my contribution to self-reflection on the research-community level. I expect to find several ES/ESE imageries which will overlap to varying degrees. In other words, diverse ways of imagining ES/ESE and futures to create that are a necessary but not sufficient foundation to build sustainable futures upon. Not sufficient because for a foundation to support what is built sustainably, the foundation has to be utilized in a robust manner. How the foundation is utilized is what argumentative zoning and citation network analysis help me to unravel. Overall, I intend to map the complex Western ES/ESE research landscape by putting together the different ES/ESE imageries how they relate to each other, and where tensions and co-action occur. A map that can help us orient ourselves in a complex landscape ES/ESE of discourse and to stimulate co-actions.

  • 5.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ontogenetic bottlenecks: effects on intraguild predation systems and ecosystem efficiency2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Size-dependent differences between individuals in size-structured organisms have fundamental effect on population and community dynamics. Intraguild predation (IGP) is one specifically interesting constellation that often arises when two size-structured populations interact. Ontogenetic bottlenecks that determine population size-structure are affected by both population intrinsic as well as population extrinsic factors, and are therefore context-dependent. Surprisingly, size-structured IGP systems have mainly been investigated theoretically and especially long-term empirical studies are widely lacking. In this thesis I investigate empirically how habitat complexity, interaction strength, and stage-specific resource availabilities affect population processes and their effects on the dynamics of a size-structured IGP system. I conducted multi-generation experiments in a size-structured IGP system, with the Least Killifish (Heterandria formosa) as IG prey and the Common Guppy (Poecilia reticulata) as IG predator. With no alternative resource next to the shared resource, IG predator and IG prey could not coexist. Weak interactions only increased IG prey and IG predator persistence times and observed exclusion patterns depended on habitat complexity. An alternative resource for either the juvenile IG predator or the juvenile IG prey on the other hand promoted coexistence. However, this coexistence was context-dependent. Ontogenetic bottlenecks played a central role in the dynamics of the size-structured IGP system in general. In the final study I show that an ontogenetic bottleneck can, through changes in stage-specific resource availabilities, be affected in a way that leads to increased trophic transfer efficiency with potential effects on higher trophic levels.

    Overall, the results emphasize importance of the broader context in which size-structured communities are embedded. Especially, when managing natural communities it is important to account for the combined effects of size-structure, stage-specific resource availabilities, and habitat structure. Specifically, when managing species that connect habitats or ecosystems all life-stages’ environmental conditions must be consider in order to ensure strong predictive power of tools used for ecosystem management planning.

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  • 6.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, Andre M.
    Univ Amsterdam, Inst Biodivers & Ecosyst Dynam, NL-1090 GE Amsterdam, Netherlands.
    Ontogenetic asymmetry modulates population biomass production and response to harvest2015In: Nature Communications, E-ISSN 2041-1723, Vol. 6, article id 6441Article in journal (Refereed)
    Abstract [en]

    Patterns in biomass production are determined by resource input (productivity) and trophic transfer efficiency. At fixed resource input, variation in consumer biomass production has been related to food quality, metabolic type and diversity among species. In contrast, intraspecific variation in individual body size because of ontogenetic development, which characterizes the overwhelming majority of taxa, has been largely neglected. Here we show experimentally in a long-term multigenerational study that reallocating constant resource input in a two-stage consumer system from an equal resource delivery to juveniles and adults to an adult-biased resource delivery is sufficient to cause more than a doubling of total consumer biomass. We discuss how such changes in consumer stage-specific resource allocation affect the likelihood for alternative stable states in harvested populations as a consequence of stage-specific overcompensation in consumer biomass and thereby the risk of catastrophic collapses in exploited populations.

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  • 7.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, André M.
    Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands.
    Coexistence in a size-structured intraguild predation system promoted by an ontogenetic diet shift in the consumerManuscript (preprint) (Other academic)
    Abstract [en]

    In life history omnivore (IGP) systems coexistence between omnivore and consumer at high productivity has only been demonstrated when the omnivore undergoes a complete ontogenetic niche shift at or before maturity from feeding on the shared resource to feeding on the consumer. Here we investigate the effects of an exclusive resource for juvenile consumers on coexistence between omnivore and consumer. We demonstrate that an alternative resource for juvenile consumers allows for coexistence between omnivore and consumer species even when the adult omnivore feeds on the shared resource to a substantial extent. Coexistence is promoted by a strong niche separation in the consumer and when the productivity of the shared resource is high relative to the juvenile consumer exclusive resource. At high shared resource productivity coexistence is promoted by either a low or a high niche separation in the omnivore. In general our results suggest that for coexistence to occur at high productivities a strong life-history separation in resource use is necessary in either the consumer or the omnivore. Strong life-history separation in the omnivore results in predation driven coexistence, while strong life-history separation in the consumer results in competitive coexistence. 

  • 8.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, André M.
    Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands.
    Exclusive juvenile predator resource promotes coexistence in a size-structured intraguild predation systemManuscript (preprint) (Other academic)
    Abstract [en]

    Coexistence in size-structured intraguild predation systems is limited, and is predicted to occur when the IG predator exhibits a complete ontogenetic niche shift, has a similar asymptotic size as the IG prey, or has access to an exclusive resource. Here we experimentally test the effect of a juvenile IG predator exclusive resource by mimicking an ontogenetic habitat shift in the IG predator that switched either to a more or a less productive habitat at maturity. We show that coexistence depends on relative habitat productivities when refuges are present and cannibalism in the IG predator is low, but does not so when refuges are absent and cannibalism in the IG predator is substantial. Overall compared to previous experimental studies without an ontogenetic habitat shift, we how that an exclusive resource for juvenile IG predators promotes coexistence with context-dependent differences in the manifestation of this effect. 

  • 9.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, André M.
    Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands.
    Predator life history affects persistence times of predators and consumers in an intraguild predation systemManuscript (preprint) (Other academic)
    Abstract [en]

    Complex habitats and thereby weaker predator-prey interactions have been suggested to promote coexistence between predator and prey in intraguild predation (IGP) systems. For a size-structured IGP system spatial refuges have been shown to weaken interactions but not to promote coexistence. Spatial refuges however also affect the spatial distribution of small and large individuals. Here we report the results of a multi-generation laboratory experiment where we manipulated interaction strength by using the same IG predator (Common guppy, Poecilia reticulata) but a population with a different life-history evolution and lower predation voracity. Resident IG prey (Least Killifish, Heterandria formosa) were invaded by large or small IG predators, invasion success was recorded. Compared to the invasion by more voracious IG predator individuals, weaker predation per se (no refuges) did not affect invasion success but did increase IG prey and IG predator persistence times. Compared to the invasion by more voracious IG predator individuals in the presence of refuges, weaker predation per se (no refuges) resulted in similar persistence times but different invasion success.  We conclude that the effect on community dynamics depends on the context in which weak interactions are realized. Both spatial refuges and life-history differences affected predation strength and competitive relationships quantitatively but only when spatial refuges were present was this quantitative change coupled to qualitative changes in species interactions. Though under stable environmental conditions in our experiment coexistence did not occur we argue that in temporarily or spatially variable systems weak interactions have the potential to promote coexistence by prolonging IG predator and IG prey persistence times.

  • 10.
    Reichstein, Birte
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Schröder, Arne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    De Roos, A. M.
    Habitat complexity does not promote coexistence in a size-structured intraguild predation system2013In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 1, p. 55-63Article in journal (Refereed)
    Abstract [en]

    Size-dependent interactions and habitat complexity have been identified as important factors affecting the persistence of intraguild predation (IGP) systems. Habitat complexity has been suggested to promote intraguild (IG) prey and intraguild predator coexistence through weakening trophic interactions particularly the predation link. Here, we experimentally investigate the effects of habitat complexity on coexistence and invasion success of differently sized IG-predators in a size-structured IGP system consisting of the IG-predator Poecilia reticulata and a resident Heterandria formosa IG-prey population. The experiments included medium-long and long-term invasion experiments, predator-prey experiments and competition experiments to elucidate the mechanisms underlying the effect of prey refuges. Habitat complexity did not promote the coexistence of IG-predator and IG-prey, although the predation link was substantially weakened. However, the presence of habitat structure affected the invasion success of large IG-predators negatively and the invasion success of small IG-predators positively. The effect of refuges on size-dependent invasion success could be related to a major decrease in the IG-predator's capture rate and a shift in the size distribution of IG-predator juveniles. In summary, habitat complexity had two main effects: (i) the predation link was diminished, resulting in a more competition driven system and (ii) the overall competitive abilities of the two species were equalized, but coexistence was not promoted. Our results suggest that in a size-structured IGP system, individual level mechanisms may gain in importance over species level mechanisms in the presence of habitat complexity.

  • 11.
    Schröder, Arne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Karin A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    van Kooten, Tobias
    Wageningen IMARES, PO Box 68, 1970 AB Ijmuiden, The Netherlands.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Invasion success depends on invader body size in a size-structured mixed predation-competition system2009In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 78, no 6, p. 1152-1162Article in journal (Refereed)
    Abstract [en]

    1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation.

    2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment.

    3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated.

    4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity.

    5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck.

    6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.

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