Predation plays a central role in evolutionary processes, but little is known about how predators affect the expression of heritable variation, restricting our ability to predict evolutionary effects of predation. We reared families of three-spined stickleback Gasterosteus aculeatus from two populations-one with a history of fish predation (predator sympatric) and one without (predator naive)-and experimentally manipulated experience of predators during ontogeny. For a suite of ecologically relevant behavioural ('personality') and morphological traits, we then estimated two key variance components, additive genetic variance (V A ) and residual variance (V R ), that jointly shape narrow-sense heritability (h 2 Z V A /(V A C V R )). Both population and treatment differentially affected V A versus V R , hence h 2 , but only for certain traits. The predator-naive population generally had lower V A and h 2 values than the predator-sympatric population for personality behaviours, but not morphological traits. Values of V R and h 2 were increased for some, but decreased for other personality traits in the predator-exposed treatment. For some personality traits, V A and h 2 values were affected by treatment in the predator-naive population, but not in the predator-sympatric population, implying that the latter harboured less genetic variation for behavioural plasticity.Replication and experimental manipulation of predation regime are now needed to confirm that these population differences were related to variation in predator-induced selection. Cross-environment genetic correlations (r A ) were tight for most traits, suggesting that predator-induced selection can affect the evolution of the same trait expressed in the absence of predators. The treatment effects on variance components imply that predators can affect evolution, not only by acting directly as selective agents, but also by influencing the expression of heritable variation.

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Abstract.Ecosystem engineering research has recently demonstrated the fundamental importance of non-trophic interactions for food-web structure. Particularly, by creating benign conditions in stressful environments, ecosystem engineers create hot beds of elevated levels of recruitment, growth, and survival of associated organisms; this should fuel food webs and promote production on the ecosystem scale. However, there is still limited empirical evidence of the influence of non-trophic interactions on the classical food-web processes that determine energy transfer, that is, consumer-resource interactions. On the basis of a biomanipulation experiment covering 600 m 2 of an intertidal flat, we show that ecosystem engineers influence resource uptake efficiency and the accumulation of algae following nutrient enrichment in a soft-sediment food web. Nutrient additions increased chlorophyll a concentrations in the sediment by 90%, but only in plots where we also introduced high densities (2000 per m 2 ) of a burrowing bivalve, the common cockle Cerastoderma edule. The artificial cockle beds increased the nutrient uptake efficiency of the biofilm and promoted sediment accumulation, which suggests that the cockles facilitated the sediment-living algae by increasing sediment stability. This indicates that ecological interactions, rather than the availability of nutrients per se, set the limits for production in this coastal ecosystem. Our results emphasize the need to include facilitation theory and recognize that positive interactions between species are key to understand, manage, and restore ecosystems under human influence.

Modern agricultural landscapes suffer heavily from biodiversity loss. To counter this loss, it is important to understand the key factors that affect biodiversity in these landscapes. We studied the relationships between breeding birds and the habitat characteristics of the small-scale hedgerow landscapes of East-Fryslân, The Netherlands, a typical agricultural landscape that is under pressure from upscaling and habitat degradation. We questioned whether our findings collaborate the results of hedgerow studies from other countries. We also analysed whether agri-environmental schemes were effective for breeding birds. In this study, breeding birds and fifteen habitat factors were surveyed along 170 transects in two different regions in East-Fryslân in 2018. 37 bird species were identified, of which 19 were woodland species, 18 shrub species and 7 hedgerow specialists. We found five habitat characteristics to be key factors for breeding bird numbers. Four of these factors were intrinsic factors of the hedges (i.e. shrub cover, cover of brambles and nettles, crown width, hedge width at the base) and one spatial factor (i.e. number of hedge corners within a 150-m radius, corresponding to hedge intersections). Four key factors were the same for the two regions, but effect sizes differed between factors and species groups. As proxies for habitat volume (amount of habitat), the intrinsic key factors for hedgerow breeding birds in East-Fryslân correspond to those found in Britain and Eastern Europe, despite considerable differences in botanical composition, structure and management of the hedges. In contrast to studies on British hedges, we found mainly quantitative key factors and only one qualitative factor (cover of brambles and nettles). We found one spatial key factor (hedge intersections) and no correlation of bird numbers with density of hedges in the vicinity. We discuss the ecology of the key factors with respect to food provisioning and breeding. We also conclude that agri-environmental schemes favour key habitat factors and through this shrub birds. Implications of our findings are that traditional management favours breeding birds, but also that management should partly be extensified.