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.

No abstract

No abstract

Large herbivores are key drivers of nutrient cycling in ecosystems worldwide, and hence they have an important influence on the productivity and species composition in plant communities. Classical theories describe that large herbivores can accelerate or decelerate nitrogen (N) mineralization by altering the quality and quantity of resource input (e.g. dung, urine, plant litter) into the soil food web. However, in many situations the impact of herbivores on N mineralization cannot be explained by changes in resource quality and quantity. In this paper, we aim to reconcile observations of herbivores on N mineralization that were previously regarded as contradictory. We conceptually integrate alternative pathways via which herbivores can alter N mineralization. We illustrate our new integrated perspective by using herbivore-induced soil compaction and subsequent changes in soil moisture and soil aeration as an example. We show that the net effect of herbivores on mineralization depends on the balance between herbivoreinduced changes in soil physical properties and changes in the quality and quantity of resource input into the soil food web. For example, soil compaction by herbivores can limit oxygen or water availability in wet and dry soils respectively, particularly those with a fine texture. This can result in a reduction in N mineralization regardless of changes in resource quality or quantity. In such systems the plant community will shift towards species that are adapted to waterlogging (anoxia) or drought, respectively. In contrast, soils with intermediate moisture levels are less sensitive to compaction. In these soils, N mineralization rates are primarily associated with changes in resource quality and quantity. We conclude that our integrated perspective will help us to better understand when herbivores accelerate or decelerate soil nutrient cycling and improve our understanding of the functioning of grazed ecosystems.