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Prey species are often non-randomly distributed along predator gradients but according to how they trade off growth against predation risk. The foraging-mediated growth/predation risk trade-off is well established, with increased foraging accelerating growth but also increasing predator induced mortality. While adaptations in digestive physiology may partly modify the relationship between foraging and growth in response to predation risk, studies exploring the impact of digestive physiology on growth in prey subjected to predation risk are still scarce. Larvae of the dragonfly genus Leucorrhinia segregate at the species level between lakes either being dominated by predatory fish (fish-lakes) or predatory invertebrates (dragonfly-lakes). Predators of these two lake types differ dramatically in their hunting style like searching and pursuing mode causing different selection pressure on prey traits including foraging. In a laboratory experiment we estimated growth rate, digestive physiology (ingested food, growth efficiency, assimilation efficiency, conversion efficiency) and metabolic rate (oxygen consumption) in the presence and absence of predator cues. Whereas fish-lake and dragonfly-lake Leucorrhinia species did not differ in growth rate, they evolved different pathways of digestive physiology to achieve similar growth rate. Because fish-lake species expressed a higher metabolic rate than dragonfly-lake species, we assume energy to be differently allocated and used for metabolic demands between species of both predator environments. Further, growth rate, but not digestive physiology was plastic in response to the presence of predator cues. Our results highlight the impact of digestive physiology in shaping the foraging-mediated growth/predation risk trade-off, with digestive physiology contributing to species distribution patterns along predator gradients. [ABSTRACT FROM AUTHOR]

This study was conducted in the course of a fen rewetting project in NE Germany aiming to restore a heavily drained spring-percolation mire used as pasture land for more than 100 years. Shallow top soil removal (TSR) up to 40 cm was applied to remove the upper degraded peat layer in order to eliminate accumulated nutrients and unwanted seed banks as well as generating material for infilling drain ditches and building dams. This measure has well known positive effects on species development, but very little was known about the phosphorus (P) status in the newly exposed peat soils and porewater. Therefore, we investigated (i) the P mobilisation potential of surface peat soils, (ii) net P release rates in intact soil cores with different degree of peat decomposition, and (iii) P concentrations in porewater of rewetted fen areas with TSR compared to areas without removal and refilled drain ditches. We highlighted that TSR strongly reduced the P mobilisation potential and thereby also the concentration of dissolved P in the porewater at the peat surface. Furthermore, we found low net P release rates close to 0 mg P m −2 d −1 (median, n = 9) in the cut-over areas with less degraded peat similar to those documented for natural fens. Despite of high P concentrations up to 2.6 mg L −1 in rewetted areas without TSR (about 50% of total peatland area) there was no evidence of elevated P export to other low-nutrient areas of the fen or in a close-by lake due to high P retention capacity of the iron-rich degraded peat (molar Fe:P ratios >10). It can be concluded that TSR is a suitable measure to recover nutrient poor conditions in rewetted fens in a relatively short timeframe instead of decades to centuries compared to rewetting measures without TSR. This measure is highly recommended if degraded peatlands are characterised by a low P retention capacity or low molar Fe/P ratios in degraded peat (<10) respectively and above all if downstream areas include nutrient-poor systems highly sensitive regarding slightly increased P inputs. [ABSTRACT FROM AUTHOR]