When an opportunistic predator is looking for a given type of prey and encounters another one from different species, it tries to utilize this random opportunity. We characterize the optimal levels of this opportunism in the framework of stochastic models for the two prey-one predator case. We consider the spatial dispersal of preys and the optimal diet choice of predator as well. We show that when both preys have no handling time, the total opportunism provides maximal gain of energy for the predator. When handling times differ with prey, we find a conditional optimal behavior: for small density of both prey species the predator prefers the more valuable one and is entirely opportunistic. However, when the density of the more valuable prey is higher than that of the other species, then the predator prefers the first one and intentionally neglects the other. Furthermore, when the density of the less valuable prey is high and that of the other one is small, then predator will look for the less valuable prey and is therefore totally opportunistic. We demonstrate that prey preference is remunerative whenever the advantage of a proper prey preference is larger than the average cost of missed prey preference. We also propose a dynamics which explicitly contains two sides of shared predation: apparent mutualism and apparent competition, and we give conditions when the rare prey goes extinct.
Authors:M. Mori, M. Inagaki, T. Inoue, and M. Nachit
In rain-fed agricultural regions, limited rainfall and frequent unpredictable droughts have resulted in low and variable wheat yields. Balanced water use between root water-uptake and remaining soil moisture is a key factor for drought adaptation. Thirteen recombinant inbred lines selected from a backcross population of synthetic-derived bread wheat were examined for the association among root water-uptake ability, grain yield and root elongation under limited water conditions using pot and field experiments. The effect of wax coating on grain formation under soil desiccation was also studied in two selected genotypes. There were significant variations in both root water-uptake ability estimated in pot experiments and grain yield obtained in field experiments among wheat genotypes. Infrared thermography indicated that canopy temperature was related to the leaf transpiration due to root water-uptake. A significant negative correlation was found between root water-uptake ability and grain weight, suggesting that lower root water-uptake ability was associated with higher grain weight. Genotype SYN-10 had the lowest water-uptake ability and the highest grain weight, indicating a type of ‘water-saving wheat’. Wax coating significantly reduced root water-uptake in wheat genotypes SYN-8 and SYN-10. Infrared thermography showed an increased leaf temperature due to the transpiration-suppression effect of the wax coating. Reductions in grain yield due to soil desiccation were found in SYN-8, but not in SYN-10. The higher grain yield of SYN-10 was attributed to more grains under soil desiccation. Grain yield of SYN-10 was decreased by the wax coating under soil desiccation. Dehydration tolerance of SYN-10 might be associated with the transpiration process of the leaves.