Biotic Stress and Yield Loss

Although literature is drawn from a series of managed ecosystems, e.g., rangelands,this review emphasizes the changes associated with plant domestication in agriculture.Examination of the contrasts between wild and domesticated genotypes ultimatelyleads to a progressively entangling set of hypotheses that, like many hypothesesin ecology or agroecology, have mixed support. Difficulties quickly arise as eachhypothesis builds on the next until a potential house of cards is erected which may ormay not have a solid foundation. Alternatively, approaching each hypothesis independentlycarries the risk of failing to understand the interplay of the differentfactors.10.2 CROP DOMESTICATIONGiven that plant physiological and morphological traits have been shown to affectplant response to herbivory, contrasting wild and domesticated plants requires anunderstanding of the changes associated with domestication that might prove importantfor predicting responses to herbivory. The domestication of wild plants was initiatedapproximately 10,000 years ago and has been followed by a rapid spread fromtheir sites of origin by humans. Changes in almost all aspects of crop phenology,tolerance to environmental stress, physiology, and form have been reported, as wellas significant changes in the cropping ecosystem (Table 10.1). 13–22Overviews of crop domestication and the associated changes in genetic, physiological,and morphological attributes are discussed relative to their effects on yieldpotential, stability, and adaptiveness. 23–28 Kennedy and Barbour 10 provide a reviewof the genetically based changes in resistance to herbivory among wild and domesticatedplants. Because the authors provide a thorough review of phytochemical andTABLE 10.1Changes of Wild and Crop Plants and Their Environments Relevantto HerbivoryCharacter Crop WildLife History TraitsReproductive allocation High LowGenetic diversity Low HighDeterminism Increased VariablePopulation LevelIntraspecific competition High VariableDensity dependent mortality Little SignificantCommunity LevelHigh resource availabilityNutrient High LowWater High LowSoil structure Homogeneous HeterogeneousInterspecific competition High Variable