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Tolerance is the ability of plants to mitigate the negative fitness effects caused by herbivory. It is one of the general plant defense strategies against herbivores, the other being resistance, which is the ability of plants to prevent damage (Strauss and Agrawal 1999). Plant defense strategies play important roles in the survival of plants as they are fed upon by many different types of herbivores, especially insects, which may impose negative fitness effects (Strauss and Zangerl 2002). Damage can occur in almost any part of the plants, including the roots, stems, leaves, flowers and seeds (Strauss and Zergerl 2002). In response to herbivory, plants have evolved a wide variety of defense mechanisms and although relatively less studied than resistance strategies, tolerance traits play a major role in plant defense (Strauss and Zergerl 2002, Rosenthal and Kotanen 1995). Traits that confer tolerance are controlled genetically and therefore are heritable traits under selection (Strauss and Agrawal 1999). Many factors intrinsic to the plants, such as growth rate, storage capacity, photosynthetic rates and nutrient allocation and uptake, can affect the extent to which plants can tolerate damage (Rosenthal and Kotanen 1994). Extrinsic factors such as soil nutrition, carbon dioxide levels, light levels, water availability and competition also have an effect on tolerance (Rosenthal and Kotanen 1994). ==History of the study of plant tolerance== Studies of tolerance to herbivory has historically been the focus of agricultural scientists (Painter 1958; Bardner and Fletcher 1974). Tolerance was actually initially classified as a form of resistance (Painter 1958). Agricultural studies on tolerance, however, are mainly concerned with the compensatory effect on the plants' yield and not its fitness, since it is of economical interest to reduce crop losses due to herbivory by pests (Trumble 1993; Bardner and Fletcher 1974). One surprising discovery made about plant tolerance was that plants can overcompensate for the damaged caused by herbivory, causing controversy whether herbivores and plants can actually form a mutualistic relationship (Belsky 1986). It was soon recognized that many factors involved in plants tolerance, such as photosynthetic rates and nutrient allocation, were also traits intrinsic to plant growth and so resource availability may play an important role (Hilbert et al. 1981; Maschinski and Whitham 1989). The growth rate model proposed by Hilbert et al. (1981) predicts plants have higher tolerance in environments that does not allow it to grow at maximum capacity, while the compensatory continuum hypothesis by Maschinski and Whitham (1989) predicts higher tolerance in resource rich environments. Although it was the latter that received higher acceptance, 20 years later, the limiting resource model was proposed to explain the lack of agreement between empirical data and existing models (Wise and Abrahamson 2007). Currently, the limiting resource model is able to explain much more of the empirical data on plant tolerance relative to either of the previous models (Wise and Abrahamson 2008a). It was only recently that the assumption that tolerance and resistance must be negatively associated has been rejected (Nunez-Farfan et al. 2007). The classical assumption that tolerance traits confer no negative fitness consequences on herbivores has also been questioned (Stinchcombe 2002). Further studies using techniques in quantitative genetics have also provided evidence that tolerance to herbivory is heritable (Fornoni 2011). Studies of plant tolerance have only received increased attention recently, unlike resistance traits which were much more heavily studied (Fornoni 2011). Many aspects of plant tolerance such as its geographic variation, its macroevolutionary implications and its coevolutionary effects on herbivores are still relatively unknown (Fornoni 2011). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plant tolerance to herbivory」の詳細全文を読む スポンサード リンク
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