Department of Rangeland Resources, Utah State Univ., Logan, Utah 84322-5230, USA.
Nutr Res Rev. 1998 Dec;11(2):199-222. doi: 10.1079/NRR19980015.
A herbivore faces challenges while foraging-ongoing changes in its physiological condition along with variation in the nutrient and toxin concentrations of foods, spatially and temporally-that make selecting a nutritious diet a vital affair. Foraging behaviours arise from simple rules that operate across levels of resolution from cells and organs to individuals and their interactions with social and physical environments. At all these levels, behaviour is a function of its consequences: a behaviour operating on the environment to induce changes is itself changed by those events. Thus, behaviour emerges from its own functioning-behaviour self-organizes-not from that of its surroundings. This ostensible autonomy notwith-standing, no self-organizing system (cell, organ, or individual) is independent of its environs because existence consists of an ongoing exchange of energy and matter. According to this view, the notion of cause and effect is replaced with functional relationships between behaviours and environmental consequences. Changes in physical environments alter the distribution, abundance, nutritional, and toxicological characteristics of plants, which affect food preference. Social interactions early in life influence behaviour in various ways: animals prefer familiar foods and environments, and they prefer to be with companions. Animals in unfamiliar environments often walk farther, ingest less food, and suffer more from malnutrition and toxicity than animals in familiar environments. An individual's food preferences-and its ability to discriminate familiar from novel foods-arise from the functional integration of sensory (smell, taste, texture) and postingestive (effects of nutrients and toxins on chemo-, osmo-, and mechano-receptors) effects. The ability to discriminate among foods is critical for survival: all problems with poisonous plants are due to an inability to discriminate or a lack of alternatives. Animals eat a variety of foods as a result of nearing or exceeding tolerance limits for sensory and postingestive effects unique to each food. After eating any food too frequently or excessively, the likelihood increases that animals will eat alternative foods owing to exceeding sensory-, nutrient-, and toxin-specific tolerance limits. Cyclic patterns of intake of a variety of foods reflect seemingly chaotic interactions among flavours, nutrients, and toxins interacting along continua.
草食动物在觅食时面临挑战——其生理状况不断变化，同时食物的营养和毒素浓度也在变化，空间和时间上的变化使得选择营养丰富的饮食成为至关重要的事情。觅食行为源自简单的规则，这些规则在从细胞和器官到个体及其与社会和物理环境的相互作用的各个分辨率水平上运作。在所有这些水平上，行为都是其后果的函数：作用于环境以引起变化的行为本身会被这些事件改变。因此，行为是从自身的功能中产生的——行为自我组织——而不是来自其周围环境的组织。尽管存在这种表面上的自主性，但没有自我组织的系统（细胞、器官或个体）是独立于其环境的，因为存在是一个持续的能量和物质交换的过程。根据这种观点，因果关系的概念被行为和环境后果之间的功能关系所取代。物理环境的变化改变了植物的分布、丰度、营养和毒理学特性，从而影响了食物偏好。生命早期的社会互动以各种方式影响行为：动物更喜欢熟悉的食物和环境，更喜欢与同伴在一起。在不熟悉的环境中的动物通常走得更远，摄入的食物更少，并且比在熟悉环境中的动物更容易受到营养不良和毒性的影响。个体的食物偏好及其区分熟悉食物和新颖食物的能力来自于感官（气味、味道、质地）和后消化（营养物质和毒素对化学、渗透压和机械感受器的影响）效应的功能整合。区分食物的能力对生存至关重要：所有与有毒植物有关的问题都是由于无法区分或缺乏替代品造成的。动物吃各种食物是因为接近或超过了每种食物特有的感官和后消化效应的耐受极限。由于超过了特定的感官、营养和毒素耐受极限，动物在吃过任何食物过于频繁或过量后，食用替代食物的可能性就会增加。各种食物的摄入周期性模式反映了味道、营养和毒素沿着连续体相互作用的看似混乱的相互作用。
