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Whether foraging on pastures or rangelands, herbivores encounter plant species that differ in their concentrations of nutrients. They also all contain various secondary compounds that at too high doses can be toxic, but at the appropriate dose many of these toxins may have medicinal benefits. The quantity of forage an animal consumes depends on the other forages it selects because nutrients and toxins interact. Food intake also depends on an individual's morphology and physiology, and marked variation is common, even among closely related animals, in needs for nutrients and abilities to cope with toxins. Thus, individuals can better meet their needs when offered a variety of foods that differ in nutrients and toxins than when constrained to a single food. Nonetheless, we have focused on a few species, often grown in monoculture, and we have reduced concentrations of secondary compounds with little appreciation for their roles in protecting plants against herbivores, pathogens, and competitors. In nature, where diversity of plants is the rule and not the exception, eating a variety of foods is how animals cope with, and may benefit from, secondary compounds. The potential benefits of creating mixtures of plant species whose nutrient and secondary compound profiles complement one another are obvious, though much remains to be learned about how to reconstruct agro‐ecosystems with plants that complement and enhance one another structurally, functionally, and biochemically.

: Among other functions, melatonin exerts both antioxidative and immunoregulatory roles. The indoleamine is secreted in the saliva, although its role into the mouth is not known. Diabetic patients frequently display oral cavity pathologies such as periodontal disease (PD), an inflammatory disease coursing with an increase in free radical production. Thus, we compared the degree of PD and interleukin‐2 (IL‐2) levels with melatonin concentrations in plasma and saliva of diabetic patients. A total of 43 diabetic patients (20 with type I and 23 with type II diabetes) and 20 age‐ and sex‐matched controls were studied. Dental and medical history of all patients was in accordance with the criteria of the WHO. The periodontal status was evaluated by the Community Periodontal Index (CPI). Plasma and salivary melatonin levels were determined by specific commercial radioimmunoassays, and plasma IL‐2 was measured using a commercial enzyme‐linked immunosorbent assay kit. Diabetic patients had plasma and saliva melatonin levels of 8.98 ± 7.14 and 2.70 ± 2.04 pg/mL, respectively. These values were significantly lower (P < 0.001) than those obtained in plasma and saliva of controls (14.91 ± 4.75 and 4.35 ± 0.98 pg/mL, respectively). Plasma and salivary melatonin concentrations show a biphasic response in diabetic patients. Melatonin decreased in patients with a CPI index of 2, and then increased reaching highest levels in patients with a CPI index of 4. By contrast, IL‐2 levels decreased from CPI index 1 to 4. The results indicate that, in diabetic patients, the presence of a marked impairment of the oral status, as assessed by the CPI index, is accompanied by an increase in plasma and salivary melatonin. The increase in salivary melatonin excretion may have a periodontal protective role.

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G. 2004. Experience influences diet mixing by herbivores: implications for plant biochemical diversity. Á/ Oikos 107: 100 Á/109.We often assume the intrinsic value of a food or habitat is similar for individuals of a species and above a certain threshold density more profitable foods should always be preferred over less profitable foods. Nevertheless, individual herbivores differ in their preferences for foods due in part to experience, and experience in variable environments is variable. In this report, we show that how sheep learned about their foraging environment was crucial to the development of their dietary habits, and that experience with foods that contained plant secondary metabolites (PSM) markedly enhanced their use of PSM-containing foods, even when familiar, nutritious alternatives were available ad libitum. Lambs who learned to eat foods that contained either tannins, terpenes, or oxalates ate more when they could select two of the foods offered simultaneously (tannins-terpenes, tannins-oxalates, or terpenes-oxalates) than when they were offered only one food. Lambs offered foods containing all three toxins ate more than lambs offered two of the toxins, and their intake was comparable to lambs offered the food that contained no toxins. Experience and the availability of nutritious alternatives both influenced food choice when the preferences of lambs with 3 months' experience mixing tannin, terpenes, and oxalates were compared with lambs naive to the toxin-containing foods. During these studies, all lambs were offered five foods, two of them familiar to all of the lambs (ground alfalfa and a 50:50 mix of ground alfalfa:ground barley) and three of them familiar only to experienced lambs (a ground ration containing either tannins, terpenes, or oxalates). Half of the lambs were offered the familiar foods ad libitum, while half of the lambs were offered only 200 g of each familiar food daily. Throughout the study, naive lambs ate much less of the foods with toxins if they had ad libitum as opposed to restricted access to the nutritious alternatives (66 vs 549 g d (1 ). Experienced lambs also ate less of the foods with toxins if they had ad libitum, as opposed to restricted, access to the nutritious alternatives (809 vs 1497 g d (1 ). In both cases, however, lambs with experience ate remarkably more than naive lambs of the foods containing the toxins, whether access to the alfalfa-barley alternatives was ad libitum (811 vs 71 g d (1 ) or restricted (1509 vs 607 g d (1 ). These differences in food preferences and intake persisted during trials 8 months later. Plant communities offer a diverse matrix of biochemicals to herbivores, which may produce an array of interactions not accounted for by the traditional approach of studying nutrients and plant secondary metabolites (PSM) in isolation. How herbivores experience nutrient-PSM interactions may influence defoliation patterns and the potential for plant survival within plant communities. Thus, learning to mix foods that differ in kinds and concentrations...

Concentrations of nutrients and plant secondary metabolites (PSM) vary temporally and spatially, creating a multidimensional feeding environment. Interactions between nutrients and PSM are poorly understood because research has relied largely on studying the isolated effects of nutrients or PSM on foraging behavior. Nevertheless, their interactions can influence food selection and the dynamics of plant communities. Our objective was to explore how interactions between nutrients and PSM influence food selection. For 7 d, three groups of lambs received intraruminal infusions of three different doses of a PSM (0=Control; low and high) and 2 h later they were offered two foods that contained either low (high in energy) or high (high in protein) protein/energy ratios. The foods were offered 7 d before (baseline) and 7 d after PSM infusions. We conducted five trials each with a different PSM‐ terpenoids, cyanogenic glycosides, sodium nitrate, quebracho tannin, and lithium chloride. Lambs consistently preferred the food high in energy to the food high in protein, but toxins modified the degree to which this preference was manifest. Terpenoids, nitrate, and lithium chloride depressed intake of the food high in energy. Cyanogenic glycosides had the opposite effect, and at higher doses they depressed intake of the food high in protein. Tannins enhanced intake of the food high in energy at lower doses and they depressed its ingestion at higher doses. Thus, PSM selectively depressed or enhanced intake depending on the macronutrient composition of the foods. These results imply that the probability of a plant being eaten will depend not only on its chemical defenses but also on the quantity and quality of nutrients in the plant and its neighbors, and that the ability of herbivores to learn associations between nutrients and PSM may have a substantial impact on the way herbivores regulate ecosystem processes.

Animals function and maintain well-being within the internal milieu through behavioural interactions with the external milieu. These interactions are complex. They involve an ongoing dynamics influenced by history, necessity and chance such that at any time an animal's foraging behaviour is a function: (i) of its evolutionary history, genetically expressed, in concert with its uniquely individualistic history of the social and biophysical environments where it was conceived and reared; (ii) of necessity due to its current nutritional, toxicological and medicinal state relative to the biochemical characteristics of foods it can potentially consume at any moment; and (iii) to chance occurrences that involve gene expression and environmental variability. This chapter discusses the various interactions and factors affecting the foraging behaviour of domestic herbivores, such as learning foraging behaviour by consequences, the need for homeostatic regulation, flavour-feedback associations and grazing behaviour regulation due to interaction of substances (nutrient-nutrient, toxin-toxin and nutrient-toxin interactions).

We review the evidence for behavioral avoidance of plant secondary metabolites (PSMs) and identify how, and the circumstances under which it occurs. Behavioral strategies of avoidance of PSM can only be fully understood in relation to the underlying physiological processes or constraints. There is considerable evidence that animals learn to avoid PSMs on the basis of negative postingestive effects. The extent to which this process determines foraging choices is limited by the ability of animals to experience the consequences of their behaviors and associate particular cues in foods with their specific effects in the body. The proposed learning mechanisms require that animals must at least "sample" plants that contain PSMs. They do not completely avoid PSMs, but there is evidence that they restrict their ingestion to within limits that they are physiologically able to tolerate, and that the amounts of PSM ingested result from a balance between toxicological considerations and the nutrient content of the plant material. These limits are influenced by the kinetics of PSM elimination, which underlies patterns of bite and patch selection from plant parts to landscapes. We suggest that altering spatial location of feeding (to alternative food patches or alternative foods within patches, including plant parts), and temporal distribution of feeding activity, by either cessation of feeding or by continuing to feed, but on alternative foods, can both lead to reduction of the intake and toxic effects of PSMs. We propose that the strategy of avoidance or reduction of intake of PSMs coevolved with the animal's ability to physiologically tolerate their ingestion, and that avoidance and tolerance are inversely related (the avoidance-tolerance continuum). The animals' propensity and ability to seek alternatives also vary with the dispersion of their food resources. Further work is required to test these proposals and integrate temporal and spatial aspects of foraging behavior and its nutritional consequences in relation to PSMs.