Animal Behavior: Food selection sudeshrathod


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Food selection depends on the energy strategy of the feeder. The food size, quantity and quality varies with species to species and also depends on the ability of feeder, its body size etc.
Feeders are either specialists or opportunists. Food selection depends on competitive principle, learned aversion and food energy budget.

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Animal Behavior: Food selection sudeshrathod

  1. 1. T Y B Sc. Zoology Notes: Paper IV –Animal BehaviorFood is one of the important commodities for all living organisms. It is a source of energy required formovement, migration, courtship, performing various activities, even for foraging for food and digestingit. All animals select specific food in their natural habitat, some more so than others. Dependent ontheir feeding habits animals are classified into 11 groups viz. a. Predators 2. Grazers 3. Browsers 4. Scavengers 5. Particle feeders 6. Filter feeders 7. Fruit eaters 8. Seed eaters 9. Flower feeders 10. Food borrowers 11. ParasitesEcologically animals are classified as carnivores, herbivores, scavengers, and saprophytes dependingupon their food types. No two species living together at the same time and place eat exactly the samestaple food, called as phenomenon of competitive principle (Lack, 1954; Mayr, 1963). The feedingelectivity is a subject of major biological importance to find out relationship between the problems ofinterspecific competition for food and studies of their nutrition.1. Carnivores: Carnivores occupy topmost trophic level. They live largely by killing and devouring other animals. Some of the carnivores are specialists and others are opportunists. a. Specialists: These predators tend to live a sort of lazy life e.g. eagles, big cats, snakes, owls etc. specialist predators may spend only a very small percentage of their time in the pursuit of food. They generally select bigger prey which they can feast for some days which allows them to rest and digest flesh. This food is highest in nutritive quality. The feeding technique in this category involves good efficiency and risk of physical injury e.g. lion feeding on large ungulates such as beast, deer, antelope. Big cats when initiate hunting they first observe the prey population in the vicinity and find out the easiest target from all of them. e.g. the injured or weaker individual from buffalo. This way tiger requires less energy and effort to kill the prey. The smaller prey catching is laborious, time and energy consuming as each time they are to be tracked and killed. As they provide less amount of food, must be killed in large numbers to satiate the hunger e.g. anteaters feeding on ants or insects. But the advantage is that there are plenty of prey populations and no other competitor predator to share the food. Ant-eater (Specialist) By Prof. S D Rathod Dept. of Zoology B N Bandodkar College of Science, Thane, India
  2. 2. T Y B Sc. Zoology Notes: Paper IV –Animal Behavior b. Opportunists: opportunists are always on the lookout for a new kind of meal e.g. crows, mongoose, dogs, leopards, foxes etc. are typical busy opportunists. They kill anything they can catch and devour it with relish. Opportunistic feeders must have a rich and complex environment for their survival. Leopard is another opportunist having pronounced individual feeding habit. One living near a farm along with antelope and bush pigs was seen to be selecting bush pigs. Another individual fed largely on Tilapia fish living nearby a bank of river or lake. Another leopard residing near farm-field was observed to select the baboon prey. Thus leopard can shift from one prey to another according to its availability. Leopard (Opportunist)2. Herbivores: these are direct plant feeding heterotrophs e.g. hare, horse, deer, antelope, buffalo, giraffe, zebra etc. The ones which feed on grasses are known as grazers and others which feed on tree foliage and tree parts are called as browsers. Herbivores need lot of food being it contains less nutritive value. They eat large amount of food and digest it slowly as it mostly contains cellulose. Therefore they spend most of their life’s time in foraging. Although the plants are abundant the herbivores select a few varieties of them while feeding. Some plants are preferred to others, depending upon the concentrations of tannins, alkaloids, and other toxic compounds. Plants containing high toxic compounds concentrations are avoided. Buffalos, zebra and wildebeests, topi and Thomson gazelle live together in huge groups. These ungulates make up some 90% of the total weight of the mammals living in the Serengeti. Bell et al. studied the stomach contents of the four (except Buffalo); they found that each species was living on a different part of the vegetation. Study revealed that, Thomson gazelle ate nutritious fruits whereas rest fed on different proportions of succulent leaves and harder stems. Therefore their food selectivity differed greatly. Zebra being non ruminant largely browsed on bigger fresh leaves which are low in nutritive quality. Thus zebra has to explore new feeding grounds for more leaves before other herbivores move in. Therefore zebras are fast in/fast out feeders. After grazing and trampling by zebra, the ruminant wildebeest and topi arrive to eat the nutrition rich stems and left- out succulent leaves. The above three including zebra requires more food proportionate to their body size, so they eat abundant food. Whereas Thomson gazelle prefer, rich fruits being small in body size. By Prof. S D Rathod Dept. of Zoology B N Bandodkar College of Science, Thane, India
  3. 3. T Y B Sc. Zoology Notes: Paper IV –Animal Behavior Clockwise from top-left: Thomson’s gazelle, zebra, wildebeest and topi.3. Important Aspects of Food Selection: How do animals determine where to look for and how do they decide what food is and what is not? The environment of an animal contains all sort of things, some of which are edible some of which are not. The problem for the hungry animals is to distinguish non-edible and edible things and select the best suitable. The complexity of the problem depends on the type of food and the specificity of the feeder. Specialist feeder eats one or two types of preys or omnivorous feeder eats many kinds of food. Omnivorous feeder like rats will initially sample in a small quantities of food to eat. It samples almost anything but if they find that it makes them sick then they avoid eating it again and vice versa. Thus rats land up with variety of potentially edible things around and survive on any of them. a. Competitive principle- Lack (1954) and Mayr (1963) stated that no two species living together at the same time and place, eat exactly the same staple food. This avoids the interspecific competition for food. e.g. four spp. of Serengeti (wildebeest, Topi, Zebra and Thomson’s gazelle) and finches of Galapagos Island. By Prof. S D Rathod Dept. of Zoology B N Bandodkar College of Science, Thane, India
  4. 4. T Y B Sc. Zoology Notes: Paper IV –Animal Behavior b. Learned aversion- The larvae and adults of some insects such as Monarch butterfly, contains toxic chemicals (Glycosides). This causes illness in birds which eat them. Bird starts nausea and regurgigates the eaten monarch butterfly or its larva. Next time when a bird encounters the monarch butterfly or its larva again it associates the appearance of the insect with the illness it produced and avoids eating it again. Such phenomenon is called as learned aversion. Learned aversion protects many animals from eating toxic or dangerous foods. c. Energy budget in foraging strategy- The animal selecting a food depends on foraging energy budget. The energy required to search, stalk, grab and devour should be always lower than the energy obtained from that food. The zebra requires more food proportionate to its body size so it eats more amount of food. Whereas Thomson’s gazelle prefers a few nutrients rich fruit being small in body size. Lion stalking big prey herd like buffalo, zebra or wildebeest first observes all individuals and finds which one is crippled or sick and attacks it. This saves energy and avoids chances of losing the attempt likewise lion save energy.By Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India