Page 1 : 236, , Ww, , 4, , BIOLOGY, , vector (mosquito) to spread to other hosts. Majority of the parasites, harm the host; they may reduce the survival, growth and, reproduction of the host and reduce its population density. They, might render the host more vulnerable to predation by making it, physically weak. Do you believe that an ideal parasite should be, able to thrive within the host without harming it? Then why didn’t, natural selection lead to the evolution of such totally harmless, parasites?, , Parasites that feed on the external surface of the host organism., are called ectoparasites. The most familiar examples of this group, are the lice on humans and ticks on dogs. Many marine fish are, infested with ectoparasitic copepods. Cuscuta, a parasitic plant that, is commonly found growing on hedge plants, has lost its chlorophyll, and leaves in the course of evolution. It derives its nutrition from, the host plant which it parasitises. The female mosquito is not, considered a parasite, although it needs our blood for reproduction., Can you explain why?, , In contrast, endoparasites are those that live inside the host, body at different sites (livery kidney, lungs, red blood cells, etc.)., The life cycles of endoparasites are more complex because of their, extreme specialisation. Their morphological and anatomical features, are greatly simplified while emphasising their reproductive potential., , Brood parasitismin birds is a fascinating example of parasitism, in which’the parasitic bird lays its eggs in the nest of its host and, lets the host. incubate them. During the course of evolution, the, eggs of the)parasitic bird have evolved to resemble the host's egg in, size and colour to reduce the chances of the host bird detecting the, foreign eggs and ejecting them from the nest. Try to follow the, movements of the cuckoo (koel) and the crow in your neighborhood, park during the breeding season (spring to summer) and watch, , brgod parasitism in action., (p-Commensatism: hiss he neato in which one specesbenes, her harmed nor benefited. An orchid growing, , as an epiphyte on a mango branch, and barnacles growing on the, back of a whale benefit while neither the mango tree nor the whale, derives any apparent benefit. The cattle egret and grazing cattle in, close association, a sight you are most likely to catch if you live in, farmed rural areas, is a classic example of commensalism. The, egrets always forage close to where the cattle are grazing because, the cattle, as they move, stir up and flush out insects from the, vegetation that otherwise might be difficult for the egrets to find, and catch. Another example of commensalism is the interaction, , 2020-21

Page 2 : ORGANISMS AND POPULATIONS, , Figure 13.7 Mutual relationship between fig tree and wasp: (a) Fig flower is pollinated, , (v), , , , (b), , by wasp; (b) Wasp laying eggs in a fig fruit, , between sea anemone that has stinging tentacles and the clown, fish that lives among them. The fish gets protection from predators, which stay away from the stinging tentacles. The anemone/does, not appear to derive any benefit by hosting the clown fish», Mutualism: This interaction confers benefits‘on-both.the interacting, species. Lichens represent an intimate*mutualisti¢ relationship, between a fungus and photosynthesising algae or cyanobacteria., Similarly, the mycorrhizae are associations‘between fungi and the, roots of higher plants. The fungi help theplant in the absorption of, essential nutrients from the soil while the plant in turn provides the, fungi with energy-yielding carbohydrates., , The most spectacular and evolutionarily fascinating examples, of mutualism are found in plant-animal relationships. Plants need, the help of animals for pollinating their flowers and dispersing their, seeds. Animals obviously have to be paid ‘fees’ for the services that, plants expect from them. Plants offer rewards or fees in the form of, pollen and nectar for pollinators and juicy and nutritious fruits for, seed dispersers. But the mutually beneficial system should also, be safeguarded against ‘cheaters’, for example, animals that try to, steal nectar without aiding in pollination. Now you can see why, plant-animal interactions often involve co-evolution of the, mutualists, that is, the evolutions of the flower and its pollinator, species are tightly linked with one another. In many species of fig, trees, there is a tight one-to-one relationship with the pollinator, species of wasp (Figure 13.7). It means that a given fig species can, be pollinated only by its ‘partner’ wasp species and no other species., The female wasp uses the fruit not only as an oviposition (egg-laying), site but uses the developing seeds within the fruit for nourishing, , 2020-21, , , , , Nn, wo, ™~

Page 3 : BIOLOGY, , , , , its larvae. The wasp pollinates the fig inflorescence while, searching for suitable egg-laying sites. In return for the, favour of pollination the fig offers the wasp some of its, developing seeds, as food for the developing wasp larvae., Orchids show a bewildering diversity of floral, patterns many of which have evolved to attract the right, pollinator insect (bees and bumblebees) and ensure, guaranteed pollination by it (Figure 13.8). Not all, orchids offer rewards. The Mediterranean orchid, Ophrys employs ‘sexual deceit’ to get pollination done, by a species of bee. One petal of its flower bears an, uncanny resemblance to the female of the bee in size,, colour and markings. The male bee is attracted to what, it perceives as a female, ‘pseudocopulates’ with the, flower, and during that process is dusted with pollen, Figure 13.8 Showing bee-a pollinator from the flower. When this same bee ‘pseudocopulates’, on orchid flower with another flower, it transfers pollen to it and thus,, , pollinates the flower. Here you can see how co-evolution, , operates. If the female bee’s colour patterns change even slightly for any, , reason during evolution, pollination success will be reduced unless the, , orchid flower co-evolves,to maintain the resemblance of its petal to the, , —S Ee eeeoS:—, , SUMMARY, , As a branch ofvbiology, Ecology is the study of the relationships of, living organiSins with the abiotic (physico-chemical factors) and biotic, components’ (other species) of their environment. It is concerned, with four’ levels of biological organisation-organisms, populations,, communities and biomes., , Temperature, light, water and soil are the most important, physical factors of the environment to which the organisms are, adapted in various ways. Maintenance of a constant internal, environment (homeostasis) by the organisms contributes to optimal, performance, but only some organisms (regulators) are capable of, homeostasis in the face of changing external environment. Others, either partially regulate their internal environment or simply, conform. A few other species have evolved adaptations to avoid, unfavourable conditions in space (migration) or in time (aestivation,, hibernation, and diapause)., , Evolutionary changes through natural selection take place at, the population level and hence, population ecology is an important, area of ecology. A population is a group of individuals of a given, species sharing or competing for similar resources in a defined, geographical area. Populations have attributes that individual, organisms do not- birth rates and death rates, sex ratio and age, , i}, ro, fo}, , WII WT, , , , , , 2020-21