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| Negative Interactions |
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| Negative Interactions amongst different species in a community |
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| Negative interactions in a community is classified into |
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| 1) Predation |
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| 2) Parasitism |
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| 3) Competition |
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| 4) Amensalism |
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| 5) Mimicry. |
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| It is a negative, direct food related interspecific interaction between two species of animals in which larger species called predator attacks, kills and feeds on the smaller species called prey. |
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| Predator population adversely affect the growth and survival of smaller prey population and therefore predation is considered an antagonistic interaction. |
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| Examples: |
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| i) There are certain carnivorous plants also referred, as insectivorous plants that act as predators in nature. Plant like Nepenthes (pitcher plant), Drosera (sundew), Dionoeae (Venus fly trap) etc. feed on insects to fulfil their nitrogen requirement. |
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| ii) All carnivorous animals and scavengers are predators. |
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| Some predators (such as frog) act as prey for others (snake) which inturn are prey to a higher carnivores (eagle). |
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| iii) Herbivorous animals, eating plants or seeds, are also predators as they feed on individuals or future individuals. |
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| Significance of Predation |
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| a) Local species diversity is directly related to the efficiency with which the predators prevent the monopolization of an environmental area by any species. |
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| b) Predation keeps the prey population under check, so as to maintain an ecological balance. |
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| c) Weak and less efficient members in the prey population are removed. |
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| d) Most important significance is in the practical utility of prey predator relationship on biological control of weeds and pests. |
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| Many insect pests are kept under check by introducing their predator into the area. For e.g., Opuntia, which become a serious problem in Australia was brought under control by introducing its natural herbivore Cactoblastis (cochineal insects). |
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| It is a type of antagonistic interspecific interaction in which smaller partner, called parasite, derives food and shelter from in or on the body of larger partner, called host, which inhibits the survival of the host. |
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| The host can survive without the parasite, but the parasite cannot survive without the host. |
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| Parasitism can be rightly explained as weaker attacking the stronger. Parasitic interaction is generally found among protozoans, flat forms, nematodes and arthropods. |
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| Types of Parasitism |
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| On the basis of host- parasite relationship, there are different types of parasitism. |
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| a) Temporary parasitism and |
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| b) Permanent parasitism. |
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| Temporary parasitism is also referred as partial or intermittent parasitism. Here, the parasite spends most of its life cycle as independent free living organisms. Only a part of its life cycle is spent as a parasite (usually the period of feeding). |
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| Leech (Hirudinaria), bed bug (Cimex), mosquito (female Anapheles) are common temporary ectoparasites of man. |
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| Glochidium larva of Unio (fresh water mussel) undergoes metamorphosis as ectoparasite on a fresh water fish. |
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| Permanent parasitism is also referred as holoparasitic parasitism in this the organisms spend their whole life cycle as parasites, which is of two types based on where the parasites are found. |
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| a) Ectoparasites |
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| b) Endoparasites. |
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| Ectoparasites where the parasites live outside i.e. on the surface of the hosts body. Ectoparasites suck the body blood, or juice, or feed on living tissues from outside. |
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| For e.g., Bugs, fleas, ticks, lice, numerous crustaceans etc. |
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| Petromyzon (sea lamprey) is a sanguivorous agnathan, which attachés itself to the larger fish (such as shark) by the sucking action of its buccal funnel, makes a hole in the hosts body with its rasping and toothed tongue mixes the anticoagulant and sucks the blood. |
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| Pediculus (head louse), Xenopsylla (rat flea), Dermacentor (tick) are common examples of human ectoparasites. |
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| Endoparasites are those parasites, which live inside the body of the host and feed on the host cells, or tissues or body fluid. |
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| Examples: |
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 Taenia, Ascaris, Entamoeba etc. live in the intestine of man and cause taeniais, ascareasis and amoebic dysentery respectively. |
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 Plasmodium (malarial parasite) lives in the liver cells and RBCs of man and cause malaria. |
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 Wuchereria (filarial worm) lives in the lymph vessel of man and cause filariasis (elephantiasis). |
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 Trypanosoma lives in the cerebrospinal fluid of man and causes sleeping sickness. |
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| Some animals show ectoparasitic and endoparasitic interactions with great differences in morphology in the two phases. |
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| For e.g., Sacculina (root headed barnacle) |
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| II. Pathogenic and non-pathogenic parasites |
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| Pathogenic parasites are those, which not only derive food from the host but also cause certain diseases to the latter. Majority of the parasites are pathogenic. |
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| For e.g., Bacterial parasites cause several diseases in man such as |
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| Fungi are known to cause rust, smut, powdery mildew diseases in plants. |
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| Non-pathogenic parasites are those, which derive only food from the host but do not cause any disease to the latter. |
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| Example: Several nematodes like hookworms, pinworms and roundworms are all non-pathogenic parasites of man. |
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| III. Facultative and obligate parasites |
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| Facultative parasites are those which become a parasite only when they are in access to a host (or in association with a host), otherwise they lead a free, independent life. |
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| Examples: Prawn, Oyster etc. |
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| Obligate parasites are those, which cannot live independently and necessarily need a host for food and shelter. Obligate parasites are usually host specific. |
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| Examples: Taenia, Trypaaosoma, Entamoeba, Cuscuta etc. |
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| IV. Holoparasites and Hemiparasites |
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| Holoparasites are those organisms, which are dependent upon their host for their entire nutritional requirement. |
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| Example: Cuscuta a total parasite of Acacia |
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| On the other hand, hemiparasites (or semi parasites) derive only a part of nourishment (usually water and minerals) from their host and synthesize their own food by photosynthesis. |
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| Example: Viscum (mistletoe) and Loranthus are partial stem parasites. |
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| Santalum is a partial root parasite. |
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| Parasitic plants grow haustorial roots into the host plant tissues, which make connections with the vascular tissue of the host plant and suck in the required nutrients. |
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| V. Hyperparasites are those parasites, which live on another parasite for food and shelter. |
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| Example: Bacteriophage (bacterial virus) feed on bacteria. |
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 Nosema notabilis (a sporozoan) is an obligatory parasite of Sphaerospora polymorpha (a protozoan) which inturn is a parasite of urinary bladder of toad fish. |
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 Pasteurella pestis (a bacterium) is an endoparaite of Xenopaylla cheopsis (rat flea), which inturn is the ectoparasite of rat. |
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| It is an antagonistic interaction in which two or more members of same species (intraspecific), or two or more members of different species (interspecific) of same trophic level compete for common resource like light, moisture, space, nutrients etc. which are in short supply in relation to the member of individuals. |
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| On the basis of nature of struggle, competition is of two types. |
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| a) Direct interference type |
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| Where members of two different populations are mutually and actively inhibitory to each other. |
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| In such a case competition benefits the organism, which is more suitably adapted while the other is at a disadvantage. The size of population of the latter decreases, finally leading to its elimination. |
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| Example: Crombie conducted experiments on two beetle populations. Tribolium confusum and Oryzaephilus surinamensis, in a wheat flour medium. After sometime it was observed that O.surinarnensis population died out. |
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| b) Competition resource use type |
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| In this each population inhibits the other indirectly for the resource in short supply. |
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| Example: Trees, shrubs and herbs in a forest, struggle for sunlight, water and nutrients. |
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| Similarly, grasshoppers, rats, rabbits, deer (herbivores) compete for food especially during draught and less food availability. |
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| Significance of competition |
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| Competition is |
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 extremely important in determining the distribution of closely related species. |
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 essential in determining habitat range and speciation. |
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| It is an antagonistic interspecific interaction in which one species is inhibited while other species is neither benefitted nor harmed. |
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| In simple words, in amensalism, one organism does not allow other organism to grow or live near it. It is also called antibiosis and the affected species is called amensal and the affecting species is called inhibitor. Such inhibition is achieved through the secretion of certain chemicals called allochemics or allelopathic substances. |
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| Examples: |
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 Most common phenomenon of antibiosis is formation of antibiotics that are antagonistic to the microbes. |
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| 1) Penicillium notatum releases the antibiotic substance Penicillin, which inhibits the growth of variety of bacteria. |
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| 2) Streptomyces griseus produce antibiotic Streptomycin, which again inhibits the growth of many bacteria. |
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| 3) Roots of certain plants produce allochemic substances which check the growth of other plants to conserve resources, such as, Convolvulus arvensis, a weed inhibits the germination and growth of wheat. |
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| 4) Older plant of Grevillea robusta inhibits the growth of its own seedling. |
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| It is a phenomenon in which a living organism modifies its form, appearance, structure or behaviour and looks like another living organism or some inanimate (non- living) object so as to defend from its predators, or to increase the chances of capturing the prey. |
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| Individual which shows mimicry is called mimic while the animate or inanimate object with which it resembles is called model. |
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| Mimicry increases the survival value of the organism. |
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| Henry Bates, an English naturalist, first explained the concept of mimicry and so the phenomenon is referred as Batesian mimicry also. |
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| There are three types of mimicry: |
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| a) Protective mimicry |
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| b) Aggressive mimicry |
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| c) Conscious mimicry. |
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| Protective mimicry |
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| Is usually called used by a prey to defend itself from the predator, by resembling the surrounding or another organism. Protective mimicry is again of two types concealing and warning. |
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| 1) In concealing or cryptive type of protective mimicry, the organism resembles the surrounding so that it cannot be easily detected by the predator. |
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| Crypsis is a defensive strategy of palatable organisms. |
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| Examples: a) Carausius morasus (stick insect) the body of the insect resembles thin, dry braches. |
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| b) Phyllium frondosum (leaf insect) body is flat and green resembling a leaf. |
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| 2. In warning type protective mimicry the mimic resembles a distasteful or poisonous organism. This is usually exhibited by a palatable species. |
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| Example: Viceroy butterfly (Bosilarchia archippus), a palatable species resembles a distasteful Monarch butterfly (Donascus plexippus) commonly called Batesian mimicry. |
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| In another type of Warning mimicry, two or more unpalatable and related species resemble each other. This increases the chances of survival of mimitic individuals. This is usually called Mullerian mimicry. (after Fritz Muller) |
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| Aggressive mimicry |
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| Is generally employed by the predator, which resembles a harmless species to deceive potential prey. |
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| There are two types of aggressive mimicry - Concealing type and Alluring type. |
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| 1) In concealing type, the predator camouflages, so that it remains unnoticed from the prey. |
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| Example: |
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| Praying mantis (Mantis religiosa) is not noticed in the green foliage by the prey (small insects). |
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| Similarly, a yellow spider (predator) on a marigold flower is invisible to insects (prey). |
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| 2. In alluring type, the predator attracts the prey by resembling an object of interest to the prey. |
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| Example: |
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 A carnivorous spider resembles an orchid flower |
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 Mouth corner of African lizard resembles a flower. |
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| Conscious mimicry |
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| Also called feigning death where certain individuals, on sensing danger from predators, pose as if they are dead objects. |
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| Example: Tenebrinoid beetles become motionless and pebble like when in danger. |
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