Interrelationships of Organisms II PDF

Interrelationships of Organisms II Symbiosis Is a type of a close and long-term biological interaction between two biological organisms of different species, termed symbionts, be it mutualistic, commensalistic or parasitic. Symbiosis can be obligatory, which means that one or more of the symbionts...

Interrelationships of Organisms II Symbiosis Is a type of a close and long-term biological interaction between two biological organisms of different species, termed symbionts, be it mutualistic, commensalistic or parasitic. Symbiosis can be obligatory, which means that one or more of the symbionts depend on each other for survival, or facultative (optional), when they can generally live independently. When one partner is really small and lives inside of the other partner, the other partner is called the host. The really small partner can be called a mutualist, a commensalist, or a parasite (depending on the type of relationship). Sometimes, the small partner is called the symbiont. This is a general term and does not imply a type of relationship. Mutual relationship is seen in all living organisms including human beings, animals, birds, plants and other microorganisms like bacteria, virus, and fungi. Mutualism is a sort of symbiosis. Mutualism is a type of relationship between the host and a symbiont, where both organisms benefit and no one is harmed. This relationship may either continue for longer or for shorter-term. The term mutualist is used to indicate the small partner and the host are the other partners present in the Mutualism. For example, Ants live and feed on the nectar of acacia trees. Here ants are the mutualist and acacia trees are the host. The acacia tree provides home and food for the ants. As they have hollow huge thorns – homes for the ants and yellow swellings on the leaves- food for the ants. In reverse ants acts a guard attacking insects and protects the tree from grazing animals. Types of Mutualism Obligate Mutualism In obligate mutualism the relationship between two species, in which both are completely dependent on each other. For example, Yucca plant and the moth. The flower of the yucca plant relies on the moth for the pollination process. In turn, the moth is benefited by laying its eggs on the flower and feeding the larvae with the seeds. Termites have a symbiotic relationship with microorganisms called protozoa that live in the insect’s gut. The termite benefits from the ability of the protozoa to digest cellulose, a carbohydrate important in plant structure. However, the protozoa are able to digest cellulose only because of the presence of symbiotic bacteria within their cells that produce the cellulase enzyme. The termite itself cannot do this; without the protozoa, it would not be able to obtain energy from its food (cellulose from the wood it chews and eats). The protozoa benefit by having a protective environment and a constant supply of food from the wood chewing actions of the termite. Facultative Mutualism In facultative mutualism, the partners may coexist without a depending on each other. For example, Honeybees and plants. Honey bees visit many different plants species for the nectar from the flower and these plants will be visited by the number of the insect as pollinators for pollination. Lichen is a symbiotic relationship between a fungus and algae (or a photosynthetic bacteria). In lichen, the algal cells are fully surrounded by the fungus. The sugars produced by the algae through photosynthesis provide nourishment for both organisms. The physical structure of the fungus protects the algae from the elements and makes certain nutrients in the atmosphere more available to the algae. The algae of lichens can sometimes live independently when given the right environment, but many of the fungal partners are unable to live on their own. Trophic Mutualism In trophic mutualism, the partners are specialized in complementary ways to obtain energy and nutrients from each other. For example, cows and the bacteria. Cows cannot digest the plant’s cellulose. The bacteria present in the rumens of cows helps in digesting plants cellulose. In reverse bacteria gets food and warm environment, which is required for their growth and development. Figure: Type of Trophic Mutualism Defensive Mutualism In defensive mutualism, one partner receives food and shelter and in return, it helps the partner by defending against the herbivores or predators or parasites. For example, the aphids and the ants. The aphids produce honeydew to the ants, which is carried to their nests at night for protecting them from the predators and escort. These aphids are carried back to the plant the next morning. In return, ants are benefited by assembling the aphid’s eggs and storing in their nest chambers to survive the cold winter months. Dispersive Mutualism In dispersive mutualism, one partner receives food in return for helping flower in transferring their pollen. For example, Honeybees and the Plants. Honey bees travel from one flower to another in search of nectar from the flower which is required to prepare honey, in return plants are benefited by the pollination as the honey bee spread the pollen from one plant to another. Commensalism Commensalism is a symbiotic relationship between two organisms where one organism is benefited from the other, whereas the other is neither harmed nor benefited. It is a biological interaction that organisms form, in the quest of food and shelter. Commensalism is in contrast with mutualism, where both organisms benefit from each other; ammensalism, where one organism is harmed and the other is unaffected; and parasitism, where one organism is harmed and the other is benefited. The organism that benefits from this biological interaction is known as the commensal and the other is known as the host species. The commensal, in such cases, is usually a small organism and the host species is often larger in size. The commensal benefits in transportation, food, shelter and support from the host species. The remora and the shark are commensal symbiosis. The top fin of the remora is modified into a sucker with which it forms an attachment to the shark. When the shark feeds, the remora picks up scraps. Additionally, the remora gains transportation and protection. The shark makes no attempt to prey on the remora and is unaffected by it. Figure: Cow and Egrets Types Phoresy Phoresis or phoresy is a commensalistic interaction where one organism attaches to another organism solely for the purpose of locomotion. It is a non-permanent type of interaction. Examples of phoresy include mites on insects, and millipedes on birds. Inquilinism Inquilinism is a type of commensalism where one organism lives permanently on the second organism. The organism that uses the second organism for housing is known as inquiline. Examples include birds that live on trees, and insects that live in the burrows of rodents. Metabiosis Metabiosis is a type of commensalism where indirect dependency is observed, one organism produces a suitable environment for the other organism. Examples hermit crabs that use shells of gastropods to protect their bodies. Parasitism “Parasitism is defined as the relationship between different species in which one organism lives on or in the other organism and benefits from it by causing some harm.” The organism that is benefitted is called the parasite, while the one that is harmed is called the host. A few examples of parasites are tapeworms, fleas, and barnacles. Tapeworms are flatworms that are found attached to the insides of the intestines of animals such as cows, pigs, etc. They feed on the host’s partly digested food, depriving it of the nutrients. Types of Parasitism There are various types of parasitism and are classified based on their size, characteristics, interactions with their hosts and their life cycles. Obligate Parasitism This is the kind of parasitism in which the parasite is completely dependent on the host to complete its life cycle. Obligate parasites cannot survive without the host. Therefore, they do not severely harm the host. Fungi, bacteria and viruses exhibit obligate parasitism. For eg., head lice, when removed from the human scalp, dies. Facultative Parasitism In this kind of parasitism, the parasite is not completely dependent on the host to complete its life cycle and can survive without the host. A nematode species Strongyloides stercoralis is found free- living but causes a disease strongyloidiasis when it infects humans. Ectoparasite The parasites that live outside the body of the host exhibit ectoparasitism. For eg., lice on the body of human and ticks on the body mammals such as cattle Endoparasite Parasites that live inside the body of a host exhibit endoparasitism. For eg., hookworms seen in the gut of man and other nematodes in blood and tissue of man.