BIOTIC INTERACTIONS
Environment
Species Interactions in Ecosystems
Organisms in every ecosystem interact constantly. These interactions are essential for their survival and for maintaining the structure and functioning of the ecosystem. When interactions occur among members of the same species, it is called intraspecific interaction; when they occur between different species, it is called interspecific interaction.
Interspecific interactions may be direct (lion and deer) or indirect (elephant affecting beetle populations through habitat modification). These interactions may benefit, harm or have no effect on the species involved.
Types of Interspecific Interactions
Amensalism
A negative interaction where one species is harmed while the other remains unaffected.
Example:
- Penicillium secretes penicillin, which inhibits bacteria.
Allelopathy:
- A form of amensalism in plants.
- Shrubs like mint and sagebrush release chemicals that inhibit the growth of neighbouring plants.
Predation
One species (predator) kills and eats another species (prey).
- Predators such as lions, tigers, leopards, snakes, birds of prey benefit.
- The prey is harmed.
Parasitism
One species (parasite) benefits at the expense of another (host). The parasite lives in or on the host and derives nourishment.
Examples:
- Tapeworms
- Roundworms
- Malarial parasite
- Dodder plants (Cuscuta)
- Mistletoe
- Ticks
Competition
Both species involved are harmed to some degree because they compete for limited resources like food, shelter, water, space, or mates.
Types:
- Interspecific competition: between different species.
- Intraspecific competition: within the same species; usually more intense.
Example:
- Two male birds competing for the same female.
Commensalism
One species benefits while the other is neither harmed nor benefited.
Examples:
- Remora fish attach to sharks for transportation and leftover food.
- Epiphytes (orchids, mosses, ferns) grow on trees for sunlight and support without harming them.
Mutualism
Both interacting species benefit.
Mutualism ranges from loose associations to obligate symbiosis.
Examples:
- Sea anemone on hermit crab’s shell – anemone gains transport; hermit crab gains protection.
- Bees and flowers – bees get nectar; flowers get pollinated.
- Termites and intestinal protozoans – protozoans digest cellulose for termites; both depend on each other completely (symbiosis).
Neutralism
Two species interact but neither benefits nor suffers.
True neutralism is extremely rare in nature because species indirectly influence each other through food webs, nutrient cycling, or habitat modification.
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Subject: Environment
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