CBSE · Class 12 · Biology · Organisms and PopulationsExplain population interactions with examples. Describe mutualism, competition, predation, parasitism, commensalism, and amensalism in detail.

Introduction to Population Interactions\nIn nature, animals, plants, and microbes do not live in isolation but interact in various ways to form a biological community. Interspecific interactions arise from the interaction of populations of two different species. These interactions could be beneficial, detrimental, or neutral to one of the species or both.

1. Mutualism (+/+)\nThis interaction confers benefits on both the interacting species.

• Example: Lichens represent an intimate mutualistic relationship between a fungus and photosynthesizing algae or cyanobacteria.
• Example: Mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant absorb essential nutrients from the soil, while the plant provides the fungi with energy-yielding carbohydrates.

2. Competition (-/-)\nIt is a process in which the fitness of one species is significantly lower in the presence of another species.

• Gause's Competitive Exclusion Principle: States that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.
• Example: In some shallow South American lakes, visiting flamingos and resident fishes compete for their common food, the zooplankton in the lake.

3. Predation (+/-)\nIn this interaction, one animal consumes another. Predators are vital for transferring energy across trophic levels and keeping prey populations under control.

• Example: Tigers hunting deer, or sparrows eating seeds. Predators also act as conduits for energy transfer across trophic levels and maintain species diversity in a community by reducing the intensity of competition among competing prey species.

4. Parasitism (+/-)\nIn this mode, one organism (the parasite) depends on another (the host) for food and shelter, damaging the host in the process.

• Adaptations of Parasites: Loss of unnecessary sense organs, presence of adhesive organs or suckers, loss of digestive system, and high reproductive capacity.
• Example: Human liver fluke, ticks on dogs, and Cuscuta growing on hedge plants.

5. Commensalism (+/0)\nIn this interaction, one species benefits, while the other is neither harmed nor benefited.

• Example: An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of whales.
• Example: The cattle egret and grazing cattle; as the cattle move, they flush out insects that the egrets easily catch and feed upon.

6. Amensalism (-/0)\nIn this interaction, one species is harmed, whereas the other is unaffected.

• Example: The fungal secretion penicillin from Penicillium inhibits or kills the growth of nearby bacteria without being affected itself.