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First notebook entry: Introducing myself

Food Chains and Webs
• Living organisms in an ecosystem are interrelated in terms of what gets eaten. For example, in a desert ecosystem, a food chain could start with prickly pear cactus eaten by pack rats, which are eaten by rattlesnakes, which are eaten by red-tailed hawks. More complex interrelationships can be depicted in non-linear food web diagrams, with organisms interconnected by arrows to indicate food usage. A food web can show that prickly pears are eaten by pack rats and long-horned cactus beetles and javelina; javelina also eat hedgehog cacti and saguaro fruit; pack rats are also eaten by bobcats and gopher snakes; long-horned cactus beetles are eaten by bats and toads; cactus wrens eat saguaro fruit and are eaten by rattlesnakes, gopher snakes and bobcats.
Sources of Food
• Organisms are interrelated in how they get food. Producers or autotrophs manufacture the food they need from basic nutrients and an energy source, usually sunlight. Consumers cannot make all their own food and rely on organic molecules manufactured by producers. These consist of herbivores, which feed on plants directly, and carnivores, which feed on herbivores and other carnivores. Organisms that derive food from decomposing organic matter, either plant or animal, are called detritovores or decomposers. They break down organic matter into its inorganic components, which are then available to be recycled back into organic molecules.
• Each organism has its own niche within an ecosystem, which varies over time and life stage of the organism. This tends to lessen competition but can still limit species abundance. For example, termites, earthworms, sowbugs, bacteria and fungi compete for decaying organic material. Sowbugs need moist shady environments, termites need warm underground burrows or protected above-ground galleries, earthworms need moist soil with cooler temperatures, and bacteria and fungi need particular conditions of soil temperature, moisture and pH. Each organism competes for the same resource and contributes to decomposition but action is often separated seasonally or stratigraphically.




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