A food web is composed of various food chains and includes all the producers and consumers in an ecosystem. Generally, the food web contains primary producers, consumers and predators (of consumers). There could be various levels of consumers and predators in a food web. If there was a large increase in amount of producers, generally plants, there would be a lot more food in the food web. This will result in higher population of primary consumers (animals who feed on producers directly), since there is a higher availability of food. The predators who consume these consumers will also rise in turn and same will happen at every trophic level. This trophic cascade effect will increase population at all levels and can be considered a bottom-up cascade.
Generally, the producers increase only when there is a decrease in the population of primary consumers (due to over-predation, etc.).
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