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Definition: A substance or object required by an organism for normal maintenance, growth, and reproduction. If the resource is scarce relative to demand, it is referred to as a limiting resource. Nonrenewable resources (such as space) occur in fixed amounts and can be fully used; renewable resources (such as food) are produced at a rate that may be partially determined by their use.
Source: Ricklefs, Robert E (2001). The Economy of Nature (5th Edition).