Capital breeding and income breeding refer to the methods by which some organisms perform time breeding and use resources to finance their breeding. Capital breeders utilize stored endogenous resources (typically lipids) to finance reproduction, whereas income breeders use exogenous resources (typically carbohydrates).
In capital breeding, organisms invest a significant portion of their energy reserves (capital) acquired during non-reproductive periods into reproduction. This typically involves storing energy in the form of fat or other resources during times of plenty, such as favorable environmental conditions or abundant food availability. Once sufficient reserves are accumulated, these organisms allocate stored energy towards reproduction, which may include activities like producing gametes (eggs and sperm), building nests, and caring for offspring. These activities often require a substantial amount of energy. Capital breeding is commonly observed in species that experience predictable periods of resource abundance followed by periods of resource scarcity or environmental stress. Examples include many migratory birds that build up fat reserves before embarking on long-distance migrations or mammals that hibernate during winter months.
In income breeding, organisms rely predominantly on resources acquired during the reproductive period (income) to fuel reproductive efforts. Unlike capital breeders, income breeders do not store large reserves of energy during non-reproductive periods but instead acquire energy as needed during reproduction. Income breeding is often observed in species that have continuous access to food resources or experience relatively stable environmental conditions throughout the year. These organisms can allocate energy directly from food sources towards reproduction without the need to store reserves. Many species of insects, amphibians, and fish exhibit income breeding strategies, as they often have access to abundant food resources in their habitats and can reproduce multiple times throughout the year as conditions allow.