Definition of Ecology
Ecological Zones

Life Histories
Life History Stages
- Stage 1 to 4
- Stage 5 to 8
- Stage 9 to 12

Definition of a Life History

There are two vitally important parts of a living organism's life that play a central role in the functioning of an ecosystem. This includes changing population densities over time. The two parts of an organism's life are its life cycle and something that can be described as a life history.

Life cycle of a species

The life cycle of an organism is a repeated series of biological life stages that occur in rhythms over time. Each type of organism has its own life cycle type and set of stages.

Examples of life cycles include:

  • Plants - seed, to seedling, to adult, to flowering, to seed production.
  • Plants - spores, to seedling, to adult, to new spores released.
  • Crustacean - egg, to veliger, to subadult, to juvenile, to adult.
  • Bird - egg, to chick, to adult.
  • Insect - egg, to nymph, to adult.
  • Insect - egg, to larvae, to pupa, to adult.

Life cycles vary across the phylum of organisms but they usually have a clear set of stages of growth. In an ecosystem, life cycles are best seen as natural rhythms. This is highly evident in places of crop production, where grains are grown in season, year after year.

It is also very obvious when huge populations of insects swarm but often at very particular times of the year. Migrations are another indicator of a life cycle stage in progress - birds will often migrate to breed and then leave for feeding elsewhere with their young.

Life history of a species

An organism's life history is a more individual phenomena, which applies to every single individual of a species. Life histories also have particular stages, just as life cycles do, except that not every individual will pass successfully through all the stages of a life history.

As a species, one can observe and document the progress of a life cycle over time and see how that species has effects in the ecosystem. A life history on the other hand, refers to the key activities that each individual must be successful in, to live to its full age and succeed in the reproductive cycle. Life histories vary in their content between species, but many elements are common to whole groups of species.

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