Irruption

Irruptive growth, sometimes called Malthusian growth, is a growth pattern over time, defined by population explosions and subsequent sharp population crashes, or diebacks. It is an extension of the Malthusian growth model, specifically the growth pattern that causes a Malthusian catastrophe, and can occur when populations overshoot their carrying capacity, a phenomenon typically associated with r-strategists. Populations which exhibit irruptive growth do not stabilize around their carrying capacity, a feature of logistic growth. Irruptive growth occurs when a species reproduces more rapidly than the environment is capable of supporting with the available resources. Irruptive growth is studied in population ecology.

An irruption is any sudden change in the population density of an organism.

r-strategist species (species that evolve according to r-selection) are characterized by rapid development, early reproduction, small body size, and shorter lifespans, whereas K-strategist species (species that evolve according to K-selection) exhibit slow development, delayed reproduction, large body size, and longer lifespans. These are the main two evolutionary strategies for ensuring the continuation of the species by passing down its genetic code.

r-strategist species have variable population sizes and are more likely to exhibit irruptive growth than K-strategist species, whose populations are usually constant and remain at or close to the carrying capacity of the environment. r-selection leads to high productivity, while K-selection leads to high efficiency. Productivity refers to the number of offspring produced, whereas efficiency refers to the quality and the probability of survival of individual offspring.

The human species is K-strategist; that is, each mating pair has a small number of offspring, of which the majority will survive to adulthood and reach reproductive age. Reproductive age is later in life for K-strategists. r-strategist species, such as some insects, have very large numbers of offspring, the majority of which will die before reaching physical maturity. If there is a change in their environment, more of these offspring may survive than is typical, leading to irruptive growth.

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