Irruptive growth is a growth pattern over time, defined by a sudden rapid growth in the population of an organism. Irruptive growth is studied in

population ecology Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration. The discipline is import ...

Population cycle A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population ...

s often display irruptive growth, but with a predictable pattern subsequent decline. It is a phenomenon typically associated with

r-strategists In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individ ...

. Humans do not show irruptive growth. Irruptive growth occurs when a species reproduces rapidly. It is especially common in large herbivores, such as pronghorn or elk (red deer), which have high fecundity and delayed density-dependent effects on

recruitment Recruitment is the overall process of identifying, sourcing, screening, shortlisting, and interviewing candidates for jobs (either permanent or temporary) within an organization. Recruitment also is the processes involved in choosing individua ...

. All populations show

logistic growth A logistic function or logistic curve is a common S-shaped curve (sigmoid curve) with equation f(x) = \frac, where For values of x in the domain of real numbers from -\infty to +\infty, the S-curve shown on the right is obtained, with the ...

, but in species which exhibit irruptive growth this is especially rapid. Populations of some species initially show a lack of response to density-dependent factors that limit population size as it nears the

carrying capacity The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as ...

of the

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

. The exhibition of irruptive growth is dependent on a number of elements including resource availability, degree of both interspecific and intraspecific competition, and strength of

predator-prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

relationships. In

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

s with more than one species feeding on a certain resource, the populations of certain species can irrupt in non-predictable ways depending upon the complex feedback mechanisms caused by competition. A species population may sometimes irrupt when predators are removed, or when favourable weather causes food supplies to rapidly increase. Similar to white-tailed deer in North America, roe deer in Europe have shown similar

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

even as the population density doubles three or four times. The deer are able to irrupt because the species is able to double its population yearly and populations show delayed response to density-dependent factors, in other words -the females remain just as fertile despite having lower body weights and other characteristics affiliated with

overpopulation Overpopulation or overabundance is a phenomenon in which a species' population becomes larger than the carrying capacity of its environment. This may be caused by increased birth rates, lowered mortality rates, reduced predation or large scale ...

. Irruptive growth patterns are also seen in mammal herbivores with a relatively small body size, or such creatures in Arctic ecosystems which are subject to

population cycle A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population ...

s. In cases where a single herbivore prey species is dominant in an ecosystem, there is likely to be a strong link with predator species which serves to control the population (see

Lotka–Volterra equations The Lotka–Volterra equations, also known as the predator–prey equations, are a pair of first-order nonlinear differential equations, frequently used to describe the dynamics of biological systems in which two species interact, one as a pre ...

). The populations of rabbits and house mice introduced Australia show irruptive growth, for example. A possible reason may be that after drought ends, they reproduce at a rapid rate while predator reproduction is still seasonal in occurrence. This allows for the population to explode and to be limited more by a return of dry conditions than by predators.

Invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...

which can reproduce rapidly may show this pattern of growth because when a new area is being colonized predator species are often not present to limit growth, and there is little intraspecific and/or interspecific competition in early settlement of a location which means there is abundant resource availability.

K-strategist and r-strategist species

Species that are r-strategist (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. Species that are r-strategist are more likely to exhibit irruptive growth than K-strategist species. 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 probability of survival of individual offspring. The

human species Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, an ...

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. r-strategist species, such as some

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s and most plants, 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. Because K-strategist species have less offspring they are less likely to exhibit irruptive growth.

References

{{reflist Population ecology

K-strategist and r-strategist species

See also

References