Irruptive growth

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 cycles often display irruptive growth, but with a predictable pattern subsequent decline. It is a phenomenon typically associated with r-strategists. 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. All populations show logistic growth, 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 of the environment. 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 relationships. In ecosystems 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 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. 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 cycles.