Population Growth and Limiting Factors

Population Growth Population Growth - An increase in the size of a population over time. Populations of organisms do not experience linear growth. That is they do NOT grow at equal rates over equal time. Instead, populations grow exponentially. As the population gets larger, it also grows faster. The graph looks like the letter …….. J NOT

Exponential Population Growth Exponential growth is shown by a J-shaped graph. This indicates as more individuals are added to a population, the faster the population will grow. Number of Individuals Time

Exponential Population Growth Populations will continue to grow exponentially if there are unlimited resources and NO limiting factors – plenty food, space, etc. Limiting factor – ANYTHING in the environment which limits the growth of a population Limiting factors include biotic and abiotic factors. All regulate the size of populations & prevent further growth Examples- food, space, disease, natural disaster, etc.

Environmental Limits Density Dependent Limiting Factors- When a population increases & becomes more densely populated (more individuals per space) these factors will limit the population. For these things to limit the size of a population, it DOES depend on how many organisms are in an area. Examples – disease, competition, parasites, food, predation When there are more individuals these factors have an increasing effect

Environmental Limits Density Independent Limiting Factors - affect all populations regardless of their density. The size of a population does not influence the affect of these factors. They limit population growth anytime they are present. Most of these factors are abiotic - such as temperature, storms, floods, drought, and habitat disruption. They can limit a population ANYTIME

Another way to classify factors: Biotic Biological influences on organisms within an ecosystem how living things affect other living things “density dependent factors” Abiotic Physical, non-living factors that influence organisms within an ecosystem “density independent factors”

Limits to the Environment The MAX number of organisms of one species that an environment can support is its carrying capacity. Carrying capacity is often influenced by the limiting factors of an area – harsh winter, food availability, etc.

Carrying Capacity If populations are UNDER the carrying capacity they will continue to grow exponentially, with the birth rate exceeding the death rate If populations reach carrying capacity, the birth rate & death rate begin to equal out and the population begins to level off. This is called LOGISTICAL growth and is shown with an S-curve on a graph. A population which exceeds the carrying capacity can no longer be supported by the environment in which it lives

Reaching Carrying Capacity Number of Individuals S-shaped graph shows LOGISTICAL growth TIME

Interactive Limits A population can reach its growth “limit” due to: Predation (read about Isle Royale) Competition for resources (food, space, etc) – occurs in crowded populations and even among different species Stress (manifests as disease, aggression, decrease in parental care)

Population Impacts on Other Populations Predator-prey – populations cycle – more food for predator, more deaths of prey & vice versa Prey Number Of Individuals Predator Time

Population Impact on the Environment Large populations need more natural resources – shelter, food, water Densely populated areas can be extremely devastating to the environment – placing demands on space & resources Overuse of natural resources can also devastate other populations of species Population control is needed to “protect” environmental resources in cases of wildlife. Humans need to be educated in wise practices concerning use of resources and land.