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8.9. Self-regulation of the ecosystem, the population and the community

Ecosystem self-regulation

Ecosystems have great resistance to changes that occur in their environment. The self-regulation of an ecosystem consists of a set of mechanisms (relationships, interactions, feedbacks, natural selection and other ecological phenomena) that keep the ecosystem stable in a dynamic balance. If the balance is broken, the ecosystem is destroyed. Thus, over time, ecosystems can overcome the alterations that, due to natural or human causes, could have affected them. Two examples of these ecosystem self-regulation mechanisms are:

Feedback between predators and prey

The relationship between an ecosystem's predators and its prey is also self-regulating.

If there are many prey in an ecosystem, there is a lot of food available for predators and they will be able to have more young, so in a short time the number of predators will increase.

The high number of predators will need many prey to feed, so the number of prey will decrease, leaving less food available to predators. As a consequence, some will die, have fewer young, and the number of predators will decrease. Then, as the predators will hunt less prey, the number of these will increase, returning to the starting point, keeping the balance between the two populations stable.

Modelo depredador - presa

By AspidistraK (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Simulator: Predator-prey model.

Simulator: Rabbits and wolves (rabbits and wolves).

Game: Ecodetectives. The Peril River problem.

Self-purification of polluted water

When ecosystems are altered by human activities, they also have mechanisms to resist and maintain themselves, if the damage is not too great.
Water has self-purification mechanisms when pollutant discharges or organic remains alter its quality.
When contaminated water is discharged from industrial, urban, agricultural or livestock activities, these substances cause a loss of quality of these waters.
The self-purification of water occurs when physical, chemical and biological processes that take place in the water, naturally, destroy the substances that have been incorporated into the river. The aerobic bacteria mainly consume organic matter, and aquatic plants assimilate some substances as nutrients, so that these get the biodegradation of pollutants and recovering clean water quality.

Interactive activity: Self-regulation of the ecosystem.

Population dynamics

Growth rate of a population

The growth rate of a population is the increase (or decrease) of the population due to births and deaths that have occurred in a certain period of time.

We must consider that the population is a system, with its own dynamics and relationships. If it had no limits, the population would grow progressively.

Growth curves

According to the population growth strategy, two different types of growth curves are distinguished:

S-shaped growth curves

This type of growth curve is characteristic of balanced media, in which the environmental characteristics are relatively constant.

"J" shaped growth curves

The "J" growth curve is characteristic of environments where ecosystems are easily created and destroyed. Growth proceeds exponentially to environmental limits instead of reaching equilibrium and then almost disappearing when the nutrients in the environment are depleted. For example, herbaceous plants with annual growth or insects that depend on annual crops.

Curvas de crecimiento de la población
Imagen de dominio pública tomada de 
Interactive activity: Growth curves.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.