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11.3. Balance in ecosystems

Balance in ecosystems

As we have seen, an ecosystem is made up of the set of living beings that live in it, the physical environment in which they live and the relationships established between these living beings and between them and their environment.Since all the elements are related, one depends on the other. If these relationships are disturbed, the balance in the ecosystem also changes.

The number of populations, and of individuals of each population of the ecosystem, tend to remain stable over time and are adapted to the environmental factors of that ecosystem. This balance will be maintained if there are no major changes in the ecosystem.

The ecosystem is more stable the more complex it is. If the food web is complex, it will be easier for a species to obtain food when its main food source is scarce. On the other hand, if it feeds only on another species, if it disappears, it will also disappear.

The ecosystem tends to be in a dynamic equilibrium in which they remain stable over time, when the relationships between their components are stable and allow the survival of the different populations that compose it.

Ecosystem self-regulation

The ecosystem is in equilibrium, but it is a dynamic equilibrium, since the populations that live in it are subject to continuous changes that can modify both the number of populations and individuals. The ecosystem has some mechanisms that try to counteract these changes to regain stability.

An example is the relationship between predators and their prey, which is also self-regulating.

If there is a lot of prey (food), predators eat it and reproduce. When there are many predators, the number of prey decreases and the predators have a harder time feeding, so they reproduce less. With fewer predators, the number of prey increases again. This keeps it in a stable equilibrium.

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).

Answer in your notebook

According to the graph of the predator-prey model, which population increases first? What if the other population increased first?

Loss of balance in the ecosystem

The variations that occur in populations can have two types of causes:

  • Natural causes, such as seasonal changes that mean that, for example, migratory birds do not have food in winter and have to go to other places with better conditions to feed and live.
  • Human causes, as a consequence of human intervention in the ecosystem, such as overexploitation of resources, urbanization, pollution, fires, etc.

The main alterations that modify the balance of ecosystems are:

  • Changes in abiotic factors, such as a strong variation in temperature, floods, droughts, etc. that cause the disappearance of many individuals from a given population.
  • Changes that cause a sharp decrease in the food resources of a population.