Population Dynamics: Autoregulation and Ecological Interactions

Population Autoregulation

A population is constituted by a set of individuals of the same species living in a given location. Environmental resistance is a set of factors that prevent a population from reaching its maximum biotic potential. These factors include:

• External factors: These may be biotic (predators, parasites) or abiotic (climate change, food shortages, disasters, etc.).
• Internal factors: Increasing population density adversely affects individuals.

There are two forms of reproduction strategies:

• r strategists: These are simple organisms with very high biotic potential. They have many offspring with no parental care. Consequently, only a few manage to survive and reach adulthood. The population size remains relatively stationary (e.g., insects, fish).
• k strategists: These have fewer offspring and provide more parental care. As a result, almost all offspring manage to reach adulthood (e.g., mammals, oak trees).

Ecological Valence

Ecological valence refers to the range of tolerance of a species to a particular environmental factor (light, temperature, moisture, phosphorus, nitrogen) that acts as a limiting factor. From the perspective of ecological valence, we can consider two types of species:

• Eurioic species: These have a wide tolerance range for a certain factor, exhibiting a very wide ecological valence. R strategists are often eurioic.
• Stenoic species: These have narrow tolerance ranges. However, when conditions are optimal, the number of individuals can be very high. K strategists are often stenoic, responding more effectively when environmental conditions are favorable.

Symbiotic and Other Ecological Relationships

• Symbiosis: A close relationship between individuals where both benefit. They cannot live separately and would die without the other (e.g., lichens).
• Mutualism: A relationship between two individuals where both benefit, but they can live separately.
• Commensalism: A relationship where one organism benefits without affecting the other, and the other organism (the commensal) benefits (e.g., remora and shark).
• Inquilinism: One organism lives on another (e.g., hermit crab).
• Predation: A relationship between a predator and its prey, where the prey dies.
• Competition: A relationship between organisms of the same or different species that compete for a resource. One species is always better adapted and displaces the other.
• Parasitism: A relationship where one organism (the parasite) benefits, and the other (the host) is harmed but does not die.