Population Dynamics and Ecosystem Relationships

Population Dynamics

Expanding Populations

In expanding populations, there is a high birth rate. The growth of these populations follows an exponential model.

Stable Populations

In stable populations, the number of individuals stabilizes after passing a phase of exponential growth. This occurs because factors limit population growth, such as competition between individuals for space and food, or pressure from predators. This growth limit imposed by the ecosystem is called the carrying capacity (K). In this case, the model that represents the stable population is a logistic or sigmoidal function.

Declining Populations

In declining populations, the number of older individuals predominates. The decline may be due to a low birth rate or a decrease in the mortality rate of older individuals. Stable populations will tend to produce fluctuations due to:

• Environmental changes
• Migration
• Variations in the proportion of predators and prey

Intraspecific Relations

These are established between individuals of the same species. Relations can be perennial or temporal.

Interspecific Relationships

They are established between individuals of different species. Each of the individuals involved can be harmed, benefited, or the relationship can be neutral.

Terrestrial and Aquatic Biomes

A biome is a large land area that has its own ecological characteristics. They fall into two main groups: terrestrial and aquatic. Within each, different ecosystems can be identified.

Terrestrial Biomes

Terrestrial biomes are characterized by their climate and vegetation. The climate is defined by two variables: rainfall and average temperatures throughout the year. The vegetation is conditioned by the climate and other factors such as topography and lithology. The type of vegetation determines the biodiversity of ecosystems.

• Tundra
• Taiga
• Grasslands and Steppes
• Deciduous Forest
• Mediterranean Forest
• Savannah
• Tropical Forest

Trophic Levels

Trophic or alimentary relationships represent the mechanism of transfer of matter and energy from some organisms to others as food. The first trophic level in an ecosystem are the producers: the energy source is the sun, and nutrients (inorganic) come from soil, water, and the atmosphere; therefore, they are photoautotrophs. Though rare, some systems are based on chemoautotrophic producers. The second trophic level consists of phytophagous herbivores (plant eaters).