How do populations behave?

There are variables that affect how do populations change over time (growing or decreasing), and these are called limiting factors. These keep populations in check and can be classified into:

• Density dependent factors
• Density independent factors

Density dependent factors are those that, as its name implies, depend on population density. This means that the impact these factors have depends on how many individuals there are. These are usually biotic factors, such as biomass, predation, competition.

Density independent factors are those that affect a population regardless of its size. These are usually abiotic factors. Some examples are pH, temperature, salinity, and also natural disasters such as tornadoes, earthquakes, volcanic explosions.




GROWTH CURVES

Growth rate can be graphed. There are two different types of curves:

• J-curve
• S-curve

Each shows a different type of population growth.
J-curves show exponential growth. The population grows exponentially and then crashes or suffers what is known as a dieback. This is because the population overshoots and exceeds the carrying capacity (K), which is the maximum amount of individuals an ecosystem can support without being affected. This is known as a boom and bust pattern. This growth rate is common in organisms.
S-curves start out as exponential growth, but then stabilize as the population reaches its carrying capacity. This growth rate is consistent with density dependent factors. This is known as a logistic curve.

In the image above shows in the left a J-curve and in the right a S-curve

S- and J-curves are idealized. In nature, both types of limiting factors act on the same population and the result is a combination of both curves.

·        There also exist  Population strategies:

o   K-Strategies:

§  Long lifespan

o   R-strategists:   

§  Short lifespan