What is population density dependent and density independent?

Answer 1

A population is "density-dependent" when it is affected by its size. An example might be population growth: as a population gets large, it might grow slower since there are less resources to use up or diseases become prevalent. The growth rate depends on the population size (also called population density).

A population is "density-independent" when the current size doesn't change anything. For example bacteria populations are largely density-independent when they are small. For example they roughly double in size every few minutes. Whether you start with one single bacterium or a colony of 100, the total count will double every few minutes. This is exponential growth.

Only after the bacteria colony gets extremely large (millions or billions of individual cells) will the density begin to affect the colonies growth rate, at which point its population growth is then density-dependent.

Another example of a density-independent process might be radioactive decay. No matter how much of the radioactive matter is left at any point in time, half of it will be left after one half-life length of time into the future. It does not matter how the material is arranged, it could be one big clump of material (densely packed together), or it could be smashed into many bits separated far away from each other.