Variations within a species are an important part of Charles Darwin's theory of evolution. Which example can be explained by individual variation? The food source in a lake is not enough to support the bass population, but it can support the trout.
A population of brown bears has doubled in the past 10 years as its habitat size has increased.
Owls and foxes compete fiercely against each other for small rodents in their habitat.
Brightly colored cardinals are better able to survive and to reproduce than darker cardinals.