Density-Dependent vs. Density-Independent Factors

What are density-dependent factors?

Internal factors that limit population growth and whose effects increase as population density rises (e.g., competition, disease, stress).

What are density-independent factors?

External factors that affect population growth regardless of density (e.g., weather, natural disasters, pollution).

Give 3 examples of density-dependent factors in animals.

Food availability, breeding territory, disease/parasites.

Give 3 examples of density-dependent factors in plants.

Competition for sunlight, water, and soil nutrients.

Why does predation increase as prey density rises?

Predators focus on the most common prey because they are easier to find → higher predation pressure.

How does aggression or stress function as a density-dependent factor?

At high density, some species (e.g., mice) become more aggressive or stressed → lower survival and reproduction.

What happens to populations when waste accumulates under high density?

Toxic build-up (feces, urine) pollutes the habitat → increases mortality and lowers health.

Give 3 examples of density-independent factors.

Extreme weather, volcanic eruptions, droughts.

Why are cold winters considered a density-independent factor for Japanese beetles in Canada?

Cold weather wipes out beetle populations regardless of their size.

How does climate change act as a density-independent factor for Japanese beetles?

Warmer winters let more beetles survive → population explodes, even if numbers were small before.