It can cause a chain reaction. Every cause has an effect.
Example: Someone throws a cigarette out their window, causing a grass fire
Scenario A: A prairie dog population was killed in the grassfire simply because they had no time to escape.
Scenario B: The grasshoppers don't have grass to eat, so the prairie dogs don't have meat to survive because the grasshoppers are starving. Either way, the person who threw the cigarette caused a decrease in the population.