Ecology is the science of the relationships between organisms and their environments. It includes the study of biomes, ecosystems, biological and geological systems, biotic and abiotic factors, biological classification, autotrophs and producers, consumers, decomposers, food chains and webs, resources, habitats, niches, limiting factors, carrying capacity, and the environmental impacts of human activity. Humans can cause ecological imbalance through introduced species, fossil fuel use, habitat destruction, pollution, overhunting, and overgrazing.