An ecosystem is a living system that includes the sun as an energy source, soil, rocks, water, air, plant life and living beings. We humans are only one part of any ecosystem, but many people believe that we have a disproportionate effect. Our actions tend to affect not just our surroundings, but the world at large. To live more responsibly on the Earth, we must understand how the things we do can have lasting effects. FoodWhile people who live in towns and cities may not ever see the farms that support them, we are all dependent on agriculture. That agriculture has a huge effect on our ecosystems: pesticides and other toxic chemicals used in food production can wash downstream, killing many types of animals, polluting our waterways and even making humans ill. Fertilizers can wash downstream, causing "blooms" or large populations of algae and bacteria, which can harm fish populations. In addition, GreenFacts states that we are depleting fish populations in the oceans and seas, causing us to fish further offshore and deeper underwater as more and more fish disappear.