To understand ecosystems, I have to learn what’s in them (organisms, land, water, air) and what’s happening (water cycle, climate and weather, disturbances such as storms and floods, flow of organisms, material, nutrients, and energy). There’s also the complex interactions among all those things which make ecosystems continuously changing. It’s important to learn those interactions and what has made them possible in the first place.
First, the physical environment and processes introduce what’s possible and what’s available. If the land is good and there’s enough water, it’s possible that a lot of organisms will thrive (just like how early human civilizations started and thrived near rivers). Also, the organisms that are already there will influence the “attraction” of the next set of organisms. For example, it’s often a requirement that the place already has plants or other photosynthetic organisms for animals to feed on. And those animals can be a food source for other animals and organisms (bacteria and insects that will feed on the animals’ death). Among those organisms there could be competition, predation, and other interactions that go into some level of equilibrium after some time.
However, from time to time things happen that shake things up. A storm can destroy some trees and habitats. Floods and fires can kill many of the creatures or get them to migrate to safe areas. The disturbance can cause temporary or permanent change. The area might still recover or the creatures will totally desert the place. Or the place might become the home for a new set of organisms (including us humans).
Change always happens in ecosystems and there are always dynamic interactions among the organisms, the physical environment, and the surroundings. Because of the dynamics and the complexity, we have to be careful when we do something to the environment. There could be unintended consequences and cascading effects that might permanently damage the ecosystems. It’s our job then to first understand what’s in the ecosystem and what’s happening in and on it. This way we can better predict what will happen and avoid disasters as well as decide whether we should really do something in the first place.