One example:
Energy moves through an ecosystem through different organisms. For example, plants can absorb energy from the sun. Animals, such as grasshoppers, can eat the plants and the energy goes to them. Progressing higher up the food chain, the energy continues to transfer through different animals - grasshoppers can be eaten by mice, mice by snakes, snakes by eagles, etc. etc.
The answer is Overproduction
By definition in biological terms, overproduction means that each generation has more offspring that can be supported by its environment and it results to competition for limited resources.
The survival of the fittest's main idea is that the organisms or species that are well adapted to their environment have higher chances of survival.
The descent with modification proposes the idea that species undergo changes over time that produces new species in whcih they share a common ancestor.
Adaptation means organisms learn to adjust to their new environment.