Organisms higher in a food web eat everything that is lower in the web. The top of a food chain has the most energy because it accumulates up the chain. Populations higher on a food web increase in number, because they deplete those lower in the web. Traits are developed by individuals in response to the needs of the individual. Traits develop because they are part of a predetermined grand plan.
Traits are properties of populations.
Traits are passed on by the bigger, stronger organisms that replace the smaller, weaker ones. Populations exist in states of either constant growth or decline depending on their position in a food a chain. Some ecosystems are limitless resources and provide an opportunity for limitless growth of a population. Varying the population of an organism will only affect the others that are directly connected through a food chain. Varying the population of an organism may not affect an ecosystem, because some organisms are not important.