Large predators are found at higher trophic levels becausespecialized bodies are needed to extract the small energy that gets to them.
The energy that gets to successive trophic levels decreases progressively because much of it is lost as heat. This means that a small percentage of the energy from the producers that form the bases of trophic levels to the predators that are somewhat at the top of trophic levels.
With big body size, the bodies of predators are organized into systems that work together to efficiently extract the small energy that gets to them from immediate lower trophic level.
The neurotransmitter in the body
which prepares it for "fight or flight" reaction is EPINEPHRINE. The
level of Epinephrine is remarkably high in patients who have anxiety-related
disorders. Also known as adrenalin or adrenaline, epinephrine is a hormone and at the same time a neurotransmitter; it is also used as medication.