Dissipate actually means loss or disappearance of energy.
There is energy flow taking place in the ecosystem.In this energy flow,initially plants (producers/first tropic level) make use of solar energy for synthesizing food which is eaten by primary consumers(second tropic level).
During this consumption only ten percent of the total energy produced is transferred from one level to the next. Remaining energy is lost in the form of heat to the ecosystem due to certain metabolic processes occurring in the organism like respiration,growth etc.
Hence this loss of energy in the form of heat to the ecosystem is known as energy dissipation.
