The energy transfer in an ecosystem is not 100% efficient. Why ?

According to the second law of thermodynamics, when energy is put to work, a part of it is always converted in unuseful form mainly as heat, due to friction and radiation. In all such cases the total sum of useful and unuseful energy remains constant. So, similar to machines, in ecosystems also the energy transfer is not 100% efficient. The energy used in respiration and in decay (or death) appears as unuseful heat energy because this energy does not reach to the consumer of next stage. This aligns with the second law of thermodynamics.