Evolution and selection what mechanisms lead to changes in the diversity of species on earth?

The answer is genetic drift and genetic shift. The former occurs when small changes occur in the genotype of a population that accumulates over time and changes the allelic frequency of the population. The latter (genetic shift) occurs abruptly and is usually caused by a bottleneck effect.

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.