Two ecosystems have almost equal number of animals and are equally rich, that is having similar number of different types of species present in the ecosystem. However, the first ecosystem has 75% water buffaloes. And the second ecosystem has almost equal number of different species. Thus, ecosystem 2 is more diverse than ecosystem 1.
Species evenness is a parameter that determines how evenly are different species spread across the population of all organisms in the ecosystem. When two ecosystem are equally rich in different types of species, the evenness with which the species are spread across the ecosystem is taken into consideration to determine the diversity. That is, if there are 40 foxes, and 1000 water buffaloes, the community is not very even. But if there are 40 foxes and 42 water buffaloes, the community is quite even. In the above case, we see that the ecosystem 1 has water buffaloes as the major constituent of herbivores, when compared to ecosystem 2 that is quite even, thus ecosystem 2 is more diverse.