Most species of lemur are endangered, and some have already gone extinct.  The IUCN Red List says that ring-tailed lemurs are endangered.  Lemurs are important to nature in Madagascar because they eat fruit and spread the seeds all over the island.  Without lemurs as a part of the environment fruit trees would die.

Their population is going down because their habitat is being destroyed.  It is being turned into farmland or the trees are being burned for charcoal.  Because there are less trees, there is less food for the lemurs to eat.  This makes there be a lower chance of survival.  Because of fewer trees and less food, lemurs might try to steal food from farms, and farmers might kill them.  It is illegal to kill lemurs in Madagascar, but farmers still do it.