Lemur - Ecology

Ecology

See above: Diet, Metabolism, Activity patterns, and Locomotion

Madagascar not only contains two radically different climatic zones, the rainforests of the east and the dry regions of the west, but also swings from extended drought to cyclone-generated floods. These climatic and geographical challenges, along with poor soils, low plant productivity, wide ranges of ecosystem complexity, and a lack of regularly fruiting trees (such as fig trees) have driven the evolution of lemurs' immense morphological and behavioral diversity. Their survival has required the ability to endure the persistent extremes, not yearly averages.

Lemurs have either presently or formerly filled the ecological niches normally occupied by monkeys, squirrels, woodpeckers, and grazing ungulates. With the diversity of adaptations for specific ecological niches, habitat selections among lemur families and some genera are often very distinct, thus minimizing competition. In nocturnal lemurs from the more seasonal forests in the west, up to five species can coexist during the wet season due to high food abundance. However, to endure the extreme dry season, three of the five species utilize different dietary patterns and their underlying physiological traits to allow them to coexist: fork-marked lemurs feed on tree gum, sportive lemurs feed on leaves, and giant mouse lemurs sometimes feed on insect secretions. The other two species, the Gray Mouse Lemur and the fat-tailed dwarf lemur (Cheirogaleus medius), avoid competition through reduced activity. The gray mouse lemur uses bouts of torpor, while the fat-tailed dwarf lemur hibernates completely. Similarly, on the east coast entire genera focus on specific food to avoid too much niche overlap. True lemurs and ruffed lemurs are frugivorous, indriids are folivorous, and bamboo lemurs specialize in bamboo and other grasses. Once again, seasonal dietary differences as well as subtle differences in substrate preferences, forest strata used, activity cycle, and social organization enable lemur species to coexist, although this time the species are more closely related and have similar niches. A classic example involves resource partitioning between three species of bamboo lemur that live in close proximity in small forested areas: the golden bamboo lemur, the greater bamboo lemur, and the eastern lesser bamboo lemur (Hapalemur griseus). Each utilizes either different species of bamboo, different parts of the plant, or different layers in the forest. Nutrient and toxin content (such as cyanide) help regulate food selection, though seasonal food preferences are also known to play a role.

Dietary regimes of lemurs include folivory, frugivory, and omnivory, with some being highly adaptable while others specialize on foods such as plant exudates (tree gum) and bamboo. In some cases, lemur feeding patterns directly benefit the native plant life. When lemurs exploit nectar, they may act as pollinators as long as the functional parts of the flower are not damaged. In fact, several unrelated Malagasy flowering plants demonstrate lemur-specific pollination traits, and studies indicate that some diurnal species, such as the red-bellied lemur and the ruffed lemurs, act as major pollinators. Two examples of plant species that rely on lemurs for pollination include Traveller's Palm (Ravenala madagascariensis) and a species of legume-like liana, Strongylodon cravieniae. Seed dispersal is another service lemurs provide. After passing through the lemur gut, tree and vine seeds exhibit lower mortality and germinate faster. Latrine behavior exhibited by some lemurs may help improve soil quality and facilitate seed dispersal. Because of their importance in maintaining a healthy forest, frugivorous lemurs may qualify as keystone mutualists.

All lemurs, particularly the smaller species, are affected by predation and they are important prey items for predators. Humans are the most significant predator of diurnal lemurs, despite taboos that occasionally forbid the hunting and eating of certain lemur species. Other predators include native euplerids, such as the fossa, feral cats, domestic dogs, snakes, diurnal birds of prey, owls, and crocodiles. Extinct giant eagles, including one or two species from the genus Aquila and the giant Malagasy Crowned Eagle (Stephanoaetus mahery), as well as the giant fossa (Cryptoprocta spelea), previously also preyed on lemurs, perhaps including the giant subfossil lemurs or their subadult offspring. The existence of these extinct giants suggests that predator-prey interactions involving lemurs were more complex than they are today. Today, predator size only restricts owls to the smaller lemurs, usually 100 g (3.5 oz) or less, while the larger lemurs fall victim to the larger diurnal birds of prey, such as the Madagascar Harrier-hawk (Polyboroides radiatus) and the Madagascar Buzzard (Buteo brachypterus).