Lemur - Behavior - Diet

Diet

Lemur diets are highly variable and demonstrate a high degree of plasticity, although general trends suggest that the smallest species primarily consume fruit and insects (omnivory), while the larger species are more herbivorous, consuming mostly plant material. As with all primates, hungry lemurs might eat anything that is edible, whether or not the item is one of their preferred foods. For instance, the Ring-tailed Lemur eats insects and small vertebrates when necessary and as a result it is commonly viewed as an opportunistic omnivore. Coquerel's giant mouse lemur (Mirza coquereli) is mostly frugivorous, but will consume insect secretions during the dry season.

A common assumption in mammalogy is that small mammals cannot subsist entirely on plant material and must have a high-calorie diet in order to survive. As a result, it was thought that the diet of tiny primates must be high in protein-containing insects (insectivory). Research has shown, however, that mouse lemurs, the smallest living primates, consume more fruit than insects, contradicting the popular hypothesis.

Plant material makes up the majority of most lemur diets. Members of at least 109 of all known plant families in Madagascar (55%) are exploited by lemurs. Since lemurs are primarily arboreal, most of these exploited species are woody plants, including trees, shrubs, or lianas. Only the ring-tailed lemur, the bamboo lemurs (genus Hapalemur), and the black-and-white ruffed lemur (Varecia variegata) are known to consume herbs. While Madagascar is rich in fern diversity, these plants are rarely eaten by lemurs. One possible reason for this is that ferns lack flowers, fruits, and seeds—common food items in lemur diets. They also occur close to the ground, while lemurs spend most of their time in the trees. Lastly, ferns have an unpleasant taste due to the high content of tannins in their fronds. Likewise, mangroves appear to be rarely exploited by lemurs due to their high tannin content. Some lemurs appear to have evolved responses against common plant defenses, however, such as tannins and alkaloids. The golden bamboo lemur (Hapalemur aureus), for instance, eats giant bamboo (Cathariostachys madagascariensis), which contains high levels of cyanide. This lemur can consume twelve times the typically lethal dose for most mammals on a daily basis; the physiological mechanisms that protect it from cyanide poisoning are unknown. At the Duke Lemur Center (DLC) in the United States, lemurs that roam the outdoor enclosures have been observed eating poison ivy (Taxicodendron radicans), yet have shown no ill effects.

Many of the larger lemur species consume leaves (folivory), particularly the indriids. However, some smaller lemurs such as sportive lemurs (genus Lepilemur) and woolly lemurs (genus Avahi) also primarily eat leaves, making them the smallest primates that do so. The smallest of the lemurs generally do not eat much leaf matter. Collectively, lemurs have been documented consuming leaves from at least 82 native plant families and 15 alien plant families. Lemurs tend to be selective in their consumption of the part of the leaf or shoot as well as its age. Often, young leaves are preferred over mature leaves.

Many lemurs that eat leaves tend to do so during times of fruit scarcity, sometimes suffering weight loss as a result. Most lemur species, including most of the smallest lemurs and excluding some of the indriids, predominantly eat fruit (frugivory) when available. Collectively, lemurs have been documented consuming fruit from at least 86 native plant families and 15 alien plant families. As with most tropical fruit eaters, the lemur diet is dominated by fruit from Ficus (fig) species. In many anthropoid primates, fruit is a primary source of vitamin C, but unlike anthropoid primates, lemurs (and all strepsirrhines) can synthesize their own vitamin C. Historically, captive lemur diets high in vitamin C-rich fruits have been thought to cause hemosiderosis, a type of iron overload disorder, since vitamin C increases iron absorption. Although lemurs in captivity have been shown to be prone to hemosiderosis, the frequency of the disease varies across institutions and may depend on the diet, husbandry protocols, and genetic stock. Assumptions about the problem need to be tested separately for each species. The ring-tailed lemur, for instance, seems to be less prone to the disorder than other lemur species.

Only eight species of lemur are known to be seed predators (granivores), but this may be under-reported since most observations only report fruit consumption and do not investigate whether the seeds are consumed as well. These lemurs include some indriids, such as the diademed sifaka (Propithecus diadema), the golden-crowned sifaka (Propithecus tattersalli), the indri, and the aye-aye. The aye-aye, which specializes in structurally defended resources, can chew through Canarium seeds, which are harder than the seeds that New World monkeys are known to break open. At least 36 genera from 23 families of plants are targeted by lemur seed predators.

Inflorescences (clusters of flowers) of at least 60 plant families are eaten by lemurs ranging in size from the tiny mouse lemurs to the relatively large ruffed lemurs. If the flowers are not exploited, sometimes the nectar is consumed (nectarivory) along with the pollen (palynivory). At least 24 native species from 17 plant families are targeted for nectar or pollen consumption.

Bark and plant exudates such as tree sap are consumed by a few lemur species. The exploitation of exudates has been reported in 18 plant species and only in the dry regions in the south and west of Madagascar. Only the Masoala fork-marked lemur (Phaner furcifer) and Coquerel's giant mouse lemur regularly consume tree sap. Bark has never been reported as an important food item in lemur diets, but at least four species eat it: the aye-aye, the red-tailed sportive lemur (Lepilemur ruficaudatus), the common brown lemur (Eulemur fulvus), and Verreaux's sifaka (Propithecus verreauxi). Most bark feeding is directly linked to exudate feeding, except for the aye-aye's bark feeding on Afzelia bijuga (genus Afzelia) at Nosy Mangabe in the northeast.

Soil consumption (geophagy) has also been reported and likely helps with digestion, provides minerals and salts, and helps absorb toxins. Sifakas have been observed eating soil from termite mounds, possibly adding beneficial intestinal flora to aid the digestion of cellulose from their folivorous diet.