the long gestation time, long period of parental care, and infant mortality, a female gorilla will only give birth to an offspring that survives to maturity every six to eight years. Western lowland gorillas are long-lived and may survive for as long as 40 years in the wild. A group's home range may be as large as , but is not actively defended. Wild western lowland gorillas are known to use tools. Western lowland gorillas' diets are high in fiber, including leaves, stems, fruit, piths, flowers, bark, invertebrates, and soil. The frequency of when each of these are consumed depends on the particular western lowland gorilla group and the season. Furthermore, different groups of western lowland gorillas eat differing numbers and species of plants and invertebrates, suggesting they have a food culture. Fruit comprises most of the western lowland gorillas' diets when it is abundant, directly influencing their foraging and ranging patterns. There is a correlation between the amount of time a western lowland gorilla travels and the season in which fruits are available. The western lowland gorillas spend more time traveling and feeding during the seasons when fruits are abundant compared to when there is less fruits available. Fruits of the genera Tetrapleura, Chrysophyllum, Dialium, and Landolphia are favored by the western lowland gorillas. Low-quality herbs, such as leaves and woody vegetation, are only eaten when fruit is scarce. In the dry season from January to March, when fleshy fruits are few and far between, more fibrous vegetation such as the leaves and bark of the low-quality herbs Palisota and Aframomum are consumed. Of the invertebrates consumed by the western lowland gorillas, termites and ants make up the majority. Caterpillars, grubs, and larvae are also consumed in rarity. Some ethnographic and pharmacological studies have suggested a possible medicinal value in particular foods consumed by the western lowland gorilla. The fruit and seeds of multiple Cola species are consumed. Given the low protein content, the main reason for their consumption may be the stimulating effect of the caffeine in them. Western lowland gorillas inhabiting Gabon have been observed consuming the fruit, stems, and roots of Tabernanthe iboga, which, due to the compound ibogaine in it, acts on the central nervous system, producing hallucinogenic effects. It also has effects comparable to caffeine. There is also evidence for medicinal value for the seed pods of Aframomum melegueta in western lowland gorillas' diets,