Ecological Islands within the Continent of Africa (Part 3–The Forests of Biafra)

The bight of Biafra, the “armpit” shaped region of western Africa, hosts the wettest rainforests on the continent.  Over 6000 species of plants grow here including oil date palms, and many species of cassia trees, liana vines, and orchids that sprout in organic matter deposited on the crooks of tree branches.  Before humans deforested the greater part of the region, it was a lush, green, and shady environment.  Species such as the giant ginger plant (Aframomum gigantea) exist as long-lived roots until a tree falls, allowing sunlight to reach the forest floor.  Then the ginger plant sprouts up to 18 feet tall to benefit from life-giving photosynthesis.  The spicy hot compounds in the root protects the ginger from foraging animals, insects, and microbes for decades while the plant awaits its chance to sprout.  The stems, however, are a favorite food of the gorilla.  Ginger is used in human cuisine, but try taking a bite of raw ginger root and find out why animals avoid eating it.

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Illustration of the giant ginger plant.

Primates and squirrels like to eat the nuts of the 20 species of colas that grow here.  Yes, this is the nut that flavors Coca-Cola.  The caffeine in the nuts is poison to some animals but many species, including humans eat them.

予約商品[コーラの木]コーラ・レピドータ(Cola lepidota)種子

Cola nuts are native to Africa.  Extract from the caffeine-laden nuts is used to flavor Coca-Cola.

The American persimmon (Diospyros virginianus) is 1 of just 2 species of ebony trees native to North America.  Africa has 40 species in this genus.  They produce a heavy valuable wood, a trait that has led to deforestation of the region.  The fruit of ebony trees resemble those of American persimmons and are edible, but the leaves are toxic.  An area of Biafra, known as the Sanaga Delta, experiences heavy rains and has sandy soils.  Ebony trees thrive on these poor soils and dominate the forest canopy.  The toxins in the ebony tree leaves help the trees conserve nutrients by discouraging animals from eating them.  Most colobus monkeys primarily eat leaves but can’t eat the toxic ebony tree leaves.  Therefore, most species of colobus monkeys live in lower densities on the Sanaga Delta than elsewhere in Biafra.  But the satanic colobus monkey (Colobus satana) evolved the ability to eat seeds and do better here with reduced competition from other monkeys.

Diospyros crassiflora

Ebony trees are endangered because of the high quality dense wood they produce.  Most fruits are edible, similar to American persimmons, but the leaves are toxic.

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The satanic or black and white colobus monkey.

The mandrill (Mandrillus leucopheus) evolved from a ground dwelling baboon-like monkey.  It became adapted to more forested conditions.  The colorful faces and genitals of the males is likely an adaptation to communal living in the forest.

A male drill (Mandrillus leucophaeus). Photo by: Ola Olsson.

Male mandrill.

Over 1000 species of butterflies live in Biafra–the richest diversity in the world–and over 500 species of birds occur here, rivaling the Amazon basin’s diversity.  There are 8 endemic genera of frogs as well.  The goliath frog (Conraua goliath), weighing over 7 pounds, is the largest frog in the world.  This species occurs in a small range within Biafra.  Its large size and slow rate of reproduction make it vulnerable to predation, yet it has found a survivable niche in this rich region.

i-5964e5a8e493bd24a9a4a1202dd9ea0a-kids with offensively big frog.jpg

The goliath frog is endemic to this region.  It can weigh over 7 pounds.

Reference:

Kingdon, Jonathan

Island Africa: The Evolution of Africa’s Rare Animals and Plants

Princeton University Press 1989

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