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Dragon fruit. (Photo by R. Butler)
SEEDS and FRUITS
Many of the seeds and fruits produced by canopy trees fall to the ground where they provide food for seed gatherers (rodents, birds, fish, etc) and create a natural seed bank in the leaf litter. There are two growth strategies once seeds reach the ground. One strategy is to produce large seeds with food reserves enabling the seedling to survive in the low-light conditions of the understory. The second method characteristic of many pioneer species is to produce huge numbers of small seeds which only germinate under certain conditions (usually light gaps). When a light gap opens, these seeds sprout and the seedlings rapidly grow to once again plug the hole in the canopy.
Since seeds are the agents for future growth, many have defenses against predators to ensure some will be left untouched to germinate. Plants reduce herbivory and seed eating with structural defenses like thorns, stinging hairs, or spines and the production of toxic compounds which interfere with digestion or are unpalatable. Often the seed is surrounded by an edible fleshy material to make it palatable to birds and mammals who can disperse it, but the seed is toxic or indigestible so it will be passed out or discarded. For example, the cashew has a sweet and juicy stem but a toxic seed, so monkeys eat the fleshy stem and discard the seed.
Many rainforest trees, especially those of the forest interior, produce large cauliflorous fruits that grow directly out of the surface of the tree. This mechanism enables the tree to grow large, conspicuous fruits that attract larger animals. One of the largest cauliflorous fruits is the jackfruit of Southeast Asia which may be three feet long (1 m) and 110 pounds (50 kg). The jackfruit produces a strong odor that attracts nocturnal mammals like the flying fox. A famous cauliflorous fruit of Southeast Asia is the durian, a thorn covered fruit that is said to "taste like heaven but smell like hell." The odor of the durian is so offensive that its presence has been banned in some public places. Nevertheless, the durian is an important export for Malaysia, Indonesia, and Thailand, which exported nearly 1 million metric tons in 1992. Both cocoa and coffee beans grow as cauliflorous fruit.
Seeds and fruits provide an important food resource for forest-floor animals. To survive, a seed must elude these predators and many do so by being dispersed by specialized birds, mammals, and fish. These dispersers eat the fruit flesh without destroying the seed. Other seeds escape by being poisonous. Some of these toxins are useful to insects, which sequester them for their own purposes, and to humans. For example, many seed toxins have been chemically isolated and used to formulate drugs for humans, while umpteen insects naturally incorporate these compounds to render themselves toxic or use these toxins to produce scents to attract mates. For example, the male butterflies of the Danaiidae family convert alkaloids in the crotalaria plant into a scent to attract females.
Many large seeds have structured defenses against seed predators. In some cases seeds designed for gut passage by large mammals will have a sturdy seed coat, while bird-dispersed large-seeded fruit will often have seeds that are chemically defended. For example, the fruit of the nutmeg splits open to reveal a large seed covered with an orange-colored aril. The seed is highly aromatic, and the odor acts as a warning and toxic deterrent.
Review questions:
How do animals help the reproductive cycle of plants?
Deforestation emissions should be shared between producer and consumer, argues study
(11/19/2009) Under the Kyoto Protocol the nation that produces carbon emission takes responsibility for them, but what about when the country is producing carbon-intensive goods for consumer demand beyond its borders? For example while China is now the world's highest carbon emitter, 50 percent of its growth over the last year was due to producing goods for wealthy countries like the EU and the United States which have, in a sense, outsourced their manufacturing emissions to China. A new study in Environmental Research Letters presents a possible model for making certain that both producer and consumer share responsibility for emissions in an area so far neglected by studies of this kind: deforestation and land-use change.
Oil palm workers still below poverty line, despite Minister's statements
(11/19/2009) On October 19th, Plantation Industries and Commodities Minister Tan Sri Bernard Dompok told parliament that oil palm harvesters and rubber tappers are living above Malaysia's national poverty line, according to a story in the Malaysian Insider. But now representatives of the workers are saying Dompok lied.
REDD may increase the cost of conservation of non-forest ecosystems
(11/19/2009) Policy-makers designing a climate change mitigation mechanism that will reduce emissions from deforestation and degradation (REDD) aren't doing enough to ensure that the scheme protects biodiversity outside carbon-dense ecosystems, argues an editorial published in Current Biology by a group of scientists.
Indonesian government suspends license of logging company in controversial forest area
(11/19/2009) The Indonesian government today temporarily suspended the license of Asia Pacific Resources International Holding Limited (APRIL) for developing an area of forest and peatland in Sumatra pending a review of the company's permits, reports Greenpeace.
