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ENVIRONMENT

BIOGEOGRAPHY

One of the most intriguing processes in nature is the colonisation of Islands by plants and animals. How do these tiny, remote specks in the ocean become populated by myriads of plants and animals? For centuries, it has been a source of wonder to explorers and scientists to discover how remote islands, thousands of kilometres from the nearest land, become populated by rich assemblies of living organisms.

Three methods have been identified as the principal means by which plants are dispersed over the oceans - wind, water and transport by birds.

Many seeds are tiny and can be blown hundreds of kilometres in wind currents; or larger seeds may have a parachute of silky hairs attached, enabling them to float on air currents over long distances. Some insects can similarly be blown in wind currents, or some spiders weave a parachute of silk for air transport.

Many oceanic island plants have arrived as seeds that float; they must be buoyant and have a tough seed coat to survive in sea water.

Birds can carry seeds in their stomach or on their feathers; and even carry eggs of snails or crustaceans on their feet.

Certain groups of plants and animals are specially adapted for long distance dispersal, and many islands in the Pacific share similar species or genera. For example the Mountain rose Metrsosideros nervulosa of Lord Howe Island has relatives across the Pacific to Hawaii. Metrosideros seeds are tiny and blow long distances in wind currents; plus they survive cold temperatures encountered as they are carried aloft by winds.

Floating seeds

Mountain Rose

Ocean-dispersed Mangrove seeds

bird dispersed fruits

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