Biodiversity is the long-term result of evolutionary forces which can be natural or originating from the way people interact with nature. On a small island like Niue, both have had important consequences. The way organisms change or adapt by evolution works like people breeding better plants, flowers or livestock, simply by selecting the ones to survive. In the case of breeding, people do the selection and in the case of evolution it is done by nature. Both result in the survival of the fittest, meaning the types with the required (‘better’) characteristics. To better understand the principles of biodiversity, visit the important biodiversity chapteron this site.
Niue is a very small island in the large southern Pacific Ocean. Ocean surface currents flow mostly with the trade winds in a north-westerly direction, arriving from a cooler area of the Pacific without neighbouring islands. But occasionally a reversal happens. During such instances, larvae or mature animals from neighbouring islands to the north may arrive at Niue. The gene pool in Niue is thus periodically updated, preventing unique endemic species to evolve here. Thus Niue is not likely to play a role in the world’s biodiversity and it is unlikely to find species here that are found nowhere else in the world.
When species arrive in Niue’s coastal seas, they are subjected to the following deselecting influences:
The seas around Niue are cool for the tropics, as cool water arrives from the south-east. It limits growth and deselects species unable to cope with these temperatures. Thus many species from warmer waters are unsuccessful in establishing themselves at Niue.
Niue has very little hard shore, the place where most marine organisms are found. So there is precious little room for large numbers of each species. This has serious consequences and deselects those species unable to cope in small numbers on small territories.
The clear blue water contains very little food. Energetic and wasteful species such as sardines cannot possibly live here. It deselects the energetic and wasteful species while selecting for frugal ones who also expend little energy by being ‘lazy’.
On the one hand Niue is insufficiently isolated to produce its own endemic species, but on the other hand is sufficiently isolated in a large desert ocean to cause persistent recruitment failure. This has selected for animals that grow old or care for their brood or have some other strategy to cope.
Hurricanes bring large and deep waves that destroy the shores in their path. The sheer speed of the water when it shears over the shore is enough to water blast all soft life to death, and the rubble in its path scours coral structures to their basic shapes. Although large hurricanes are very infrequent, they nonetheless have a prominent and lasting effect on the northward shores of Niue which they lay barren, to be grazed by tangs and urchins.
The opposing side of Niue is constantly buffeted by a swell which has an equally important influence on the life below and the shape of the coral slope. It creates shallow barrens as it is not strong enough to create deep ones.
On land the natural species have been exploited in many ways, and the sea has always been fished. The coralline reef flats have particularly been harvested intensively.
the slush hypothesis
In 2005 we discovered a new method to measure decomposer activity and biodensity in sea water. The Dark Decay Assay (DDA) has been treated extensively in its own section. With it we proved that the degradation in the sea is mainly caused by an imbalance between the nurturing and the bacterial side of the plankton. We also discovered that natural decomposition cannot complete because the energy locked up in biomolecules is insufficient to decompose them. What remains is a group of organic molecules we call slush as in incompletely molten snow. In July 2005 we measured the sea water around Niue and established that although it has almost ten times less phytoplankton than the sea around New Zealand, it has a large amount of slush, in fact equating to half the phytoplankton around NZ. Slush is neither food for plants nor animals, nor is it food for bacteria unless another form of energy is added to help them decompose it further. Such energy can be provided by plants alone when living in symbiosis with decomposing bacteria on their skins. Animals with plant cells and bacteria combined (mixotrophs) can decompose the abundant slush and become very productive, even though the water is so devoid of plant and animal plankton. It explains the success of corals and the algal slime covering the barrens of Alofi.
Please note that the slush hypothesis has not yet been confirmed by traditional science.
On land, nature has very similar influences. Sea birds for instance are too wasteful (energy-spending) to survive here because they depend on rich sea life in the sea around Niue. On land we can recognise the following selective factors:
Niue is sufficiently isolated for most forms of life by the 500km of ocean between it and the nearest islands. But birds, bats and plant seeds can be brought there by cyclonic winds. People found it only some 1500 years ago. The plant and animal communities on Niue are thus not easily disturbed by natural newcomers.
Niue’s land surface (260km2) is very much larger than its rocky shore (4km2) but even so, this is insufficient to maintain the biodiversity of a tropical rain forest. Furthermore, Niue has four distinct habitat zones extending from the reef flats towards its centre.
Niue receives about 2m of rainfall, about twice that of Auckland, New Zealand. But the soils cannot retain it as it seeps quickly down into a labyrinth of channels eventually leading to the sea. Niue has no creeks or rivers, no springs no wetlands.
Niue has a wet and a dry season but occasionally two or more successive years of drought, which upsets life on the island considerably.
steady trade winds of 15-25 knots (25-45km/h) blow from the southeast for most of the year. In the months with the warmest water in the tropics (Nov-Jan) a tropical cyclone may descend on Niue with variable strength. It brings very strong winds (120-300km/h) capable of stripping leaves from branches, felling trees and blowing insects and birds off the island. Powerful cyclones like Heta leave a lasting influence.
Niue does not have volcanic rock or soil. It consists of a coral limestone rock extending at least 100 metres under water and 70 above. Niue’s soils were formed in a very slow process by the weathering of coral rock under a canopy of vegetation. Where forest trees stand, the soil is deepest and in the coastal saltspray zone shallowest.
In addition to natural influences, people have also made important changes to what lives on Niue:
selecting useful species
everywhere in the world, already in their nomadic stage, people have knowingly and unknowingly promoted the species of use to them.
- by clearing competing species around them
- by collecting fruits and seeds and spreading these around
- by defecating in the areas of productive species and thereby fertilising them
introducing wanted species
when settling on a new island, people brought important food crops with them such as the taro root. Edible and ornamental species were also traded between islands.
introducing unwanted species
wherever people went, they took with them unwanted species such as flies, rats and weeds. Also on Niue chickens went wild.
introducing noxious species
often wanted food species spread, upsetting the natural environment. cats, chickens and pigs have caused much damage. It is feared that the introduction of honey bees has been detrimental to the population of colourful parakeets who also depend on honey for sustenance.
in order to suit the environment to their needs, people have always made habitat changes for dwelling, cultivation, roading, fortification and so on. With the aid of fossil fuel this could be done on a grand scale. In Niue most of the land has been changed but some natural areas remain.
slashing the new growth and burning it has always been part of shifting agriculture, Niue’s predominant way of cultivation, but arrowroot (an important source of starch) was always the first to emerge after burning. When the traders expressed interest in arrowroot, wildfires became a new way of life, encouraging the regrowth of arrowroot. As we now know, this had a disastrous effect on the soil’s quality as valuable nutrients also went up in smoke.
in addition to habitat change for cultivation, people exploited the natural world by hunting. On Niue the most important hunted animal species are: fruit bats, coconut crabs and birds. Many plant species are exploited, particularly for housing, canoes, weaving, food and more.
with Niue’s population steady at 4000-5000, the locals were living within ecological boundaries, exerting a high pressure on the environment. But after World War Two most left for better pastures in New Zealand and Australia. At the turn of the millennium, 20,000 Niueans were living in Acukland, leaving about 1000 to mind the island. This significant emigration has relieved the pressure on resources, giving both the land and nature respite.