ANIMALS IN DANGER
Until a century ago, the earth still contained large areas of wilderness, where animals had little or no contact with human beings. Since then, the human population has soared closer to 7.5 billion, and our increasing use of energy and raw materials affects the entire planet. Natural habitats are disappearing, and the earth’s biodiversity — the sum total of all living species — is in sharp decline.
This is a dangerous situation for humanity, because it reduces the earth’s biological resources, and makes the world a less stable place. For animals, the results can be disastrous. Some changes are local ones, which threaten individual species, but others, particularly climate change, are global in their reach.
Humans first started to alter habitats when they discovered fire, but with the start of farming, about 10,000 years ago, habitat destruction rapidly increased. Agriculture has been the main driving force behind deforestation, which swept across the northern hemisphere in historical times, and continues in the tropics today. It has also been responsible for the destruction of some of the world’s major natural grasslands, and of marshes and other freshwater wetlands that supply many wild animals with their food. In recent times, urbanization has become almost as important as a threat — towns and cities take up space, and the roads between them use up even more.
The pattern of habitat change is often as important as its scale. For example, if large areas are preserved, the habitat can often function as before, although on a reduced scale. But if the same amount of habitat is divided up into smaller isolated fragments, the effect on animals is much more severe. This is because many species – particularly predators at the top of food chains — need extensive territories to survive. These fragmented habitats are also exposed to more intrusion and disturbance from humans and domestic animals, making it much harder for wild animals to feed and breed.
Pollution occurs when chemicals or other agents disrupt natural ecosystems. Sometimes it has a natural origin, but in most cases it is the result of human activity. It can affect animals physically — for example, entangling them in waste, or clogging them with oil — but its chemical effects are often more serious, and harder to identify or predict.
The most problematic chemical pollutants are synthetic organic (carbon-containing) substances, such as solvents, pesticides, and herbicides. Hundreds of thousands of these chemicals now exist, and new kinds are produced every year. Their chemical structure means that they are often absorbed by living tissue, where they are ideally placed to cause the most damage. Some of these substances are toxic to all forms of life, but others are more selective. They are passed on when predators eat their prey, and as a result, they accumulate in species at the top of food chains, such as whales, polar bears, and birds of prey.
As well as dissolved pollution. marine animals have to cope with solid plastic waste. Taking decades or even centuries to degrade, this forms huge eddies or gyres in the world’s oceans, which can often be hundreds of kilometers across. Small particles of these plastics are often ingested by animals, weakening them or killing them outright. Animals are also affected by air pollution, which is created mainly when fuels are burned. Air pollution causes localized problems such as acid rain. which can have a highly damaging effect on freshwater fish. On a much broader scale, it is also responsible for global warming — the biggest environmental change of all.
HUNTING, FISHING AND COLLECTING
Unlike many of the world’s other resources animals can reproduce . This means that in theory useful species can be harvested without them ever running out. Unfortunately may species have been over-exploited, with result that some have died out while others are now in serious danger.
The list of past causalities from hunting includes the African blue-buck, which died out in about 1800, and the North American passenger pigeon, which becomes extinct in 1914, despite formerly being one of the most numerous birds in the world. These animals were killed primarily for food, a practice that continues today in a more diverse way, in the bush-meat trade. Once a subsistence activity, the bush-meat trade has recently become a global business, focusing on all kinds of forest animals that can be caught and sold as food. Primates are particularly threatened, but the trade also endangers many other animals, from snakes and pangolins.
Animals are also hunted to meet less pressing needs. Elephants are in demand for their ivory, and rhinos for their horns. Tigers are hunted for their fur and body parts, which fetch increasingly inflated prices as the number of surviving animals falls. At sea, fish have become victim to the kind of over-exploitation once reserved for animals on land. Plummeting stocks of once-common species, such as tuna and cod, are typical of a resource that is often only weekly regulated, or not at all.
Some fish breed at an early age and can recover from over-fishing if the pressure is reduced. But with species like tuna, maturity takes time, so adult fish can become too rare to guarantee a future supply of young. Comparatively little is known about the effect of this relentless harvesting on marine and coastal life. However, fish play a key part in many food chains, and with their numbers fall, the effects are felt by countless other animals, from sea-bed invertebrates to fish-eating birds.
Even before Columbus discovered America, explorers and colonists had spread animals to new parts of the world. The process increased rapidly with the Age of Exploration, and the result – hundreds of years later – is that the wildlife of isolated regions has been overwhelmed by a host of intruders, from rats and cats to mosquitoes Some of these introduced species cause problems by actively preying on local wildlife. Others harm native animals indirectly, by competing with them for food, or by transmitting diseases such as avian malaria.
In Australia, introduced species have disrupted the ecology of an entire continent. Kangaroos still thrive, but many small marsupials now live in a tiny fraction of their original range.In marginal habitats that introduced species find difficult to reach. Similar problems affect New Zealand and Madagascar, and on much smaller oceanic islands, the situation is often more severe. Their native birds are often wiped out by cats and rats — tenacious newcomers that are extremely difficult to eradicate.In this age of rapid travel and expanding tourism, the threat from introduced species is never far away.
The world’s climate has always changed, but the current period of rapid warming is without precedent in modern times. Most scientists believe that the cause is increasing levels of atmospheric greenhouse gases, caused by human activities. Greenhouse gases include water vapor, chlorofluorocarbons (CFC’s), and carbon dioxide.
They make the atmosphere trap outgoing heat, warming up the earth. Wildlife has coped with changes in the past, but the speed and severity of this episode could result in extinction on a worldwide scale. Atmospheric warming, in itself, is only part of the story, because global warming has dozens of knock-on effects. It makes sea ice melt and changes the pattern of oceanic currents, altering climatic conditions on land. Over the longer term.
It makes the oceans more acid, threatening shelled animals and coral reefs. It also makes sea levels rise, both by melting ice caps, and by making sea water expand. This expansion happens very slowly, but once started, will take centuries to reverse. The United Nations Framework Convention on Climate Change negotiated the so called Paris Agreement for cutting greenhouse gas emissions, it entered into force in November, 2016 and has, to date, been ratified by 132 parties. Many see this as the critical turning point in reducing global warming.
ANIMALS ON THE BRINK
The International Union tor Conservation of Nature (lUCN) maintains The IUCN Red List of Threatened Species (trademark), which is constantly updated by the work of scientists worldwide. In 2017, nearly 76,000 species were assessed, representing about 3 per cent of those that have been formally classified. Although this is only a small portion of the world’s species, this sample indicates how life on earth is faring, how little is known, and how urgent the need is to assess more species, comprehensive assessments have been carried out for birds, mammals, amphibians, sharks, reef-building, coral, cycads, and conifers, and the statistics are disturbing, with one in 8 birds, one in 4 mammals, one in 3 corals, and more than one in 3 amphibians at risk of extinction. Being “on the brink” means different things for different species. Some animals — particularly invertebrates — can reproduce rapidly when conditions are good.
Which means that they have the potential to make a fast comeback. But many species on the lUCN Red List are slow breeders, and take a long time to recover if their numbers fall. Albatrosses are typical examples: they take up to 7 years to become mature, lay just one egg, and often breed only in alternate years.
To make matters more complex, animals cannot necessarily breed if they find a suitable habitat, and a partner of the opposite sex. This is because many species breed in groups, and rely on the stimulus of others around them to trigger essential behavior, such as courtship and nest – building. The passenger pigeon was a classic example of a communal breeder, nesting in colonies many square kilometers in extent. Even when many thousands were left, it had already stepped over the threshold into oblivion.