Extinction and endangered species

Sorry, I have been overseas, and returned with significant vertebral problems that have limited my ability to add things, but deadlines had to come first. Normality (and my vertebrae) are now more or less restored.

It will possibly be my last book, but Not Your Usual Science is going to be HUGE, close to 1.5 million words, equal to a dozen 'airport books', the thick tomes you buy to read on a long flight. It collects together many of the articles and essays that I have generated over the past 35 years, covering science, how science works and how what we now call science was put together. It even includes some of the blog entries that have appeared here. In due course, it will be released as an e-book.

Here's a small taste of it...

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What makes a species endangered? A trained biologist’s quick stab at a general answer would be “a loss of biodiversity”, meaning no longer having a wide range of species living in a system, so they interact with each other, and provide checks and balances for each other.

In simple terms, a forest is more than just a bunch of trees. A plantation of pine trees (or any other trees, for that matter) is not really a forest because it is a monoculture, and worse than that, all of the trees are of the same age, with no old growth forest.

At times, populations may rise and fall in old growth forest, but over a long enough period of time, there is a balance in the species found there. In any ecosystem, very few species are really essential.

In most cases, a species which is eliminated will be replaced in its function by some other species, either one that is present already, or one that moves in when a competitor is removed. Unfortunately, there are a few species that are keystone species, and like the keystone in a stone arch, take that away, and the whole structure will collapse.

Worse, some unexpected and inconspicuous life form may prove to play an essential role, so that removing a mere fungus, or a tiny mammal, or an insignificant spider, may be all that is needed to trigger wild swings in populations that eliminate more species, until all that is left is sterile ground.

What this means is that if there is an endangered species in a forest or any other ecosystem, the whole community may be at risk. In the same way, if biodiversity, the range of species present, is reduced, other species will be put at risk.

While biodiversity, having a range of species present, is important, it is equally as important to have genetic diversity within each species, a range of genetic adaptations that may be needed in a population under different conditions.

This is an important consideration when zoos are engaged in captive breeding programs, where it is important to exchange animals from different zoo populations, or where it may even be necessary to remove a dominant male who is siring too many offspring.

Biodiversity can be affected in many ways. One serious problem comes from introduced species which usually have no controls in their new environment. Introduced species can arrive either by themselves, carried by the wind, the waves, or migrating birds, but many more arrive when aircraft or ships carry species to new places, deliberately, or by accident.

Yet other species just invaded with humans. Hawaii has a problem with what they regard as the brown tree snake of Guam (Boiga irregularis). This snake wiped out many bird species on Guam after it arrived there from either Australia or New Guinea, probably by plane during World War II. In recent times, it has been known to travel to the islands of Micronesia by plane, riding in cargo crates.

With no natural predators and no competition from other species, it thrived on Guam. Twelve bird species have since disappeared from the island, and several others are approaching extinction, and lizards, small mammals and domestic poultry are under threat.

Even forest trees are at risk, now that the birds that pollinate their flowers have been wiped out. In the next century, gaps will begin to appear in the canopies of these forests. Usually, spindly young trees live on the forest floor, waiting for an opening to give them light to grow. When a gap appears, they race to be the first to plug the gap, but in time, there will be no seeds, and no small trees lying in wait.

Native bat numbers are also down. Yet in spite of all this damage, it was almost 50 years before the snake was identified as the cause of the decline in bird numbers on Guam.

In their own environment, most species are controlled, because over time, predators and diseases have evolved ways to eat them or kill them, so that when their numbers increase, there is a natural checking system in place.

When outside species arrive in a new place, there are no predators available to control them, so the only real population control comes when they run out of food. By the time that happens, they are likely to have reduced a number of food species, and a number of competitors which rely on that resource, to the brink of extinction.

When rats were accidentally introduced into New Zealand, for example, they found a number of ground-nesting birds, whose eggs were an excellent food source. Because there were a number of bird species, and because rats can eat many other things as well, the rats could continue to flourish, even when the bird numbers crashed.

In Australia, many small marsupials found themselves facing a double threat. The first half came from rabbits, which out-competed and outbred them, while sheep and cattle reduced the available food and also changed the habitats forever.

If that wasn’t enough, the second threat came from foxes and feral cats, which were able to survive on rabbits, but found the small marsupials to be easy and tasty morsels. Once again, even when their numbers crashed, the predators were able to live on rabbit, while still taking the odd marsupial.

The small marsupials, generally ranging in size from about that of a mouse to that of a young rabbit, were able to survive normal predation from dingoes, but introducing rabbits allowed dingo numbers to increase. As we will see in a moment, that brought a further problem for the small marsupials.

Another threat, at least to some animals, can be hunting, usually for food, but also for trophies, or even because of rarity. One of the best-documented hunting extinctions is the story of the great auk, a flightless bird that looked like a cross between a duck and a penguin.

We really should look at the auk, so that's up next.