There are all sorts of things about conserving endangered species that turn out to be controversial. For instance, whose land are you going to conserve a rare plant or animal on? I may want you to conserve them, but definitely not on my land. If they are on my land and they are covered by the Red Book, I may not be able to sell them, not even to give them away if it means transporting them off my land. But at least I can just go out and kill them if I want to plant corn and soybeans, or want to build a strip mall. Just as long as they or their remains stay on my patch of ground.
Another controversial question is can I conserve a rare animal or a rare plant in a zoo or botanical garden? One would assume the answer would simply be, "Yes," because that's what is being done to a large extent. There are those, however, who deny that any conservation not on the original habitat of the species is really conservation at all. Conserving rare plants and animals in their original habitat is called "in situ" conservation; it means "in place." Preserving a rare species outside its original native habitat is called "ex situ" conservation. It's what zoos and botanical gardens do. Conservation purists demand pure "in situ" conservation. Let's call these folks the "fundamentalists."
Another controversial subject relating to conservation is climate change. There are those who deny it is real, and there are others who admit it might happen, but vigorously deny that human activity has had anything to do with it. Both camps are spitting into the wind if you have any trust at all in science. They are both dead wrong. Climate change is happening, and it is going to affect the native habitats of practically every wild species on the earth. Already observers are reporting that birds are migrating to their summer feeding or breeding grounds earlier than ever before. Some are moving into new ranges. There are reports that some alpine plant species are growing higher up on the mountains than they used to. The climate is changing, and wild species are already starting to change their habits or where they live in response to it.
A revealing discussion of the difference between "introduced" species and "invasive" species is to be found in The Scientist for Sept. 7, 2011 entitled "The Invasive Ideology." I have a problem with scientists who become too engaged with the non-scientific and very political process of fighting against introduced/invasive species. Things from tea roses to wheat are introduced species.
This is unquestionably the best type of conservation, at least for the moment. Safeguarding endangered animals and plants in their own native habitats. The U.S. National Parks do this. Think of Yellowstone Park with its bison, elk, bears, and wolves. Kruger Park in South Africa is the same. But even in national parks, they build roads and lodges for tourists. Even there, the protection isn't perfect.
This is sometimes the only option, when all the natural habitat for a rare species has already been modified beyond the point where it can support the species. Then the surviving members of the species may be gathered into some safe place. In less extreme cases, representatives of the species may be collected in zoos or nature preserves. Most modern zoos are examples of this. The Cheetah Conservation Fund in Namibia is probably an example of this as well, or maybe a modified in situ situation.
Evolution and Conservation
The most common effect that endangers species' survival is habitat destruction by human civilization. All the other processes mentioned here and elsewhere are almost trivial in comparison. Still, all of these processes contribute to the extinction of species, and we need to consider all of them.
Besides climate change, there is another process that has a significant affect on our efforts to preserve rare and endangered species of plants and animals. Evolution is a constant, continuing activity that can act to stabilize a species' genetic constitution, or it may modify it. Natural selection is constantly changing the species. Genetic drift is constantly affecting the genes of small populations. Time changes everything.
Natural selection may be our opponent in conservation in another way. Many rare species may be rare because they have become unfit for their environment. That is, the climate may have changed and those changes may have altered the habitat of the species to the place where the species is no longer adapted to survive there and may be insufficiently flexible genetically to adapt to the new conditions. Here, human intervention is definitely called for: Moving the species to a new, more suitable habitat; or perhaps introducing genes from a related species that improve the endangered species' ability to survive in the changing habitat.
Another question that bothers me is what was the North American continent's ecology like at the previous warm interglacial period, say maybe 120,000 years ago? We know that the population density of African elephants plays a decisive role on the kind of ecology one finds in Africa: Elephants control the growth of thorn thickets and preserve savannah landscapes. We have at least a vague idea what it was like when Europeans first arrived on the mainland, with a heavily wooded eastern third of the United States and the open grasslands of the Great Plains. How much did the new human immigrants from Siberia (the ones who arrived about 12,000 years ago) contribute to that? What roles did mammoths (grazers) and mastodons (browsers) play in the pre-ice age ecology, before any humans were in North America? How much did their elimination, probably by the human immigrants, play in creating the immediate pre-European ecology? What is the real baseline for a "natural environment" in North America -- pre-European or pre-human? Cold Ice Age or warm Interglacial?
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Good gardening, from here in central Indiana
Look up technical terms in the Glossary of Plant Biology