Does it sound uncaring that ecologists "shrugged" when the tortoise died? According to yesterday's author, ecologists are primarily concerned with the healthful functioning of the natural environment as a whole. Extinction of a "keystone" species (like the sea otter for example) that is "essential to the welfare of many other species" would be very serious.
One way to measure the health of an ecosystem is by "biodiversity," which is simply the number of species present. In the era of the woolly mammoth, the number of animals on a square kilometer of earth was hundreds of times more than it is today.
In northern siberia, "on each square kilometre of pasture there lived one mammoth, five bison, eight horses, and 15 reindeer. Musk ox, elk, woolly rhinoceros, antelope, snow sheep, and moose were also present. Wolves, cave lions, and wolverines occupied the landscape as predators. In total, over 10 tons of animals lived on each square kilometre of pasture – hundreds of times higher than modern animal densities in the mossy northern landscape.’ That’s bioabundance."
That author is now working on the de-extinction of woolly mammoths.