Relative Importance of Human Actions?

After several posts on how different human activities can alter both the environment and the ecosystem, I was just thinking which of those is/are relatively important. Today, endangered species have caught greater attention from conservationists, who often blame humans for it (Well, it is quite reasonable). Mace and Lande argued that habitat loss constitutes the most immediate threat. In fact, they even argued that hunting of species might not be a pressing problem, if the population did not experience fragmentation.

Summary of biodiversity and threat data in Asia and Australia. Shaded
and italicised countries were identified as global and continental areas
of critical concern respectively.

In many countries, deforestation is one of the requirements for urban development. Habitat loss is strongly correlated to rapid forest destruction and increasing pressure form human population. As shown on the left, a large proportion (14%) of countries were areas of critical concern in Australia-Asia. China, India, Philippines, Sri Lanka, Taiwan and Thailand were all among the top 20 countries of forest loss. At the same time, they were also countries that experienced high population pressure. For instance, Philippines ranked fifth for both forest loss and population pressure. In addition, human population pressure also poses threat on species richness. 

The relationship between biodiversity and the threat of habitat loss, as represented by indices developed for 135 continental and large island nations. Shaded regions represent areas of critical concern. 

Yangtze River dolphin

Of course, human population pressure does not only result in the form of habitat loss. Previously, I mentioned that the construction of dams and habitat alterations have affected freshwater species in my blog post Humans, Freshwater, Species. But they are not the main threats to Yangtze River dolphin in China. It was estimated that the species declined from 400 in 1979-1981 to only 13 of them during 1997-1999. By 2006, there was no evidence found on the survival of the dolphins. Unsustainable fishing of local fishers greatly increased by-catch. For example, the use of rolling hooks and nets and other fishing practices were considered to be the major extinction drivers. Again, human population pressure has increased the pressure on extinction through higher demand for local fisheries. Fishermen are anxious to catch more fish with different methods, some of which may involve ill practices. As the result, Yangtze River dolphin has become one of the victims.

It is difficult to decide what the dominant factor behind extinction is given the many facets of human activity. More importantly, it is even harder to discuss all the human practices that lead to the edge of extinction. So all I can do is to explore as many risks behind the Sixth Extinction as possible. Is it or is it not happening? If human population pressure is one of the key extinction drivers, I can foresee a bleak future for currently endangered species. Population will only continue to rise, especially how China, the country with the highest population on Earth, has just relaxed its one-child policy. Perhaps, the resolutions of NGOs and governments will now be to conserve endangered species by tackling the misbehaviours of humans instead (Carbon emission, forest destruction.. and more).