Conslusion

There is now 7 billion of us on Earth, and our presence have wide-ranging impacts all around the globe. Climate change is arguably the most significant and important global change phenomenon we face, and it has wide-ranging impacts on the distribution of biological organisms. As Earth gets warmer and warmer, species can potentially respond in three different ways: one is evolutionary adaption. This however, because the pace of change is too fast, is only possible for the most quickly evolving species. Secondly, species may move polewards and upwards to colder and colder areas. This response is widely observed, and models predict that it is going to be even more common in the future, therefore affecting current biogeographical patterns. Not all species can however move continually to cooler areas. Some are limited by their dispersal ability, and others face geographic barriers, such as mountain ranges, which prevents them from moving to cooler climates. Mountain dwelling species and those inhabiting polar regions find themselves in yet an other difficult situation, as once they reach the top of a mountain or the northern/southernmost tip of a landmass, they simply can not go further. These species undoubtedly face extinction.

The changes in precipitation and warming patterns are however not homogenous around the globe, and some areas will experience more adverse warming or more extreme precipitation patterns than others. These regions will suffer most from extinctions and will show the greatest biogeographical change. The polar regions for example, the Arctic and the Antarctic, are predicted to warm to a much greater extent than other parts of the world, resulting in more adverse ecosystem effects and more extinctions. However the increased warming in these areas will not only mean that more species will go extinct, but actually polar will be able to support more species rich communities: as permafrost melts, many plants and animals will colonise these areas, and therefore despite the high loss of biodiversity, these areas will see an increase in biodiversity.

Beside climate change of course, many other processes alter species distribution around the globe. One of the most significant other factor, with effects quite different from that of climate change is species invasions and colonizations. With the help of humans, many species are transported all around the world, and if they find suitable habitat, they colonise it. Biological invasions have two major consequences: firstly, invasive species often outcompete or predate on local species, causing a decrease in biodiversity. Good examples are introduction of rats to small islands, where they readily prey on chicks and eggs of seabirds, and cause a dramatic decline in bird populations. The other consequence of introductions and invasions is that 'everything is found everywhere'. If at any location the conditions are suitable for the persistence of a species, it is increasingly likely that the particular species got there with human aid, and will indeed be present at that location. This of course breaks down the regional differences between biota, resulting in more homogenous biogeographic patterns.

To sum up, there are three biogeographic processes we witness today. These are not specific to certain regions, are pretty much observable all around the globe.

1. A trend of poleward and upward movement of species and communities.
2. A trend of decreasing biodiversity, caused by a variety of processes including for instance climate change, habitat loss and modification.
3. Homogenisation of species composition due to species introductions and invasions.

There are a number of issues which I have not discussed on this blog, so there is much more to explore. However the examples I've given illustrate well the kind of changes we are inducing, and the biogeographical consequences these changes have. The list could therefore be continued endlessly, but the major types of effects these processes have has been described and illustrated.
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