At first thought, elephants (Loxodonta africana), lions (Panthera leo), giant pandas (Ailuropoda melanoleuca), and koalas (Phascolarctos cinereus) have nothing in common. Well, maybe a little in common, they are all mammals and icons of conservation. But a far more disturbing commonality is that they are all losing habitat.
Animals need food, water, and shelter to survive. These can all be found within the habitat where they live. In the simplest sense, the more habitat there is, the more animals can live within that space until there are too many animals thus too much competition for limited resources (e.g. the habitat reaches carrying capacity). When we consider all of the threatened and endangered species, many of them are imperiled due to habitat loss. Habitat loss can be either direct (i.e. clear cutting a forest for timber or agriculture, filling in a wetland for suburb development, etc) or indirect (i.e. pollution can degrade the habitat so that fewer individuals can live on those resources).
In Africa, habitat that supports wildlife is increasingly converted into agricultural fields or pastures for grazing animals. While this does not seem as dramatic as land conversion in other parts of the world (like paving over ecosystems), it can increase human-wildlife conflict leading to the persecution of wildlife. Lions and elephants are both directly impacted from shrinking habitat and loss of population connectivity, but also the additional impact of this conversion to agriculture as lions kill livestock and elephants raid crops like corn. While people try to deter these behaviors, ultimately this conflict encourages people to kill wildlife to protect their resources. In this way habitat loss is a double whammy for many species.
Additionally, roads and fences also change the landscape. To prevent animal deaths on roads, some have fences that run along each side. The fences do prevent animals from becoming roadkill; however, they have the unintended consequence of preventing migration. Or for elephants, if a fence is built without a gap for crossing, the matriarch may not be able to lead the herd to a preferred watering hole. Even though the habitat is not truly lost, it can be effectively lost to the species which use it.
The habitat of giant pandas is also very limited, to a mere six mountain ranges in central China. These patches were connected once, where the full range of the giant panda extended westward to the Tibetan Plateau and southward into Vietnam and Cambodia. As agriculture expanded over the past 120 years the habitat fragmented. The six patches are far enough apart that pandas cannot travel between them. Complicating this picture is that pandas do not utilize the entire habitat patch, only the dense stands of bamboo which makes up 99% of their diet.
As mentioned earlier, habitat loss can be a direct problem thereby reducing resources for animals, but it can also lead to unique indirect problems. The loss of koala habitat is a good example. While koalas as a species are not threatened with extinction, individual populations may be extirpated (i.e. go locally extinct). Koalas spend much of their time in eucalyptus trees munching leaves and napping. As tree density decreases, koalas become exposed to predators, have a higher chance of becoming roadkill, and diseases spread more readily. These problems increase as the density of animals surpasses the carrying capacity, and in extreme cases can lead to population crashes.
Where is the hope?
Elephants, lions, giant pandas, and koalas each face a threat from habitat loss, although to different extents (and notably with different additional threats such as poaching, disease, wildfires, etc). In many ways this is bad news as habitat loss may be slow to reverse. However, the good news is that identifying the causes of species declines is the first step in conservation. Without this knowledge conservationists will be unable to alleviate those threats so that population size may increase. If the willingness to stop or reverse habitat loss is present in human communities, then many wildlife species will benefit.
To find out more about the intersection of conservation and evolution check out the Wildlife SNPits website.