Reptiles are a diverse and important group of vertebrates. They include the primarily terrestrial squamates (lizards, snakes, and amphisbaenians) and the largely aquatic turtles and crocodiles.
While comprehensive extinction risk assessments exist for birds, mammals and amphibians, no such assessment has been available for reptiles until now. This new global assessment may help inform conservation action.
From crocodiles and turtles to chameleons and snakes, reptiles are a diverse group. They play unique ecosystem roles and have evolved over billions of years. But they are also vulnerable to global threats like habitat loss, disease and predators.
A recent comprehensive global extinction risk assessment found that 1,829 reptile species (21.1%) are threatened with extinction, confirming the results of earlier extrapolations3 and adding to the growing awareness of a biodiversity crisis4. Reptiles are also under threat from climate change, as they rely on external sources of heat for body temperature control. In many areas, warming temperatures are pushing populations to the limit and threatening their survival.
Habitat destruction and degradation is a significant problem for reptiles, particularly in agricultural landscapes and urban centers. This occurs from a variety of causes, including land clearing and conversion for agriculture and development, water withdrawals and stream diversions, pollution and the introduction of non-native species (e.g., fire ants) into previously occupied habitats. Intentional collecting for the pet trade can also be a serious threat, as it can lead to the destruction of cracks and crevices that serve as shelters for many species, such as the twin-spotted rattlesnake (Crotalus pricei) in the United States, which is found only in four disjunct mountain ranges in southeastern Arizona.
Efforts to conserve reptiles must be holistic in nature. While traditional habitat restoration typically focuses on improving or maintaining native vegetation attributes and functions, it is essential to restore non-living structural elements, such as rock cover, in landscapes where these are declining.
Reptile habitat needs include adequate space to roam, bask and forage, sheltered from harsh sunlight and wind. These spaces also need to contain suitable vegetation, a diversity of other species, and adequate water.
The main reason why reptiles are vulnerable to extinction is habitat loss. Since the start of the 20th century, a majority of their natural habitat has been destroyed or severely degraded. This includes savannahs, forests, deserts, mountain ranges, coastal regions and marine environments. The causes of habitat loss and degradation are numerous. These include urban/suburban development, water diversion from rivers and streams, agriculture, forestry, logging and livestock grazing (Figure 3).
Habitat loss or degradation can have severe consequences on populations of amphibians and reptiles. For example, it can result in a decrease in population size or rate of dispersal that can prevent the establishment of new populations following local extinctions. This problem is particularly acute for tropical reptiles as their natural habitats are often highly fragmented, exacerbated by the anthropogenic factors described above.
The most prominent anthropogenic factors increasing reptile extinction risk are habitat destruction, hunting and invasive species. These threats are more prevalent for all tetrapod groups, but they affect terrestrial reptiles more than aquatic ones. For crocodiles and turtles, the most common threat is hunting and for squamates, it is agriculture (Figure 4). The reasons for these differences lie in the different habitat types, biological characteristics of the two groups and their evolutionary histories.
Reptiles can be affected by a wide range of diseases that impact their health and ability to reproduce. These diseases can be caused by viruses, bacteria, or fungi. They can also be caused by parasites, such as mites and ticks. Often, the effects of these diseases are not immediately apparent and may only manifest themselves over time. These diseases can also have a negative impact on humans who interact with reptiles.
In addition to disease, another threat that many reptiles face is a lack of proper habitat. This can be due to pollution, development of natural habitats into housing developments, or other human activities. Some reptile conservation programs try to protect these animals by working with local governments and land owners. They also incorporate educational components into their conservation efforts to inform citizens of the importance of these species and to encourage people to support conservation efforts.
Many reptile species are threatened with extinction, and their conservation requires collaboration between scientists and government agencies. Some of these projects involve the use of captive breeding programs. These programs are used to preserve endangered species while preparing them for reintroduction into the wild. The risks of introducing pathogens to the wild are considerable and must be carefully considered. Fortunately, there are a number of tools available that can be employed to minimize the risk of disease during reptile translocations.
Predators are essential to the function of ecosystems by maintaining species diversity, and by transferring energy in a balanced way. However, humans often interfere with this balance by over-hunting, which can cause a predator population to decline dramatically and lead to extinction. Predator populations are also impacted by disease and habitat loss.
In some cases, predators may be displaced by introduced species that become dominant in their habitat. This can have devastating impacts for local reptile populations. In addition, illegal reptile collecting for the pet trade can also impact local populations by exposing animals to predators and destroying shelters that they use for hiding from predators (Prival et al. 2002).
This is exacerbated by the fact that most reptile species have very limited ranges, meaning that they are vulnerable to changes in their habitats. For example, the range of twin-spotted rattlesnake (Crotalus pricei) is limited to four disjunct mountain ranges in southeastern Arizona, and has been heavily fragmented by human activity.
While compensation and insurance schemes can reduce the financial costs of carnivores, they do not address the underlying drivers of these cost-benefit trade-offs in people’s decisions to invest in reptile conservation. In addition, these mechanisms are often not well implemented in developing countries, where illiteracy and poor institutions increase the potential for fraud and corruption. Despite their limitations, these mechanisms can play an important role in incentivizing effective “on-the-ground” conservation.