Adaptation to high altitudes is a concept associated with air-breathing animals and the challenges they must overcome in these environments in order to survive. In general, the introduction of terrestrial life presented challenges such as reducing respiratory water loss and the need to maintain a higher metabolic rate. In terms of life on land but, at higher altitudes, further obstacles manifested for species venturing to these heights.
Some of the major challenges animals face at high altitudes are as follows:
- Lower temperatures which could potentially lead to hypothermia.
- A reduced partial pressure of oxygen, which for lung breathing animals is a huge problem. For tracheal organisms (i.e. arthropods) and aquatic species this is not a grave concern.
- The atmospheric pressure is lower and this can lead to dehydration.
In order to adapt to these condition which are not present on ground-level, animals have had to evolve physiological responses to conquer these challenges. Some physiological responses which allow have allowed for vertebrate (not birds in this case) life at high altitudes include:
- An increase in hemoglobin and red blood cells so that the carrying capacity for oxygen is increased.
- Increasing capillary density so that the diffusion distance for oxygen is shorter.
- Decreasing the diameter of muscle fibers.
For example, some human populations have adapted to live at high altitudes. Ethiopian societies have been found living 3530 m above sea-level, Andean cultures 3900 m above ground and Tibetans a remarkable 4200 m above ground. Interestingly, in studies, it has been found that pulmonary nitric oxide concentrations are higher in Tibetans and Andeans and have helped them to survive. Nitric oxide helps oxygenate hemoglobin and increase blood flow (vasodilation), among other things.
Furthermore, birds are the epitome of a species which has adapted to life at high altitudes. Birds have a very efficient respiratory system with a cross-current gas-blood flow arrangement, a larger heart and myoglobin with a high affinity for oxygen saturation, among other adaptations. Clearly, the anatomical and physiological features of birds allow them to live at high altitudes remarkably well.