The High Life

Mountainous regions with high altitude habitats, generally defined as those found above 10,000 feet, are found in only a few places around the world.  They include the Tibetan plateau and Himalayas in Asia, the Andean Altiplano in South America, the Ethiopian Highlands of Central Africa, the Rocky Mountains in western North America, and the Haleakala Mountains of Hawaii.  High altitude regions have common characteristics that provide an array of challenges for the plant and animal species that live there. 

Air is composed of several gases including oxygen which makes up a consistent 21% of it.  Barometric pressure is a measurement of the weight of the atmosphere above, and with more weight pressing down, air molecules are more compacted together.  As one ascends, the pressure decreases with the result being that the air is thinner, less compacted, breathing becomes more difficult with less oxygen entering the lungs for every breath taken.  About 3% of available oxygen is lost for every 1,000 feet of elevation gain. At 10,000 feet, there is 30% less oxygen available to breathe.

As one ascends, along with thinning atmosphere, the temperature decreases by 4^◦F for every 1,000 feet, and may decrease even faster in drier air.  At 10,000 feet, the average temperature is 40^◦F lower than at sea level in the same region, resulting in cool summers and frigid winters.  Snow may cover these areas for much of the year, but many higher mountain peaks are too dry for snow.  Vegetation is shorter, smaller in size, and slower growing.  The tree-line defines a point where tress cannot survive the lower temperatures and general lack of moisture of higher altitudes.

When animals or humans who normally live in lower altitudes venture higher, they often experience acclimatization issues – changes in bodily functions that occur for short periods while at a higher altitude.  As an example, one may experience difficulty breathing as air becomes thinner, and this strain eases after several minutes or hours.  However, these changes occur every time a person ascends to those elevations.  Permanent changes, which we call physiological adaptation, are known in relatively few animal species. 

Physiological adaptations in birds include altered hemoglobin genes, allowing more oxygen to be carried in each molecule of blood.  Birds optimize the process of getting oxygen into their blood as air moves across breathing surfaces during both inhalation and exhalation.  High altitude fliers have larger hearts  providing increased blood volumes for every heartbeat.  In addition, they have more capillaries than other bird species, so oxygen-rich blood has to travel a shorter distance in the body to reach muscles, increasing the ability to maintain energy and movement in an efficient manner.

Mammals create their own body heat and maintain a consistent internal temperature through regulation of heat gained from burning calories and heat lost through layers of hair to the external environment.  Many species living permanently in higher altitudes are able to decrease their body temperature for long periods, making it easier to adjust to a colder environment.  Some species have a higher percentage of fat cells containing carbohydrates that can be called upon for extra energy for short periods.

Typical plant life in these regions consist of grasses, sedges, lichens, and mosses.  These are adapted to low temperatures, dry conditions, high ultraviolet radiation, and a short growing season.  Mosses are found at the highest levels, growing above 21,000 feet on Mt. Everest.  The flowering plant Arenaria bryophylla, a sandwort, lives above 20,000 feet.

In our next blog, we will take a look at the animal species that call these regions home, but you can check out mountain region displays at your favorite nature museum including the Jurica-Suchy Nature Museum.