Terrestrial vertebrate species include mammals and birds, which maintain their body temperature nearly constant around 37°C regardless of the ambient temperature, and reptiles and amphibians which do not. Homeotherm species (those that keep their temperature constant, sometimes called ‘warm-blooded’) are able to colonize places cooler than is optimum for animal physiology, but become progressively less able to regulate their temperature as the air temperature approaches or exceeds their body temperature. Poikilotherm (variable temperature or ‘cold-blooded’) species become quite sluggish in the cold and are much more active in warm places. They also adjust their body temperature, but mainly by changing their behaviour rather than their metabolism. Both warm- and cold-blooded species have upper and lower thermal limits, beyond which they are severely impaired or even die.

In South Africa there are many museum records of where plants, mammals, birds, reptiles and various species of insects occurred in the past. Amateur naturalists’ notes add to the record of where species have been seen and are currently distributed. Around the world it has been observed that many species are now found closer to the poles, or higher up mountains, than where they were first recorded. How fast and how far they have moved depends on whether they are highly mobile organisms, such as birds, or species fixed to one spot for their lifetime, such as plants.

In South Africa, warm-area birds such as the African paradise flycatcher and the crimson-breasted shrike, found historically in the Low-veld, are now commonly observed in previously cooler places, such as the Highveld. There are several factors contributing to these changes, including bush encroachment (see Sec. 2, Q4) and the creation of ‘urban forests’ in Highveld cities, but climate change is very likely one of the causes. Section 2, Question 6 discusses changes in bird distribution more comprehensively.

Mammals are also relatively mobile so, in theory, they can migrate to remain in their preferred environmental conditions. The problem many face is loss of suitable habitat to migrate into. Large reserves such as the Kruger National Park provide space for many animals to move, but even it does not provide the climate range needed.