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Figure 162.
The forest gardenia is a small tree with distinctive flowers that is federally listed as endangered. 
Only five of the Hawaiian Islands contain it, and there are only a few small populations of it there
128
. 
Energy Sources 
Green plants, algae, cyanobacteria, and photosynthetic protists all absorb solar energy. These 
microbes transform solar energy into the chemical energy that all living things require to function. 
Light availability has the potential to have a significant impact on how photosynthesizers evolve 
adaptations. For instance, when the trees in the canopy above them in the late spring completely leaf 
out, the plants in the understory of a temperate forest are shaded. 
Temperature 
Temperature affects the physiology of organisms as well as the density and state of water. 
Temperature exerts an important influence on living things because few living things can survive at 
temperatures below 0 °C (32 °F) due to metabolic constraints. It is also rare for living things to survive 
at temperatures exceeding 45 °C (113 °F); this is a reflection of evolutionary response to typical 
temperatures near the Earth’s surface. Enzyme efficiency is limited to a small, precise temperature 
range; at higher temperatures, enzyme degradation can take place. As a result, organisms either need 
to keep their internal temperature constant or live in environments that allow them to maintain a body 
127
(credit a: modification of work by Derrick Coetzee; credit b: modification of work by Allan Whittome)
128
(credit: Forest & Kim Starr)

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234 
temperature that supports metabolism. Some animals have evolved to allow their bodies to withstand 
large temperature swings, as seen in reptilian torpor or hibernation. Similar to how some Archaea 
bacteria have developed to withstand extremely hot temperatures, like those present in Yellowstone 
National Park's geysers. These bacteria are an example of an extremophile, an organism that can 
survive in harsh conditions. 
The distribution of living things may be constrained by temperature (in both the water and the 
air). Animals may respond to temperature changes by adapting, such as migrating, in order to survive. 
Migration
, the regular movement from one place to another, is an adaptation found in many animals, 
including many that inhabit seasonally cold climates. Finding food, a mate, and temperature issues 
are all resolved by migration. For instance, the Arctic Tern (
Sterna paradisaea
), which breeds in the 
Arctic Ocean and travels 40,000 km (24,000 mi) round trip annually to feed, travels between its 
feeding grounds in the southern hemisphere and its breeding grounds there. Monarch butterflies 
(
Danaus plexippus
) live in the eastern and western United States in the warmer months, where they 
build up enormous populations, and migrate to areas around Michoacan, Mexico as well as areas 
along the Pacific Coast, and the southern United States in the wintertime. Some species of mammals 
also make migratory forays. Reindeer (
Rangifer tarandus
) travel about 5,000 km (3,100 mi) each year 
to find food. Because they typically lack the ability to migrate, the distribution of amphibians and 
reptiles is more constrained. Not all animals that have the ability to migrate do so because it is risky 
and requires a lot of energy. 
Some animals 
hibernate
or 
estivate
to survive hostile temperatures.