306 



ECOLOGICAL FACTORS: 



internal control enables individual birds and mam- 

 mals to remain active within greater temperature ex- 

 tremes that can other organisms. Most other groups 

 can carry on their life processes only between 35° 

 and 110°F.; temperatures above or below this range 

 prevent reproduction and, if they depart too far, 

 cause death. However, this does not mean that life 

 other than birds or mammals cannot exist at extreme 

 temperatures. Subarctic coniferous forests are 

 found where — 80°F. has been recorded and certain 

 buttercups and other plants can germinate under and 

 grow through snow. Temperatures above the gen- 

 eral range are found in deserts where the vegetation 

 is heated to over 130° F. and in hot springs where a 

 few blue-green algae and bacteria are known to sur- 

 vive in situations over 190° F. 



The temperature tolerance of plants varies in dif- 

 ferent climatic regions. Tropical plants have a rel- 

 atively narrow range in which life processes prosper, 

 and slight deviations from this range are likely to be 

 fatal. On the other hand, temperate zone plants have 

 a wider range of temperature tolerance. They carry 

 on their functions over a broad range and can with- 

 stand greater deviations from their optimum ranges 

 than can tropicals. Even within the temperate zone 

 there is variation in plant temperature tolerance. 

 The greatest tolerance is found in desert plants and 

 is necessitated by the desert environment. For ex- 

 ample, in an area of Death Valley, California, a tem- 

 perature range of over 100° F. was recorded in less 

 than twenty-four hours. Plant adaptations to cold 

 climates will be discussed in the section on alpine 

 plants, in reference to wind as an atmospheric factor. 



In animals definite temperature reactions take 

 place. There are comalike states, winter hibernation 

 and summer aestivation, which enable survival dur- 

 ing unfavorable extremes in temperature. Also, in 

 desert situations animals often retreat to burrows 

 during a hot day but are active on the surface at 

 night. Other animal-temperature relations include 

 animals' changing their habits and body structures, 

 conditions associated with annual temperature 

 fluctuations. 



In marine organisms, temperature appears to be a 

 prominent factor in the determination of geographic 

 distribution. Also of importance and associated with 

 temperature is salinity. This may be surprising, be- 

 cause ocean currents allow only very small tempera- 

 ture and salinity changes to exist. In spite of this, 

 temperatures are related to the geographic limits of 

 many Pacific Coast marine species at Cape Flattery, 



Washington; Point Conception, California; and San 

 Diego, California. However, these "barriers" seem 

 to be losing much of their effectiveness at the present 

 time, a situation that is allied to a general warming 

 of eastern Pacific Ocean waters. Owing to the warm- 

 ing, there is now a northward shifting of many 

 Pacific Ocean animals, including the northward 

 movement of sharks dangerous to man. 



VERTEBRATE DORMANCY 



Dormancy is characteristic of many plants and 

 animals; however, further mention of the subject 

 here is limited to vertebrates. 



Because many people are somewhat familiar with 

 the concept of hibernation, dormancy is frequently 

 believed to be an adaptation to temperature alone. 

 However, as more is learned about dormancy, it ap- 

 pears to be a general response to various unfavor- 

 able environmental conditions of a temporary nature. 

 For example, it can be associated with reduced food, 

 high temperature, low temperature, and reduced 

 moisture. Therefore, dormancy probably is a re- 

 sponse that conserves body materials, especially 

 water and sources of energy. The conservation of 

 materials comes from considerable slowing down of 

 body processes as the animal assumes a comalike 

 state, or torpor. The effects of the comalike state are 

 pronounced in endothermic birds and mammals 

 which have the greatest regulation and stability of 

 their life processes. Some endotherms enter a rela- 

 tively complete comalike state. In these species 

 dormancy results in reduction of body temperature 

 to essentially that of the surroundings, in drastic low- 

 ering of breathing and heart rates, and in a general 

 slowing of life processes. One might say that life 

 processes are reduced to a point that approaches the 

 bare minimum rate for survival. 



Degree of dormancy varies among vertebrates, es- 

 pecially the endotherms. In some, reduction of life 

 processes is so slight that it is hardly proper to call 

 the phenomenon dormancy. This is the case with 

 bears. Although breathing rate might be greatly re- 

 duced in some bears, heart rate and body tempera- 

 ture generally are normal. In addition, the animals 

 do not become torpid; disturbances are likely to 

 awaken them. For practical purposes, bear reactions 

 are only a very deep sleep. 



Dormancy frequently is seasonal. When dormancy 

 is mentioned, one is likely to limit his thoughts to 

 winter hibernation. However, dormancy frequendy 



