336 



ECOLOGICAL FACTORS: 



sonal phenomena of plants, animals, and environ- 

 ment and the time of appearance of characteristic 

 annual events in the life cycle of organisms under 

 natural conditions of the related environmental cycle. 

 All phases of aspectation are closely related to the 

 sun-controlled climatic cycle; hence in any area pos- 

 sessing seasonal changes in climate there are sea- 

 sonal changes in most to all ecological factors and 

 in aspects. 



DIURNATION 



The majority of living creatures have some relation- 

 ship to daily cycles of ecological activity. In animals, 

 especially, such associations become pronounced be- 

 cause most animals are active only during certain 

 portions of the daily cycle. On the basis of period of 

 activity, animals active during the night are nocturnal, 

 those active during daytime are diumal, and those ac- 

 tive during the late evening and early morning hours 

 of limited light are crepuscular. Those animals not dis- 

 playing such distinct relationships, the irregular spe- 

 cies, are arhythmic. Arhythmic animals are in the 

 minority, including mostly subterranean creatures, 

 especially cave animals, and perhaps burrowing 

 forms such as ants, termites, moles, and gophers. 



Activity of the periodic animals is not uniform. In 

 this respect, crepuscular animals with two periods of 

 activity indicate the nature of diurnal and nocturnal 

 animals. Diurnal animals display their greatest ac- 

 tivity during the earlier daylight hours, but often have 

 a secondary activity peak before dusk. Nocturnal 

 animals, in similar manner, have their major activity 

 during the first part of the night and often a sec- 

 condary peak just before dawn. 



ASPECTATION 



The presence of four annual aspects, or seasons, is 

 familiar to most people of temperate climates. In 

 temperate and arctic climates ecological factors gen- 

 erally vary in such a way that winter {hiemal aspect), 

 spring {vernal aspect), summer [aestival aspect), and 

 autumn {autumnal aspect) can be recognized. On the 

 other hand, in tropical rainforest climate there is very 

 little seasonal variation, the climate being generally 

 uniform throughout the year. However, in those 

 tropical climates with a wet and dry climatic rhythm, 

 there are at least two seasons and, therefore, two con- 

 trasting periods in the life of the area. 



SEASONAL VARIATIONS 



The four aspects are most contrasting in deciduous 

 forests of temperate climates. Here, seasonal changes 

 in available food and shelter are most pronounced 

 and the consequences of such changes are easiest to 

 observe. In addition, two or three subdivisions of the 

 four aspects, called sectors, often are recognizable. Al- 

 though most to all aspects and their sectors normally 

 are present in temperate areas, they vary from year 

 to year with regard to character and distinctiveness 

 and to their time and duration. The particular nature 

 of local expression and variation of aspectation is re- 

 lated to the weather conditions of a given year, to the 

 latitude of the locale, and to the type of community. 



Table 17.5 summarizes the general features that 

 help define the aspects and their sectors in areas of 

 temperate climate. Although it must be reempha- 

 sized that these data represent only trends, the tabu- 

 lated material should be sufficient for determination 

 of aspect and sector at any time if all aspects and 

 their sectors are present. Not included in Table 17.5 

 are the relationships with environmental factor varia- 

 tions during the annual climatic cycles. The related 

 factors include temperature, relative humidity, pre- 

 cipitation, light, and evaporation. 



ECOLOGICAL SUCCESS 



The success or failure of an individual species is the 

 consequence of the reaction of ecological amplitude to 

 the environment. This is no more than saying that an 

 organism is as successful as its hereditary pattern 

 allows it to be, but little more than this can be gen- 

 eralized. For success, ecological amplitude must per- 

 mit the organism to become a part of its total environ- 

 ment and to obtain its requirements there. The full 

 implication of what becoming part of a population, 

 community, or ecosystem means can be appreciated 

 after these levels of the life spectrum are studied. This 

 "becoming a part" is a very intricate thing, requiring 

 integration within processes and relationships of ex- 

 tremely complex and dynamic phenomena. The com- 

 plex and rather tenuous nature of ecological success is 

 indicated by the fact that many more species have 

 become extinct than are living today. Therefore, suc- 

 cess is dynamic rather than static. Degree of success 

 fluctuates through time, and history records that it is 

 most likely to change eventually to failure — that is, 

 extinction. 



