590 - Heredity and Evolution 



START 

 BARE FIELD 



1-2 YEARS 

 GRASSLAND 





3 -20 YEARS 

 GRASSES 

 SHRUBS 





25-100 YEARS 

 PINE FOREST 



100-200 YEARS 

 CLIMAX: FOREST OF OAK AND HICKORY 



Fig. 30-14. An ecological succession, or sere, observed after abandonment of farm land in the Piedmont 

 region of the United States. (After E. P. Odum.) 



nity an adjustment must be made in the other 

 parts. Thus the animal species fluctuate along 

 with the plants. Indeed, it has been aptly 

 said that when an ecologist enters a field or 

 forest he sees not only what is there but also 

 what will be there in coming generations. 



ECOLOGY AND EVOLUTION 



In summary, plants and animals display a 

 tremendous variety of adaptation to almost 

 every kind of environment. The natural rate 



of reproduction gives rise to many more or- 

 ganisms than can survive and creates a pres- 

 sure for organisms to spread into new en- 

 vironments. Environmental conditions in the 

 different regions of the earth do not directly 

 determine adaptations, but the indirect in- 

 fluence of the environment — through the 

 agency of natural selection — has been de- 

 cisive in shaping the evolution of the species 

 toward fitness, each to occupy some particu- 

 lar niche in the ecosystem of one or another 

 of the many available types. 



TEST QUESTIONS 



1. Distinguish between the biotic and abiotic 

 factors of the environment, citing a specific 

 example in each case. 



2. Cite three examples to illustrate the observa- 

 tion that changes in the population of one 

 species may bring about changes in the popu- 

 tion of neighboring species. 



3. Explain the statement that animal popula- 

 tions in a given region tend to display a 

 "pyramidal" distribution. Cite two examples. 



4. Cite examples to show how the prevalence 



of insects has influenced the evolution of 

 other species. 



Give two examples of each of the following: 

 (a) offensive adaptations: (b) defensive adap- 

 tations; (c) protective coloration; (d) protec- 

 tive mimicry. 



Specify two adaptations commonly encoun- 

 tered among parasitic species. Discuss. 

 What is an infectious disease? Specify ten 

 such diseases. In each case, give the causative 

 agent and the best curative method (if any). 



