EXERCISE XI 

 ECOLOGY AND ADAPTATION 



In this exercise will be studied two species of animal found in terri- 

 genous bottoms of lakes, with special reference to the structures and hab- 

 its which fit them for such habitat. Animal reactions will be studied 

 in forms from other habitats. Drawings, answers to questions, and a 

 summary should be handed in. 



A. TERRIGENOUS BOTTOMS 

 Character of Terrigenous Bottoms 



Examine photographs of portions of some lake showing (1) a consider- 

 able area of barren, sandy shoal, and (2) a photograph of a limited portion 

 of the bottom of such a shoal. If such habitat is easily available for 

 actual observation, this part of the work could be done in the field with 

 considerable profit. The first two animals to be studied were taken in 

 such a situation. Note: 



1. The almost complete absence of vegetation. How is this feature 



accounted for? 



2. The waves, showing the beach to be wind-swept. What relation 



does this fact bear to (1) above? On which shore of a lake 

 might such a beach be located? 



3. The sand ripples. What causes them? Relation to (1) and (2) 



above? 



4. Flecks of foam on the surface of the water. Cause? 



5. In such an environment what are the conditions with respect to 



(a) dissolved oxygen content of the water, (6) carbon dioxide, 

 (c) decaying organic matter, (d) extremes of temperature as 

 compared with the deeper water, (e) light, (/) molar agents, (g) 

 materials for holdfasts, shelter, or abode? 



6. By what methods can animals normally inhabiting such a situation 

 maintain their positions there? 



Fauna of Terrigenous Bottoms 



(a) Lampsilis or Anodonta (Freshwater Mussels). 



1. Study living specimens in shallow dishes or in small aquaria 

 containing water and provided with sand bottoms. Be careful not to 

 jar them. 



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