FIG. 7-4 Increase In weight of bluegills upon removal from an 

 overpopulated pond to a pond of lower fish populations (from 

 Bennett, Thompson, and Parr 1940). The cross-hatched portion 

 represents the circumstance of overpopulation; a = autumn, 

 b = summer, c = spring. 



Smith 1942). When the available food supply must 

 be apportioned to a relatively large population, 

 growth of individuals is retarded, but with small 

 populations there is more food available per indi- 

 vidual, and growth is surprisingly rapid (Fig. 7-4). 

 In Europe, fish, chiefly carp, are raised for food in 

 small artificial ponds and are handled in much the 

 same manner as other domestic animals (Snieszko 

 1941). Problems involved in stocking and maintain- 

 ng suitable fish populations in small artificial ponds 

 n various parts of North America are summarized 

 n the Journal of IVildlife Management (16, 1952, 

 233-288). 



A problem involved in the management of ponds 

 and marshes is the control of mosquitoes. Oiling the 

 water surface will kill mosquitoes, but also renders 

 the habitat unsuitable for other organisms. Mos- 

 quito larvae and pupae are good food for such min- 

 nows as Fundidus and Gambusia that regularly feed 

 at the surface. Stocking of these fish species will 

 often keep mosquitoes under control. Elimination of 

 aquatic vegetation in the shallow marginal areas will 

 do away with hiding places and leave the larvae 

 more exposed to fish predators. 



Because ponds and marshes produce great num- 

 bers of fish, muskrats, and waterfowl, and are a 

 source of recreation for hunting, fishing, boating, and 

 swimming as well, the actual economic value of main- 



taining such areas is often greater than it would be 

 if they were drained and planted to crops (Bellrose 

 and Rollings 1949). Proper management of them 

 is therefore a challenge to applied ecologists. 



BOGS 



Characteristics 



Bogs or moors typically develop in the hydro- 

 seres of cold northern regions ; while marshes and 

 swamps, which are markedly different than bogs 

 (Dansereau and Segadas-Vianna 1952), are charac- 

 teristically southern in their location. Bogs commonly 

 develop into a coniferous forest climax ; swamps suc- 

 ceed to deciduous forest or other southern climax 

 types. Several thousand years ago, when glacial cli- 

 mates gripped the northern states, extensive bogs 

 developed and have persisted as relic communities 

 in spite of the warming of the climate. These bogs 

 are slowly being replaced by pond-marsh species at 

 equivalent serai stages bv cliseral succession (Table 

 7-6). 



Bogs occurring in the Great Lakes region are 

 ordinarily small in area and have little or no drain- 

 age. There may be oxygen present in the open water 

 of the larger bogs, but it is characteristically in very 

 low concentration, at most, in small bogs or in the 

 marginal zones. Bog water has a distinct brown 

 color ; a low nitrogen content ; a low temperature 

 beneath the surface; a low pH, at least in the mar- 

 ginal vegetated zones ; and a low dissolved salt con- 

 tent. 



A false bottom is characteristic of bogs. It con- 

 sists of finely divided plant material of a light brown 

 color, held suspended in the water at varying depths 

 below the surface. This false bottom may extend 

 downward several meters before a true solid bottom 

 is reached. The material disperses on slight disturb- 

 ance and may render all the open water turbid. Ordi- 

 narily, the surface waters are quiet and clear. Dead 

 vegetation does not completely decompose : as it ac- 

 cumulates, it becomes compressed to form peat. 



The plant bog sere 



In the early stages of development of the bog, 

 organic detritus may accumulate mostly in the deep- 

 est portions (Potzger 1956). As time goes on, how- 

 ever, a definite concentric-circle zonation of vegeta- 

 tion is established around the margin. As peat 

 accumulates, each zone encroaches on the next inner ; 

 the inmost shrinks until all open water disappears. 

 The area becomes finally covered with climax forest 

 (Dachnowski 1912). 



92 Habitats, communities, succession 



