SUCCESSION OF COMMUNITIES 151 



present. With them are often found leeches, especially Macrobdella 

 decora, which is a brilliant red-and-green form. The only character- 

 istic insect is the dytiscid beetle (Agabus semipunctatus Kirby) (99^), 

 a slender reddish-brown form. The other forms found here are inci- 

 dental in the vegetation. Hollow logs are probably used for breeding- 

 places by the fishes, such as the bullheads (105), while the eggs of Physa 

 and of water-mites, and some of the aquatic insects, are also placed here. 

 The mammals of these ponds are the muskrat, which occurs in all the 

 stages, and the mink, which is now rare. 



Tendencies of the association: This association is unstable. Its 

 fate is heralded by the incoming of different amphibious plants at the 

 sides. This is the form Proserpinaca, with the divided leaves above 

 water and the entire ones below. This is often associated with Equisetum 

 and plants that have the growth form of grasses. Following these are 

 the shrubs, such as the buttonbush (6). Before these have captured 

 the entire pond it becomes dry during the dry season and the end of the 

 aquatic community is come. The formation which follows is the tempo- 

 rary pond, swamp, or marsh type. 



Characters of the formation: The formation composed of the two 

 associations mentioned may be characterized as made up of forms 

 which require but little oxygen, and no bare bottom. The reproduction 

 is one of two types: either the young are carried or the eggs are attached 

 to plants. Some of those carrying the young are the Sphaeridae, the 

 amphipods, and the isopods. Those sticking the eggs onto or into the 

 vegetation are the snails (all), the Dytiscidae, all the species recorded, the 

 Hydrophilidae, the Notonectidae, the Belostomidae, the Ranatras, the 

 caddis-flies, the Donacias, and in fact most of the forms of the formation. 



IV. SUCCESSION 



The first formation to take possession of a pond when it is first 

 separated from a lake like Lake Michigan is the bare-bottom formation; 

 chara soon makes its appearance in the deeper parts and we have the 

 beginning of the chara association. The chara association so acts upon 

 the bottom by covering it with humus and vegetation that it renders 

 the continued existence of the bare-bottom formation impossible (6, 

 112, 114, 1140). At the same time it prepares a way for the vegetation 

 which reaches to and above the surface. This, in turn, fills the pond 

 still further, and the strictly marsh vegetation takes possession. The 

 history of the true pond is then at an end and the story of the marsh 

 begins. Our series of 95 ponds illustrates the series of stages. The 



