fauna is an increase in variety and abundance of 

 plankton ( F.ddy 1934) and fish. The construction 

 of a beaver dam in a small Ontario river changed tiie 

 riffle habitat into that of a pond and brougiit a reduc- 

 tion in mayfly naiads, stonefly naiads, and caddisfly 

 larvae within two years. Other stream animals fell 

 from 68.7 to 1 5.6 per cent of the total population while 

 midge fly larvae increased from 31.3 to 84.4 per cent 

 ( S|)rules 1940). Shallow ponds develop more rapidly 

 than deep ones, and nnid bottom ponds develop more 

 rapidly than sand- (Shelford 1911) or rock bottom 

 |x)nds (Krecker 1919). The increase in number of 

 species and individuals in ponds depends on an in- 

 crease in the variety of microhabitats, types and 

 amount of food, and vegetation. With the develop- 

 ment of the pond into a marsh there is generally an 

 increase in humus and an increase in bacteria effect- 

 ing its decomposition, carbon dioxide, and marsh 

 gases. O.xygcn and ])H decrease. 



Two predominantly terrestrial orders of insects, 

 Coleo])tera and Hemi])tera, have invaded the pond 

 comnnmity but are not found in lakes except those 

 wiiich have [wnd-like margins. The Coleoptera are 

 rei)resented by three families of diving beetles, 

 Haliplidae, Dytiscidae, and Hydrophilidae, and by 

 the whirligig beetles, Gyrinidae. The haliplids are 

 herbivorous : the dytiscids are jjredacious ; some hy- 

 drojiliilids and gyrinids are predators, others are 

 scavengers. The a(|uatic bugs or Hemiptera are the 

 Corixidae. which feed on the bottom ooze, the No- 

 tonectidae, which prey upon small Entomostraca, the 

 Xepidae. the Helostomatidae, and the Naucoridae, 

 which are all carnivorous ; and the Veliidae, Meso- 

 veliidae, Gerridae, and Hydrometridae, which are 

 Ijrobably both carnivores and scavengers. Some of 

 tiiese species, as already noted, are usually found on 

 the surface film, I)ut they may occasionally dive and 

 cling^ to submerged vegetation. The true diving 



TABLE 7-2 Succession of dragonfly and damselfly naiads i 



Lake Erie (after Kennedy 1922). 



Gomphus plagiatus 

 Gomphus vastus 

 Neurocorduiia yamaskinensis 

 Macromia illinoiensis 

 Argia moesta 



Enallagma carunculatum 

 Enallagma exsulans 

 Enallagma ebrium 

 Ischnura verticalis 

 Tramea lacerate 



Anax Junius 

 Enallagma signatum 

 Libellula luctuosa 

 Libellida pulchella 

 testes rectangularis 



Leucorrhinia intacla 

 Erythemis simplicicollis 

 Plathemis lydia 

 Nehalennia irene 

 Pachydiplax longipennis 



testes forcipatus 

 Sympetrum obtrusum 

 Sympetrum vicinum 

 Sympetrum rubicundulum 

 Enallagma hageni 



testes uncatus 

 testes unguiculatus 



Ponds, marshes, swamps, and bogs 



83 



