1932, Kenk 1949). It is an interesting experiment 

 to collect top soil from a dried-out pool, place it in 

 an aquarium with fresh water, and see what comes 

 out of it (Dexter 1946). When water returns to the 

 pond the hatching of plankton organisms and their 

 growth to reproductive maturity is very rapid. The 

 life cycle of some species appears shorter than could 

 be readily sustained in a normal year ; perhaps this 

 is an adaptation to survive extreme years (Table 

 7-5 ) . During years when the pond does not fill with 

 water at all, eggs and cysts remain in a dormant con- 

 dition ; some have hatched in a year of good condi- 

 tions after they had continued dormant for several 

 poor years. Some, but not all, species of crayfish sur- 

 vive dry periods by burrowing down to the water 

 table. 



Among the more interesting inhabitants of tem- 

 porary ponds are the phyllopods. The fairy shrimp 

 is not found in permanent ponds, except those with 

 a wide, shallow shore that dries out during the sum- 

 mer. Shrimp nauplii develop quickly from the egg, 

 usually in January or February after the ice melts, 

 but sometimes as early as November if the pond be- 

 comes filled with water after an autumn dry period. 

 In the spring, adults mature in three or four weeks, 

 egg-laying takes place forthwith, and the species may 

 be gone by late May. The period when the pond is 

 dry is passed through in the egg stage, and either 

 the drying or freezing of the eggs facilitates their 

 hatching (Weaver 1943). 



Some toads, Bufo spp., Microhyla olivacea, and 

 spadefoot frogs lay their eggs, after a warm spring 

 rain, in temporary pools rather than permanent 

 ponds. Development is rapid, and metamorphosis of 

 the tadpoles may be completed in a month's time, 

 before the pool evaporates (Bragg et al. 1950). 



LIFE HISTORIES 



On hatching from the egg, copepods first pass 

 through six free-swimming naupUus stages by a 

 series of molts, during which the small compact ani- 

 mal possesses only three pairs of appendages : then 

 through five copepodid stages, when additional ap- 

 pendages are added ; and, finally, into the adult form. 

 Both sexes occur regularly. 



Ostracod eggs also hatch into nauplii, but these 

 already possess a shell like that of the adult. Several 

 molts are required, however, before maturity. Some 

 species always reproduce sexually ; others are par- 

 tially or always parthenogenetic. 



The reproduction of the cladocerans is of special 

 interest. Most of the time only females are present, 

 and eggs develop parthenogenetically during the sum- 

 mer into more females. The thin-shelled eggs are 

 held in a brood pouch on the dorsal side of the body. 



and the young are well grown before they are set 

 free. There are no free-swimming larvae. After a 

 number of generations, the number varying with the 

 species, and as the pond begins to dry up in the sum- 

 mer or winter, conditions reach a point where there 

 is a crowding of females, an accumulation of ex- 

 cretory products, and a decrease in available food. 

 Parthenogenetic male as well as female eggs are then 

 produced. The resulting males are usually smaller 

 than the females, but, subsequent eggs are fertilized 

 by them and a thick shell is formed around them. 

 These ephippial eggs are produced in smaller num- 

 bers and are very resistant to drying and freezing. 

 When the pond again becomes filled with water, the 

 ephippial eggs develop into reproducing females to 

 start the cycle over again (Pennak 1953). 



The life-cycle of the rotifers bears some resem- 

 blance to that of cladocerans. A few species are vi- 

 viparous, but in most forms development of the egg 

 takes place outside the body and is direct into the 

 adult form. Two kinds of females are not distinguish- 

 able by external characters. One kind, amictic, pro- 

 duces large diploid eggs that are never fertilized and 

 only develop parthenogenetically into more females. 

 The other kind of female, mictic, occurs only at critical 

 times of the year and produces smaller haploid eggs. 

 If not fertilized, these small eggs develop into males ; 

 if fertilized, they form the thick-walled winter eggs 

 which, under subsequent favorable conditions, de- 

 velop into females. The males are usually small com- 

 pared with the females ; they lack an alimentary 

 tract, and consequently live only two or three days. 

 Females live one to three weeks or longer. The 

 production of males appears to be periodic and is 

 often correlated with a change in type or amount of 

 food, or degree of crowding. Males have never been 

 seen, and may not occur in, some groups (Pennak 

 1953). 



The amphipod Hyalella aztcca breeds only dur- 

 ing the warmer months of the year. The male carries 

 the female on his back for 1 to 7 days before copula- 

 tion occurs. Oviposition follows copulation by 12 to 

 24 hours. The incubation period is 21 days, and the 

 female may carry the young another 1 to 3 days in 

 her brood pouch. A period of 24 to 36 days elapses 

 between successive broods, and each brood is larger 

 than the last. The females may live into a second 

 summer and reproduce again. The young on hatch- 

 ing in the spring have all the adult appendages and 

 can reproduce later in the summer (Gaylor 1921). 



In the spring, aquatic Hemiptera commonly glue 

 their eggs to submerged vegetation. Some species 

 insert their eggs into incisions made in leaves or 

 stems. The young emerge directly into the water and 

 resemble the adults except that they do not acquire 

 wings until after several molts. In the Sialidae of the 

 Megaloptera, eggs are deposited in masses on leaves 



Habitats, communities, succession 



