COMMUNITY ORGANIZATION: STRATIFICATION 



487 



to a particular substratum of the floor. Such 

 spruce-eating phthiracarids oviposit in the 

 needle, subsequent larvae and nymphs com- 

 plete their last molt, and the adult mite 

 crawls out of the needle, mates, and the 

 cycle is renewed. This takes place at a 

 level at which fungi are acting upon the 

 needles, that is, the F2 substratum of the 

 floor (Fig. 54, p. 217). 



The collective feces of these arthropodan 

 and molluscan residents are augmented by 

 the abundant castings of the soil earth- 

 worms of the subterranean stratum, by the 

 feces falling from occupants of higher strata 

 (caterpillars, Homoptera, chrysomelid beet- 

 les, squirrels, monkeys, birds), and by 

 larger floor animals (rabbits, peccaries, 

 deer). All add to the richness of the 

 floor. Some feces, as those of the cater- 

 pillars of Antheraea cytherea, compare 

 favorably with dung of the large grassland 

 mammals in relative proportions of nitrogen, 

 lime, and phosphoric acid (Juritz, 1920). 



In addition to the mold eaters, there are 

 numerous predaceous and scavengeristic 

 patobionts. Here belong such animals as 

 predaceous mites, lycosid spiders, roaches 

 (Parcoblatta) , ants, and beetles (Park, 

 1947). Among beetles characteristic of 

 north temperate deciduous forest floors of 

 America may be cited the speciahzed snail- 

 eating carabids (Cychrinae), the purple 

 carabid (Dicaelus ptirpuratus) , and the 

 green tiger beetle (Cicindela sex guttata) . 



Ants are abundant and important. The 

 army ants of tropical American forests and 

 their ecological equivalents, the driver ants 

 of tropical Africa, are notable. Their num- 

 bers, relatively large size, relatively large 

 amount of floor covered by their raiding 

 columns (Schneirla, 1938, 1940; Wheeler, 

 1926), place them with the most influential 

 floor predators. Predation by army ants has 

 been evaluated quantitatively by Williams 

 (1941) in the Panama Canal Zone. Leaf 

 mold residents were at minimal population 

 density on the Barro Colorado floor on days 

 following raids by Eciton. 



The red-backed salamander (Plethodon 

 cinereus) is a typical vertebrate patobiont 

 of the temperate forest floor (Fig. 163). Its 

 entire life is passed in this stratum; the 

 eggs are deposited in soft log mold, and 

 the adults feed upon smaller floor animals, 

 such as ants, beetles, sowbugs, mites, and 

 spiders (Bishop, 1941; Hamilton, 1932). 



Turning to floor transients, the first, from 

 the viewpoint of numbers, are insects. Many 

 oviposit in the floor debris and pass their 

 nymphal or larval and pupal stages in log 

 and leaf mold (McColloch and Hayes, 

 1922). Other insects move into the forest 

 floor litter from adjacent communities 

 (Weese, 1924) or from higher forest strata 



ikj> .^^ . ■ . . . . . ' 



Fig. 163. Plethodon cinereus, a salamander 

 with eggs. (Courtesy Am. Mas. Nat. Hist.) 



for overwintering. In their horizontal or 

 vertical movements these animals benefit 

 from the moderate forest climate. 



Some of these overwintering migrants 

 form extensive, heterotypical place aggre- 

 gations (Allee, 1931; Holmquist, 1926). 

 The aphid-eating coccinellid, Ceratomegilla 

 fuscilabris, and several genera of leaf-eating 

 chrysomehd beetles commonly hibernate 

 in mixed aggregations in such numbers that 

 both floor and subterranean strata are in- 

 volved (Park, 1930). 



A few vertebrates belong in this second 

 category of floor animals. After passing 

 their aquatic egg and larval stages, many 

 species of salamanders (Ambystoma) hunt 

 for small floor residents, chiefly insects, and 

 seldom leave the floor except for their an- 

 nual spring migration to the aquatic breed- 

 ing grounds (Bishop, 1941). The common 

 box turtle (Terrapene c. Carolina), in the 

 more northern parts of its range, lives on 

 the forest floor save for hibernation in the 

 subterranean stratum (Pope, 1939). Par- 

 alleUng the interstratal diurnal movement of 

 some insects and spiders, the large frog. 



