706 



ECOLOGY AND EVOLUTION 



tinue, in spite of vigorous attempts to con- 

 trol the pest. The caterpillars defoliate 

 large areas of forest trees, and one com- 

 plete defoliation will kill a pine or a hem- 

 lock (Sheals and Brown, 1944), Several 

 native predators and parasites have helped 

 reduce the moth populations, but the dep- 

 redations are still much more severe in 

 New England forests than they are in the 

 original European habitat. 



into the Hawaiian Islands and soon after- 

 ward came close to wiping out the sugar 

 cane industry. The insect was later found 

 to be native to Australia, where it was 

 neither common nor considered a pest. 

 Parasites and predators were introduced 

 into Hawaii from Australia and were so ef- 

 fective in controlling the leaf-hopper that 

 it is no longer seriously injurious (Zimmer- 

 man, 1943; see also J. H. Smith, 1944). 



100 



75 



P 50 



100,000 



Seven successive warnings 



First fawn storved 



60% of herd starved in two winters 



25 



Damage seen ^ x, 



first warning given' / n 



10,000 



1905 



1940 



YEARS 



Fig. 252. The effect of removal of predators on populations of deer on the Kaibab plateau 

 in Arizona (727,000 acres). Six hundred pumas were removed in 1907-1917, 74 in 1918-1923, 

 and 142 in 1924-1939. Eleven wolves were removed in 1907-1923 and were exterminated by 

 1926. Three thousand coyotes were removed in 1907-1923 and 4388 in 1923-1939. ( Redrawn 

 from Leopold.) 



For control purposes, many species of 

 predators and parasites of the gypsy moth 

 have been brought into New England, and 

 the search continues for others. Some of 

 these enemies, including ten species of 

 parasites, have become established and give 

 promise of checking the populations of the 

 moth. However, the equilibrium reached 

 through long evolution of the community in 

 Europe has not been attained during the 

 relatively short history of this species in 

 New England (see also Dowden, 1946). 



About 1900, the sugar cane leaf-hopper 

 (Perkinsiella saccharicida) was introduced 



Predation is not always wholly dele- 

 terious for the species preyed upon. A 

 balance or relative equihbrium may develop 

 that is somewhat beneficial to both preda- 

 tor and prey. The deer population in the 

 Kaibab plateau of Arizona was probably 

 originally adjusted to its food supply and 

 to its predators. Pumas and wolves seem 

 to have kept the number of deer well be- 

 low the carrying capacity of the range. 

 The original population is estimated to 

 have been about 4000 deer. After the 

 shooting of the pumas, the deer population 

 increased beyond the carrying capacity of 



