S76 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Iviiown, as seen in periodic multiplication of the hares 

 in British Columbia cited above. The United States 

 Biological Survey has recorded the startling total of 

 10,000 to 12,000 field mice to the acre in certain parts 

 of Nevada. 



We may therefore reasonably consider the part 

 which the rapid multiplication of the smaller browsing 

 animals may have played during the Tertiary period of 

 Europe. 



Food competition especially intense on islands. — -The 

 influence of the goats on islands is cited by Wallace 

 (1881. 1, pp. 280, 283-286) and Palmer. 



Palmer (1899.1, p. 89) observes: 



Sheep and goats when numerous are likely to caus3 widespread 

 injury, particularly in forested regions. An instructive example 

 of the damage done by goats is that on St. Helena, described by 

 Wallace. St. Helena is a mountainous island scarcely 50 square 

 miles ia extent, and its highest summits reach an elevation ot 

 2,700 feet. At the time of its discovery, about the beginning of 

 the sixteenth century, it is said to have been covered by a dense 

 forest; to-day it is described as a comparatively barren rocky 

 desert. This change has been largely brought about by goats 

 first introduced by the Portuguese in 1513, which multiplied so 

 fast that in 75 yeai's they existed by thousands. Browsing on 

 the young trees and shrubs, they rapidly brought about the 

 destruction of the vegetation whicn protected the steep slopes. 

 Witn the disappearance of the undergrowth began the washing 

 of the soil by tropical rains and the destruction of the forests. 

 In 1709 the governor reported that the timber was rapidly 

 disappearing and that the goats should be destroyed if the forests 

 were to be preserved. This advice was not heeded, and only 

 a centur3' later, in 1810, another governor reported the total 

 destruction of the forests by the goats. 



The Santa Barbara Islands and Santa Catalina, off the coast 

 of southern California, and the island of Guadalupe, off the 

 Lower California coast, are utilized as ranges for goats. All 

 these islands are dry and more or less covered with brush, but 

 arborescent vegetation is comparatively scarce. The goats 

 practically run wild and already exist in considerable numbers. 

 As yet the goats have not been on the islands long enough 

 to cause any serious effects on the vegetation, and they may 

 never bring about the ruin which has been wrought on St. 

 Helena. But it is scarcely possible for the islands to be grazed 

 by goats for an indefinite length of time without suffering serious 

 damage. 



Herhivora in relation to the Carnivora. — In all the 

 examples of recent conditions of life cited above the 

 imrestricted feeding and rapid multiplication of small 

 Herbivora have taken place under artificial conditions 

 of protection of these animals from Carnivora. 



It is quite possible that m certain regions under 

 natural conditions the Carnivora may have become 

 diminished through epidemics or other causes, thus 

 promoting the multiplication of the smaller browsing 

 animals, so fatal to vegetation and to the normal 

 distribution of food supply of a country. For a long 

 period South America was singularly deficient in 

 Carnivora and was overrun with the smaller Herbivora. 



Introduction oj Carnivora. — Among the striking 

 examples of the effects of the introduction and com- 

 petition of Carnivora in past and recent times are: 



1 . In the Eocene epoch the true or higher Carnivora 

 entered into competition with the lower Creodonta of 

 Europe and North America; this was followed by the 

 final extinction of the last of the Creodonta in the 

 lower Oligocene. 



2. In the Pliocene epoch true Carnivora, namely, 

 the Canidae and two destructive types of Felidae — the 

 saber-tooths (Machaerodontinae) and the true cats 

 (Felinae) — suddenly invaded South America. They 

 entered a faunal region which, subsequent to the ex- 

 tinction of the marsupial carnivores (Thylacinidae) 

 in the Oligocene epoch, had been entirely free from 

 large Carnivora. 



3. The introduction of the dingo {Canis dingo) in 

 the Australian mainland was followed by the extinction 

 of the Tasmanian wolf (Thylacinus) and "devil" 

 (Sarcopliilus) , animals which survived only in Tas- 

 mania. The fox, which was introduced into Australia, 

 like the rabbit, has increased so rapidly that it has 

 become a veritable menace to native life. 



4. The introduction of the mongoose (Herpestes) in 

 various countries has been fatal to the entire small 

 endemic fauna. 



In each instance superior mechanical adaptation, 

 intelligence, and plasticity in respect to change of 

 habitat have played an important part. The Car- 

 nivora, therefore, in their relation to the balance of 

 nature, to the destruction of competing Carnivora and 

 Herbivora, and especially in relation to the young of 

 the larger Herbivora, form special topics for examina- 

 tion with regard to extinction. 



Direct elimination hy carnivores. — The question as 

 to how far the mammals of prey have been a direct 

 cause of extinction at various times of various forms 

 of quadruped life is considerably disputed. Morris 

 (1895.1) observes: "So far as existing evidence goes, 

 then, it seems probable that hostile aggression, while 

 it may have been occasionally an indirect has rarely 

 been the direct cause of the extinction of species." 

 A similar opinion has been orally expressed to the 

 author by D. G. Elliot — that no wild animal causes 

 the extinction of another wild animal directly. Such 

 a negative conclusion may hold true of undiminished 

 herds and of conditions where carnivorous and her- 

 bivorous animals have evolved together and, as in the 

 evolution of the modern battleship, modes of defense 

 have evolved simultaneously with modes of attack. 



This negative view in our opinion does not hold 

 true where newly introduced Carnivora find quad- 

 rupeds unprovided with adequate means of defense, 

 as in the invasion of South America by carnivores 

 from North America in late Pliocene time. Nor does 

 it hold true of diminished herds of quadrupeds that 

 are unable adequately to defend their young. 



Therefore we must consider the Carnivora as among 

 the direct causes of the final extinction of diminished 

 groups or reduced herds of animals which are struggling 



