522 LAND ANIMALS 



large proportions of the population as compared with conditions that 

 obtain on neighboring continents. The unbalance in weevil population 

 is a case in point. When insects are considered, on islands there tends 

 to be a dominance of small-sized forms, dull coloring, obscure habitats, 

 erratic distributions with absence of many families, superfamilies, and 

 even entire orders, and a sparse representation of fresh-water forms. 

 Insect groups which are typically reduced or absent in oceanic 

 islands include stone flies, caddis flies, may flies, and scorpion flies, 

 aquatic Hemiptera, and the cicadas, membracids, aphids, Cercopidae, 

 and many groups of fulgorid bugs; most families of Neuroptera, many 

 beetles such as the lamellicorn series ; many families of flies ; the sub- 

 order Symphyta (sawflies) from the Hymenoptera, and most families 

 of aculeates. The absence of such groups is strong evidence against 

 the existence of extensive land areas in the Pacific at any time in the 



past. 



Space limitation. — The limitation of available space in the 

 smaller islands is reflected in the composition and development of their 

 faunae. Any animal requires a certain space to enable it to develop 

 and live freely, and this space varies with the size, activity, and mode 

 of feeding of the animal in question. For a springtail or mite, a moss- 

 covered stone may suffice; a rock projecting from the ice of Greenland 

 may support a gnat or a spider; a single plant is enough for a cater- 

 pillar, whereas sheep require a considerable extent of meadow. The 

 deer of Germany are distributed approximately in the proportion of 

 one to every 10 to 15 hectares of forest. Roe deer and hare are unable 

 to withstand confinement in zoological gardens, doubtless on account 

 of restriction of their movements. Herbivores require less space than 

 carnivores, the woodchuck, for example, less than the fox. The species 

 naturally requires a much greater area than its individuals, since a 

 minimum numerical strength is required to safeguard it from extermi- 

 nation, whether by fluctuations caused by the struggle for existence, 

 or by inbreeding. Small islands, consequently, can have only small 

 mammals. The Balearic Islands have only mice, weasels, hedgehogs, 

 and bats, and forms of equivalent size. The red deer declines in 

 forests of too small an area. The island of Bali, with about 5000 sq. 

 km., seems to be the smallest area which will support the tiger. 



Other conditions being equal, an insular area must accordingly have 

 a smaller fauna than an equal or even much smaller area on the main- 

 land. Even when the area is large enough for individuals of a species 

 of given size, it may not suffice for the breeding and other necessary 

 activities of the species. The botanical gardens at Bonn harbor about 

 43 species of nesting birds, on an area of 8.8 hectares, while the central 



