ECOLOGICAL FACTORS 405 



eating animals, however, are specialists; caterpillars, longicorn beetles, 

 and others may be restricted to a certain species of plant and are 

 therefore isolated like it. 



The lack of a definite periodicity in tropical climates has important 

 further effects on animal life. In plants the development of leaves, 

 blossoms, and fruits is not associated with a definite season as in the 

 temperate zones. The number of species of trees blooming throughout 

 the year especially is larger, and the time during which blossoming 

 specimens of a species may be found is, in general, longer in the tropics 

 than in places where the seasons display very great temperature varia- 

 tions; the phenomenon of repeated blossoming at short intervals, 

 though occurring in the latter case almost as an anomaly, is a normal 

 and ordinary occurrence among many tropical plants. 04 Only under 

 such conditions could plant-eating animals develop that are dependent 

 upon blossoms or upon pulpy fruits through the year. The nectar or 

 pollen-eating birds are wholly confined to the tropical and subtropical 

 regions (Nectarinidae in Africa, Madagascar, and the Indian region) . 

 The hummingbirds of South and Central America have representatives 

 that advance into the temperate belts as summer residents but remain 

 there only a short time. 



In convergent development the tongue of all these nectar-feeding 

 birds is long, extensible, and brush-like or rolled up like a tube, in 

 adaptation to the sucking of nectar. These birds arc the means of 

 pollination of many of the blossoms which they visit, and just as many 

 flowers possess special contrivances for the enticement of the pollinat- 

 ing insects, so in the tropics many flowers are adapted to the visits of 

 birds by the size of the flower, provision of special resting places, rigid 

 and solid formation of pistils and stamens, and abundant honey- 

 production. About 84% of such "ornithophilous" flowers are orange- 

 red, scarlet, cinnabar, carmine, or purple in color. 05 In like manner 

 birds and mammals that are dependent essentially upon pulpy fruits 

 have their principal distribution in the tropics, where such fruits may 

 be obtained during the entire year; this is true of many parrots, of 

 the plantain-eaters (Musophagidae), the toucans and others birds, and 

 of many monkeys. 



The distribution of the reproduction period over the entire year is 

 usual among tropical animals in uniform climates. In our zones the 

 breeding period of almost all the invertebrates and most of the verte- 

 brates is in the warm seasons of spring and summer, and there are 

 usually only one or at most two generations a year. Tropical insects, 

 on the other hand, have many generations each year. In the Philip- 

 pines, for example, eggs, caterpillars, and butterflies of Papilio yamnon 



