The New Neotropical Companion

in the Old World. This means that in the 2 million or so

years since kingfishers colonized the New World tropics,

they have evolved a local diversity equal to that found in

any other global habitat where kingfishers occur. This

pattern, like that of Inga (described earlier), suggests that

speciation events may occur in geologically short time

periods and that species richness is not directly dependent

on long time periods.

The major premise of the stability- time hypothesis,

taken alone, is insufficient to explain high diversity,

though the fact remains that the tropics have never been

climatically severe. That said, there is almost universal

agreement among climatologists, geologists, and

biogeographers that tropical regions have not, in fact,

been climatically stable, though they have remained

warm and relatively equable. Recall the refugia model

discussed in chapter 8.

The Productivity- Resources Hypothesis

One frequent suggestion to explain high diversity in the

tropics is that high plant productivity allows for more

species; the more plant biomass, the more energy, the

more of everything. As discussed above, this may be

the case in the Neotropics. Variables of climate clearly

affect plant productivity and correlate with latitudinal

Plate 9- 8. The diminutive American Pygmy Kingfisher
(Chloroceryle aenea) is the smallest (13 cm/5 in) of the green-
backed kingfishers. It forages on small prey in streams and
pools. This bird is female. Photo by John Kricher.

Plate 9- 9. The Green Kingfisher (Chloroceryle americana) is the

next largest (18 cm/7 in). This bird is female. Photo by John

Kricher.

Plate 9- 10. The Green- and- rufous Kingfisher (Chloroceryle inda)

is more secretive than the other green- backed kingfishers,

inhabiting quiet and shaded streams. It is 23 cm (9 in) long.

This bird is a male. Photo by John Kricher.

Plate 9- 11. The Amazon Kingfisher (Chloroceryle amazona)

measures 28 cm (11 in) and is the largest of the four green-

backed kingfisher species. This one is a male. The species is

common and widespread along rivers and streams. Photo by

John Kricher.

142 chapter 9 why are there so many species?