colonization process require more detailed attention.
Both island biogeography and succession theory go
back a long way. Biologists have been studying
them in combination since the nineteenth cen-
tury (e.g. references in Whittaker et al. 1989),
although not necessarily within the same frame-
works we use today. Ridley may well have been
influenced by the early Krakatau data when he
wrote in the preface to his classic text on plant
dispersal (Ridley 1930, p. xii):
An island rises out of the sea: within a year some plants
appear on it, first those that have sea-borne seeds or rhi-
zomes, then wind-borne seeds, then those borne on the
feet and plumage of wandering seafowl, and when the
vegetation is tall enough, come land birds bringing seeds
of the baccate or drupaceous fruits which they had eaten
before their flight.
This provides the first elements of a dispersal-
structured or successional model of island
assembly.
Successional effects were discussed in relation to
equilibrium theory by MacArthur and Wilson
(1967), but in a fairly simplified fashion and with
little empirical data. Following their work, one of
the more interesting contributions was provided by
the data for the two volcanically disturbed islands
from Diamond’s (1974) study of New Guinea
islands. Ritter was sterilized in 1888, and Long was
devastated about three centuries before Diamond’s
survey of the two islands in 1972. Vegetation recov-
ery on each island was found to be incomplete:
Ritter supported Pandanus(screw-pines) up to 12 m
high on its gentler slopes, but was bare in steeper
areas, succession being retarded by landslides,
strong prevailing winds, and erosion. Long’s
recovery was more advanced, but its forests
remained comparatively open and savanna-like.
The species–area plot in Fig. 5.5 reveals that both
Ritter (4 species) and Long (43 species) remained
depauperate (Diamond 1974). Observations of
failed arrivals of other species on Ritter, including
feathers at the plucking perch of a resident pere-
grine falcon, provided further support for a habi-
tat/successional limitation explanation. Diamond
compared his data with a survey from 1933,
calculating by the means explained in Chapter 4
that its species number was approximately 75% of
the equilibrium value. He found that species
numbers had increased only slightly in the interim,
with a degree of turnover occurring—a result he
attributed to the slow pace of forest succession
‘arresting’ the progress of the Long avifauna
towards its equilibrium value. As turnover was not
greater than on older islands he termed it a quasi-
steady state. This hierarchically determined pattern
provides an interesting parallel with subsequent
studies of the build-up of bird numbers from the
Krakatau group (below).
Diamond’s line of argument was of much
broader biogeographical scope, as we have seen,
but the successional dynamics represented by
Ritter and Long held a key place in the overall
theory of the dynamics of the New Guinea islands.
Diamond’s reasoning was as follows. Small islands,
on which extinction rates should be high, will have
a high incidence of the best dispersing species,
i.e. they have a high incidence of tramps. Larger
defaunated islands will first be colonized by the
r-selected supertramps. Other, less dispersive
tramps arrive subsequently and eventually crowd130 COMMUNITY ASSEMBLY AND DYNAMICS
0.001 0.01 0.1Number of speciesArea (km^2 )1 10 100 1, 00010, 000 100, 000RitterLong20010050201052Control islands
Exploded volcanoes
Tidal-wave-defaunated
isletsKeyFigure 5.5The relationship between log species number and log-
island area for resident, non-marine, lowland bird species on the
Bismarck Islands (redrawn from Diamond 1974). The line of best fit is
for the so-called control islands. The explosively defaunated islands of
Long and Ritter remain significantly (P0.001) below the line of best
fit, which Diamond interpreted as demonstration of incomplete
succession and failure to attain equilibrium in the period since their
volcanic disturbance.