between 1871 and 1964 an average of 4.6 hurricanes
per year was recorded, the island of Puerto Rico
having a return period of just 21 years (Walker et al.
1991 a; Chapter 2). Hurricanes are high-energy
weather systems, involving wind speeds in excess
of 120 km/h, affecting paths tens of kilometres
wide. They can have huge ecological impacts on
island ecosystems (e.g. Walker et al. 1991b; Elmqvist
et al. 1994).
During post-hurricane succession in the
Caribbean, it has been found that the animal
community may continue to change long after the
initial ‘greening-up’ of the vegetation, through
invasions and local extinctions as the vegetation
varies through successional time (Waide 1991).
Initially, nectarivorous and frugivorous birds suffer
more after hurricanes than do populations of insec-
tivorous or omnivorous species, a consequence of
their differing degrees of dependence on re-
establishment of normal physiognomic behaviour
in the vegetation.
Turnover patterns in response to disturbances of
this and other kinds can be anticipated on theoreti-
cal grounds to be dependent upon taxon choice (e.g.
Diamond 1975a, p. 369). Schoener (1983) established
empirically that percentage species turnover
declines from ‘lower’ to ‘higher’ organisms, as
follows (approximate figures): 1000%/year in
protozoa, 100%/year in sessile marine organisms,
100–10%/year in terrestrial arthropods, and
10–1%/year in terrestrial vertebrates and vascular
plants. Moreover, across this range of organisms,
turnover declines approximately linearly with gen-
eration time. Given which, and restricting consider-
ation only to islands subject to such environmental
dynamics, the attainment of a dynamic (biotically
balanced) equilibrium in certain K-selected (long-
lived, only moderately dispersive) taxa may be
postulated to be comparatively rare.Variation in species number in the short and medium term
It might be argued that islands devastated by
events such as volcanoes and hurricanes are
extremes: Krakatau is just a special case. However,TEMPORAL VARIATION IN ISLAND CARRYING CAPACITIES 157Table 6.3How might the capacity for richness of an island vary through time? Left and right boxes provide hypothetical examples of how
increase/decrease might arise from factors under the same general heading (Modified from Whittaker 2004).
Factors leading to an increase Factors leading to a decrease
Primary succession, increasing biomass, system complexity and Late successional stages if passed through simultaneously
niche space, in part driven by species colonization, in part enabling across an isolate might see competitive exclusion of suites of
further colonization earlier successional species (e.g. Wilson and Willis (1975),
data from Barro Colorado Island, Panama)
Arrival of ‘keystone species’ (e.g. fig trees on Krakatau Arrival of a ‘superbeast’ (e.g., first vertebrate predator),
(Whittaker and Jones 1994a,b; Thornton 1996) ) may over-predate naive prey species
Humans may increase habitat diversity, introduce new species, Humans may clear habitat, introduce new pest/predator
manipulate ecosystems to raise productivity, etc. or highly competitive species, degrade habitats, etc.
Area/habitat gain, e.g., through coastal deposition, uplift, Area/habitat loss, e.g., through coastal erosion, subsidence,
sea-level fall sea-level increase
Moderate disturbances might open up niche space, e.g., for Major disturbance (e.g. hurricane or volcano) may wipe
non-forest species on an otherwise forested island out much standing biomass, massively reducing populations
Increasing climatic favourability, increasing biological activity, Climatic deterioration, lower NPP
increased NPP
Evolution, on remote islands, a similar effect to primary succession, In situco-evolution is unlikely to generate reductions in richness,
primarily operating through hierarchical links between organisms but as oceanic islands age they subside and erode (Chapter 2),
at different trophic levels such that in parallel with the processes of speciation, carrying
capacity will first peak and then decline through time (Chapter 9)