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was being degraded and would be converted to grassland, or even desert, if elephant num-
bers were not controlled (Beuchner and Dawkins 1961, Glover 1963, Myers 1973). In contrast,
other ecologists argued that fluctuations in elephant numbers were natural and, in keeping
with the preservationist ideal of non-intervention, they recommended a laissez-faire
approach (Caughley 1976).
The debate touched on some of the issues at the core of management dilemmas - the
balance between the welfare of a single species and the well-being of an ecosystem, the
ethical considerations of culling, and the philosophical difficulties of interfering in a sys-
tem which, according to the beliefs of the time should have been in a natural balance (Ladle
and Gillson 2009. The observed decline in tree cover and increasing elephant population
size did not match the prevailing ecological beliefs and expectations (Gillson et al. 2003).
The science of the time could provide no clear-cut answer as the system was not behaving
as would be expected, if indeed it was in equilibrium. Neither were there any long-term
data that could attest to the resilience and natural range of variability of the ecosystem
prior to the colonial era.
In response to this conundrum, a 'compression hypothesis' was proposed, which sug-
gested that the increase in numbers was due to immigration, as elephants moved away from
areas of hunting and other forms of conflict with humans towards the comparative safety of
the Park (Glover 1963, Myers 1973). This compression would have led to the carrying capacity
of the Park being exceeded, and an imbalance between vegetation composition and popula-
tion size. Fortunately for the elephants, an alternative explanation was proposed. Rather than
a stable balance between tree density and elephant numbers, Caughley suggested a more
dynamic system of woodland-grassland cycles, analogous to those in some predator-prey
systems, which continue to cycle between high and low numbers without reaching stability
(Figure 2.1a). Caughley predicted that increasing elephant populations would drive declines
in tree cover, which in turn would reduce elephant numbers due to food shortage, thereby
allowing tree cover to return. No equilibrium point can be reached because of the long delay
between tree decline and elephant population response; according to this hypothesis,
change, not stasis, was the norm (Caughley 1976).
The Tsavo ecologists of the day accepted Caughley's explanation and chose not to cull ele-
phants. They were at least partially vindicated because a natural die-off of elephants took
place in Tsavo in the droughts of the early 1970s, demonstrating a form of natural population
regulation in the face of scarce resources (Corfield 1973). Further, the die-offs were significant
because they countered one of the central tenants of the compression hypothesis—that ele-
phants would migrate in times of scarce resources, thus reducing pressure on areas experi-
enced drought or resource scarcity. What was observed during these bleak years was that
matriarchal herds would gather around the remaining permanent water resources, and
would stay there, even when all forage had been consumed, because their mobility was
limited by the youngest calves.
The Tsavo experiment clearly showed some feedback between resource availability, cli-
mate, and population size, which hinted at the potential for natural regulation of elephant
populations and the recovery of tree density. Later, a seminal work by Behnke and Scoones
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