100 Influential Papers - page 12

Anderson, R.M. & May, R.M. (1978)
Regulation and stability of host-parasite population
interactions. I. Regulatory processes.
Journal of Animal Ecology,
47, 219-247.
The models described in this paper, together with its sister paper ’II.
Destabilizing processes’ (May and Anderson 1978), changed the way
ecologists and epidemiologists viewed host-parasite associations as a
special class of predator-prey interactions. The first paper showed (1) how
overdispersion of parasite numbers per host, (2) non-linear functional
relationships between parasite burden per host and host death rate, and (3)
density dependent constraints on parasite population growth within individual
hosts, stabilise the dynamical behaviour of host-parasite and enhance the
regulatory role of the parasite. The second paper, on destabilizing processes,
again identified three important categories of biological processes: parasite-
induced reduction in host fecundity, parasite reproduction within a host
which directly increases parasite population size, and time delays in parasite
reproduction and transmission.
Both papers are citation classics, the former cited over 800 times in the
last 35 years, and have provided the theoretical framework for empiricists
to test hypotheses about the role of parasites in the population dynamics
of their hosts. For example, work on the controversial mechanisms causing
regular cycles in the population dynamics of both invertebrate pests and the
game-bags of red grouse, as well as the role of parasites in the more chaotic
dynamics of reindeer.
Steve Albon
Hassell, M.P. & May, R.M. (1973)
Stability in insect host-parasite models.
Journal of Animal Ecology, 42, 693-726.
The population dynamics of predator-prey and
other consumer-resource interactions have a
natural propensity to oscillate. Predator numbers
increase and drive down the population of their
prey which leads to starvation and predator
decline. With their predators rare, the prey
population recovers and the cycle can begin
again. Simple models often predict diverging
cycles leading to the extinction of predator or
prey. Understanding the biological mechanisms
that allow consumer-resource interactions to
persist has been a major goal of population
ecology. Much of this research has involved
parasitoids, insects that lay eggs in the bodies
of other insects. Parasitoids are very important
in biological control, and the relatively simple
manner in which a successful attack results in
typically one new parasitoid greatly simplifies
modelling. Hassell & May summarised what
was known about the factors that might stabilise
parasitoid-host interactions and developed a
series of models to unify and extend existing
theory. They concluded that non-random search
leading to refuges for hosts when parasitoids
were at high density was the most biologically
likely stabilising mechanism. Over the next
twenty years the authors and other groups
developed a sophisticated theory of parasitoid
and predator searching upon which our current
understanding of resource-consumer persistence
is based.
Charles Godfray
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