StabilityAbsence of fluctuations in populations; ability to withstand perturbations
without large changes in composition. (See also resilience.)
Stable age distributionThe proportions of individuals in various age classes in a
population that has a constant instantaneous rate of growth, r.
Stable equilibriumThe state to which a system returns if displaced by an outside force.
Stage-classified populationA population containing individuals of different devel-
opmental states (e.g. adults and larvae) in the same or different habitats.
Static life tableThe age-specific survival and fecundity of individuals of different
ages within a population at a given time; also called a time-specific life table. It is
a cross-section of all cohorts in the population at a given time.
Stochastic modelMathematical model based on probabilities; the prediction of the
model is not a single fixed number but a range of possible numbers. (Cf. deter-
ministic model.)
SuccessionReplacement of one kind of community by another kind; the pro-
gressive changes in vegetation and animal life that may culminate in the climax
community.
Survival (lx)Proportion of newborn individuals alive at age x; also called
survivorship.
Survivorship curveCurve showing the number of individuals surviving to age x
(log scale) plotted against age.
SusceptibleAccessible to or liable to infection by a particular parasite.
Susceptible individualEither naive (previously uninfected) or having lost immunity.
SwitchingA change in diet to favor food items of increasing suitability or abundance.
SympatricOccurring in the same place; usually refers to areas of overlap in species
distributions. (Cf. allopatric.)
SynecologyStudy of groups of organisms in relation to their environment; includes
population, community, and ecosystem ecology.Time-specific life tableSee static life table.
Total response of predatorThe product of the functional and numerical responses
plotted as per capita mortality of prey against prey density.
TransmissionThe process by which a parasitepasses from a source of infectionto
a new host. There are two major types: horizontaland verticaltransmission. The
majority of transmission processes operate horizontally, for example by direct
contact between infected and susceptibleindividuals or between disease vectorsand
susceptibles. There are six main methods of horizontal transmission: (i) ingestion
of contaminated food or drink; (ii) inhalation of contaminated air droplets;
(iii) direct contact; (iv) injection into a tissue via an animal’s saliva or bite;
(v) invasion via open wounds; and (vi) penetration of the host by active parasite
transmission stages (e.g. schistosome miracidia or cercariae). Vertical transmission
occurs when a parent conveys an infection to its unborn offspring, as occurs in
HIV in humans or in many arboviruses.
Transmission thresholdLevel of transmission below which an infectionis unable to
maintain itself within the host population (or populations, in the case of indirectly
transmitted infections).
Trophic levelPosition in the food chain, determined by the number of energy trans-
fer steps to that level. The first trophic level includes green plants; the second tropic
level includes herbivores, and so on.GLOSSARY 399
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