We consider 27 population and community terms used frequently by parasitologists when describing the ecology of parasites. We provide suggestions for various terms in an attempt to foster consistent use and to make terms used in parasite ecology easier to interpret for those who study free-living organisms. We suggest strongly that authors, whether they agree or disagree with us, provide complete and unambiguous definitions for all parameters of their studies.

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1987. Individual variability in reproductive success of Triaenophorus crassus Forel (Cestoda: Pseudophyllidea), with comments on use of the Lorenz curve and Gini coefficient. Can. J. Zool. 65: 2878-2885. Maturity, mass, and lifetime fecundity were detemined in individual Triaenophorus crassus from spawning pike (Esox lucius) from Falcon Lake, Manitoba. Only 33% of worms contained eggs, and only 73% of these could release their eggs (up to 4 400 000 per worm). Inequalities in mass and fecundity were quantified using Lorenz curves and Gini coefficients calculated for worms pooled across hosts, and separately for worms in each host. Inequalities in mass were correlated with, but always lower than, corresponding inequalities in fecundity, although inequalities in fecundity and mass were more similar at high infection intensities. Consequently, inequalities in worm mass did not provide an accurate estimate of inequalities in reproductive success but could be used as an indirect index for comparative purposes. These inequalities can potentially modify parasite transmission. Ten percent of worms accounted for 85% of all parasite fecundity and, as a result of a contagious distribution of worms among pike and a lack of detectable intensity-dependent effects on parasite fecundity, 55% of worm eggs came from 10% of spawning pike. Worm numbers and distribution among hosts, maturity, and inequalities in mass and fecundity were consistent over 3-4 consecutive years, indicating that these inequalities are a normal component of the life cycle. The concentration of parasite fecundity in relatively few worms or hosts suggests that the population dynamics of T. crassus may be affected by short-term changes in parasite genotype, host activity patterns, or mortality of the few heavily infected hosts. SHOSTAK, A. W., et DICK, T. A. 1987. Individual variability in reproductive success of Triaenophorus crassus Forel (Cestoda:Pseudophyllidea), with comments on use of the Lorenz curve and Gini coefficient. Can. J. Zool. 65 : 2878-2885. La maturitk, la masse et la feconditk totale ont pu &tre dkterminkes chez des individus de Triaenophorus crassus, parasites de brochets (Esox lucius) captures sur les frayitres du lac Falcon, au Manitoba. Seulement 33% des vers portaient des oeufs et seulement 73% de ceux-la pouvaient les liberer Uusqu'a 4 400 000 oeufs par individu). Les differences de masse et de fecondite des vers ont kt6 quantifiees, tant chez l'ensemble des n6tes que chez un seul hbte, a l'aide de courbes de Lorenz et de coefficients de Gini. Les differences de masse sont toujours en corrklation avec les diffkrences de feconditk qui sont toutefois plus importantes; les diffkrences de masse et de feconditk sont cependant du m&me ordre au cours des infections graves. Consequemment, les differences de masse ne mesurent pas adkquatement les diffkrences dans le succes de la reproduction; elles peuvent neanmoins servir d'indice indirect dans des ktudes comparatives. Ces diffkrences peuvent ini'luer sur la transmission des parasites. Dix pour...

Density-dependent constraints on parasite growth, survival or reproduction are thought to be important in preventing the unchecked increase in parasite numbers within individual hosts or host populations. While it is important to know where, and with what severity, density dependence is acting within the parasite life-cycle, interpretation of data from natural infections is difficult. In this paper, we present a Monte Carlo simulation technique for examining such data for evidence of density dependence. We also describe how this technique may be used to distinguish among mechanisms hypothesized to generate density-dependent phenomena.

The survival of first-stage larvae (L1) of Parelaphostrongylus odocoilei and P. tenuis (Nematoda: Metastrongyloidea) and their infectivity to the snail Triodopsis multilineata were determined experimentally in a variety of temperature and moisture conditions. Survival of larvae of P. odocoilei increased with decreasing temperature. Survival of larvae in water was similar to survival in air at 17 and 45% RH; survival of larvae in air at 75, 85, and 95% RH was considerably lower at corresponding temperatures. The infectivity of larvae of P. odocoilei that survived desiccation was greatly reduced. Repeated freezing or repeated desiccation resulted in reduced survival of P. odocoilei and P. tenuis. Larvae of Parelaphostrongylus odocoilei from mule deer of Jasper National Park, Canada, were better able to resist the effects of freezing, but less able to resist the effects of desiccation, than were larvae of P. tenuis from white-tailed deer of Pennsylvania, USA.

Morphological variability of Echinorhynchus gadi, E. leidyi, and E. salmonis was evaluated from 30 collection sites in northern Canada. Nine new hosts were recorded. Mixed infections with the three species, in addition to their high morphological variability, made the identification of Echinorhynchus spp. from northern waters unreliable in the absence of information on morphological variability from local and geographically distant populations. Worm age, host species, and geographic location contributed to the variability of several taxonomically important characters: proboscis size and shape, hook size and number, body shape, and egg size. These characters had considerably greater variability and interspecific overlap in ranges than previously reported. Identifications were most reliable when based on gravid females. Individual males and immature females could generally be identified, with about 90% or greater reliability, using a multivariate comparison of proboscis measurements to a data set based on gravid females from the entire study area. Meristogram analysis revealed some intraspecific similarities and interspecific differences in proboscis hook shape but patterns varied geographically. While meristograms corroborated specimen identifications based on more comprehensive analyses, they were unreliable, when used alone, on Arctic and north temperate populations of echinorhynchids. Morphological variability between populations of Echinorhynchus spp. in different lakes was greater than could be accounted for by host species and the environment. It is hypothesized that this geographic variability may be a consequence of restricted gene flow between isolated populations causing geographic isolation of morphological variants.

The cestode Hymenolepis diminuta (Cyclophyllidea) uses a variety of insects as its intermediate host, where ingestion of eggs results in development in the hemocoel of a cysticercoid that is infective to a rat definitive host. Species in 2 genera, Tenebrio and Tribolium (Coleoptera: Tenebrionidae) have been used extensively as laboratory intermediate hosts. This review examines experimental studies on ecological aspects of the relationship between H. diminuta and tenebrionid beetles, including the acquisition and establishment of the parasite, host effects on the parasite, and parasite effects on the host. A meta-analysis of infection results from the literature revealed strong relationships across host species and strains between (1) prevalence and intensity of infection, (2) efficiency of cysticercoid production and exposure conditions, and (3) variance in abundance or intensity of infection relative to their respective means. The underlying mechanisms producing these patterns remain elusive. Comparative studies are infrequent, and the use of divergent methodologies hampers comparisons among studies. In spite of these problems, there is much to recommend this as a terrestrial host-parasite model system. It represents those relationships in which mostly minor, but occasionally major, responses to parasitic infection occur, and in which host genetics and environmental conditions can serve as modifying factors. Moreover, this is a tractable experimental system, and is backed by an extensive literature on host biology.

We studied the 'crowding effect' in Tribolium confusum infected with Hymenolepis diminuta. Manipulations included age and number of parasites, and diet, sex, age and number of exposures of hosts. Volume per parasite was unaffected until an intensity of at least 5-10 parasites per host, then declined approximately inversely as intensities increased. Parasite size was affected by host sex but not age or reproductive status. Host diet affected parasite size and the impact of crowding. Daily gain in parasite volume peaked partway through the developmental period and preceded the first evidence of a crowding effect. Parasites that established during a second exposure had a transient developmental delay but eventually grew as large or larger than parasites from a single exposure with the same total intensity. Parasites responded to crowding by differential allocation of resources. Cercomer volume decreased even with slight crowding, the capsule surrounding the scolex was not reduced until crowding became more severe, and scolex width was reduced only in the most extreme conditions. The data support the hypothesis that the crowding effect in this system is driven primarily by nutrient, rather than space limitations.