Population regulation: a dynamic complex of interactions

Holmes, John C.

doi:10.1071/wr9950011

Cited by 74 publications

(60 citation statements)

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“…Parasites are thought to contribute to the regulation of natural populations of their hosts by reducing their fecundity and survival. If this is density dependent, then there must be a relationship between host density and parasitism, irrespective of the mechanism of the regulatory effect (Holmes, 1995). At the host densities and parasite abundances observed in our study, evidence for such a relationship was equivocal.…”

Section: Resultscontrasting

confidence: 43%

Factors Influencing the Fecal Egg and Oocyst Counts of Parasites of Wild European Rabbits Oryctolagus cuniculus (L.) in Southern Western Australia

Hobbs¹,

Twigg²,

Elliot³

et al. 1999

The Journal of Parasitology

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Abundance of intestinal parasites was monitored by fecal egg and oocyst counts for samples of wild rabbits Oryctolagus cuniculus with different levels of imposed female sterility from 12 populations in southwestern Australia. Differences in egg counts of Trichostrongylus retortaeformis between seasons and age groups were dependent on the sex of the host. Pregnancy may have been responsible for these differences because egg counts were consistently higher in intact females than in females surgically sterilized by tubal ligation. Egg counts for Passalurus ambiguus were influenced by season and host age but there were no differences between sexes or between intact and sterilized female rabbits. No differences were detected in the oocyst counts of the 8 species of Eimeria between male and female rabbits or between intact and sterilized females. Seasonal differences were detected in oocyst counts of Eimeria flavescens and Eimeria stiedai. The overwhelming determinant of coccidian oocyst counts was host age, with 6 species being much more abundant in rabbits up to 4 mo of age. There was a suggestion that egg counts of T. retortaeformis and oocyst counts of several species of Eimeria were reduced in populations where rabbit numbers had been depressed for at least 2 yr, but there was no evidence that short-term variations in rabbit numbers had a measurable effect on parasite abundance.Nematode and coccidian parasitism of wild European rabbits (Oryctolagus cuniculus (L.)) is influenced by host age and sex.In Australia, the influence of age is particularly important for species of Eimeria (Mykytowycz, 1962). Host age, sex and reproductive status all affect parasitism with Trichostrongylus retortaeformis, and pregnancy is a risk factor (Dunsmore and Dudzinski, 1968). A field study set up to determine the effects of imposing 4 levels of female sterility (0%, 40%, 60%, 80%) on rabbit populations in southwestern Australia (Twigg et al., 1998) provided an opportunity to investigate further the effects of host age and sex, pregnancy, and season on parasitism by coccidia and nematodes. The 12 discrete free-ranging populations varied considerably in rabbit numbers particularly because some of the higher sterility regimes were successful in reducing population size (Hobbs et al., 1999). This variation enabled us to investigate the relationship between host population size and parasite abundance. Although there has been a great deal of attention given to theoretical aspects of the population dynamics of infectious disease since the introduction of the mathematical models of Anderson and May (1979), there have been calls for more empirical studies on the dynamics of these diseases, particularly with respect to the density-dependent relationships between host and parasite (e.g., Dobson and Hudson, 1995;McCallum, 1995). MATERIALS AND METHODSThe rabbit sterility trials were located in the wheat belt region of southwestern Western Australia near Wellstead (34?30'S 118?36'E). Climate is Mediterranean, with long dry summers duri...

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Section: Resultscontrasting

confidence: 43%

Factors Influencing the Fecal Egg and Oocyst Counts of Parasites of Wild European Rabbits Oryctolagus cuniculus (L.) in Southern Western Australia

Hobbs¹,

Twigg²,

Elliot³

et al. 1999

The Journal of Parasitology

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“…The multiple factor hypothesis of population regulation (Holmes 1995) argues that there are no necessary conditions or predictable relationships between ecological factors like predation and disease and changes in population density. What happens in one population in a given year cannot be predicted from its density, from what happened last year, or from any set of mechanistic relationships.…”

Section: (D ) Large Mammalsmentioning

confidence: 99%

Two complementary paradigms for analysing population dynamics

Krebs

2003

Wildlife Population Growth Rates

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To understand why population growth rate is sometimes positive and sometimes negative, ecologists have adopted two main approaches. The most common approach is through the density paradigm by plotting population growth rate against population density. The second approach is through the mechanistic paradigm by plotting population growth rate against the relevant ecological processes affecting the population. The density paradigm is applied a posteriori, works sometimes but not always and is remarkably useless in solving management problems or in providing an understanding of why populations change in size. The mechanistic paradigm investigates the factors that supposedly drive density changes and is identical to Caughley's declining population paradigm of conservation biology. The assumption that we can uncover invariant relationships between population growth rate and some other variables is an article of faith. Numerous commercial fishery applications have failed to find the invariant relationships between stock and recruitment that are predicted by the density paradigm. Environmental variation is the rule, and nonequilibrial dynamics should force us to look for the mechanisms of population change. If multiple factors determine changes in population density, there can be no predictability in either of these paradigms and we will become environmental historians rather than scientists with useful generalizations for the population problems of this century. Defining our questions clearly and adopting an experimental approach with crisp alternative hypotheses and adequate controls will be essential to building useful generalizations for solving the practical problems of population management in fisheries, wildlife and conservation.

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“…Wildlife populations are regulated by the complex interactions of various factors, including weather, predation, food, and disease (Holmes, 1995). By investigating the influence of these factors on birth and death rates, we gain insights that improve our understanding of dynamic populations in dynamic natural systems (Krebs, 1995).…”

Section: Introductionmentioning

confidence: 99%

Wolf Reproduction in Response to Caribou Migration and Industrial Development on the Central Barrens of Mainland Canada

Frame¹,

Cluff²,

Hik³

2009

ARCTIC

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ABSTRACT. Reproductive success of mammals is greatly influenced by food availability. Where wolves (Canis lupus) prey on migratory barren-ground caribou (Rangifer tarandus), caribou migration patterns strongly influence food availability for wolves. However, industrial development in formerly undeveloped wolf range could also negatively influence wolf reproduction, either directly (by disrupting normal feeding behavior) or indirectly (by impacting caribou migrations). We used a cross-sectional timeseries regression to analyze eight years of wolf reproductive data with respect to spatial and temporal variation in caribou migration and economic development in a 49 900 km 2 area of the Northwest Territories, Canada. Reproductive success decreased as the distance from wolf dens to caribou migration routes increased, while the timing of caribou migrations had little effect. There was no measurable effect of current levels of economic development on reproductive success, although evidence suggests the potential for indirect effects. Continued monitoring is required to identify possible thresholds of adverse effects for wolf populations.Key words: wolf, Canis lupus, caribou, Rangifer tarandus, cumulative effects, disturbance, migration, Northwest Territories, Nunavut, predator-prey, reproductive success RÉSUMÉ. La réussite de reproduction des mammifères dépend beaucoup de la disponibilité de la nourriture. Là où les loups (Canis lupus) ont comme proie le caribou de la toundra en migration (Rangifer tarandus), le schéma des migrations du caribou joue un grand rôle sur la disponibilité de nourriture des loups. Cela dit, l'expansion industrielle dans d'anciennes aires de répartition non aménagées du loup pourrait aussi avoir une influence négative sur la reproduction du loup, directement (perturbation du comportement d'alimentation habituel) ou indirectement (impact sur la migration du caribou). Nous avons recouru à une régression chronologique transversale pour analyser huit années de données de reproduction du loup par rapport à la variation spatiale et temporelle de la migration du caribou et au développement économique dans une zone de 49 900 km 2 des territoires du Nord-Ouest, au Canada. La réussite de reproduction diminuait au fur et à mesure que la distance entre les tanières de loups et les routes de migration du caribou augmentaient, tandis que le moment choisi pour les migrations du caribou avait peu d'effets. Le développement économique actuel n'avait aucun effet mesurable sur la réussite de reproduction, bien que certains indices laissent croire qu'il pourrait avoir des effets indirects. Il y a donc lieu d'effectuer une surveillance continue afin de déterminer les seuils possibles d'effets nuisibles sur les populations de loups.

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Population regulation: a dynamic complex of interactions

Cited by 74 publications

References 50 publications

Factors Influencing the Fecal Egg and Oocyst Counts of Parasites of Wild European Rabbits Oryctolagus cuniculus (L.) in Southern Western Australia

Factors Influencing the Fecal Egg and Oocyst Counts of Parasites of Wild European Rabbits Oryctolagus cuniculus (L.) in Southern Western Australia

Two complementary paradigms for analysing population dynamics

Wolf Reproduction in Response to Caribou Migration and Industrial Development on the Central Barrens of Mainland Canada

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