Abstracts


Combined impacts of Allee effects and parasitism

Anne Deredec & Franck Courchamp. 2006. OIKOS 112: 667 /679.

Abstract:

Despite their individual importance for population dynamics and conservation biology, the combined impacts of Allee effects and parasitism have received little attention. We built a mathematical model to compare the dynamics of populations with or without Allee effects when infected by microparasites. We show that the influence of an Allee effect takes the form of a tradeoff. The presence of an Allee effect in host populations may protect them, by reducing the range of population sizes that allow parasite spread. Yet if infection spreads, the Allee effect weakens host populations by reducing their size and by widening the range of parasite species that lead them to extinction. These results have important implications for predicting the survival of threatened populations or the success of reintroductions, and may help define size ranges within which given populations should be maintained to prevent both epidemics and Allee effects driven extinctions. .


Use of biological invasions and their control to study the dynamics of interacting populations.

Franck Courchamp & Caut Stéphane. 2005. In M.W. Cadotte, S.M. McMahon & T. Fukami (eds) Springer, 253–279.0.

Abstract:

The best response to the effects of biological invasions is almost always to control, and when possible eradicate, the alien population. In many cases, the elimination of the alien invasive species is followed by a rapid and often spectacular recovery of the invaded communities. However, the sudden removal of the alien species may generate further dysfunction, resulting in similar or greater damage to the ecosystem. These unexpected chain reactions have helped realize that biological invasions as well as the control of introduced species can be used as excellent opportunities to understand the numerous and often complex interactions among populations. In this chapter we use selected examples to illustrate how the study of the impacts of introducing, or removing, species from trophic webs can reveal indirect and fascinating relationships as well as understudied ecological processes. We use simple, deterministic mathematical models to study processes involving more than two populations, such as mesopredator release, hyperpredation process or competitor release in the context of biological invasions. We illustrate these ecological processes with concrete examples of actual cases faced by conservation biologists, and discuss them in a broader context of population dynamics and functional ecology.


Predators and Prey in the Channel Islands.

Gary Roemer, Rosie Woodroffe & Franck Courchamp. 2004. Science. 305 : 777-778.

Abstract:

Replies- No abstract.


Removing Protected Populations to Save Endangered Species.

Franck Courchamp, Rosie Woodroffe & Gary Roemer. 2003. Science. 302, 5650 : 1532

Abstract:

Conservation of species threatened with imminent extinction may require drastic measures that can be emotionally charged, politically unsavory, and legally challenging. A complex example relates to the decline of the island fox (Urocyon littoralis), endemic to the California Channel Islands, off the coast of the United States..


Extinction thresholds in host-parasite dynamics.

Anne Deredec & Franck Courchamp. 2003. Annales Zoologici Fennici 40: 115-130.

Abstract:

In this paper, we review the main thresholds that can influence the population dynamics of host-parasite relationships. We start by considering the thresholds that have influenced the conceptualisation of theoretical epidemiology. The most common threshold involving parasites is the host population invasion threshold, but persistence and infection thresholds are also important. We recap how the existence of the invasion threshold is linked to the nature of the transmission term in theoretical studies. We examine some of the main thresholds that can affect host population dynamics and then relate these to parasite thresholds, as a way to assess the dynamic consequences of the interplay between host and parasite thresholds on the final outcome of the system. We propose that overlooking the existence of parasite and host thresholds can have important detrimental consequences in major domains of applied ecology, including in epidemiology, conservation biology and biological control.


Mammal invaders on islands, impact, control and control impact.

Franck Courchamp, Michel Pascal & Jean-Louis Chapuis. 2003. Biological Reviews. 78: 347-383.

Abstract:

The invasion of ecosystems by exotic species is currently viewed as one of the most important sources of biodiversity loss. The largest part of this loss occurs on islands, where indigenous species have often evolved in absence of strong competition, herbivory, parasitism or predation. As a result, introduced species thrive in those optimal insular ecosystems affecting their plant food, competitors or animal prey. As islands are characterised by a high rate of endemism, the impacted populations often correspond to local subspecies or even unique species.
One of most important taxa concerning biological invasions on island is mammals. A small number of mammal species is responsible for most of the damages to invaded insular ecosystems: rats, cats, goats, rabbits, pigs and a few others.
The effect of alien invasive species may be simple or very complex, especially since a large array of invasive species, mammals and others, can be present simultaneously and interact among themselves as well as with the indigenous species. In most cases, introduced species generally have a strong impact and they often are responsible for the impoverishment of the local flora and fauna.
The best response to these effects is almost always to control the alien population, either by regularly reducing their numbers, or even better, by eradicating population as a whole from the island. Several types of methods are currently used: physical (trapping, shooting), chemical (poisoning) and biological (e.g., directed use of diseases). Each has its own set of advantages and disadvantages, depending on the mammal species targeted. The best strategy is almost always to combine several methods. Whatever the strategy used, its long term success is critically dependent on solid support from several different areas, including financial support, staff commitment, public support, to name a few.
In many cases, the elimination of the alien invasive species is followed by a rapid and often spectacular recovery of the impacted local populations. However, in other cases, the removal of the alien is not sufficient for the damaged ecosystem revert to its former state, and require complementary actions, such as species re-introduction. A third situation may be widespread: the sudden removal of the alien species may generate a further disequilibrium, resulting in similar or greater damages to the ecosystem. Given the numerous and other complex population interactions among island species, it is difficult to predict the outcome of the removal of key species, such as a top predator. This justifies careful pre-control study and preparation prior to initiating the eradication of alien species eradication, in order to avoid an ecological catastrophe. In addition, long term monitoring of the post-eradication ecosystem is crucial to assess success and prevent reinvasion.


Golden eagles, feral pigs, and insular carnivores: How exotic species turn native predators into prey

Gary W. Roemer, C. Josh Donlan, & Franck Courchamp. 2002. Proc. Natl. Acad. Sci. USA 99(2): 791-796.

Abstract:

Island ecosystems are particularly vulnerable to exotic species. Here we show how an introduced prey has led to the wholesale restructuring of an island food web, including the near extinction of an endemic carnivore. Introduced pigs, by providing abundant food, enabled golden eagles to colonize the California Channel Islands. Eagles preyed heavily on the island fox, whose resulting decline toward extinction released populations of the competitively inferior island skunk. The presence of exotic pigs led to major ecosystem shifts by indirectly causing predation to replace competition as the dominant force shaping these island communities.


Small pack size imposes a trade-off between hunting and pup guarding in the painted hunting dog Lycaon pictus.

Franck Courchamp, Greg S.A. Rasmussen & David Macdonald. 2002. Behavioral Ecology 13(1): 20-27.

Abstract:

The painted hunting dog or African wild dog, Lycaon pictus, is one of the most endangered large carnivores in Africa, with extinction predicted within a few decades if their dramatic decline is not stopped. It has recently been hypothesized that because of their constraining need for helpers, group size was of major importance in obligate cooperative breeding species, and that the resulting likely existence of a threshold number of adults could create an Allee effect, increasing the group extinction risk. One example where the importance for a critical number of adults may have major repercussions for painted hunting dogs concerns baby-sitting, or pup guarding, a behavior typical of obligate cooperative breeders. We propose that, as forgoing this behavior is costly because pup guards have the potential to decrease pup mortality, its use is costly too, especially in small packs, because helpers are strongly needed for their cooperative foraging (hunting, protecting the kill and bringing back food to the pups). We present a simple model showing how pup guarding imposes a cost because it implies that less food per hunt is brought back to more individuals at the den. We complete these analyses with empirical tests of the effect of pack size on the probability of pup guarding, from field data from the Hwange population in Zimbabwe. Our model, as well as our five years of empirical data, both suggest a critical threshold at a size of about five individuals.


Crucial importance of pack size in African wild dogs Lycaon pictus.

Franck Courchamp & David Macdonald. 2001. Animal Conservation 4: 169-174.  

Abstract:

Although the massive organised slaughter of African wild dogs, Lycaon pictus, largely ended several decades ago, this endangered canid continues to decline and faces extinction. Compared to other, sympatric, large carnivores, Lycaon populations are unstable, and local extinctions common. Several lines of evidence suggest that this instability arises directly from obligate cooperative breeding, which makes Lycaon more sensitive to anthropogenic mortality. A number of behaviours in this species are characterised by a reliance on helpers. These include cooperative hunting, defence from kleptoparasitism, pup feeding and baby-sitting. As a result, there are strong, positive relationships between pack size and the production and survival of pups, and pairs of wild dogs are often unsuccessful at raising offspring without the assistance of helpers. Consequently, a pack which membership drops below a critical size may be caught in a positive feedback loop: poor reproduction and low survival further reduces pack size, culminating in failure of the whole pack. Here, we review the literature to reveal the importance of pack size in the African wild dog. Most importantly, we argue that there is a critical minimum threshold, below which packs face an increasing probability of extinction- an Allee effect with consequences for the conservation of this species, and of other obligate cooperators.


Multipack dynamics and the Allee effect in African wild dogs Lycaon pictus.

Franck Courchamp, Bryan Grenfell & Tim Clutton-Brock. 2000. Animal Conservation 3(4) : 277-286.

Abstract:

Since it does not affect similarly sympatric large carnivores, the causes of the decline of the highly endangered African wild dogs (Lycaon pictus) may be linked to specific population dynamics induced by their particular social system. African wild dogs are obligate cooperators, and their need for helpers could generate inverse density dependence at the pack level. We show, through a mathematical model, that this can create an Allee effect, leading to a lower population size and a higher risk of population extinction, compared to populations with direct density dependence. This is due to three different processes, each being able to increase population extinction on its own, and each probably occuring simultaneously in African wild dogs. First, inverse density dependence causes significantly higher rates of pack extinction. Second, it also increases the probability of failure of empty territory colonisation by founders. Third, the Allee effect at the pack level (with a critical number of individuals), generates an Allee effect at the population level (with a critical number of packs). Furthermore, our results suggest that quantitative and qualitative habitat destruction, as well as increased human pressure increase the effects of inverse density dependence, whereas a lower frequency of anthropogenic random mortality events decreases them.


Modelling Virus Vectored Immunocontraception to control cats introduced onto islands.

Franck Courchamp & Stephen Cornell. 2000. Journal of Applied Ecology. 37(6): 903-913.

Abstract:

1- The idea of controlling mammalian pests through immunocontraception is the subject of growing interest. This is partly due to the announced development of new technologies, such as virus vectored immunocontraception (VVIC), which, if satisfyingly developed, will improve the feasibility of this control strategy within the coming years.
2- However, immunocontraception has not hitherto been considered for the control or eradication of domestic cats (Felis catus) that have been introduced onto oceanic islands and represent a major threat to the endemic vertebrate fauna.
3- With simple mathematical models, we compare the relative efficiency of immunocontraception using different disseminating systems: by baits; by genetically modified viral vectors (VVIC); or by a combination of both. We take into account several forms of compensation likely to arise in a population with artificially reduced fertility.
4- We conclude that, under the assumptions of our model, immunocontraception can control or eradicate feral cat populations in oceanic islands. VVIC is theoretically more efficient than baits, and the integrated method is the most likely to eradicate the cat population. In addition, many of the disadvantages of VVIC could in fact be advantages in the case of cats introduced onto remote uninhabited islands.


Transmission of Feline Immunodeficiency Virus in a population of cats (Felis catus).

Franck Courchamp, Ludovic Say & Dominique Pontier. 2000. Wildlife Research 27: 603-611.

Abstract:

The increasing awareness of the ecological impact of domestic cats (Felis catus) as wildlife predators has given rise to much effort in research on cat control, but studies related to the spread of pathogens in natural populations remain almost non-existent. We aimed to determine the infection strategy of Feline Immunodeficiency Virus (FIV) in a natural population of cats, focusing on qualitative and quantitative aspects of its transmission. FIV is a lethal retrovirus infecting cats world-wide and is transmitted by bites. It has an interesting potential as a control agent for this species. We studied an urban population of stray cats over three years, monitoring its epidemiology, and its social and spatial structures. Despite a high cat density, both transmission rate and prevalence of FIV were relatively low. Socially dominant males were more likely to be infected. In addition, males of the study population were less often infected than in another population, where a polygynous mating system involved more fights. Infected individuals lived long enough to acquire the virus and infect another cat. Because they were subordinates, non-infected cats had a shorter life expectancy, which would not have permitted the spread of FIV. Thus, FIV infected predominantly at-risk individuals which social ranking allowed a high probability of retransmitting the virus.


Detection, identification and correction of a bias in an epidemiological study.

Franck Courchamp, Ludovic Say & Dominique Pontier. 2000. Journal of Wildlife Diseases 36/1: 71-78.

Abstract:

The relative lack of epidemiological studies of natural populations is partly due to the difficulty of obtaining samples that are both large enough and representative of the population. Here, we present the result of an epidemiological study (December 1992-August 1995) of feline immunodeficiency virus (FIV) in a free-roaming population of domestic cats (Felis catus), with a special emphasis on sample bias. Over five trapping periods, the prevalence of FIV in sampled cats steadily declined. Across these samples we consistently achieved a very large sampling fraction (approximately 60% of the population), the sex ratio, age and weight distributions remained stable with time in the samples, and the sex ratio was similar in the samples and the population. These indices would normally indicate that our samples were representative, suggesting the decline in FIV prevalence to be real. However, a concomitant ecological study of the whole population revealed an important bias in the samples, with an initial high probability of capturing a few individuals, which appeared significantly more likely to be FIV-infected, and then a lower probability of recapturing them. Since our protocol resulted in a non-random sampling, subsequent trappings were designed to avoid this bias, by also capturing individuals who had previously learned to escape capture. This modified capture regime revealed that FIV prevalence was in fact constant in the population. This study shows how samples of large size, which are stable and appear representative of the population, can still be biased. These results may have major implications for other studies based on trapping.


Population dynamics of obligate cooperators.

Franck Courchamp, Bryan Grenfell & Tim Clutton-Brock. 1999. Proceedings of the Royal Society of London, Biological Sciences 266: 557-564.

Abstract:

Obligate cooperative breeding species demonstrate a high rate of group extinction, which may be due to the existence of a critical number of helpers below which the group cannot subsist. Through a simple model, we study the population dynamics of obligate cooperative breeding species, taking into account the existence of a lower threshold below which the instantaneous growth rate becomes negative. The model incorporates successively: (i) a distinction between species that need helpers for reproduction, for survival, or for both; (ii) the existence of a migration rate accounting for dispersal; and (iii) stochastic mortality to simulate the effects of random catastrophic events. Our results suggest that the need for a minimum number of helpers increases the risk of extinction for obligate cooperative breeding species. The constraint imposed by this threshold is higher when helpers are needed for reproduction only, or for both reproduction and survival. By driving them below this lower threshold, stochastic mortality of lower amplitude and/or lower frequency than for non-cooperative breeders may be sufficient to cause the extinction of obligate cooperative breeding groups. Migration may have a buffering effect only for groups where immigration is higher than emigration; otherwise (when immigrants from nearby groups are not available) it lowers the difference between actual group size and critical threshold, thereby constituting a higher constraint.


Impact of natural enemies on obligate cooperators.

Franck Courchamp, Bryan Grenfell & Tim Clutton-Brock. 2000. OIKOS 91(2) : 311-322.

Abstract:

Obligate cooperative breeding species demonstrate a high rate of group extinction, which may be due to the existence of a critical number of helpers below which the group cannot subsist. Through a simple model, we study the population dynamics of obligate cooperative breeding species, taking into account the existence of a lower threshold below which the instantaneous growth rate becomes negative. The model incorporates successively: (i) a distinction between species that need helpers for reproduction, for survival, or for both; (ii) the existence of a migration rate accounting for dispersal; and (iii) stochastic mortality to simulate the effects of random catastrophic events. Our results suggest that the need for a minimum number of helpers increases the risk of extinction for obligate cooperative breeding species. The constraint imposed by this threshold is higher when helpers are needed for reproduction only, or for both reproduction and survival. By driving them below this lower threshold, stochastic mortality of lower amplitude and/or lower frequency than for non-cooperative breeders may be sufficient to cause the extinction of obligate cooperative breeding groups. Migration may have a buffering effect only for groups where immigration is higher than emigration; otherwise (when immigrants from nearby groups are not available) it lowers the difference between actual group size and critical threshold, thereby constituting a higher constraint.


Inverse density dependence and the Allee effect.

Franck Courchamp, Tim Clutton-Brock & Bryan Grenfel. l1999. Trends in Ecology and Evolution 14: 405-410.

Abstract:

The Allee effect describes a scenario in which populations at low numbers are affected by a positive relationship between population growth rate and density. The importance of this dynamic process in ecology has been under-appreciated and accumulating evidence suggests that it may have an impact on the population dynamics of many plant and animal species. Studies of the causal mechanisms generating Allee effects in small populations may provide a key to understanding their dynamics.


Biological control of alien predator populations to protect native island prey species from extinction.

Franck Courchamp & George Sugihara. 1999. Ecological Applications 9: 112-123.

Abstract:

Introduced feral cat (Felis catus) populations are an important threat to many island vertebrate populations and bird species in particular. Elimination of feral cat populations is desirable in most of these ecosystems. Release of a parasite species in these mostly immune-naive populations is thought to be an efficient eradication measure. Such an approach is theoretically investigated here using a mathematical model. The model describes the effects of the introduction of a virus into the cat population on the population dynamics of both the cat and its prey. The effect of the introduction of two types of feline viruses is studied: Feline Immunodeficiency Virus and Feline Leukemia Virus, both being good candidates for the eradication of a cat population. Results show that eradication is possible with Feline Leukemia Virus, if natural immunity is sufficiently low. Feline Immunodeficiency Virus cannot fully eradicate cat populations, but can be an effective agent for long-term control of cat populations on islands where total cat eradication is not possible (high likelihood of continued introduction of cats) or not desirable (presence of rats). Culling, which by itself would require a very prolonged and logistically demanding effort to eliminate cat populations, may be more efficient when applied simultaneously with virus introduction.


Cats protecting birds: modelling the mesopredator release effect.

Franck Courchamp, Michel Langlais & George Sugihara. 1999. Journal of Animal Ecology 68: 282-292.

Abstract:

1- Introduced predators account for a large part of the extinction of endemic insular species, which constitutes a major component of the loss of biodiversity among vertebrates. Eradication of alien predators from these ecosystems is often considered the best solution.
2- In some ecosystems, however, it can generate a greater threat for endemic prey, through what is called the "mesopredator release". This process predicts that, once superpredators are suppressed, a burst of mesopredators may follow that leads their shared prey to extinction.
3- This process is studied through a mathematical model describing a three species system (prey-mesopredator-superpredator). Analysis of the model, with and without control of meso- and superpredators, shows that this process does indeed exist and can drive shared prey to rapid extinction.
4- This work emphasises that, although counter-intuitive, eradication of introduced superpredators, such as feral domestic cats, is not always the best solution to protect endemic prey when introduced mesopredators, such as rats, are also present.


Rabbits killing birds: modelling the hyperpredation process.

Franck Courchamp, Michel Langlais & George Sugihara. 2000. Journal of Animal Ecology 69: 154-164.

Abstract:

1- Introduced rabbits are known to have catastrophic effects on oceanic islands, either by direct destruction of the vegetative cover, or by the resulting disturbance of indigenous vertebrates.
2- Another dramatic effect, less known but potentially of major importance, is the hyperpredation process. This process, related to apparent competition, predicts that an introduced prey species, well adapted to high predation pressure, could induce the extinction of an indigenous prey, through the sudden increased population size of an introduced predator. In many island ecosystems, the simultaneous presence of introduced feral cats and rabbits is thus potentially a further threat for small vertebrates endemic of these islands.
3- Through a mathematical model, we tested this hypothesis, using a tri-trophic system comprising an indigenous prey (birds), an introduced prey (rabbits) and an introduced predator (cats), and we demonstrated the theoretical existence of the hyperpredation process.
4- In addition, the numerical analysis of the model allowed a quantification of this process. It shows that the conditions required for an indigenous species to cope with the hyperpredation process imply very high intrinsic growth rates and/or carrying capacity, as well as behavioural anti-predator response to the introduced predator. Since these conditions are unlikely to be met, this process is a further potential threat to most indigenous vertebrate prey.
5- Finally, our model shows that, although it can be induced by both together or alone, behavioural adaptations alone are more powerful in generating the hyperpredation process, than are life history traits adaptations.


Control of rabbits to protect birds against cat predation.

Franck Courchamp, Michel Langlais & George Sugihara. 2000. Biological Conservation 89: 219-225.

Abstract:

Both introduced predators (e.g., domestic cats) and introduced small grazers (e.g., rabbits) are harmful to many island vertebrate species. The effects of cats on indigenous species are direct (predation), whereas the most obvious effects of rabbits are often indirect and in the longer term. Thus, in situations where both cats and rabbits are present, priority is frequently given to control of cats. However, the presence of rabbits can allow an increased predator population which can lead to extinction of the indigenous and less well adapted prey species, and increase the difficulty of predator control. Through a mathematical model, we show that control of introduced prey facilitates the control of the introduced predator population. Moreover, predator control may fail to protect the indigenous prey if control of the introduced prey is not undertaken simultaneously. Therefore, control of both introduced species is the best strategy.


Backcasting population sizes of Ringed and Grey Seals in the Baltic and Lake Saimaa during the 20th century.

Hanna Kokko, Eero Helle, Jan Lindström, Esa Ranta, Tero Sipilä & Franck Courchamp. 1999. Annales Zoologici Fennici 36: 65-73.

Abstract:

Populations of the ringed seal (Phoca hispida) and grey seal (Halichoerus grypus) in the Baltic Sea have been dramatically declining throughout this century. Populations are currently recovering from a population low in the 1980s, but their sizes before the decline remain unknown. The land-locked Saimaa ringed seal (Phoca hispida saimensis) has similarly been declining over much of the century. We use past bounty statistics to calculate possible sizes of these three populations at the beginning of this century, and investigate the sensitivity of our results regarding assumptions on population growth, density dependence or independence, the true extent of kills, and the age of killed individuals. We confirm that a previous estimate of 300 000 ringed seals in the Baltic is within a possible range, which in fact extends from 50 000 to 450 000 individuals. Similarly, the grey seal population estimates range from 30 000 to 200 000 individuals. The larger estimates apply if hunting tended to remove adult individuals with high reproductive value, and if the initial population was regulated by density dependence rather than kept below its true carrying capacity by previous, nineteenth-century hunting. For the first point it is known, however, that hunting has been more likely juvenile-biased. For the Saimaa seal, the estimates indicate a low population size in 1893, ranging from 100 to 1300 individuals, whereas the carrying capacity of the lake has been estimated to be at least 2000-2500 seals. This result may either indicate that the Saimaa seal was initially less abundant than thought, or that the known hunting statistics simply do not capture the true magnitude of the decline.


Epidemiology of Feline Immunodeficiency Virus within a rural cat population.

Franck Courchamp, Marc Artois, Nigel Yoccoz & Dominique Pontier. 1998. Epidemiology and Infection 121: 227-238.

Abstract:

Prevalence of Feline Immunodeficiency Virus (FIV) infection was measured during six consecutive years in a natural rural population of domestic cats. Sex, age, weight, origin, group size and presence of antibodies to FIV were recorded for each sampled cat. Logistic regressions were used to estimate the influence of the recorded parameters on infection. FIV prevalence rates are as high as 19.6% in the total population, and do not statistically change between years, after controlling for changes in samples age structure. FIV infection is characterized by risk factors linked to aggressive behaviour: old mature male adults having dispersed are more likely to be infected. A study of the cats group size and of the spatial distribution of infected individuals indicates the absence of infection clusters in males, and suggests the importance of roaming in the spreading of FIV. In conclusion, FIV infection spreads, with low contagiousness, mainly between particularly aggressive individuals, and the virus is endemic in this population.


Infection strategies of retroviruses and social grouping of domestic cats.

Emmanuelle Fromont, Franck Courchamp, Marc Artois & Dominique Pontier. 1997. Canadian Journal of Zoology 75: 1994-2002.

Abstract:

It is thought that parasites may exert a selective pressure on the social structure of host populations. We compared the impact of Feline Immunodeficiency virus (FIV) and Feline Leukemia Virus (FeLV), two retroviruses commonly found in domestic cats (Felis catus). Because of low transmissibility and virulence, both infections show a worldwide distribution and low prevalence. Transmission modes differ: FIV is transmitted only through biting, while FeLV transmission occurs by biting, licking, grooming, sharing food and from mother to fetus. FeLV is also more pathogenic than FIV. We compared FIV and FeLV prevalence and risk factors within five populations of cats. FIV infection occurred almost exclusively among adult male cats fighting to acquire and maintain dominant status. At-risk classes for FeLV infection included sexually intact cats allowed to roam freely. The impact of FeLV on host population size was greater than that of FIV but differed between populations. Our results show that FIV is favoured by individual aggressiveness and a hierarchical social system, while FeLV is more prevalent among socially-active cats. FeLV may constitute a selective pressure against numerous amicable contacts, particularly in urban cat populations where aggression among cats is reduced.

Résumé:

Les parasites sont susceptibles d'exercer une pression de sélection sur la structure sociale des populations hôtes. Nous avons comparé l'impact du virus d'immunodéficience féline (FIV) et du virus leucémogène félin (FeLV), deux virus courants du chat domestique (Felis catus). En raison de leur transmissibilité et de leur virulence faibles, les deux infections ont une répartition mondiale et une prévalence faible. Leur mode de transmission diffère: le FIV est transmis seulement par morsure, alors que la transmission du FeLV se produit lors de morsure, léchage, toilettage, partage de plats de nourriture et de la mère au foetus. Le FeLV est également plus pathogène que le FIV. Nous avons comparé la prévalence et les facteurs de risque du FIV et du FeLV dans cinq populations de chats. L'infection par le FIV était rencontrée presque exclusivement chez les mâles adultes, qui se battent pour acquérir et maintenir un statut dominant. Les classes à risque pour l'infection par le FeLV étaient les chats non castrés autorisés à vagabonder. L'impact du FeLV sur l'effectif des populations hôtes était plus important que celui du FIV mais plus variable selon les populations. Ces résultats montrent que le FIV est favorisé par l'aggressivité entre individus et par un système social hiérarchique, alors que le FeLV est plus fréquent chez les chats actifs socialement. Le FeLV pourrait constituer une pression de sélection contre les relations amicales fréquentes, notamment dans les populations urbaines où l'agressivité entre chats est réduite.


Retroviruses and sexual size dimorphism in domestic cats (Felis catus L.).

Dominique Pontier, Emmanuelle Fromont, Franck Courchamp, Marc Artois & Nigel Yoccoz. 1998. Proceedings of the Royal Society of London, Biological Sciences. 265: 167-173.

Abstract:

Hochberg et al. (1992) predicted that an increase in host adult mortality due to parasites is balanced by an earlier age at first reproduction. In polygynous species we hypothesize that such a pattern would lead to diverging selection pressure on body size between sexes and increased sexual size dimorphism. In polygynous mammals, male body size is considered to be an important factor for reproductive success. Thus, under the pressure of a virulent infection, males should be selected for rapid growth and/or higher body size to be able to compete successfully as soon as possible with opponents. In contrast, under the same selection pressure, females should be selected for lighter adult body size or rapid growth to reach sexual maturity earlier. We investigated this hypothesis in the domestic cat Felis catus. Orange cats have greater body size dimorphism than non-orange cats. Orange females are lighter than non-orange females, and orange males are heavier than non-Orange males. Here we report the extent to which orange and non-orange individuals differ in infection prevalence for two retroviruses, Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV). FIV is thought to be transmitted almost exclusively through aggressive contacts between individuals, whereas FeLV transmission occurs mainly through social contacts. The pattern of infection of both diseases is consistent with the higher aggressiveness of orange cats. In both sexes, orange cats are significantly more infected by FIV, and tend to be less infected by FeLV than other cats. The pattern of infection is also consistent with an earlier age at first reproduction in orange than in non-orange cats at least for females. These results suggest that microparasitism may have played an important role in the evolution of sexual size dimorphism of domestic cats.


Dynamics of two feline retroviruses (FIV and FeLV) within one population of cats.

Franck Courchamp, Christelle Suppo, Emmanuelle Fromont & Catherine Bouloux. 1997. Proceedings of the Royal Society of London, Biological Sciences. 264: 785-794.

Abstract:

We present a deterministic model of the dynamics of two microparasites simultaneously infecting a single host population. Both microparasites are feline retroviruses, namely Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV). The host is the domestic cat Felis catus. The model has been tested with data generated by a long-term study of several natural cat populations.
>Stability analysis and simulations show that, once introduced in a population, FIV spreads and is maintained, while FeLV can either disappear or persist. Moreover, introduction of both viruses into the population induces a equilibrium state for individuals of each different pathological class. The viruses never induce the extinction of the population. Furthermore, whatever the outcome for the host population (persistence of FIV only, or of both viruses), the global population size at the equilibrium state is only slightly lower than it would have been in the absence of the infections (i.e
. at the carrying capacity), indicating a low impact of the viruses on the population. Finally, the impact of the diseases examined simultaneously is higher than the sum of the impact of the two diseases examined separately. This seems to be due to a higher mortality rate when both viruses infect a single individual.


Modelling the Feline Leukemia Virus (FeLV) in a natural population of cats (Felis catus).

Emmanuelle Fromont, Marc Artois, Michel Langlais, Franck Courchamp & Dominique Pontier. 1997. Theoretical Population Biology. 52: 60-70.

Abstract:

A compartmental model was built in order to study the circulation and impact of Feline Leukemia Virus (FeLV) in populations of domestic cats. The model was studied and tested with data provided by a long-term study of several feline populations.
The study of stability shows that FeLV is maintained in the population with a stable equilibrium stage, and a slight reduction of the population size. Estimation of the transmission rate shows that the actual value for this parameter may be much higher than previously estimated in the literature. We compared the impact of mass vaccination or removal programmes in controlling FeLV infection, and concluded that the first one seems to be more efficient.


Population dynamics of Feline Immunodeficiency Virus within populations of cats.

Franck Courchamp, Dominique Pontier, Michel Langlais & Marc Artois. 1995. Journal of Theoretical Biology. 175/4 : 553-560.

Abstract:

A deterministic model was constructed to study the circulation of Feline Immunodeficiency Virus (FIV), a feline retrovirus homologous to Human Immunodeficiency Virus (HIV), within populations of domestic cats. The model has been tested with data generated by a long-term study of several natural cat populations.

Simulations and a study of stability show that once introduced, the retrovirus is maintained within the population, with a stable equilibrium stage reached by both numbers of susceptible and infected individuals.
An estimation of parameters indicates that the transmission rate is low and depends of the structure of the population. In addition, FIV has a low impact on the population in that the total number of cats at equilibrium when this virus is present is almost always equal to the habitat carrying capacity in the absence of the virus. These results, in agreement with other observations, suggest the possibility that FIV arose originally some considerable time in the past.


Feline Immunodeficiency Virus: an epidemiological review.

Franck Courchamp & Dominique Pontier. 1994. Compte Rendus de l'Académie des Sciences de Paris, série III, Sciences de la Vie. 317: 1123-1134.

Abstract:

From a synthesis of 59 serosurveys, we estimate and discuss influence of several parameters on Feline Immunodeficiency Virus (FIV) infection.

The overall infection rate estimated from 85,529 tested cats is high, 11.04%, besides the virus seems to be rather endemic. Parameters influencing FIV infection are sex, age and roaming habits. Neutering, breed and group size effects seem to be rather indirect. Prevalence differences between countries and potential cofactors are also discussed.
Results show that FIV transmission is influenced by behavior. We highlight the important bias of this kind of surveys and propose to sample rather natural populations of cats, taking into account their dynamical and ecological parameters. This synthesis highlights arguments in accordance with the hypothesis that FIV is not a recent virus.

Virus de l'Immunodéficience Féline: revue épidémiologique

Résumé:

L'effet de plusieurs paramètres sur l'infection par le Virus de l'Immunodéficience Féline (VIF) est évalué à partir d'une synthèse de 59 études épidémiologiques.
La prévalence globale calculée à partir de 85 529 chat testés est élevée, 11,04%, bien que le virus semble être endémique. Les paramètres influenßant l'infection par le VIF sont le sexe, l'âge et le mode de vie. Les effets de la stérilisation, de la taille du groupe et de la race semblent plutôt indirects. Les différences de prévalence entre pays et les éventuels cofacteurs sont aussi discutés.
Ces résultats indiquent que la transmission du VIF est fortement influencée par le comportement. Nous mettons en évidence les biais importants engendrés par ce type d'études épidémiologiques, et préconisons d'échantillonner plutôt des populations naturelles de chats, en prenant en compte les paramètres dynamiques et écologiques qui les caractérisent. Cette synthèse apporte plusieurs arguments en accord avec l'hypothèse selon laquelle le VIF serait relativement ancien du point de vue évolutif.


Impact of two feline retroviruses on natural populations of domestic cat.

Franck Courchamp, Dominique Pontier, Emmanuelle Fromont & Marc Artois. 1995. Mammalia. 59/4 : 589-598.

Abstract:

We compared the pattern of spread and the impact of two retroviruses, feline immunodeficiency virus (FIV), and feline leukemia virus (FeLV) within natural populations of domestic cats. A four years epidemiological study shows that FIV is present in three studied rural cat populations, whereas FeLV is absent in one out of the three, with no evolution in time for either virus. Factors influencing FIV transmission are directly linked to aggressive behavior, while factors influencing FeLV transmission are rather characteristic of amicable interactions. Results of a deterministic model show that, both infections are maintained in the population as a stable equilibrium between susceptible and infected animals, slightly reduce the number of individuals at equilibrium, and have low transmission rates. Results of a long term dynamical study indicate that the probability of dying from these viruses is low in natural conditions, and that, despite their presence the size and structures of the populations remain stable.
In conclusion, despite FIV and FeLV have different spread patterns (FIV infects and kills at-risk individuals, while FeLV infects individuals more indiscriminately), the impact of both retroviruses on cat populations seems to be low.

Résumé:

Nous comparons la circulation et l'impact de deux rétrovirus félins dans des populations de chats domestiques: le Virus de l'Immunodéficience Féline (VIF) et le Virus Leucémogène Félin (VLF). Une étude épidémiologique de quatre ans indique la présence du VIF dans trois populations étudiées, tandis que le VLF est absent de l'une d'elles, sans évolution de la prévalence des virus. Les facteurs influenßant l'infection par le VIF sont liès aux comportements agressifs, tandis que la transmission du VLF est plutôt caractéristique d'interactions amicales. Les résultats d'un modèle déterministe montrent que les deux virus se maintiennent sous la forme d'un équilibre stable entre individus infectés et sensibles, réduisent sensiblement le nombre d'individus à l'équilibre et ont des taux de transmission lents. Les résultats d'une étude dynamique à long terme indiquent que la probabilité de mourir de l'infection de ces virus est faible en milieu naturel, et que malgré leur présence, la taille et la structure des populations restent stables.
En conclusion, bien que les deux virus aient des modes de circulation différents (le VIF infecte des individus à risque, tandis que le VLeF infecte les individus socialement proches), l'impact de ces deux virus sur les populations de chats semble faible.


Modelling the Feline Immunodeficiency Virus within populations of domestic cats (Felis catus).

Franck Courchamp, Dominique Pontier & Marc Artois. 1995. Journal of Biological Systems. 3/3 : 769-777.

Abstract:

We attempt to model the circulation of the Feline Immunodeficiency Virus (FIV), a retrovirus analogous to the HIV, within populations of domestic cats. Domestic cats exhibit different patterns of population dynamics, social behavior and reproductive strategies. In fact, cats can be either solitary or living in large social groups, with many intermediate states.
The aim of the presented model is to provide a conceptualization of the mechanisms of spread of FIV rather than to be a predictive tool. As one of our goals is to integrate easily new informations when available, and to remain simple and close to the biological reality, parameters, such as sex, age classes and dispersion, have been incorporated successively. This model can also be adapted to different types of cat populations by simple changes, as it could be to other host populations. A study of the stability of the model has been done. Based on available data, values of two parameters has been estimated: the carrying capacity and the transmission rate. Results are in good accordance with biological data.


Le "SIDA du chat" et son virus.

Franck Courchamp, Dominique Pontier, Jean-Marie Legay & Marc Artois. 1994. La Recherche. 94: 890-896.

Résumé:

Parmi les virus proches de celui qui cause le sida (VIH), il en est un, le FIV, qui affecte le chat domestique. Il provoque un syndrome comparable à celui qui est observé chez l'homme. Une estimation indique qu'environ douze millions de chats seraient infectés par ce virus dans le monde, dont un à trois millions en France. Aucun traitement ni vaccin n'étant efficace, une meilleure connaissance du FIV est indispensable pour lutter contre cette maladie, d'autant que certains félins sauvages déjà en voie de raréfaction sont, eux aussi, infectés. En outre, ce virus s'avère un très intéressant modèle d'étude du VIH et des processus d'infection et de destruction des cellules immunitaires.


L'epidemiologie des lentiviroses dans les populations naturelles de felins.

Marc Artois, Franck Courchamp, Emmanuelle Fromont & Dominique Pontier. 1994. Le Point Veterinaire :26(163): 689-694 .

Abstract :

Recent epidemiological studies allow an overview of the demographic importance of FIV infection in wild cat populations. In the domestic cat, infection rates are in the order of 10 p. cent but in certain wildliving felines, they may be as high as 80 p. cent. There still is a lot to be discovered on risk exposure factors and on the limiting role of this kind of virus in ecology. In spite of imcomplete knowledge, the hypothesis may be put forward of a stable balance between the virus and its host populations.


Etude de l'épidémiologie du Virus de l'Immunodéficience Féline dans les populations de chats domestiques (Felis catus).

Franck Courchamp. 1996. Thèse de l'Université Claude Bernard, Lyon I. 263 p.

Résumé:

Le Virus de l'Immunodéficience Féline (VIF) est un lentivirus induisant une immunosuppression létale chez le chat domestique (Felis catus). Le mode de transmission du VIF le plus probable est la morsure, infligée lors de combats.
La dynamique du VIF au sein de populations de chats est étudiée par un modèle mathématique déterministe. Ce modèle montre que lorsque le virus est introduit dans une population, il s'y développe et s'y maintient toujours. L'infection ne mène ni à l'extinction des individus sensibles, ni à celle de la population totale, mais à un état d'équilibre stable des effectifs d'individus sensibles et infectés. Les proportions des effectifs d'individus des différentes classes pathologiques dépendent des paramètres spécifiques de la population considérées. Le modèle montre également que lorsque la population atteint l'équilibre, la réduction de son effectif est faible. Enfin, le taux de transmission, estimé à partir du modèle, est toujours faible, et diffère selon les caractéristiques de la population considérée. La modélisation simultanée de la dynamique du VIF et de celle du virus de la leucose féline montre que deux situations sont possibles: la persistance des deux maladies dans la population, ou celle du VIF seul. Ces deux situations se font également sous la forme d'équilibres stables.
L'étude épidémiologique de quatre populations naturelles de chats domestiques vivant dans des environnements contrastés a également été entreprise. Il s'agit de trois populations rurales comprenant approximativement 60, 250 et 300 chats étudiées pendant une période de quatre ans, et d'une population urbaine de 35 à 75 chats, étudiée pendant trois ans. Des échantillons sanguins ont été prélevés sur des chats capturés au moins une fois par an dans chaque population. Des analyses statistiques ont été menées sur ces résultats sérologiques afin d'étudier la dynamique et la circulation de l'infection par le VIF dans ces populations (simples test t, Chi-deux et test de tendance, tests non paramétriques, Analyse Multiple des Correspondances, Régressions Logistiques, ...). Ces études nous ont permis de valider les résultats théoriques obtenus grâce au modèle mathématique, et montrent que le VIF est toujours présent dans les quatre populations, avec des taux de prévalence stables, de l'ordre de 10%. Les principaux facteurs de risque sont le sexe, le poids, l'âge, les habitudes de vagabondage et le rang hiérarchique: les mâles adultes vagabonds les plus lourds et de rang hiérarchique élevé sont les plus à même d'être infectés. Ceci est principalement dª au mode d'infection par morsure du virus. De ce fait, la probabilité d'infection des individus dépend de leur probabilité de mener des combats, et de leur statut social. Pour les mêmes raisons, le taux de prévalence dépend des caractéristiques sociales de la population. Le modèle mathématique et les résultats des études épidémiologiques, en plus des données de la littérature, montrent qu'actuellement le VIF a un impact faible sur les populations de chats domestiques.


Epidemiological study of Feline Immunodeficiency Virus in populations of domestic cats (Felis catus).

Franck Courchamp. 1996. Ph. D. Thesis, University of Lyon I. 202 p. (version sur article de la thèse classique, en Anglais).

Abstract:

Feline Immunodeficiency Virus (FIV) is a lentivirus that induces lethal immunosuppression in domestic cats (Felis catus). It is thought that FIV is transmitted through bites during fights.
We studied the dynamics of FIV within cat population through a mathematical model that we built. This compartimental deterministic model shows the following. Once introduced in a population, FIV is always maintained. Infection leads neither to the extinction of susceptible individuals nor of the whole population, but to a stable equilibrium stage of susceptible and sensible cats. The proportions of these pathological classes are dependent upon parameters specific to the population. The model also shows that when the population has reached an equilibrium, the reduction of the population size is low. In addition, the transmission rate, estimated throught the model, is always low and differs according to the population. When FIV dynamics is modeled simultaneously with the dynamics of Feline Leukemia Virus, it can be maintained alone, or together with the other virus (which also presents a stable equilibrium of individuals numbers). Theses two possibilities are the only ones encountered in the litterature or on the field.
We also conducted, over a span of three years, epidemiological studies of four natural populations of domestic cats living in contrasting environments: three rural populations of approximately 60, 250 and 300 cats and one urban population of 35 to 75 cats. Blood samples were taken from trapped cats at least once each year in each population, and statistical analyses (simple t, chi-square and non-parametric tests, Multiple Correspondence Analysis, Logistic Regressions, ...) were applied to serological results, to analyze the dynamics and circulation of FIV infections within these populations. These studies permitted us to validate the theoretical results obtained by the mathematical model, and show that FIV is present in all populations, with stable prevalence rates, of approximatively 10%. The main infection risk factors are sex, weight, age, and roaming habits: heavy roaming male adults are more likely than others to be infected. This is mainly due to the fact that FIV is transmitted by bites. Thus FIV infection probability depends on individual fight probability, and of the social status of the cat. Consequently, the prevalence rates depend upon the social characteristics of the population. The results of our mathematical model agree with field epidemiological studies and the literature. All seem to suggest that currently FIV have a low impact on domestic cat populations.