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Feeding Ecology of a Feral Cat Population on a Small Mediterranean Island

E. Bonnaud , K. Bourgeois , E. Vidal , Y. Kayser , Y. Tranchant , J. Legrand
DOI: http://dx.doi.org/10.1644/06-MAMM-A-031R2.1 1074-1081 First published online: 20 August 2007

Abstract

Domestic cats (Felis catus) have been introduced on many islands in the world and are responsible for much damage to native insular faunas. The worldwide success and spread of this opportunistic predator is generally associated with its trophic adaptability. We examined the diet of a long-established feral cat population on a small Mediterranean island through the analysis of 1,219 scats collected during a 4-year period. Our results confirm that feral cats are generalist predators, able to feed on a wide range of prey. However, only a few prey species formed the major part of its diet. Two introduced mammals and a Mediterranean endemic seabird provided 93% of the yearly biomass consumed by cats (ship rats, 70%; wild rabbits, 7%; and yelkouan shearwaters, 6%). Ship rats remained by far the staple prey for cats throughout the year, but the diet of feral cats was more diversified in spring and early summer, frequently including insects, reptiles, and migrant birds. Endemic yelkouan shearwaters were preyed upon most frequently in autumn and winter, that is, during the shearwaters' prelaying period. Because rats provide the majority of the food of cats, they could help to maintain or inflate this alien predator population with deleterious consequences to the endemic shearwater. A cat eradication campaign would help protect the population of shearwaters on this island.

Key words
  • feeding ecology
  • Felis catus
  • feral cat
  • hyperpredation
  • introduced species
  • islands

Island ecosystems are particularly vulnerable to introduced species because they generally have low species diversity, simplified trophic webs, high rates of endemism, and often naïve native species (Fritts and Rodda 1998; Vitousek et al. 1995; Williamson 1996). Most ecosystem damage on islands has been caused by the introduction of a few mammal species that have generally led to the impoverishment of the local flora and fauna through competition or predation (Atkinson 2001; Courchamp et al. 2003).

The domestic cat (Felis catus) is a successful invader of island ecosystems. The spread of domestic cats on islands 1st began in the Mediterranean (Vigne et al. 2004) and afterwards expanded worldwide, with feral cat populations now found from the equator to 54° latitude (Apps 1983; Konecy 1987a). Cats have caused many extinctions and extirpations and are a major driver of biodiversity loss (Bloomer and Bester 1992; Nogales et al. 2004). Therefore, it is important to understand the impacts of feral cats on island ecosystems, particularly by examining their diet and foraging ecology. Diets of feral cats have been the subject of several studies over the last few decades, especially on subantarctic, tropical, and temperate islands (Furet 1989; Nogales et al. 1992; Turner and Bateson 2000). However, few investigations have been carried out on Mediterranean insular ecosystems (Clevenger 1995; Nogales et al. 1992) despite the fact that the oldest signs of domestication of cats were discovered on Mediterranean islands (Vigne et al. 2004) and that these ecosystems often are home to endangered and endemic vertebrate species.

Our study was conducted to examine the feeding ecology of a long-established (not less than 2 centuries) feral cat population on a small northern Mediterranean island now protected by National Park status. General characteristics of the feeding ecology of feral cats were investigated by quantifying the percent frequencies of prey categories in scats in order to determine overall diet composition over a 4-year period. Using these data, we described the annual variation in diet for this introduced apex predator on this multi-species-invaded island. We then focused our analyses on the last 12 months of data to examine seasonal changes in diet composition according to percent frequencies and biomass of prey categories. We calculated the prey species biomass contributing to the diet of cats to estimate the specific importance of each prey in the daily food requirements of cats. Because this island is home to several endangered and endemic animal species, and also to other introduced species and notably rodents, particular attention was given to the presence and abundance of these species as well.

Materials and Methods

Study site.—Our study was conducted on Port-Cros Island (6.40 km2), protected by National Park status since 1964 and located in the northwestern Mediterranean Sea (43°00′N, 6°21′E). This hilly island has a maximum elevation of 196 m above sea level and is 15 km from the mainland. Climate is subhumid, temperate Mediterranean with an average annual rainfall of 776 mm and an average annual temperature of 15.1°C (Levant Island Meteorogical Office, 1973–1997). The 1st human settlement was established during the Neolithic (8000–4800 years ago). Current human activity is limited and restricted to the port area with a village of 40 permanent inhabitants, but more than 100,000 tourists now visit the island each year.

The siliceous island is 80% covered by mixed forests of sclerophyllous oaks Quercus ilex and Quercus suber and pines Pinus halepensis. Other vegetation types include Mediterranean scrublands and some sparse, open grasslands. Port-Cros Island is home to vertebrate species of particular conservation concern, especially Mediterranean endemics or species absent on the continent such as the Tyrrhenian painted frog (Discoglossus sardus), the European leaf toed gecko (Euleptes europaea), Hermann's tortoise (Testudo hermanni), Cory's shearwater (Calonectris diomedea) and the yelkouan shearwater (Puffinus yelkouan)

All nonvolant mammals present on Port-Cros Island were introduced. Cats were introduced at least by the 18th century, whereas ship rats (Rattus rattus) were probably introduced during the Roman period (Cheylan 1984). The wood mouse (Apodemus sylvaticus), the house mouse (Mus musculus), and the wild rabbit (Oryctolagus cuniculus) were, more recently introduced to the island.

Scat collection and prey identification.—The diet of feral cats was studied through scat analysis (Clevenger 1995; Fitzgerald et al. 1991; Konecy 1987b). We opportunistically collected scats from February 2000 to August 2004 on nearly all the island paths. At the beginning of the study, scats were more intensively collected in spring and at the end of summer, but starting in November 2002, scats were collected every 2 months. Because all scats found in the field were removed, we assumed that each sampling set represented the diet of feral cats for the 2 previous months. Scats of cats were dissected, and the contents separated into mammals, birds, reptiles, invertebrates, anthropogenic refuse, and plant material. Scats were analyzed by washing over a 0.5-mm sieve under a stream of hot water and separating all items such as hairs, feathers, bone fragments, teeth, and insect chitin (Furet 1989; Nogales et al. 1988). Each item was then identified and compared to reference materials to determine species within each food category when possible.

Overall diet of feral cats.—We expressed the overall diet of feral cats as the percent frequency of prey in scats, which is the percentage of scats that contained remains of a particular prey species or food category.

Seasonal variation in the diets of feral cats.—We examined seasonal variation in diet based only on the last 12 months of data, that is, from September 2003 to August 2004 (6 sampling sessions), because examinations of scats were analyzed in 2 additional ways: the percent frequency of prey in scats every 2 months, and the consumed biomass provided by each prey species.

To analyze seasonal variations in feral cat diet, we used randomization tests because they allow the comparison of even very small percentages (Manly 1997). First, the percent frequencies of each food category or prey species were compared between all the different sampling periods, using R statistical software (R Development Core Team 2004), to assess if the diet of feral cats fluctuated according to season. Second, percent frequencies were analyzed using 2-group randomization tests (1,000 randomizations) to compare 2 successive sampling periods (PD = observed percentage differences—Manly 1997).

Estimating the biomass consumed daily (DCB) by cats requires counting the number of individuals (NI) for each prey ingested per day and per cat and determining the body mass of each prey (MP—Le Roux et al. 2002). DCB was calculated using the equation: Embedded Image

All identifiable fragments found in each scat were counted and compared to determine the minimum number of individuals of each prey present in each scat. If the fragments of a prey were not countable, all of these were considered to come from a single prey (Fitzgerald et al. 1991; Karl and Best 1982). Because cats usually defecate 1 scat per day (Konecy 1987b), the number of individuals per scat corresponded to the number of individuals ingested per day and per cat (NI). Mean body mass was obtained from the literature for mice, birds, insects, and reptiles. These prey are relatively small, have low intraspecific variation in body mass, and are generally entirely ingested by cats when feeding (Artois et al. 1997).

The body masses for yelkouan shearwaters, ship rats, and rabbits were estimated more precisely on a case-by-case basis. These are heavier prey for which body mass could vary substantially from one individual to another. Following Keitt et al. (2002) and Cuthbert (2003), we estimated that cats eat 50% of the adult yelkouan shearwater weight (mean weight of yelkouan shearwater = 433 g—Bourgeois 2006), leaving behind wings, feathers, and head. Thus, we estimated that a cat consumes 216.5 g of tissue per shearwater.

The ship rats susceptible to feral cat predation have a body mass that ranges from 35 to 295 g (E. Bonnaud et al., in litt.). To estimate the body mass of all the rats eaten by cats, we produced an equation that compares incisor thickness and individual mass for 40 rats trapped in the field. This equation (regression coefficient r = 0.86) was then used to estimate the body mass of rats preyed upon by cats, based on the measurements of all incisors found in scats (E. Bonnaud et al., in litt.).

For the wild rabbit, several studies on the diet of cats have suggested that feral cats prey principally upon juveniles (Jones 1977; Keitt et al. 2002; Mukherjee et al. 2004). This assumption was confirmed in the laboratory because all incisors found in scats were thin, indicating young individuals. Following Alterio and Moller (1997), we assumed that the mean body mass for rabbits found in cat scats was 500 g because this value corresponds to the limit between juveniles and adults. However, based on the contents of scats, we assumed that 546 g of tissue was the maximum biomass consumption per cat and per day on Port-Cros Island. Thus, when rabbit remains were present in scats with other prey species, the mass of rabbit tissue ingested was calculated so as not to exceed this maximum daily biomass: Rabbit biomass consumed = 546 g − sum (mass in grams of all other prey items present).

We estimated trophic niche breadth for feral cats from relative prey category frequencies using Levins B index (Cavallini and Nordi 2005). All field procedures followed guidelines approved by the American Society of Mammalogists (Animal Care and Use Committee 1998).

Results

Overall diet of feral cats.—During the more than 4-year sampling period, 1,219 cat scats were collected from paths on Port-Cros Island and their composition was analyzed (Table 1). Almost all cat scats (94%) contained mammal remains. Birds occurred in 14% of scats (22 bird species), whereas reptiles appeared in 10% (1 species) of scats and insects in 11% (3 orders). Plant material was commonly found (present in 25% of samples) and anthropogenic refuse was found in only 6% of cat scats, but these 2 food categories were not further consider because of their low energetic resources. Cory's shearwater, bats, and amphibians were not present in any scats examined. Cats on this small island incorporated most of the available animal species into their diet, but they specialized on only a few, especially introduced mammals and yelkouan shearwaters. Only 3 species of mammals were found in the scats. Rats were most frequently encountered (80%), followed by the wood mouse (39%) and the rabbit (4%). The yelkouan shearwater, found in 4.7% of cat scats, was the bird species most frequently encountered.

View this table:
Table 1

Overall diet composition of Felis catus on Port-Cros Island, expressed in frequency occurrence of prey categories found in cat scats from February 2000 to August 2004 and from August 2003 to August 2004.

Food categoriesFebruary 2000–August 2004 (1,219 feces analyzed)August 2002–July 2003 (302 feces analyzed)August 2003–August 2004 (386 feces analyzed)
Mammals94.0989.0794.30
Rattus rattus79.2575.1780.31
Apodemus sylvaticus38.8030.7937.82
Oryctolagus cuniculus4.103.978.81
Unidentified3.774.300.78
Birds13.8624.1710.88
Puffinus yelkouan4.686.625.18
Other birds9.1917.555.70
Unidentified3.937.283.37
Unindentified passerine1.894.641.04
Phoenicurus sp.0.41
Phoenicurus phoenicurus0.411.320.52
Troglodytes troglodytes0.410.33
Jynx torquilla0.16
Sylvia melanocephala0.160.33
Sturnus sp.0.160.26
Unindentified shorebird0.16
Erithacus rubecula0.160.33
Turdidae0.160.66
Turdus merula0.160.330.26
Turdus philomelos0.160.66
Calidris sp.0.160.33
Rallidae0.160.330.26
Gallinago sp.0.08
Sylvia sp.0.08
Sylvia atricapilla0.08
Streptopelia sp.0.08
Larus sp.0.08
Alaudidae0.08
Parus major0.08
Caprimulgus europaeus0.080.33
Coturnix coturnix0.080.26
Luscinia megarhynchos0.080.26
Phasianidae0.080.33
Reptiles9.9812.254.40
Podarcis muralis8.599.602.85
Unidentified1.392.651.55
Insects11.4618.215.44
Plant material24.8017.2232.38
Anthropogenic refuse6.068.944.66

During the last year of the sampling period (August 2003–August 2004), the diet of the feral cat population exhibited very similar characteristics compared to the entire 4-year period (Table 1). However, only the last 2 years (August 2002–July 2003 and August 2003–August 2004) could be compared statistically because they were strictly conducted using the same sampling protocol. When all food categories were taken into account, these 2 years were significantly different (χ2 = 72.49, d.f. = 5, P < 0.001). However, for the most frequent prey, mammals and yelkouan shearwaters, these 2 years were not significantly different (χ2 = 6.36, d.f = 3, P > 0.5). We thus concluded that there was little variation between years.

More precise subsequent investigations were only conducted on data from the last year of sampling (n =386 scats), that is, from August 2003 to August 2004.

Seasonal variation in the diet of feral cats.—The percent frequencies of different food categories in cat scats were significantly different among the 6 periods of the last year of sampling (randomization test with 1,000 iterations, P =0.042). Broadly speaking, the trophic niche breadth of feral cats was wider in spring and early summer, as estimated from the Levins B index (Table 2). Thus, the diet of cats changes seasonally, probably in relation to prey availability.

View this table:
Table 2

Number of prey found in feral cat scats in each sampling period and mean weight of each prey species ingested by cats on Port-Cros Island from July 2003 to August 2004. The Levins B index also is indicated.

No. prey found in scat/period
July–September 2003September–December 2003December–February 2003February– April 2004April–June 2004June–August 2004
Prey(72 scats)(39 scats)(80 scats)(49 scats)(61 scats)(85 scats)Weight (g)Reference
Mammals108509688105159
Rattus rattus764170395387149.6aThis study
Apodemus sylvaticus279214248608.8Michaux 1996
Oryctolagus cuniculus5057412500.0aAlterio and Moller 1997
Birds28183141
Puffinus yelkouan268121433aBourgeois 2006
Other birds015160
Unidentified passerines00112036.5Snow and Perrins 1998
Rallidae001000221.0Snow and Perrins 1998
Phoenicurus00200015.0Snow and Perrins 1998
phoenicurus
Turdus merula00002095.0Snow and Perrins 1998
Luscinia megarhynchos00002021.0Snow and Perrins 1998
Coturnix coturnix010000104.0Snow and Perrins 1998
Sturnus sp.001000155.0Snow and Perrins 1998
Reptiles021225
Podarcis muralis02122510.0Snow and Perrins 1998
Insects1010009
Coleoptera (Cetonia)1100026.3Lepley et al. 2004
Orthoptera7000041.7Fitzgerald and Karl 1979
Homoptera (Cicada)2000030.7Fitzgerald and Karl 1979
Total1206011092115174
Levins index2.1711.9962.2182.5342.5572.651
  • a See “Materials and Methods.”

Mammals were the predominant food category (Fig. la) with high and constant percent frequencies all year long (89.7–98.6%), even though a significant increase was detected when comparing the December–February and February–April periods (PD = −0.1, P = 0.007). The ship rat was the predominant mammal in all seasons (Fig. 1 b).

Fig. 1

Frequency of occurrence of the different food categories in the scats of Felis catus on Port-Cros Island for the 6 sampling periods between September 2003 and August 2004. a) Six food categories; b) mammals; and c) birds. Number of scats per period: August–September, 72; October–November, 39; December–February, 80; February–April, 49; April–May, 61; and June–July, 85.

Birds were the 2nd most frequently eaten prey category for most of the year. A peak in predation on birds occurred during the October–November, December–February, and April–May periods, corresponding to the passage of migratory birds, although a significant difference was found only between the April–May and June–July periods (PD = 0.1, P = 0.010). The yelkouan shearwater was singled out among bird species because it is the most common bird preyed upon and is of conservation concern. A clear peak in predation on yelkouan shearwaters (Fig. 1 c) occurred during autumn (the October–November and December–February periods), with a significant increase in percent frequencies in scats between the August–September and October–November periods (PD = −0.1, P =0.031).

Reptiles were consistently but infrequently consumed throughout the year (Fig. 1 a) with a slight increase during early spring (the February–April period). Presence of insects in cat scats decreased significantly between the August–September and October–November periods and increased significantly between the April–May and June–July periods (PD = 0.1, P =0.029 and PD = −0.1, P = 0.008, respectively).

On a year-round basis, feral cats on Port-Cros Island consumed a mean daily prey biomass of 201.2 g ± 17.7 SD (Fig. 2), ranging from 171.6 ± 118.6 g in the April–May period to 227.3 ± 113.3 g in the October–November period. Ship rats provided by far the predominant part (70%) of the biomass consumed throughout the year (minimum 57.9% in the February–April period, maximum 82.0% in the October–November period). Although infrequently preyed upon, rabbits represented the 2nd most consumed prey in terms of biomass (annual mean: 17.2%), especially in early spring (the February–April period: 31.4%) and early summer (the June–July period: 30.8%).Wood mice were most frequently found in cat scats in spring and early summer (the February–April, April–May, and June–July periods), but represented a low part of the biomass consumed (annual mean: 5.1%).

Fig. 2

Percent contribution of each prey category during the 6 sampling periods on Port-Cros Island between September 2003 and August 2004. The total biomass (g) is given above each bar. Insects and reptiles were too few to be shown on this figure.

Following mammals, birds were the 2nd most consumed food category in terms of biomass. Biomass of birds in the diet of feral cats was primarily represented by the yelkouan shearwater (annual mean: 6.1%), especially during the peak in predation occurring from October to February (the October–November period: 14.7%, and the December–February period: 11.4% of the biomass consumed). This makes the yelkouan shearwater the 3rd major prey item of feral cats in terms of biomass consumption, after the ship rat and the wild rabbit. Other prey categories (reptiles and insects) contributed only slightly to the daily biomass consumed by cats.

Discussion

Overall diet of feral cats.—Our study supported the common observation that feral cats are highly generalist predators, able to feed on prey ranging from small insects to birds and mammals that weigh more than 500 g (Nogales and Medina 1996; Tidemann et al. 1994; Turner and Bateson 2000). However, cats can specialize on what is available and only a few species represented the majority of its diet. This study demonstrates the adaptability of feral cats to different insular environments.

On Port-Cros Island, introduced mammals (rodents and rabbits) formed the most frequent prey of feral cats. This was consistent with observations made on other islands in the world (Fitzgerald et al. 1991; Furet 1989; Pontier et al. 2002). In general, when rabbits and rodents are simultaneously present on islands, rabbits are the predominant prey for cats (Apps 1983; Jones 1977; Pontier et al. 2002). However, because Port-Cros is a highly forested island, rabbits are found in very low densities; this may explain why rabbits occurred in lower frequency in scats (4%) compared to ship rats (79%) on our study site. The 2nd most frequent prey category found in cat scats in our study was birds, primarily represented by the yelkouan shearwater. Seabirds, especially small and medium-sized procellariids, are known to be very vulnerable to introduced predators because they have generally not developed the defenses or shunning behavior necessary to escape from introduced predators (Stattersfield and Capper 2000; Warham 1996). Species from the genus Puffinus in particular are known to be frequent prey for medium-sized predators, especially cats (Cuthbert 2003; Keitt et al. 2002; Martinez-Gomez and Jacobsen 2004). Most of the other bird species that could be identified in cat scats were small passerine species, both resident and migrant. Reptiles and insects appeared only in low frequencies in the diet of feral cats. This pattern was frequently reported for many sites around the world, but occasionally these prey can be locally abundant and consumed in large numbers by feral cats (Berruti 1986; Tidemann et al. 1994). The percent frequencies of anthropogenic refuse in cat scats were very low, confirming that on Port-Cros Island the feral cat population was not dependent on human food sources.

Seasonal variation in the diet of feral cats.—The diet of feral cats varied significantly (randomization test with 1,000 iterations, P = 0.042) among the six 2-month periods in 2003–2004. The diet of feral cats was more diversified in spring and early summer (the February–April, April–May, and June–July periods) with more frequent predation on birds (except yelkouan shearwater), reptiles, and insects, compared to the late summer through winter (the August–September, October–November, and December–February periods), which were characterized by a higher percent frequency of occurrence of ship rats and yelkouan shearwaters (Fig. 2). Feral cats on Port-Cros Island may adjust their diet according to prey availability. This opportunistic feeding behavior has been reported to facilitate the settlement and the persistence of feral cat populations on islands (Apps 1986; Pontier et al. 2002). However, some general patterns described in several other insular populations were highlighted by the present study. Mammals, that is, introduced rodents and rabbits, were the most frequent food category found in the diet of feral cats all year long, whereas birds were the 2nd food category in percent frequencies during the October–November, December–February, and April–May periods. Introduced ship rats were the most frequent prey species throughout the year, which is a common pattern found in diets of feral cats (Karl and Best 1982).

Patterns of cat predation upon yelkouan shearwaters also can be explained by an adjustment in diet composition according to prey availability and diversity. Even if predation upon yelkouan shearwaters was detected throughout the year, a clear peak in predation occurred in autumn and in the beginning of winter (the December–February and February–April periods). This period, which corresponds to the prelaying stage of the yelkouan shearwater breeding cycle, is characterized by intense activity of both nonbreeders, vocalizing on the ground outside burrows during long periods of nights, and breeders, preparing their burrows and reuniting with their mates (Mougeot and Bretagnolle 2000; Ristow 1998; Warham 1996). Moreover, yelkouan shearwaters, like many seabirds, are awkward on land and therefore they are easy prey. Thus, these birds are likely easier to catch and represent an abundant and nutritious prey (433 g) during this cold period when the energy requirements of predators are probably high and other food sources particularly scarce. Later in the year, nonbreeders are less numerous and breeders spend less time on the open ground while they are incubating or feeding their chicks, thus other bird species became more prevalent in the diet.

The biomass ingested daily provided a more complete representation of the diet than the percent frequencies of prey items in scats, because neither the number of individual prey nor their weight are taken into account by percent frequencies (Le Roux et al. 2002; Moleon and Gil-Sanchez 2003; Nogales and Medina 1996). The daily biomass consumption by cats on Port-Cros Island, calculated to be 201.2 ± 17.7 g on a yearly average, agreed with values given by other studies (Keitt et al. 2002). Ship rats represent 70.4% of the entire yearly biomass consumed by cats. Moreover, the biomass represented by rats in the diets of feral cats never fell below 57%. Consequently, ship rats should be considered as a primary prey for feral cats, largely contributing to the survival and persistence of this top predator in a small Mediterranean island environment. Although the percent frequencies of wild rabbit appeared low in cat scats, this heavy species provided a significant part of the daily food intake by feral cats (17.2%), especially during spring and early summer (the February–April, April–May, and June–July periods). In comparison, wood mice were quite frequent in cat scats, but their proportion of the biomass ingested (5.1%) was much smaller because of the small size of the species. The yelkouan shearwater represented 6.1% of the yearly biomass consumed by cats and this value was greater than for all the other bird species. Yelkouan shearwaters provided one-seventh of the total biomass consumed during peak predation period.

Implications for conservation.—Five vertebrate species of particular conservation interest are present on Port-Cros Island and represent potential prey for feral cats: 2 shearwater species, a terrestrial tortoise, a gecko, and an amphibian. Among them, only the yelkouan shearwater appeared among the 30 prey types identified in the 1,219 cat scats that were collected and analyzed over the 4-year study. The absence of these reptile and amphibian remains was quite intriguing, even if for one of them, the terrestrial tortoise, the low abundance of this population could explain this absence. However, the presence of cats is still a threat for all of these species. The strong negative impact of predation by cats on seabird population dynamics is well known and several studies have demonstrated that some shearwater populations cannot survive in the presence of this predator (Jones 2002; Keitt et al. 2002; Martinez-Gomez and Jacobsen 2004). Although there are many factors that can contribute to the endangerment of Port-Cros shearwater populations, this study suggests that removal of feral cats from the island could benefit shearwater conservation (Keitt and Tershy 2003; Nogales et al. 2004). Because introduced ship rats provided a year-round abundant food resource that probably facilitates the maintenance and persistence of cat populations on this small and resource-poor island, these cat populations could subsequently depredate yelkouan shearwaters: a process known as “hyperpredation” (Courchamp et al. 1999b). There also is a concern that, after cat eradication, a rise in the population of rats could lead to a further increase in predation on yelkouan shearwaters (Courchamp et al. 1999a). A way to address the cat and rat interaction problem could be to simultaneously target both cats and rats in an eradication campaign. Subsequent monitoring of the different ecological components would be required during and after the eradication campaign to detect and avoid unexpected secondary effects (Zavaleta et al. 2001).

Acknowledgments

We are very grateful to the Director and managers of Port-Cros National Park for granting permission and providing support for this research, and to all those from IMEP, LPO PACA, and Port-Cros National Park who helped us during field work (especially H. Berger and S. Dromzée). We also thank F. Torre and P. Roche for helping with statistical analyses and C. Suehs for improving the English. We are grateful to C. J. Donlan and 3 anonymous referees for their helpful comments on previous drafts of this manuscript. Funds and support were provided by the Port-Cros National Park (contracts 03 011 83400PC and 05.013.83400PC), the Conseil Régional PACA (contracts 2002-01625 and 2003-15028), the European Union, and the DIREN PACA via a Life Nature project (LIFE03NAT/F000105). This work was supported by a CR PACA Ph.D. fellowship to EB.

Footnotes

  • Associate Editor was Rodrigo A. Medellín.

Literature Cited

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