Mastozoología Neotropical ISSN: 0327-9383 [email protected] Sociedad Argentina para el Estudio de los Mamíferos Argentina
Fernández, Alfonso; Sáiz, Francisco The european rabbit (Oryctolagus cuniculus L.) as seed disperser of the invasive opium poppy (Papaver somniferum L.) in Robinson Crusoe Island, Chile Mastozoología Neotropical, vol. 14, núm. 1, enero-junio, 2007, pp. 19-27 Sociedad Argentina para el Estudio de los Mamíferos Tucumán, Argentina
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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Mastozoología Neotropical, 14(1):19-27, Mendoza, 2007 ISSN 0327-9383 ©SAREM, 2007 Versión on-line ISSN 1666-0536 www.cricyt.edu.ar/mn.htm THE EUROPEAN RABBIT (Oryctolagus cuniculus L.) AS SEED DISPERSER OF THE INVASIVE OPIUM POPPY (Papaver somniferum L.) IN ROBINSON CRUSOE ISLAND, CHILE
Alfonso Fernández1 and Francisco Sáiz2
1 Instituto de Agrobiotecnología y Recursos Naturales, Universidad Pública de Navarra, Campus de Arrosadía sn, 31006, Pamplona, Navarra - España. Teléfono (34) 948362629
ABSTRACT: We investigated whether introduced European rabbit on Robinson Crusoe Island, Chile, has the potential to spread the seeds of the exotic Papaver somniferum (opium poppy) via endozoochory. A total of 1320 rabbit droppings were collected during early autumn in the study area and analyzed in laboratory with binocular magnifying glass. Seeds from six different species were found in the droppings: Papaver somniferum (Papaveraceae), Centaurea melitensis (Asteraceae), Amaranthus sp. (Amarantaceae), Melilotus indicus (Fabaceae), Rumex acetosella (Polygonaceae), and one unidentified species. Poppy seeds were dominant. Most seeds (82%) were destroyed during ingestion, but some of the intact seeds found in pellets remained viable. Germination rate of ingested seeds was similar to control seeds but germination success was lower in the former. Poppy seeds were found in pellets deposited inside poppy patches but also up to 100 m away from patches. In this way, rabbit expands the seed shadow of the plant. Our results suggest that, although poppy lacks morphological adaptations to long distance dispersal, seeds reach favor- able places for seedling germination and recruitment via consumption by rabbits, an unspecialized seed disperser. Rabbit activity, together with the effect of other animals and some abiotic factors—wind and rain water, principally—contributes to the spread of poppy with implications for the management of both invasive species in the island.
RESUMEN: El conejo europeo (Oryctolagus cuniculus L.) como dispersor de la amapola de opio (Papaver somniferum L.) en la isla de Robinson Crusoe, Chile. Se ha investigado si el conejo europeo, introducido en la isla de Robinson Crusoe, Chile, tiene capacidad para dispersar semillas de la amapola del opio (Papaver somniferum) vía digestiva. Se recolectaron 1320 fecas a comienzos de otoño en el área de estudio y fueron analizadas en laboratorio con lupa binocular. Se encontraron semillas de seis especies: Papaver somniferum (Papaveraceae), Centaurea melitensis (Asteraceae), Amaranthus sp. (Amarantaceae), Melilotus indicus (Fabaceae), Rumex acetosella (Polygonaceae) y una no identificada. Las semillas de amapola fueron las más numerosas. La mayoría de las semillas (82%) fueron destruidas durante la ingestión, pero algunas de las que aparecieron intactas en las fecas se mantuvieron viables tras el tránsito por el aparato digestivo. La tasa de germinación de las semillas ingeridas fue similar a la de las semillas control, pero el éxito germinativo fue menor en las primeras. Se encontraron semillas de amapolas en fecas depositadas dentro de las manchas de amapola pero también en fecas depositadas hasta 100 metros de distancia. Por lo tanto, el conejo expande semillas de esta planta. Nuestros resultados sugieren que, a pesar de que la amapola carece de adaptaciones morfológicas específicas para la dispersión a larga distancia, sus semillas pueden alcanzar lugares favorables para la germinación y establecimiento a través del
Recibido 5 abril 2006. Aceptación final 9 febrero 2007. 20 Mastozoología Neotropical, 14(1):19-27, Mendoza, 2007 A Fernández and F Sáiz www.cricyt.edu.ar/mn.htm
conejo, un dispersor no especializado. La actividad del conejo, junto al efecto de otros anima- les y de algunos factores abióticos, principalmente el viento y la lluvia, contribuyen a la expansión de la amapola con implicaciones para el manejo de ambas especies invasoras en la isla.
Key words. Endozoochory. Gut passage. Invasive species. Seed dispersal.
Palabras clave. Dispersión de semillas. Endozoocoria. Especies invasoras. Tránsito intestinal.
INTRODUCTION The role of European rabbit (Oryctolagus cuniculus) as seed disperser has been studied The accidental or voluntary introduction of from a quantitative perspective mainly in species by humans has removed biogeographic mediterranean continental environments barriers for many organisms which can reach (Soriguer, 1986; D’Antonio, 1990; Zedler and new regions, beyond the limits of their own Black, 1992; Muñoz, 1993; Malo and Suarez, historical dispersal capabilities (Everett, 2000). 1995; Nogales et al., 1995; Cervan and Pardo, Human-facilitated biological invasions are an 1997). These works lead to the general con- increasing world-wide environmental concern, clusion that rabbit acts as a non-specific dis- as invasive species alter ecosystem processes perser of dry, small (<1mm) seeds (Malo et al., and cause functional and compositional 1995). Some studies dealt with the influence of changes in the biota, becoming a long-term rabbit dispersal on the structure and dynamics of conservation problem when native species are these communities (Zedler and Black, 1992; displaced (Ramakrishnan and Vitousek, 1989; Malo et al., 1995). However, its role as seed Vitousek, 1997). Furthermore, new evidence disperser in insular ecosystems where it has been suggests that the main factors driving global introduced remains largely unknown, although it change (i.e., increased atmospheric CO2 con- is of prime conservation interest. centration, climate change, habitat fragmenta- The prolonged evolution in isolation in re- tion) are likely to increase the frequency of mote oceanic island ecosystems has led to the biological invasions (Dukes and Mooney, existence of very singular floras and faunas 1999). Still, the expansion rate of an intro- (Crawford et al., 1987). These fragile ecosys- duced plant species is conditioned, among tems are particularly vulnerable to biological other factors, by its dispersal mechanisms invasions (Fritts and Rodda, 1998; Bergstrom (Rejmanek and Richardson, 1996). and Chown, 1999). The aim of this investiga- Dispersal of seeds via the digestive tract of tion was to assess the importance of rabbit as herbivores endozoochory has long been known seed disperser of the exotic opium poppy (Pa- (Ridley, 1930). The coevolutionary implica- paver somniferum) in Robinson Crusoe Island, tions of endozoochory have been discussed at off the Chilean coast, where the poppy has length but almost exclusively for species with been introduced and is currently perceived as fleshy fruits (Janzen, 1980, 1983; Herrera, a potential soil protector (Cuevas and van 1985, 1995). Species conventionally classified Leersum, 2001). Specific goals of the study as unspecialized regarding the dispersal mecha- were to detect and quantify: 1, poppy seeds nism have received less attention, although they consumption by rabbit; 2, distance dispersal may have morphological adaptations for by rabbit; and 3, seed viability. endozoochorous dispersal such as small size and a hard coat (Bruun and Poschlod, 2006). MATERIAL AND METHODS Even in the absence of conspicuous morpho- logical adaptations, endozoochory may become The case of Robinson Crusoe island an efficient mechanism for the spread of non- as a conservation problem native species into new environments Robinson Crusoe Island contains one of the most (D’Antonio, 1990). interesting island floras on the planet (Stuessy et POPPY SEED DISPERSAL BY RABBIT IN A CHILEAN ISLAND 21
al., 1992). This singular flora comprises 131 en- Bautista village. Climate is Mediterranean with demic species (62% of the vascular native flora), intense oceanic influence; mean annual tempera- 12 endemic genera and 1 endemic family ture is 15.4 ºC and total precipitation is 890 mm. (Marticorena et al., 1998). However, 400 years of However, the extremely rough topography gener- human interference including repeated burning, ates strong microclimatic differences in short dis- overgrazzing an introduction of animal and plant tance (Cereceda et al., 1994). As a consequence, species have left deep traces in the native plant two main environments can be distinguished in the communities. Nowadays, 212 introduced plant island. The relatively mesic NE zone, with highest species occupy the island (Marticorena et al., 1998), altitudes and woody vegetation, and the SW zone 73% of the endemic vascular flora has been taken (our study area), a semi-arid biome where vegeta- to the verge of extinction, and many native herbs tion today consists mainly of a impoverished grass- have been replaced by invasive species (Matthei et land of introduced weeds including Erodium al., 1993; Stuessy et al., 1998). These factors have cicutarium, Hordeum murinum, Acaena argentea, great impact at all conservation levels including ge- Anthoxanthum odoratum, Centaurea melitensis netic, populational, specific, and at community levels and Conium maculatum (for more information (Pimm, 1987; Ramakrishnan and Vitousek, 1989). on exotic vegetation see Matthei et al., 1993). One of the most important conservation prob- Native species such as Dendroseris pruinata, D. lems in the island is the high density of European marginata and Wahlenbergia berteroi have al- rabbit (Oryctolagus cuniculus), with 20-22 rabbits most disappeared (Stuessy et al., 1998). In this per hectare and a total population of ca. 50 000 zone, soils are highly eroded as a consequence individuals (Cuevas and van Leersum, 2001). This of topography and overgrazing by cattle and rab- small herbivore is responsible for overgrazing of bits. Overall, about 40% of the island is affected native flora in those habitats where it has been by severe or extremely severe erosion (Cuevas introduced, as is the case in other oceanic islands and van Leersum, 2001). (Flux and Fullagar, 1992; Towns et al., 1997; Pridell et al., 2000). The rabbit was introduced in Rabbits and livestock Robinson Crusoe in 1935 (Jacksic, 1998) and since then it has occupied the entire area of the island. Livestock population greatly exceeds carrying The rabbit has caused great damage on prairie veg- capacity of the island and concentrates in the SW etation raising erosion risk (Cuevas and van area, where rabbit densities are also highest (Sáiz, Leersum, 2001). Despite its importance as a men- 1999). Rabbits eat seedlings of native and invasive ace to habitat integrity, information about the bi- species and erode the hillsides with their extensive ology and ecology of rabbit in the island is still warrens (Acevedo, 1990). These factors, combined very scarce. with other natural erosion factors such as precipi- Opium poppy (Papaver somniferum, L.) was tation, strong wind, steep slopes, and soils with introduced in 1980 (pers. obs.) in the aerodrome low water retention capacity, have led to the gradual area as ornamental. Since then it has widely ex- impoverishment of soils, one of the most impor- panded its range over the Western sector of the tant conservation problems nowadays (Cuevas and island, where rabbits occur in higher densities. van Leersum, 2001). Although it may protect the soil from erosion, it Opium poppy (Papaver somniferum L.) has the potential to displace native species (Cuevas and van Leersum, 2001). One of the most recently introduced weeds in the island is the opium poppy. Papaver species are Physical features of the study area considered highly invasive weeds, characteristic of Robinson Crusoe island is located in the Pacific disturbed habitats, roadsides and cultivate land Ocean, some 670 km West off the Chilean coast (Hanf, 1983). Papaver somniferum is an annual (Juan Fernández archipelago – Chile; 78º 51’ W, herb, toxic or narcotic that contains more than 25 33º 45’ S). This small island (47.9 km2) of volca- alkaloids which make the poppy unpalatable for nic origin (4.5 million years) presents a very rough most herbivores (Mattson, 1980). The fruit is a topography with less than 3% of the surface below capsule in the end of a long (ca. 1 m) stalk, and 15% inclination. Maximum altitude is 915 m a.s.l. houses many small seeds (0.5 mm aprox.) with no at El Yunque. The island has been protected as a evident morphological adaptation for dispersal. National Park since 1935, and it was declared Seeds fall just below the plant from dehisced cap- World Biosphere Reserve by the UNESCO in 1977. sules and become dormant, showing a long drawn Local human population is 500, all in San Juan out sequence of seedling emergence. As a conse- 22 Mastozoología Neotropical, 14(1):19-27, Mendoza, 2007 A Fernández and F Sáiz www.cricyt.edu.ar/mn.htm quence, the plant shows a contagious distribution cases, samples were labeled, preserved dried in pa- in patches of variable size (Hanf, 1983). per bags and individually analyzed in laboratory.
Sampling design and data collection Fecal analysis A subsample (n = 30) of randomly chosen feces Feces were collected in autumn 2001 just before from those collected at each point from both sam- the rainy season. Two sampling procedures were pling regimes (a and b above) were individually carried out in order to (a) quantify and compare searched for poppy seeds using a binocular mag- the presence of seeds in rabbit feces collected in- nifying glass. Previous estimates showed that the side and outside poppy patches, and (b) evaluate volume 30 feces occupy once grounded is ca. 50 the dispersal distance of seeds in feces. cm3; this made a baseline comparison for soil a. Fecal sampling stations (n = 10) were se- samples. Poppy seeds are easily detected due to lected in the study area. Each station consisted of their dark colour, small size and reticulated sur- an isolated poppy patch surrounded by grassland. face. They were counted and measured to the near- Feces (50 approximately) were collected randomly est 0.01 mm. Three seed categories were distin- both inside and outside patches, 25 m away in the guished: (i) whole, not damaged after gut passage; direction of the slope, which was considered the (ii) unviable, totally or partially digested; (iii) frag- most probably dispersal direction. In addition, a ments of seeds destroyed during the process. In soil sample of 50 cm3 (see below) was taken inside this later case, the following ratio was fixed a priori and outside patches close to the fecal collection for seed quantification: 3 fragments = 1 seed in- spot. Poppy seeds were also collected directly from gested. Seeds from species other than poppy found plants as controls for germination experiments. in feces were preserved and, if they could not be Additional separate stations (n=4) were sampled in identified directly, they were sown and growth until the same way in order to detect seeds of other seedling was identified. weed species (Acaena argentea, Conium maculatum, Silybum marianum and Centaurea Germination experiments melitensis) in rabbit feces. Results from these last A germination test of three treatments, namely stations were not included in poppy analysis but control from plants, seeds from soil bank, and used in determining the general spectrum of seeds undamaged seeds from feces, was carried out with found in rabbit feces (Table 1). n = 135 for each treatment. Seeds were planted b. Distance transects (n = 4). In each of four of individually in sown-trays with sterile substratum the poppy sampling stations a distance sampling (pine bark) and maintained under controlled con- transect was conducted. Rabbit feces (ca. 50) were ditions (22ºC and ambient light) until no further collected in the border of the patch and outside germination was detected in controls (35 days). every 25 m along a transect up to 100 m away in Before sowing, seeds were measured individually. the direction of the slope. A soil sample (50 cm3; Germination experiments with other species found see below) was also taken at each distance. In all in feces were also conducted in the same manner.
Table 1 Number (n) and size ± sd (mm) of seed species found in feces. Germination experiments results are also given. (n: number of whole seeds; Sown: number of seeds sown; % Germ: percentage of seeds germinated). Differences in frequencies of germinated seeds (feces vs. soil) were tested by Chi-square test. * p < 0.05; ** p < 0.01.
Species n Size Percentage germinated In feces In soil
Papaver somniferum 582 0.79 ± 0.76 6 16 * Centaurea melitensis 41 2.23 ± 0.61 32 32 n.s. Amaranthus sp. 15 0.90 ± 0.31 25 67 ** Melilotus indicus 23 1.44 ± 0.25 15 20 n.s. Rumex acetosella 20 0.62 ± 0.08 10 40 ** Undetermined 15 1.2 ± 0.35 - - POPPY SEED DISPERSAL BY RABBIT IN A CHILEAN ISLAND 23
Statistical analyses seeds (82%) were physically destroyed by ingestion while 18% were whole, probably 2 Normality of data was tested with Kolmogorov- viable seeds (E = 1267; d.f. = 1; p<0.001). Smirnov and Lilliefors methods. Chi-square test Total number of whole seeds in feces collected was used to check differences in expected frequen- in the center of patches (n = 241) was sig- cies of seeds found in feces (with Yates correction nificantly higher than in feces collected 25 for continuity) and frequencies of germinated seeds. m away from patches (n = 105; 300 feces Parametric t-tests were used for comparison of seed 2 sizes. ANOVA was used to check differences analyzed in each location; E = 52.67; d.f. = among sizes of plant and soil seeds and whole 1; p < 0.01). The mean (± SD; range) number seeds from feces and, when significant, a poste- of whole seeds found in positive droppings riori Tukey test was employed for two by two com- was 2.33 (± 2.35; 1-15) inside patches and parisons of means (Sokal and Rohlf, 1981). Ger- 2.05 (± 1.55; 1-8) outside. mination cumulative distributions of the different treatments were analyzed with non-parametric Distance dispersal Kolmogorov-Smirnov test. All analyses were per- The limited dispersal capability of poppy formed using STATISTICA v. 4.5 (Stat Soft, 1995). seeds is reflected by the fact that, for both a and b sampling designs (see Methods), only RESULTS 10 seeds were found in soil samples 25 m A total of 1320 feces were analyzed from both away from poppy patches while a much higher sampling schemes; 1080 of them were col- number (651 seeds) was found in samples lected in poppy sampling stations, 39% inside collected inside patches. A total of 582 whole patches and 61% outside. All whole seeds (n seeds were found in rabbit feces analyzed. = 696) belonged to five invasive weeds plus Therefore, seeds were significantly more nu- 2 one unidentified species (Table 1). Papaver merous in soil samples than in feces (E = somniferum seeds were dominant (84%) and 4.48; d.f. = 1; p < 0.05), likely reflecting a only this species is considered in further analy- cumulative history of deposition. However, the ses. presence of an important number of seeds in feces outside patches is again verified. Feces Poppy seed dispersal collected inside patches contained a total of Poppy seeds were present in 44% (n = 473) 338 whole poppy seeds, while as many as 244 of feces. A similar proportion of positive fe- seeds came from feces outside patches, even ces were collected inside patches (49%) and 100 m away from the patches (Table 2). outside patches (51%). From these positive feces, 231 (49%) were collected inside patches Germination and viability of poppy seeds and 242 (51%) outside. Differences in mean size across the three On the assumption of a 3:1 ratio of types of seeds used in germination experiments fragment:whole seed, a total of 3168 seeds (i.e. control seeds from plants and soil samples were removed from feces. The majority of and whole seeds from feces) were significant
Table 2 Pooled number of P. somniferum whole seeds found in rabbit feces and in soil samples at varying distances away the center of poppy patches (n= 4 transects).
Origin Distance
Center Border 25 m 50 m 75 m 100 m
Feces 110 105 45 40 37 35 Soil 305 105 7 0 0 0 24 Mastozoología Neotropical, 14(1):19-27, Mendoza, 2007 A Fernández and F Sáiz www.cricyt.edu.ar/mn.htm
(F2405 = 14.02; p < 0.005). A posteriori Tukey mination rate was significantly different (D = Tests showed that differences were due to the 0.165; p = 0.05; Fig. 1). smaller size of whole seeds in feces with re- spect to both controls (soil and plant) seeds, DISCUSION while no differeces were observed between both controls. Seeds from all three treatments Our results demonstrated the potential for exhibited, in general, low germination percent- endozoochorous seed dispersal of the exotic ages (6% in whole seeds in feces, 16% in seeds opium poppy by European rabbit in Robinson from the soil bank, and 0.75% in seeds from Crusoe Island. Previous works have shown that plant controls) but these differences were sig- rabbits select specific parts of plants for con- 2 nificant across treatments (E = 22,19; d.f. = sumption (Catling and Newsome, 1992; Mar- 2; p < 0.01). When comparing germination tin et al., 2003) even consuming plants with a frequencies between seeds from feces and high content of salt (Dawson and Ellis, 1979) pooled control seeds, differences were also or important physical and chemical defenses 2 significant (E 1df (YATES) = 5.63; p < 0.05). No (Pakeman et al., 1998). Ingestion by rabbits differences were found in the size of whole of capsules still on the plants is difficult as seeds found in feces that germinated (0.841 ± stalks grow over one meter above the ground. 0.064 mm; n = 8) and germinated control seeds Seed ingestion is accidental (Janzen, 1984) and (0.849 ± 0.054 mm; n = 23) (t = 0.18; n.s.). occurs when rabbits eat poppy capsules Germination started very soon for soil con- dropped on the ground, which had lost most trol seeds and very late for the single plant of their seeds by dehiscence (pers. obs.). seed that germinated; 63% of seeds from soil When evaluating the effectiveness of a seed that germinated, did so in the first 10 days. disperser, several quantitative and qualitative No differences were observed in the germina- factors ought to be considered: (i) the amount tion rate of whole seeds from feces and soil of seeds ingested, (ii) the effect of manipula- controls (Kolmogorov-Smirnov test; D = 0.11; tion and gut passage in their viability, and (iii) p = 0.2). The same was true for whole seeds the adequacy of the seed shadow they produce versus plant seeds (D = 0.059; p = 0.7). Only (McKey, 1980). In the case of the poppy, a differences between soil and plant seeds ger- high proportion of seeds are destroyed chemi-
Fig. 1. Seed germination rate of Papaver somniferum control seeds collected directly from plants and soil, and whole seeds foundfounded in rabbit droppings (n = =135 in each treatment). POPPY SEED DISPERSAL BY RABBIT IN A CHILEAN ISLAND 25
cally and mechanically (82%). Nevertheless, capsules, followed by deposition and subse- 18% of seeds survive gut passage, which can quent incorporation of some seeds to the seed be considered a rather good survival rate for bank away from parent plants. Thus, gut pas- a generalist herbivore (Schupp, 1993; Mouissie sage seems to cause partial scarification com- et al., 2005). Actually, the abundance of rab- pleted in the soil (see Taylor, 1981). Feces bits may compensate for individual seed loses. may constitute temporary refuges for seeds, In addition, an important number of seeds are avoiding early germination or destruction by deposited outside poppy patches in rabbit drop- pathogens or predators (Schupp, 1988). Also, pings, which modifies the size and spatial the small number of seeds in each dropping pattern of the seed shadow without dispersers. indirectly aids seedling establishment because In this way, seeds are widely spread on the in this way seeds avoid early competitive in- landscape and some of them have the chance teractions with other seedlings (Janzen, 1983). to reach adequate places for establishing a new We contend that, altogether, these processes poppy patch (“dispersal bridgeheads” sensu contribute to the success of the opium poppy Cerván and Pardo, 1997). as an invading species on a limited individual Seed dispersal distance is a function of: (i) basis, but have the potential to be greatly the seed retention time, quite short in rabbits amplified due to rabbit abundance. due to their small body size (Staniforth and In summary, interaction between these two Caves, 1977), and (ii) the movements of the introduced species confirms that precise co- dispersal agent. Seeds have been detected in evolutionary adjustment between plant and feces up to 100 meters away from poppy dispersers is not necessary for successful dis- patches but even longer displacements are persal under certain conditions (Herrera, 1985). expected since in Robinson Crusoe Island rab- An unspecialized species as opium poppy may bit movements are not affected by predators take advantage of a generalist herbivore like (Sáiz and Ojeda, 1988). As a consequence, the rabbit for seed dispersal. From the conser- fecal deposition is unrestricted. We have veri- vation point of view, this interaction is having fied elsewhere that other non-native vertebrate an important effect on the current distribution species such as cattle and pigeons are also of this aggressive weed in the island. Its rapid contributing to this dispersion (Fernández and expansion, to which the rabbit contributes, Sáiz, 2002). creates a conservation dilemma: the trade off Undamaged poppy seeds in feces are sig- between the potential benefit of the poppy as nificantly smaller than controls; this is prob- a soil protection, and the damage it causes ably because when rabbits eat fallen capsules displacing native flora (Cuevas and van on the ground only the smallest seeds remain Leersum, 2001). We suggest that any strategy inside the capsule (pers. obs.). Nevertheless, to control non-native plants in the island must some of those seeds are viable after gut pas- involve an understanding of the mechanisms sage and no differences in size are detected of dispersal and the management of animals between germinated fecal and control seeds. acting as generalized dispersers (Constible et Our results show low percentages of germi- al., 2005). nation in general, which affords evidence of a “low-investment” reproductive strategy of the ACKNOWLEDGEMENTS plant (McKey, 1980). Our results also indi- cate that entire seeds from feces germinated at This research was funded by Gobierno Regional de the same rate than control seeds from soil, but Valparaiso, Chile. We are grateful to CONAF (Corporacion Nacional Forestal) rangers and authorities in lower percentage. Low germination success for their help with field work. The author benefited from in the plant control suggest the need of a scari- a MUTIS scholarship from the AECI (Agencia Española fication or a dormancy process. Thus, the dis- de Cooperación Internacional). Jordi Figuerola, Luis persal effect of rabbits derives from acciden- Santamaria and Manuel Nogales made very valuable comments that helped us to improve the final manu- tal consumption of seeds trapped in poppy script. We are very grateful to reviewers for their helpful 26 Mastozoología Neotropical, 14(1):19-27, Mendoza, 2007 A Fernández and F Sáiz www.cricyt.edu.ar/mn.htm comments. We would also like to thank Rolando Bernal FERNÁNDEZ A and F SÁIZ. (2002). La verdadera isla for his help with early drafts of this article and to dedi- de Robinson Crusoe. Quercus 202:40-44. cate it to his memory. FLUX JE and PJ FULLAGAR. 1992. World distribution of the rabbit Oryctolagus cuniculus on islands. LITERATURE CITED Mammal Review 22:151-205. FRITTS TH and GH RODDA. 1998. 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