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WHY ARE THERE SO MANY SPECIESIN EYNE (, PYRÉNÉES-ORIENTALES, CERDAGNN)T

P. Rasmon4 E.-4. Durieux, S. IserbVt & M. Barscetti

SUMMARY

With 32 speciesof burnblebeesfound in an areaof 2000ha,the commune of Eyne may be the most diversified place in West-Palaearctic,perhaps also in the whole world. The authorsdiscuss shortly somehypotheses to explain this high specific richness.Within the same commune, the biogeographical and ecologicai conditions are extremely diverse. However, the number of speciesis obviously too high to fit the rules of resource sharing. The authors suggest that the well known Pyrenean climatic instability brings about a high, random non specific mortality. This factor, linked with a very high floral diversityand abundance,could reduceinter- and intra-specificcompetition, leading to the coexistenceof a largenumber of species.

INTRODUCTION

The origin of bumblebeediversity has been often discussed.The most extremeview in this freld has been held by Inouye (1977a, 1977b, 1978).His temptingbut misleadingsirnplification has beenchallenged by Ranta& Vepsâlâinen(1981) who notedthat in the tundraand the taiga of northernFennoscandia, up to twelve speciesmay coexist.Hanski (1982) modulated the theory of Inouye by considering that interspecific competitionfor resourcesplays a major role in the occurrenceof the most abundantspecies only. Hanski calls thesedominant species,the "core" species,each of them accountingfor more than 3 oÂof the total population.In his view, the "satellite"species - i. e. thoseaccounting for less than 3 % - would be a rnere "random combinationof the resional speciespool".

According to Rasmont(1989). theseconceptions of Inouye and Hanski may not apply to the bumblebeefauna of some locationsin France, w'herethe local speciesdiversity, as well as the numberof "core" species largely exceedstheir predictions.The most species-richregions in France

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Figure 1. Map of France and adjacent countries showing the location of Eyne (Pyrénées - Orientales, C erdagne)

Table II. Main recorders of bumblebees in the commune of Eyne (Pyrénées-Orientales, Cerdagne)

Recorder specimensnumbers

R. DELMAS rr82 F. LECLANT 316 P. RASMONT 291 R. BENOIST 2 J. HAMON 1 H. MARION I unl*town 75

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RESULTSAND DISCUSSION

Lisl species inP 'ientulesand in ol E,"neup to 1998 Pyrénées- Et,rre Orientales Bombus nderarirs (Mùller) l19l 337 Bo mbus s i ch e I i i Radoszkowski 413 t -)/ Bombushortonm (L.) 586 130 Bombuspvrenaeus Pérez 256 126 Bombusst lvestris(Lepeletier) JIJ 120 B ombus soroeensis(Fabricius) 534 ll9 Bom bus meso ntelas Gerstaecker 378 119 Bonbus lucorum (L.) 550 108 Bonbus bohemicusSeidl 262 85 Bombus wurfl enii Radoszkowski 464 76 Bombuspratonm (L.) 407 .70 Bombus lapidarius (L.) 477 )t B ombus rupes tris (Fabricius) t66 50 B o mbus gers ta ec ke r i Mor aw itz l5l 46 Bombus quadricolor (Lepeletier) 87 Àa Bo mbus pas cuo runr (Scopoli) 513

Bo mbus subter raneus (L.) 155 JJ Bombus sylvarum (L.) t76 )z Bombusflavidus Eversmann 143 30 Bombus humilis llliger ztJ zo Bo mbus nte ndax Gerstaecker 87 z) Bombus mucidus Gerstaecker 162 t6 Bombus monticola Smith 163 l3 Bombus hypnorunt (L.) 7 Bombus cont'ilsusSchenck 68 o (L.) 515 o B om b us cam pe stris (Panzer) 62 4 Bombus (Allo ps ith.vrus) sp. 24 3 Bombus cullumanus (Kirby) 5 3 Bombus ruderatas (Fabricius) 56 2 Bombus magnus Yog! 49 Bombus muscorum(L.) l9 Bombus norvegicas (Spane Schneider) l6 Bombus barbutellus (Kirby) Bombus jonellus (Kirby) Bombus mocsaryi Kriechbaumer

Nombretotalde spécimens : 8761 1859 Nombretotal d'espèces : 36 30 (32-) * New observationsmade bv the authors in the summer 1999.

As much as 32 different bumblebeesspecies have been observedin the Eyne commune(Tab. III).

Pekkarinen & Terâs (1993), reviewing the places of maximal diversity in the West-Palaearcticregion. mentionsno other place where 32 speciescan be found on an areaas small as 2000 ha.

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The particular situation of Eyne, with its large ecological and biogeographicaldiversity may partly explain the diversity of its bumblebeesfauna. However, the same factors may be presentin other placesthrough , without resulting in the sarneeffects. Other factors shouldtherefore be looked for.

The speciesdiversity in Eyne is in clear contradictionwith Inouye's theory : there are well over four speciesin the commune,as well as in any of its biotopes.

The Hanski theory does not fare better: there is no clear-cut distinctionbetween core and satellitespecies, and well over four species account, each, for more than 3 % of the total population. The diversity cannot be simply explainedby a sharing of ecological and nutritional resources.

Ranta & Vepsâlâinen (1981) explain the great diversity of the northern bumblebeesfaunas by the frequent occurrenceof "catastrophic environmentalvicissitudes". These may randomly restrict the populations to levels below the competition threshold, allowing a great diversity of small populations - and species- to coexist. This explanation is appealing in the case of Eyne. Indeed, the Pyreneansare well known for their clirnatic instability. The weather may tum from torrid to ice-cold within the same day, with temperaturedifferences of 30' C. and almost daily thunderstorms.Such harsh conditions can be expectedto impose a heavy toll on bumblebeespopulations and make for the kind of situation describedby Ranta& Vepsâlâinen.

There is one difference, however, between the taiga and tundra biotopes described by these authors and the Eyne region. The very abundant and varied vegetation of the Pyreneansmay have allowed the coexistenceof many species,with a very low level of interspecific competition.

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The caseof Bombusgerstaeckerl is a specialone. This speciesis a strict specialist: it is found almostexclusively on Aconitum vulparia. It lives in the subalpinestages and its distributionis very narrow. In W Europe,close to 90 oÂof the recentobservations concentrate in three regions: the High Pyrénées,the eastemPyrénées and the Alpes-Maritimes (Fig. 3). More than half of the observationshave been made in two localities of the PyrénéesOrientales: the Eyne valley and the nearby Madresmassif. This speciesmay be oneof the morenalrowly localisedin Europe.

Our currentresearch program may shedsome more light on the questionsraised here, and confirm invalidate - some of our hypotheses.Whatever the prospect,we'll keepmarvelling at the amazing diversityof the bumblebeesfauna in Eyne.

ACKNOTTLEDGMENTS

The authorsacknowledge the OPlE-Languedoc-Roussillon(Prof. J- P. Lumaret, G. Pinault), the Mairie and M. the Maire of Eyne for their fundsand their help.

REFERENCES

BARBIER, Y. & P. RASMONT, 1995.Carto Fauna-Flora - Cartographiedes données biologiques- Cartographyof biological data. Universitéde Mons-Hainaut, 93+38pp,4 disquettes. BARBIER, Y., & P. RASMONT, 1996.Carto Fauna-Flora 1.2 - Cartographiedes donnéesbiologiques - Cartography ofbiological data - Nouveautésde la version 1.2 et utilitaires - Changesin version 1.2and tools. Universitéde Mons-Hainaut,62pp.,I CD-rom ^ BARBIER, Y., P. RASMONT, M. DUFRENE& J.-M. SIBERT, 1999.Data Fauna Flora. Guided'utilisation. Universitéde Mons-Hainaut,Région Wallonne, Mons,Namur,94pp, I CDROM. DELMAS, R., 1976.Contribution à l'étudede la faunefrançaise des Bombidae (,Apoidea, Bombidae). Annls Soc.ent. Fr. QV.S'),12:247-290. HANSKI, 1.,1982. Communities of bumblebees:testing the core-satellitespecies hypothesis.Annales Entomologici F ennici, 19: 65-73. INOUYE, D., 1977A.Species Structure of BumblebeeCommunities in North America and Europe.pp. 35-49 ft.' Mattson,W.J., Therole of inforest ecosystems.Springer, Berlin - Heidelberg- New york. INOUYE, D., 19778. Resourcepartitioning in bumblebees.New York entomological Soc ie ty, 85(4): 253-25 4. INOUYE, D., 1978.Resource partitioning in bumblebees:experimental shrdies of foraging behavior.Ecologr, 59(4):67 2-67 8.

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