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Journal of Animal Ecology 0888\ 57\ 359Ð360 Habitat selection as a major resource partitioning mechanism between the two sympatric sibling bat species Myotis myotis and Myotis blythii RAPHAE Ý L ARLETTAZ Institute of Zoology and Animal Ecology\ University of Lausanne\ CH!0904 Lausanne\ Switzerland Summary 0[ Ecomorphological studies have described local bat communities as densely!packed species assemblages arising from non!deterministic processes[ Together with the obser! vation that insectivorous bats readily exploit patchy\ often unlimited trophic resources\ this has even led to the claim that partitioning of niche space may be absent[ However\ the paucity of data on resource exploitation per se among bat guilds rarely allows these assertions to be veri_ed[ In particular\ the mechanisms allowing the co! existence of similar species have proved di.cult to determine[ 1[ As a subset of an insectivorous guild\ the vespertilionid bats Myotis myotis and M[ blythii o}er an opportunity to examine this question[ Genetically closely!related\ they are morphologically almost identical[ Yet\ as established by faecal analysis\ they exploit distinct trophic niches\ preying upon ground! and grass!dwelling prey taxa\ respectively[ The distinct habitat requirements of their basic prey suggest that eco! logical segregation may stem primarily from a di}erential allocation of foraging space[ 2[ The present study tests the hypothesis that sympatric M[ myotis and M[ blythii segregate spatially to an extent which prevents competitive interference[ I performed radio!tracking on Swiss sympatric populations[ Using multivariate analyses and ran! domized contingency table procedures\ I looked for "i# habitat overlap and overall inter!speci_c di}erences in habitat choice\ and "ii# the habitat preferences exhibited by individuals when foraging within their own feeding areas[ 3[ Primary foraging habitats were largely species!speci_c[ Not only were they spatially segregated\ but they also di}ered structurally[ All habitats selected by M[ myotis o}ered a high accessibility to ground!dwelling prey "freshly!cut meadows\ mown grass in intensively cultivated orchards\ forests without undergrowth#\ whereas grassland predominated in all habitats of M[ blythii "steppe\ unmown meadows\ pastures#[ This corroborates the predictions drawn from dietary niches[ 4[ This study shows that re_ned mechanisms of resource partitioning\ not predictable by the study of morphological characters or echolocation alone\ may still account for the organization of parts of insectivorous bat guilds[ It also supports the view that habitat selection may prove to be a major mode of resource allocation amongst similar insectivorous bats\ particularly for species exploiting limited food supplies[ Key!words] Chiroptera\ community ecology\ guild structure\ niche\ species evolution[ Journal of Animal Ecology "0888# 57\ 359Ð360 Introduction Understanding the mechanisms of co!existence of species within local assemblages is one of the major Þ 0888 British Ecological Society 359 Correspondence] R[ Arlettaz\ Rue de Paradis 30\ CH!0856 Bramois!Sion\ Switzerland[ Fax] ¦30 16 192 28 91[ E!mail] Raphael[ArlettazÝizea[unil[ch issues addressed by community ecologists "Pianka 0870^ Ricklefs 0889#[ The observation that local bat faunas are packed assemblages usually consisting of a majority of morphologically very similar species\ with only a few outlying forms\ has led some bat biologists to believe that competitive niche arrangement might play a minor role\ if any\ in bat community organ! ization\ because strong morphological resemblance is 350 R[ Arlettaz Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 assumed to re~ect similarity of niches "e[g[ Fenton 0871^ Findley + Black 0872^ Aldridge + Rautenbach 0876^ Crome + Richards 0877^ Willig + Moulton 0878^ Findley 0882^ Arita 0886#[ Also\ the majority of bat species appear to be opportunistic foragers which readily exploit patchily distributed\ ephemeral trophic resources\ i[e[ locally and temporally unlimited food supplies\ which may prevent competitive niche par! titioning from occurring[ As a consequence\ the organization of bat communities would be under the control of non!deterministic processes "Willig + Moulton 0878^ Findley 0882^ Arita 0886#[ Yet\ this unorthodox view about the structure of bat faunas has not been challenged by appropriate\ re_ned ecological studies[ In this respect\ ecomorphological and ech! olocation studies may well provide insights into the structure of bat communities "e[g[ Fenton 0871\ 0874^ Neuweiler 0873^ Aldridge + Rautenbach 0876^ Fin! dley 0882^ Kalko 0884^ Arita 0886#\ but they both represent indirect approaches since they consider the attributes through which organisms acquire resources rather than resource acquisition per se "i[e[ they use mere characters\ and infer mechanisms from patterns^ Wiens 0878#[ For instance\ a spacing in resource par! titioning has been suggested from the even apportion! ment of ultrasonic frequencies within bat assemblages including up to 01 syntopic rhinolophoids "Heller + Helversen 0878#\ but ecological evidence is still lack! ing[ It may be argued that the ecomorphological approach aims _rst to look at trends within or amongst communities\ not to predict subtle di}er! ences at the micro!evolutionary level[ Recognizing its intrisic limitations is important\ however "Saunders + Barclay 0881#[ As no comprehensive data about dietary niches\ foraging strategy and habitat use are simultaneously available from the same guilds "Saunders + Barclay 0881#\ it is di.cult to appreciate how bat communities are structured "Kalko 0884#[ Detailed studies of the mechanisms involved in resource exploitation\ especially among morphologically similar bats\ are thus needed until we can solve this apparent dilemma and start envisioning the micro!evolutionary pro! cesses involved in bats| niche evolution "Aldridge 0875^ Saunders + Barclay 0881#[ Sympatric cryptic species are simpli_ed subsets of communities "Mayr 0866#[ Among pairs of species which look alike\ those which are not only mor! phologically similar\ but also phylogenetically closely related provide the best opportunities not only to chal! lenge the ecomorphological paradigm\ but also to investigate the processes shaping niche evolution in general[ Henceforth\ the terms {sibling species| delib! erately refer to pairs of morphologically similar spec! ies that share a recent common ancestor to whom they are more closely related than any other species[ Inter! speci_c di}erences "either morphological\ physio! logical or behavioural# between those species can reasonably be seen as having some adaptive value in the context of niche separation[ Inter!speci_c com! parisons between such species could therefore eventu! ally yield information about the processes which have been involved in the apportionment of ecological space during the formation of those foraging guilds[ The greater and lesser mouse!eared bats\ M[ myotis "Borkhausen 0686# and M[ blythii "Tomes 0746#\ which are the largest species within their genus "Nowak 0880#\ correspond to this de_nition of sibling species[ First\ the separation between these two Palae! arctic taxa probably took place during the Pleistocene "Ruedi\ Arlettaz + Maddalena 0889^ Arlettaz et al[ 0886a#[ Secondly\ these two species are extremely simi! lar and overlap in all their external morphological features "Arlettaz\ Ruedi + Hausser 0880#[ Their identi_cation thus remains particularly di.cult and blood isozyme electrophoresis is currently the only absolute method available to distinguish between live individuals of these two species "Ruedi et al[ 0889^ Arlettaz et al[ 0886a#[ Despite the fact that M[ myotis and M[ blythii have very similar\ if not identical\ kar! yotypes Ð they should therefore not experience any barrier to gene ~ow due to chromosomal incom! patibilities "Ruedi et al[ 0889# Ð and usually occupy the same colonial roosts in sympatry\ either for breed! ing or mating "Arlettaz et al[ 0883#\ genetic analyses carried out on several hundred individuals from sym! patric populations have as yet failed to establish hybridization "Arlettaz et al[ 0886a#[ This suggests the existence of strong behavioural reproductive barriers isolating the two species[ Arlettaz\ Perrin + Hausser "0886b# have shown that mouse!eared bats occupy very distinct trophic niches throughout their ranges[ Myotis myotis specializes in the predation of ground!dwelling prey "e[g[ ~ightless carabid beetles#\ whereas M[ blythii is primarily a predator of grass!dwelling arthropods\ mainly bush crickets^ mouse!eared bats are therefore essentially gleaning bats\ i[e[ capturing prey from substrates[ Without being conclusive\ that previous study of diet! ary niches has suggested that ecological segregation might stem primarily from the utilization of foraging habitats which di}er spatially and structurally\ because of the distinct habitat requirements of their basic prey "Arlettaz et al[ 0886b#[ The present study tests the hypothesis that spatial segregation of for! aging activity actually takes place between M[ myotis and M[ blythii under sympatric conditions[ Temporal segregation\ another possible mode of resource par! titioning is also addressed brie~y[ Methods RADIO!TRACKING Foraging activity and habitat of sympatric mouse! eared bats were investigated in the Alps of Valais "south!western Switzerland\ c[ 35>04? N\ 6>29? E# between May and September 0878Ð81[ Twenty!six 351 Habitat selection in sibling bat species radio!tracking sessions "a session is here de_ned as a period of several successive days with uninterrupted radio!tracking of a given bat# were carried out on 13 individuals "01 M[ myotis and 01 M[ blythii*68) of which were adult females#\ during a total of 088 nights "Table 0#[ Two individuals were radio!tagged twice\ during two consecutive years[ Owing to transmitter defect\ four individuals were not considered in the subsequent analyses "1 M[ myotis and 1 M[ blythii#[ Therefore\ a total of 09 M[ myotis and 09 M[ blythii yielded good data[ Individual bats of the two species were captured at the same mixed nursery roosts[ Potential habitat around the roosts was therefore similar for both spec! ies[ Bats were _tted with radiotransmitters _xed around their necks with a silicone collar "Telemetrie! Systeme fur die Wildbiologie\ Dr F[ Kronwitter\ Glonnerstrasse 11\ DÐ7900 Oberpframmern\ Ger! many^ tag weight was ¼ 0=3Ð0=7 g#[ A piece of re~ector tape "ScotchliteTM# glued on the upper side of trans! mitters enhanced location and identi_cation of tracked individuals in the _eld through direct visual observation with the help of a night scope "BIG III\ Wild!Leitz and Leica SA\ CHÐ0919 Renens\ Swit! zerland# coupled with an infra!red halogen lamp[ At the end of each radio!tracking session\ individuals were recaptured at their roost or mist!netted in their feeding grounds\ and transmitters removed[ Radio! tracking sessions took place between dusk and dawn\ without interruption[ Bats were tracked from a car until they reached their foraging grounds which were located up to 14 km from the roost[ Radio!tracking was then performed on foot\ usually by a single observer equipped with a radio!receiver and an H! antenna "Telonics\ Telemetry!electrical consultants\ 821 E[ Impala av[\ Mesa\ Arizona 74193Ð5588\ USA^ Yaesu FT!189RII adapted by Karl Wagener\ HS ¦ NFÐTechnikÐTelemetrie\ Herwarthstrasse 11\ DÐ4999 Koln 0\ Germany#[ Because of the bats| high ~ight speed "usually 29Ð39 km:h\ but up to 49 km:h^ Arlettaz 0885a#\ complex alpine topography and availability of a single observer\ monitoring of bat activity was interrupted frequently and location was achieved essentially by homing!in on the animal "White + Garrott 0889#[ The accessibility of foraging grounds to the observer also di}ered between the two species[ Myotis myotis visited primarily agricultural habitats and forests with a good road network\ whereas M[ blythii exploited\ _rst\ steep rocky slopes "up to 32># with few if any roads\ which sometimes Table 0[ The 15 radiotracking sessions carried out on 13 individuals in 0878Ð0881 Individual "ring number# Sex\ age and reproductive state0 Period Number of nights with radiotransmitter M[ myotis M[ myotis M[ blythii M[ blythii M[ blythii M[ blythii M[ blythii M[ blythii M[ myotis M[ blythii 972G 985G 989G 766G 313G 329G 323G 403G 634H 638G 648G 652G idem 667G 713G idem 764G 657G 609H 842G 851G 884G 886G 888G 290G 355G fem[ ad[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ imm[ fem[ ad[ preg[ male ad[ fem[ ad[ lact[ fem[ ad[ preg[ fem[ imm[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ lact[ fem[ imm[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ ad[ lact[ male imm[ fem[ ad[ lact[ fem[ ad[ lact[ fem[ad[lact[ 15Ð29 Jun 89 09 Jul 89 00Ð05 Jul 89 92Ð94 Sep 80 08Ð13 Jun 89 93Ð19 Sep 78 08Ð16 Jul 89 92Ð98 Jul 89 18 AugÐ92 Sep 80 91Ð95 Jul 80 95Ð97 Jul 80 97Ð00 Jul 80 94Ð29 Jun 81 05Ð07 Jul 80 18 JulÐ90 Aug 80 03Ð18 May 81 12Ð15 Aug 80 04Ð05 Jun 80 93Ð10 Aug 80 00Ð11 Aug 80 07Ð12 Jul 80 91Ð93 Aug 80 03Ð12 Aug 80 12Ð18 Jul 80 29 Jul 89Ð96 Aug 89 13Ð18 Jul 89 4 01 5 2 51 06 81 6 5 4 2 3 15 2 3 05 3 11 07 01 5 3 09 6 8 5 Total 13 Species M[ myotis M[ myotis M[ myotis M[ myotis M[ blythii M[ blythii M[ blythii M[ blythii M[ blythii M[ myotis M[ myotis M[ myotis M[ myotis M[ myotis Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 0 088 fem[ female^ ad[ adult\ imm[ immature^ lact[ lactating[ radiotransmitter defect] individuals not retained for analysis owing to scarce data[ 1 Number of nights Number of with recorded foraging areas foraging activity "−_ve 0!ha cells# 3 * 4 2 * 6 * 3 2 3 1 2 8 1 2 5 1 * 4 1 5 1 2 2 6 5 80 1 * 1 0 * 0 * 0 0 1 1 2 0 3 0 * 2 1 3 0 0 0 0 0 24 352 R[ Arlettaz rendered radio!tracking\ even on foot\ quite haz! ardous "see habitat photographs in Arlettaz 0884#[ To avoid any inter!speci_c methodological bias in data collection\ habitat use was therefore de_ned by con! sidering the proportion of the di}erent types of habitat visited by a bat\ and not by considering the time spent in the di}erent habitat types[ Despite obvious poten! tial shortcomings\ this simple spatial approach per! mitted direct inter!speci_c comparisons about habitat use[ Five di}erent types of activity were recognized] 0[ 1[ 2[ 3[ 4[ resting at day roost^ night resting in foraging area^ commuting ~ight^ foraging activity^ and unidenti_ed activity[ Commuting and foraging were easily distinguished\ since "i# foraging usually consisted of gleaning from the ground\ thus giving a signal of variable intensity due to micro!topography and frequent changes in ~ight direction^ and "ii# commuting consisted of fast straight ~ights\ possibly at some meters above the ground\ thus providing a strong\ constant signal "Arlettaz 0884#[ Contacts were classi_ed with respect to the estimated accuracy of localization\ which cor! responded to the proximity of the bat to the observer[ Only locations referring to foraging activity "type 3# and with an accuracy of ¾ ¼ 49 m\ including visual observations\ were considered for habitat selection analysis[ Bats selected for radio!tracking were _rst identi_ed in the _eld according to the morphological method outlined in Arlettaz et al[ "0880#[ Correctness of identi! _cation was then ascertained in the laboratory on the basis of protein analysis of blood samples "Ruedi et al[ 0889^ Arlettaz et al[ 0886a#[ Radio!tracking was car! ried out under licence from the Nature Conservancy Service of the State of Valais[ HABITAT MAPPING AND FORAGING AREAS Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Foraging habitats were divided in 0!ha cells according to the o.cial reference grid of the Swiss Federal Topo! graphic Service[ Each foraging contact was attributed exclusively to one of these grid cells\ and each cell was described by the dominant habitat type[ Overall\ 29 habitat types were recognized "Table 1#[ As far as poss! ible\ habitat mapping took place during the day fol! lowing radio!tracking nights\ usually from certain vantage topographic points^ however\ in the case of steep\ remote habitats\ aerial photographs provided by the Swiss Topographic Service were consulted[ The area exploited by each radio!tracked bat was estimated by summing the number of 0!ha cells "either isolated or not\ see below# visited at least once by a given foraging individual "White + Garrott 0889#[ One habitat cell was considered in these calculations even if the bat visited only parts of it[ Because indi! vidual bat foraging areas amounted to several dozens of hectares each "see below#\ we considered any poten! tial shortcomings inherent in this method as back! ground noise which would not have substantially biased overall inter!speci_c comparisons[ The altitude of foraging grounds and the distance of foraging grounds to the nursery roost were estimated from the geometric centre of the minimum area poly! gon drawn for each foraging ground "Harris et al[ 0889^ White + Garrott 0889#[ For one given indi! vidual\ I arbitrarily considered as one separate for! aging ground every group of at least _ve neighbouring 0!ha cells which was isolated from the next closest group by at least 799 m^ groups of less than _ve cells were not considered for the study of the altitude of feeding grounds and their distance to the roost[ If there were more than one foraging ground per indi! vidual\ I took their average altitude and distance to the roost for every individual bat[ HABITAT OVERLAP Intra! and inter!speci_c overlaps in the use of the di}erent types of foraging habitats were estimated from the proportions of the 29 habitat types visited "Table 1#\ with the FreemanÐTukey statistic "Matusita 0844^ Krebs 0878#] k FTij s "pir = pjr #0:1 eqn 0 r0 where FTij is Freeman|s and Tukey|s measure of habi! tat overlap between individual i and individual j^ for intra!speci_c overlap\ i and j belong to the same spec! ies^ for inter!speci_c overlap\ i and j belong\ respec! tively\ to species A and B^ k total number of habitat types^ pir and pjr proportions habitat r is of total habitat utilized by individuals i and j\ respectively[ This measure of overlap ranges from 9 "no habitats used in common# to 0 "complete overlap#[ For intra! speci_c habitat overlap\ the overlap coe.cient is cal! culated for every possible pair of individuals of one species[ For inter!speci_c habitat overlap\ the statistic is calculated for every possible inter!speci_c pair of individuals[ For comparing the magnitude of habitat overlap between and within species\ I relied on randomization procedures to avoid statistical pseudo!replication inherent in pairwise comparisons ðsee Manly "0880# and Arlettaz et al[ "0886# for more details about the conceptŁ[ Mean intra!speci_c overlaps were calculated for both species\ as well as mean inter!speci_c overlap[ In order to test for di}erences between means\ the following two!step procedure was repeated 4999 times] "i# random permutations of rows and columns of the habitat overlap matrix "as would be done for a Mantel test^ Manly 0880#^ "ii# calculation of the intra! and inter!speci_c means of the shu/ed matrix[ The test probability was then the proportion of shu/ed matrices that gave niche overlap as large as or larger 353 Habitat selection in sibling bat species Table 1[ Habitat categories "IÐX# and habitat types "0Ð29# mapped within the di}erent bat foraging areas\ from the more open environments "top# to the cluttered ones "bottom#[ The dominant tree species are indicated for some habitats Habitat category Habitat type I[ Rocky 0 1 2 3 4 5 6 7 8 09 00 Cli} Stony outcrop Scree Human settlements Open _elds Vineyard Stream\ river Steppe on stony outcrop or scree Open steppe "³ 49) bushes# Bushy steppe "× 49) bushes# Wooded steppe "³ 49) trees# 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 Steppic pasture Xeric pasture or abandoned meadow Wet pasture Meagre meadow Mesophilous meadow Meagre meadow Mesophilous meadow Traditional orchard Traditional orchard Intensively cultivated orchard Xerothermic forest Xerothermic forest Chestnut forest Riparian forest Xerophilous forest 16 17 18 29 Pine forest Spruce forest Larch forest Mixed coniferous forest II[ Urbanized III[ Arable IV[ Water V[ Steppe VI[ Pasture VII[ Dense meadow VIII[ Mown meadow IX[ Orchard X[ Deciduous forest "× 49) deciduous# X[ Mixed forest X[ Coniferous forest "× 49) coniferous# than the observed "the program used was written by J[ Goudet\ and may be obtained upon request from its creator at the same institutional address as the author#[ HABITAT SELECTION Species!speci_c habitat utilization[ Di}erences in the habitats visited by M[ myotis and M[ blythii were visualized in the multivariate space using a principal component analysis performed on the 09 main habitat categories "_rst column in Table 1# obtained by a logi! cal regrouping of the 29 fundamental habitat types recognized "second column in Table 1#[ Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Habitat selection within individual foraging grounds[ Habitat preferences and avoidances were established by comparing the absolute frequencies of the di}erent habitats "number of 0!ha cells# which were visited or not by the bats inside the minimum area convex polygon"s# delimited for "each of# their main foraging ground"s#[ It was assumed that habitats of non!visited cells were actually avoided since foraging bats had to ~y over them when moving from one part of their foraging ground to another[ All cells with −49) of Dominant tree species Quercus pubescens Quercus pubescens\ Betula pendula\ Larix decidua\ Pinus sylvestris Apple Apricot Apple\ pear Quercus pubescens Sorbus aria\ Fraxinus excelsior\ etc[ Castanea sativa Populus alba\ P[ nigra\ Salix sp[ Larix decidua\ Picea abies\ Betula pendula\ Sorbus aria\ Castanea sativa\ Pinus sylvestris Pinus sylvestris Picea abies Larix decidua Larix decidua\ Picea abies\ Abies alba\ Pinus sylvestris their area "i[e[ 9=4 ha# enclosed within one given poly! gon were considered[ It was possible to distinguish between positive and negative selection\ in which habi! tat is over!exploited with respect to its frequency of occurrence or under!exploited "avoided#\ respectively[ Statistical tests performed on the overall species data sets consisted of randomized contingency table pro! cedures "program MACACTUS\ G[ F[ Estabrook\ Uni! versity of Michigan Herbarium\ Ann Arbor\ MI 37098\ USA^ Estabrook + Estabrook 0878#[ This method provides a level of probability "to the nearest 9=990# for every deviation between observed and expected frequencies\ that is for every box or every habitat group in a contingency table[ In order to avoid very small expected values in contingency tables\ some habitat types had to be regrouped within higher habi! tat sorts prior to performing statistical comparisons "those habitat sorts are depicted on x!axes in Fig[ 2#[ Results FORAGING ACTIVITY AND FEEDING AREAS Bats carried transmitters for a total of 088 nights "average] 6=6 nights per session#\ but only 80 nights 354 R[ Arlettaz "35)# provided satisfactory data on foraging activity "average] 3=0 nights per successful session#[ The gen! eral chronology of foraging activity did not di}er between the two species[ All tagged individuals left roosts after dusk and had returned before dawn[ Hunting activity was essentially unimodal\ even dur! ing lactation\ and concentrated in the darkest hours of the night[ This excludes inter!speci_c resource par! titioning by temporal segregation[ Thirty!_ve foraging grounds were delimited "Table 0#[ Sixty!eight "02 out of 08# of the foraging grounds of M[ myotis were on the north!facing slope "i[e[ south of the river Rho¼ne#\ 15) in the plain and only 5) on the south!facing slope "north of the river Rho¼ne#[ In contrast\ 45) "8 out of 05# of M[ blythii|s foraging areas were situated on the south!facing slope\ 5) in the plain and 27) on the north!facing slope[ Overall\ inter!speci_c di}erences in the use of the plain and the slopes were highly signi_cant "x1 00=4\ d[f[ 1\ P 9=992# and randomized contingency tables showed that M[ myotis avoided the south!facing slope "P 9=903# which\ conversely\ was selected by M[ blythii "P 9=926#[ Since 0=4 foraging grounds\ on average\ were delimited per individual "Table 0#\ these patterns denote overall species!speci_c trends in space use and not mere individual specializations[ There was no inter!speci_c di}erence in the size of the individual|s foraging areas] they amounted to 25=1 2 06 ha "mean 2 SD# in M[ myotis and to 27=0 2 00 ha in M[ blythii "MannÐWhitney U 27=4\ n 09 and 09\ P 9=273#[ The altitude of the for! aging grounds did not di}er statistically between the two species] 766 2 217 m a[s[l[ "mean 2 SD# in M[ myotis and 0901 2 206 m a[s[l[ in M[ blythii "t −9=825\ n 09 and 09\ P 9=251#[ The highest feed! ing areas were located at 1999 m a[s[l[ for M[ blythii and around 0599 m a[s[l[ in M[ myotis\ whereas the roosts were at between 369 and 564 m altitude[ The distance of foraging areas from nursery roost was signi_cantly greater in M[ myotis than in M[ blythii] 7579 2 5950 m vs[ 2751 2 0437 m "mean 2 SD# "t 1=324\ n 09 and 09\ P 9=915#[ The farthest feeding grounds were situated at 14\ 07=4\ 06\ 03 and 02 km from the nursery colony in M[ myotis\ but only at 8\ 5=4 and 4=4 km for M[ blythii[ HABITAT OVERLAP Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 The two intra!speci_c overlaps ðM[ myotis] FT 9=188 2 9=15 "mean 2 SD#\ n 34^ M[ blythii] FT 9=317 2 9=12\ n 34Ł were signi_cantly greater than the inter!speci_c one "FT 9=079 2 9=05\ n 099^ P ³ 9=92 in the _rst case\ and P ³ 9=990 in the second case^ randomization tests#\ whereas the magnitude of intra!speci_c overlap did not di}er between species "P 9=04^ randomization test\ not illustrated#[ HABITAT SELECTION Species!speci_c habitat use[ The overall utilization of the 09 main habitat categories "Table 1# di}ered sig! ni_cantly between the two species "x1 329\ d[f[ 8\ P ³ 9=990#[ Inter!speci_c di}erences "all P ³ 9=90^ Fig[ 0# appeared for steppe\ pastureland and dense meadow which were predominantly exploited by M[ blythii\ and for freshly mown meadow\ orchard and forest that were more frequently visited by M[ myotis[ There were no obvious di}erences between the habitat choice of the four tagged yearlings "1 M[ myotis and 1 M[ blythii# and that of adult individuals\ but no statistical tests could be performed because of the small sample sizes available[ A principal component analysis performed on the frequencies "i[e[ number of 0!ha cells# of the 09 main habitat categories showed a distinct clustering of indi! viduals of the two species in the multivariate space\ with no inter!speci_c overlap "Fig[ 1#[ The _rst two factors accounted for 43) of variance "21 and 11)\ respectively#[ The _rst component was positively cor! related with freshly cut meadow "r 9=545\ P 9=991# and forest "r 9=401\ P 9=910#\ but negatively correlated with steppe "r Ð9=735\ P ³ 9=990#[ The second component was positively cor! related with pasture "r 9=471\ P 9=996#\ but nega! tively associated with orchard "r Ð9=735\ P ³ 9=990#[ Individual selection[ The percentage frequencies of the habitats available and e}ectively used within the main foraging areas are shown in Fig[ 2[ Myotis myotis posi! tively selected freshly cut meadow "P ³ 9=990#\ inten! sively cultivated orchard\ mixed forest "both P ³ 9=90#\ and "lowland# Pinus sylvestris forest "P ³ 9=94#[ It avoided dense meadow and Larix decidua forest "P ³ 9=990#\ mixed coniferous forest\ human settlements and open _elds "all P ³ 9=90#\ vine! yards and Picea abies forest "P ³ 9=94#[ Myotis blythii showed a very highly signi_cant preference for open steppe and dense meadows "P ³ 9=990#\ and selected for rocky steppe and pastures "P ³ 9=94#[ It avoided rocky areas\ human settlements\ vineyards\ xeric deciduous forest "P ³ 9=990#\ open _elds\ chestnut forest and mixed forest "P ³ 9=94#[ Discussion SPATIAL SEGREGATION DURING FORAGING This study demonstrates that the di}erences in diets between M[ myotis and M[ blythii "Arlettaz et al[ 0886b# correlate with a sharp spatial segregation of foraging activities\ with the inter!speci_c overlap in habitat use being much smaller than the two intra! speci_c ones "9=07 vs[ 9=29 and 9=32\ respectively#[ According to niche theory\ this is su.cient to permit 355 Habitat selection in sibling bat species Fig[ 0[ Inter!speci_c di}erences in the mean percentage frequency of utilization of the 09 main habitat categories "see Table 1#^ habitats are ranked according to their approximate degree of clutter\ from left to right[ Chi!square and randomization tests were carried out on overall absolute frequencies "not on percentages# of visited habitat categories "number of 0!ha cells\ see Methods^ ns non!signi_cant^ ¦¦ P ³ 9=90^ ¦¦¦ P ³ 9=990#[ Fig[ 1[ Relationship between the _rst two factors "PC0 and PC1# obtained from a principal component analysis per! formed on the absolute frequencies "number of 0!ha cells# of the di}erent habitat categories visited by the 19 radio!tracked mouse!eared bats "each symbol depicts a radio!tracked bat#[ The variables which are signi_cantly "positively or nega! tively# correlated with factors are indicated along axes[ Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 the stable co!existence observed in sympatry "Pianka 0870#[ In the study area\ M[ myotis avoided the south! facing slope north of the river Rho¼ne\ whilst M[ blythii preferred to forage there[ In the upper Rho¼ne valley\ xeric grassland habitats "including steppe\ a climactic grassland found in the driest valleys of the Alps# are widespread on the south!facing slope\ but nearly absent on the north!facing one\ south of the river Rho¼ne\ which is much more wooded[ Given that M[ blythii captures mostly grass!dwelling prey "bush crickets#\ whereas M[ myotis feeds mainly on ter! restrial prey "carabid beetles#\ this major spatial seg! regation across the valley correlates with the trophic requirements of these two bat species "Arlettaz et al[ 0886b#[ Within their individual foraging habitats\ M[ myotis selected freshly cut meadows and intensively cul! tivated orchards[ Both habitats yield ground surfaces that are not cluttered by dense grass] hay meadows are exploited by the bats only during the _rst nights after mowing "Arlettaz 0885a#\ and orchards provide extensive surfaces of short grass which is frequently cut by farmers[ The avoidance of meadows\ prior to mowing\ and larch forests\ which have a dense grass undergrowth\ further illustrates the bats| preference for uncluttered substrates[ Among the woodland\ only lowland forests with no undergrowth "neither grass nor bushes# were selected[ Moreover\ some forests exploited by M[ myotis were heavily grazed by cattle[ In conclusion\ each type of habitat visited by M[ myotis o}ers a high accessibility to terrestrial arthro! pods\ apparently enabling a ~ying bat to land on the substrate to catch prey "Arlettaz 0885a#[ Despite a seemingly appropriate micro!habitat structure\ some other habitats avoided by greater mouse!eared bats* such as high altitude coniferous forests\ open _elds and vineyards*probably yield insu.cient numbers of suitable prey owing to their low arthropod pro! ductivity "personal _eld observations#[ 356 R[ Arlettaz Fig[ 2[ Percentage frequency of the di}erent habitat types available to\ and visited by M[ myotis "top# and M[ blythii "bottom# in their individual foraging grounds "minimum area polygons\ see Methods#[ Tests were run using absolute frequency data "number of 0!ha cells#[ The symbols indicate the direction of selection] ¦ over!exploitation "habitat preference#\ Ð under! exploitation "habitat avoidance#^ ns non!signi_cant^ one symbol] P ³ 9=94^ two symbols] P ³ 9=90^ three symbols] P ³ 9=990#[ In order to avoid very small expected values in contingency tables\ habitat types have been grouped "see x!axis# di}erently in each species prior to running tests[ Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Interestingly\ M[ myotis in the Swiss Alps did not show the preference for forested habitats reported by Rudolph "0878# and Audet "0889# in Germany[ This probably results from a greater habitat and:or food diversity in the Alps\ due in particular to the per! sistence of ancient farming practices which help to preserve a rich invertebrate fauna within grassland habitats "Arlettaz 0885a\b^ Arlettaz et al[ 0886b#[ However\ it cannot be ruled out\ a priori\ that M[ myotis may experience somewhat sub!optimal for! 357 Habitat selection in sibling bat species aging conditions in mountainous environments "e[g[ lack of productive mature deciduous forests typical of lowland areas#\ forcing it to seek prey in more open areas[ In their individual foraging grounds\ M[ blythii selected steppe and unmown meadows[ They also appeared to choose the relatively dense steppe veg! etation more frequently than the sparse xeric grass! land which grows on stony outcrops[ In contrast\ they avoided the patches of xeric deciduous forests as well as the chestnut forests covering some south!facing slopes[ Clearly\ there is an association between M[ blythii and relatively dense grass vegetation[ Like M[ myotis\ M[ blythii avoided rocky areas\ human settle! ments\ open _elds and vineyards[ This is again likely due to the very low arthropod productivity of these habitats[ The individual foraging grounds of M[ myotis were\ on average\ situated at greater distances from the nur! sery roosts than the individual feeding grounds of M[ blythii "8 vs[ 3 km#\ although they covered similar areas and were situated at comparable altitudes[ Fre! shly mown meadows appeared to be the most impor! tant habitat of M[ myotis in the study area^ inter! estingly\ cut meadows also represented the most ephemeral food patches amongst all habitats recorded either in M[ myotis or M[ blythii "Arlettaz 0885a#[ Since they o}er highly attractive food sources for M[ myotis\ owing both to massive occurrences of very pro_table prey and high accessibility to ground prey "Arlettaz 0885a#\ it is not surprising that greater mouse!eared bats commuted such long distances to reach these habitats[ Again\ however\ possible sub! optimal feeding habitats in the Alps could also con! strain M[ myotis to forage farther away from roosts[ Set in a broader zoogeographical context\ the pre! sent data provide an ecological explanation to the new view about the distribution of M[ myotis and M[ blythii in the Palaearctic region "Arlettaz et al[ 0886a#[ M[ myotis typically inhabits environments o}ering bare!ground habitats\ from the central European beech forest to the denuded or even desert areas of North Africa\ including also the main Mediterranean islands\ whereas M[ blythii is restricted to the main! land and appears primarily to be a species of the warm steppe which has extended its range throughout Eurasia[ WHAT UNDERLIES HABITAT SEGREGATION< Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Considering their foraging strategy\ I described mouse!eared bats as opportunistic predators which were able to maximize energy intake by searching for the most abundant:pro_table prey "Arlettaz 0885a#[ However\ this applied only to situations when mouse! eared bats exploited ephemeral food patches\ par! ticularly freshly!mown hay meadows "Arlettaz et al[ 0886b#[ Nonetheless\ if the bats can so readily take advantage of sudden concentrations of prey\ why do they still allocate most of their foraging time to well segregated\ species!speci_c habitats\ as demonstrated in the present study< There are two possible answers[ First\ it might be the pressure of inter!speci_c com! petition which may be the source of a di}erential use of space[ Yet\ this would contradict the conclusion by Arlettaz et al[ "0886b# that inter!speci_c competition is not a major drive in trophic partitioning between these bats[ As there is no evidence for niche shift Ð towards the occupation of the other species| niche Ð between sympatric and allopatric populations in either species\ those authors excluded inter!speci_c competition as a factor of niche di}erentiation in sym! patry[ Given that the prey which form the bulk of the diets of mouse!eared bats are largely habitat!speci_c over their entire geographical range\ the same con! clusions readily apply to the bats| foraging habitats[ As a consequence\ it is unlikely that inter!speci_c com! petition is the key mechanism responsible for habitat segregation under sympatric conditions[ The second series of arguments pertains to possible species!speci_c functional adaptations evolved as proximate factors in resource partitioning[ Energetic advantages Ð which should be measurable in terms of food intake\ and ultimately as reproductive success and _tness Ð must be linked with these putative adap! tations\ making the sharp habitat segregation a _xed strategy[ I predict above all that subtle di}erences in ~ight morphology enable one species\ M[ blythii\ to exploit habitats structurally more complex[ Gleaning a prey item from grass stalks requires a better ~ight ability than landing upon a prey on the ground[ Spec! ies would therefore concentrate their foraging e}ort on the energetically more suitable habitat con_gur! ation[ However\ this seems insu.cient to explain why M[ blythii does not exploit easily accessible bare! ground habitats[ Additional mechanisms providing bats with di}erent search images may also be involved[ Prey palatability may di}er^ for instance\ carabid beetles\ the basic prey of M[ myotis\ have a strong smell and may not be edible for M[ blythii[ Also\ di}erent auditory capabilities may indirectly in~uence patterns of habitat selection[ As mouse!eared bats are primarily passive!listening predators "own unpub! lished data#\ auditory sensitivities tuned to the fre! quency emitted by their basic prey\ such as the mating calls of bush crickets in the case of M[ blythii\ could drive the two species to di}erent kinds of habitats in search of their preferred prey[ MODES OF CO!EXISTENCE WITHIN BAT GUILDS Community studies that have alluded to resource use by insectivorous bats have usually involved groups which did not particularly include rather similar spec! ies "Black 0861\ 0863^ Kunz 0862^ Fenton et al[ 0866\ 0879^ Fenton + Bell 0868^ Fenton 0871\ 0874^ Swift + Racey 0872^ Fenton + Rautenbach 0875^ McKenzie + Rolfe 0875^ Aldridge + Rautenbach 0876^ Rydell 358 R[ Arlettaz Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 0878^ Barclay 0880^ Barataud 0881#[ It is therefore not surprising that coarse!grained niche di}erences have been established in most cases\ except maybe when resources were apparently not limited in supply "Bell 0879#[ In order to recognize _ne!grained patterns behind species co!existence\ the following discussion is deliberately restricted to pairs of cryptic and sibling species\ as comprehensive ecological and behavioural data on entire guilds is still lacking "Kalko 0884#[ Despite the fact that pairs of cryptic bat species exist all over the world\ they have been the subject of ecological studies mainly in the depauperate faunas of the temperate zones of the northern hemisphere[ In the Palaearctic region\ there has been only one further pair of cryptic bat species subjected to intensive stud! ies\ although several such pairs would be available[ Jones + Van Parijs "0882#\ Jones "0886# and Barratt et al[ "0886# have shown that the 34! and 44!kHz phonic types in the taxon Pipistrellus pipistrellus are\ in fact\ two sympatric\ cryptic species of bats[ Jones "0886# has predicted that species!speci_c di}erences in tuning of ultrasound call frequencies of the two phonic types could allow syntopic resource par! titioning through the capture of di}erent sizes of prey\ but faecal analyses have provided equivocal evidence "Barlow 0886#[ Indeed\ Barratt et al[ "0884# have established that the two phonic types of P[ pipistrellus are actually not sibling species\ as de_ned in this paper\ but more distantly related\ cryptic species "Jones 0886#[ It is therefore questionable whether the inter!speci_c di}erences in sonar systems relate directly to niche di}erentiation "the disruptive selec! tion hypothesis by Jones + Van Parijs 0882#\ or whether they merely represent plesiomorphic charac! ters which have been acquired independently of niche segregation\ for instance\ during the gradual spe! ciation events "character drift#[ Furthermore\ accord! ing to Vaughan\ Jones + Harris "0886#\ the means by which sympatric co!existence is achieved could instead be di}erential use of space\ although the mechanism behind this is still to be uncovered[ In North America\ Husar "0865# has suggested that Myotis evotis and M[ auriculus diverge in their diets only while occurring sympatrically\ but do not under allopatric conditions[ However\ these two species co! occur over a small part of their distributions "only three localities according to Findley 0859# and must\ hence\ be considered as competitive parapatric species rather than members of the same guild[ Although that study would probably be the most convincing example of competitive exclusion between bat species\ Husar "0865# did not present decisive data about actual food supply at the various foraging locations so that it is questionable whether dietary changes between sym! patric and allopatric conditions were actually the consequence of niche release alone[ Woodsworth "0870#\ Herd + Fenton "0872# and Saunders + Barclay "0881# have established that the pairs Myotis leibiiÐ M[ californicus\ M[ lucifugusÐM[ yumanensis and M[ lucifugusÐM[ volans\ respectively\ segregated more or less through distinct patterns of habitat use[ The scarce evidence gathered so far suggests that sibling bat species partition niche space primarily by exploiting distinct micro!habitats "McKenzie + Rolfe 0875^ Kalko 0884#[ Microchiroptera\ at least insec! tivorous species\ would not therefore di}er sub! stantially from other vertebrates "Pianka 0858\ 0862^ Schoener 0857\ 0875^ MacArthur 0861^ Rosenzweig 0870\ 0876^ Bell 0873^ but see Grant 0875^ Brown 0878#[ Interestingly\ most pairs of cryptic and sibling species for which habitat segregation has been estab! lished conclusively belong to the taxon Myotis[ Con! trary to the majority of temperate zone bats that cap! ture airborne prey\ the genus Myotis includes many species that glean prey from substrates "Beck 0883^ Arlettaz 0885a\c#[ While aerial!hawking bats readily exploit ephemeral\ patchy trophic resources\ such as swarming insects which provide temporally and spa! tially unlimited food supplies\ gleaning bats are appar! ently less prone to do so\ probably because similar concentrations are far less common among {substrate! dwelling| arthropods[ One can therefore wonder if the exploitation of more predictable trophic resources\ as in the case of Myotis\ may imply more structured modes of community organization among insec! tivorous bats< It seems clear that ecomorphology would hardly have been able to predict the subtle nature and the contrasted patterns of resource and space use by M[ myotis and M[ blythii[ Morphologically almost indis! tinguishable\ the sibling mouse!eared bats project far apart into ecological space[ We can therefore wonder how many species described as merging in mor! phospace do actually di}er radically in their use of resources[ Acknowledgements The author would like to thank S[ Vogel\ I[ Horacek\ T[ Kokurewicz\ F[ Matt and J[ M[ Serveau for assist! ance in the _eld[ Professor G[ Estabrook kindly pro! vided a b!version of his program MACACTUS\ O[ Glai! zot and H[ Saiah helped with computer analyses and literature research\ and J[ Goudet performed the ran! domization tests[ I am indebted to P[ Vogel and C[ Konig for logistic support\ and to N[ di Marco who assisted me in the electrophoretical laboratory[ I am grateful to Ph[ Christe\ M[ Desfayes\ J[ Hausser\ G[ Jones\ C[ Neet\ P[ Racey\ J[ Rydell and\ particularly\ K[ Barlow\ who made a thorough appraisal of the manuscript and improved the English[ Financial sup! port was provided by grants of the Conseil de la cul! ture de l|Etat du Valais and the Fondation Dr Ignace Marietan[ References Aldridge\ J[D[J[N[ "0875# Manoeuvrability and ecological segregation in the little brown bat "Myotis lucifugus# and 369 Habitat selection in sibling bat species Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Yuma "M[ yumanensis# bats "Chiroptera] Vesper! tilionidae#[ Canadian Journal of Zoology\ 53\ 0767Ð0771[ Aldridge\ H[D[J[N[ + Rautenbach\ I[L[ "0876# Morphology\ echolocation and resource partitioning in insectivorous bats[ Journal of Animal Ecology\ 45\ 652Ð667[ Arita\ E[ "0886# Species composition and morphological structure of the bat fauna of Yucatan[ Mexico[ Journal of Animal Ecology\ 55\ 72Ð86[ Arlettaz\ R[ "0884# Ecology of the sibling mouse!eared bats "Myotis myotis and Myotis blythii#] zoogeography\ niche\ competition\ and foraging[ PhD thesis\ University of Lau! sanne\ Lausanne\ Switzerland[ Horus Publishers\ Martigny\ Switzerland[ Arlettaz\ R[ "0885a# Feeding behaviour and foraging strategy of free!living mouse!eared bats "Myotis myotis and Myotis blythii#[ Animal Behaviour\ 40\ 0Ð00[ Arlettaz\ R[ "0885b# Ernahrung und Jagdhabitatwhal beim Grossen und Kleinen Mausohr] Neue okologische For! schungsresultate als Basis fur Schutzmassnahmen fur diese zwei Arten in der Schweiz[ Fledermaus!Anzeiger\ Extra! blatt\ 0\ 6Ð8[ Arlettaz\ R[ "0885c# Foraging behaviour of the gleaning bat Myotis nattereri "Chiroptera\ Vespertilionidae# in the Swiss Alps[ Mammalia\ 59\ 070Ð075[ Arlettaz\ R[\ Beck\ A[\ Guttinger\ R[\ Lutz\ M[\ Ruedi\ M[ + Zingg\ P[ "0883# Ou se situe la limite nord de repartition geographique de Myotis blythii "Chiroptera[ Ves! pertilionidae# en Europe centrale< Zeitschrift fur Sau! getierkunde\ 48\ 070Ð077[ Arlettaz\ R[\ Perrin\ N[ + Hausser\ J[ "0886b# Trophic resource partitioning and competition between the two sibling bat species Myotis myotis and Myotis blythii[ Jour! nal of Animal Ecology\ 55\ 786Ð800[ Arlettaz\ R[\ Ruedi\ M[ + Hausser\ J[ "0880# Field mor! phological identi_cation of Myotis myotis and Myotis bly! thi "Chiroptera\ Vespertilionidae#] a multivariate approach[ Myotis\ 18\ 6Ð05[ Arlettaz\ R[\ Ruedi\ M[\ Iban½ez\ C[\ Palmeirim\ J[ + Hausser\ J[ "0886a# A new perspective on the zoogeography of the sibling mouse!eared bat species Myotis myotis and Myotis blythii] morphological\ genetical and ecological evidence[ Journal of Zoology "London#\ 131\ 34Ð51[ Audet\ D[ "0889# Foraging behaviour and habitat use by a gleaning bat\ Myotis myotis "Chiroptera[ Vesper! tilionidae#[ Journal of Mammalogy\ 60\ 319Ð316[ Barataud\ M[ "0881# L|activite crepusculaire et nocturne de 07 especes de chiropteres\ revelee par marquage lumi! nescent et suivi acoustique[ Le Rhinolophe\ 8\ 12Ð46[ Barclay\ R[M[R[ "0880# Population structure of temperate zone insectivorous bats in relation to foraging behaviour and energy demand[ Journal of Animal Ecology\ 59\ 054Ð 067[ Barlow\ K[E[ "0886# The diets of two phonic types of the bat Pipistrellus pipistrellus in Britain[ Journal of Zoology "London#\ 132\ 486Ð598[ Barratt\ E[M[\ Bruford\ M[W[\ Burland\ T[M[\ Jones\ G[\ Racey\ P[A[ + Wayne\ R[K[ "0884#[ Characterization of mitochondrial DNA variability within the mic! rochiropteran genus Pipistrellus] approaches and appli! cations[ Symposium of the zoological Society of London\ 56\ 266Ð275[ Barratt\ E[M[\ Deaville\ R[\ Burland\ T[M[\ Bruford\ M[W[\ Jones\ G[\ Racey\ P[A[ + Wayne\ R[K[ "0886# Pipistrelle bat species[ DNA answers the call[ Nature\ 276\ 027Ð028[ Beck\ A[ "0883# Fecal analysis of European bat species[ Myotis\ 21Ð22\ 098Ð008[ Bell\ G[P[ "0879# Habitat use and response to patches of prey by desert insectivorous bats[ Canadian Journal of Zoology\ 47\ 0765Ð0772[ Bell\ G[P[ "0873# A bird community of lowland rainforest in New Guinea[ 5[ Foraging ecology and community struc! ture of the avifauna[ Emu\ 73\ 131Ð147[ Black\ H[L[ "0861# Di}erential exploitation of moths by the bats Eptesicus fuscus and Lasiurus cinereus[ Journal of Mammalogy\ 42\ 487Ð590[ Black\ H[L[ "0863# A north temperate bat community] struc! ture and prey populations[ Journal of Mammalogy\ 44\ 027Ð046[ Brown\ J[S[ "0878# Desert rodent community structure] a test of four mechanisms of coexistence[ Ecological Mono! graphs\ 48\ 0Ð19[ Crome\ F[J[J[ + Richards\ G[C[ "0877# Bats and gaps] Mic! rochiropteran community structure in a Queensland rain forest[ Ecology\ 58\ 0859Ð0858[ Estabrook\ C[B[ + Estabrook\ G[F[ "0878# Actus] a solution to the problem of small samples in the analysis of two!way contingency tables[ Historical Methods\ 71\ 4Ð7[ Fenton\ M[B[ "0871# Echolocation calls and patterns of hunt! ing and habitat use of bats "Microchiroptera# from Chil! lagoe\ North Queensland[ Australian Journal of Zoology\ 29\ 306Ð314[ Fenton\ M[B[ "0874# The feeding behaviour of insectivorous bats] echolocation\ foraging strategies\ and resource par! titioning[ Transvaal Museum\ 10\ 4Ð05[ Fenton\ M[B[ + Bell\ G[P[ "0868# Echolocation and feeding behaviour in four species of Myotis "Chiroptera#[ Can! adian Journal of Zoology\ 46\ 0160Ð0166[ Fenton\ M[B[\ Boyle\ N[G[H[\ Harrison\ T[M[ + Oxley\ D[J[ "0866# Activity patterns\ habitat use\ and prey selection by some African insectivorous bats[ Biotropica\ 8\ 62Ð74[ Fenton\ M[B[ + Rautenbach\ I[L[ "0875# A comparison of the roosting and foraging behaviour of three species of African insectivorous bats "Rhinolophidae\ Vesper! tilionidae\ and Molossidae#[ Canadian Journal of Zoology\ 53\ 1759Ð1756[ Fenton\ M[B[\ Van Zyll de Jong\ C[G[\ Bell\ G[P[\ Campbell\ D[B[ + Laplante\ M[ "0879# Distribution\ parturition dates\ and feeding of bats in South!central British Colum! bia[ Canadian Field Naturalist\ 83\ 305Ð319[ Findley\ J[ "0859# Identity of the long!eared Myotis of the Southwest and Mexico[ Journal of Mammalogy\ 30\ 05Ð 19[ Findley\ J[ "0882# Bats\ a Community Perspective[ Cambridge University Press\ Cambridge\ UK[ Findley\ J[S[ + Black\ H[ "0872# Morphological and dietary structuring of a Zambian insectivorous bat community[ Ecology\ 53\ 514Ð529[ Grant\ P[R[ "0875# Ecology and Evolution of Darwin|s Finches[ Princeton University Press\ Princeton\ USA[ Harris\ S[\ Cresswell\ W[J[\ Forde\ P[G[\ Trewhella\ W[J[\ Woollard\ T[ + Wray\ S[ "0889# Home!range analysis using radio!tracking data\ a review of problems and techniques particularly as applied to the study of mammals[ Mammal Review\ 19\ 86Ð012[ Heller\ K[G[ + von Helversen\ O[ "0878# Resource par! titioning of sonar frequency bands in rhinolophoid bats[ Oecologia\ 79\ 067Ð075[ Herd\ R[M[ + Fenton\ M[B[ "0872# An electrophoretic\ mor! phological\ and ecological investigation of a putative hybrid zone between Myotis lucifugus and Myotis yum! anensis "Chiroptera[ Vespertilionidae#[ Canadian Journal of Zoology\ 50\ 1918Ð1949[ Husar\ S[L[ "0865# Behavioural character displacement] evi! dence of food partitioning in insectivorous bats[ Journal of Mammalogy\ 46\ 220Ð227[ Jones\ G[ "0886# Acoustic signals and speciation] the roles of natural and sexual selection in the evolution of cryptic species[ Advances in the Study of behaviour\ 15\ 206Ð243[ Jones\ G[ + Van Parijs\ S[M[ "0882# Bimodal echolocation in pipistrelle bats] are cryptic species present< Proceedings of the Royal Society of London B\ 140\ 008Ð014[ 360 R[ Arlettaz Þ 0888 British Ecological Society Journal of Animal Ecology\ 57\ 359Ð360 Kalko\ K[V[ "0884# Echolocation signal design\ foraging habitats and guild structure in six Neotropical sheath! tailed bats "Emballonuridae#[ Symposium of the Zoological Society of London\ 56\ 148Ð162[ Krebs\ C[J[ "0878# Ecological Methodology[ Harper and Collins\ New York[ Kunz\ T[H[ "0862# Resource utilization] temporal and spatial components of bat activity in Central Iowa[ Journal of Mammalogy\ 43\ 03Ð21[ MacArthur\ R[H[ "0861# Geographical Ecology[ Harper and Row\ New York[ Manly\ B[J[F[ "0880# Randomization and Monte Carlo Methods in Biology[ Chapman and Hall\ London[ Matusita\ K[ "0844# Decision rules based on distance\ for problems of _t\ two samples and estimation[ Annals of Mathematics and Statistics\ 15\ 520Ð539[ Mayr\ E[ "0866# Populations\ Species and Evolution\ 5th edn[ Harvard University Press\ Cambridge[ McKenzie\ N[L[ + Rolfe\ J[K[ "0875# Structure of bat guilds in the Kimberley mangroves[ Australia[ Journal of Animal Ecology\ 44\ 390Ð319[ Neuweiler\ G[ "0873# Foraging\ echolocation and audition in bats[ Naturwissenschaften\ 60\ 335Ð344[ Nowak\ R[M[ "0880# Walker|s Mammals of the World[ 4th edn[ The John Hopkins University Press\ Baltimore\ USA[ Pianka\ E[R[ "0858# Sympatry of desert lizards "Ctenotus# in Western Australia[ Ecology\ 49\ 0901Ð0929[ Pianka\ E[R[ "0862# The structure of lizard communities[ Annual Review of Ecology and Systematics\ 3\ 42Ð63[ Pianka\ E[R[ "0870# Competition and niche theory[ Theor! etical Ecology] Principles and Applications "ed[ R[ May#\ pp[ 056Ð085[ Sinauer Associates\ Sunderland\ Mas! sachusetts[ Ricklefs\ R[E[ "0889# Ecology\ 2rd edn[ Freeman\ New York[ Rosenzweig\ M[C[ "0870# A theory of habitat selection[ Ecol! ogy\ 52\ 216Ð224[ Rosenzweig\ M[C[ "0876# Editor|s coda] central themes of the symposium[ Evolutionary Ecology\ 0\ 390Ð396[ Rudolph\ B[U[ "0878# Habitatwahl und Verbreitung des Mau! sohrs "Myotis myotis# in Nordbayern[ Unpublished PhD thesis\ University of Erlangen!Nurnberg\ Erlangen\ Ger! many[ Ruedi\ M[\ Arlettaz\ R[ + Maddalena\ T[ "0889# Distinction morphologique et biochimique de deux especes jumelles de chauves!souris] Myotis myotis "Bork[# et Myotis blythi "Tomes# "Mammalia[ Vespertilionidae#[ Mammalia\ 43\ 304Ð318[ Rydell\ J[ "0878# Food habits of northern "Eptesicus nilssoni# and brown long!eared "Plecotus auritus# bats in Sweden[ Holarctic Ecology\ 01\ 05Ð19[ Saunders\ M[B[ + Barclay\ R[M[R[ "0881# Ecomorphology of insectivorous bats] a test of predictions using two mor! phologically similar species[ Ecology\ 62\ 0224Ð0234[ Schoener\ T[W[ "0857# The Anolis lizards of Bimini] resource partitioning in a complex fauna[ Ecology\ 38\ 693Ð615[ Schoener\ T[W[ "0875# Resource partitioning[ Community Ecology] Pattern and Process "eds J[ Kikkawa + and D[ J[ Anderson#\ pp[ 80Ð015[ Blackwell Scienti_c Publications\ Victoria[ Swift\ S[M[ + Racey\ P[A[ "0872# Resource partitioning in two species of vespertilionid bats "Chiroptera# occupying the same roost[ Journal of Zoology "London#\ 199\ 138Ð 148[ Vaughan\ N[\ Jones\ G[ + Harris\ S[ "0886# Habitat use by bats "Chiroptera# assessed by means of a broad!band acoustic method[ Journal of Applied Ecology\ 23\ 605Ð629[ White\ G[C[ + Garrott\ R[A[ "0889# Analysis of Wildlife Radio!Tracking Data[ Academic Press\ San Diego[ Wiens\ J[A[ "0878# The Ecology of Bird Communities[ Cam! bridge University Press\ Cambridge[ Willig\ M[R[ + Moulton\ M[P[ "0878# The role of stochastic and deterministic processes in structuring neotropical bat communities[ Journal of Mammalogy\ 69\ 212Ð218[ Woodsworth\ G[C[ "0870# Spatial partitioning by two species of sympatric bats\ Myotis californicus and Myotis leibii[ PhD thesis\ Carleton University\ Ottawa[ Received 01 January 0887^ revision accepted 00 July 0887