Patterns Of Alpha-diversity And Abundance In Breeding Bird .
Condor, 81:21-27@ The Cooper Ornithological Society 1979PATTERNSBREEDINGJEFFREYOF ALPHA-DIVERSITYBIRD COMMUNITIESAND ABUNDANCEINACROSS NORTH AMERICAJ. SHORTCommunity diversity can be examined bynoting the number of species within a singlehabitat of known area (alpha-diversity),thechanges in species composition along a seriesof habitats (beta-diversity), or the total species richness of a large geographic region(gamma-diversity;Whittaker1960, 1972).The diversity of breeding birds in a community is closely related to the structure ofthe vegetation (MacArthurand MacArthur1961, MacArthur et al. 1962, 1966, Tramer1969, Karr and Roth 1971, Peterson 1975, Roth1976). Studies of beta-diversity in birds havefocused on species composition or rates ofspecies turnover between adjacent habitats(Cody 1970, 1975, Tramer 1974a, Karr 1976).Gamma-diversity patterns have been examinedfor breeding birds (MacArthur and Wilson1967, Cook 1969, Bock and Lepthien 1975)and wintering birds (Bock and Lepthien1974, 1976, Tramer 1974a, b) but these studiesbased their comparisons on extensive areaswhich obscured fine patterns of diversity.Since birds respond to the proximate releasersof their habitat (James 1971), not arbitrarygeographic blocks, an analysis of local aviancommunities could provide insights into diversity pertaining to the structure of breedingbird populations.Cook ( 1969), Tramer (1974a), and Bockand Lepthien (1974, 1975, 1976) have tracedthe diversity of North American birds tochanges in earth history and its subsequenteffects on climate, vegetation, and resourceavailability. These analyses considered relative species richness and disregarded the effects of relative species abundance, or speciesequitability.My objectives here are to describe and interpret patterns of species frequency distribution within breeding bird communities in North America.METHODSMaps were prepared for the United States and southern Canadadepictingbreedingbirdpopulationdensity, the number of species, species diversity, andspecies equitability.These maps show isopleths,lines connecting points along which a given variablehas a specified constant value. They are based upondata gleaned from 445 Breeding Bird Censuses (inNational Audubon Society publications)conductedbetween 1936 and 1973. Generally, these censusesare carefully planned and executed; in each census,participants who are familiar with their area followstandardized methods to evaluate the birds withina relatively uniform habitat. They accurately list allspecies present but are less accurate in estimatingthe number of pairs present (MacArthur1965).I screened individual censuses to ensure that thecensus plots had mature, relativelyhomogeneousvegetation.Those censuses containing early seralstages, such as the “old field” of eastern forests, wereexcluded. The censuses were classifie’d into twelvecategories according to the dominantvegetation,closely following those recognized by Kiichler ( 1964).Since the censuses varied considerably in size, onlythose with areas between 8 and 40 ha (15 to 100acres) were used in the analysis, to minimize theintroductionof bias when calculatingpopulationdensities.All densities were standardizedto thenumber of territorial males per 40 ha, an estimateof the number of breeding pairs.Breeding Bird Censuses use the spot-map method(Williams1936, Kendeigh1944),which is mosteffective when censusing landbirds with limited territories.Therefore, I excluded all species that inhabit large bodies of water and certain landbirdssuch as owls, hawks, or vultures, which have verylarge territories.Some species that do not establishterritories,such as the Brown-headedCowbird( Molothrus ater), were included because they werepresent in a majority of habitats.The analysis included 310 species.Alpha-diversityfor each census was calculatedusing the Shannon and Weaver (1963)informationtheorem,H’ -xpt log,t 1pi,where pt is the proportion of species i of the totalnumber of individuals in the population.This is theindex most used to calculate alpha-diversity(Pielou1969).Tramer (1974a)suggested that patterns ofresource partitioning within avian communities couldbe compared on the basis of the relative frequenciesof each species in the population.To measure theevenness of species distribution( equitability),Iused,J’ W/log,s,where H’ is the species diversity of a census withS species, because it allows cross-comparisons of communities that support different species or disparateproportions of species. Logically, if the species areequally distributed, then the habitat and resourcesnecessary for each species should also be equitablydistributed.I used several different mapping programs to confirm results, but will present only maps created byCONTOUR(University of Calgary).The data wereanalyzed with the CDC 6400 at the University ofArizona. The maps were drawn by a CALCOMP665Plotter. Many of the censuses used covered the sameplot in different years, hence, the spatial coordinatesof their plots were identical. CONTOURwas unableto assimilate these duplications so I averaged cen-Kill
JEFFREYJ. SHORTNUMBEROFSPECIES’8”total per 40FIGURE1. The species richness, or simple species count, withinica (based on 445 Breeding Bird Censuses).suses with the same location to obtain a mean foreach of the four indices. A continental outline wasdrawn by CONTOURby assigning a zero value tothe coordinates of 50 coastal and border cities. This4ohectarehomogeneous habitats across NorthAmer-produced a steep border on the maps due to the increment differences between the nearest grid values(calculated by CONTOUR)and the zero value alongthe outline.1.2SPECIES DIVERSITY3224162.02.42.83.2 H’ FIGURE2. Species diversity of breeding birds (see text for explanation),North America.within homogeneous habitats across
23600TOTAL ABUNDANCEnumber of pairs per 40FIGUREica.3.hectareTotal abundance, or density, of breeding pairs within homogeneous habitats across NorthRESULTSFigures 1 and 2 show the similarity betweenspecies diversity (H') and the raw number ofspecies present in a community. These mapsindicate that diversity is highest in the northeastern forests, mid-continentally along thewestern Mississippi River drainage and to alesser extent in the Pacific northwest. Diversity declines westward in the prairie biome.Landbirds are generally more abundantwest of the Appalachian region than in therest of the eastern forests (Fig. 3). Prairiessupport the smallest total bird populations.Densities in the west are approximately halfthose found in the east. Birds are especiallynumerous in two parts of the north-centralregion, reflecting the many censuses frommarshes there.Breeding bird equitabilities (Fig. 4) werehighest across the southern tier of states, withnorthward extensions up both coasts. Theavifauna was evenly distributed throughoutthe mid-continental region. Table 1 subdivides the avian populations by habitat typeand confirms the geographic patterns shownby the maps.DISCUSSIONFigures 1 through 4 depict the character ofsmall communities of nesting landbirds acrossAmer-North America. Comparisons with similarstudies based on species range maps (MacArthur and Wilson 1967, Cook 1969 ) orwintering birds (Bock and Lepthien 1974,Tramer I974a, b) are difficuh, since thesestudies include some waterfowl, or their samples spanned many types of habitats. Breeding Bird Surveys evaluate the avifauna alonga changing habitat which has considerableedge effect (24% X % mi) resulting in anestimate of diversity between habitats. However, Figures 1 and 2 show diversity patternsthat are comparable with those in the mapconstructed by Bock and Lepthien (1975)based upon Breeding Bird Surveys. Table 1likewise yields interpretations that parallelPeterson’s (1975) analysis of species diversityby habitat type. Thus, patterns of alphadiversity and beta-diversity appear to be similar, differing from gamma-diversity (Cook1969) primarily in the west because the rangesof many species overlap there (Bock andLepthien 1975). Combining the species foundacross vast distances or sampling areas withthe propensity for many species creates patterns of more diversity than when consideringrelatively local populations in homogeneoushabitats ( this study).Alpha-diversity in birds can be simply expressed as the number of species present in
24JEFFREYJ. SHORTJ’ SPECIESFIGURE4.across North0.64The evenness of species distributionAmerica.(see text for explanation),.a8withinhomogeneous habitats.96suggest that this region contains areas of highand low diversity. Birds are most diverse(Figs. 1 and 2) in the vegetationally complexeastern forest communities, not only becauseof the high numbers of species breeding there,but also because of the dense and evenly distributed populations (Table 1). The areas ofslightly lower diversity in the southeast aredue to the relatively sterile coniferous forests(Tramer 1974a). These are less complex thanTABLE 1. Means ? standard deviations of four avian populationCensuses) in twelve habitat types in North America.Vegetationaltype( and region)Prairie (central)MarshlandDry scrubland (west)Riparian forest (west )Montane coniferousforest (west)Western mixed forestNorthern deciduousforest (northeast )Northern coniferousforest (northeast)Northern mixedforest (northeast)Southern deciduousforest (southeast)Southern coniferousforest (southeast)Southern mixedforest (southeast)forI30EQUITABILITYa community (Tramer 1969). Although H’(Fig. 2) appears to be more sensitive to smallvariations than the simple species count (Fig.1 ), their isopleths match almost exactly, indicating that these two measures are analogous.Tramer (1974a) reported that avian alphadiversity was “virtually constant” throughoutthe eastern forests. Figures 1 and 2 show nodistinct latitudinal gradients in the east, but* See 6184characteristics (based on 445 Breeding BirdNUlllLF3of iesdiversity’1.6261.5062.0692.547 7,414.496559201 k 122227 f 12716.03 c 6.8015.78 8.172.381 t .4912.066 c .6920.894 c .1020.797 k .20439253 f16220.53 -c 8.192.614 -c .4460.886 zk .06448225 -c- 10418.25 - - 6.102.463 k .3820.867 k .07939220 k8322.64 -c 5.362.637 k .3320.854 -I- .07562335 & 17420.82 ? 7.552.651 2 .3840.894 c .04322250 k8518.50 -c 4.992.515 & .3500.879 -I .08449223 f13818.63 I!I 6.352.535 r0.890 -I- .064.4350.8450.7590.8770.852k*fk.082.166.071.121
DIVERSITYthe deciduous floodplain forests in the Mississippi River basin ( pers. observ. ), whichhave relatively more diversity but similarequitability (Fig. 4). The seasonal influx ofbreeding birds into northern communitiesprobably is responsible for the high diversitiesin these regions (MacArthur1959, Tramer1974a). Higher equitabilities in the easternforests (Table 1) suggest that resources (nesting sites, food, and mates) are more evenlydistributed here than in the west.Communities with dense, evenly distributedpopulations would tend to restrict “nichebreadth compensation for low alpha-diversity”(Cody 1975) which is niche expansion byspecies into depauperate habitats. This restriction apparently is diminished along theecotone between the eastern forests and thegrasslands, where Shugart and James (1973)found typical woodland birds inhabitinggrassy successional stages. They believed thatthis represented an historic adaptation of theforest species to the previous prairie “interdigitations” in northwestern Arkansas, thatwas not available to the birds in comparableeastern studies (Johnston and Odum 1956).The high diversity found by Shugart andJames in the grassy seres represents a type ofniche-breadth compensation by the woodlandbirds in this region.Cook (1969) and Peterson (1975) foundthat species diversity increased with an increase in latitude in the mid-continental grasslands. Figures 1 and 2 do not support theirfindings but show lowered diversity withinhabitats throughout the prairies, with corresponding low densities (Fig. 3).Cody(1966, 1970) and Wiens (1969, 1973) notedthis phenomenon, which results from a combination of environmental and vegetationalfactors there. The uneven distribution of theavifauna (Table 1) suggests that a few speciesare dominating these communities. Wiens(1974) reported a dominance of mediumsized birds in shortgrass prairies and Tramer(1969) showed that marshland aggregationsof breeding birds are often unevenly distributed because of behavioral differences innesting and feeding. The marshland censusesused in my study typically contained highnumbers of Red-winged Blackbirds ( Ageluiusphoeniceus) and Yellow-headed Blackbirds( Xanthocephalus xanthocephalus ), whose gregarious behavior created peaks of high nestingdensity in the northern grasslands (Fig. 3)with less equitable distribution of the species(Fig. 4) in the same regions.Species diversity is steeply graded in thewest (Figs. 1 and 2) with less overall changeINBREEDINGBIRDCOMMUNITIES25in densities (Fig. 3) from place to place.Diversity within habitats decreases eastwardin response to the high north-south mountainranges. MacArthur and Wilson (1967), Cook(1969) and Bock and Lepthien (1975) foundsimilar patterns of gamma-diversity, especiallyin the Great Basin region. Habitats havingmostly evenly-spaced vegetation (montaneconiferous forests and dry shrubby communities) also have evenly distributed avifaunas(Table I).Historical explanations have been offerednot only for avian speciation (Miller 1951,Mengel 1964, 1970), but also gamma-diversityof wintering birds (Tramer 1974a) or breedingbirds ( Cook 1969), and avian alpha-diversityin Florida (Noel Warner, pers. comm. ) . Regional patterns of avifaunal richness doubtlesspersist as a result of Pleistocene glaciation thatrepeatedly separated and reunited large tractsof habitat and the birds that lived there. However, local populations of birds probably aremore responsive to short-term environmentalfluctuations than to geologic events whichtake thousands of years. Bock and Lepthien(1975) found that breeding bird diversity inNorth America was correlated primarily withrelative moisture and to a lesser degree withtemperature. Figures 1 and 2 show the samepatterns in diversity, which reflect the moisture patterns in North America described byVisher (1966). The mountain ranges in theGreat Basin region influence avian diversityby their effects on the type and availabilityof moisture and habitat.Winter environmental conditions can alsoaffect diversity during the breeding season(MacArthur1959, Fretwell1972, Tramer1974a) by limiting resources which mightaffect the evenness of species distribution. Mymap of breeding bird equitability (Fig. 4)resembles Bock and Lepthien’s (1974, 1975)diversity map of wintering birds; therefore,I visually compared my map to the climaticmaps in Visher (1966).Figure 4 resemblesthe maps of temperature patterns more thanthose of precipitation-humidity regimes, whichare more longitudinal.The equitability ofbreeding birds also bears a remarkable likeness to various temperature-related patternssuch as: (1) regions with hot summers andcold winters, (2) a decreasing probability offrost during late spring, (3) the proportion ofmoisture falling as snow, (4) the date whenthe mean daily temperature rises above or,(5) falls below 35”F, the temperature atwhich some vegetative growth occurs.The region of low equitabilities (Fig. 4)also resembles Mengel’s (1964) composite pic-
26JEFFREYJ. SHORTture of the maximum extent of the Pleistoceneglaciation, especially the subarctic components. This may indicate a historic relationship between temperature and avian equitability.Avian communities with high diversityusually occupy diverse habitat which is closelyrelated to the amount of available moisture.High equitability of breeding birds impliesequal distribution of the habitat and its resources among the species. Those communities with high equitability probably reflectmore stable year-round production of resources than those with large oscillations ofthe avifauna. Overall annual production of resources is higher in the south than the north,due to more solar input. Although southerncommunities have fewer neotropical migrants(MacArthur1959) to exploit the resourcesthan northern communities, both the northeastand northwest display very high equitabilities(Fig. 4) along with the southern deserts andswamps. This appears to be contradictoryunless the stabilizing effect of moisture ontemperature is considered; the northwesternand northeastern regions receive maritime buffering which moderates temperatures. Evidently, breeding bird diversity depends on thehabitat of the community, which reflects themoisture regimes of a region. The evennessof species distribution appears to be relatedto resource availability and stability, whichreflect temperature regimes and glacial history.SUMMARYIsopleth analysis of Breeding Bird Census datawas used to examine patterns of within-habitatspecies richness, diversity, and abundance inNorth America. Richness and diversity wereparallel measures; they were high in the eastand northwest and low in the prairie and intermountain regions. Densities in the east wereapproximately twice those of the west, with alarge mid-continental trough. The specieswere evenly distributed across the south andnorthward along both coasts. The equitabilityof species abundance appears closely tied withweather patterns relating to temperature andits effects on resource equilibrium.ACKNOWLEDGMENTSI thank all those involved with the original study, mymajor professor, Douglas James, and the Departmentof Zoology at the Universityof Arkansas.TheArkansas Audubon Society Trust provided financialsupport. William Rasmussen and Alma Sperr, at theUniversity of Arizona, provided expertise with variousmapping programs.Chris VanDyckprepared thefigures. I am especially beholden to Frances James,Kimberly Smith, and the reviewers for helpful comments on the study.LITERATURECITEDBOCK, C. E., AND L. W. LEPTHIEN.1974.Winterpatterns of bird species diversity and abundancein the United States and Canada. Am. Birds28:557-562.BOCK, C. E., AND L. W. LEPTHIEN.1975.Patternsof bird snecies diversitv revealed bv ChristmasCounts versus Breeding Bird Surieys.West.Birds 6:95-100.BOCK, C. E., AND L. W. LEPTHIEN.1976.Synchronous eruptions of boreal seedeating birds.Am. Nat. 110:559-571.1966.The consistency of intra- andCODY, M. L.intercontinentalgrassland bird species counts.Am. Nat. 100:371-376.CODY, M.L.1970.Chileanbirddistribution.Ecology 51:455-464.CODY, M. L.1975.Towards a theory of continentalspecies diversities: bird distributions over Mediterranean habitat gradients, p. 214-257.In M.L. Cody and J. M. Diamond [eds.], Ecology andevolution of communities.Harvard Univ. Press,Cambridge, Mass.COOK, R. E.1969. Variation in species density ofNorth American birds. Syst. Zool. 18:63-84.FRETWELL, S. D.1972.Populations in a seasonalenvironment.Princeton Univ. Press. Princeton,NJ.JAMES, F. C.1971.Ordinations of habitat relationshius among breeding birds. Wilson Bull. 83:215-230.c’JOHNSTON, D. W., AND E. P. GDUM.1956.Breedingbird populations in relation to plant successionon the Piedmont of Georgia. Ecology 37:50-62.KARR, J. R., AND R. R. ROTH. 1971.Structure ofavian communities in selected Panama and Illinois habitats. Ecol. Mononr. 41:207-233.KARR, J. R. 1976. Within- 8‘ nd between-habitatavian diversity in African and neotropical lowland habitats. Ecol. Monoar. 46:457481.1944.Measurement of bird popuKENDEIGH, S. C.lations. Ecol. Monogr. 14:67-106.K CHLER, A. W.1964. Potential natural vegetationof the coterminous United States. Am. Geogr.Sot. Spec. Publ. 36.MACARTHUR, R. H.1959.On the breeding distributionpattern of North American migrantbirds. Auk 76:318-325.MACARTHUR, R. H.1965.Patterns of species diversitv. Biol. Rev. 40:510-533.MACARTHUR, R. H., AND J. W. MACARTHUR.1961.On bird species diversity.Ecology 42:594-598.MACARTHUR, R. H., J. W. MACARTHUR, AND J. PREER.1962.On bird species diversity:II. Predictionof bird census from habitat measurements. Am.Nat. 96: 167-174.MACARTHUR, R. H., H. RECHER, AND M. CODS. 1966.On the relation between habitat selection andspecies diversitv.Am. Nat. 100:319-322.MACARTHUR, R. H.,.AND E. 0. WILSON.1967.Thetheory of island biogeography.Princeton Univ.Press, Princeton, NJ.MENGEL, R. M.1964.The probable history ofspecies formation in some northern wood warblers ( Parulidae) . Living Bird 3:9-43.MENCEL, R. M.1970. The North American centralplains as an isolating agent in bird speciation,
DIVERSITYp. 279340.In W. Dort, Jr., and J. K. Jones, Jr.reds.], Pleistocene and recent environments ofthe Central Great Plains. Dept. Geology, Univ.Kansas Spec. Publ. 3.1951.An analysis of the distribuMILLER, A. H.tion of the birds of California. Univ. Calif. Publ.Zool. 50:531-644.PETERSON, S. R.1975.Ecological distributionofbreeding birds, p. 22-38.In Proceedings of thesymposium of management of forest and rangehabitats for nongame birds. U.S. Dept. Agr.,For. Serv. Gen. Tech. Rep. WO-1.PIELOU, E. C. 1969. An introductionto mathematical ecology. Wiley-IntersciencePress, NY.1976.Spatial heterogeneity and birdROTH, R. R.species diversity.Ecology 57:773-782.SHANNON, C. E. AND W. WEAVER.1963.TheUniv.mathematicaltheory of communication.of Illinois Press, Urbana, Ill.SHUGART, H. H., AND D. A. JAMES. 1973. Ecological succession of breeding bird populations innorthwestern Arkansas. Auk 90:62-77.ComTRAMEH, E. J. 1969. Bird species diversity:ponents of Shannon’s formula. Ecology 50:927929.Latitudinalgradients inTRAINER, E. J. 1974a.avian diversity. Condor 76: 123-130.@ COMMUNITIES27TRAMER, E. J. 197410. An analysis of the speciesdensity of U.S. landbirds during the winter usingthe 1971 Christmas Bird Count.Am. Birds28: 563-567.Climatic atlas of the UnitedVISHER, S. S. 1966.States. Harvard Univ. Press, Cambridge, Mass.1960.Vegetation of the SiskiyouWHITTAKER, R. H.Mountains, Oregon and California. Ecol. Monogr.30: 279-338.1972.Evolution and measureWHITTAKER, R. H.ment of species diversity. Taxon 21:213-251.WIEKS, J. A.1969.An approach to the study ofecological relationships among grassland birds.Ornithol. Monogr. 8: l-93.WIENS, J. A.1973. Pattern and process in grassland bird communities.Ecol. Monogr. 43:237270.J. A.1974. HabitatheterogeneityandWIEXS,avian community structure in grasslands. Am.Midl. Nat. 91:195-213.The composition and dyWILLIAMS, A. B. 1936.namics of a beech-mapleclimax community.Ecol. Monogr. 6:317408.AFESCIDEVN(BASH),Tyndall Air ForceFL 32403. Accepted for publication 14 MarchBase,1978.1979PUBLICATIONSDucks, Geese & Swans of North America.-FrankC. Bellrose. 1976. Stackpole Books, Harrisburg, PA.540 p. 15.00. Here is a completely new and expanded version of the classic work by F. H. Kortright,which first appeared in 1942. Introductory chapterstreat classification, molts and plumages (by MiltonW. Weller),migration, conservation (by Glen C.Sanderson), hunting regulations (by Arthur S. Hawtechnique,and mortalityandkins ) , identificationdisease. The species accounts cover on,migration,breeding, postbreeding activity, and food habits. Virtually the only unchanged elements of the originalare T. M. Shortt’s color plates, and even these arenow grouped together and some of them are not wellprinted.New additions are many maps of rangesand migration corridors and the graphs of seasonal/geographic population changes. List of references,appendixes, index. This book contains a wealth ofclearly-organized information, especially on migrationand populations. It will be invaluable to ornithologistsas well as waterfowl researchers, managers, and hunters. For an in-depth comparison of this work withthose by Paul A. Johnsgard and by Ralph S. Palmer,see the special reviewAuk 94 :172-177 ) .by MiltonW.Weller(1977.Ducks, Geese, and Swans of the World.-PaulA.Johnsgard. 1978. University of Nebraska Press, Lincoln. 404 p. 35.00. The indefatigable Dr. Johnsgardhas provided here a systematic review of the biology ofevery recent species ( 148) in the family Anatidae.No such comprehensive work in English has appearedsince the classic multi-volumetreatises by Phillipsand by Delacour, which have long been out ofprint and are very scarce. This book complements theauthor’s previous ones on waterfowl and summarizeshis long-term studies on their comparative behaviorand relationships.Each species account gives vernacular names, a list of subspecies, if any, measurements and weights, identificationand field marks,natural history, status, relationships, and suggestedreadings. The book is attractively designed and generously illustrated with drawings, distribution maps,and color photographs, all by the author. It will be aninvaluable starting reference on waterfowl,particularly for those species that are not covered in regionalworks on these birds.
Community diversity can be examined by noting the number of species within a single habitat of known area (alpha-diversity), the changes in species composition along a series of habitats (beta-diversity), or the total spe- cies richness of a large geographic region (gamma-diversity; Whittaker 1960, 1972).
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Alpha, beta and gamma diversity and their development Alpha and gamma diversity As Whittaker (1960) noted, alpha and gamma diversity are descriptors of species within one certain area, but they differ in the units considered. Alpha diversity is measured within a sample (in
tion diversity. Alpha diversity Dα measures the average per-particle diversity in the population, beta diversity Dβ mea-sures the inter-particle diversity, and gamma diversity Dγ measures the bulk population diversity. The bulk population diversity (Dγ) is the product of diversity on the per-particle
local diversity (alpha diversity) and the complement of species composition among sites within the region (beta diversity), and how these diversities contribute to regional diversity (gamma diversity) [35, 37]. The influence of alpha and beta diversities on gamma diversity is an essential aspect of local and landscape level conservation plans [38].
alpha, beta, and gamma diversity. Alpha (α) diversity is local diversity, the diversity of a forest stand, a grassland, or a stream. At the other extreme is gamma (γ) diversity, the total regional diversity of a large area that contains several communities, such as the eastern deciduous forests
Alpha, gamma and beta diversity are theoretical constructs that describe the hierarchical, multiscale nature of diversity. Phyto-chemical alpha diversity is the average diversity at the scale of a single sampling unit (i.e. ‘local’ diversity). Gamma diversity is
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