Parus Caeruleus)
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PATTERNS AND SIGNIFICANCE OF GEOGRAPHICAL VARIATION IN THE BLUE TIT (PARUS CAERULEUS) JEAN-LOUIS MARTIN CentreNational de la RechercheScientifique et Centre d'l•cologie Fontionnelle et Evolutive, (CEFE/CNRS), B.P. 5051, F-34033 MontpellierCedex, France, • and AmericanMuseum of Natural History,Department of Ornithology, Central Park West at 79th Street, New York, New York 10024-5192 USA ABSTRACT.--Istudied geographicalvariation in mensural charactersand plumage pattern over the breeding range of the Blue Tit (Paruscaeruleus). In Eurasiabody size decreases clinally from north-northeastto south-southwest,and bill thinnessand relative tarsallength increaseclinally from the northeastto the southwest.This variationis consistentwith changes in environmental factorsknown to affect these characters.Geographical isolates in North Africavary in sizeand in bill andtarsus morphology in a way consistentwith habitatvariation among isolates.Similarities in mensural charactersamong samplesare more consistentwith similaritiesin ecologicalconditions than with taxonomy.Geographical variation in plumage pattern essentiallyis clinal in Eurasiabut discontinuousin North Africa. On a broad scale, plumagepattern variation is consistentwith the populationgroups defined by taxonomists (Eurasianand North African populationgroups). Within eachpopulation group consistency between variation in plumage pattern and the probable population phylogeny is poor. My resultssubstantiate the importanceof the unifying effectof gene flow in adjacentsamples even over a large geographicalarea and the necessityof geographicalisolation to fosterthe appearanceof gaps in clinal variation or of markedly different population characteristics. Received20 June1990, accepted 11 March 1991. NUMEROUS authors have stressed the rela- though plumage color has been used exten- tionshipsbetween morphologicaltraits and en- sively to study geographicalvariation in birds vironmental characteristics (for reviews on eco- and to establishtheir taxonomy(Mayr 1969;for logicalinferences from morphologicaldata, see the Blue Tit, Hartert 1910, 1923, 1932-1938; Vau- Hespenheide 1973, Leisler 1980, Leisler and rie 1957). Climatic variation or variation in Winkler 1985, James1982; for relations between quality of food can influencevariation in color bill sizeor shapewith prey sizeand shape,see (Gloger 1933,Snow 1954b,Slagsvoid and Lifjeld Snow 1954b; Betts 1955; Schoener 1965; John- 1985, Vevers 1985). son 1966;Lack 1971;Grant 1972;Partridge 1976; Basedon this knowledgeI undertooka com- Herrera 1978, 1981; for relations between tarsus prehensive analysisof the variation in men- lengthand perching substrate, see Fretwell 1969, sural characters(size and shape of bill, wing, Lack 1971, Grant 1971; and for relations be- and leg) and plumage(extent of color patches) tweenwing shapeand maneuverabilityin flight, in the Blue Tit (Parus caeruleus)over its entire seeNachtigall and Kempf 1971, Hespenheide breeding range (Fig. 1). I attempt to define the 1973,Kokshaysky 1973). The heritabilityof these principal pattern of geographicalvariation in- morphologicaltraits has been demonstrated dependentof currently recognizedsubspecies. (Smithand Zach 1979,van Noordwijk et al. 1980, I compared patterns of differentiation in iso- Dhondt 1982,Boag 1983, Grant 1985,Schluter latedversus continuously distributed continen- and Smith 1986, Alatalo and Gustafsson 1988). tal populationssubject to greatergene flow un- However, geographicalvariation in morphol- der the assumptionthat geographicalisolation ogyis not alwaysgenetically based (James 1983, allows a better match between the species'mor- Zink 1989). phology and the localenvironment by reducing The relation of plumage pattern to environ- gene flow (Slatkin 1981, 1987; Rockwell and mental featuresis more poorly documented,al- Barrowclough1987). For this, I first identified patterns of geographicalvariation in the se- lected characters.I then searchedfor congru- Addressto which reprint requestsshould be sent. ence of these patterns with geographicalvari- 820 The Auk 108: 820-832. October 1991 October1991] Variationin theBlue Tit 821 0 500 •000krn N •3 5 21 N3 NE4• 3• •0, •8 I t5 to • t9 t0 I 6 I 5 I t5 1- .... 't ...... t ..... • r ......... I 8 _3• 33 I I 44 23 i t2 20 9 : 5 i 33 • 28• t2 •7,% ........SES•:_ '-.• zr• i'.-- ", sE4: .... .--- '-,,;',,, 15 •e Fig. 1. Range of tSe Blue Tit (stippled line) and definition of tSe 54 sampling units. Letters represent 9 main geographicalareas of Eurasia(NE = northeast;E = east;5E = southeast;N = north; C = central; 5 = south;NW = northwest;W = west;and SW = southwest),6 Mediterraneanislands (MI1 = Majorca;MI2 = Corsica;MI3 = Sardinia, MI4 = 5icily; MI5: Crete; and MI6 = Greek islands),a samplefrom Cyrenaica, Libya(CY), samplesfrom tSe MagSreb(NA), and samplesfrom tSe Cana• Islands(CA). TSe numberattacSed to letters(e.g. CA2) identifiessampling unit witSin eac5 geograpSicalarea. NumberswitSin eac5 sampling unit refer to samplesizes (male value above female value). ation in the species'environment; for example, more local scale, consistencybetween sample climaticvariation or habitatvariation (vegeta- similarity in plumage pattern and recognized tion structure and composition,feeding re- subspecieswas weak. sources).Finally, I analyzed the relation be- tween the presenceof geographicalbarriers to MATERIAL AND METHODS dispersalof individualsand the amountof phe- The Blue Tit occupiesmost of the western Palearctic notypicgeographical variation. I followedmany (Fig. 1). It inhabits deciduousbroad-leaved forests of the recommendations of Zink and Remsen (Snow 1954a, Lack 1971, Perrins 1979) except in the (1986)for improvingthe studyof geographical Mediterranean region where it inhabits a variety of variation. deciduousand evergreenhabitats distributed in a mo- I demonstratedthat geographicalvariation in saic pattern (Blondel 1985, Blondel et al. 1987, Isen- mensural characters is consistent with variation mann 1987). In contrastto the northern part of its in environmental factors known to affect the breeding range, the hot dry Mediterraneansummer charactersunder study. Variation is stronglyen- probablyis the seasonwhen it is most difficult for birds to obtain food and water (see Blondel et al. hanced in geographicalisolates. The type of 1987).As the high number of overwinteringbirds variation observedin isolateschanges with the from the north implies (Blondel 1969), the wet and habitat type used by species.The consistency mild winter is more benign than the centralEuropean of morphologicalsimilarity with population winter (see Blondel et al. 1987). On the Canary Is- systematicsis poor. Broadpatterns of plumage lands,where the Blue Tit is the only memberof the variation seembest explained by history. On a genus Parus,it breeds in Tamarixwoodlands on the 822 J•,N-LouIs MARTIN [Auk, Vol. 108 two dry easternmostislands (Bannerman 1963, Ba- larger (Fig. 1). I decidedto report only the resultsfor callado 1976), and is more or less restricted to pine the 1,276 male specimens,with the understanding forests on the five outer islands (Lack and Southern that they can be generalizedto the females. 1949,Cullen et al. 1952, Hemingsen 1963,Grant 1979). Standardized(or mean centered) principal com- Vaurie (1957)distinguished two subspeciesgroups. ponent analysis(PCA) was used to analyze the un- The first, caeruleus,includes all Eurasianpopulations. transformed data (SAS software; for details on the The second,teneriffae, includes all populationsfrom method and its usein biology, seePielou 1977,Orloci North Africa (Maghreb and Cyrenaica), the Cana,-y 1978, Gauch 1982). This method is well suited to dis- Islands, and Pantelleria (a small Italian island lying closecharacter sets related to size and shapefactors off the Tunisian coast) (Brichetti and Violani 1986). (Morrison 1967),and to elucidatethe phenetic group- Vaurie (1957) recognized8 subspeciesin the caeruleus ings of individuals. The calculationswere made with group and 6 subspeciesin the teneriffaegroup pri- the individual male specimensas active elements. marily on the basisof color. However, to get a graphic reduction of the data to Differencesin colorationwithin the caeruleusgroup manageableproportions, I figured the averagecoor- are slight and clinal. The southern and westernmost dinates of the individuals collected in a given geo- forms are darker and more brightly colored than the graphicalunit in the principal componentspace (see northern and easternmost forms (see Snow 1954b, Fig. 1 for samplesizes in the 54 samplingunits). The 1955).In the teneriffaegroup, the groundcolor of the analysisof the characters'correlation circles in the backis slategray insteadof olive green,as in caeruleus, PCA plane providesa descriptionof the characters' and the head cap is of dark ultramarine blue instead "position"and "representativehess"on the plane (best of light blue; the light gray neckring is absent(Etch- for charactersplaced on the circle'scircumference). ecopar and Hiie 1964). In contrastto the caeruleus This allowsinterpretation of the axesin termsof phe- group, the six subspeciesof the teneriffaegroup are notypic characters. well defined by unambiguouscolor characters.The Clusteranalysis was used to get further insightinto geographicalrange of eachof them is clearly iden- between-samplesimilarities on a hierarchical basis. tified, correspondingto one or severaladjacent geo- First, I constructedclasses of sampling units by "Dy- graphicalisolates (Vaurie 1957,Etchecopar and Hiie namic Clouds"