Geographical Variability In, and Temperature Effects On, the Phenology of Maniola Jurtina and Pyronia Tithonus (Lepidoptera, Satyrinae) in England and Wales

Ecological Entomology (1987) 12, 139-148

Geographical variability in, and temperature effects on, the phenology of Maniola jurtina and Pyronia tithonus (Lepidoptera, Satyrinae) in England and Wales

PAUL M. BRAKEFIELD Department of Zoology. University College, Cardiff

ABSTRACT. 1. Geographical variability in. and temperature effects on, the mean date of adult flight period and the SD about this date are analysed for two univoltine, grassland butterflies in England and Wales from 1976 to 1985. Data were collected on the Butterfly Monitoring Scheme for Maniola jurtina (L.) at twenty-nine sites and Pyronia tithonus (L.) at twenty sites. 2. Substantial variability for mean date and SD occurs between years and between sites. Changes in mean date between years tend to occur consistently at different sites. The species show some parallel in variation between sites, especially for mean date. 3. June maximum temperature accounts for 95% and 75% of the variation in mean date between years in M. jurtina and P.tithonus. respectively (r=-0.97 and -0.87). Similar relationships occur for temperatures cumulated over the period of post-winter development from March to July or August. 4. Greater geographical variability in phenology, and a generally less synchronized flight period in M.jurtina may be associated with broader habitat preferences than in P. tithonus. 5. The mean date of adult flight period remains at roughly the same date at more northerly latitudes. In M.jurtina the flight period becomes more synchronized, begins later and ends earlier in the north. P. tithonus shows little or no indication of such a response to latitude. This is discussed with regard to changes in season length and factors limiting the species' range.

Key words. Maniola jurtina, Pyronia tithonus, butterfly, phenology, geographical variability, temperature, development, emergence, distribution, latitude.

Introduction tribution of the British butterfly fauna (e.g. Dennis. 1977; Heath ft til.. 1984). Dennis There is renewed interest in factors which examined isotherms coinciding with the influence the historical and contemporary dis- northern limits of many species .ind showed that Correspondence: Dr Paul M Brakefield. Depart- a numher of ™ogeograph,cal and climatic fac- ment of Zoology. University College. P.O. Box 78. tors- including July temperatures, act .is good Cardiff CF1 1XL. predictors of differences between regions in 140 Paul M. Brakefield species diversity. More recent studies have con- timing of the adult flight period in a population centrated on analysing patterns in 10 km square of a North American butterfly, Papilio glaucus, distribution maps given by Heath et al. (1984). using data describing the degree-days above the Nearly 80% of the variation in species diversity developmental threshold required for complete is accounted for by summer temperature and development. The present study is an analysis of sunshine together (Turner, 1986) or by latitude the influence of temperature during post- (Barbour, 1986). Turner et al. (1986) showed diapause, pre-adult development on the timing that climate was able to explain some part of the and duration of the flight period of two strictly variation in diversity which is independent of univoltine, satyrine butterflies at grassland sites latitude. Barbour ( 1986) also found that patterns throughout England and Wales. The study of extinction since pre-1970 records were correl- species are the meadow brown Maniola jurtina ated with richness of the epiphytic flora and air (L.) and the gatekeeper Pyronia tithonus (L.). pollution levels. Dennis & Williams (1986) Geographical variability in their phenology is emphasized the many covarying factors and the also examined. The analysis was made possible necessity of taking into account the great by data recorded over the period 1976-85 on the variability in the biology of the species of Butterfly Monitoring Scheme (BMS) and butterfly. generously made available by Dr E. Pollard. Ecological studies of small numbers of populations of certain species of butterfly in Britain have indicated that temperature can influence their population dynamics (e.g. Methods Pollard, 1979a; Thomas, 1983; Warren et al., 1986; and see discussion in Thomas, 1984). The methods used in the BMS are fully docu- Pollard's population study and survey work on mented elsewhere (Pollard et al., 1975; Pollard, Ladoga Camilla strongly suggested that a con- 1977). It is based on standardized counts usually traction and subsequent expansion in its range made at least once a week along fixed transects was associated with changes in weather patterns at sites throughout Britain. Sites are visited from and, in particular, in June temperature. Unusual April until the end of September which covers weather frequently results in local extinctions or the whole flight period of P. tithonus and all but marked fluctuations in population size (Pollard, the extreme tail for M.jurtina in a small propor- 1984; see also Ehrlich étal.. 1980). The larvae of tion of its populations. Estimates of the expecta- certain species exhibit thermoregulatory tion of adult life in a meadow habitat near behaviour, absorbing radiant energy from the Liverpool in 1976 and 1977 were similar for each sun to gain some independence from air temp- species, varying from 3.5 to 8.5 days (Bra- erature (Porter, 1982, and see Dennis, 1985). kefield, 1979a, 1982a, b). Both species were also Such behaviour may enable populations to per- quite sedentary. Therefore, the probability of an sist in more northerly latitudes. Geographical individual insect being recorded along a transect variability in the number of annual generations on more than one date is likely to be similar for or changes in voltimsm between years has been M.jurtina and P. tithonus and although the BMS documented for several species in Britain (see counts describe their flight periods they should Heath et al., 1984; Dennis, 1985). Such also be related to adult emergence in a similar phenomena seem to be associated with variation way for each species. The sexes are not recorded in the length of time available for development separately in the BMS. Counts are made only ('season length', sensu Roff, 1980). Systematic when weather conditions meet specified mini- investigations of temperature effects on the mum criteria, for example for sunshine. In a few development rate of British butterflies and cases prominent gaps occurred in the records hence on the timing of emergence or phenology and these were filled with an estimate calculated of natural populations have not been carried out as the average of the single preceding and although such effects are ubiquitous in other following counts. The BMS was started in 1976 insects. An understanding of them is likely to with many more sites being added in 1977 and provide important insights into the constraints of fewer in later years (Pollard, 1984). Two sets of season length on the butterfly fauna. A study by sites are analysed here; those covering the peri- Hagen & Lederhouse (1985) has examined the ods of 1976-85 and of 1977-85 (including those Phcnologv of satvrine butterflies 141

this date (SD). These represent estimates of the mean date of adult flight period and of the degree of synchronization of the flight period at each individual site. In P.tithonus there is no relationship between the site means for SD and total annual counts (r=-0.14). In contrast, for M.jurtina this relationship is quite strong (r=0.61, df=27, P<0.001). However, the latter correlation is entirely due to the five sites with counts substantially higher than the others (excluding the five sites: r=—0.03). Therefore there is some indication of a non-linear relationship in M.jurtina but the results described below are unchanged when these five sites are excluded from the analyses. Both species overwinter as early to mid-mstar larvae exhibiting semi- (in M.jurtina) or wholly arrested development Regular night-time feeding on grasses commences during March. Larvae begin to pupate in late May (M.jurtina) or June. In both species nearly all adults have emerged by the end of August. Monthly mean daily max- FIG. 1. Map of the BMS sites (circles) in England and imum and minimum temperatures for the post- Wales used in this study. Map numbers refer to silc winter period of pre-adult development during names in Table 1. The large circle shows position of the five sites with the prefix A. Squares indicate March-August inclusive were abstracted from meteorological stations providing temperature data. the Monthly Weather Reports (H.M.S.O., 1976-85) for a representative series of twelve meteorological stations distributed over the region covered by the BMS sites (Fig. 1). recorded in 1976). This choice enables a good Cumulative daily temperatures were also calcul- coverage of England and Wales (Fig. 1) and ated for this period using the average of monthly yields the longest possible periods of continuous means for daily maxima and minima. The latter recording. It also provides a means of examining statistics were used in the absence of the necess- the effect of the exceptionally hot summer of ary data to calculate day-degrees. Statistical pro- 1976. Three of the sequences for individual sites cedures were performed using the MINITAB (two for M.jurtina and one for P.tithonus) package on the mainframe computer at Univer- included a year with no records. These sity College, Cardiff. sequences were completed by substituting the overall means for the appropriate year and species. A total of twenty-nine sites were recorded in M.jurtina and twenty in P.tithonus. Results Their distribution is shown in Fig. 1. The nature of the individual data sets, particularly the The overall means for each species and site are variability between sites in the frequency of given in Table 1. The mean date of adult flight recording visits, means that some caution must period is nearly 10 days earlier in M.jurtina (27 be exercised when comparing estimates of tim- July) but the SD about this date is 50% greater. ing of the adult flight period for small numbers of Analysis of the estimates for all individual sites particular sites. However, any trends present in in each year shows that the SD is quite closely the complete data are likely to have some bio- related to the duration of the flight period as logical significance. measured by the length of time between first and For each species at each site and in each year last records in each species (M.jurtina: r=0.69, the (weighted) mean date of the counts is calcul- df=278; P.tithonus: r=0.59, df=194, P^O.OOl ated together with the standard deviation about for each value). Thus the adult flight period is 142 Paul M. Brakefield

TABLE 1. Overall means of mean date of adult flight period (days from 1 July) and standard deviation about this date (days) for Maniola jurtina and Pyronia tithonus at the sites indicated in the period 1976- 85. Pooled means and SDs are given for all sites recorded in 1976. Map numbers as in Fig. 1. Site Maniola jurtina Pyronia tithonus Map no. Name Mean date SI) Mean date SI) Al Woodwalton Farm 29.1 11.8 34.5 8.1 A2 Bevills Wood 22.4 13.8 37.8 7.9 3 Holkham 23.9 12.5 32.7 8.4 A4 Monks Wood 27.8 14.5 39.3 11.8 6 Yarner Wood 19.5 14.4 37.9 9.6 8 Old Winchester Hill 41.2 20.0 36.5 9.2 9 Kingley Vale 36.0 17.6 35.1 9.2 10 Oxwich 39.8 15.8 41.3 12.2 12 Leigh Marshes 18.1 13.2 - - 14* Gomm Valley 21.0 13.8 - - 15 Foxholes 20.8 13.9 _ _ 16 Swanage 38.1 18.0 - - 17 Buttler's Hanging 20.5 16.1 - - A18 Wood hurst 21.8 12.0 34.5 8.3 19 Studland Heath - _ 37.0 10.9 21 Castor Hanglands 19.8 14.2 36.5 9.1 24 Dyfi 27.0 15.5 36.9 11.3 26 Rostherne Mere 27.1 13.5 - - A27 Holme Fen 27.4 14.2 34.2 10.5 28 Walberswick 27.2 13.9 37.5 9.8 30 Aston Rowant S 31.5 17.9 33.9 9.2 31 Waterperry Wood 19.8 10.7 36.3 10.4 32 Wye 27.3 16.0 38.8 10.3 39* Saltfleetby 22.8 13.8 34.8 9.2 43* Leighton Moss 20.1 11.5 - - 44* Radipole Lake 19.0 13.5 - - 45* Gibraltar Point 32.0 10.6 36.8 8.8 47* Skomer 28.2 11.4 33.2 9.4 54* Nagshead 29.3 13.8 - - 60* Lindisfarne 37.9 12.9 - - Pooled mean 26.95 14.73 36.51 9.78 Pooled SD 5.19 2.29 3.56 1.72 'Sites not recorded in 1976.

substantially longer and less synchronized in Variability between sites and years M.jurtina. These differences in phenology are shown at nearly all sites common to both species The results of the ANOVAs given in Table 2 (Table 1). When all individual sites in each year show that in each species there are highly signifi- are analysed there is also a correlation between cant differences in both the mean date of adult the mean date and SD (M.jurtina: r=0.32; flight period and the degree of synchronization P.tithonus: r=0.36, P<0.001 for each value). of the flight period between sites and between Therefore, although this correlation is not very years. The variability in both these parameters high there is apparently a tendency for popula- between sites is greater for M.jurtina (e.g. for tions with a later flight period to be less syn- the summary values given in Table 1, mean date : chronized in emergence. This is probably a F=10.0, df=28,19, P-^0.001; SD: F=3.48, consequence of greater variability in the timing P<0.01). This is also apparent in the larger pro- of the end of the flight period than of the begin- portions of the total variance accounted for by ning (analyses of all first and last records: M.jur- the Site terms in the ANOVAs given in Table 2 tma: F=1.60; P.tithonus: F=2.Q4, with P<0.001 for M.jurtina than for P.tithonus. This is for each value). especially evident for mean date. In contrast, Phenology of satyrine butterflies 143

TABLE 2. Two-way ANOVAs of (a) mean date of adult flight period, (b) change in mean date between consecutive generations, and (c) standard deviation about mean date for Mamola jurtina and Pvronia tnhonus at sites in England and Wales Results are given for both the 1976-85 and 1977-85 data set-. Source of Mamola jurtina Pyronia tithonus variation df SS MS F P df SS MS F f (a) Mean date, 1976-85 Site 20 9743.6 487.2 18.1 «0.001 16 771.8 48.2 3.8 <0.001 Year 9 7360.6 817.8 30.4 «0001 9 7066.6 785.2 62.3 «0.001 Error 180 4840.3 26.9 144 1821.0 12.6 Total 209 21944.5 169 9659.4 1977-85 Site 28 14262.7 5094 11.3 «0.001 9 843.9 44 4 4.0 <0.001 Year 8 3153.2 394.1 8.7 «0.001 8 3651.9 456.5 41.5 «0.001 Error 224 10109.2 45.1 152 1668.9 110 Total 260 27525.1 179 6164.7 (b) Change in mean date between years. 1976-85 Site 20 175.7 8. K 0.2 NS 16 71.9 4.5 0.1 NS Period 8 10143.8 1268.0 25.4 «0.001 8 9122.4 1140.3 37.0 «0.001 Error 160 7992.1 50.0 128 3938.9 3(1.8 Total 188 18311.6 152 131332 1977-85 Site 28 231.2 8.3 0.2 NS 19 72.4 3.8 0.1 NS Period 7 3703.5 529.1 12.5 «0.001 7 3872.4 553.2 209 «0.001 Error 196 8265.5 42.2 133 3530 3 26.5 Total 231 12200.3 159 7475.0 (c) SD about mean date, 1976-85 Site 20 1059.0 53.0 10.0 «0.001 16 261.6 16 .4 5.5 <0.001 Year 9 270.2 30.0 5.7 <0.001 9 107.0 11.9 4.0 <0.001 Error 180 946.2 5.3 144 424.7 3.0 Total 209 2275.5 169 793.4 1977-85 Site 28 1522.7 54.4 8.9 «0.001 19 247.4 130 5.0 <0.(X)1 Year 8 312.1 39.0 6.4 <0.001 8 111.3 13.9 5.3 <0.001 Error 224 1372.2 6.1 152 395.5 2.6 Total 260 3207.1 179 754.3 relatively more of the total variance is accounted ences between sites. This strongly suggests that for by variation between years in P. tithonus. The in each species the sites are behaving similarly analysis of changes in mean date between con- with regard to changes in timing of the adult secutive generations (Table 2b) shows that less flight period between years. Such consistency is than 2% of the total variance is due to differ- indicative of general effects of weather. Further-

TABLE 3. Spearman rank correlations between Kititudc and the indicated mean statistics describing the adult flight period of Mamola jurtina and Pvronia tithonus at sites in England and Wales. Values are given for the 1976-85. and the 1977-85 (larger no. of sites) data sets. Statistic Maniola jurtina Pyronia tithonus No. of sites: 29 21 20 17 Mean date -0.21 -0.33 -0.37 -0.42 First date 0.42* 0.42 -0.09 -0.26 Last date -0.41' -0.48* -0.03 -0.14 SD -0.58** -0.57* -0.42 -0.36 Total count -0.29 -0.41 0.31 0.16 */><0.05; **P<0.01. 144 Paul M. Brakefield more, analysis of the data for individual years at the nineteen sites common to both species shows -£•5 *f ^^» 00 10 a highly significant correlation between species "f- r-; oo for mean date (r=0.59. df=184). The correla- T3 M o o 3?rJ \ \ S pj ^ S £ ° tion for SD is much weaker (r=0.17, P<0.05). U « oöo ö""~ ÖÖÖÖÖÖ .a S U ~~8.X; 1 J^J,— -L^L-L <— < O^ (N 00 Oi (N — i. — ^ r—l O W") QO Ov (N O — - ^ ^ ^ /^ r*l (**> change in the mean date of adult flight period CL- Ö1 f*"! >— » ' J^Ö 3 u sLës>L>Li with latitude in Britain for either species u ë^"*""'o' # #* ^."L although the correlations are all negative sug- 8J 0 J c ÖÖÖÖÖÖ ÖÖÖÖÖÖ gesting, if anything, earlier mean dates further **"* ïd 's 1 1 1 1 1 1 1 1 1 3 • north. Analysis of the first and last dates on *- (*) which each species was recorded indicates that in TO 2 M.jurtma emergence begins earlier, and adults H • a * fly until later in the south. There are no corres- *u- ~2 o ^ 5 -c °. ^Co?^? ponding relationships for P.tithonus. Associated E ^ o o £! ,L^J_ ö <^ ö ö ö ö 0 J^^LO,» * « ^s'Ss^^- ••** with the changes in dates in M.jurtina is a more (C' •2 U — ; ïï o oo oo oo synchronized flight period in the north. The cor- X 1 cd ÖÖÖÖÖÖ ÖÖÖÖÖÖ responding correlation is also negative in fl Cï 1 1 1 1 1 3 -S c 1 1 1 1 1 P.tithonus but does not reach formal signifi- E S cance. The four sites for M.jurtina with the 3 .=, longest flight period are all near the south coast ïl * oo cd c ^"^ *~^ ' — ö e ,^—s ^v y-^ or in southern England (8, 9, 16 and 30). Three SöB?t^ K ^ ^o"^. "^ of the corresponding sites for P.tithonus are in ö ö —; "i ö o 1-.2 (J £- ^»^ S- ""^ * * ^_^s , -^^ ^-^ S_^ ^_^ southwest England (6) or west Wales (10 and E a r- o i/-) v~) \o r~- oo \o i/~i ro r-i o^ 3 M 24), and the other is on the south coast (19). E ÖÖÖÖÖÖ öööööo 3 II III 's i U 1 1 1 1 E r . 3 Relationships to temperature ^ cd cd * The interpretation of correlations between li s s^ ^ statistics describing phenology and monthly E a a '* ^„^^ss öSSS^ d temperatures is not greatly complicated by auto- .5 -o ö ö ö Î 1 ! 1 ö ö ö * J^ correlations between the temperature variables. g -0 U E n ° . f^l -* f) OO >/1 f^ ^rt v~> o o r-- m Thus for the matrix of sixty-six correlation C "2 c ÖÖÖÖÖÖ öööööo 1 1 1 1 1 coefficients between the mean monthly max- i I 'Ë 1 1 1 1 imum and minimum temperatures for the 10-year period there were only six (all positive) * 3 S 6 € : significant values (i.e. r>0.63) and many nega- S-S S gl S-*. v | oa S r" a. tive values. Four of the six significant values are SS 'C a c ^f~> O ^ • fsj i—^ 1^* «"^ S t! • for maximum x minimum values for the same s ^- '•^ ESs^f j^ ö^^ofö month. This matrix and that for cumulative g -g, S U esté* ^j g j^èé^^^ - "o : « m 't in ^- r- "/i monthly temperatures suggest that there is a cd ^ 'M S rï ° cï P P: 'V ~ïj "3 ""' a cd ÖÖÖÖÖÖ 'i* ö o o o ö o B. trend towards consistent temperatures during ? n cd r- u •S i 'i' • each of the periods March-May and June- •a >t , 1 cd ^ - August. C j-| T3 j- (A - V Examination of the correlation coefficients •5 « o.ra 1c ^ ^ CL, c • given in Table 4(a) for mean date of adult flight 0 |S

22 a)

O I. 24

2 20 o o> o. • .83 ,82 E • S -,82 E ra D & 22 18 - ,83

0) '78 C • 3 -3 E O ie 20 20 40 20 40 Mean date of adult flight period, days from 1 July FIG. 2. Relationships between mean date of adult flight period of Maniola iiiriuni (•) and of Pyroma inlwnwt (o) and (a) mean maximum temperature in June and (h) cumulated daily temperatures for March to August. Figures indicate years. tures in the three summer months, especially period or SD and the temperature variables for June (Fig. 2a), are associated with later flight the period March-August in the preceding year. periods. The earlier months have little influence on timing of flight. The similarity of the effects on the two species is emphasized by the values for cumulative daily temperatures. The relation- Discussion ships for average temperature over the whole period of post-winter development are shown in This study shows that 94.5% of the variation Fig. 2(b). Exclusion of the exceptionally hot between years in mean date of adult flight period r year of 1976 with a very early adult flight period in M.jurtina, and 75.5 r in P.tithonus, is in each species has little effect on the correlation accounted for by changes in mean maximum matrix. The difference between the earliest and June temperature. There are similarly close rela- latest years is about 3 weeks in each species (Fig. tionships to temperatures cumulated over the 2). period of post-winter development from March Evidence for strong temperature effects on to July or August. Cooler summers result in a the synchronization of the adult flight period is later flight period by up to about 3 weeks. That less apparent (Table 4(b)). However, the flight these relationships arc, at least in large part, due period is probably more spread out in M.jurtina to effects on the timing of emergence rather than in years when July and, possibly, August are on adult longevity is indicated by strong correla- relatively cool. A similar effect may operate in tions between the mean date of adult flight P.tithonus but is not significant for the present period and the date of first record (M.)urtnni data. In M.jurtina there is an indication th.it .1 r=0.64, df=278; P.tithonus. r=0.67. df=194, warm April, and perhaps May, tends to produce P«0.(X11 for each value). However, adult a more synchronized flight period. The flight longevity may have some influence because of a period was most synchronized in 1983 in both lower expectation of adult life in hot and dry species and most spread out in 1985 and 1980 summers (Brakefield, 1982b). Temperatures (M.jurtina only). There are no clear relation- earlier in the post-winter period are apparently ships between either mean date of adult flight much less significant in determining mean date 146 Paul M. B rake field of adult flight period than those in the last 2 or 3 are also smaller in size (references in Brakefield, months. It is possible that spring temperatures 1984; Brakefield & Macnair, unpublished are relatively more important to the synchro- observations). nization of the flight period. These findings indi- The variability between years in mean date of cate that substantial temperature effects on total adult flight period and in SD about this date is development time in natural populations occur similar for M.jurtina and P.tithonus. Why then is during the period of late instar larvae and pupae. the flight period of M.jurtina both substantially These may be most marked in the pupal stage less synchronized and more variable between because any damping of such effects by populations? The answer may lie in the wider modification of activity and feeding patterns is habitat preferences of M.jurtina (Brakefield, not possible. Pupation occurs from late May 1979a, 1982a). In a population study in a (M.jurtina) or June until early or mid-August. meadow near Liverpool, P.tithonus was largely The length of the pupal stage is temperature- restricted to rough grassland immediately adja- dependent in the laboratory. In M.jurtina its cent to shrubs or scrub while M.jurtina was much duration is 15-18 days at 15°C and 9-11 days at more widely distributed throughout the habitat. 25°C(Brakefield, 1979a). Cooler periods in mid- This difference is characteristic of the species at summer will produce delays in emergence and, all stages of the life cycle (Brakefield, unpub. therefore, the observed later and more pro- data; and see e.g. Heath et al., 1984). The grea- longed adult flight period. Interestingly. Turner ter variability in microhabitat shown by M.jur- et al. (1986) showed that the relationship tina is likely to result in more heterogeneity in between summer climate and species diversity in development time and emergence both within Britain was closely similar for ectothermic but- and between populations. At a site in the Isles of terflies and endothermic moths (as adults). One Scilly post-winter larvae of M.jurtina from possible explanation suggested by Turner et al. sheltered grass gullies between thickets were for this similarity is that the relationship is not a more advanced than those of open grassland direct one through adult thermorégulation but (Brakefield, 1979a). may be associated with climatic effects on larval The absence of a strong relationship between development. latitude and mean date of adult flight period is The great variability in the length of the flight unexpected because of the south-west to north- period in M.jurtina has been recognized for a east decline in mean annual temperature (Tout, long time. Localities with the longest flight peri- 1976). However, the pattern is less clear-cut in ods include many with shorter turf, especially on mid-summer. In July most of England south of a chalk soils (Pollard, 1979b). They have also been line from sites 26 to 39 in Fig. 1 has a mean reported on the Isles of Scilly (Ford, 1975) and temperature of about 16°C (reduced to sea- the Isle of Wight (Thomson, 1971). In some level). The northward decline is only marked in populations there may be more than one over- the region above this line which includes but two lapping peak of emergence of each sex (Bra- study sites (where only M.jurtina occurs). Coas- kefield, 1982b). Males tend to emerge before tal areas are generally cooler than inland areas at females and the degree of protandry can be this time of year (Tout, 1976). The apparent extremely marked. It would be interesting to relationships between latitude and synchroniza- investigate the relationships between variation tion of the flight period (Table 3) are unlikely to in protandry, the form of emergence and result from a latitudinal change in adult habitat. Breeding experiments in which sibs of longevity since estimates of expectation of adult M.jurtina with differing wing spotting life of M.jurtina provide no evidence for this phenotypes showed differences in timing of (Brakefield, 1982b). emergence strongly suggest that there is genetic Although the peak of adult emergence in variability for development rate (Brakefield, M.jurtina remains at roughly the same date at 1984). Such variability was demonstrated by more northerly latitudes, the flight period selection experiments on the pattern of volti- becomes more compressed, begins later and nism in stocks of the satyrine Coenonympha ends earlier. This species appears to respond to a pamphilus (Lees, 1962, 1965). In many popula- shorter season length by an increase in the syn- tions of M.jurtina, butterflies emerging later in chronization of emergence. This is likely to be the season have less extensive wing spotting and associated with selection on development time Phenology of satyrine butterflies 147 becoming more stabilizing in nature towards the M.jurtina. Unpublished Ph.D. thesis. University margins of the species' range (see Brakefield, of Liverpool Brakefield. P.M. (1979b) Spot-number in Mamola nir- 1979b). A contributing factor could be that initi Variation between generations and selection grassland habitats become less diverse north- in marginal populations Heredit\. 42, 259-266 wards in England and Wales. Such effects could Brakefield. P.M. (1982a) Ecological studies on the play an important role in determining northern butterfly Mamola jurtina in Britain I. Adult limits in range. M.jurtina occurs up to the north behaviour, microdistribution and dispersal. Jour- nal of Animal Ecology, 51, 713-726. of Scotland while P.tithonus reaches its limits Brakefield. P.M. (1982b) Ecological studies on the along the Cumbrian coast and in Yorkshire not butterfly Mamola jurtina in Britain II Population far north of site 39 (Fig. 1 : Heath et al.. 1984). dynamics: the present position Journal of Animal The later and shorter flight period of P.tithonns Ecology. 51, 727-738. Brakefield. P.M. (1984) The ecological genetics of may be related to more restrictive thermal con- quantitative characters of Mamola \urnna and straints than in M.jurtina. There is no evidence other butterflies. The Biology of Butterflies. Sym- that the adult flight period of P.tilhonu\ posium of the ROMI/ Entomological Society of Lon- becomes more synchronized in northern popula- don. 11 (ed. by R I Vane-Wright and P. R. tions although the correlation is negative (Table Ackery). pp. 167-190 Academic Press. London. Dennis. R.L H (1977) The British Butterflies. Their 3). There is no change in the timing of the begin- Origin and Estahlishment. E. W. Classes. ning or end of the flight period. Thus this species Faringdon. Oxon may be responding more passively to climatic Dennis. R.L.H. (1985) Voltmism in British Aglaix change than M.jurtina and consequently be less urticae (L.) (Lep.: Nymphalidae): variation in space and time. Proceedings and Transactions of able to extend its range so far northwards. While the British Entomological and Natural History the influences of climate during the adult flight Society. 18, 51-61. period on the population dynamics and distribu- Dennis. R.L.H. & Williams. W.R. (1986) Butterfly tion of butterfly species are clearly important, 'diversity' Regressing and a little latitude. Ante- those acting through development rate should nna. Bulletin of the Royal Entomological Society of London. 10, 108-112. not be neglected. Ehrlich. P.R.. Murphy. D.D. Singer. M.C.. Sher- wood. C.B.. White. R.R & Brown. I.L. (1980) Extinction, reduction, stability and increase: The responses of checkerspot butterfly (Euphydr\as> Acknowledgments populations to California drought Oecologni (Berlin). 46, 101-105. It is a pleasure to thank Ernie Pollard for help Ford.E.B. (1975) Ecological Genetics, 4th edn. Chap- and advice at all stages of this project. The man & Hall. London efforts of all individual BMS recorders and the Hagen. R.H. & Lederhouse. R.C (1985) Polymodal emergence of the tiger swallowtail. Papilio glaucus support for the scheme by the Institute of Ter- (l.epidoptcra Papiliomdae) source of a false restial Ecology and the Nature Conservancy second generation in central New York State. Council are also gratefully acknowledged. R. L. Ecological Entomology. 10, 19-28. H. Dennis, N. A. C. Kidd. J. A. Thomas. J. R. Heath. .1 . Pollard. E. & Thomas. J A ( 1984) Atlas of Butterflies in Britain and Ireland. Viking. G. Turner and an anonymous referee provided Harmondsworth useful comments on the manuscript. Initial 1 ecs. E. (1982) On the voltmism of Coenonympha impetus for this study came from an examination pamphilus (L.) (Lep.. Satyridae). Entomologist. of data for mean date in M.jurtina at five south- 95, 5-6. western sites (1976-84) supported by a grant Lees. E. ( 1965) Further observations on the voltmism of Coenonympha pumpliilux (L.) (1 ep . (No. GR3/4909) to M. R. Macnair from the Satyridae). Entomologist, 98, 43-45. Natural Environment Research Council. Pollard. E. (1977) A method of assessing changes in the abundance of butterflies Biological <. 'on.ierva- non. 12, 115-134. Pollard. E. (1979a) Population ecology and change in References range of the white admiral butterfly Ladoga Camilla L. in England. Ecological Entomology. 4, Harbour. D.A. (1986) Why arc there so few butterflies 61-74. in Liverpool ' An .inswcr. Antenna. Bulletin of the Pollard. E. (I979h) A national scheme for monitoring Rovul Entomological Societ\ of London. 10, the abundance of butterflies the first three years. 72-75. Proceedings und Transaction* of the British Brakefield. P.M. (1979a) An cxpenment.il study of I inonio/ogical and Natural History Sociel\. 12, the maintenance of variation in spot pattern in 77-90. 148 Paul M. Brakefield

Pollard. E. (1984) Fluctuations in the abundance of Thomson, G. (1971) The possible existence of temp- butterflies. 1976-82. Ecological Entomology, 9, oral sub-speciation in Maniola jurtina (L.). 179-188. Entomologist's Record and Journal of Variation, Pollard, E., Elias, D.O., Skelton, M.J. & Thomas, 83, 87-90. JA. (1975) A method of assessing the abundance Tout, D. (1976) Temperature. The Climate of the Bri- of butterflies in Monks Wood National Nature tish Isles (ed. by T. J. Chandler and S. Gregory), Reserve in 1973. Entomologist") (iazette, 26, pp 96-128. Longman, London. 76-88. Turner, J.R.G. ( 1986) Why are there so few butterflies Porter, K. (1982) Basking behaviour in larvae of the in Liverpool? Homage to Alfred Rüssel Wallace. butterfly Euphydryas aurmia. Oikos, 38, 308-312. Antenna, Bulletin of the Royal Entomological Roff, D (1980) Optimizing development time in a Society of London, 10, 18-24. seasonal environment: the 'ups and downs' of cli- Turner, J.R.G.. Gatehouse, C.M. & Corey, C.A. nal variation Oeco/ogia (Berlin), 45, 202-208. ( 1986) Does solar energy control organic diversity? Thomas, J.A. (1983) The ecology and conservation of Butterflies, moths and the British climate ()iko\ Lysandra bellargus (Lepidoptera Lycaemdac) in (in press) Britain. Journal of Applied Ecology, 20, 59-83. Warren, M.S., Pollard, E. & Bibby, T.J. (1986) Thomas, J. A. ( 1984) The conservation of butterflies in Annual and long-term changes in a population of temperate countries Past efforts and lessons for the wood white butterfly Leptidea smapis. Journal the future. The Biology of Butterflies, Symposium of Animal Ecology, 55, 707-719. of the Royal Entomological Society of London, 11 (ed. by R. I. Vane-Wright and P. R Ackery), pp. 333-353. Academic Press, London Accepted 18 October 1986