Oecologia (Berl) (1981) 48:377-384 Oecologia Springer-Verlag 1981

Population Structure of the Rare , lschnura gemina (Kennedy) (: )

Rosser W. Garrison 1. and John E. Hafernik, Jr. 2 1 201 Wellman Hall, University of , Berkeley, Ca. 94720 2 Department of Biology, State University, 1600 Holloway Ave., San Francisco, Ca. 94132, USA

Summary. The population structure of the endemic San Fran- Ehrlich (1961, 1965) and Ehrlich et al. (1975) have shown that cisco Bay Area damselfly, gemina, is examined using different populations of the checkerspot butterfly, Euphydryas mark-recapture methods. Average daily movements, sex ratios, editha Boisduval, exhibit contrasting behavioral regimes. For population size, maturation times, survivorship, and dispersion example, mark-recapture studies show demes from the southern patterns were recorded and calculated from two small (each San Francisco Peninsula to be extremely local, apparently con- less than one hectare) sites 150 m apart in Glen Canyon, San fined to small grass islands within a chaparral biome, and exhibit Francisco. Of 563 adults marked over 36 days, 412 (73%) were little gene flow. Individuals of another population at Del Puerto recaptured at least once. Average daily movements for males Canyon, Stanislaus Co., about 84 km ESE of the first study and females were less than 6 m, suggesting local movements. site, show wide-ranging movements, an indication of panmixis. However, directional movements of 150 m were observed from Besides arousing biological interest, such studies provide va- one site to the other, indicating dispersal potential. One of the luable insights into the population structure and status of rare populations was a satellite composed entirely of emigrating indi- and local species. Perhaps the greatest merit of such studies viduals from the other site; no larvae or teneral adults were is in indicating what actions should be taken to enhance the found at the satellite area. Males were more aggregated than survival of rare species. females at both sites. Both sexes were highly clumped at one Ischnura gemina (Kennedy) is a small damselfly endemic to site, but were nearly randomly dispersed at the other site. Total the of California. It occurs from Point population size for both sexes tended to be constant throughout Reyes (Limantour Pond, Pt. Reyes, Marin Co.) south to Santa the sampling period, at about 250. Adult population estimates Cruz (Santa Cruz Co.). Described in 1917 (Kennedy 1917), showed more males were present than females, but larval counts it has since remained unknown for over 50 years. Nothing is at one site indicated only a slight excess of males. Average life known of its biology and, until recently, it was represented in span estimates ranged from 6.5 days (females) to 23.3 days museums and collections by fewer than 30 specimens. (males). One male lived at least 36 days. Maturation time for After discovering several small populations of I. gemina, we males was about 5-7 days, 7-10 days for females. A long life noted strikingly different behavior patterns relative to other lsch- span and long flight season (March to November) are probably nura species we have observed in the field. For example, L gemina adaptations to the foggy San Francisco climate. All populations is on the wing from early March to mid-November, while another of I. gemina located to date are small, possibly originating from local species, L erratica (Calvert), flies for only about a month founders from nearby demes, and may be subject to different (Cannings and Doerksen 1979). Mature L gemina usually sit selection pressures. The dispersal potential of L gemina may on horizontal substrates, while other western Ischnura species increase its chance of survival should small urban demes be alight on vertical strands of grass or sedges. Unlike other species, threatened with destruction. L gemina seems largely confined to disturbed sites within urban areas. The purpose of this study is to describe the population struc- ture of this rare species, to compare the results with studies Introduction of other common species, and to suggest how I. gemina is able to exist within urban areas. We describe the population sizes, One way to understand the distribution and abundance of organ- movements, survivorship, dispersion patterns, sex ratios, and isms is to perform mark-recapture studies on a species within maturation times of two small demes. Another paper in prepara- its environment. If field studies are intensive, the data will not tion will describe the mating expectancies and frequencies, activi- only help ascertain the role of a species in its environment, ties, and lek behavior. but the study can serve as a model for analyzing other popula- tions of the same or similar species. Comparative studies between two different populations of the same species are especially valu- Description of the Study Sites able because the results may illustrate differences and flexibility The studies were performed at two sites within Glen Canyon, San in behavioral patterns of a species in different environments. Francisco, California. The first is a small seepage area on a 30~ incline. The northeast-facing slope measures 28 m by 12 m (Fig. 1). The site * Present address: Calle Iris UU18B, Rio Piedras, Puerto Rico 00926, USA is mostly open, covered with clumps of sedge (Juncus sp.). Isolated willows (Salix sp.) are present within the study site and a thicket Offprint requests to. R.W. Garrison occurs farther up the NE slope. The southwestern part of the site

0029-8549/81/0048/0377/$01.60 378

e-~-% These were also classified as mature. Classification of males into juve- W,LLOW O nile and mature categories was more difficult, because there was no

:"" - %,,,- - SEDGES obvious way to differentiate age classes. All males found in tandem or copula were classified as mature. Males with slightly glistening wings and freshly developed coloration were classified as juvenile. All others .... ~ .,J...... ~-~ ,.,,~ were classified as mature. Scott's (1974, 1975) methods of analyzing movements for individu- STREAM ~ .,,. ." ! . .... als were used in this study. Total straight line distances between capture points (dl) were summed and divided by the total time in days (tl) to yield the velocity for each individual according to the formula: /r An averaging of all va, all, and h gives Vi, Di, and T~, average movement parameters for each sex at each site. Rmax is the maximum distance between two capture points, and indicates the range for each ...... -- _ - _ _ _ J -s ~_ Z-~-s- - ~-R-E-Z-K- :(? 6 gO-re-d- -b'y- -v~ i] (o-w s- f - individual. Comparison between male and female dispersion patterns for both Fig. 1. Seepage site, Glen Canyon, San Francisco. The study area is sites was accomplished using Morisita's (1959) index: outlined

q ni(n i -- 1) is a level, bare earth trail, mostly wet from the seepage above. The 15_ i=1 far southern edge of the site is bordered by rows of willows along N(N- 1) ' Islais Creek. A small underground water source emerges 15 m NW of the study site and crosses the earth trail before entering Islais where q=total samples, ni=numbers in the ith sample, and N= Creek. This short section of stream was also sampled (Fig. 1). The number of individuals found in all the samples. Values < 1 indicate trail and surrounding areas are highly disturbed from heavy foot and uniformity, values = 1 indicate randomness, and values > 1 indicate ag- motorbike travel. Most Ischnura adults were found within the 70 2 m 2 gregation. quadrats at and surrounding the trail (Fig. 1), although the surround- The Jolly (1965) and Manly-Parr (1968) methods were used to ing areas were regularly searched for stray individuals. Marking oc- compute daily population numbers (IVi) , survival rates (~i), recruitment curred daily from 13 26 May 1979, and at approximately two-day rate (/~), proportion of marked in total population (&i), and intervals thereafter until 17 June 1979, for a total of 36 days. number of animals marked at risk (~r These stochastic methods The second site consists of a linear asphalt water channel about allow for variable ingress and egress rates. The Manly-Parr method 0.3 m wide and 100 m long. The trough lies 150 m up the slope north does not assume that the survival rate is independent of age and of the first study site. The channel is mostly exposed, with a little probably incorporates the most realistic population parameters if mor- watercress (Nasturtium officinale R. Br.), and contains a 5 m stretch tality is high early in the life span and the sampling intensity is also of cattails (Typha sp.) in the ditch. About 15 cm of standing water high. is present at the southeastern end for about 60 m, but farther north, Average survival rates were calculated two ways using the methods more vegetation obscures any water. The channel is fed in part by of Scott (1973). The first is a modification of Jolly's (1965) estimation two or three underground springs directly above the trough and also of the daily survival rate and is discussed by Garrison (1978). The second by occasional excess water runoff from a nearby grocery store. The method averages all the daily survival rates. Survival rates based on far southern end forms a circular storm drain. Adult Ischnura were an interval of more than one day were converted to one day rates confined to the southern 61 m of the ditch. The area was divided by the following formula: one day rate= (survival rate) TM, where d= into a linear series of 61 quadrats of 1 m x 2 m. Sampling occurred number of days from the day just before the missed period, i, to daily from 20-26 May 1979, and at approximately two-day intervals the day just after the missed period, i+ 1. For example, the daily thereafter until 11 June 1979, for a total of 22 days. survival rate for seepage males from 26-29 May was 0.86 (Table 3), Except for two stray Ischnura perparva Selys, and a few Argia and d=4. The one-day rate=(0.86)S=0.96, and this value was used vivida (Hagen), no other odonates were found at the channel site. for days 26, 27, and 28 May in averaging the overall survival rates. The following species were present at the seepage area below: Argia This method was also used for values greater than 1.00, since taking vivida (abundant), Enallagma cyathigerum (Charpentier) (rare), lsch- the square or cube root yields a smaller value, nearer to 1.00. nura erratica (rare), Ischnura gemina (common), Aeshna californica Overall survival rates were converted to longevity in days using Calvert (occasional), A. multicolor Hagen (occasional), Sympetrum illo- the formula of Cook etal. (1967): expected life span in days= -1 turn (Hagen) (occasional), and S. corruptum (Hagen) (rare). ~. Comparisons of the two methods should yield similar results if the data are good, except when the overall survival rates are high Materials and Methods (i.e., @ave.>0-95), because minor differences translate to large magni- tudes of day differences. Thus, a difference between 0.95 and 0.96 Individuals were marked on the wing with a unique number using will add five days to the result. a permanent "Pilot" felt-tipped pen and released at the place of cap- ture. Individuals from the channel site were marked with a dash (e.g., 180-) to prevent confusion with individuals from the seepage below. Results The following data were recorded for each capture: 1) number, 2) sex, 3) state of maturity, 4)activity, 5)time, and 6)quadrat. Adults Five hundred sixty-three adults were marked and 412, or 73%, were classified into three states of maturity: teneral, juvenile, or ma- were recaptured. Recapture rates were high for males, ranging ture, Tenerals had just eclosed and possessed glistening wings, soft from 90% (seepage, Table 1) to 81% (channel), compared to bodies, and pale colors. Tenerals were delicate and required great females, where 52% and 54% were recaptured from the seepage care in marking. Juveniles possessed a hardened cuticle but were not and channel respectively. These values are higher than the recap- sexually mature. We classified all bronze-colored females as juveniles. ture rates recorded for most other (Garrison 1978, Mature adults were reproductively active. Mature females were green 1979), but favorably compare with Parr and Parr's (1979) recap- with a bronze reflection. Some bronze females were also found in copula, but they were probably near to changing color. This classifica- ture percentages for Ceriagrion tenellum (de Villers) in England. tion was substantiated by observations made during the study. Several The differences between male and female recapture rates are unpaired females were found with mud encrustations on their posterior attributable to behavioral differences between the sexes. Females abdominal segments, suggesting that oviposition had taken place. were cryptically colored and were difficult to find compared 379

Table 1. Number of I. gemina marked (N), number recaptured (RC), 5 9 7 4 10 28 5 7 5 100~ percent recaptured (%RC), and average number of recaptures per individual (RCav)

Site Sex N RC %RC RCav 50~ Seepage ~ 122 110 90 5.02 Seepage 9 73 38 52 1.30 Channel c~ 244 197 81 3.47 Channel ~ 124 67 54 0.93 O ~ 24 ,26 ,Ill28 30 1 3 7 9 11 13 15 17 Totals ~d' 366 307 84 ~ 197 105 53 2 May June Fig. 2. Percentages of new daily captures (males) at seepage. Black= Grand total 563 412 73 previously marked males from channel. White=new unmarked cap- tures. Numbers on top of bars = total number of new daily captures

others were each captured 10 times. Of 32 males initially cap- Table 2. Population movement data and Morisita's index of dispersion tured there, 16 (50%) remained throughout the sampling period. (/6) for L gemina. All indices indicate significant aggregation. See Only six (19%) males initially marked at the stream were found text for further explanation there less than 50% of the time. Seepage site Channel site Very few damselflies were found within the 15 m stretch be- tween the seepage and stream. There was a greater tendency for individuals initially caught at the stream to move to the seepage area (10 of 32, or 13%) than for those initially caught Mean T (days) 10.4 8.4 10.9 9.0 near the seepage to move to the stream (4 of 77, or 5%). The Mean D (m) 40.2 43.7 47.7 27.0 seepage area was a much larger habitat and was more frequently Mean V (m/day) 3.4 5.1 4.7 3.6 encountered by dispersing I. gemina. No females originally Mean R (m) 16.5 32.2 46.1 24.0 marked at the stream remained there permanently ; all emigrated q 70 70 61 61 to the seepage, but four of 29 females (14%) initially captured I6 7.14 5.17 1.30 1.15 at the seepage moved to the stream. No directional movement was apparent within the channel site. The average distances moved per day by males and females with the males. Females were more often found away from the were similar to those at the lower sites. water sites and had longer intervals between recaptures. Many There was a distinct directional movement between the chan- males were recaptured almost daily, because they aggregated nel and seepage sites. Two males and three females from the at the water areas of the study sites. Despite the low female seepage travelled 150 m to the channel, but 37 males and 11 fe- recapture rates, individuals were recaptured an average of about males flew from the channel to the seepage. Directional move- once (Table 1). ments down to the seepage were detected five days after marking We assumed that marking had little effect on the behavior began at the channel site. Figure 2 shows that the proportion of marked individuals relative to unmarked ones. Calculations of new catches of previously marked males from the channel of frequencies of recaptures compared with expected Poisson became higher as the study progressed. On 2 and 14 June, over distributions (Sokal and Rohlf 1969: 86) revealed contagious dis- 70% of the new males found at the seepage had been previously tributions (coefficient of dispersion s2/~-> 1) for both males and marked at the channel. One female marked at the seepage travel- females. This may have been due to marking effect, change led to the channel, but returned to the thicket above the seepage. of life expectancy of the marked population over time, or sam- Forty-eight of 405 (12%) channel adults moved to the seepage, pling error, since the total population size was small and the but only five of 192 (3%) seepage adults emigrated to the chan- proportion of marked population was large. nel. Movement to the seepage was not passive because the pre- Recently, Parr and Parr (1979) tested for a marking effect vailing winds blow NNE up the canyon wall. on a population of Ceriagrion tenellum using the method of Though average movements were small for males and fe- Manly (1971). However, this method requires values of about males, adults had the capacity to move greater distances. One 10 or more for newly-captured animals (Ui) and newly-captured male moved 366 m in 19 days, and a female moved 262 m in animals subsequently captured again (li) for each day. We rarely 12 days. Average maximum ranges were from 15.5 m for males captured more than 10 new adults each sampling period, so those to 46.1 m for females. These values plus the high recapture rates calculations could not be used with confidence. indicate that Glen Canyon individuals of I. gemina do not require a large area in which to roam. Movements Dispersion Mean velocities (Table 2) show male and female I. gemina from both sites to move less than 6 m per day, despite behavioral Movement data were similar for males and females for both differences between the sexes. Female movements may be under- sites, but there were dramatic differences between their dispersion estimates because only 53% of the marked adults were recap- indices. Because the seepage area was topographically varied tured. The remaining 47% may have left the study site, but (earth trail, open seepage, sedges, willows), adult Ischnura they were more likely overlooked during the sampling periods. showed a highly contagious distribution (Table 2). Males were Some males showed a remarkable fidelity to the 2 m 2 stream more clumped (/6=7.14) than the females because most were quadrat (Fig. 1). Two were captured there I6 times, and four found on the damp earth areas of the trail. Females were secre- 380

100 200

150

I [ [ i i 1 1 1 [ I i [ i i i i I i i i i i i i i i I i i i ~ i i i i Fig. 3. Population (Ni) estimates of I. gemina males from the seepage. Solid circles=estimates by Jolly and Manly-Parr methods, bars are approximate 1.96 SE of Jolly estimates. Abscissa as for Fig. 4 ,z-lOOtl I J 5o i i ' ax 150 A

v I [ I 216 I I I 30 [ I I I t I I [ I I f t 1oo 20 22 24 28 1 3 5 7 9 11

May June Fig. 6. Population (Ni) estimates of 1. gemina females from the channel. 5O Solid circles = estimates by Jolly method, open triangles ~- estimates by Manly-Parr method. Bars are approximate 1.96 SE of Jolly estimates

13 15 17 19 21 23 25 27 29 31 2 4 6 8 10 12 14 16 Table 3. Population parameters estimated from Jolly's multiple recap- 4 May June ture data for L gemina males, seepage site. c~i= proportion of marked Fig. 4. Population (]~i)estimates of L gemina females from the seepage. animals, ~/~ = total marked population, .g'~= total population estimates, Solid circles = estimates by Jolly method, open triangles = estimates by I}~= daily survival rate. Numbers in parentheses are calculations from Manly-Parr method. Bars are approximate 1.96 SE of Jolly estimates. Manly and Parr (1968) method Manly-Parr estimates are shown for days only where they differ from 1.96 }~ }~ Jolly estimates &i ~rj & 1.96 Ari SE SE

200 May 13 - - - 0.99 (0.99) 14 0.86 48.5 56.4 3.8 (56.5) (3.9) 0.95 (0.99) 15 0.91 52.0 57.1 5.7 (57.0) (5.6) 1.02 (1.16) 16 0.98 55.2 56.4 3.0 (56.7) (3.2) 0.96 (0.95) 150 17 0.95 54.0 56.8 4.3 (56.5) (4.0) 0.89 (0.96) 18 0.97 50.4 52.0 3.3 (51.8) (3.3) 0.93 (i.00) 19 0.86 47.8 55.6 4.8 (55.7) (5.1) 0.86 (0.92) 20 0.97 46.1 47.5 4.0 (47.5) (4.0) 0.83 (0.94) &-100 2i 1.00 39.0 39.0 0 (39.0) (0) 1.02 (1.11) 22 0.94 39.8 42.3 2.6 (42.2) (2.6) 0.91 (0.87) 23 0.93 38.0 40.8 3.6 (41.1) (3.8) 0.97 (0.99) 50 24 0.85 38.7 45.5 5.0 (45.3) (4.9) 0.83 (0.84) 25 0.83 36.2 43.6 1.8 (43.6) (1.8) 0.98 (0.99) 26 0.94 42.1 44.8 4.5 (45.2) (1.5) 0.86 (0.87) 29 0.79 38.0 48.1 3.9 (48.2) (4.0) 0.76 (0.77) 5 llIllllIllll 31 0.81 35.8 44.2 3.9 (45.4) (5.1) 0.92 (0.89) Fig. 5. Population (Ni) estimates of L gemina males from the channel. Solid circles=estimates by Jolly method, open circles=estimates by June 2 0.88 38.4 43.7 4.3 (42.2) (3.8) 1.09 (1.15) Manly-Parr method. Bars are approximate 1.96 SE of Jolly estimates. 4 0.95 46.4 48.8 13.2 (45.7) (11.4) 0.62 (0.72) Manly-Parr estimates are shown for days only where they differ from 6 0.71 29.4 41.4 4.5 (40.5) (4.6) 0.75 (0.81) Jolly estimates. Abscissa as for Fig. 6 9 0.44 29.6 67.2 14.2 (66.7) (14.1) 0.79 (0.73) 11 0.83 45.4 54.7 12.1 (52.9) (10.9) 0.76 (0.81) 14 0.79 38.3 48.5 10.2 (49.7) (11.9) - tive, most often occurring up the hill among the sedges. The 17 0.80 ..... few found at the trail were almost always in tandem or copula. Males and females at the channel were almost randomly distributed (Ic5r 1.30, I5~= 1.15) along the 61 m sampled. This for both sites (Figs. 3-6, Tables 3 6). Population estimates for indicates that males and females showed no preference for any males at the seepage ranged from a low of 39 (21 May) to one quadrat, despite the vegetation differences in some of them. a high of 67 (9 June), with an overall average population size Though comparisons between the two sites are not possible due of 49.3 (s= 7.2) (Jolly) or 49.0 (s=7.2) (Manly-Parr). There was to differences in quadrat size, it is probably safe to generalize close agreement between the Jolly and Manly-Parr methods. that the adults from the channel exhibited a more random distri- Standard errors were small for all daily estimates. Population bution than the adults from the seepage. estimates for males at the channel were consistently higher than for the seepage site (Figs. 3, 5). There were never fewer than Population Size and Longevity 100 males present, and the average population size estimates Because of the larger numbers of males captured, population were 125.9 (s=13.3) (Jolly) or 121.3 (s=11.6) (Manly-Parr). size estimates were more reliable for males than for females Standard errors were only a little greater than for males at 381

Table 4. Population parameters estimated from Jolly's multiple recap- the seepage. Manly-Parr daily estimates tended to yield slightly ture data for I. gernina females, seepage site. Manly and Parr estimates lower estimates than the Jolly method. Population estimates for are in parentheses. See Table 3 for further explanation males from both sites indicate a relatively stable population size during May and June. &i hl N~ 1.96 Ni 1.96 ~)~ 0~ Due to the longer gaps between recaptures and lower recap- SE SE ture rates, daily population size estimates are variable for fe- May 13 - - - 1.13 (0.91) males, especially at the channel (Fig. 6). Daily population esti- 14 0.29 10.2 35.2 38.6 (31.5) (32.5) 0.86 (1.86) mates for seepage females began at about 25 30 individuals, 15 0.50 13.0 26.0 18.2 (26.0) (18.3) 1.19 (3.33) reached highs of 62 (Jolly) or 81 (Manly-Parr) on 21 May and 16 0.80 19.0 23.8 13.3 (25.0) (16.0) 0.89 (0.61) 63.6 (Jolly) or 54 (Manly-Parr) on 22 May, but then declined 17 0.46 17.8 38.7 20.5 (39.0) (21.9) 0.85 (0.40) to near zero by 2 June. A few females were marked after 2 June, 18 1.00 21.0 21.0 0 (21.0) (0) 1.39 (1.79) but recapture data were so few that daily population estimates 19 0.50 29.1 58.2 34.3 (57.6) (35.6) 1.13 (0.57) could not be computed. Standard errors were large during 19- 20 0.67 42.0 62.7 51.3 (81.0) (93.3) 0.77 (0.43) 21 0.75 34.0 45.3 33.6 (30.4) (14.0) 0.76 (1.14) 21 May, indicating that these estimates are not reliable. Overall 22 0.44 28.0 63.6 40.2 (54.0) (32.8) 0.67 (0.46) average population size estimates were 32.4 (s= 17.3) (Jolly) or 23 1.00 25.5 25.5 12.6 (25.5) (12.6) 0.75 (0.54) 33.5 (s= 17.9) (Manly-Parr). Because of the lower recapture rates 24 1.00 19.2 19.2 5.7 (19.2) (5.7) 1.09 (0) these estimates are probably not indicative of the true number 25 0.67 21.0 31.3 17.8 (31.5) (19.4) 1.03 (0.93) of females. Daily population estimates at the channel were vari- 26 1.00 24.8 24.8 14.5 (24.8) (14.5) 0.52 (0.44) able with high daily standard errors (Fig. 6). There were large 29 0.56 13.0 23.2 10.2 (24.0) (12.4) 0.46 (0.26) discrepancies between Jolly and Manly-Parr estimates on 21, 31 0.60 9.7 16.2 14.3 (11.7) (6.4) - 22, 29 May, and 2, 4, 6, and 9 June. Overall population size June 2 1.00 - - 4 1.00 3.0 3.0 - - - estimates between the Jolly (137.7, s=72.1) and Manly-Parr (64.2, s=31.7) were different. The Manly-Parr estimates are probably more realistic, because we observed fewer females than Table 5. Population parameters estimated from Jolly's multiple recap- males throughout the sampling period. ture data for L gemina males, channel site. Manly and Parr estimates Life span estimates for all L gemina were high, resulting are in parentheses. See Table 3 for further explanation in high overall survival rates. One male lived 36 days, the dura- &~ 3~ri & 1.96 Ni 1.96 ~i ~i tion of the study period. Average survival rates for males at SE SE the seepage were 0.9579, or 23.3 days using Scott 1 method and 0.9363, or 15.2 days using Scott 2. The survival rates are similar, May 20 - - - 1.00 (0.99) but the small differences magnify into an 8.1 day difference. 21 0.80 87.7 109.6 13.0 (108.7) (12.7)0.94 (0.91) The more reliable Scott 1 method shows male I. gemina at the 22 0.75 90.9 121.2 9.2 (119.8) (8.6) 1.01 (0.97) seepage to have the greatest life span estimate of any recorded 23 0.86 113.1 131.5 13.1 (121.2) (9.2) 0.87 (0.86) 24 0.95 107.6 113.3 6.0 (109.5) (3.9) 0.93 (0.96) damselfly (excluding additions of maturation periods by various 25 0.85 103.7 122.0 8.8 (122.4) (9.0) 0.99 (1.03) authors). Parr and Parr (1979) recorded an average survival 26 0.90 114.3 127.0 12.1 (123.0) (10.2)0.88 (0.79) rate of 0.9445, or 17.5 days using the Fisher-Ford method for 29 0.82 106.4 129.8 14.4 (122.4) (4.4)0.80 (0.82) Ceriagrion tenellum, a small, local damselfly in Britain which 31 0.74 96.0 129.7 11.9 (128.2) (11.1) 0.97 (0.99) seems to be similar to L gemina in behavior patterns. Various June 2 0.80 114.1 142.6 14.7 (141.1) (14.7) 0.98 (0.98) authors (Lord 1961; Parr 1965, 1973a, 1973b; Parr and Parr 4 0.83 128.1 154.3 23.2 (140.0) (18.2) 0.71 (0.71) 1972; Van Noordwijk 1978) have quantitatively analyzed Euro- 6 0.82 100.0 121.9 16.9 (116.5) (15.3) 0.75 (0.73) pean populations of [schnura elegans (Vander Linden). These 9 0.78 84.4 108.2 15.9 (102.6) (12.5) - authors recorded average survival rates for males from 0.7450 11 0.74 .... (3.3 days) (Parr 1973b) to 0.9278 (13.5 days) (Parr and Parr 1972). We have found all populations of I. gemina to be local, Table 6. Population parameters estimated from Jolly's multiple recap- the largest not covering more than a hectare, and this fact is ture data for I. gemina females, channel site. Manly and Parr estimates probably responsible for the high recurrence of captures at Glen are in parentheses. See Table 3 for further explanation Canyon, thus translating to high survival rates. Females at the seepage showed an average survival rate of &~ ~t i ~ 1.96 & 1.96 ~i {~i 0.8565, or 6.5 days (Scott 1) and 0.9222, or 12.4 days (Scott 2), SE SE a considerably shorter estimate than for males, but longer than the greatest estimate presented for female L elegans (0.811, or May 20 ..... 0.88 (0.65) 21 0.08 10.8 135.0 254.2 (91.0) (158.7) 1.00 (0.38) 5.3 days, Lord 1961). The low estimated survival rate for female 22 0.10 20.1 201.0 212.0 (144.7) (143.7) 0.91 (0.85) I. gemina is the result of the small numbers found at the site; 23 1.00 56.0 56.0 42.3 (31.0) (7.3) 0.82 - no recaptures were recorded after 4 June, and the averaging 24 0.42 34.3 81.7 37.7 (63.8) (25.1) 1.06 (1.18) methods of Scott 1 and 2 encompassed a shorter period than 25 0.68 51.8 76.1 31.1 (52.8) (15.9) 0.75 (1.14) for males. We suspect that females from the seepage live longer 26 0.50 43.4 86.8 50.4 (66.0) (32.6) 1.03 (0.70) than 6.5 days, and that the Scott 2 estimate of 12.4 days is prob- 29 0.42 60.5 144.1 83.5 (83.5) (32.0) 2.33 (0.51) ably more realistic. One female marked at the seepage that later 31 1.00 (37.0) (10.2) 0.43 - moved to the channel lived at least 24 days. June 2 0.67 57.5 85.8 57.5 (48.3) (18.8) 1.51 Survival rates of male L gemina from the channel site were 4 0.38 91.0 239.5 358.2 (69.3) (62.1) 0.52 - only a little less than at the seepage. Overall survival rates were 6 0.47 63.0 134.0 115.1 (50.7) (24.3)3.17 (0.42) 0.9517, or 20.2 days (Scott 1) and 0.9520, or 20.3 days (Scott 2). 9 0.62 170.0 274.2 523.8 (32.0) (15.3) - - One marked male from the channel that later flew to the seepage 11 0.38 .... lived at least 29 days. Only the Scott 1 method (0.9443, or 382

17.5 days) could be calculated for females from the channel; mature andromorph state 5.9 days. By confining newIy emerged the Scott 2 estimate was greater than 1.00. The survival rate L verticalis (Say) in aquaria and observing color changes, Grieve for females from the channel was probably more realistic than (1937) estimated a maturation time of about 74 days for fe- the estimates derived for females from the seepage. The estimated males. survival rates and life spans are shorter for females than for We determined maturation time for L gernina by marking males because of lower recapture rates for females. Females teneral males and females and recording color changes through may actually have a shorter life span than males, due to potential time. Sample sizes were small, due to few successive recaptures hazards during egg-laying. We found only one male of four of initially marked tenerals, but estimates are probably similar dead specimens that died by predation (spider), and our last to true maturation times. Teneral periods were 1-2 days in both sightings of several other specimens were of old, feeble, worn males (n= 3) and females (n = 1). No color differences exist be- specimens unable to fly, probably indicating imminent death tween juvenile and mature males of I. gernina, so we used earliest by old age. copulation time as an indication of maturity. Three males were found in tandem or copula 5, 7, and 14 days after initial marking Sex Ratios as teneral, indicating an average maturation time of 5 7 days. Observed sex ratios heavily skewed in favor of males are common Of nine teneral heteromorphic females, one was found in for adult damselflies at water sites (Bick and Bick 1961, 1963; copula nine days after marking, and the rest were found in Corbet 1952, 1962; Garrison 1978; Parr and Palmer 1971), be- copula 1~19 days after marking. However, females probably cause females are usually secretive and remain away from water. mature faster than these times suggest, since large gaps existed Overall population size estimates for I. gernina show males to between successive recaptures for most females. One female outnumber females at both sites. We attempted to determine marked when teneral was bronze when found 2-3 m away from true sex ratios by collecting and tabulating larvae. Despite inten- the channel after 6, 7, and 10 days. This bronze female was sive searching, we found larvae only in the channel. Two samples in copula 14 days after marking, but turned bronze-green t 8 days were collected: the first, on 20 May 1979, yielded 41 larvae, 22 after marking, when it was again in copula. We estimate the of which were males (X 2 for 1:1 sex ratio=0.22, ns); the second, maturation period in heteromorphic I. gernina to be about 7- on 24 July 1979, yielded 99 larvae, 56 of which were males (X2= 10 days. 1.71, ns). The slight, but statistically non-significant, preponder- Andromorphs were rare in Glen Canyon: only two were ance of males is less than the higher overall population estimates marked, and no ontogenetic data could be obtained. for males at the channel. All previous studies reporting larval sex ratios for Anisoptera Discussion have shown a predominance of females, but different patterns of sex ratio imbalance have been reported by various authors The biological dat a presented above suggest several interesting for the Zygoptera (see Lawton, 1972, for review and references). attributes of L gernina. The relatively long life span of the small Reasons for surplus male numbers in damselfly populations are I. gernina is greater than recorded for other Zygoptera. Other unknown. Johnson (1975) believes that the metallic colored males unusual attributes of I. gernina are its long flight season (March ofL damula Calvert are more prone to predation than the crypti- through November) and its ability to maintain activity on cool, cally colored females. Male I. gernina are also metallic and may windy, foggy days. We believe these characteristics are adapta- also experience higher predation rates than their females. If true, tions for life in the San Francisco Bay Area, which is often more males relative to females would be killed as adults and foggy during the summer months. Many diurnal are inac- the slight excess of male larvae may compensate for differential tive during these foggy days, while L gemina continues to perform mortality between the sexes. But the data show male L gernina many normal activities. Its long life span allows it to take advan- to be longlived insects which, in Glen Canyon, probably suffer tage of more optimal, sunny, warm days than would otherwise little predation. be possible. Furthermore, the tendency for adult males to perch horizontally on exposed reflective substrates, a behavior unusual Maturation Time in western species of Ischnura, allows them to take advantage Some authors (Corbet 1952; Garrison 1978; Logan 1971; Parr of a warmer microclimate. Our temperature measurements indi- 1976) have added 1-2.5 week maturation times to calculated cate that these well-insolated sites are often five or more degrees survival rates of various Zygoptera, since these calculations gen- Celsius warmer than ambient temperatures 30 40 cm above the erally assume insects to be zero days old when marked. If the ground. Parr (1973b) noted a similar ability to maintain activities animals marked are all mature, this assumption seems valid. in "dull and cool" weather for a related English species, L Maturation time has been measured as the period between peak elegans, in an often cool, cloudy climate. emergence and highest adult density at water in Pyrrhosorna Parr (1973b) noted that many juvenile I. elegans did not nymphula (Sulzer) (Corbet 1952) and Enallagma boreale Selys leave the waterside during their maturation period. We did not and E. carunculatum Morse (Logan 1971). Parr (1973a) deter- observe great differences between the distribution of juvenile mined average maturation times for Ischnura elegans by marking and mature I. gernina. At the channel, juveniles tended to inhabit freshly emerged tenerals and recording color changes during the short, dry grass area just beyond the edge of the asphalt successive recaptures. Males were observed to remain teneral channel, but none was ever found more than five meters away from one to two days, changed to a juvenile green phase from water. As with L elegans, female L gernina were often (3.5 days), then to a sexually mature blue-green phase (9.9 days) seen at water, and we agree with Parr's assessment that their before turning to a blue phase. Females are polymorphic. Juve- cryptic coloration probably resulted in this sex being under- nile heteromorphs (form rufescens) had a maturation period of represented in the population size samples. However, the slightly about eight days. Juvenile andromorphs (form violacea) change higher male larval sex ratio suggests slightly higher numbers into females similar in coloration to males (true andromorphs) for adult male I. gernina, if no differential mortality exists be- or olive-yellow forms (form infuscans). Average maturation time tween young adults. from violacea to infuscans was 6.9 days and from violacea to Of particular interest in this study are the low movement 383 rates (less than 6 m/day) and high recapture rates for adults, would not have been possible without their help. Our wives, Jo A. especially for males. During the first week of the study, we Garrison and Johnnie J. Hafernik, helped with the study and provided were convinced that adult L gemina were very sedentary insects, encouragement during the long routines of sampling. We thank Jo reminiscent of Ehrlich's studies on the Jasper Ridge Euphydryas A. Garrison for editorial advice and typing of the original manuscript. butterflies. Two observations changed our minds. Despite an Mr. Charles Hansen of the San Mateo Mosquito Abatement District provided invaluable aid in locating new demes of L gemina and showed intensive search for larvae and tenerals, none could be found us Sharon Pond in Palo Alto. Drs. John T. Doyen (University of Califor- at the seepage, yet there were always a few new unmarked adult nia), C.D. Johnson (University of Florida), M.J. Parr (University of individuals with each day's sampling. All I. gemina from the Salford, United Kingdom), and W.J. Winstanley (Victoria University seepage appeared to be mature or nearly so, and several females of Wellington, New Zealand) criticized the manuscript and provided were observed ovipositing in the stream and seepage areas, but helpful comments. The U.S. National Park Service provided one of apparently the larvae cannot survive there. Second, we believed us (RWG) with a permit to investigate localities for I. gemina at that the new arrivals had probably originated from another col- Point Reyes National Seashore. To all these people, we express our ony, and this led to the discovery of the channel site 150 m sincere thanks. above the seepage. The relatively high percentages (often > 50 %) of individuals from the channel subsequently comprising each References day's catch of new individuals strengthen this belief. Bick GH, Bick JC (1961) An adult population of Lestes disjunctus We believe that the population from the seepage is a satellite australis Walker (Odonata: Lestidae). Southw Nat 6:111 137 composed entirely of immigrants from the channel. If this is Bick GH, Bick JC (1963) Behavior and population structure of the true, then every individual from the seepage travelled 150 m damselfly, Enallagma civile (Hagen) (Odonata: Coenagrionidae). and was at least five days older than the average life spans Southw Nat 8:57 84 recorded. The average life span for males would be 23 (Scott 1)+ Cannings RA, Doerksen GP (1979) Description of the larva of Ischnura 5 7 days (maturation period), or 27-29 days. Individual I. ge- erratica (Odonata: Coenagrionidae) with notes on the species in mina exhibit local movements within their habitat, but are capa- British Columbia. Canad Entomol 111 : 327-331 ble of longer movements and can colonize new areas. This behav- Cook LM, Brower PP, Croze HJ (1967) The accuracy of a population ior is necessary for a species which inhabits highly disturbed estimation from multiple recapture data. J Anim Ecol 36:57-60 Corbet PS (1952) An adult population study of Pyrrhosoma nymphula water sites within an urban environment to colonize new sites. (Sulzer) (Odonata: Coenagrionidae). J Anita Ecol 21:206-222 One of the original localities for L gemina was Sharon Pond Corbet PS (1962) A biology of dragonflies. Quadrangle Books Chicago in Palo Alto (Kennedy 1917), but that habitat has changed: p 247 it is now a concrete basin that supports no emergent vegetation Ehrlich PR (1961) Intrinsic barriers to dispersal in the checkerspot or L gemina. butterfly, Euphydryas editha. Science 134: 108-109 Daily population size estimates for males show a remarkable Ehrlich PR (1965) The population biology of the butterfly, Euphydryas constancy. (The same may be true for females, despite the lower editha. II. The structure of the Jasper Ridge colony. Evolution recapture rates.) This may indicate that adults have reached 19:327-336 the carrying capacity for both environments. The limiting factors Ehrlich PR, White RR, Singer MC, McKechnie SW, Gilbert LE (1975) Checkerspot butterflies: a historical perspective. Science 188:221- are not known. The available water area for L gemina larvae 228 at the channel is small and puts some constraint on the overall Garrison RW (1978) A mark-recapture study of imaginal Enattagma population size. The channel deme was of a heterogenous age cyathigerum (Charpentier) and Argia vivida Hagen (Zygoptera: structure throughout the sampling period. The total daily adult Coenagrionidae). Odonatologica 7: 223-236 population size was probably about 200, but an excess of individ- Garrison RW (1979) Population dynamics and systematics of the dam- uals probably emerged which later emigrated to the seepage. selfly genus Enallagma of the western United States (Odonata: Another factor for the regulation of the total population size Coenagrionidae). PhD thesis University of California p 256 at the seepage (probably about 70 or 80) may be population Grieve EG (I937) Studies on the biology of the damselfly Ischnura density at the channel site. It is possible that increased interac- verticalis Say, with notes on certain parasites. Entomol Amer 17:121-153 tions, especially among males, encourage emigration. The total Johnson C (1975) Polymorphism and natural selection in ischnuran population size at the seepage may be the surplus adults which damselflies. Evol Theory 1:81-90 later emigrate to the seepage. The total standing crop of I. ge- Jolly GM (1965) Explicit estimates from capture-recapture data with mina, then, during each day of the sampling regime, may have both death and immigration-stochastic model. Biometrika 52:225- been about 27G280, of which 200 remained at the channel, while 247 the remaining 70 80 occupied the seepage. Kennedy CH (1917) Notes on the life history and ecology of the Small populations of I. gemina, based on the demes we have dragonflies (Odonata) of Central California and Nevada. Proc US found and on the data presented here, may owe their origins Nat Mus 52:483 635 to founders from nearby demes. Such founder populations are Lawton JH (1972) Sex ratios in Odonata larvae, with particular refer- ence to the Zygoptera. Odonatologica 1:209-219 small and probably subject to different selection pressures. Some Logan ER (1971) A comparative ecological and behavioral study of demes coexist with other Ischnura species (I. cervula Selys and two species of damselflies, Enallagma boreale (Selys) and Enallagma I. perparva), and competition may result in patterns of behavior carunculatum Morse (Odonata: Coenagriidae). PhD thesis Wash- different from the Glen Canyon demes. One population at Li- ington St University p 82 mantour Pond, Point Reyes, Marin Co., exists behind sand dunes Lord PM (1961) A study of the colour varieties of some damselflies. next to the Pacific Ocean and obviously- experiences different PhD thesis University of Wales temperature regimes than the more sheltered Glen Canyon popu- Manly BFJ (1971) Estimates of a marking effect with capture-recapture lations. Morphometric, cytogenetie and electrophoretic data sampling. J Appl Ecol 8:181-189 should prove useful in measuring interpopulational differences Manly BFJ, Parr MJ (1968) A new method of estimating population size, survivorship, and birth rate from capture-recapture data. among I. gemina. Trans Soc Br Entomol 18:81-89 Acknowledgments. This study was funded by a grant from the Xerces Morisita M (1959) Measuring the dispersion of individuals and analysis Society to study the distribution and biology of L gemina. This work of the distributional patterns. Mere Fac Sci Kyushu Univ 2:215-235 384

Parr MJ (1965) A population study of a colony of imaginal Ischnura (de ViUers) in southern England (Zygoptera: Coenagrionidae). elegans (Vander Linden) (Odonata: Coenagriidae) at Dale,' Pem- Odonatologica 8:171 194 brokeshire Field Studies 2:237-282 Scott JA (1973) Convergence of population biology and adult behavior Parr MJ (1973a) Ecological studies of Ischnura elegans (Vander Lin- in two sympatric butterflies, Neominois ridingsii (Papilionoidea: den) (Zygoptera: Coenagrionidae). I. Age groups, emergence pat- Nymphalidae) and Amblyscirtes simius (Hesperioidea : terns and numbers. Odonatologica 2 : 139-157 Hesperiidae). J Ecol 42:663 672 Parr MJ (1973b) Ecological studies of Ischnura elegans (Vander Lin- Scott JA (1974) Adult behavior and population biology of two skippers den) (Zygoptera: Coenagrionidae). II. Survivorship, local move- (Hesperiidae) mating in contrasting topographic sites. J Research ments and dispersal. Odonatologica 2:159 174 Lepidoptera 12:181-196 Parr MJ (1976) Some aspects of the population ecology of the damselfly Scott JA (1975) Flight patterns among eleven species of diurnal Lepi- Enallagma cyathigerum (Charpentier) (Zygoptera: doptera. Ecology 56 : 1367-1377 Coenagrionidae). Odonatologica 5:45-57 Sokal RR, Rohlf FJ (1969) Biometry, the principles and practice of Parr MJ, Palmer M (1971) The sex ratios, mating frequencies and statistics in biological research, WH Freeman and Co San Francisco mating expectancies of three coenagriids (Odonata: Zygoptera) in p 776 northern England. Entomol Scand 2:191-204 Van Noordwijk M (1978) A mark-recapture study of coexisting zygop- Parr M J, Parr M (1972) Survival rates, population density and preda- teran populations. Odonatologica 7 : 353-374 tion in the damselfly, Ischnura elegans (Vander Linden) (Zygoptera: Coenagrionidae). Odonatologica 1:137-141 Parr MJ, Parr M (1979) Some observations on Ceriagrion tenellum Received September 9, 1980