Odonalologica 17(3): 249-262 September I, 1988 Community structure of coexisting Sympetrum species in the central Japanese paddy fields in autumn (Anisoptera: Libellulidae)* M. Watanabe and M. Taguchi² 'Department of Biology, Faculty of Education, Mie University, Tsu-shi, Mie 514, Japan 2 Hashimoto High School, Sagamihara, Kanagawa 229, Japan Received August 19, 1987 / Revised and Accepted March 14, 1988 The method used for 9 in mark-recapture was coexisting spp. Kanagawa (Oct., 1981-1984). In the 4 paddy fields studied. S. parvulum, S. eroticum and S. darwi- downstream nianum (in 2 fields) were dominant resp. in direction. Mating occurred mainly in the morning, and the flying activities decreased during the afternoon. 5. parvulum and S. eroticum covered short distances during a day, while S. darwi- baccha had low nianum. S. frequens and S. recapture rates, suggesting larger flight the distances. In the hills, the community structure was more complex than in paddy fields, though the population density was lower, and no mating behaviour occurred there. Consequently, the hills are considered to represent the Sympetrum roosting The fields in the of the area. paddy community structure Oct. depended on extent available habitats. INTRODUCTION Studies on the Anisoptera fauna have been reported in various habitats (e.g. MOORE, 1953, 1964; BENK.E & BENK.E, 1975; RUDOLPH, 1978; JOHNSON et al„ 1980; ARTHINGTON & WATSON, 1982; CROWLEY & JOHNSON, 1982). An abundance of informationexists on qualitative aspects of odonate ecology, such as descriptions of life histories (e.g. SAKAGAMI et al., 1974; UBUKATA, 1974). However, quantitative field data necessary for under- standing odonate community structure are scarce. The present paper attempts of with to integrate the quantitative aspect community structure the mark-re- • Ecological studies on dragonfliesin paddy fields surrounded by hills. V. 250 M. Watanabe & M. Taguchi method for of capture a group Sympetrum species, coexisting in paddy fields of central Japan in autumn. S. parvulum. S. e. eroticum, S. darwinianum, S. pedemontanum elatum, S. S. baccha S. croceolum frequens, matutinum, infuscatum, S. and S. r. risi. were recorded in paddy fields around Anakawa-Yato, Kanagawa Prefecture (TAGUCHI & WATANABE, 1984). The last two were rare and the others were It is known that common. generally many Sympetrum species fly over a wide range, including paddy fields(e.g. M1ZUTA, 1978; TAGUCHI & WATANABE, 1985, 1987), though TAGUCHI & WATANABE (1985) reported that the diurnal whereabouts of restricted S. pedemontanum are to the paddy fields throughout its adult life. A life history characterization of each species is essential to the understanding of odonate community structure. All of the paddy field Sympetrum seem to hibernate at the egg stage and to hatch in early May, the germination time ofrice. BAN & K1RITAN1 (1980) and URABE et al. (1986) pointed out that odonate larvae be of insect in fields. appear to important predators pests paddy Such larval dragonfly species might develop synchronously throughout stages as if they were a single species (BENKE & BENKE, 1975). Upon emergence, however, the of is development Sympetrum more asynchronous, as suggested by TAGUCH1 & WATANABE (1984). Temporal partitioning among sympatric species were also reported in other dragonfly species (e.g. MILLER, 1982). In this adult in fields paper, Sympetrum coexisting paddy were studied simulta- in neously order to gain an understanding of community structure as well as single-species population dynamics. STUDY AREA AND METHODS The experimental paddy fields (6.5. ha) were surrounded by hills, covered mainly with secondary deciduous the hills forest. Four study sites in the paddy fields and a subsidiary onein were selected before the conducted Each site mark-recapture samplings were (Fig. I). was indicated by a letter. Site D the and (ca. 11.720 m-) was largest area, was adjacent to an extensive open paddy field eastwards. Site M (ca. 8,910 m-) located around of main was a junction a stream and a branch with natural Site R bogs. was in a cul-de-sac (ca. 1.560 m-). Site G. which was the smallest paddy field, included small : and bogs (ca. 1,020 m ) was completely isolated from the other sites. The hills with deciduous forest lie around The site G. shortest sunlit period in a day. due to the shadow of such hills, observed at in was site G. Site U (ca. 2.030 m-) in the hills was an open deforested area 1978. Rice reaping is carried out during early October in the paddy fields. T AGUCHI & WATANABE (1986) that, due to rice the reported reaping, behaviour of S. frequens was different in early and late October, but of the other showed none species any change in flight behaviour. number The of adults found within each area was counted mainly on each holiday (5 or6days)of from October, 1981 to 1984. On each sampling day, all individuals found during 15 min periods, from 9 a m. to 5 were and marked their hind felt p.m., captured by net on wings with a pen. The condition of the wings, as well as that of the abdomen, was recorded. Individuals wounded by marking were treated as dead in this study. Community structure ofcoexisting Sympeirum 251 I. Anakawa-Yato. Fig. Study area: Kanagawa prefecture, Honshu, G, R. M, D and U arethe study sites. Shaded area represents the paddy fields. RESULTS SPECIES COMPOSITION AND POPULATION DENSITY All of the 9 recorded species (TAGUCHI & WATANABE, 1984) were captured in October, 1981 to 1984. Most of the males were mature individuals, judging from the red colour of the abdomen. Most of the females were also their coloration mature, because thorax was powdery red and, due to oviposition, in some species mud adheredto parts ofthe abdomen. Some individuals perched on rice leaves, while others made freqent hovering flights. All of them made intermittent sometimes the feeding flights, repeatedly using same perch, and showing weak interactions. Since the seasonal trend in the number ofindividuals in October was similarin each the for each site year, figures respective study were averaged (Tab. I). Six in each site species appeared study every year, and they mated and oviposited in the fields. S. at site the paddy infuscatum was rare any during season. One male of croceolum S. and one male of S. risi were found in 1981 and 1983, respectively, the of though number sampling days was not equal each year. In the 4 the dominant paddy fields, species were ,S. parvulum, S. eroticum, S. darwinianumand 5. darwinianum, in site G, R, M and D, respectively. Few S. were in site D, which parvulum flying was a relatively open paddy fieldarea. Most S. parvulum captured in site M were immigrants from the shady natural bogs southwards. The habitat of S. parvulum seemed to be restricted to the paddy fields with shaded areas. S. eroticum also preferred the paddy fields with shaded but seemed site sections, not to select G, the most shaded paddy fields, as S. did. 5. darwinianum parvulum preferred open paddy fields. S. frequens also to seemed do so, though its density was low, because its local breeding season is 252 M. Watanabe & M. Taguchi Table 1 of individuals in in Mean number (± SE) Sympetrum observed per day October, 1981-1984 = five ecologically different study areas — (n number of sampling days) G M U Species Sex n n n n No. No. n No. n No. n No. 3a 9 58.9± 12.2 14 I4.9±4.314.9±4.3 12 4I.8±41.8± 7.2 6 0.0±0.0± 0.0 6 8.2±2.0 parvulum 9 9 8.3±8.3 ± 3.1 14 3.4±0.7 1212 5.8±5.8 ± 1.3 66 0.2± 0.2 6 I0.0±2.lI0.0±2.1 3a 9 I6.2± 2.0 14 67.9± 1.0 12 9I.9± 13.0 6 42.042.0±± 7.0 6 22.2±5.422.2±5.4 eroticum 9 9 9.0± 1.8 14 I5.4±3.4 12 I2.l±12.I± 1.9 6 4.3±4.3± 1.5 6 I7.5±3.7 3a 9 5.9± 3.2 14 28.4±8.8 12 I28.8±128.8±16.016.0 6 I33.0±37.7 6 7.7± 1.7 darwinianumJarw inianum 9 9 I9.3±19.3± 8.6 14 27.2±8.7 12 92.0± 16.9 6 84.5±32.7 6 I8.3±3.818.3±3.8 <îa 9 3.3± 1.4 14 I5.3±4.8 1212 112.12. 1 ± 2.5 6 20.5±20.5± 3.4 6 l.0±0.41.0±0.4 pedemontanumoedemontanum 9 9 3.4± 1.0 14 6.0± 1.6 12 I2.3± 1.6 6 I6.7±16.7± 3.6 6 3.8± 1.4 3a 9 6.1± 3.0 14 11.6±3.6 12 9.3± 3.0 6 3.7± 1.2 6 7.3±4.4 frequens 9 9 5.2± 1.3 14 9.6±3.2 12 I2.8± 3.1 6 4.3± 1.4 6 7.3±3.4 3a 9 l.6± 0.60.6 14 4.4±0.9 12 I0.3± 2.1 6 0.7± 0.4 6 0.7±0.3 bacchatoc cha 9 9 l.0± 0.3 14 2.1 ±0.5 12 4.3±4.3± 0.9 6 l.0± 0.4 6 l.0±0.4l.0±0.4 3a 9 0.2± 0.1 14 0.0±0.0O.OiO.O 12 0.4± 0.1 6 0.3±0.3± 0.2 6 0.3±0.2 nfuscatum 9 9 0.1±O.I± 0.1 14 0.0±0.00.0±0.0 12 0.2±0.2± 0.2 6 0.3±0.3± 0.3 6 0.0±0.0 not until November (TAGUCHI & WATANABE, 1986).