Jpn. J. Environ. Entomol. Zool. 28（3）：133－142（2017） 環動昆 第 28 巻 第 3 号：133－142 （2017） Original Article

Early community assembly of aquatic in experimental ponds established across the forest margin of a Satoyama coppice

Suzuki Masahiro*, Norio Hirai and Minoru Ishii

Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Nakaku Gakuen-cho 1-1, Sakai, Osaka 599-8531, Japan

（Received : May 30, 2017；Accepted : September 7, 2017）

Abstract We investigated early community assembly of aquatic insects across the forest margin in Satoyama, the traditional rural landscape in Japan. In April 2011, we established six experimental ponds using plastic tanks (220 L, 20 cm in depth) filled with tap water, with two each outside (Plot A), at the margin (Plot B) and inside (Plot C) a Satoyama coppice in Osaka Prefecture. We surveyed aquatic insects twice monthly between May and December and canopy openness as the indicator of environmental factors related to coppice forest seasonally. A total of 72,324 individuals belonging to 25 taxa were recorded in this study with 14,076, 5,699, 4,098, 14,079, 19,935 and 14,437 individuals from 17, 5, 10, 12, 13 and 12 taxa recorded at Ponds A1, A2, B1, B2, C1 and C2, respectively. In all ponds, taxa richness gradually increased until July or August and thereafter gradually decreased or remained constant. Abundance of each abundant family except Libellulidae differed significantly among the three plots or in time–plot interactions. The most dominant taxa changed from Chironomidae to Notonectidae (Notonecta triguttata) and then to Baetidae (Cloeon spp.) in Ponds A1 and A2, from Chironomidae to Libellulidae (Orthetrum melania) and again to Chironomidae in Pond B1 and from Chironomidae to Baetidae in Pond B2. Only Chironomidae was dominant in Ponds C1 and C2. Non-metric multidimensional scaling showed that community assembly differed among plot locations across the forest margin, although canopy openness was similar at Plots B and C. Our results show that aquatic insect communities developed rapidly in newly created habitats in Satoyama and the environmental gradient across the forest margin generated taxonomic diversity. With regard to the functional characteristics of aquatic insects, predatory plankton, herbivorous neuston and detritivores colonized abundantly inside the forest, and predatory divers and herbivorous benthos colonized abundantly outside the forest. Our results demonstrate that creation of aquatic habitats across a forest margin would be effective for conserving taxonomic and functional diversity of aquatic insect communities in Satoyama, one of the biodiversity hotspot habitats in Japan.

Keywords : Canopy openness, colonization, diver, environmental gradient, life type, pioneer

Introduction components in the ecosystem, although in recent years their hydroperiod has been limited to spring through autumn in most The rice paddy ecosystem, including temporary and regions or locations in Japan (Hidaka, 1998). However, species permanent water bodies such as rice paddies and irrigation diversity has been declining due to destruction, fragmentation ponds, respectively, has been maintained in Satoyama, the and degradation of the rice paddy ecosystem with land traditional rural landscape in Japan consisting of mixtures of consolidation, abandonment and urbanization (e.g. Hidaka, coppices, farmlands and settlements. Satoyama has long 1998; Ishii, 2005; Takeuchi, 2010). There is an urgent need to provided habitats for a variety of wild aquatic and conserve the species diversity of aquatic insects, many species plants (e.g. Takeuchi, 2003). Diverse aquatic assemblages have of which are considered to depend on the rice paddy ecosystem been observed especially in rice paddies, the largest in Japan (e.g. Nishihara et al., 2006).

*Corresponding author: [email protected]

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The rice paddy ecosystem in Japan is embedded in the fine-grained mosaic Satoyama landscape (Takeuchi, 2010) and the water bodies are often surrounded by or adjacent to coppices. Some aquatic insects, such as the dragonfly Sympetrum infuscatum, depend on both rice paddies and coppices during their life histories (Iwasaki et al., 2009). Therefore, the terrestrial landscape within Satoyama may affect aquatic communities in the rice paddy ecosystem. Thus far, however, studies of variation in the landscape have focused on factors related to terrestrial organisms such as ground beetles (e.g. Kagawa and Maeto, 2009), butterflies (e.g. Ohwaki et al., 2007), spiders (Miyashita et al., 2012) and birds (e.g. Nakatsu et al., 2004). Few studies have investigated why diverse aquatic insects inhabit temporary waters such as rice paddies, Fig. 1 Surrounding landscape and arrangements of six how early community assembly progresses in spring because experimental ponds established outside (A1 and A2), at the margin (B1 and B2) and inside (C1 and C2) forest in the rice paddies are only irrigated for half the year, and what roles Sakai Nature Forest (SNF) in Osaka, Japan, in April 2011. Satoyama coppices play in the community assembly process. In this study, we investigated the establishment of aquatic fields, golf courses and other land uses. With regard to aquatic insect communities for a short period between spring and habitats, there are approximately 70 small ponds and about 50 winter using newly created experimental ponds established in a paddy fields (6 and 3 ha in total area, respectively) and other Satoyama landscape as a model of temporary habitats in a rice temporary pools in the area within 1.0 km of SNF. paddy ecosystem. To understand the early community assembly and roles of Satoyama coppice, our study requires a Experimental ponds comparison approach of the assembly progress among the On 24 April 2011, we established six experimental ponds ponds established across the forest margin in Satoyama using plastic tanks (220 L: 174 × 74 cm in bottom area, 20 cm landscape. We can consider the hypothesis that different in depth; Risu Kogyo, PLABUNE 220, green color), with two communities assemble in response to the environmental each outside (Plot A), at the margin (Plot B) and inside (Plot C) heterogeneity across the forest margin. We also investigated the coppice forest. The ponds outside the forest (Ponds A1 and canopy openness as the indicator of the environmental factors A2) and inside the forest (Ponds C1 and C2) were located related to coppice forest (e.g. leaf-litter input and ease of approximately 10 m away from the forest margin, and the other detection of water surface for aquatic insects). We also discuss two ponds were located under the canopy forming the forest the effects from the perspective of the functional edge (Ponds B1 and B2) (Fig. 1). The two ponds were placed characteristics of aquatic insects to evaluate the relationship 2, 3 and 4 m apart at Plots A, B and C, respectively. There were between the community structure and differences in distances of approximately 20, 45 and 65 m between Plots A–B, environmental factors across the forest margin. B–C and C–A, respectively. Each pond was set on the ground and filled with tap water subjected to advanced water treatment. Study site and methods A concrete block that had been left in water for years was placed in each pond as a climbing substratum for aquatic Study site animals. Organic sediment in the pond bottom was mainly The study site was the Sakai Nature Forest (SNF) in the composed of algae and particulate detritus in Ponds A1 and A2, southern suburbs of Sakai City in southern Osaka Prefecture, algae and leaf litter in Pond B1, and leaf litter in Ponds B2, C1 central Japan (34.458582° N, 135.526004° E; elevation, 85 m). and C2 during the experimental period. The water depth was SNF has about a 17 ha area composed of a remnant of maintained at approximately 15–20 cm by adding tap water Satoyama coppice, dominated by broad-leaved oak trees, such during the experimental period, when necessary. We also kept as the deciduous Quercus serrata Murray and evergreen Q. the height of vegetation around the ponds low so as to glauca Thunberg and Lithocarpus glaber (Thunberg) Nakai. maximize the water surface of the ponds during the The area within 1.0 km of SNF comprises forests, agricultural experimental period.

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Aquatic insect monitoring stress value, which was a measure of deviation from Aquatic insects were collected from each pond using a 30 monotonicity in the relationship between observed cm-wide hand net with 0.5 mm mesh until no more individuals dissimilarities and ordination distances. The analysis was were found in five consecutive samplings over the whole pond; stopped when the stress value was less than 0.2 with additional sampling was conducted twice a month between May and dimensions, corresponding to a useful representation (Kruskal, December, for a total of 16 times, in 2011. Small dipteran taxa 1964). The abundance data for NMDS were of Chaoboridae, Culicidae and Chironomidae were estimated square-root-transformed prior to the analysis to moderate monthly by collecting from two 30 × 30 cm areas on the weights of extremely dominant taxa. bottom of each pond (18% of the bottom area) using the hand All statistical analyses were performed using R version 3.1.2 net. Collected specimens were released back into each pond (R Core Team, 2014), with the package “vegan” (Oksanen et after counting the number of individuals of each species or al., 2015) for NMDS. In all abundance data from the taxa, although a few individuals in taxa that we could not experimental ponds, holometabolous taxa (Coleoptera) were identify on site were placed in 70% ethanol and identified with divided into life stages (adult and larva) due to their ecological a microscope in the laboratory. differences.

Canopy monitoring Results Canopy openness was estimated from hemispherical images taken at 1.0-m height near each pond on 28 April, 30 July, 5 Total abundance of each taxon November and 28 December in 2011, using a digital camera During the experimental period, we collected 72,324 with a fisheye lens (Nikon COOLPIX4300; Fisheye Converter individuals belonging to 25 insect taxa (Table 1). In total, FC-E8 0.21x). The calculation of canopy openness was 14,076, 5,699, 4,098, 14,079, 19,935 and 14,437 individuals performed using “CanopOn 2” (Takenaka, 2009). The original from 17, 5, 10, 12, 13 and 12 insect taxa were observed at images by the equidistance projection were transformed into Ponds A1, A2, B1, B2, C1 and C2, respectively. There were the images by the orthogonal projection, prior to the great differences in total abundance between the two ponds at calculation. Plots A and B, and Ponds A2 and B1 had the least abundance among the six ponds. In Plot A, total taxa richness also differed Statistical analyses significantly between the two ponds. Dominant taxa were The significance of the plot factor and the temporal change Cloeon species (Ephemeroptera: Baetidae) in Ponds A1, A2, in the effect (i.e. time–plot interaction) for taxa richness and B1 and B2 (87%, 95%, 20% and 42% in relative abundance, abundance of each taxonomic family was evaluated using respectively); Chironomidae species (Diptera) in Ponds B1, B2, repeated measures ANOVA (rANOVA) using a split-plot C1 and C2 (54%, 53%, 83% and 87%, respectively); and design. Only the abundant taxa (>100 individuals in total Orthetrum melania (Selys) (: Libellulidae) only in among all ponds and periods) were analyzed. The abundance Pond B1 (20%). Each of the other taxa represented 10% or less data were square-root-transformed prior to analysis to meet in relative abundance in each pond. ANOVA assumptions. To examine variation in community structures among Temporal change in communities experimental ponds and the temporal change, the relative Taxa richness was not significantly affected by the plot and abundance of each family was calculated in monthly periods time–plot interaction over time (rANOVA, df = 2, P > 0.05) when insects of all taxa including small dipterans were counted (Fig. 2). However, the richness in all ponds gradually (see Aquatic insect monitoring). The families that were not increased until July or August (i.e., 3 or 4 months after their most dominant in any period were combined into a group establishment), and thereafter gradually decreased or remained (others). Moreover, Non-metric Multidimensional Scaling at the same level. (NMDS; Minchin, 1987) with the Bray-Curtis dissimilarity Abundance of adult Hydraenidae, Chirinomidae, Culicidae, index (Bray and Curtis, 1957) was performed based on Chaoboridae and adult Dytiscidae differed significantly among abundance data of species (or taxa) in monthly periods. The the three plots (df = 2, P < 0.05, respectively) and the number of dimensions in NMDS was determined based on the time–plot interaction was significant for Baetidae, adult

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Hydraenidae, Chaoboridae and Notonectidae (df = 30, 30, 14 15 and 30, P < 0.001, respectively) (Fig. 3). Only Libellulidae showed no significant differences in abundance across the three plots and time–plot interaction (df = 2 and 30, P > 0.05, 10 respectively). In particular, Baetidae became most abundant at Plot A. Adult Hydraenidae, Chirinomidae, Culicidae and

5 Chaoboridae were most abundant at Plot C, and the abundance

Number oftaxa of adult Hydraenidae and Chaoboridae at Plot C changed greatly after July. Adult Dytiscidae showed the greatest

0 100 Apr May Jun Jul Aug Sep Oct Nov Dec A1 Time (Months) 50 Fig. 2 Temporal change in taxa richness in six experimental ponds established outside (A1 and A2: 0 open and filled circles), at the margin (B1 and B2: 100 open and filled triangles) and inside (C1 and C2: A2 open and filled squares) forest in the Sakai Nature 50 Forest in Osaka, Japan, in April 2011.

1800 180 Baetidae Adult Hydraenidae 0 P ns P * T*P *** T*P *** 100 900 90 B1

50 0 0 5000 1400 Chironomidae Culicidae P * P * 0 T*P ns T*P ns 100 2500 700 B2 Relative abundance 0 0 50 240 1400 Libellulidae Chaoboridae P ns P * T*P ns T*P *** 0 120 700 100 Number of individuals C1

0 0 160 40 50 Notonectidae Adult Dytiscidae P ns P * T*P *** T*P ns 80 20 0 100 C2 0 0 Jul Jul Apr Oct Apr Oct Jun Jun Aug Sep Nov Dec Aug Sep Nov Dec May May 50 Time (Months) Fig. 3 Temporal change in abundance of taxa in six 0 experimental ponds established outside (A1 and A2: open May Jun Jul Aug Sep Oct Nov Dec and filled circles), at the margin (B1 and B2: open and filled Time (Months)

triangles), and inside (C1 and C2: open and filled squares) Fig. 4 Temporal change in relative abundance of taxa in forest in the Sakai Nature Forest in Osaka, Japan, in April six experimental ponds established outside (A1 and A2), 2011. Significance of the plot (P) and time–plot interaction at the margin (B1 and B2) and inside (C1 and C2) forest (T*P) in rANOVA was shown (ns no significance, * P < in the Sakai Nature Forest, Osaka, Japan, in April 2011. 0.05, ** P < 0.01, *** P < 0.001). The abundant taxa (> 100 The patterns of white, dot, check, stripe and black show individuals in total among the all ponds and periods) only Baetidae, Chironomidae, Notonectidae, Libellulidae and were shown and the coleopteran families were divided into others, respectively. life stages (adult and larva).

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Table 1 Total abundance of each insect species observed in six experimental ponds established outside (A1 and A2), at the margin (B1 and B2) and inside (C1 and C2) forest in the Sakai Nature Forest in Sakai City, Osaka, Japan, between April and December 2011. The life stages (adult, A; larva, L) of Hemiptera and Coleoptera are

indicated after the species names. Note: * The total abundance was doubled because sampling occurred half as frequently as for other taxa.

Taxa A1 A2 B1 B2 C1 C2 Total Japanese names Ephemeroptera カゲロウ目 Baetidae コカゲロウ科 Cloeon spp. 12,220 5,419 829 5,957 - - 24,425 フタバカゲロウ属spp. Odonata トンボ目 アオイトトンボ科 peregrinus --1--- 1ホソミオツネントンボ Aeshnidae ヤンマ科 Polycanthagyna melanictera - - - - 16 11 27 ヤブヤンマ Libellulidae トンボ科 Lyriothemis pachygastra 24-----24ハラビロトンボ Orthetrum albistylum 454-----454シオカラトンボ Orthetrum melania - - 828 18 2 49 897 オオシオカラトンボ Crocothemis servilia 12 - - 9 - - 21 ショウジョウトンボ Hemiptera カメムシ目 Notonectidae マツモムシ科 Notonecta triguttata (L) 122 18 33 21 - - 194 マツモムシ Notonecta triguttata (A) 1 1 12 87 1 - 102 マツモムシ Gerridae アメンボ科 Gerris sp. (L) - - 2 - - - 2 ヒメアメンボ属sp. Gerris latiabdominis (A)1----- 1ヒメアメンボ Gerris insularis (A) - -3511 10ヤスマツアメンボ Coleoptera コウチュウ目 Dytiscidae ゲンゴロウ科 Hydroglyphus japonicus (L)1611----27チビゲンゴロウ Hydroglyphus japonicus (A)2979----108チビゲンゴロウ Leiodytes frontalis (A) ----21 3マルチビゲンゴロウ Copelatus kammuriensis (A) 13 - 12 15 1 1 42 カンムリセスジゲンゴロウ Eretes griseus (A) 2----- 2ハイイロゲンゴロウ Hydaticus rhantoides (A)11-----11ウスイロシマゲンゴロウ Hydraenidae ダルマガムシ科 Hydraena miyatakei (A) 15 - 22 69 301 221 628 ミヤタケダルマガムシ Hydrophilidae ガムシ科 Enochrus sp. (L) -----4 4ヒラタガムシ属sp. Enochrus japonicus (A) 1 - - 3 24 9 37 キベリヒラタガムシ Sternolophus rufipes (A)29-----29ヒメガムシ Scirtidae マルハナノミ科 Scirtes sp. (L) ----65873トビイロマルハナノミ属sp. Diptera ハエ目 Culicidae カ科 Culicinae spp.* 119 9 114 128 1,092 484 1,946 ナミカ亜科spp. Chaoboridae フサカ科 Chaoborus sp.* - - 47 318 1,908 1,073 3,346 フサカ属sp. Chironomidae ユスリカ科 Chironomidae spp.* 992 161 2,194 7,445 16,511 12,567 39,870 ユスリカ科spp. Ceratopogonidae ヌカカ科 Ceratopogoninae sp. 15 -----15ヌカカ亜科sp. Stratiomyidae ミズアブ科 Odontomyia sp. 1----- 1Odontomyia 属 sp. Syrphidae ハナアブ科 Eristalis sp. - - - 4 12 8 24 ナミハナアブ属sp.

Total abundance 14,076 5,699 4,098 14,079 19,935 14,437 72,324 Total number of taxa 17 5 10 12 13 12 25

- 137 - Suzuki et al. abundance at Plot A. Notonectidae peaked at Plot A in June, between May and July (i.e. the first three months), Ponds B1, and thereafter appeared constantly in both ponds at Plot B. B2, C1 and C2 had similar community structure in the range of Libellulidae increased primarily in Ponds A1 and B1 in July. NMDS1 > 0, whereas Ponds A1 and A2 had large-scale The temporal change in relative abundance of dominant temporal variation in community structure in the range of families was clearly different between Plots A and C (Fig. 4). NMDS1 < 0. Between August and December, the community The most dominant taxa in Ponds A1 and A2 changed from structure in Ponds B1 and B2 became more similar to that in Chironomidae (88% and 89% in the first month) to Ponds A1 and A2. However, the temporal trajectories in Ponds Notonectidae (50% and 100% in the second month) and then to B1 and B2 were different in the direction of NMDS2. Baetidae (54–98% and 75–99% in the subsequent months) in temporal sequence, respectively. On the other hand, only Canopy openness Chironomidae dominated in Ponds C1 and C2 throughout the Canopy openness was similar among the four ponds at Plots experimental period (75–94% and 66–95%). The most B and C during the experimental periods (17–43%; Fig. 6a). dominant in Pond B2 changed gradually from Chironomidae Pond B2 was 17 and 20% in openness in July and November, (94–97% for the first three months) to Baetidae (68–76% for respectively, and they were as low as those of Ponds C1 and the last three months). In Pond B1, Libellulidae (August and C2 in July and November. The canopy cover at Pond B2 was as September: 53–62%) and Chironomidae (the other months: large as Ponds C1 and C2 between July (Fig. 6b) and 49–100%) were the most dominant. Baetidae, Notonectidae November. Ponds A1 and A2 remained at higher level of 47% and Libellulidae in B1 consisted of Cloeon, Notonecta or more. With regard to temporal variation, canopy openness triguttata Mostschulsky and O. melania alone, respectively was lower at all experimental ponds between July and (Table 1). November. The results of NMDS were well represented in two dimensions (stress value = 0.119). The analysis showed that the Discussion pond communities at Plots A, B and C were arranged along the direction of the NMDS1 axis, and the temporal variation was Community assembly in a Satoyama landscape larger in the order of Plots A > B > C (Fig. 5). In particular, Aquatic insect communities developed rapidly in newly created habitats (i.e. experimental ponds) in Satoyama landscape through the colonization by as many as 25 taxa. The D species observed at Plot A (Table 1) included many species D common in temporary waters such as Cloeon species (Mukai et D D al., 2014) and dytiscids such as Hydroglyphus japonicus Sharp D D (Saijo, 2001; Ohba et al., 2013; Watanabe et al., 2013; Mukai M M et al., 2014) and Eretes griseus (Fabricius) (Watanabe et al.,

NMDS2 M 2013; Ohba and Ushio, 2015). The notonectid N. triguttata, M which colonized and reproduced at Plots A and B (Table 1, M Fig. 3), reproduces in paddy fields rather than permanent M

-1.5 -1.0 -0.5 0.0 0.5 1.0 reservoirs (Saijo, 2001). These species are characterized as pioneers that are replaced by the subsequently colonizing -1.5 -1.0 -0.5 0.0 0.5 1.0 species through the succession process. The observed NMDS1 colonization by many species suggests that aquatic insect Fig. 5 Non-metric multidimensional scaling showing communities in rice paddy ecosystems are composed of many trajectories over the monthly periods between May (M) and pioneer species. During the community assembly process, December (D) for each community in six experimental replacement of the dominant species was especially strong at ponds established outside (A1 and A2: open and filled circles), at the margin (B1 and B2: open and filled triangles) Plot A (Fig. 4). Chironomidae and Notonectidae, the first and and inside (C1 and C2: open and filled squares) forest in the second dominants respectively, can easily colonize ephemeral Sakai Nature Forest in Osaka, Japan, in April 2011. ponds with few food resources, because of their small body size and the availability of terrestrial food resources on the water surface, such as falling insects. The persistent dominance

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(a) (b) 60

40

20 A1 A2

Canopy openness (%)

0 Apr May Jun Jul Aug Sep Oct Nov Dec Time (Months)

B1 B2

C1 C2

Fig. 6 Temporal changes in canopy openness (a) and the hemisphe rical images by the orthogonal projection in July (b) at six experimental ponds established outside (A1 and A2: open and filled circles), at the margin (B1 and B2: open and filled triangles) and inside (C1 and C2: open and filled squares) forest in the Sakai Nature Forest in Osaka, Japan, in April 2011. by Chironomidae at Plot C may be related to the accumulation between the ponds at Plots B and C (Fig. 3). Thus, of leaf litter from the early period onward. colonization by aquatic insects is likely affected not only by Community assembly in the experimental ponds differed canopy openness but also other terrestrial landscape factors, among the three plots. In particular, most of abundant taxa such as the distance to open fields, which differs between the showed significant variation in abundance across the forest forest margin and inside. Our results suggest that the location margin or significant time–plot interactions in abundance over of aquatic habitats across a forest margin can have a greater the experimental period (Fig. 3). Community structure effect on early community assembly of aquatic insects than differed greatly between Plots A and C (Figs. 4, 5), and the canopy openness. communities at Plot B were intermediate and showed trajectories from Plot C to A (Fig. 5). The results demonstrate Functional characterization that the terrestrial landscape gradient across the forest margin Takemon (2005) noted that variation in aquatic communities of Satoyama coppice generated taxonomic diversity in aquatic is often explainable in terms of the component organisms’ insect communities. functional characteristics rather than their taxonomic identity. The variation in community structure did not correspond The functional characteristics related to trophic and spatial well to the variation in canopy openness among the three plots niches also may be useful here to understand the community (Fig. 6a). The canopies covering Ponds B1 and B2 grew assembly process. The abundant taxa found in this study (Fig. seasonally and became as similar level as Ponds C1 and C2 in 3) can be divided into herbivores like periphyton or alga openness (Fig. 6a, b), contrary to our expectation. However, feeders (Baetidae and adult Hydraenidae), detritivores during colonization, the dominant taxon Cloeon discriminated (Chironomidae and Culicidae) and predators (the other four

- 139 - Suzuki et al. families), according to the classification of trophic levels Table 2 Differences in colonization across the forest margin in (Cummins et al., 2008). Most of the observed Chironomidae functional groups of aquatic insects categorized based on trophic levels and life types (see Discussion). were identified as members of Chironominae, a subfamily of Trophic levels Life types Colonization variation across forest margin mostly detritivores (Coutrtney et al., 2008). Predator Benthos Unclear Baetidae (i.e. Cloeon), the dominant benthos at Plot A (Fig. Predator Plankton Ponds outside forest < Ponds inside forest 4), is considered to respond to the production of benthic algae. Predator Diver Ponds outside forest > Ponds inside forest Herbivore Benthos Ponds outside forest > Ponds inside forest In contrast, adult hydraenids (i.e. Hydraena miyatakei, Satô) Herbivore Neuston Ponds outside forest < Ponds inside forest depend on periphyton on floating leaf litter, as found at Plot C. Detritivore Benthos Ponds outside forest < Ponds inside forest Detritivore Diver Ponds outside forest < Ponds inside forest Adult hydraenids, which cannot swim, live around the sides of water bodies (White and Roughley, 2008). Chironomidae and those under a closed canopy. However, our results showed that Culicidae, which colonized most abundantly at Plot C (Fig. 3), there are many taxa and certain functional groups that colonize appeared to respond to the accumulation of detrital leaf litter. abundantly in ponds inside the forest (Tables 1, 2). Although Blaustein and Kotler (1993) reported that a culicid species our experimental ponds were just filled with water, they oviposited preferably at water bodies with more food resources. permitted colonization of diverse taxa including endangered As for the predatory families, Chaoboridae (i.e. Chaoborus sp.), species of Gerris insularis (Motschulsky) (Osaka Prefectural which colonized most abundantly at Plot C, had the opposite Government, 2014), Leiodytes frontalis (Sharp) (Ministry of tendency as that of Notonectidae and adult Dytiscidae (Fig. 3). the Environment, 2014; Osaka Prefectural Government, 2014) They also have different forms of mobility: chaoborids float in and Hydaticus rhantoides Sharp (Osaka Prefectural water, whereas notonectids and adult dytiscids can dive and Government, 2014) (Table 1). Therefore, creating aquatic swim actively by using their legs. The difference in their habitats across forest margins is considered as one of the colonization sites may be related to these mobility differences, effective approaches for conserving taxonomic and functional which influence their life histories. diversity of aquatic insect communities in the fine-grained Thus, the abundant taxa in this study can be divided into mosaic of forests and fields in Satoyama landscapes. four types: benthos (Baetidae, Chironomidae and Libellulidae) of the type without constant floating, plankton (Chaoboridae) Acknowledgements of the type with it, divers (Culicidae, Notonectidae and adult

Dytiscidae) of the type with an ability to dive by swimming The authors are grateful to Dr. T. Ohtsuka of the Lake Biwa and neuston (adult Hydraenidae) of the type without this ability. Museum of Shiga Prefecture for his invaluable advice on the The former two and latter two types can be divided based on statistical analyses in this study. We are also grateful to Dr. T. whether they require atmospheric oxygen (Resh et al., 2008). Fujitani of Civil Engineering and Eco-technology Consultants Our census revealed that predatory plankton, herbivorous Co., Ltd., and T. Yamamoto of the Kansai Research Group of neuston and all detritivores colonized abundantly in the early Odonatology for their helpful assistance in identification of ponds inside the forest, and predatory divers and herbivorous aquatic insect species. We are also indebted to the Sakai Nature benthos colonized abundantly in the early ponds outside the Forest for allowing us to conduct this study. Thanks are also forest (Table 2). Thus, aquatic insect communities developing due to our laboratory members for their kind cooperation and in newly formed ponds vary in the functional structure based assistance. This study was supported in part by a Grant-in-Aid on trophic levels and life types. for Scientific Research (23510297) from the Ministry of

Education, Culture, Sports, Science and Technology. Conservation of aquatic insect diversity in Satoyama

As aquatic habitats are created for the conservation of References aquatic animals and plants in many parts of the world (e.g. Gee et al., 1997), we must conserve the habitats of aquatic insects Binckley, C. A. and W. J. Resetarits Jr (2007) Effects of forest in rice paddy ecosystems in Satoyama landscapes and further canopy on habitat selection in treefrogs and aquatic investigate how communities and their species diversity is insects. Oecologia 153: 951–958. generated in these ecosystems. Binckley and Resetarits (2007, Binckley, C. A. and W. J. Resetarits Jr (2009) Spatial and 2009) reported that more diverse and abundant coleopterans temporal dynamics of habitat selection across canopy and hemipterans colonized in open experimental ponds than in

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里山林内外に設置した実験池における水生昆虫群集の初期形成過程

鈴木真裕・平井規央・石井 実 大阪府立大学大学院生命環境科学研究科

里山の水生昆虫群集の初期形成過程を解明するために， 2011 年 4 月に大阪府内の里山の林外，林縁，林内（順に A，B，C 区）に各2個の220 L のプラスチック容器に水深 20cm の水道水を張った実験池（A1，A2，B1，B2，C1， C2）を設置し，5～12 月に月 2 回の水生昆虫調査，季節ごとに樹林に関する環境要因の指標として樹冠開空度調査 を行った．調査の結果，A1，A2，B1，B2，C1，C2 の各池では，のべ 17 分類群（以下，種）14,076 個体，5 種 5,699 個体，10 種 4,098 個体，12 種 14,079 個体，13 種 19,935個体，12 種 14,437 個体，合計 25 種 72,324 個体の水生 昆虫が観られた．どの池でも種数は 7，8 月まで徐々に増加した後，緩やかに減少するか同レベルで推移した．最 優占群は A1，A2 でユスリカ科，マツモムシ科，コカゲロウ科， B1 ではユスリカ科，トンボ科，ユスリカ科，B2 ではユスリカ科，コカゲロウ科の順で変化したが，C1，C2 ではユスリカ科が継続的に優占した．樹冠開空度は B， C 区で類似したが，群集形成過程はほぼ池の設置区に対応することが NMDS によって示された．また，栄養段階と 生活型に基づく機能群の構成も設置区に依存する可能性が示された．以上のことから，里山林内外の生息場所の創 出は水生昆虫の種と機能群の多様性の保全に有効と考えられた．

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