2. Response of Ground Beetle (Coleoptera: Carabidae) Communities to Effect of Urbanization in Southern Osaka
Unexpectedly, species richness, density, body size, habitat type, species diversity, and species evenness did not differ between the different urban green areas. Furthermore, the community structure of ground beetles was similar in different areas. It seems that ground beetle communities formed by the effect of urbanization may become similar regardless of area. Ishitani et al.
[16] showed that in urban habitats, large-sized forest specialists may completely disappear, whereas small-sized forest specialists and medium-sized habitat generalists were in higher abundance. Fragmentation and isolation as well as lower habitat quality of remnant urban habitat patches may cause generalist species to increase
[13]. Lee and Ishii
[17] studied riverbank, urban park, rice paddy, and coppice remnants in southern Osaka and showed that forest specialist, open-habitat specialist, large-sized, and endemic species have been reduced by urbanization. In our study, four large-sized forest species (
Carabus yaconinus,
Leptocarabus kumagaii,
Haplochlaenius costiger, and
Galerita orientalis) were recorded. Ishitani et al.
[16] considered
C. yaconinus and
H. costiger as forest generalists.
L. kumagaii and
G. orientalis might be forest generalists based on collected records such as riverbanks, paddy fields, and urban green areas around forests in previous studies
[18][17][19]. Among three dominant species,
Synuchus nitidus and
Dolichus halensis were considered forest generalist and habitat generalist, respectively
[17]. This result seems to be consistent with previous studies.
Remnant forests may be one of the reasons why ground beetle assemblages were similar regardless of area. Although SU was the smallest area in this study, 22 ground beetle species were recorded, and this value was higher than the average (20 species). SU is located near Hatadaimyou temple where there are remnant forests dominated by evergreen oaks (
Quercus species). Forests associated with shrines and temples are recognized as important components of urban green spaces and can potentially function as a key role in ecosystem conservation in urban areas
[20]. Although urban forests have less species richness and abundance and different species composition and dominant species compared with rural forest, they can provide habitats for wildlife and potentially be used as stepping stones in the urban green space network
[20][21]. Connectivity for ground beetles in urban areas will be another important factor. Both UM and TA are located in landfill areas. However, species richness in UM was the highest, whereas that in TA was the lowest. UM is located near the mouth of Yamato River, whereas TA is connected to inland with two bridges. Yamato River is a class A river in the Kansai region and flows from Nara and Osaka Prefectures to the Osaka Bay
[19]. Lee and Ishii
[19] reported that 53 ground beetles were found in various places such as gravelly riverbeds, sand lands, and grassy riverbanks in Yamato River. Among ground beetles found in UM, 86% species composition was the same as that found by Lee and Ishii
[19]. In addition, this result showed that
Carabus yaconinus was collected in IZ, KU, and KM, which are connected to natural habitats. Lee and Ishii
[17] reported that
Carabus yaconinus was not found in urban parks which are separated from natural forests in southern Osaka. Lee and Kwon
[22] suggested that short-winged
Carabidae species, poor dispersers, disappear in fragmented forests. These species may not be able to disperse through corridors or stepping stones. Our results suggest that remnant forests and connectivity will contribute to keeping ground beetle diversity in the urban area.
Although there is no significant relationship between ground beetle communities and area, community indices were positively or negatively correlated with area. Among them, ground beetle species richness, species diversity, and species evenness showed positive correlations with area. Urban area and road were negatively correlated with species richness of all species, small-sized species, medium-sized species, large-sized species, open land species, and density of large-sized species and open land species, and species diversity and species evenness. Koivula and Vermeulen
[23] showed that carabid populations isolated by highways were significantly affected by patch size, and forest carabids rarely cross roads. Keller and Largidèr
[24] reported that the isolation caused by major roads has a significant impact on the genetic structure of ground beetle populations. Urbanization substantially influences all levels (species group, population, and community) of the biological organization of ground beetles living in urban green areas
[13]. Our results were consistent with previous studies. However, there are no uniform patterns in year, field, park and green space, forest, or open space with community index. Future studies should increase the sample size to enhance the statistical rigor.