Ecological Research

We have compared biomass-allocation patterns and frequency of sprouting among saplings of four tree species (Larix kaempferi, Betula platyphylla var. japonica, Populus maximowiczii, and Populus sieboldii) growing on a volcanic mountain in Hokkaido, northern Japan. Growing conditions were very harsh on the mountainside. Leaf mass and fine root mass relative to root mass were larger in L. kaempferi, and L. kaempferi root mass was less than for the other species. Sprouting ratios were high for the broadleaved species. Different allometries and sprouting ratios among species suggest that survival strategies for L. kaempferi were different from those for the broadleaved species. L. kaempferi has greater ability to increase leaf mass under harsh growing conditions; this probably results in large photosynthetic production by L. kaempferi on the volcano. In contrast, the two Populus species and Betula platyphylla seem to maintain populations through their ability to produce sprouts from large root systems.

Reproductive traits of three ocypodid crabs,Scopimera globosa, Ilyoplax pusillus andMacrophthalmus japonicus, were compared.S. globosa andI. pusillus, inhabiting the upper-middle intertidal zone, produced 1–2 large broods per year, whereasM. japonicus, inhabiting the lower intertidal zone, produced 4–5 small broods per year. InS. globosa andI. pusillus, ovigerous females remained in their plugged burrows without feeding until their eggs hatched. On the other hand, femaleM. japonicus fed actively on surface mud while incubating. We concluded that few large broods may be advantageous in crab species that incubate in burrows, whereas continuous small broods may be advantageous in species that feed actively while incubating.

Effects of environmental variables on the distribution of benthic macroinvertebrates inhabiting sediments were studied at 25 sites along the shoreline of Lake Takkobu in the Kushiro wetland of northern Japan in summer 2003. During the last decade, the lake’s status has undergone a drastic shift from clear water dominated by submerged macrophytes to turbid water dominated by phytoplankton. The canonical correspondence analysis showed that four environmental variables explained the significant variation in the macroinvertebrate species composition: submerged plant biomass, bottom sediment organic matter content (OMC), distance from the mouth of the Takkobu River, and bottom-layer pH. Five species of Chironomidae [Chironomus sp. (except plumosus group), Psectrocladius sp., Corynoneura sp., Parachironomus sp. arcuatus group, and Zavreliella sp.] occurred in sites with relatively lower pH and a high submerged plant biomass, whereas three species of Tubificidae (Tubifex tubifex, Aulodrilus limnobius and Aulodrilus sp.) and two of Chironomidae (Nanocladius sp. and Monodiamesa sp.) occurred in sites with high pH and little vegetation. The three Tubificidae species also preferred organic-rich sediments. Irrespective of aquatic vegetation, Sphaerium sp. (Bivalvia) and Monodiamesa sp. (Chironomidae) occurred in low-OMC sites, whereas Tanypus sp. (Chironomidae) preferred high-OMC sites. The number of macroinvertebrate taxa showed the highest correlation with the number of submerged plants, suggesting that macroinvertebrate species richness was related mostly to submerged plant species diversity in this lake. The quantity and species richness of submerged plants and OMC are thus important determinants of the community structure of macroinvertebrates inhabiting sediments in Lake Takkobu.

Soil inorganic nitrogen supply and fine root mass in the top layers of mineral soil (0–5 and 5–10 cm) were investigated at upper and lower sites of a cool temperate forest where Fagus crenata and Quercus crispula dominate. At both sites, soil inorganic nitrogen supply was greatest in the 0–5 cm layer. The predominant forms of soil inorganic nitrogen supply were NH4 +-N at the upper site and NO3−-N at the lower site. Fine roots were concentrated in the 0–5 cm layer at the upper site, but not at the lower site. The form of supplied soil inorganic nitrogen supply can be important in determining the vertical distribution of fine roots.

Understanding the controls on temporal variation in plant leaf δ2H and δ18O values is important for understanding carbon–water dynamics of the biosphere and interpreting a wide range of proxies for past environments. Explaining the enrichment mechanisms under field conditions is challenging. To clarify the leaf water isotopic enrichment process at the ecosystem scale, four models with a range of complexities that were previously conducted at the leaf scale have been tested to simulate canopy foliage water in a multispecies grassland ecosystem. Although the exact importance of considering non-steady-state or/and isotopic diffusion in bulk leaf isotopic simulations has been reported in previous studies, our findings suggested that the steady-state assumption (SSA) is practically acceptable as a first-order approximation. The SSA two-pool model was the best option for reproducing seasonality of the bulk-leaf-water isotopic ratio for a grassland ecosystem. Relative humidity at canopy layer as the most controlling factor for canopy foliage water stable isotope composition because of its high sensitivity and variation. The results highlighted that canopy foliage water was a well-behaved property that was predictable for a multispecies grassland ecosystem at hourly or daily time-scales.

Latrine sites, or areas where otters scent-mark and deposit feces, are a habitat feature that serve an important role in communication for many otter species. The small-clawed otter (Aonyx cinereus) inhabits both natural and rice field landscapes in Southeast Asia. However, latrine site use by small-clawed otters in rice field landscapes is largely unknown. Based on a 53-week field survey and landscape analyses, we investigated latrine site use by small-clawed otters in rice field landscapes in West Sumatra, Indonesia. Using land use and/or local environmental variables as predictors, we performed generalized linear model analyses to explain the spatial patterns of latrine site occurrence and otter visitation frequency to latrine sites. We determined that small-clawed otters use some latrine sites repeatedly over time; 10 latrine sites were still in use more than 7 years after their initial discovery. Generalized linear model analyses revealed that an intermediate number of rice field huts was the single most important predictor of latrine site occurrence, whereas distance to the nearest settlement, distance to the river, and mean water depth of the rice field adjacent to the latrine site were important predictors of otter visitation frequency to latrine sites. These results indicate that the latrine site preferences of small-clawed otters in rice field landscapes are strongly associated with intermediate levels of rice farming activities. Indonesian rice fields are being degraded or disappearing at an accelerated rate because of land conversion and modernization of agriculture. We emphasize an urgent need for design and implementation of otter-friendly rice farming to conserve small-clawed otters.