Mutual trophic interactions between contiguous habitats have remained poorly understood despite their potential significance for community maintenance in ecological landscapes. In a deciduous forest and stream ecotone, aquatic insect emergence peaked around spring, when terrestrial invertebrate biomass was low. In contrast, terrestrial invertebrate input to the stream occurred primarily during summer, when aquatic invertebrate biomass was nearly at its lowest. Such reciprocal, across-habitat prey flux alternately subsidized both forest birds and stream fishes, accounting for 25.6% and 44.0% of the annual total energy budget of the bird and fish assemblages, respectively. Seasonal contrasts between allochthonous prey supply and in situ prey biomass determine the importance of reciprocal subsidies.forest-stream ecotone ͉ allochthonous prey flux

Dynamics of headwater stream ecosystems are generally regarded as occurring at the interface of aquatic and terrestrial ecosystems. Terrestrial arthropod inputs can provide an energy subsidy and increase the abundance of predatory fish, and the ensuing effects potentially can cascade through the food web and ultimately affect primary producers. Nevertheless, the community‐based effects of such inputs on stream food web dynamics are still poorly understood. We present experimental evidence that terrestrial arthropod inputs have an indirect but prominent effect on a stream benthic community by altering the intensity of fish predation in the food web. Two key elements of the stream food web, terrestrial arthropod inputs and the presence of predatory fish, were experimentally manipulated by using greenhouse‐type covers and enclosures (or exclosures) in a forest stream located in northern Japan. When terrestrial arthropod inputs to the stream were experimentally reduced, fish predation pressure shifted dramatically from terrestrial to aquatic arthropods. The ensuing depletion of aquatic arthropods resulted in a subsequent increase in periphyton biomass. This field experiment revealed that terrestrial arthropod inputs were a primary factor controlling cascading trophic interactions among predatory fish, herbivorous aquatic arthropods, and benthic periphyton. These results provide empirical support for the perspective that transfers of energy and biomass from donor systems are frequently significant for the maintenance of biotic communities in recipient systems.

It is believed that the polymorphism observed in calcium carbonate crystals, such as aragonite and calcite in mollusk shells, is controlled by organic matrix proteins secreted from the mantle epithelia. However, the fine structures of these proteins are still unknown, and to understand the molecular mechanisms of mineralization process, detailed structural analyses of the organic matrix proteins are essential. For this, we have carried out purification, characterization, and cDNA cloning of nacrein, which is a soluble organic matrix protein in the nacreous layer of oyster pearls.Northern blot analysis showed that the nacrein transcript was specifically expressed in mantle pallial. Analysis of the deduced amino acid sequence revealed that the protein contained two functional domains: one was a carbonic anhydrase and another was a Gly-Xaa-Asn (Xaa = Asp, Asn, or Glu) repeat domain; however, the carbonic anhydrase domain was split into two subdomains with insertion of the Gly-Xaa-Asn repeat domain between them. Our findings suggest that nacrein actually functions as a matrix protein whose repeated Gly-Xaa-Asn domain possibly binds calcium and as a carbonic anhydrase that catalyzes the HCO-formation, thus participating in calcium carbonate crystal formation of the nacreous layer.Crystallization, observed in many organisms, is a genetically regulated process. In the mammal, several factors regulating bone morphogenesis are identified. Osteopontin, an acidic calcium binding protein, is isolated from the mineralized phase of bone (1). Another bone matrix protein, osteocalcin (2), contains 'y-carboxyglutamic acid residues, which participate in calcium binding. In general, the mollusk shell is mainly composed of two layers, a prismatic layer and nacreous layer. Both layers are in the forms of calcium carbonate crystal; however, the prismatic layer forms calcite and the nacreous layer forms aragonite. Such crystal polymorphism in the two closely situated layers is a highly elaborated phenomenon in the mollusk. In such regulated processes, organic matrices secreted from the mantle epithelia have been suggested to play critical roles (3); the major components of soluble organic matrices are aspartic acid-rich calcium binding proteins (4-8). Recently, Falini et al. (9) and Belcher et al. (10) reported that macromolecules extracted from the nacreous shell layers induced aragonite formation in vitro.Pearl oysters (Pinctada fucata) produce pearls inside the shells. Such a pearl is equivalent to the mollusk shell layer, which is composed of the aragonite crystal and organic matrices. Therefore, to isolate the organic matrix protein, we have chosen the pearl as a starting material. Staining with Coomassie brilliant blue and Stains-all (Nacalai Tesque, Kyoto), we have identified a 60-kDa protein that we named nacrein. Analysis of cDNA encoding nacrein revealed that it had a similar domain to carbonic anhydrase (CA). Furthermore, the native nacrein purified from the pearl possessed CA enzymatic activity. To our knowledge, t...

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream. 
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×103±0.3×103 mg m−2 year−1) was 1.7 times greater than that in the grassland reaches (5.1×103±0.8×103 mg m−2 year−1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types. 
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×103±0.4×103 mg m−2 year−1) of the annual, total prey consumption (10.9×103±1.7×103 mg m−2 year−1) by salmonids in the forest and 53% (2.0×103±0.3×103 mg m−2 year−1) (3.8×103±0.6×103 mg m−2 year−1) in the grassland reaches. 
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in. 
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.

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Summary1. Foraging behaviour, diet and interference competition were examined for two morphologically similar charrs, Salvelinus malma (Dolly Varden) and S. leucomaenis (white-spotted charr), under varying food resource conditions over four summers in a Japanese mountain stream. Data were used to test predictions from a mechanistic model of resource partitioning developed from an earlier ®eld experiment. 2. The charrs adopted one of two distinct foraging modes, ambushing drifting invertebrates from relatively ®xed foraging positions or actively searching for benthic prey over large areas. The proportion of benthos foragers increased markedly when drifting prey declined, and was much greater in S. malma than S. leucomaenis when drift was lean, upholding predictions made from our earlier experiment. 3. For drift foragers of both species, frequency of foraging attempts decreased as drift rate declined, and aggressive encounters increased. In contrast, for benthos foragers of both species the frequency of foraging attempts was essentially constant across the range of benthos biomass measured, and aggressive encounters remained low. 4. Salvelinus leucomaenis ate larger drifting prey than S. malma, even though the former charr were smaller. In contrast, S. malma foraged on benthic prey at a higher rate than S. leucomaenis, although there was no dierence in prey mass. Thus, the optimal point to shift to benthic foraging is at a higher drift threshold for S. malma than S. leucomaenis, most probably due to dierences in jaw morphology. Moreover, because dominance for favourable drift foraging positions was based on size alone, S. malma shifted to benthos foraging at a larger size than S. leucomaenis, as predicted by a simple model. 5. Charr consumed distinct prey types according to their foraging mode. Drift foragers primarily ate terrestrial invertebrates, whereas benthos foragers ate mainly chironomid larvae. Consequently, diet overlap was high when drift was abundant and both species were drift foragers, but declined as drift declined and S. malma shifted to benthos foraging. Therefore, species-speci®c dierences in foraging mode shifts across the resource gradient explained the¯exible resource partitioning we observed, and probably account for the coexistence of these congeneric charrs in zones of sympatry in northern Japan.

Summary1. Riparian zones serve several ecological functions for bats. They provide a source of prey and likely provide favourable structural habitats and shelter from predators. Many studies have shown that bats use the space above streams, ponds or riparian vegetation as feeding habitat. These studies, however, have never distinguished between the effects of habitat structure and prey availability on the foraging activities of bats. Such effects can only be distinguished by an experimental approach. We predicted that bat activity along a stream is influenced by the number of emerged aquatic insects. 2. We evaluated the response of terrestrial consumers, insectivorous bats, to changes in the abundance of emergent aquatic insects by conducting a manipulative field experiment. In a deciduous riparian forest in Japan, aquatic insect flux from the stream to the riparian zone was controlled with an insect-proof cover over a 1·2 km stream reach. 3. We estimated the abundance of emergent aquatic and flying terrestrial arthropods near the treatment and control reaches using Malaise traps. The foraging activity of bats was evaluated in both treatment and control reaches using ultrasonic detectors. 4. The insect-proof cover effectively reduced the flux of emergent aquatic insects to the riparian zone adjacent to the treatment reach. Adjacent to the control reach, adult aquatic insect biomass was highest in spring, and then decreased gradually. Terrestrial insect biomass increased gradually during the summer at both treatment and control reaches. 5. Foraging activity of bats was correlated with insect abundance. In spring, foraging activity of bats at the control reach was significantly greater than at the treatment reach, and increased at both sites with increasing terrestrial insect abundance. 6. Our result suggests that the flux of aquatic insects emerging from streams is one of the most important factors affecting the distribution of riparian-foraging bats. As is the case with other riparian consumers, resource subsidies from streams can directly enhance the performance or population density of riparian-dependent bats. To conserve and manage bat populations, it is important to protect not only forest ecosystems, but also adjacent aquatic systems such as streams.

SUMMARY 1. The compound influence of habitat complexity and patch size on stream invertebrate assemblages associated with submerged macrophytes was investigated through field sampling of two natural macrophyte species with contrasting leaf morphologies (complex, Ranunculus yezoensis; simple, Sparganium emersum) and an experiment with two artificial plants with different levels of morphological complexity. 2. The artificial plant experiment was designed to separate the effects of habitat area (patch size) and habitat complexity, thus enabling a more rigorous assessment of complexity per se than in previous studies where only a single patch size was used. Simple and complex artificial plants were established with five different patch sizes corresponding to the range found in natural plants. 3. Invertebrates occurred on both complex and simple forms of natural and artificial plants at similar abundances with dipterans and ephemeropterans being predominant. Taxon richness was higher on structurally complex Ranunculus than on simple Sparganium and was similarly higher on the complex artificial plant than on the simple one, over the entire range of habitat patch sizes. Thus, architectural complexity affected the taxon richness of epiphytic invertebrates, independently of habitat scale. 4. On the natural plants there was no difference in the abundance (both number of individuals and biomass) of invertebrates between simple and complex forms, while on artificial plants more invertebrates occurred on complex than on simple forms. The amount of particulate organic matter, >225 μm (POM) and chlorophyll a showed mixed patterns on natural and artificial plants, suggesting that the availability of these resources is not an overriding proximate factor controlling invertebrate abundance on plants. The difficulty of extrapolating from experimental results involving use of artificial plants is discussed, especially when considering the relationship between habitat structure and the occurrence of epiphytic invertebrates on natural plants.