Abstract
Resource subsidies exert critical influences on recipient habitats with relatively higher perimeter-to-area ratios, such as headwaters in watersheds. However, little is known about how those subsidies contribute to the energy sources in recipient habitats where the perimeter-to-area ratio is low, such as large stream channels. Here, we show that the diet of small Japanese eels (Anguilla japonica) <500 mm in total length inhabiting natural shoreline areas in large stream channels consists largely of terrestrial earthworms (Metaphire spp.). Stable isotopic analyses showed that the earthworms were the prey animal that contributed most to the eels’ diet (45%–47%). Earthworms constituted the largest portion of the eels’ stomach contents (7%–93%). Eels ingested earthworms within 2 days after rainfall during spring, summer, and autumn, and their consumption increased as the precipitation increased. These findings indicate that the pulsed earthworm subsidy that is driven by rainfall could temporarily bias the eels’ diet toward this allochthonous resource, which may explain the large contribution of the subsidy for consumers inhabiting large stream channels. Furthermore, diverse earthworm species could drive multiple pulsed subsidies across seasons and provide the predators with a prolonged subsidy, enhancing the long-term contribution of the subsidy to the predators’ diet.
Highlights
Local habitats are linked tightly by reciprocal energy subsidies from contiguous habitats, and across-habitat transfers of both materials and organisms frequently have key effects on local consumers and their communities (Polis et al 1997; Nakano and Murakami 2001)
Pulsed resource subsidies infrequently occur with short duration (Holt 2008; Yang et al 2008), but can temporally increase the ratio of the subsidy resources to the equivalent resources in the recipient habitat, which may explain the effective input of resource subsidies to habitats with low PAR
Despite there being ubiquitous evidence for the positive effects of resource subsidies on consumers in habitats with high PAR (Polis et al 1997), little is known about either how the subsidies contribute to the energy source in recipient habitats with low PAR or how they are supplied to these habitats
Summary
Local habitats are linked tightly by reciprocal energy subsidies from contiguous habitats, and across-habitat transfers of both materials and organisms frequently have key effects on local consumers and their communities (Polis et al 1997; Nakano and Murakami 2001). The effects of subsidies are related to the PAR of habitats, and to the ratio of subsidy resources to equivalent resources in the recipient habitat (Marczak et al.2007). Pulsed resource subsidies infrequently occur with short duration (Holt 2008; Yang et al 2008), but can temporally increase the ratio of the subsidy resources to the equivalent resources in the recipient habitat, which may explain the effective input of resource subsidies to habitats with low PAR. Despite there being ubiquitous evidence for the positive effects of resource subsidies on consumers in habitats with high PAR (Polis et al 1997), little is known about either how the subsidies contribute to the energy source in recipient habitats with low PAR or how they are supplied to these habitats.
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