Earthworm communities along a forest-coffee agroecosystem gradient: Preliminary evidence supporting the habitat-dependent feeding hypothesis

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Earthworms often constitute an important component of agricultural foodwebs. As such, knowledge of their feeding preferences is relevant to the sustainable management of carbon and nutrient cycling in agroecosystems. We used natural abundances of stable isotopes (δ13C and δ15N) in earthworms and two of their putative food sources - soil and leaf litter - to test hypotheses regarding the feeding plasticity of earthworm communities of secondary forests (FOR) and coffee (Coffea arabica L.) farms with differing management practices (partial shade (SHD) or full sunlight (SUN)) in western-central Puerto Rico. Previous analysis of earthworm abundance indicated that 96 - 100% of the earthworms in these ecosystems were endogeic, suggesting that their diet should consist primarily of soil across ecosystem types (habitat-independent hypothesis). There were clear differences in food sources utilized by earthworm communities among ecosystem types, as indicated by the magnitude of differences in the δ13C and δ15N of earthworms and their putative food sources. These results suggest that, despite being made up almost entirely of endogeic species, there may be considerable dietary plasticity among earthworm communities from different ecosystems (habitat-dependent hypothesis). We found the magnitude of differences in both δ13C and δ15N between earthworms and their putative food sources differed by habitat type, increasing with greater plant diversity (SUN < SHD < FOR), a pattern associated with feeding at higher trophic levels. Our results provide preliminary support for the habitat-dependent hypothesis to explain the feeding behavior of earthworm communities dominated by endogeic species in common tropical ecosystems with differing habitat complexity. © International Society for Tropical Ecology.

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Tropical Ecology





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