Eric _Moore_MS_BGSU_Metadata_Summer_2016

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Macroinvertebrate detritivores directly and indirectly affect ecosystem processes and nutrient cycling, but the effects of detritivore interactions on ecosystem processes remain poorly understood. Furthermore, mounting evidence emphasizes the importance of understanding the effects and implications of environmental disturbance on interactions between soil organisms, including invasive species and climate change.
In this study, we asked: Is there evidence of competitive or complementary interactions between a native detritivore and two non-native detritivores? Additionally, can detritivore species-specific and interspecific interaction effects on soil ecosystem processes and microbial activity, be moderated by temperature?
To answer these questions, we performed a mesocosm experiment which included three detritivore species, a millipede native to North America (N. americanus) and two introduced earthworm species (L. rubellus and L. terrestris). We fully replicated a Simplex mixture design using these species under two temperature treatments, ambient and warmed 3.3°C.
We expected to observe species-specific and complementary effects of the study organisms due to differences in functional traits. Furthermore, we anticipated that temperature would alter species interactions, and warming would exert a disproportionately greater negative effect on surface dwelling millipedes. Overall, we expected invasive earthworm effects to overwhelm the effects of millipede presence.
An interaction between L. rubellus and N. americanus predicted an increase in litter mass lost and microbial biomass C, indicating a potential complementarity effect. N. americanus reduced both NAG and BG enzyme activity. L. terrestris reduced NAG and BG activity at warmed temperature, but increased activity at ambient temperature. An interaction effect between L. rubellus and L. terrestris also predicted a reduction in NAG activity. Earthworm biomass was significantly reduced over the duration of the experiment regardless of temperature treatment. L. terrestris significantly increased NH4+ leaching, and detritivores did not significantly affect carbon (CO2) efflux.
There was no evidence to indicate that interspecific interactions between these detritivores are moderated by temperature. However, these results indicate that N. americanus may exert some biotic resistance to invasion pressures by L. rubellus and L. terrestris. Future experiments may consider manipulations of food resources, additional trophic levels, and physical soil characteristics to parse out underlying mechanisms.

Publication Date: 
Friday, August 11, 2017
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