Effects of native deer on invasive earthworms depend on earthworm functional feeding group and correlate with earthworm body size
Publication date: 1 March 2019
Source: Forest Ecology and Management, Volume 435
Author(s): Colin G. Cope, Jean H. Burns
Above and belowground interactions between animals can influence species abundances, biological invasions, and ecosystem processes. A deeper understanding of above and belowground interactions among animals might benefit from considering functional groups or functional traits, yet most studies have focused on plant functional traits. Here, we consider the possible role of functional group and body size for interactions between invasive earthworms and deer. White-tailed deer are overabundant and are often times considered ecosystem engineers within many forest communities, while invasive earthworms have become an emerging threat to forest communities. We therefore asked a series of questions determine if there were any connections between these two species, with the first being: Do white-tailed deer influence invasive earthworm populations? Because invasive earthworms are divided into different functional groups based on their placement in the soil column and feeding mode, we asked if each of the earthworm functional groups would respond differently to the presence of deer. Finally, we asked if earthworm body size might correlate with the effects of white-tailed deer. We sampled earthworms across 44 paired deer exclosure and control sub-plots across four spatial regions in Ohio, USA. Our analysis controlled for phylogenetic relationships among invasive earthworms, to ensure that confounding effects of evolutionary history did not obscure our ability to detect trait correlations. We found that control sub-plots had more than twice as many endogeic, or soil-dwelling earthworms (e.g. Octolasion tyrtaeum) than paired deer exclosure sub-plots, in the three regions in which they were found. Smaller earthworms were more likely to have higher abundance in the presence of deer, including in phylogenetically corrected tests. If deer overpopulation has a positive effect on some functional groups of invasive earthworms, this suggests that managing deer is important, not only for their aboveground effects on plant communities, but also for their belowground effects on invasive earthworms. More generally, studies of above and belowground interactions might benefit from considering animal functional traits, such as body size, which correlates with functional feeding group.
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