Abstract
AbstractDistorted plant diversity patterns due to ungulate herbivory could be explained by changes in community assembly processes, but the effects of ungulate herbivory on plant community assembly remain unclear. Here, we examined the role of deer herbivory in the regulation of the assembly processes of a forest floor plant community by assessing species and functional diversity in over‐ and no‐grazing plots (control and exclosure plots, respectively) in Shiretoko National Park in Japan. Compared with the exclosure plot, vegetation coverage was considerably lower, and species richness and diversity were higher in the control plot. Functional traits associated with competitive ability (leaf area and chlorophyll content) were significantly higher in the exclosure plot. The pattern of functional diversity changed from overdispersion to clustering with an increase in local crowdedness. This trait clustering indicates that the local communities that were free from ungulate disturbance gradually became dominated by some competitively superior plant species, which led to low species diversity and biotic homogenization. In contrast, the reduction in vegetation due to overgrazing by deer resulted in an increase in the relative importance of stochastic assembly processes, which enabled the coexistence of various species, including less competitive ones. Our results emphasize that although deer overabundance is of concern, their complete exclusion has a negative consequence from an ecological perspective. Because deer herbivory is an inherent process that affects the biodiversity of plants on the forest floor, the establishment of fences requires careful consideration to ensure the conservation of ecological processes and their associated biodiversity.
Highlights
In terrestrial ecosystems worldwide, overgrazing by large ungulates has created major problems that have impacted the biodiversity, as well as other properties, of the ecosystems that these animals inhabit (Rooney 2001; Coteet al. 2004; Mori et al 2015)
This trait clustering indicates that the local communities that were free from ungulate disturbance gradually became dominated by some competitively superior plant species, which led to low species diversity and biotic homogenization
Deer have direct and indirect impacts on the biotic interactions among coexisting plant species (Rooney and Waller 2003). The former includes selective herbivory that is associated with the palatability of plants (Augustine and McNaughton 1998), while the latter is exemplified by changes in habitat conditions due to browsing that can result in gap formation and altered nutrient cycling (Wardle et al 2002; Bardgett and Wardle 2003)
Summary
In terrestrial ecosystems worldwide, overgrazing by large ungulates (e.g., deer) has created major problems that have impacted the biodiversity, as well as other properties, of the ecosystems that these animals inhabit (Rooney 2001; Coteet al. 2004; Mori et al 2015). Deer have direct and indirect impacts on the biotic interactions among coexisting plant species (Rooney and Waller 2003). The former includes selective herbivory that is associated with the palatability of plants (Augustine and McNaughton 1998), while the latter is exemplified by changes in habitat conditions due to browsing that can result in gap formation and altered nutrient cycling (Wardle et al 2002; Bardgett and Wardle 2003). 2004; Inatomi et al 2012) To understand these contradictory results, a rigorous assessment of how intense herbivory alters the structure of biodiversity is necessary, and in doing so, it is worth focusing on the theory of community assembly. To better guide conservation and management activities in the face of ungulate overabundance, this gap in our knowledge must be urgently addressed
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