BIOLOGICAL SCIENCES / ECOLOGY
Relative resource abundance explains butterfly biodiversity in island communities
Naoaki Yamamoto , Jun Yokoyama , and Masakado Kawata*
Department of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Aoba-ku Sendai 980-8578, Japan
Edited by James H. Brown, University of New Mexico, Albuquerque, NM, and approved May 1, 2007 (received for review February 20, 2007)
Ecologists have long been intrigued by the factors that control the pattern of biodiversity, i.e., the distribution and abundance of species. Previous studies have demonstrated that coexisting species partition their resources and/or that the compositional similarity between communities is determined by environmental factors, lending support to the niche-assembly model. However, no attempt has been made to test whether the relative amount of resources that reflects relative niche space controls relative species abundance in communities. Here, we demonstrate that the relative abundance of butterfly species in island communities is significantly related to the relative biomasses of their host plants but not to the geographic distance between communities. In the studied communities, the biomass of particular host plant species positively affected the abundance of the butterfly species that used them, and consequently, influenced the relative abundance of the butterfly communities. This indicated that the niche space of butterflies (i.e., the amount of resources) strongly influences butterfly biodiversity patterns. We present this field evidence of the niche-apportionment model that propose that the relative amount of niche space explains the pattern of the relative abundance of the species in communities.
neutral theory | niche theory | relative species abundance
PNAS June 19, 2007 vol. 104 no. 25, 10524-10529. OPEN ACCESS ARTICLE.
Biodiversity is often considered to be synonymous with species richness and relative species abundance (1). For more than half a century, ecologists have paid attention to the factors that determine the relative species abundance in ecological communities; i.e., the commonness and rarity of species (2). Host plants and their herbivore communities are good systems for examining how the diversity of herbivores is influenced by their resources; indeed, insect ecologists have focused considerable attention on the question of how host plant communities affect the species richness and composition of insects. Although a recent review (3) pointed out that little progress on this subject has been made since the 1980s, a number of important studies have demonstrated that a large number of plant species is frequently correlated with a large number of insect species (4–6). Experimental studies have also demonstrated a positive relationship between the diversity of plant species and the diversity of consumers (7–9). The abundance of resources also represents an important factor in the structuring of insect communities (10). A number of studies have demonstrated that resource abundance explains the variation in the abundance and species richness of herbivorous insects (11–14). However, these studies on host plant and herbivore communities have treated species richness and species composition as components of the diversity, and no studies have examined the relative abundance patterns of both host plants and herbivores.
On the other hand, recent theoretical arguments have focused on whether the neutral or niche theory better explains the patterns of relative species abundance. The neutral theory (1) of biodiversity based on a dispersal-assembly perspective assumes that the relative abundance of species in communities is determined by random dispersal and stochastic local extinction. Conversely, the niche-assembly view proposes that coexisting species should have different niches so that the abundance and diversity of species is determined by interspecific competition and the diversity of resources. Many studies have demonstrated that coexisting species partition their resources (15–17), which lends support to the niche-assembly model. However, recent studies have shown that the neutral theory can explain the biodiversity of several plant communities (1, 18), although other studies have refuted the theory (17, 1920–21). An appropriate test that differentiates between the niche and neutral models is to assess the different predictions from the competing theories (17, 19). The neutral model predicts that the compositional similarity between communities will decrease as the distance between two points increases (17). In contrast, the niche-apportionment model predicts that the similarity of relative species abundance between communities will increase with an increase in the similarity of relative resource abundance. The relative contribution of distance and resource abundance to the similarity should be evaluated (22).
Previous studies supporting the niche theory have demonstrated that coexisting species partition their resources or that community composition is related to environmental conditions. However, these studies did not evaluate the relative abundance of available resources; consequently, the relationships between niche space and species abundance were not directly tested. Thus, to date, there has been no attempt to test whether the relative abundance of available resources, i.e., available niche space, affects the relative abundance of species. In this study, butterfly communities were examined because both the larval and adult stages of butterflies depend almost entirely on specific plants for their dietary requirements, and information as to which host plant a butterfly uses is generally available. In addition, we could estimate the host plant abundance using a high-resolution aerial photograph and field surveys. Therefore, using the host plant–butterfly system, we were able to directly test the relationship between fundamental niche space and relative species abundance.