Abstract
BackgroundOne major challenge in understanding how biodiversity is organized is finding out whether communities of competing species are shaped exclusively by species-level differences in ecological traits (niche theory), exclusively by random processes (neutral theory of biodiversity), or by both processes simultaneously. Communities of species competing for a pulsed resource are a suitable system for testing these theories: due to marked fluctuations in resource availability, the theories yield very different predictions about the timing of resource use and the synchronization of the population dynamics between the competing species. Accordingly, we explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource.Methodology/Principal FindingsWe analyzed the time partitioning of the exploitation of oak acorns by the four weevil species in two independent communities, and we assessed the level of synchronization in their population dynamics. In accordance with the niche theory, overall these species exhibited marked time partitioning of resource use, both within a given year and between different years owing to different dormancy strategies between species, as well as distinct demographic patterns. Two of the four weevil species, however, consistently exploited the resource during the same period of the year, exhibited a similar dormancy pattern, and did not show any significant difference in their population dynamics.Conclusions/SignificanceThe marked time partitioning of the resource use appears as a keystone of the coexistence of these competing insect species, except for two of them which are demographically nearly equivalent. Communities of consumers of pulsed resources thus seem to offer a promising avenue for developing a unifying theory of biodiversity in fluctuating environments which might predict the co-occurrence, within the same community, of species that are ecologically either very similar, or very different.
Highlights
Ecologists have been intrigued for decades by how competing species coexist in ecological communities [1,2,3,4], and they have proposed two radically opposed theories to explain species diversity
We studied insect communities composed of four weevil sister species of the genus Curculio (C. glandium, C. elephas, C. pellitus, C. venosus) that infest acorns on the same individual oak trees
Oak acorns as a limiting resource To find out whether the availability of oak acorns can be limiting some years for the weevil species, and whether this might impede their population dynamics, we investigated the relationship between the annual acorn crop of each tree during five consecutive years (2004–2008) and 1) the number of mature larvae emerging from these oak acorns or 2) the competition strength between weevils for this resource
Summary
Ecologists have been intrigued for decades by how competing species coexist in ecological communities [1,2,3,4], and they have proposed two radically opposed theories to explain species diversity. The niche theory suggests that the dynamics and structure of ecological communities are mainly attributable to differences in ecological traits between species (niche partitioning). These differences, which have the effect of lowering interspecific relative to intraspecific competition, may favor the coexistence of several species by giving any one of them a greater propensity to increase when it is rare than when it is common [2,5,6]. We explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource
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