Competition as a structuring force in leaf miner communities

Abstract

The role of competition in structuring communities of herbivorous insects is still debated. Despite this, few studies have simultaneously investigated the strength of various forms of competition and their effect on community composition. In this study, we examine the extent to which different types of competition will affect the presence and abundance of individual leaf miner species in local communities on oak trees Quercus robur. We first use a laboratory experiment to quantify the strength of intra-and interspecific competition. We then conduct a large-scale field experiment to determine whether competition occurring in one year extends to the next. Finally, we use observational field data to examine the extent to which mechanisms of competition uncovered in the two experiments actually reflect into patterns of cooccurrence in nature. In our experiment, we found direct competition at the leaf-level to be stronger among conspecific than among heterospecific individuals. Indirect competition among conspecifics lowered the survival and weight of larvae of T. ekebladella, both at the branch and the tree-level. In contrast, indirect competition among heterospecifics was only detected in one out of three species pairs examined. In the field experiment, the presence of a given moth species in one year affected the relative abundance of leaf miner species in the next year. Nevertheless, patterns of competition observed in these experiments did not translate into repulsion among free-ranging leaf miners: conspecific larvae of four leafmining species were aggregated on the same trees, shoots and leaves. In contrast, heterospecific larvae were only aggregated at the tree-level. We propose that despite the fact that leaf miners do compete and that such effects extend through time, the incidence and strength of competition is relatively small at realistic densities. Hence, competition will likely be of minor importance in shaping the distribution of leaf miners in a natural setting.

Associational resistance and associational susceptibility: specialist herbivores show contrasting responses to tree stand diversification

“…Previous studies on other lepidopteran species suggest that such selective behavior may enhance the probability for successful development and survival of the offspring (Hern et al 1996;Doak et al 2006;Bonebrake et al 2010). By selecting host trees in the mixed stands, and therefore more isolated hosts compared to the monocultures, the female E. gastralis moth may search for 'competitor-free space', thereby accessing resources for their offspring that are less exploited by other herbivores such as W. inscripta (Root and Kareiva 1984;see also Fisher et al 2000;Tack et al 2009 for intraguild competition for resources).…”

Lethal effects of habitat degradation on fishes through changing competitive advantage

“…Intraspecific competition is often stronger than interspecific competition [40,41]. The present study dealt with a simple system of two recruits on a habitat patch, which is a common situation during the recruitment season [22].…”

The relative importance of host-plant genetic diversity in structuring the associated herbivore community

“…As individual leaf-miner species within the genera Phyllonorycter and Stigmella are morphologically indistinguishable, these two taxa were treated as compound groups (see also Tack et al 2009). A given species of galler (Cynips divisa) was disproportionately abundant in our study area, precluding the separate counting of every individual.…”