Species diversity in a mycophagous insect community: the case of spatial aggregation vs. resource partitioning

1. Previous work has suggested that species diversity in resource-limited i nsect communities on patchy resources is maintained by spatial aggregation, not by resource partitioning. The most comprehensive test of this claim to date was by Shorrocks & Sevenster (1995), but some of their datasets inclu ded only a few resource types, which reduces the likelihood of finding a st rong effect of resource partitioning. Also, methods of analysis have since been refined, e.g. to account for patch size. 2. We collected 733 mushroom samples belonging to 66 taxa in a Dutch woodla nd area. From these mushrooms, 38,891 insects were reared, belonging to 60 taxa of Diptera and Hymenoptera. Drosophilid species and their parasitoids were identified to the species level; other taxa to the family level. We ar gue that the community is resource limited. 3. Generally, the insects have fairly narrow diets, including only a few of the available mushroom species. The degree of niche overlap varies widely in this community. 4. Within single resource types, co-existence can be explained by intra-spe cific aggregation over patches alone, in accordance with previous studies. 5. This conclusion remains unchanged for the mycophagous community as a who le: intra-specific aggregation of competitors is a sufficient and necessary mechanism for co-existence in this diverse community, while resource parti tioning does not contribute detectably to species diversity. This is the fi rst time that this pattern has been demonstrated in a dataset involving suc h a large number of resource types. 6. Our conclusions are strongly supported by data manipulations in which we removed or intensified the effect of resource partitioning and spatial agg regation. 7. We argue that this community may be close to saturation, but we emphasiz e that saturation is a gradual phenomenon in patchy systems. 8. Since differential use of resource types does not reduce competitive int eractions among the insects, it seems unlikely that inter-specific competit ion constitutes the selective pressure favouring specialization.