Community structure in ichneumonid parasitoids at different spatial scales

Abstract

The processes underlying parasitoid community structure are little known. Stochastic niche-apportionment models provide one route to underlying assemblage rules in this and other groups. Previous work has applied this approach to parasitoids found on single host species in single populations. However, parasitoid communities are known to extend across multiple hosts and scales. The patterns of relative abundances generated by five niche-apportionment models were compared to those observed in assemblages of two sub-families of the Ichneumonidae, the Diplazontinae and Pimplinae, at landscape and patch scales, Yorkshire, UK. Three of the five models produced patterns that were significantly different to the observed pattern for all taxonomic levels at both spatial scales. The Diplazontinae fit the random fraction (RF) model at the landscape scale in broadleaved woods. This suggests that hierarchical structuring and biotic interactions may play a role in the structuring of Diplazontinae assemblages at this scale. In contrast the Pimplinae fit the RF model only at the patch scale and only at one site. However, the Pimplini tribe (all chiefly parasitoids of Lepidoptera) fit the random assortment (RA) model at both the landscape and the patch scales, whilst the Ephialtini tribe (wide range of hosts) fit no model at either scale. The ecological interpretation of the RA model suggests that the Pimplini tribe is an unsaturated assemblage, where some of the total available resources are unused. Our results show, through the fit of mechanistic niche-apportionment models, that the processes that may structure ichneumonid parasitoid assemblages are not consistent across taxa and spatial scales.

Idiosyncrasy and overdominance in the structure of natural communities of arbuscular mycorrhizal fungi: is there a role for stochastic processes?

“…This pattern of locally abundant taxa but with widespread species present in a sample is likely to generate a classic log‐normal distribution at the landscape scale, due to the multiplicative effects of independent data sets and the consequences of the central‐limit theorem (May 1975), but without the overdominance observed from small‐scale samples of AM fungal communities. Indeed, subtle changes in the exact form of SADs when analysed at different spatial scales have been observed in both plant and animal taxa (Anderson & Mouillot 2007; Fraser et al. 2008).…”

“…This pattern of locally abundant taxa but with widespread species present in a sample is likely to generate a classic log-normal distribution at the landscape scale, due to the multiplicative effects of independent data sets and the consequences of the central-limit theorem (May 1975), but without the overdominance observed from small-scale samples of AM fungal communities. Indeed, subtle changes in the exact form of SADs when analysed at different spatial scales have been observed in both plant and animal taxa (Anderson & Mouillot 2007;Fraser et al 2008). Thus, in order to understand fully the processes regulating the structure and diversity of microbial communities, further theory specific to microbial taxa is required (Prosser et al 2007) and explicit examinations of large-scale biogeographical patterns and local-scale community and population dynamics are needed.…”

Comparative life‐history traits in a fig wasp community: implications for community structure

“…West et al, 1996;Kerdelhué et al, 2000;Elias et al, 2008), is indicative of a common structure across fig wasp communities. However, since all wasp species in this study did not occur in all syconia, some species were rare, and several species varied locally and seasonally in their presence at a population level (M. Ghara, unpublished), it is possible that the coexistence of seven members of this fig wasp community is only possible under conditions of such variability Morris et al, 2003;Fraser et al, 2008). Under such conditions, the life-history traits of community members will critically depend on and be driven by the spatio-temporal variation of host patches (Ellers et al, 2000), as our results suggest.…”