Abstract
The world is astoundingly variable, and individuals to whole communities must respond to variability to survive. One example of nature’s variability is the massive fluctuations in spruce budworm (Choristoneura fumiferana Clemens, Lepidoptera: Tortricidae) populations that occur over 35 years. We examined how the parasitoid community altered its parasitism of budworm and other caterpillar species in response to these fluctuations. Budworm and other caterpillar species were sampled from balsam fir in three plots for 14 years in Atlantic Canada, and then reared to identify any emerging parasitoids. We found that the parasitoid community showed a simple linear, indiscriminate response (i.e., no preference, where densities purely dictated parasitism rates) to changes in budworm densities relative to other caterpillar species on balsam fir. We also observed strong changes in topology and distributions of interaction strengths between the parasitoids, budworm and other caterpillar species as budworm densities fluctuated. Our study contributes to the suggestion that hardwood trees are a critical part of the budworm-parasitoid food web, where parasitoids attack other caterpillar species on hardwood trees when budworm populations are low. Taken together, our study shows that a parasitoid community collectively alters species interactions in response to variable budworm densities, fundamentally shifting food web pathways.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Note: This version is a preprint and has not been accepted by a peer review process.
Simplified narrative by removing idea of coherent because idea of coherent was confusing to readers. Simplified to concentrate on mainly the linear response of the parasitoid community to budworm/other caterpillar species densities. Also concentrating on aggregate response and the topology and interaction strength distributions. Mentions of hardwood resource compartment restricted to one paragraph at the end of the discussion because speculation. Removed parasitoid diversity figure. Included all parasitoid taxa that attacked budworm (in this dataset) instead of previous version which used just parasitoid taxa that attacked both budworm and other caterpillar species.
https://github.com/cgreysongaito/SpruceBudworm_Parasitoid_BalsamFir