Biomedical subjects

Jay A Rosenheim

Publications and source records attributed to Jay A Rosenheim.

7 recordsLinked to original sources

PubMed2006

Assessing trophic interactions in a guild of primary parasitoids and facultative hyperparasitoids: stable isotope analysis.

Facultative hyperparasitism is likely to be the most common form of intraguild predation among parasitoids. However, difficulties associated with studying facultative hyperparasitoids in the field have hampered a thorough understanding of their trophic ecology. In this study, we used a combination of stable isotope analysis and published natural history information to infer trophic interactions in a guild of field-collected primary parasitoids and facultative hyperparasitoids that attack a gall-making midge on Baccharis pilularis. Our three a priori hypotheses were: (1) stable isotope values should increase incrementally from the host plant to higher trophic levels; (2) the two species of ectoparasitoids should exhibit higher stable isotope signatures than the two endoparasitoids, and; (3) the two facultative hyperparasitoids should exhibit stable isotope signatures that fall between zero and one trophic level steps above that observed for the primary parasitoids. Food webs inferred from stable isotope data generally agreed with previously published accounts of community structure. As expected, both delta(13)C and delta(15)N were progressively enriched in the heavy isotope from the host plant to the herbivorous midge to the parasitic wasps. Multivariate analysis of stable isotope data revealed that the two primary ectoparasitoids occupied a similar trophic niche, but were significantly different from the primary endoparasitoids. We attribute this result to "coincidental intraguild predation" by ectoparasitoids that develop on already-parasitized midge larvae. One of the facultative hyperparasitoids, Zatropis capitis, exhibited a stable isotope signature approximately one trophic step above the primary parasitoids. Unexpectedly, the second facultative hyperparasitoid, Mesopolobus sp., appeared to be developing as a primary parasitoid at all sites. Coupled with independent assessments of community structure, stable isotope analysis validated trophic links constructed by previous researchers and identified potential taxon-specific differences in trophic interactions for two facultative hyperparasitoids in the B. pilularis gall community.

Animals↗

PubMed2006

Multiple plant exploiters on a shared host: testing for nonadditive effects on plant performance.

The combined impact of multiple plant parasites on plant performance can either be additive (the total damage equals the sum of the individual effects) or nonadditive (synergistic or antagonistic damage). Two statistical models are available for testing the independent (=additive) effects of two factors. Here we suggest that the natural history of the plant-parasite system should motivate the choice of a statistical model to test for additivity. Using in-field, manipulative experiments, we examined the interactions between the herbivorous mite Calacarus flagelliseta Fletchmann, De Moraes and Barbosa (Acari: Eriophyidae), the fungal pathogen Oidium caricae F. Noack (a powdery mildew), and their host plant Carica papaya L. in Hawaii. First, we found that herbivorous mites had a moderate negative effect on powdery mildew: when mites were absent, powdery mildew colonies were larger and more numerous. Second, we showed that each plant parasite, when evaluated alone, significantly reduced several measures of plant performance. Third, we found that the combined impact of mites and mildew on plant performance is mostly additive and, for a few variables, less than additive. Finally, we explored compensatory responses and found no evidence for nonlinearities in the relationship between plant performance and cumulative parasite impact. Plants are almost universally subject to attack by multiple herbivores and pathogens; thus a deeper understanding of how multiple plant parasites shape each other's population dynamics and plant performance is essential to understanding plant-parasite interactions.

Animals↗

PubMed2005

Isotopic enrichment in herbivorous insects: a comparative field-based study of variation.

Researchers will be able to use stable isotope analysis to study community structure in an efficient way, without a need for extensive calibrations, if isotopic enrichment values are consistent, or if variation in enrichment values can be predicted. In this study, we generated an experimental data set of delta15N and delta13C enrichment means for 22 terrestrial herbivorous arthropods feeding on 18 different host plants. Mean enrichments observed across a single trophic transfer (plants to herbivores) were -0.53+/-0.26 per thousand for delta13C (range: -3.47 per thousand to 1.89 per thousand) and 1.88+/-0.37 per thousand for delta15N (range: -0.20 per thousand to 6.59 per thousand). The mean delta13C enrichment was significantly lower than that reported in recent literature surveys, whereas the mean delta15N enrichment was not significantly different. The experimental data set provided no support for recent hypotheses advanced to explain variation in enrichment values, including the proposed roles for consumer feeding mode, development type, and diet C:N ratio. A larger data set, formed by combining our experimental data with data from the literature, did suggest possible roles for feeding mode, nitrogen recycling, herbivore life stage, and host plant type. Our results indicate that species enrichment values are variable even in this relatively narrow defined group of organisms and that our ability to predict enrichment values of terrestrial herbivorous arthropods based on physiological, ecological, or taxonomic traits is low. The primary implications are that (1) mean enrichment may have to be measured empirically for each trophic link of interest, rather than relying on estimates from a broad survey of animal taxa and (2) the advantage of using stable isotope analysis to probe animal communities that are recalcitrant to other modes of study will be somewhat diminished as a consequence.

Animals↗

PubMed2004

Predator-induced transgenerational phenotypic plasticity in the cotton aphid.

Transgenerational phenotypic changes, whereby offspring have an altered trait or a distinct alternate phenotype, frequently occur in response to increased maternal predation risk. The cotton aphid, Aphis gossypii (Glover), is unique, however, as offspring consist of four distinct phenotypes ("normal" light green apterae, "normal" dark green apterae, "dwarf" yellow apterae, and alatae), all with divergent life history patterns and resulting population dynamics. Here, we show that increased predation risk induces transgenerational phenotypic changes in cotton aphids. When exposed to search tracks from larval or adult convergent ladybird beetles, Hippodamia convergens Guerin-Meneville, cotton aphids produced greater numbers of winged offspring. In a subsequent experiment, apterous and alate individuals on clean plants were found to have primarily normal and dwarf offspring, respectively. We suggest that elevated predation risk may cause phenotypic changes in aphids over multiple generations, resulting in a more precipitous decline in herbivore populations than could be explained solely by increased predation rates.

Analysis of Variance↗

PubMed2004

Herbivore population suppression by an intermediate predator, Phytoseiulus macropilis, is insensitive to the presence of an intraguild predator: an advantage of small body size?

Recent work in terrestrial communities has highlighted a new question: what makes a predator act as a consumer of herbivores versus acting as a consumer of other predators? Here we test three predictions from a model (Rosenheim and Corbett in Ecology 84:2538-2548) that links predator foraging behavior with predator ecology: (1) widely foraging predators have the potential to suppress populations of sedentary herbivores; (2) sit and wait predators are unlikely to suppress populations of sedentary herbivores; and (3) sit and wait predators may act as top predators, suppressing populations of widely foraging intermediate predators and thereby releasing sedentary herbivore populations from control. Manipulative field experiments conducted with the arthropod community found on papaya, Carica papaya, provided support for the first two predictions: (1) the widely foraging predatory mite Phytoseiulus macropilis strongly suppressed populations of a sedentary herbivore, the spider mite Tetranychus cinnabarinus, whereas (2) the tangle-web spider Nesticodes rufipes, a classic sit and wait predator, failed to suppress Tetranychus population growth rates. However, our experiments provided no support for the third hypothesis; the sit and wait predator Nesticodes did not disrupt the suppression of Tetranychus populations by Phytoseiulus. This contrasts with an earlier study that demonstrated that Nesticodes can disrupt control of Tetranychus generated by another widely foraging predator, Stethorus siphonulus. Behavioral observations suggested a simple explanation for the differing sensitivity of Phytoseiulus and Stethorus to Nesticodes predation. Phytoseiulus is a much smaller predator than Stethorus, has a lower rate of prey consumption, and thus has a much smaller requirement to forage across the leaf surface for prey, thereby reducing its probability of encountering Nesticodes webs. Small body size may be a general means by which widely foraging intermediate predators can ameliorate their risk of predation by sit and wait top predators. This effect may partially or fully offset the general expectation from size-structured trophic interactions that smaller predators are subject to more intense intraguild predation.

Analysis of Variance↗

PubMed2004

Population dynamics and within-plant distribution of the mite Calacarus flagelliseta (Acari: Eriophyidae) on papaya in Hawaii.

An important element in developing a management strategy for a new pest is the study of its seasonal dynamics and within-plant distribution. Here, we studied the mite Calacarus flagelliseta Fletchmann, De Moraes & Barbosa on papaya, Papaya carica L. (Caricaceae), in Hawaii to quantify 1) patterns of seasonal abundance, 2) its distribution across different vertical strata of the papaya canopy, and 3) shifts in its use of the upper versus the lower surfaces of papaya leaves. Nondestructive sampling conducted in two papaya plantings revealed that 1) populations of C. flagelliseta peak during the summer; 2) mites are most abundant in the middle and lower strata of the plant canopy, and least abundant on the youngest leaves found in the upper canopy; and 3) mites are found more predominantly on the upper leaf surfaces when overall population density peaks, suggesting that individuals move from the lower to the upper leaf surfaces when food resources on the lower leaf surface have been exploited by conspecifics. These results have significant implications for the development of sampling plans for C. flagelliseta in papaya.

Animals↗

PubMed2003

Herbivorous mites as ecological engineers: indirect effects on arthropods inhabiting papaya foliage.

We examined the potential of a leaf roller to indirectly influence a community of arthropods. Two mite species are the key herbivores on papaya leaves in Hawaii: a spider mite, Tetranychus cinnabarinus Boisduval, and an eriophyid mite, Calacarus flagelliseta, which induces upward curling of the leaf margin at the end of the summer when populations reach high densities. A survey and three manipulative field experiments demonstrated that (1) leaf rolls induce a consistent shift in the spatial distribution of spider mites and their predators, the coccinellid Stethorus siphonulus Kapur, the predatory mites Phytoseiulus spp., and the tangle-web building spider Nesticodes rufipes Lucas; (2) the overall abundance of spiders increases on leaves with rolls; (3) the specialist predators Stethorus and Phytoseiulus inhabit the rolls in response to their spider mite prey; and (4) the spider inhabits the rolls in response to the architecture of the roll itself. This study shows the importance of indirect effects in structuring a terrestrial community of herbivores.

Animals↗