Bottom-up Forces Mediate Natural-Enemy Impact in a Phytophagous Insect Community

Denno, Robert F.; Gratton, Claudio; Peterson, M. J.; Langellotto, Gail; Finke, Deborah L.; Huberty, Andrea F.

doi:10.2307/3071956

Cited by 115 publications

(222 citation statements)

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“…Bottom-up cascades are generally less well studied, but are common in terrestrial systems as a structuring force (Hunter and Price 1992;Denno et al 2002). In contrast to 'top-down' cascades, most studies on 'bottom-up' cascades show directional responses that are the same for herbivores and their natural enemies, i.e.…”

Section: Introductionmentioning

confidence: 99%

Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

2008

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Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation Variation in plant quality can transmit up the food chain and may aVect herbivores and their antagonists in the same direction. Fungal endosymbionts of grasses change the resource quality by producing toxins. We used an aphid-parasitoid model system to explore how endophyte eVects cascade up the food chain and inXuence individual parasitoid performance. We show that the presence of an endophyte in the grass Lolium perenne has a much stronger negative impact on the performance of the parasitoid Aphidius ervi than on its aphid host Metopolophium festucae. Although the presence of endophytes did not inXuence the parasitism rate of endophyte-naïve parasitoids or their oVspring's survival to adulthood, most parasitoids developing within aphids from endophyte-infected plants did not reproduce at all. This indicates a delayed but very strong eVect of endophytes on parasitoid performance, which should ultimately aVect plant performance negatively by releasing endophyte-tolerant herbivores from top-down limitations.

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Section: Introductionmentioning

confidence: 99%

Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

2008

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“…Lowercase letters denote significant differences in the leaf morphology main effect tested by the Tukey-Kramer test (adjusted a ¼ 0.05); insets (F, fertilised, NF; not fertilised) indicate the direction of significant F-ratios from GLMs. Community effects of fertilisation and pubescence 435 can cascade up to natural enemies (Forkner & Hunter, 2000;Denno et al, 2002), which may suffer even more pervasive nutrient limitation (Fagan et al, 2002). Invertebrate predators, particularly spiders, may respond also to increased structural heterogeneity created in fertilised plots (Langellotto & Denno, 2004).…”

Section: Community Responses To Fertilisationmentioning

confidence: 99%

“…For example, the response of arthropods to fertilisation may be mediated by plant architecture, and increased resources can alter plant physical structure, habitat complexity, or species composition (Siemann, 1998;Haddad et al, 2000;Orians & Jones, 2001;Denno et al, 2002;Langellotto & Denno, 2004). Changes in abiotic factors, such as shading, may alter host-plant morphology in ways that influence herbivore attack and the success of their enemies (Craig, 1994;Moon et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

The effects of foliar pubescence and nutrient enrichment on arthropod communities ofMetrosideros polymorpha(Myrtaceae)

Gruner

Taylor

Forkner

2005

Ecological Entomology

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Abstract. 1. Nutrient resource availability and host-plant foliar pubescence both influence arthropod food webs, but multifactor studies are needed to understand their interdependence and relative importance. Arthropods were sampled by clipping foliage from Metrosideros polymorpha (Myrtaceae) trees of pubescent, glabrous, and intermediate leaf forms on fertilised and unfertilised plots.2. Fertilisation decreased leaf mass per area (LMA) but did not change the relative mass of pubescence within leaf morphological classes.3. Fertilisation increased densities of individuals in four taxonomic orders, densities of individuals and species of all trophic levels, and the biomass of Collembola and Homoptera. Herbivore relative diversity (Shannon H 0 ) also increased with fertilisation, but detritivore diversity declined due to increasing dominance of Salina celebensis (Schaeffer) (Collembola).4. Detritivore density, driven again by S. celebensis, increased with decreasing leaf pubescence, but Heteroptera and Acari were most abundant on the intermediate pubescence class, and Psocoptera density and biomass increased with increasing pubescence. Trophic-level species density did not change with leaf morphological class, but relative diversity of all arthropods and of detritivores increased with increasing pubescence.5. Both resource availability and leaf pubescence affected Metrosideros arthropod communities. However, the pervasive positive influence of fertilisation did not translate to compositional shifts, and there were no interactions with leaf morphological class. In contrast, the effects of leaf pubescence on arthropod density, biomass, and diversity were more restricted taxonomically, and nonparametric MANOVA and redundancy analyses demonstrated significant differentiation in community composition on the pubescent morphology.

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“…Most studies that have examined fertilization effects on herbivores have found that herbivore densities are elevated in plots with increased plant biomass and nitrogen content (Vince et al 1981, Denno et al 2002, Gratton and Denno 2003, likely because herbivores face a general problem of inadequate nitrogen in their food plants (White 1993). In this study, Orchelimum increased significantly in fertilized plots, corroborating results of an earlier experiment with the same species (Stiling et al 1991), but Paroxya did not increase.…”

Section: Herbivore Density and Food Selectionmentioning

confidence: 99%

Impact of Fertilization on a Salt Marsh Food Web in Georgia

McFarlin

Brewer

Buck

et al. 2008

Estuaries and Coasts: J CERF

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We examined the response of a salt marsh food web to increases in nutrients at 19 coastal sites in Georgia. Fertilization increased the nitrogen content of the two dominant plants, Spartina alterniflora and Juncus roemerianus, indicating that added nutrients were available to and taken up by both species. Fertilization increased Spartina cover, height, and biomass and Juncus height, but led to decreases in Juncus cover and biomass. Fertilization increased abundances of herbivores (grasshoppers) and herbivore damage, but had little effect on decomposers (fungi), and no effect on detritivores (snails). In the laboratory, herbivores and detritivores did not show a feeding preference for fertilized versus control plants of either species, nor did detritivores grow more rapidly on fertilized versus control plants, suggesting that changes in herbivore abundance in the field were driven more by plant size or appearance than by plant nutritional quality.Community patterns in control plots varied predictably among sites (i.e., 17 of 20 regression models examining variation in biological variables across sites were significant), but variation in the effects of fertilization across sites could not be easily predicted (i.e., only 6 of 20 models were significant). Natural variation among sites was typically similar or greater than impacts of fertilization when both were assessed using the coefficient of variation. Overall, these results suggest that eutrophication of salt marshes is likely to have stronger impacts on plants and herbivores than on decomposers and detritivores, and that impacts at any particular site might be hard to distinguish from natural variation among sites.

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Bottom-up Forces Mediate Natural-Enemy Impact in a Phytophagous Insect Community

Cited by 115 publications

References 0 publications

Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

The effects of foliar pubescence and nutrient enrichment on arthropod communities ofMetrosideros polymorpha(Myrtaceae)

Impact of Fertilization on a Salt Marsh Food Web in Georgia

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