Insect density–plant density relationships: a modified view of insect responses to resource concentrations

Andersson, Petter; Löfstedt, Christer; Hambäck, Peter A.

doi:10.1007/s00442-013-2737-1

Cited by 41 publications

(34 citation statements)

References 73 publications

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“…The density responses of insects, however, may be highly variable, depending on how herbivore foraging biology affects migration rates between patches (Bowman et al 2002, Bukovinszky et al 2005, Hamba¨ck and Englund 2005 and how variation in plant traits, such as nutritional quality, interacts with insect movement and reproduction (see, e.g., Bukovinszky et al 2010, Hamba¨ck et al 2012. Ultimately, densities of herbivores on focal plants will depend on whether interactions with plant neighbors translate into frequency-dependent (associational) or density-dependent (concentration or dilution) effects on herbivore movement (Andersson et al 2013). Our results indicate the possible role of associational and dilution effects of AG-BG interactions on insect population densities.…”

Section: Discussionmentioning

confidence: 99%

Disentangling above‐ and belowground neighbor effects on the growth, chemistry, and arthropod community on a focal plant

Kos

Bukovinszky

Mulder

et al. 2015

Ecology

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Neighboring plants can influence arthropods on a focal plant, and this can result in associational resistance or associational susceptibility. These effects can be mediated by above- and belowground interactions between the neighbor and focal plant, but determining the relative contribution of the above- and belowground effects remains an open challenge. We performed a common garden experiment with a design that enabled us to disentangle the above- and belowground effects of five different plant species on the growth and chemistry of the focal plant ragwort (Jacobaea vulgaris), and the arthropod community associated with this plant. Aboveground effects of different neighboring plant species were more important for the growth and quality of J. vulgaris and for the arthropod abundance on this plant than belowground effects of neighbors. This remained true when only indirect neighbor effects (via affecting the biomass or quality of the focal plant) were considered. The aboveground neighbor effects on arthropod abundance on the focal plant were strongly negative. However, the magnitude of the effect depended on the identity of the neighboring species, and herbivore abundance on the focal plant was higher when surrounded by conspecific than when surrounded by heterospecific plants. We also observed interactions between above- and belowground neighbor effects, indicating that these effects may be nonadditive. We conclude that above- and belowground associational effects are not equally strong, and that neighbor effects on plant-arthropod interactions occur predominantly aboveground.

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Section: Discussionmentioning

confidence: 99%

Disentangling above‐ and belowground neighbor effects on the growth, chemistry, and arthropod community on a focal plant

Kos

Bukovinszky

Mulder

et al. 2015

Ecology

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“…First, associational resistance has been proposed to result primarily from a reduced ability of herbivores to locate and reach their host plants among heterospecific neighbors. This may be due to patches with greater plant diversity being less attractive than monospecific patches (i.e., the resource concentration hypothesis, Root, 1973;Andersson, Löfstedt, & Hambäck, 2013) or from heterospecific neighbors reducing the physical (Castagneyrol et al, 2013;Damien et al, 2016;Floater & Zalucki, 2000) or chemical (Jactel, Birgersson, Andersson, & Schlyter, 2011;Zhang & Schlyter, 2004) apparency of host plants. Alternatively, the attractant-decoy hypothesis predicts that herbivores can be diverted from a given plant and aggregate on more apparent, more attractive, or more palatable neighbors (Atsatt & O'Dowd, 1976;Hahn & Orrock, 2016).…”

Section: Introductionmentioning

confidence: 99%

Bottom‐up and top‐down effects of tree species diversity on leaf insect herbivory

Castagneyrol

Bonal

Damien

et al. 2017

Ecology and Evolution

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The diversity of plant neighbors commonly results in direct, bottom‐up effects on herbivore ability to locate their host, and in indirect effects on herbivores involving changes in plant traits and a top‐down control by their enemies. Yet, the relative contribution of bottom‐up and top‐down forces remains poorly understood. We also lack knowledge on the effect of abiotic constraints such as summer drought on the strength and direction of these effects. We measured leaf damage on pedunculate oak (Quercus robur), alone or associated with birch, pine or both in a long‐term tree diversity experiment (ORPHEE), where half of the plots were irrigated while the other half remained without irrigation and received only rainfall. We tested three mechanisms likely to explain the effects of oak neighbors on herbivory: (1) Direct bottom‐up effects of heterospecific neighbors on oak accessibility to herbivores, (2) indirect bottom‐up effects of neighbors on the expression of leaf traits, and (3) top‐down control of herbivores by predators. Insect herbivory increased during the growth season but was independent of neighbor identity and irrigation. Specific leaf area, leaf toughness, and thickness varied with neighbor identity while leaf dry matter content or C:N ratio did not. When summarized in a principal component analysis (PCA), neighbor identity explained 87% of variability in leaf traits. PCA axes partially predicted herbivory. Despite greater rates of attack on dummy caterpillars in irrigated plots, avian predation, and insect herbivory remained unrelated. Our study suggests that neighbor identity can indirectly influence insect herbivory in mixed forests by modifying leaf traits. However, we found only partial evidence for these trait‐mediated effects and suggest that more attention should be paid to some unmeasured plant traits such as secondary metabolites, including volatile organic compounds, to better anticipate the effects of climate change on plant‐insect interactions in the future.

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“…). Consequently, a stronger odour plume due to a higher density (or concentration) of resources will not necessarily result in a higher attraction of consumers (Bossert & Wilson ; Andersson, Löfstedt & Hambäck ; Beyaert & Hilker ) and could explain why many authors have found mixed results concerning the prediction of the resource concentration hypothesis that larger patches will attract more consumers (Root ; Bach ; Kunin ; Sholes ).…”

Section: Discussionmentioning

confidence: 99%

Disentangling associational effects: both resource density and resource frequency affect search behaviour in complex environments

et al. 2016

Self Cite

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Summary1. Neighbouring resources have been found to either decrease or increase the likelihood that a consumer organism attacks a focal resource. These phenomena are referred to as associational resistance (AR) and associational susceptibility (AS), respectively. While associational effects have been observed in various field studies, little is known on how resource heterogeneity can cause associational effects. 2. We used a laboratory approach in which we studied the effects of resource density and frequency in the search behaviour of Drosophila melanogaster as a model organism for olfactoryguided behaviour in insects. We first determined whether D. melanogaster could discriminate between odour sources that differ quantitatively. Secondly, we determined what the effect of resource density and frequency was on the search behaviour of D. melanogaster by combining these resources into various patch arrangements. Finally, we used the outcome of our experiments to disentangle the role of resource density and frequency in associational effects. 3. We found that D. melanogaster has the ability to discriminate between quantitatively different resources, but that the attraction to resource density is constrained by an optimum after which attraction decreases. Furthermore, in heterogeneous environments, flies showed a strong preference towards the more apparent resource, leading to AS for the more apparent resources and AR for the less apparent resource. The strength of this interaction increased with a decreasing frequency of the more apparent resource. 4. These results imply that D. melanogaster mainly selects patches at the level of individual resources. Consequently, when a patch contains qualitatively different resources, the more apparent resource will attract a higher number of flies than the less apparent resource irrespective of the frequency of the apparent resource within the patch. 5. Our study shows that associational effects can be explained by determining the hierarchical level at which a consumer selects its resources. When a consumer selects resources at the individual level rather than at the patch level, our results can be used to explain the population dynamics of host plants and their associated consumers under field conditions.

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Insect density–plant density relationships: a modified view of insect responses to resource concentrations

Cited by 41 publications

References 73 publications

Disentangling above‐ and belowground neighbor effects on the growth, chemistry, and arthropod community on a focal plant

Disentangling above‐ and belowground neighbor effects on the growth, chemistry, and arthropod community on a focal plant

Bottom‐up and top‐down effects of tree species diversity on leaf insect herbivory

Disentangling associational effects: both resource density and resource frequency affect search behaviour in complex environments

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