Bottom‐up effect of host protective symbionts on parasitoid diversity: Limited evidence from two field experiments

Long-term resource addition to a detrital food web yields a pattern of responses more complex than pervasive bottom-up control

10.7287/peerj.preprints.2722 ◽

2017 ◽

Author(s):

Kendra L. Lawrence ◽

David H Wise

Keyword(s):

Field Experiments ◽

Abiotic Factors ◽

Short Term ◽

Bottom Up ◽

Term Experiment ◽

Two Factors ◽

Long Term Experiment ◽

Short Term Experiment ◽

Univariate Analyses

Background. Theory predicts strong bottom-up control in detritus-based food webs, yet field experiments with detritus-based terrestrial systems have uncovered contradictory evidence regarding the strength and pervasiveness of bottom-up control processes. Two factors likely leading to contradictory results are experiment duration, which influences exposure to temporal variation in abiotic factors such as rainfall and affects the likelihood of detecting approach to a new equilibrium; and openness of the experimental units to immigration and migration. To investigate the contribution of these two factors, we conducted a long-term experiment with open and fenced plots in the forest that was the site of an earlier, short-term experiment (3.5 months) with open plots (Chen & Wise 1999) that produced evidence of strong bottom-up control for 14 taxonomic groupings of primary consumers of litter and fungi (microbi-detritivores) and their predators. Methods. We added artificial high-quality detritus to ten 2 x 2-m forest-floor plots at bi-weekly intervals from April through September in three consecutive years (Supplemented treatment). Ten comparable Ambient plots were controls. Half of the Supplemented and Ambient plots were enclosed by metal fencing. Results. Arthropod community structure (based upon 18 response variables) diverged over time between Supplemented and Ambient treatments, with no effect of Fencing on the multivariate response pattern. Fencing possibly influenced only ca. 20% of the subsequent univariate analyses. Multi- and univariate analyses revealed bottom-up control by fall of Year 1 of some, but not all, microbi-detritivores and predators. During the following two years the pattern of responses became more complex than that observed by Chen & Wise (1999). Some taxa showed consistent bottom-up control whereas many did not. Variation across years could not be explained completely by differences in rainfall because some taxa exhibited negative, not positive, responses to detrital supplementation. Discussion. Our 3-yr experiment did not confirm the conclusion of strong, pervasive bottom-up control of microbi-detritivores and predators reported by Chen and Wise (1999). Our longer-term experiment revealed a more complex pattern of responses, a pattern much closer to the range of outcomes reported in the literature for many short-term experiments. Much of the variation in responses across studies likely reflects variation in factors such as rainfall and the quality of added detritus. Nevertheless, it is also possible that long-term resource enhancement can drive a community towards a new equilibrium state that differs from what would have been predicted from the initial short-term responses exhibited by primary and secondary consumers.

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Experimental Public Choice

The Oxford Handbook of Public Choice, Volume 2 ◽

10.1093/oxfordhb/9780190469771.013.46 ◽

2019 ◽

pp. 895-927 ◽

Cited By ~ 1

Author(s):

Aaron Kamm ◽

Arthur Schram

Keyword(s):

Public Choice ◽

Rational Choice ◽

Field Experiments ◽

Potential Interaction ◽

Comparative Statics ◽

Limited Evidence ◽

The Third ◽

Party Choice ◽

Mixed Support ◽

Choice Approach

This chapter contrasts rational-choice predictions of voter behavior with observations from laboratory and field experiments. Specifically, the authors discuss voters’ party choice and turnout decisions, both for elections under proportional representation and with plurality rule. The first part of the chapter studies turnout and finds mixed support for the comparative statics predicted by the rational-choice framework. In the second part, voters’ party choices are analyzed and it is shown that if we allow for non-selfish preferences, observed behavior is overall in line with the rational-choice approach. The third, and final, part of the chapter analyzes turnout behavior and party choice simultaneously so as to highlight the potential interaction effects between the two. While this question has not received much attention in the literature, the limited evidence currently available is broadly in line with rational-choice predictions.

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Ecosystem engineering strengthens bottom-up and weakens top-down effects via trait-mediated indirect interactions

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2017.0894 ◽

2017 ◽

Vol 284 (1863) ◽

pp. 20170894 ◽

Cited By ~ 13

Author(s):

Zhiwei Zhong ◽

Xiaofei Li ◽

Dean Pearson ◽

Deli Wang ◽

Dirk Sanders ◽

...

Keyword(s):

Trophic Interactions ◽

Large Scale ◽

Field Experiments ◽

Ecosystem Engineering ◽

Relative Importance ◽

Top Down ◽

Bottom Up ◽

Spatial And Temporal Scales ◽

Natural Systems ◽

Ecological Scale

Trophic interactions and ecosystem engineering are ubiquitous and powerful forces structuring ecosystems, yet how these processes interact to shape natural systems is poorly understood. Moreover, trophic effects can be driven by both density- and trait-mediated interactions. Microcosm studies demonstrate that trait-mediated interactions may be as strong as density-mediated interactions, but the relative importance of these pathways at natural spatial and temporal scales is underexplored. Here, we integrate large-scale field experiments and microcosms to examine the effects of ecosystem engineering on trophic interactions while also exploring how ecological scale influences density- and trait-mediated interaction pathways. We demonstrate that (i) ecosystem engineering can shift the balance between top-down and bottom-up interactions, (ii) such effects can be driven by cryptic trait-mediated interactions, and (iii) the relative importance of density- versus trait-mediated interaction pathways can be scale dependent. Our findings reveal the complex interplay between ecosystem engineering, trophic interactions, and ecological scale in structuring natural systems.

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Top-down and bottom-up forces in mammalian herbivore – vegetation systems: an essay review

Botany ◽

10.1139/b09-035 ◽

2009 ◽

Vol 87 (8) ◽

pp. 723-739 ◽

Cited By ~ 25

Author(s):

Roy Turkington

Keyword(s):

Field Experiments ◽

Individual Species ◽

Top Down ◽

Field Methods ◽

Bottom Up ◽

Vegetation Removal ◽

Mammalian Herbivore ◽

Resource Levels

For almost 50 years ecologists have debated why herbivores generally don’t increase in numbers to such levels as to deplete or devastate vegetation. One hypothesis is that herbivore populations are regulated at low densities by predators, and a second hypotheses is that plants are fundamentally poor food for herbivores. This has lead to two main hypotheses about the role of herbivores in structuring vegetation: the “bottom-up” and “top-down” hypotheses. Here I survey the literature, with a focus on field experiments designed to investigate the soil resource – vegetation – mammalian herbivore system, specifically asking five questions about how each trophic level responds to (i) resource addition, (ii) vegetation removal, (iii) herbivore removal or reduction, (iv) herbivore addition, and (v) the interaction of resource levels and herbivory? I use these to develop 12 testable predictions. I document the major areas of research as they relate to these 12 predictions, and use these to evaluate weaknesses and limitations in field methods. There are surprisingly few terrestrial studies that conduct factorial manipulations of multiple nutrients or herbivores, even though it is clear that these are essential. Specifically, I argue that a manipulative experimental approach is the most valuable way to advance our theory and understanding, and I advocate the continued use of long-term factorial field experiments that simultaneously manipulate soil resources levels and herbivory (preferably at multiple levels), repeated in a range of environments in which individual species or functional groups are monitored.

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Long-term resource addition to a detrital food web yields a pattern of responses more complex than pervasive bottom-up control

PeerJ ◽

10.7717/peerj.3572 ◽

2017 ◽

Vol 5 ◽

pp. e3572 ◽

Cited By ~ 3

Author(s):

Kendra L. Lawrence ◽

David H. Wise

Keyword(s):

Field Experiments ◽

Abiotic Factors ◽

Short Term ◽

Bottom Up ◽

Term Experiment ◽

Two Factors ◽

Long Term Experiment ◽

Short Term Experiment ◽

Univariate Analyses

Background Theory predicts strong bottom-up control in detritus-based food webs, yet field experiments with detritus-based terrestrial systems have uncovered contradictory evidence regarding the strength and pervasiveness of bottom-up control processes. Two factors likely leading to contradictory results are experiment duration, which influences exposure to temporal variation in abiotic factors such as rainfall and affects the likelihood of detecting approach to a new equilibrium; and openness of the experimental units to immigration and emigration. To investigate the contribution of these two factors, we conducted a long-term experiment with open and fenced plots in the forest that was the site of an earlier, short-term experiment (3.5 months) with open plots (Chen & Wise, 1999) that produced evidence of strong bottom-up control for 14 taxonomic groupings of primary consumers of fungi and detritus (microbi-detritivores) and their predators. Methods We added artificial high-quality detritus to ten 2 × 2-m forest-floor plots at bi-weekly intervals from April through September in three consecutive years (Supplemented treatment). Ten comparable Ambient plots were controls. Half of the Supplemented and Ambient plots were enclosed by metal fencing. Results Arthropod community structure (based upon 18 response variables) diverged over time between Supplemented and Ambient treatments, with no effect of Fencing on the multivariate response pattern. Fencing possibly influenced only ca. 30% of the subsequent univariate analyses. Multi- and univariate analyses revealed bottom-up control during Year 1 of some, but not all, microbi-detritivores and predators. During the following two years the pattern of responses became more complex than that observed by Chen & Wise (1999). Some taxa showed consistent bottom-up control whereas others did not. Variation across years could not be explained completely by differences in rainfall because some taxa exhibited negative, not positive, responses to detrital supplementation. Discussion Our 3-year experiment did not confirm the conclusion of strong, pervasive bottom-up control of both microbi-detritivores and predators reported by Chen & Wise (1999). Our longer-term experiment revealed a more complex pattern of responses, a pattern much closer to the range of outcomes reported in the literature for many short-term experiments. Much of the variation in responses across studies likely reflects variation in abiotic and biotic factors and the quality of added detritus. Nevertheless, it is also possible that long-term resource enhancement can drive a community towards a new equilibrium state that differs from what would have been predicted from the initial short-term responses exhibited by primary and secondary consumers.

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Long-term resource addition to a detrital food web yields a pattern of responses more complex than pervasive bottom-up control

10.7287/peerj.preprints.2722v1 ◽

2017 ◽

Author(s):

Kendra L. Lawrence ◽

David H Wise

Keyword(s):

Field Experiments ◽

Abiotic Factors ◽

Short Term ◽

Bottom Up ◽

Term Experiment ◽

Two Factors ◽

Long Term Experiment ◽

Short Term Experiment ◽

Univariate Analyses

Background. Theory predicts strong bottom-up control in detritus-based food webs, yet field experiments with detritus-based terrestrial systems have uncovered contradictory evidence regarding the strength and pervasiveness of bottom-up control processes. Two factors likely leading to contradictory results are experiment duration, which influences exposure to temporal variation in abiotic factors such as rainfall and affects the likelihood of detecting approach to a new equilibrium; and openness of the experimental units to immigration and migration. To investigate the contribution of these two factors, we conducted a long-term experiment with open and fenced plots in the forest that was the site of an earlier, short-term experiment (3.5 months) with open plots (Chen & Wise 1999) that produced evidence of strong bottom-up control for 14 taxonomic groupings of primary consumers of litter and fungi (microbi-detritivores) and their predators. Methods. We added artificial high-quality detritus to ten 2 x 2-m forest-floor plots at bi-weekly intervals from April through September in three consecutive years (Supplemented treatment). Ten comparable Ambient plots were controls. Half of the Supplemented and Ambient plots were enclosed by metal fencing. Results. Arthropod community structure (based upon 18 response variables) diverged over time between Supplemented and Ambient treatments, with no effect of Fencing on the multivariate response pattern. Fencing possibly influenced only ca. 20% of the subsequent univariate analyses. Multi- and univariate analyses revealed bottom-up control by fall of Year 1 of some, but not all, microbi-detritivores and predators. During the following two years the pattern of responses became more complex than that observed by Chen & Wise (1999). Some taxa showed consistent bottom-up control whereas many did not. Variation across years could not be explained completely by differences in rainfall because some taxa exhibited negative, not positive, responses to detrital supplementation. Discussion. Our 3-yr experiment did not confirm the conclusion of strong, pervasive bottom-up control of microbi-detritivores and predators reported by Chen and Wise (1999). Our longer-term experiment revealed a more complex pattern of responses, a pattern much closer to the range of outcomes reported in the literature for many short-term experiments. Much of the variation in responses across studies likely reflects variation in factors such as rainfall and the quality of added detritus. Nevertheless, it is also possible that long-term resource enhancement can drive a community towards a new equilibrium state that differs from what would have been predicted from the initial short-term responses exhibited by primary and secondary consumers.

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Electron Microscopy of the Shape of Small Metal Particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079024 ◽

1977 ◽

Vol 35 ◽

pp. 300-301

Author(s):

M. Jose Yacaman

Keyword(s):

Electron Microscopy ◽

Metal Particle ◽

Field Experiments ◽

Size Range ◽

Dark Field ◽

Metal Particles ◽

Bragg Condition ◽

Crystal Particle ◽

Small Metal Particle ◽

Small Metal Particles

In the Study of small metal particles the shape is a very Important parameter. Using electron microscopy Ino and Owaga(l) have studied the shape of twinned particles of gold. In that work electron diffraction and contrast (dark field) experiments were used to produce models of a crystal particle. In this work we report a method which can give direct information about the shape of an small metal particle in the amstrong- size range with high resolution. The diffraction pattern of a sample containing small metal particles contains in general several systematic and non- systematic reflections and a two-beam condition can not be used in practice. However a N-beam condition produces a reduced extinction distance. On the other hand if a beam is out of the bragg condition the effective extinction distance is even more reduced.

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