Deborah E. Goldberg, Tara Rajaniemi, Jessica Gurevitch, and Allan Stewart-Oaten. 1999. Empirical approaches to quantifying interaction intensity: competition and facilitation along productivity gradients. Ecology 80:1118-1131.

Supplements

Supplement 1: Data on interaction intensity among plants for a meta-analyses of patterns in competition intensity along productivity gradients.
Ecological Archives E080-006-S1.

Author
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Reference list meta-analysis
Citations

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Author

Deborah Goldberg
Department of Biology
University of Michigan
Ann Arbor, MI 48109-1048
TEL: 734 764-1490
FAX: 734 647-0884
(degold@umich.edu)

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Viewable Supplement

Data files

metadata.txt is a text file containing these metadata.
varcodes.txt is a text file describing the variables and codes for the data file.
metacomp.csv is the data file (comma-delimited ASCII)
citation.txt is a text file with the full citations that correspond to the reference numbers listed in. metacomp.csv

E080006.zip is a zip file containing all supplemental files.

Description

Abstract: This supplement contains data on interaction intensity extracted from the primary literature for a meta-analyses of patterns in competition intensity along productivity gradients in plants. Goldberg et al. (1999) report on analyses using a subset of these data and of the possible relationships among variables.

Research period and location: This work was conducted as part of the Meta-analysis Working Group (1996-1997, Meta-analysis, interaction strength and effect size: application of biological models to the synthesis of experimental data) supported by the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (DEB-94-21535), the University of California - Santa Barbara, and the State of California.

Explanation of variables and codes in the supplement (download as varcodes.txt)

Note that variable names are written in bold and possible code values the variable may take are written in italics.

General terminology: Targets are the plants whose response to interactions are being measured, neighbors are those plants that are assumed to be affecting the targets and are manipulated.

Criteria for inclusion in the database: The studies were chosen from those cited in four previous reviews of plant competition: Goldberg and Barton (1992), Gurevitch et al. (1992), Goldberg (1996), and Goldberg and Novoplansky (1997) according to the following criteria. All experiments included in the database were conducted in naturally-occurring vegetation in the field and have at least the following two treatments to quantify interaction intensity: a control in which no neighbors were removed and a removal in which roots and/or shoots of all naturally-occurring neighbors within some distance were removed or assumed to be dead. All also have either a direct measure of productivity or at least one environmental measure that should correlate with productivity (standing crop, rainfall, total N in soil). Standing crop measures usually includes both living material and litter; although many papers did not distinguish or specify which was measured. Thus, there may be considerable variation in standing crop which does not reflect productivity.

Methods: Most values in the database were garnered from descriptions in the text of the original source. The quantitative data for productivity and its estimators (Var21-23), for the means and variances in removal and control treatments (Var28-29, 37-39), and for the indices and variances of interaction intensity (Var30-32, 39) were usually copies from tables or scanned from figures (using SigmaScan, Jandel Scientific Software); see specific variable descriptions for further details.

Goldberg et al. 1999 analysis: To recreate their data set, select the following values for these variables:

In addition, because only results at the end of the first growing season were included (when multiple measurements on the same plants were taken),
This should yield 296 cases in 14 studies.

All regressions were performed using RCI or lnRR as the dependent variables and stand.crop as the independent variable, either over all cases with the same response variable (Fig. 1 in Goldberg et al. 1999) or all cases for a given taxon within a study (Fig. 2 in Goldberg et al. 1999)

CITATION

Var1. Ref: reference code (matches with full citation in citation.txt)

REPLICATION

Var2. Replsite: names of distinct sites in which the entire experiment was repeated. This does NOT include
different steps along a productivity gradient—these are considered the same site. If the experiment was only done in a single site, the value is ‘none’.
Var3. Repltime: years in which the entire experiment was repeated. This does NOT include information
on how long an experiment was monitored.
None=experiment initiated only once
yr1=results from the first time an experiment was initiated (if initiated more than once), regardless of how long the experiment was monitored
yr2=results from the second time an experiment was initiated (none were repeated more than two years in a row)

EXPERIMENTAL DESIGN--ENVIRONMENTAL VARIATION

Var4. Gradient: type of productivity gradient within study
Var5. Envt.factor: specific environmental factor varying along natural or
Var6. Amt-added: amount of resource added if an experimental productivity gradient and reported
 
 
EXPERIMENTAL DESIGN—QUANTIFYING INTERACTIONS

Var7. Parts.removed: component of vegetation removed experimentally
Var8. Pulse.press: whether or not the experimental removals were continuous through the experiment
Var9. removal.method: how vegetation components were removed
Var10. Herb.excluded: types of herbivores excluded from the experiment
Var11. Plot.size: area (m2) from which neighbors were removed in removal treatments
 
 
SPECIES DESCRIPTIONS

Var12. Genus of target taxon:
Var13. Species of target taxon
Var14. Neighbor.form: neighbor growth form
Var15. Target.form: target growth form, defined as for neighbor.form
Var16. Neighbor.stage: neighbor life history stage
Var17. Target.stage: target life history stage, defined as for neighbor.stage
Var18. Target.source: whether target individuals were naturally-occuring individuals or transplanted to
the experimental plots
natural=naturally-occurring individuals
transpl=transplanted to experimental plots
Var19. Num.targets: number of target plants per experimental plot (1000 indicates a large and unknown number)
 
ENVIRONMENT

Var20. Comm.type: community type
Var21. Productivity: estimate of productivity (g/m2/yr)
Var22. Stand.crop: standing crop (g/m2, usually at end of season but not always and usually
including both live biomass and litter (not always distinguished in the source)
Var23. TotalN: total nitrogen (mg/kg)
Var24. Rainfall: mean annual rainfall (mm/yr)
 

RESPONSE VARIABLE

Var25. Census.day: days from the beginning of the experiment to the time of measurement of the dependent variable.
This is most often the end of the experiment but some studies have series of repeated measurements which are recorded as separate cases in the database.
Var26. Response.var: variable measured on target plants
Var27. Resp.var.units: units for response variable measurements.
Var28. Mean.ctrl: mean of the response variable in the control treatment (missing if only an interaction
intensity index was reported)
Var29. Mean.rem: mean of the response variable in the removal treatment (missing if only an interaction
intensity index was reported)
 
 
INDICES OF INTERACTION INTENSITY

Three measures of interaction intensity are included in the database:
Where rem and ctrl indicate the mean value of the response variable in removal and control treatment plots, respectively. Where mean treatment values were reported in the original paper, all three indices were calculated from these means. The single exception is in cases of zero or negative growth, where ln(RR) could not be calculated. In many cases, only RCI values were reported rather than mean treatment values; this was especially likely when a continuous gradient of standing crop was used rather than two or three discrete levels with multiple replicates at a level. In this case, lnRR was calculated as lnRR=-ln(1-RCI) and ACI could not be calculated at all. In a few studies, only ACI was reported, in which case neither of the other indices could be calculated.
 
Var30. RCI: reported or calculated value as above
Var31. ACI: reported or calculated value as above
Var32. lnRR: calculated value as above
 

SAMPLE SIZES

Sample sizes are reported for the means of control and treatment treatments and for RCI and ACI if reported in the original paper (no sample sizes are given for lnRR since this index was not reported in any of the original papers). If the interaction intensity indices were calculated by Goldberg et al. (1999) from treatment means reported in the original paper, sample size for the index is reported as missing in the database. For some studies, the values of an interaction intensity index were taken from scatterplots in which each data point represented a single pair of control and removal plots—for these the sample size of the index at each value of standing crop or productivity is reported in the database as 1.
 
Var33. n.ctrl: the number of control treatment plots
Var34. n.rem: the number of removal treatment plots
Var35. n.rci: the number of paired control-removal plots for calculation of RCI
Var36. n.aci: number of paired control-removal plots for calculation of ACI
 

VARIABILITY MEASURES

The values in the datebase are for a variety of measures of variability (identified in Var36), as reported in the original papers. These measures of variability are NOT necessarily the appropriate ones for weighting in meta-analysis; the potential user of these data should see Hedges et al. (1999) and references therein.
 
Var36. Var.meas: the measure of variability reported in the original paper and in var37, var38, var39 in this database
Var37. Var.ctrl: value of the variability measure defined in Var36 for the control treatment, as reported in the
original paper
Var38. Var.rem: value of the variability measure defined in Var36 for the removal treatment, as reported
in the original paper
Var39. Var.RCI: value of the variability measure defined in Var36 for RCI as reported in the original paper
(no variability measures were given for any other interaction intensity indices in the original papers)
 
 
USEFUL VARIABLES FOR TAKING SUBSETS OF THE CASES

If any of the first three of these variables are greater than 1, the study is useful for comparisons of interaction intensity within studies (i.e., over time, among dependent variables, or among taxa) but care must be taken in meta-analyses because the data suffer from varying degrees of nonindependence.
Var40. n.times: the number of times measurements were taken on the same plants in the same expt
Var41. n.depvar: the number of different response variables taken on the same plants
Var42. n.taxa: number of different species studied in the same experiment
Var43. Use: whether (‘yes’) or not (‘no’) this case was used in the analyses reported in Goldberg et al. (1999).


CITATIONS

Goldberg, D.E. 1996. Simplifying the study of competition at the individual plant level: the consequences of distinguishing between effect and response for forest vegetation management. New Zealand Journal of Forestry Science 26: 19-38.
 
Goldberg, D. E., and A. M. Barton. 1992. Patterns and consequences of interspecific competition in natural communities: a review of field experiments with plants. American Naturalist 139: 771-801.
 
Goldberg, D. E., and A. Novoplansky. 1997. On the relative importance of competition in unproductive environments. Journal of Ecology 85: 409-418.
 
Goldberg, D.E., T. Rajaniemi, J. Gurevitch, and A. Stewart-Oaten. 1999. Empirical approaches to quantifying interaction intensity: competition and facilitation along productivity gradients. Ecology 80: 1118-1131.
 
Gurevitch, J., L. L. Morrow, A. Wallace, and J. S. Walsh. 1992. A meta-analysis of competition in field experiments. American Naturalist 140: 539-572.
 
Hedges, L. V., J. Gurevitch, and P. S. Curtis. 1999. The meta-analysis of response ratio experiments in experimental ecology. Ecology 80: 1150-1156.

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