Drought is an important stressor that affects plant growth, survival and physiology and, through plant responses, alters plant-herbivore interactions and herbivore population dynamics. Short-term drought can occur at different times during a growing season, affecting herbivore populations and plants at various stages of development and growth. As phenology influences drought response, drought timing could strongly structure plant-herbivore interactions. We grew common milkweed plants with or without its dominant aphid herbivore, allowing both plants and herbivore populations to develop over time as in a typical growing season. To determine how drought timing affects plants and aphid populations, we applied short-term (1 week) drought at different times. Plants and aphids were sensitive to drought timing, with a few weeks difference shifting the effects of drought from minimal to causing massive declines in plant growth, plant survival and herbivore population density. Aphid herbivory added to or overrode drought consequences in plants, with different plant fitness components responding distinctly to herbivory. Drought timing also affected whether plant and herbivore responses were parallel or divergent, suggesting that shifts in the seasonal timing of drought have the potential to disrupt plant-herbivore interactions and affect the larger ecological community. Our results show drought timing has important and disparate consequences for herbivores and their host plants and indicates the necessity of considering phenology and timing in assessing drought response.

This DataS1readme.txt file was generated on 2021-10-19 by Ruiping Luo.

GENERAL INFORMATION

Title of Dataset: Timing of short-term drought structures plant-herbivore dynamics

Author Information
    Principal Investigator 
        Name: Ruiping Luo
        Institution: University of Toronto    
        Email: ruiping.luo@mail.utoronto.ca

    Co-investigator 
        Name: Benjamin Gilbert
        Institution: University of Toronto
        Email: benjamin.gilbert@utoronto.ca

Date of data collection: 2019-07-10 to 2019-08-28

Geographic location of data collection: Toronto, Ontario, Canada

Funding sources that supported the collection of the data: This research was supported by funding from Natural Sciences and Engineering Research Council of Canada

DATA & FILE OVERVIEW

File List: 
DataS1.xlsx - Main data set
CodeS1.R - R code for data analysis in manuscript
Supplementary.R - R code for data analysis in supplementary materials

Relationship between files: CodeS1.R and Supplementary.R require input from DataS1.xlsx for analysis

DATA-SPECIFIC INFORMATION FOR: DataS1.xlsx (Sheet title: Photosynthesis)

Number of variables: 6

Number of rows: 280

Variable List: 
Plant - Number identification of individual plants
Block - Blocks sorted by plant size (1=smallest, 10=largest)
Treatment - Drought treatment, applied as 1-week without water addition at various times throughout a growing season (0=control)
Date - Date of data collection
Day - Day of experiment
Average - Average change in carbon dioxide in micromoles per meter squared per second (umol m^-2 s^-1)

DATA-SPECIFIC INFORMATION FOR: DataS1.xlsx (Sheet title: Plants)

Number of variables: 40

Number of rows: 100

Variable List: 
Plant - Number identification of individual plants
Block - Blocks sorted by plant size (1=smallest, 10=largest)
Treatment - Drought treatment, applied as 1-week without water addition at various times throughout a growing season (0=control)
Aphids - Presence of aphids on plants (0=no aphids, 1=aphids introduced)
nLeaf - Initial number of leaves prior to experiment
yLeaf - Final number of yellow leaves following experiment
gLeaf - Final number of green leaves following experiment
Height - Height of plant above soil surface
L1, L2, L3 - Length of youngest, second youngest and third youngest leaf prior to experiment in centimeters (cm)
W1, W2, W3 - Width of youngest, second youngest and third youngest leaf prior to experiment in centimeters (cm)
Latex - Weight of exuded latex in grams (g)
Trichomes - Density of trichomes on tip of second youngest leaf 
State - State of plant following experiment (0=dead, 1=live)
Livemass - Wet biomass of aboveground plant matter considered living following experiment in grams (g)
Deadmass - Wet biomass of aboveground plant matter considered dead following experiment in grams (g)
Rootmass - Wet biomass of belowground plant matter following experiment in grams (g)
Leafmass1, Leafmass2, Leafmass3 - Wet biomass of youngest, second youngest and third youngest leaf following experiment in grams (g)
Livedry - Dry biomass of aboveground plant matter considered living following experiment in grams (g)
Deaddry - Dry biomass of aboveground plant matter considered dead following experiment in grams (g)
Rootdry - Dry biomass of belowground plant matter following experiment in grams (g)
Litter - Biomass of leaf litter following experiment in grams (g)
Leafdry1, Leafdry2, Leafdry3 - Dry biomass of youngest, second youngest and third youngest leaf following experiment in grams (g)
Area1, Area2, Area3 - Area of youngest, second youngest and third youngest leaf following experiment in centimeters squared (cm^2)
L1a, L2a, L3a, - Length of youngest, second youngest and third youngest leaf following experiment in centimeters (cm)
W1a, W2a, W3a, - Width of youngest, second youngest and third youngest leaf following experiment in centimeters (cm)
Mortality - Day plant was first categorized as dead

DATA-SPECIFIC INFORMATION FOR: DataS1.xlsx (Sheet title: Survival)

Number of variables: 6

Number of rows: 1300

Variable List: 
Plant - Number identification of individual plants
Block - Blocks sorted by plant size (1=smallest, 10=largest)
Treatment - Drought treatment, applied as 1-week without water addition at various times throughout a growing season (0=control)
Aphids - Presence of aphids on plants (0=no aphids, 1=aphids introduced)
Day - Day of experiment
State - State of plant following experiment (0=dead, 1=live)

DATA-SPECIFIC INFORMATION FOR: DataS1.xlsx (Sheet title: Aphids)

Number of variables: 7

Number of rows: 550

Variable List: 
Plant - Number identification of individual plants
Block - Blocks sorted by plant size (1=smallest, 10=largest)
Treatment - Drought treatment, applied as 1-week without water addition at various times throughout a growing season (0=control)
Day - Day of experiment
Obs - Observation number for aphid counts
Winged - Density of winged aphids (aphids per plant)
Unwinged - Density of unwinged aphids (aphids per plant)