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Dryad

Spatial patterns of seed removal by harvester ants in a seed tray experiment

Cite this dataset

Grossklaus, Michaela; Pilliod, David; Caughlin, Trevor; Robertson, Ian (2024). Spatial patterns of seed removal by harvester ants in a seed tray experiment [Dataset]. Dryad. https://doi.org/10.5061/dryad.4b8gthtnd

Abstract

Using a selection of native grass and forb seeds commonly seeded in local restoration projects, we conducted a field experiment to evaluate the effects of seed species, distance of seed patches from nests, and distance between patches on patterns of seed removal by Owyhee harvester ants, Pogonomyrmex salinus (Olsen) (Hymenoptera: Formicidae). To provide context for ants’ seed preferences, we evaluated differences in handling time among seed species. In addition, we assessed the influences of cheatgrass, Bromus tectorum (L.) (Poales: Poaceae), and Sandberg bluegrass, Poa secunda (J. Presl), cover on seed removal. We found significant differences in removal rates among seed species. In general, seeds placed closer to nests were more vulnerable to predation than those placed farther away, and seeds in closely spaced patches were more vulnerable than seeds in widely spaced patches. However, the strength of these effects differed by seed species. Differences in handling time among seed species may help to explain these findings; the protective effect of from-nest distance was weaker for species which required less time to transport. For two of the seed species, there was an interaction between the distance of seed patches from nests and the distance between patches such that the protective effect of distance between patches decreased as distance from nests increased. Cheatgrass and bluegrass cover both had small protective effects on seeds. Taken together, these results offer insight into the spatial ecology of harvester ant foraging and may provide context for successful implementation of restoration efforts where harvester ants are present.

README: Spatial patterns of seed removal by harvester ants in a seed tray experiment

https://doi.org/10.5061/dryad.4b8gthtnd

This dataset includes six spreadsheets (seedtrayexperimentdata.csv, controlsitedata.csv, seedhandlingdata.csv, collectedforagedata.csv, groundcoverdata.csv, and trunktraildirections.csv) and the associated analysis script (grossklausetalanalysis.R).

Metadata

Seed tray experiment data (seedtrayexperimentdata.csv)

tray = unique tray identifier in the format: week.colony.tray
week = week of experiment; 1-9
colony = unique colony identifier
juliandate = Julian date
central direction = direction of center point for tray placement; degrees clockwise from North
traydirection = direction of individual tray; degrees clockwise from North
within_10 = binary variable specifying whether tray is within a 10-degree wedge around nearest trunk trail; 0 = no, 1 = yes
within_20 = binary variable specifying whether tray is within a 20-degree wedge around nearest trunk trail; 0 = no, 1 = yes
within_30 = binary variable specifying whether tray is within a 30-degree wedge around nearest trunk trail; 0 = no, 1 = yes
within_40 = binary variable specifying whether tray is within a 40-degree wedge around nearest trunk trail; 0 = no, 1 = yes
within_50 = binary variable specifying whether tray is within a 50-degree wedge around nearest trunk trail; 0 = no, 1 = yes
within_60 = binary variable specifying whether tray is within a 60-degree wedge around nearest trunk trail; 0 = no, 1 = yes
cheatgrass = extent of cheatgrass cover between tray and focal colony; meters
bluegrass = extent of bluegrass cover between tray and focal colony; meters
fromnestdist = distance between focal harvester ant colony and tray; meters
bin = from-nest distance stratum; 1 = 3.5 to 5.5 m, 2 = 5.6 to 7.6 m, 3 = 7.7 to 10 m
btwtraydist = distance between trays; meters
numtinycol = number of Pheidole ant colonies within a 10 m radius of the focal harvester ant colony
start = time that seeds were placed in their trays on the morning of seed deployment in format hh:mm
timesincestart = number of hours since seed deployment
wr_remain = number of wildrye seeds remaining at time of observation
rg_remain = number of ricegrass seeds remaining at time of observation
bg_remain = number of bluegrass seeds remaining at time of observation
p_remain = number of penstemon seeds remaining at time of observation
gm_remain = number of globe mallow seeds remaining at time of observation
wr_available = number of wildrye seeds available as of previous observation (not calculated for excluded observations)
rg_available = number of ricegrass seeds available as of previous observation (not calculated for excluded observations)
p_available = number of penstemon seeds available as of previous observation (not calculated for excluded observations)
gm_available = number of globe mallow seeds available as of previous observation (not calculated for excluded observations)
exclude = binary variable specifying observations to exclude from analysis; 0 = include, 1 = exclude
notes = notes about the observation

Control site data (controlsitedata.csv)

tray = unique tray identifier in the format: week.site.tray. tray either p (penstemon mix) or g (globe mallow mix)
week = week of experiment; 1-9
site = unique control site identifier
juliandate = Julian date
start = time that seeds were placed in their trays on the morning of seed deployment in format hh:mm
timesincestart = number of hours since seed deployment
wr_remain = number of wildrye seeds remaining at time of observation
rg_remain = number of ricegrass seeds remaining at time of observation
bg_remain = number of bluegrass seeds remaining at time of observation
p_remain = number of penstemon seeds remaining at time of observation
gm_remain = number of globe mallow seeds remaining at time of observation
tot_lost = total number of seeds lost at time of observation (not calculated for excluded observations)
exclude = binary variable specifying observations to exclude from analysis; 0 = include, 1 = exclude
notes = notes about the observation

Seed handling data (seedhandlingdata.csv)

species = seed species
juliandate = Julian date
temp = temperature at time of observation; degrees Celsius
traveltime = time taken by ant to travel 200 cm with seed from tray to nest; s
travelrate = calculated rate of travel; cm/s
securetime = time taken by ant to secure seed in its mandibles; s
numseeds = number of seeds carried

Collected forage data (collectedforagedata.csv)

colony = unique colony identifier
week = week of experiment; 2-9
juliandate = Julian date
foragetype = type of forage item collected by ant
count = number of items
notes = notes about the observation

Ground cover data (groundcoverdata.csv)

All columns in this spreadsheet are in the format: category_cover type. Values under each column are the percent understory cover of the cover type within the category (10 replicates per category).

categories: exoticmustards (exotic mustards), bluegrass (Sandberg bluegrass), fescue (Sixweeks fescue), cheatgrass (cheatgrass), debrisbareground (debris and bare ground), and mixedgrasses (mixed grasses)

cover types: bluegrass (Sandberg bluegrass), fescue (Sixweeks fescue), cheatgrass (cheatgrass), mustards (exotic mustards), debrisbareground (debris and bare ground)

Trunk trail directions (trunktraildirections.csv)

This data was used to calculate the columns within_10, within_20, within_30, within_40, within_50, and within_60 in the seedtrayexperimentdata.csv spreadsheet.

colony = unique colony identifier
week = week of experiment; 1-9
direction_1 = direction of trunk trail; degrees clockwise from North
direction_2 = direction of trunk trail; degrees clockwise from North
direction_3 = direction of trunk trail; degrees clockwise from North
direction_4 = direction of trunk trail; degrees clockwise from North
direction_5 = direction of trunk trail; degrees clockwise from North
direction_6 = direction of trunk trail; degrees clockwise from North

Data analysis

Analysis script: grossklausetalanalysis.R.

This R script has been annotated for ease of use and navigation.

Funding

Bureau of Land Management

Society for Ecological Restoration

Boise State University