DOI: 10.5061/dryad.kd51c5b80
title: Data and code from: Invasive grass indirectly alters seasonal patterns in seed predation

description: Invasive species threaten ecosystems globally, but their impacts can be
 cryptic when they occur indirectly. Invader phenology can also differ from
 that of native species, potentially causing seasonality in invader
 impacts. Yet, it is unclear if invader phenology can drive seasonal
 patterns in indirect effects. We used a field experiment to test if an
 invasive grass (Imperata cylindrica) caused seasonal indirect effects by
 altering rodent foraging and seed predation patterns through time. Using
 seeds from native longleaf pine (Pinus palustris), we found seed predation
 was 25% greater, on average, in invaded than control plots, but this
 effect varied by season. Seed predation was 24% - 157% greater in invaded
 plots during spring and fall months, but invasion had no effect on seed
 predation in other months. One of the largest effects occurred in October
 when longleaf pine seeds are dispersed, suggesting potential effects on
 tree regeneration. Thus, seasonal patterns in indirect effects from
 invaders may cause underappreciated impacts on ecological communities.
description: <strong>Study site & experimental
 design</strong> To evaluate seasonal patterns in
 indirect effects of an invasive species, we used a field experiment in
 Gainesville Florida, USA that manipulated cogongrass, an invader from
 southeastern Asia. The experiment consists of forty 4m x 4m plots with
 established longleaf pine and understory plant communities, treated with a
 factorial combination of cogongrass invasion and simulated drought. We
 used 10 invaded and 10 uninvaded control plots. Native plant communities
 were initially established in 2012 with cogongrass added in half the plots
 in 2013. <strong>Seed predation
 experiment</strong> To test if invasion altered
 seed predation by rodents, we used 26 cm x 26 cm x 6 cm (L x W x H)
 plastic trays with ~100 dry longleaf pine seeds (estimated by weight) per
 tray mixed with 1.5 liters of fine sand. Each sampling night, one seed
 tray was placed in the center of invaded and control plots (20 trays per
 night, 10 per treatment) and removed the following morning. After
 collecting trays, sand was sifted and undamaged seeds were counted by
 hand, to provide a precise count of fully intact seeds. The number of
 seeds consumed by rodents per tray was calculated by subtracting the
 number of fully intact seeds from 100. We sampled four consecutive nights
 and repeated four-night sampling sessions every two months from February
 2019 to April 2020, totaling eight sessions and 32 sample nights. Each
 sampling session was conducted within four days of full moon to control
 for variation in moonlight, which can alter rodent behavior. To account
 for any influence of cloud cover on foraging behavior, we used data from a
 regional weather station (www.timeanddate.com/weather/usa/gainesville/historic) and scored relative cloud cover per night (hourly average 7:00 pm – 8:00 am) corresponding to: clear (0), passing clouds (1), partly cloudy (2), mostly cloudy (3), overcast (4), and fog (5). Percent vegetation cover (henceforth “cover”) was measured every two months from February 2019 to April 2020, within two weeks of seed tray sampling nights. Cover was estimated by randomly selecting four 1 m2 quadrats within each plot, estimating percent cover for each, and taking the average [24]. Cover included dead and live plants 10 cm or taller, a height sufficient to conceal foraging rodents. To identify seed predators, we used seven camera traps per treatment (due to limited camera availability) suspended 1m above trays. We also examined trays for scat, tracks, and chewed seeds prior to sifting sand to better assess species that visited trays. To examine differences in rodent foraging time, we assessed camera data from April and August 2019 when average differences in cover between treatments was relatively large (18%) and small (4%). Data was collected throughout the experiement and recorded in excel sheets. Data was subsequently cleaned and combined in R to produce the final dataset uploaded here. 
description: This dataset contains data for seed predation and vegetation
 conditions of each plot during each sampling. Each row represents a single
 tray placed in one experimental plot for 1 of the sample
 nights. <br><br>Here is a description of each
 column: MonthYear: The month and year for the
 sample SamplingPeriod: each sample month we conducted a
 4 night sampling session. This column specifies which night the row comes
 from within the 4 nights of sampling during that particular
 month. PlotNumber: the plot ID number
 SampleMonth: the month  Year: the
 year TrayID: specific tray number placed in that
 plot  InitialSeedWght(g): initial weight of seeds put
 into the tray prior to sampling InitialCount: Initial
 seed count based on the weight having been callibrated each sampling
 session with the specific batch of seeds. FinalCount:
 The count of fully intact seeds Eaten: Initial count -
 final count = the total seeds consumed by rodents
 Tracks: yes/no for if animal tracks were in the tray when
 collected TrackType: specifies type of tracks observed
 if any SeedsChewed: yes/no for if there was visual
 evidence of seeds having been chewed by rodents
 Scat/Pee: NA if none, otherwise specifies the species for which
 scat and pee was found in the trays notes: general
 notes from sampling night PlotTreatment: A =
 "ambient" or control plot with no cogongrass, And  AC =
 "ambient cogon" or cogongrass invaded plot
 RowNumber: row number from which the plot is from
 EdgeOrCore: specifies if the plot was found on the edge of core
 of the experiment Lat: latitude
 Long: Longitude LowCover: % vegetation cover
 less than 100cm tall and taller than 10cm tall
 TallCover: % vegetation cover taller than 100cm tall
 Bare: % area that had no vegetation cover taller than
 10cm TotalCover: total area with cover greater than
 10cm tall AverageSky: average nightly cloud cover score
 based on a 1-5 score specified in the methods
 SumSkyScore: nightly sum of cloud cover score
 RemainingSeeds: total intact seeds remaining in each
 tray