Experimental shifts in exotic flowering phenology produce strong indirect effects on native plant reproductive success
- 1. University of Washington
Description
- By causing phenological shifts that vary among species, climate change is altering time envelopes for species interactions, often with unexpected demographic consequences. Indirect interactions, like apparent competition and apparent facilitation, are especially likely to change in duration because they involve multiple interactors, increasing the likelihood of asynchronous phenological shifts by at least one interactor. Thus, we might observe ecological surprises if intermediaries of indirectly interacting species change their mediating behavior.
- We explored this possibility in a plant-pollinator community that is likely to experience asynchronous phenological shifts. We advanced and delayed the flowering phenology of two ubiquitous exotic plants of western Washington prairies, Hypochaeris radicata and Cytisus scoparius, relative to seven native perennial forb species whose phenologies remained unmanipulated. These species interact indirectly through shared pollinators, whose foraging behavior influences plant reproductive success. We quantified impacts of experimental phenological shifts on seedset, pollinator visitation rates, and visiting pollinator composition relative to an unmanipulated control. We first verified that unmanipulated indirect interactions between native and exotic plants were strong, ranging from facilitative to competitive.
- Seedset of native plants was strongly affected by changes in exotic flowering phenology, but the magnitude and direction of effects were not predicted by the nature of the original indirect interaction (facilitative vs. neutral vs. competitive) or the change in interaction duration. The relationship between pollinator visitation and seedset changed for most species, though changes in pollinator visitation rate and pollinator composition were not as widespread as effects on native seedset.
- Synthesis. Changes in pollinator foraging behavior in response to changes in available floral resources are probably responsible for the unexpected effects we observed. Asynchronous phenological shifts have the potential to produce large and unexpected effects on reproductive success via indirect interactions.
Notes
For all the .csv files:
phentrt=phenology treatment. NAT=control plot without any exotic forb added, ECYT=potted C. scoparius placed in plots ~2 weeks in advance of typical flowering peak, RCYT=potted C. scoparius placed in plots at typical flowering peak, EHYP=potted H. radicata placed in plots ~2 weeks in advance of typical flowering peak, RHYP=potted H. radicata placed in plots around typical flowering peak, LHYP=potted H. radicata placed in plots ~2 weeks later than typical flowering peak
block=randomized block. Site was divided into 8 blocks, A-H
plot=a 5x5 m plot; 1-7
species=six-letter codons representing the 7 native western Washington prairie forbs listed above: ACHMIL=Achillea millefolium; BROELE=Brodiaea elegans; CAMQUA=Camassia quamash; CAMROT=Campanula rotundifolia; DODHEN=Dodecatheon hendersonii; EMPTY=no species flowering in plot; ERILAN=Eriophyllum lanatum; FRAVIR=Fragaria virginiana; FRIAFF=Fritillaria affinis; HIECYN=Hieracium cynoglossoides; HYPPER=Hypericum perforatum; HYPRAD=Hypochaeris radicata; LEUVUL=Leucanthemum vulgare; LOMUTR=Lomatium utriculatum; LOTMIC=Lotus micranthus; LUPLEP=Lupinus lepidus; MICLAC=Microseris laciniata; PARVIS=Parentucellia viscosa; PRUVUL=Prunella vulgaris; RANOCC=Ranunculus occidentalis; SOLSPA=Solidago spathulata; TAROFF=Taraxacum officinale; TEENUD=Teesdalia nudicaulis; TRIDUB=Trifolium dubium; VICSAT=Vicia sativa; VIOADU=Viola adunca; ZIGVEN=Zigadenus venenosus.
phenstg=a qualitative category for when the focal native forb individual flowered relative to others in the population: EARLY, PEAK, LATE, or LL ("latelate").
For seed data:
polltrt=pollination treatnent imposed: either SELF (pollinators excluded with bag) or OPEN (no manipulation, pollinators have access to inflorescence)
totheads=total number of seedheads/pods/capitulas on plant
filledheads=number with filled seeds
FILLEDseednum=number of seeds filled (i.e., successfully pollinated) in the seedhead counted
UNFILLEDseednum=number of seeds unfilled in the seedhead counted
FILLEDseedwt=weight of filled seeds in the seedhead counted
UNFILLEDseedwt=weight of unfilled seeds in the seedhead counted
plwt=aboveground dry biomass of plant from which seed was harvested and counted
infested=evidence of seed predation (insect frass, seed fragments): binary variable
seedperhead=number of filled seeds counted
For phenology data:
phenobsdate=date flowering phenology was observed
phenobsjulianday=julian date flowering phenology was observed
obsperiod=segment of season during which observations took place 1-7
square=1-25. One of 25 1x1m squares making up the 5x5m plot.
species_counted= a six-letter codon representing the identity of forb species flowering in the plot at the time of survey
blooms=# flowering stems counted for that species
For pollinator visitation data:
patch_size: number of flowering units of the focal native forb species present in a 1x1m square chosen for observation
pollobsdate: date of observation for pollinator visitation
pollobsjuliandate: julian date of observation for pollinator visitation
species_watched: focal native forb species observed for visitation
rhsp=Rhamphomyia sp.
drsp2=Drymeia sp. 2
anthsp1=Anthomyiid sp.
unfly1=k=unknown fly 1
drsp1=Drymeia sp. 1
erhi=Erystalis hirsuta
boca=Bombus californicus
bovo=Bombus vosnesenskii
ossp1=Osmia sp.
bomi=Bombus mixtus
hese=Hemihalictus series
hasp=Halictid sp.
andsp1=Andrenid sp.
apme=Apis mellifera
nomsp1=Nomada sp.
duca=Dufourea campanulae
unfly2=unknown fly 2
unbee1=unknown bee 1
unwasp1=unknown wasp 1
beetle1=unknown beetle 1
boma=Bombus melanopygus
snakefly=unknown snakefly
unbee2=unknown bee 2
other= other taxon not identified, e.g. true bug, earwig, etc.
Funding provided by: National Science Foundation Graduate Research Fellowship
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001
Award Number: DGE-0718124
Funding provided by: Mary Gates Undergraduate Research Fellowship *
Crossref Funder Registry ID:
Award Number: NA
Funding provided by: Mary Gates Undergraduate Research Fellowship
Crossref Funder Registry ID:
Files
FloweringPhenology_2011_GH.csv
Additional details
Related works
- Is cited by
- 10.1111/1365-2745.13392 (DOI)