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Community assembly anddis-assembly under global change
Elizabeth M. WolkovichUniversity of California, San Diego
November 2011
What will be species’ responses?
Changes relative to late 20th centuryA2 scenario, IPCC, WG1 summary, 2007
– Extinctions– Spatial shifts– Temporal shifts
Impacts of global change oncommunity assembly
– Diverse methods tounderstand directeffects
– Assembly theory topredict indirecteffects
Impacts of global change oncommunity assembly
– Direct: Changes in planttiming with warming Methods comparison Beyond earlier spring
– Indirect: Role of timing inplant invasions
– Direct & indirect:Mechanisms of invasioneffects on food webs
Phenology
– When you plant– Harvest dates– Ties to wild
species: Performance Ranges Extinction
1990
2006
USDA hardiness maps (Arbor Day)
Phenology most commonly used as anindicator of global climate change
– Our ability toexplain andpredict variationacross species,habitats and timeis still poor.
Global synthesis of warmingeffects on phenology
– Diverse communities– Long-term datasets– Multiple approaches
Comparison of methods
Experiments Observations– Project forward to future conditions
– Isolate effects
– Best data for how plants respondto climate change
Plant sensitivities to temperature
– Calculated sensitivities Change in days per °C
– Hierarchical mixed-effects models Accounts for non-
independence amongsites and species
Experiments underpredictresponses to climate change
1,560 species
flowering: F1,33=9.36, p=0.004
leafing: F1,20=3.58, p=0.07
Experiments underpredictresponses to climate change
1,560 species matching species
flowering: F1,16=3.67, p=0.07leafing: F1,10=8.75, p=0.014
Mismatch was not due to:
lifespan: F1,1891=6.11, p=0.014lifespan x study-type: F1,1891=0.11, p=0.74
– Speciescharacteristics No difference
between herbs &woody species
Annuals equally moresensitive
Mismatch was not due to:– Species characteristics
No difference between herbs &woody species
Annuals equally more sensitive– Species sampling– Habitat– Timescales: Genotypic shifts
30 versus 3 years– Correlations with other variables– Aspects of experimental design– Degree of warming
Mismatch may be due to:– Artifacts of
experiments Reduced irradiation Reduced soil moisture
– Improving design: Avoid artifacts, or
measure them Add light and moisture
treatments Report high-quality
temperature data
Mismatch may be due to:– Artifacts of
experiments Reduced irradiation Reduced soil moisture
– Climate changeeffects not replicatedby experiments
– Improving design: Avoid artifacts, or measure
them Add light and moisture
treatments Report high-quality
temperature data
Beyond earlier spring:Multi-seasonal effects of climate change
– Most temperatespecies haveadvanced withwarming (70-80%)
– Most speciesrespond to springwarming
– Some temperatespecies requirewinter chilling(vernalization)
Data from Chinnor, UK (Fitter & Fitter 2002)
Vernalization
– Do not respondto springwarming untilchilling iscomplete
– Lab andmodeling studiessuggest thiscould delayflowering withwarming
Data from Chinnor, UK (Fitter & Fitter 2002)
How does winter and springwarming affect phenology?
– Used 47-yr dataset: Calculate sensitivities to
temperature acrossseasons
Model-fitting approach toinclude spring versusspring + winter responses
Compared modelparameters with species’long-term responses towarming
Species’ responses to spring andwinter warming
– Of 384 species: 275 had significant cues to
spring-warming only 70 had both spring-warming
and vernalization cues⇒ Divergent responders
Data from Chinnor, UK (Fitter & Fitter 2002)
Species with diverse cues mayrespond to future warming
– Species withvernalizationrespond strongly totemperature
– But show no currenttrends due to off-setting response
– May delay in futureas chillingrequirements are notmet
What can we predict about directresponses to climate change?
– Multi-seasonal effects: Most species advance with warming 10-20% temperate species currently
showing no response have divergent climatecues, may shift in future
– Mean response is 5-7 days/ºC– Annuals are more sensitive– Sensitivities are similar across habitats– Experiments should be used
cautiously to project responses
Impacts of global change oncommunity assembly
– Direct: Changes in planttiming with warming Methods comparison Beyond earlier spring
– Indirect: Role of timing inplant invasions
– Direct & indirect:Mechanisms of invasioneffects on food webs
Impacts of global change oncommunity assembly
– Direct: Changes in planttiming with warming Methods comparison Beyond earlier spring
– Indirect: Role of timing inplant invasions
– Direct & indirect:Mechanisms of invasioneffects on food webs
Time in community ecology theory
Storage effect model uses inter-annualvariability to promote coexistence
Abundanceor relativefrequency
– Invasion biology &phenology Vacant niche Priority effects Plasticity
Extending theory to intra-annual scale
Vacant niche
– Predicts: Exotic species tend toleaf/bloom when native speciesnot in leaf/bloom
Abundanceor relativefrequency
Vacant niche
– Predicts: Exotic species tend toleaf/bloom when native speciesnot in leaf/bloom
Amur honeysuckle(Lonicera maacki) staysgreen late in season
Priority effects
– Predicts: Exotic speciesleaf/bloom earlier than nativespecies
Red brome (Bromusmadritensis ssp. rubens)greens up earlier
Plasticity & climate change
– Predicts: Leafing/blooming of exoticspecies varies across years morethan native species, co-varies withclimate.
Plasticity & climate change
– Predicts: Leafing/blooming of exoticspecies varies across years morethan native species, co-varies withclimate.
Exotic species trackclimate closer inConcord, Massachusetts
Febr
uary
May
Day of year
Wolkovich & Cleland, Frontiers in Ecology & the Environment, 2011
Mixed-effects ANOVA (species as random): F2,84=3.74, p=0.03
Exotics show earlier leafburst
– Citizen science– North Carolina– Budburst/first leaf for
all species– Supports priority
effects– Similar findings using
USDA Plants
Impacts of global change oncommunity assembly
– Direct: Changes in planttiming with warming Methods comparison Beyond earlier spring
– Indirect: Role of timing inplant invasions
– Direct & indirect:Mechanisms of invasioneffects on food webs
Impacts of global change oncommunity assembly
– Direct: Changes in planttiming with warming Methods comparison Beyond earlier spring
– Indirect: Role of timing inplant invasions
– Direct & indirect:Mechanisms of invasioneffects on food webs
– Non-native grassgrows early
– Senescence 1-2months earlierthan most nativespecies
Invasion alters plant timing of system
Food web effects
Native shrubbiomass
Grazingweb
Non-nativelitter
moisturedecompositionnutrient cycling
Detrital web
omnivorouspredators
Food web effects
Native shrubbiomass
Grazingweb
Non-nativelitter
moisturedecompositionnutrient cycling
Detrital web
omnivorouspredators
Food web vs. Ecosystem effects
Native shrubbiomass
Grazingweb
Non-nativelitter
moisturedecompositionnutrient cycling
Detrital web
omnivorouspredators
Possible paths: Top-down via directfood web shifts
Leaf-hoppers
Non-nativelitter
Ground spiders
Web spiders
Possible ecosystem and food webpaths: Bottom-up via quantity
Leaf-hoppers
Native shrub growth
Non-nativelitter
Ground spiders
Web spiders
Possible ecosystem and food webpaths: Bottom-up via quality
Leaf-hoppers
Native shrub growth
Non-nativelitter
Ground spiders
Web spiders
Native shrub leaf %N
Possible paths:Litter to shrub arthropods
Leaf-hoppers
Native shrub growth
Non-nativelitter
Ground spiders
Web spiders
Native shrub leaf %N
Strong, positive bottom-up effect
Leaf-hoppers
Native shrub growth
Non-nativelitter
Ground spiders
Web spiders
Native shrub leaf %N
-0.100.06
-0.04-0.003
-0.12
0.58*** 0.84*** 0.62***
0.34*
X2 = 7.24, p = 0.30
AIC = 22.8Wolkovich, Ecology, 2010
No support for direct food web,plant quality effects
Leaf-hoppers
Native shrub growth
Non-nativelitter
Ground spiders
Web spiders
Native shrub leaf %N
-0.100.06
-0.04-0.003
-0.12
0.58*** 0.84*** 0.62***
0.34*
X2 = 7.24, p = 0.30
AIC = 22.8
Wolkovich, Ecology, 2010
Path analysis supportsshrub growth as only major link
Leaf-hoppers
Native shrub growth
Non-nativelitter
Web spiders
0.58*** 0.85*** 0.60***
X2 = 2.01, p = 0.57
AIC = 10.0
∆ AIC > 5
As compared with 5other a priori modelsWolkovich, Ecology, 2010
Ecosystem shifts drivefood web effects
Leaf-hoppers
Native shrub growth
Non-nativelitter
Web spiders
Wolkovich et al., GlobalChange Biology, 2010
Ecosystem shifts drivefood web effects
Leaf-hoppers
Native shrub growth
Non-nativelitter
Web spiders
Wolkovich et al.,Journal of Vegetation Science, 2009
– Increased soil moisture→ shrub growth
Ecosystem shifts drivefood web effects
Leaf-hoppers
Native shrub growth
Non-nativelitter
Web spiders
Wolkovich et al.,Global Change Biology, 2010
– Increased soil moisture →shrub growth
– Rapid 20% increases incarbon and nitrogenstorage via changes: soil community decomposition
– Food web impactsoccur via ecosystemshifts
– Detrital changes dueto invasion have largeimpacts on: Native plants Arthropod food webs Ecosystem C & N Phenology
Impacts of invasion on food webs
What will be species’ responses?
Changes relative to late 20th centuryA2 scenario, IPCC, WG1 summary, 2007
Understanding & predictingcommunities with global change
– Diverse methodswith global data What direct effects
we can predict now– Assembly theory to
predict indirecteffects Role of phenology in
plant invasions
Diverse methods– Spatial gradient
studies– Field experiments– Long-term trends &
time-series– Simulation modeling– Meta-analysis– Comparison across
methods– Robust quantitative
designs
– Building up from directeffects of climate toconsequences on: Species interactions Communities Ecosystem processes
– Controls on tropicalphenology
– Evolutionary constraintson phenology
– Generalizing invasiontheory to communityassembly
Current & Future Research
– Bottom-up andtop-down Nutrient Network Top-down across
an invasiongradient
Current & Future Research
– Bottom-up andtop-down Nutrient Network Top-down across
an invasiongradient
– Climate forcing ofwinegrapes
Current & Future Research
Acknowledgements
– Doug Bolger & KathyCottingham
– Elsa Cleland & StephHampton
– Forecasting Phenologyworking group
– Ben Cook– David Holway, David Lipson,
John Moore