Bioscience – Aarhus University Measuring competitive interactions in natural plant populations...
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Transcript of Bioscience – Aarhus University Measuring competitive interactions in natural plant populations...
Bioscience – Aarhus University
Measuring competitive interactions in natural plant populations
Christian DamgaardBioscience
Aarhus University
Bioscience – Aarhus University
Evidence for competitive interactions in plant communities
How often has the competitive interactions in a plant community been measured in a natural plant community compared to the times competition has been postulated to be an important ecological mechanisms?
1/1000 is certainly too high 1/1000,000?
Measuring interspecific interactions in natural ecosystems is a non-trivial task and the results are still too sparse to allow generalization across different plant communities or even among years (Turnbull et al. 2004)
Bioscience – Aarhus University
Measuring competitive interactions in natural plant communities
Competition is a process occurring in time Just as you need more than one measurement in time to
measure a velocity or a rate, you need more than one measurement in time to measure the effect of the neighboring plants on growth (= change in biomass) of the target plant species
Longitudinal (=time series) plant abundance data Non-destructive sampling
Bioscience – Aarhus University
Measuring ecological success
𝑑𝑁𝑑𝑡 = 𝑓 (𝑁 ) 𝑁 ?
Bioscience – Aarhus University
Measuring ecological success Natural and semi-natural plant
communities are dominated by spatially structured perennial species with variable life histories
Often difficult to count individual plants
Large size variation among individuals of the same species.
The ecological success may be assessed using the pin-point method
cover (= relative area that the species cover) vertical density (= 3D space occupancy ~
biomass, plant volume, and LAI)
𝑁 ?
Bioscience – Aarhus University
Plant cover and vertical density – assumptions
i) Plant cover and vertical density measure ecological success
ii) Due to the growth form of most plant species, the vertical density will increase relatively faster than plant cover during the growing season
iii) Species with a high cover in spring will have relatively high vertical density at the end of the growing season, however, the vertical density is reduced by the cover of other species due to competition
year t year t 1
iv) A plant species that grows to a relatively high vertical density has a relatively high cover the following year, i.e., plants allocate resources into occupying resource space the following year
Bioscience – Aarhus University
Plant cover and vertical density – model
X: coverY: vertical density
P1: competitive growthP2: survival, establisment etc.
Bioscience – Aarhus University
Plant cover and vertical density – model
Competitive growth (P1):
Yi = increasing function of Xi * decreasing function of X j,k,…
Survival and establishment (P2):
Xi,y+1 = increasing function of Yi,y * decreasing function of Y j,k,…,y
Bioscience – Aarhus University
Plant cover and vertical density – model
Competitive growth (P1):
Survival and establishment (P2):
ryiPd
rytkrkd
rytjrjb
rytirirytikji XzcXzcXzaY ,,,1,,1,,,1,,,1,,,2, ))(exp())(exp()(
ryiPd
rytkrkd
rytjrjb
rytirirytikji YzcYzcYzaX ,,,2,,2,,,2,,,2,,1,1, )))(exp())(exp()((logit)(logit
constant slope( )z z
Structural variation: for predictions, , ,P i y r
Effect of environment:
M1: ), (Binomial~ ,,,,,, rytiryti Xnu 1
M2: ),(g~ ,2,,,,,, iMrytiryti YPv 1
Bioscience – Aarhus University
The effect of glyphosate on the competitive interactions between Festuca ovina and Agrostis capillaris
Christian DamgaardBeate Strandberg
Solvejg K. Mathiassen Per Kudsk
Aarhus University
Bioscience – Aarhus University
Festuca ovina and Agrostis capillaris
Permanent plots with mainly F. ovina and A. capillaris in different proportions
Four glyphosate levels: 0, 1, 5 and 25% of label rate (1440 g glyphosate/ha)
Cover and vertical density was measured twice a year for three years : two weeks after herbicide application
in the spring
: at the end of the growing season
Festuca ovina (solid)Agrostis capillaris (stripped)
Bioscience – Aarhus University
Estimating the competitive interactions
The joint Bayesian posterior distribution of the parameters and latent variables for cover and vertical density were calculated using a Markov chain Monte Carlo method (Metropolis-Hastings)
The prior distributions of all parameters and latent variables were assumed to be uniformly distributed in their specified domains. Relative informative priors of b, d, and were in initial explorations of the model found to be necessary in order to ensure a successful fitting procedure.
Plots of the deviance and the sampling chains of all parameters and latent variables were inspected in order to check the fitting and mixing properties of the used sampling procedure.
Bioscience – Aarhus University
Marginal distribution of competition parameters
Festuca ovina Agrostis capillaris Other species
Percent. 2.5% 50% 97.5% 2.5% 50% 97.5% 2.5% 50% 97.5%
Process equation 1 – during the growing season:
cconstant 0.612 0.835 0.965 0.161 1.940 2.641 -0.688 0.128 0.638
cslope 0.114 0.139 0.159 -0.509 -0.342 -0.082 -0.081 0.132 0.542
Process equation 2 – among growing seasons:
cconstant 0.413 2.279 4.335 -0.017 0.015 0.057 -0.034 0.013 0.095
cslope -0.122 0.001 0.202 -0.002 0.002 0.007 -0.013 -0.003 0.009
Significant competitive effect Competitive effect depends on glyphosate
Bioscience – Aarhus University
Importance of competitive interactions relative to the effect of glyphosate
Importance of competition is highest in the growing season
Importance of competition on A. capillaris increases with glyphosate
( , )
( , ) ( , )j
j
X i
X i z i
Y X z
Y X z Y X z
Bioscience – Aarhus University
Competitive interactions between Festuca ovina Agrostis capillaris - summary
F. ovina and A. capillaris compete for resources!
The competitive effect of F. ovina increases with glyphosate
The competitive effect of A. capillaris decreases with glyphosate
Importance of competition is highest in the growing season
Importance of competition of F. ovina on A. capillaris increases with glyphosate
Structural equation models allow the separation of structural and measuring variance
Quantitative ecological predictions with a known uncertainty
Bioscience – Aarhus University
Competitive interactions were measured using the pin-point methodI. Effect of climate change (temperature, draught, C02), on the
competitive interactions between Calluna vulgaris and Deschampsia flexuosa in dry heathlands Draught increased the probability that Deschampsia would
outcompete Calluna (Damgaard et al. 2009, Ransijn et al., 2015, in prep.)
II. Effect of glyphosate and nitrogen on the competitive interactions of Festuca ovina and Agrostis capillaris Glyphosate increased the competitive effect of Festuca ovina
(Damgaard et al. 2012, 2014)
III. Effect of water level on the competitive interactions among grassland species The importance of competition varied with water level (Merlin et al,
2015)
IV. Measure the competitive interactions of different plant traits (Damgaard, submitted)
Bioscience – Aarhus University
Evidence for competitive interactions in plant communities II
Competition is measured by the effect of neighboring plants on plant growth longitudinal plant abundance data
Macro-ecological assumption I: the biomass of neighboring plant is used as a proxy for interspecific interactions Variation in total biomass due to plot heterogeneity
Macro-ecological assumption II: plant communities are assumed to in equilibrium Generally known not to be true Problematic to assume that plant abundance is in equilibrium in a test
of the very nature of the ecological mechanism that control plant abundances
Bioscience – Aarhus University
“Demography” of space occupancy
Christian DamgaardDepartment of Bioscience
Aarhus University
Bioscience – Aarhus University
“Demography” of space occupancy Often difficult to distinguish
individuals in natural and semi-natural plant communities
Instead of measuring individual plants, record if a species is present at a fixed pin-position in at least two years
If a new species is recorded at a position, then a colonisation event may have occurred
If a species disappear at a position, then a mortality event may have occurred
Bioscience – Aarhus University
Events and transition probabilities
Event Description Transition probability
X1:At, At+1 A plant species A was present in year t and was also present in year t+1 p( s(z) + 1 ( 1 – s(z) ) c(z) )
X2:nAt ,nAt+1 A plant species A was not present in year t and was also not present in year t+1 ( 1 – p ) (1 – c(z) )
X3:At ,nAt+1
A plant species A was present in year t but was not present in year t+1
(indicates a possible mortality event)p( 1 – p ) (1 – c(z) )
X4:nAt , At+1
A plant species A was not present in year t but was present in year t+1
(indicates a possible colonization event)( 1 – p ) c(z)
Bioscience – Aarhus University
Change in cover and elasticity
𝜋=𝑝 ′
𝑝 =𝑝𝑋 1
+𝑝𝑋 2
𝑝𝑋 1+𝑝𝑋 3
=𝑐(𝑧 )𝑝 +𝑠 (𝑧 ) −𝑐 (𝑧 )𝑠 (𝑧 )
𝑐( 𝑧)𝜋
𝜕𝜋𝜕 𝑐(𝑧)=
𝑐 (𝑧 )− (𝑝𝑐 (𝑧 ) 𝑠 (𝑧 ) )𝑐 (𝑧 )+(𝑝 𝑠 (𝑧 ) )− (𝑝𝑐 (𝑧 )𝑠 (𝑧 ) )
𝑠 (𝑧)𝜋
𝜕𝜋𝜕𝑠 (𝑧 )
=1 − 𝑐 (𝑧 )𝑐 (𝑧 )+(𝑝 𝑠 (𝑧 ) ) (1 −𝑐 (𝑧 ) )
Bioscience – Aarhus University
Demography along a flooding gradientCollaboration with Anne Bonis, Rennes
Marais du Poitevin, France
,
Bioscience – Aarhus University
Survival and colonisation probabilities as a function of the flooding gradient (z)
Species
2.5% 50% 97.5% 2.5% 50% 97.5% 2.5% 50% 97.5% 2.5% 50% 97.5%
Agrostis stolonifera 0.333 0.473 0.604 -0.002 0.022 0.039 0.394 0.455 0.510 0.021 0.033 0.040
Cynosurus cristatus 0.042 0.117 0.192 -0.011 -0.001 0.020 0.072 0.112 0.161 -0.010 -0.006 0.001
Lolium perenne 0.048 0.238 0.457 -0.029 -0.009 0.019 0.226 0.278 0.336 -0.022 -0.018 -0.012
Hordeum secalinum 0.004 0.114 0.455 -0.017 0.007 0.052 0.167 0.247 0.346 -0.022 -0.014 -0.002
Carex divisa 0.004 0.086 0.284 -0.008 0.024 0.054 0.063 0.108 0.168 -0.006 0.002 0.012
Poa trivialis 0.003 0.066 0.365 -0.019 0.012 0.056 0.112 0.194 0.308 -0.019 -0.008 0.010
Bioscience – Aarhus University
Elasticity along a water gradient
Abundance Elasticity
p :0.90.50.10.01
Bioscience – Aarhus University
Elasticity along a water gradient
Abundance Elasticity
Bioscience – Aarhus University
Demography and the niche
Results support the hypothesis that colonization has a predominant role for determining the ecological success along a hydrological gradient compared to survivalConnection between the Hutchinson realized niche and demography Maguire (1973)
Results suggests that it may be possible to predict the realized niche of different species from demographic studies