Bioscience – Aarhus University Measuring competitive interactions in natural plant populations Christian Damgaard Bioscience 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

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)

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  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: cover Y: vertical density P1: competitive growth P2: survival, establisment etc.

Bioscience – Aarhus University Plant cover and vertical density – model Competitive growth (P1): Y i = increasing function of X i * decreasing function of X j,k,… Survival and establishment (P2): X i,y+1 = increasing function of Y i,y * decreasing function of Y j,k,…,y

Bioscience – Aarhus University Plant cover and vertical density – model Competitive growth (P1): Survival and establishment (P2): Structural variation: for predictions Effect of environment:

Bioscience – Aarhus University The effect of glyphosate on the competitive interactions between Festuca ovina and Agrostis capillaris Christian Damgaard Beate Strandberg Solvejg K. Mathiassen Per Kudsk Aarhus University

Bioscience – Aarhus University Festuca ovina and Agrostis capillaris Festuca ovina (solid) Agrostis capillaris (stripped)

Bioscience – Aarhus University Estimating the competitive interactions

Bioscience – Aarhus University Marginal distribution of competition parameters Festuca ovinaAgrostis capillarisOther species Percent.2.5%50%97.5%2.5%50%97.5%2.5%50%97.5% Process equation 1 – during the growing season: c constant c slope Process equation 2 – among growing seasons: c constant c slope 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

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 method I.Effect of climate change (temperature, draught, C0 2 ), 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 Damgaard Department 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 EventDescriptionTransition probability X 1 :A t, A t+1 A plant species A was present in year t and was also present in year t+1p( s(z) + 1 ( 1 – s(z) ) c(z) ) X 2 :nA t,nA t+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) ) X 3 :A t,nA t+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) ) X 4 :nA t, A t+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

Bioscience – Aarhus University Demography along a flooding gradient Collaboration with Anne Bonis, Rennes Marais du Poitevin, France,

Bioscience – Aarhus University Species 2.5%50%97.5%2.5%50%97.5%2.5%50%97.5%2.5%50%97.5% Agrostis stolonifera Cynosurus cristatus Lolium perenne Hordeum secalinum Carex divisa Poa trivialis

Bioscience – Aarhus University Elasticity along a water gradient Abundance Elasticity p :

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 survival Connection 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