TY  - JOUR
A1  - Esther, Alexandra
A1  - Groeneveld, Jürgen
A1  - Enright, Neal J.
A1  - Miller, Ben P.
A1  - Lamont, Byron B.
A1  - Perry, George L. W.
A1  - Tietjen, Britta
A1  - Jeltsch, Florian
T1  - Low-dimensional trade-offs fail to explain richness and structure in species-rich plant communities
JF  - Theoretical ecology
N2  - Mathematical models and ecological theory suggest that low-dimensional life history trade-offs (i.e. negative correlation between two life history traits such as competition vs. colonisation) may potentially explain the maintenance of species diversity and community structure. In the absence of trade-offs, we would expect communities to be dominated by 'super-types' characterised by mainly positive trait expressions. However, it has proven difficult to find strong empirical evidence for such trade-offs in species-rich communities. We developed a spatially explicit, rule-based and individual-based stochastic model to explore the importance of low-dimensional trade-offs. This model simulates the community dynamics of 288 virtual plant functional types (PFTs), each of which is described by seven life history traits. We consider trait combinations that fit into the trade-off concept, as well as super-types with little or no energy constraints or resource limitations, and weak PFTs, which do not exploit resources efficiently. The model is parameterised using data from a fire-prone, species-rich Mediterranean-type shrubland in southwestern Australia. We performed an exclusion experiment, where we sequentially removed the strongest PFT in the simulation and studied the remaining communities. We analysed the impact of traits on performance of PFTs in the exclusion experiment with standard and boosted regression trees. Regression tree analysis of the simulation results showed that the trade-off concept is necessary for PFT viability in the case of weak trait expression combinations such as low seed production or small seeds. However, species richness and diversity can be high despite the presence of super-types. Furthermore, the exclusion of super-types does not necessarily lead to a large increase in PFT richness and diversity. We conclude that low-dimensional trade-offs do not provide explanations for multi-species co-existence contrary to the prediction of many conceptual models.
KW  - Plant diversity
KW  - Plant functional types
KW  - Co-existence
KW  - Spatially explicit model
KW  - Individual-based model
KW  - CART
KW  - Regression tree analysis
KW  - Boosted regression tree
Y1  - 2011
U6  - https://doi.org/10.1007/s12080-010-0092-y
SN  - 1874-1738
VL  - 4
IS  - 4
SP  - 495
EP  - 511
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Schiffers, Katja
A1  - Tielboerger, Katja
A1  - Tietjen, Britta
A1  - Jeltsch, Florian
T1  - Root plasticity buffers competition among plants  theory meets experimental data
JF  - Ecology : a publication of the Ecological Society of America
N2  - Morphological plasticity is a striking characteristic of plants in natural communities. In the context of foraging behavior particularly, root plasticity has been documented for numerous species. Root plasticity is known to mitigate competitive interactions by reducing the overlap of the individuals' rhizospheres. But despite its obvious effect on resource acquisition, plasticity has been generally neglected in previous empirical and theoretical studies estimating interaction intensity among plants. In this study, we developed a semi-mechanistic model that addresses this shortcoming by introducing the idea of compensatory growth into the classical-zone-of influence (ZOI) and field-of-neighborhood (FON) approaches. The model parameters describing the belowground plastic sphere of influence (PSI) were parameterized using data from an accompanying field experiment. Measurements of the uptake of a stable nutrient analogue at distinct distances to the neighboring plants showed that the study species responded plastically to belowground competition by avoiding overlap of individuals' rhizospheres. An unexpected finding was that the sphere of influence of the study species Bromus hordeaceus could be best described by a unimodal function of distance to the plant's center and not with a continuously decreasing function as commonly assumed. We employed the parameterized model to investigate the interplay between plasticity and two other important factors determining the intensity of competitive interactions: overall plant density and the distribution of individuals in space. The simulation results confirm that the reduction of competition intensity due to morphological plasticity strongly depends on the spatial structure of the competitive environment. We advocate the use of semi-mechanistic simulations that explicitly consider morphological plasticity to improve our mechanistic understanding of plant interactions.
KW  - Bromus hordeaceus
KW  - competition intensity
KW  - morphological plasticity
KW  - nutrient analogues
KW  - plant density
KW  - PSI (plastic sphere of influence)
KW  - zone-of-influence model
Y1  - 2011
SN  - 0012-9658
VL  - 92
IS  - 3
SP  - 610
EP  - 620
PB  - Wiley
CY  - Washington
ER  -