TY - JOUR A1 - Ehrlich, Elias A1 - Becks, Lutz A1 - Gaedke, Ursula T1 - Trait-fitness relationships determine how trade-off shapes affect species coexistence JF - Ecology : a publication of the Ecological Society of America N2 - Trade-offs between functional traits are ubiquitous in nature and can promote species coexistence depending on their shape. Classic theory predicts that convex trade-offs facilitate coexistence of specialized species with extreme trait values (extreme species) while concave trade-offs promote species with intermediate trait values (intermediate species). We show here that this prediction becomes insufficient when the traits translate non-linearly into fitness which frequently occurs in nature, e.g., an increasing length of spines reduces grazing losses only up to a certain threshold resulting in a saturating or sigmoid trait-fitness function. We present a novel, general approach to evaluate the effect of different trade-off shapes on species coexistence. We compare the trade-off curve to the invasion boundary of an intermediate species invading the two extreme species. At this boundary, the invasion fitness is zero. Thus, it separates trait combinations where invasion is or is not possible. The invasion boundary is calculated based on measurable trait-fitness relationships. If at least one of these relationships is not linear, the invasion boundary becomes non-linear, implying that convex and concave trade-offs not necessarily lead to different coexistence patterns. Therefore, we suggest a new ecological classification of trade-offs into extreme-favoring and intermediate-favoring which differs from a purely mathematical description of their shape. We apply our approach to a well-established model of an empirical predator-prey system with competing prey types facing a trade-off between edibility and half-saturation constant for nutrient uptake. We show that the survival of the intermediate prey depends on the convexity of the trade-off. Overall, our approach provides a general tool to make a priori predictions on the outcome of competition among species facing a common trade-off in dependence of the shape of the trade-off and the shape of the trait-fitness relationships. KW - coexistence KW - competition KW - fitness KW - functional traits KW - invasion boundary KW - neutrality KW - predator-prey model KW - shape KW - trade-offs Y1 - 2017 U6 - https://doi.org/10.1002/ecy.2047 SN - 0012-9658 SN - 1939-9170 VL - 98 SP - 3188 EP - 3198 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Seiler, Claudia A1 - van Velzen, Ellen A1 - Neu, Thomas R. A1 - Gaedke, Ursula A1 - Berendonk, Thomas U. A1 - Weitere, Markus T1 - Grazing resistance of bacterial biofilms: a matter of predators’ feeding trait JF - FEMS microbiology ecology N2 - Biofilm formation in bacteria is considered to be one strategy to avoid protozoan grazing. However, this assumption is largely based on experiments with suspension-feeding protozoans. Here we test the hypothesis that grazing resistance depends on both the grazers’ feeding trait and the bacterial phenotype, rather than being a general characteristic of bacterial biofilms. We combined batch experiments with mathematical modelling, considering the bacterium Pseudomonas putida and either a suspension-feeding (i.e. the ciliate Paramecium tetraurelia) or a surface-feeding grazer (i.e. the amoeba Acanthamoeba castellanii). We find that both plankton and biofilm phenotypes were consumed, when exposed to their specialised grazer, whereas the other phenotype remained grazing-resistant. This was consistently shown in two experiments (starting with either only planktonic bacteria or with additional pre-grown biofilms) and matches model predictions. In the experiments, the plankton feeder strongly stimulated the biofilm biomass. This stimulation of the resistant prey phenotype was not predicted by the model and it was not observed for the biofilm feeders, suggesting the existence of additional mechanisms that stimulate biofilm formation besides selective feeding. Overall, our results confirm our hypothesis that grazing resistance is a matter of the grazers’ trait (i.e. feeding type) rather than a biofilm-specific property. KW - protozoa KW - biofilm KW - plankton KW - predator-prey model KW - grazing defence KW - feeding trait Y1 - 2017 U6 - https://doi.org/10.1093/femsec/fix112 SN - 0168-6496 SN - 1574-6941 VL - 93 PB - Oxford Univ. Press CY - Oxford ER -