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  -