Sex in the kitchen: non-additive effects of competition for food and reproductive interference on coexistence outcomes between sibling species

摘要: Competition for food and reproductive interference (negative interspecific sexual interactions) have been identified as major drivers of species exclusion. Still, how these biotic interactions jointly determine competitive dominance remains largely unknown. We tackle this by coupling population models and laboratory experiments with two spider mite sibling species. Using experiments specifically designed to measure the single and combined effects of food competition and reproductive interference, we first show that the strength and symmetry of reproductive interference between species changes in presence of food competition. Next, we show that population models incorporating each type of interaction alone or their effect when combined lead to markedly different predictions, from exclusion by one species or the other, to priority effects. Moreover, accounting for the non-additive effect of these interactions led to changes in the frequency threshold determining the dominant competitor, favouring the superior competitor for food. Finally, model predictions for short-term population dynamics were corroborated with an independent population cage experiment. Altogether, our results suggest that trophic and sexual interactions have non-additive effects that strongly impact population dynamics and competitive outcomes. Hence, the joint consideration of food competition and reproductive interference is critical to accurately predict and understand species coexistence.