Time series analysis showing how different environmental conditions affect the interspecific interactions of Callosobruchus maculatus and Callosobruchus chinensis

Abstract

AbstractEnvironmental changes alter the strength of interspecific interactions. However, because it is difficult to quantify interaction strength, empirical evidence remains limited on the relationships among environmental change, interaction strength, and consequences on population dynamics. Here, we evaluated how the interactions of two species of Callosobruchus seed beetles changed with increasing the cage size of the experiments and then affected the coexistence period as a property of population dynamics. Specifically, competition experiments were conducted on Callosobruchus maculatus (C. maculatus) and Callosobruchus chinensis (C. chinensis) using cages of different sizes, which altered the density of adults. We focused on two modes of interspecific interactions between these two species: larval resource competition and adult reproductive interference. Convergent cross mapping (CCM) was implemented to the experimental time series of the two species to assess how environmental change altered their interaction strength and the coexistence period (as a proxy of population dynamics). In most replications, C. maculatus persisted, whereas C. chinensis became extinct. The coexistence periods were longer with increasing cage size. However, there was no statistically significant relationship between cage size and interaction strength. Nevertheless, the stronger (or weaker) interaction strength of the competitively inferior (superior) species on competitively superior (inferior) was associated with longer coexistence periods. Overall, this study demonstrated that interaction strength affected population dynamics; however, changing interaction strength by altering environmental conditions did not necessarily mean that increasing habitat size reduces competition strength.