Assistant Professor Kansas State University, United States
Abstract: The direction and magnitude of species interaction effects on populations can be highly variable across space and time, a phenomenon generally known as context dependence. However, little is known about what causes context dependence or how context dependence varies among species. Understanding whether species exhibit similar context dependence and why is critically important to predicting how communities might respond to changes in abiotic drivers. Here, we use data from the Konza Prairie Long Term Ecological Research site to compare the magnitude and direction of context dependence in 13 forb species. Namely, we use density structured population models parameterized with multinomial logistic regression models to quantify the response of populations to bison across two types of abiotic gradients: weather condition and fire return interval (FRI). We find that most species (8/13) exhibit significant context dependence across weather conditions, but the direction of this effect varied dramatically among species. Namely, for some species bison effect on populations was higher in hot and dry conditions than in cool and wet conditions, but for others, the opposite was true. By contrast, all species exhibit significant context dependence across FRI gradients, with the direction of this effect consistent across all species; namely, bison effect was always highest at annual FRIs (rather than 4 or 20 year FRIs). Our results suggest that for some types of abiotic gradients (e.g., weather), the presence and direction of context dependence are inconsistent among species but for other types of abiotic gradients (e.g., FRI), context dependence varies little among species. Further, our results suggest that context dependence could be a key (yet underappreciated) driver of why herbivore effects on diversity and richness change across abiotic stress gradients.