Dominant deer mice show the importance of abundance in competition

Detecting competitive interactions is important for predicting species responses to environmental change but remains challenging, especially over large scales. Modern coexistence theory predicts that reduced ecological trait overlap promotes coexistence through stabilizing mechanisms, while fitness differences generate competitive asymmetries. However, as an alternative to pure coexistence theory, dominant entities may emerge: highly abundant species with broad ecological tolerances and fast life history traits that override stabilizing mechanisms and dominate community dynamics. We tested these contrasting hypotheses in small mammal communities (n = 68 species) at 44 sites in 18 regions across the United States using the US National Ecological Observatory Network (NEON). We based inference on changes in abundance over time while accounting for weather and habitat factors using a dynamic generalized joint attribute modeling framework. Under the coexistence hypothesis, we predicted that pairwise interaction strengths inferred from our model would correlate with ecological and life history trait differences. Under the dominance hypothesis, we predicted that one (or a small set of) species would meet thresholds for dominance, including >50% of site abundance, ≥45% of total interaction strength, and also have disproportionately high numbers of strong competitive interactions. Predictions of competition based on coexistence theory were not well correlated with model results (mean correlation = 0.25, SE = 0.03), but we found more sites with dominant entities than were predicted by coexistence theory. In particular, compared with prediction from coexistence theory, our model identified three generalist Peromyscus species as the dominant entities at more sites (53.1% vs. 0%), associated with higher mean interaction strength at a site (58.0% [SE = 7.5%] vs. 13.8% [SE = 1.4%]), and a higher proportion of strong interactions with other species at a site (46.2% [SE = 4.4%] vs. 26.7% [SE = 1.7%]). Empirically inferred species interactions more closely matched large-scale observed abundance patterns than did coexistence theory predictions, underscoring the need to account for dominant entities and temporal changes in abundance when characterizing competitive interactions and predicting community responses to environmental change.

Duke Scholars

Author James S. Clark Environmental Natural Science