Among-population variation in density and competitor dependence in amphibian populations

In the Anthropocene, understanding factors regulating natural populations is key to effective conservation, particularly in light of the sixth mass extinction. This study analyzed time series of Bufo bufo and Rana temporaria populations to assess how density dependence and competitor density dependence influence population growth. Data from 163 populations over 10-49 years were analyzed using state-space models. Density dependence emerged as an important driver of population dynamics, consistently negatively affecting population growth rates across both species, while competitor dependence was less important. The strength of density dependence varied strongly among populations. Density dependence was stronger in Rana temporaria than in Bufo bufo . Competitor dependence was highly variable (either absent, positive or negative). The findings highlight that density dependence plays an important role in population dynamics and that some, but not all, populations may be buffered against external stressors (e.g., pulse perturbations caused by pesticides). Conservation strategies should not simply assume that density dependence buffers populations against external stressors because it varies strongly among populations. Conservationists should embrace variation among populations, recognizing the unique characteristics of each population.