Emerging infectious diseases threaten many wildlife populations, yet there is considerable variation in pathogen impacts both within and among species. Understanding this variability is key to identifying where and when pathogens will have substantial effects. Here we use data on prevalence of the invasive pathogen Batrachochytrium dendrobatidis (Bd) in Australian frogs to test two predictions derived from the hypothesis that mismatches in host-pathogen thermal tolerances can explain prevalence patterns. We show that: 1) the slope of the relationship between Bd prevalence and temperature within host species transitions predictably from positive to increasingly negative as the host species’ thermal optima increases; and 2) among host species, mean Bd prevalence increases, peaks, and declines as the host species’ thermal optima increase. Both results align with theoretical expectations and suggest that mismatches in environmental tolerance between hosts and pathogens can explain much of the variation in pathogen impacts observed within and among species.

Phenotypic plasticity can mask population genetic differentiation, reducing the predictability of trait-environment relationships. In short-lived plants, reproductive traits may be more genetically determined due to their direct impact on fitness, whereas vegetative traits may show higher plasticity to buffer short-term perturbations. Combining a multi-treatment greenhouse experiment with global field observations for the short-lived Plantago lanceolata, we 1) disentangled the genetic and plastic responses of functional traits to a set of environmental drivers and 2) assessed the utility of trait-environment relationshisps inferred from observational data for predicting genetic differentiation. Reproductive traits showed distinct genetic differentiation that was highly predictable from observational data, but only when correcting traits for differences in their (labile) biomass component. Vegetative traits showed higher plasticity and contrasting genetic and plastic responses, leading to unpredictable trait patterns. Our study suggests that genetic differentiation may be inferred from observational data only for the traits most closely related with fitness.

Ecological processes often exhibit time lags. For plant invasions, lags of decades to centuries between species’ introduction and establishment in the wild (naturalisation) are common, leading to the idea of an invasion debt: accelerating rates of introduction result in an expanding pool of introduced species that will naturalise in the future. Here, I show how a concept from survival analysis, the hazard function, provides an intuitive way to understand and forecast time lags. For plant naturalisation, theoretical arguments predict that lags between introduction and naturalisation will have a unimodal distribution, and that increasing horticultural activity will cause the mean and variance of lag times to decline over time. These predictions were supported by data on introduction and naturalisation dates for plant species introduced to Britain. While increasing trade and horticultural activity can generate an invasion debt by accelerating introductions, the same processes could lower that debt by reducing lag times.