Population viability of a disturbance-dependent plant species in natural and human-induced environments
Many species are confronted with changes in natural disturbance regimes and the introduction of anthropogenic disturbances. Understanding how compounded, interactive effects of such disturbances affect population dynamics of disturbance-dependent species is a main priority of conservation biologists. Integral projection models (IPMs), which can explicitly incorporate covariates and their interactions into probability density functions of vital rates, offer a novel approach towards this priority. Here, we evaluated the demographic viability of an endemic carnivorous plant species for seven populations varying in time since last fire (TSF) and presence of large mammal herbivores (livestock). We parameterized IPMs based on three annual transitions, where survival, growth, reproduction, and seed-bank dynamics were quantified in situ. We estimated the stochastic population growth rate and stochastic elasticities associated with the interaction of livestock and TSF to examine the main drivers in the viability of this species.
Our results demonstrate that population dynamics in response to fire are significantly different under livestock presence than absence and suggest strong effects of compounded disturbances on population viability. Population growth rates decrease and risk of extinction increases with decreasing fire frequency in natural habitats. The opposite is true for human-induced habitats. Stochastic elasticities demonstrate that the relative contributions of vital rates to population growth rates differ between natural and human-induced habitats. The main differences can be attributed the relative roles of seed banks and above-ground individuals. We outline management options that can contribute to the persistence of disturbance-adapted plant species under variable disturbances.