Combined impacts of environmental degradation and changes in environmental variability on time to extinction
Habitat degradation and environmental variability have had strong impacts on ecosystems over the past century and these processes are projected to continue in the future. For example, tropical areas experienced high rates of deforestation over the past century, often leading to population declines, and also experienced hurricanes, events which are predicted to increase in intensity due to climate change. Some studies have looked at the separate effects of habitat degradation and environmental variability on populations, but few studies have examined these factors in combination. Understanding the joint effect of these forces is increasingly important, as our habitats are increasingly becoming degraded and the effects of climate change are strengthening.
To address the impact of the interaction between habitat degradation and increasing environmental variability on a populations’ time of extinction, we used a simulation-based approach to find the frequency of population extinction over a variety of habitat degradation and environmental stochasticity scenarios. We used declining birth rates and increasing death rates to model the effects of habitat degradation and looked at a variety of environmental variability scenarios, including uncorrelated and serially correlated environmental conditions. We explored each scenario over a variety of initial conditions, including different initial population sizes.
We found that the effects of habitat degradation and increased environmental variability led to more rapid population declines than either factor alone. Combining environmental variability and habitat degradation led to high frequencies of extinctions early on for populations starting at a low initial size, compared with a peak of extinctions shortly after by populations that started at an intermediate initial size. In all cases, populations starting at a small initial population size experienced higher extinction frequencies after shorter time periods than populations with larger initial sizes, which had more gradual tails of extinction frequencies throughout the remaining time of the simulation. This study provides new insight into the effects of multiple drivers on ecosystems today and in the future. The framework developed here is applicable to other systems to predict the impacts of various forms of habitat degradation paired with changing environmental variability.