Trophic cascades following the loss of top predators have demonstrated that predators can control the distribution and abundance of primary producers in marine and terrestrial systems. However, the prevalence of top-down as opposed to bottom-up control is contested, even in the flagship systems with sea otters or wolves as top predators. Our ability to predict the impact of top predator declines/loss is remarkably poor, although the need to do so is great given the current biodiversity crisis. We use the only contemporary example of complete insectivorous bird loss (the island of Guam) to investigate the impact of top predator loss. We ask questions including: Can birds trigger a trophic cascade on a landscape-level? Are there characteristics that make this system resilient to trophic cascades?
Avian control of spider populations
One of the most dramatic and consistent impacts of bird loss or exclusion is an increase in spiders. We are exploring the mechanism for this increase, as well as the impact of birds on spider diversity, and the follow-on ecological impacts of increased spider abundances.