The occurrence of trophic cascades has become widely accepted in ecology. However, studies of trophic cascades have generally been limited to small spatiotemporal scales with small organisms conducive to manipulation. Evidence for trophic cascades involving large mammals over large spatiotemporal scales has been building over the last decade. We conducted a meta-analysis that included 9 studies with 15 individual datasets to determine whether predator extirpation could lead to recruitment gaps in browse-sensitive tree species. We included studies that quantitatively measured tree population age structure in a location from which large predators have been functionally reduced by human activity. Age class size should decrease exponentially with time since establishment, whereas we hypothesized smaller than expected age class sizes in decades without predators. We tested this hypothesis by using age class sizes before predator extirpation and an exponential model to estimate expected post-extirpation age class sizes. Decadal effect sizes were calculated by comparing observed and expected age class sizes using the log response ratioR = ln (observed/expected). We computed average decadal effect sizes before and after predator extirpation for 12 sites exposed to cervid browsing and 3 refugia sites.
Available at: http://works.bepress.com/thomas_rooney/100/