Conceptual figure illustrating three possible ways invasive species abundance could negatively correlate with changes in diversity. A At high abundance, invaders could cause declines in diversity over time. B At low invader abundance, diversity increases through natural processes, but at high abundance, invaders prevent arrival of new species. C A combined model, where richness increases in the absence of invaders and invader presence above a threshold causes declines in diversity over time. Note that these hypothesised relationships may not be linear but may include threshold processes.