Introduction

Biological invasions—the establishment and spread of non-native species in new regions—is one of the greatest threats to the ecological security of the Great Lakes basin, which spans the United States and Canada.¹ The threat lies with the ability of a non-native introduced species to become invasive—to spread aggressively and cause undesirable impacts to the environment, economy, and human health.² However, not all non-native introduced species become invasive, at least not immediately. There can be a time lag between introduction, establishment, and harm, dictated by some local environmental condition (e.g., temperature or precipitation) that limits or suppresses the non-native species. When a shift in that environmental condition occurs, perhaps driven by changes in climate, nutrients, or water levels, a threshold may be breached, triggering an eruption in the once-inconspicuous (i.e., “sleeping”) non-native population. Once this biotic eruption has occurred, the newly invasive species may destabilize the local ecosystem, potentially even tipping an entire ecological system into an alternative state.³ Major changes or state shifts in ecosystems resulting from species invasions can undermine biodiversity, food, and economic security and even increase exposure to zoonotic diseases.⁴

The potential for non-native species to meet the “sleeper” definition is growing as climate change drives more frequent and intense fluctuations in weather events, thus providing conditions for these species to erupt. Consequently, management might require a new suite of special monitoring and response capabilities. However, the unpredictable nature of sleeper species makes it difficult for land and water resource managers to prioritize funds and conservation activities to predict and counter invasion potential. For instance, species introductions can occur in small batches and isolated areas, and species need time before they can establish populations large enough to be noticed.

Even if natural resource managers know that a non-native species is present, the complexity of how that species interacts with the environment makes it extremely difficult to pinpoint exactly how or when it may become invasive. Understanding what environmental factors currently suppress the species’ population would bring resource managers closer to identifying potential tipping points that would release the sleeper, enabling invasion (Fig. 1).⁵ This management complexity grows when also accounting for the variety of ways species are introduced to new regions.