The Invasion Ecology of Sleeper Populations: Prevalence, Persistence, and Abrupt Shifts

Abstract

It is well established that nonnative species are a key driver of global environmental change, but much less is known about the underlying drivers of nonnative species outbreaks themselves. In the present article, we explore the concept and implications of nonnative sleeper populations in invasion dynamics. Such populations persist at low abundance for years or even decades—a period during which they often go undetected and have negligible impact—until they are triggered by an environmental factor to become highly abundant and disruptive. Population irruptions are commonly misinterpreted as a recent arrival of the nonnative species, but sleeper populations belie a more complex history of inconspicuous occurrence followed by an abrupt shift in abundance and ecological impact. In the present article, we identify mechanisms that can trigger their irruption, and the implications for invasive species risk assessment and management.

Reconstructing Bioinvasion Dynamics Through Micropaleontologic Analysis Highlights the Role of Temperature Change as a Driver of Alien Foraminifera Invasion

“…However, they did not develop dense populations for at least 50 years. Protracted lag times between initial introduction and population explosion have been reported for other marine alien species, such as the mussel Brachidontes pharaonis (Fischer, 1870) in the Mediterranean Sea (Rilov et al, 2004), the barnacle Austrominius modestus (Darwin, 1854) in the North Sea (Witte et al, 2010) and the cladoceran (water flea) Bythotrephes longimanus (Leydig, 1860) in Lake Mendoka, United States (Spear et al, 2020). Such delayed population outbreaks may be due to multiple independent introduction events occurring along time, that may enrich the population gene pool and provide genotypes more fit for the local conditions (Dlugosch and Parker, 2008;Handley et al, 2011), or to changes of the receiving environment (e.g., increased vulnerability, relaxation of biotic pressure, more favorable abiotic environment, etc.…”

“…This fact, however, might be considered realistic only if invaders spread and acclimate to new recipient environments fast enough to keep pace with climate change (Hiddink et al, 2012;Marras et al, 2015;Molinos et al, 2016). Based on a literature search and meta-analyses, Sorte et al (2010) estimated that the poleward shift of marine species in response to climate change happens at an average rate of ∼ 19 km yr −1 , which is an order of magnitude faster than the estimated range shift of terrestrial species. According to a recent species distribution model (Guastella et al, 2019), A. lobifera is spreading in the Mediterranean Sea at a rate of 13.2 km yr −1 .…”

Dynamics and predicted distribution of an irrupting ‘sleeper’ population: fallow deer in Tasmania

“…Non-native sleeper populations can remain at low abundance for decades before irrupting (Crooks 2005;Spear et al 2021). Until recent decades, fallow deer remained at relatively low abundance in Tasmania (<1% of estimated carrying capacity; Potts et al 2015).…”

“…Sleeper populations of introduced species can persist at low abundance for decades before being triggered by an environmental factor to become abundant and problematic (Spear et al 2021). Deer are among the most successful biological invaders globally (Clout, Russell 2008;Davis et al 2016), and six species established wild populations in Australia in the mid-1800s (Bentley 1998;Davis et al 2016).…”

“…During the past four decades, however, deer populations across Australia have increased substantially and now pose threats to conservation and agriculture (Davis et al 2016). These recent increases (e.g., Forsyth et al 2018) are characteristic of the irruptive dynamics that can occur when non-native species (Spear et al 2021), and ungulates specifically (Caughley 1970;Forsyth, Caley 2006), are introduced to new areas, released from predation, or favoured by environmental change.…”