The timid invasion: behavioural adjustments and range expansion in a non-native rodent

Abstract

Animal behaviour can moderate biological invasion processes, and the native fauna's ability to adapt. The importance and nature of behavioural traits favouring colonization success remain debated. We investigated behavioural responses associated with risk-taking and exploration, both in non-native bank voles ( Myodes glareolus , N = 225) accidentally introduced to Ireland a century ago, and in native wood mice ( Apodemus sylvaticus , N = 189), that decline in numbers with vole expansion. We repeatedly sampled behavioural responses in three colonization zones: established bank vole populations for greater than 80 years (2 sites), expansion edge vole populations present for 1–4 years (4) and pre-arrival (2). All zones were occupied by wood mice. Individuals of both species varied consistently in risk-taking and exploration. Mice had not adjusted their behaviour to the presence of non-native voles, as it did not differ between the zones. Male voles at the expansion edge were initially more risk-averse but habituated faster to repeated testing, compared to voles in the established population. Results thus indicate spatial sorting for risk-taking propensity along the expansion edge in the dispersing sex. In non-native prey species the ability to develop risk-averse phenotypes may thus represent a fundamental component for range expansions.

Flexible males, proactive females: personality tests show increased boldness/exploration in colonists damping with time in males but not in females

“…These results are consistent with our predictions and support boldness/exploration syndrome as a specific trait of dispersers and colonists universal for many – though not all – species (Dingemanse et al 2003; Cote et al 2010a; Debeffe et al 2014; Liebl, Martin 2012, 2014; Chuang, Peterson 2016; Duckworth et al 2018), which, in midday gerbils, turned out to be a female-specific characteristic. The opposite pattern was found in the other study of colonizing rodents, the bank voles, where colonist males were shyer than residents, whereas females showed no differences (Eccard et al 2023). However, in that study, new colonies of ages 1-4 years were merged in a sample; therefore, short-term changes in behaviour post-colony establishment could be missed.…”

“…Unlike dispersal within a population range, colonization is typically associated with long-distance movements beyond the genetic neighbourhood and(or) population geographic range (Bartoń et al 2012; Jordano 2017) and often implies crossing the matrix in fragmented landscapes to settle in suitable but vacant from conspecifics habitats (Hanski 1994) – the gaps in the social landscape. Because in mammals, males and females differ in spatial behaviour and dispersal propensity, they may be exposed to differential selection pressures during the population expansion, producing sex-specific spatial sorting patterns in behavioural traits (Eccard et al 2023). For example, in bank voles, timid and risk-averse males were found at the edge of the expanding range, whereas females were not behaviourally sorted (Eccard et al 2023).…”

“…In gambusia ( Gambusia affinis ), the syndrome of correlated individually consistent traits supposed to be associated with the propensity and ability to disperse (general activity, exploration, and boldness) was not related to the dispersal distance (Cote et al 2010b). Real-time observations of invasive bank voles ( Myodes glareolus ) colonizing new areas during the ongoing range expansion in Ireland showed that males, the dispersing sex, were less bold at the expansion edge (Eccard et al 2023).…”

“…The inconsistencies in the results may be attributed to the lack of field studies of ongoing colonization processes observed in real time: very few studies investigated not only spatial variation in behavioural traits across expanding ranges but also the temporal dynamics of behavioural profiles post-colonization (see for example, Duckworth, Kruuk 2009; Eccard et al 2023). In the lack of direct observations in real time, the evidence for behavioural sorting during colonization remains equivocal.…”

“…In the lack of direct observations in real time, the evidence for behavioural sorting during colonization remains equivocal. Additionally, it is unclear which behavioural types are favourable in different spatial zones of expanding ranges and at different stages of colonization (Eccard et al 2023). Colonization begins with the arrival of the first colonists settling in the vacant area, settlers, followed by the flow of joiners, the immigrants from the core population (Clobert et al 2009; Cote et al 2010a).…”