Tests of emigration in small mammals under experimental conditions

Abstract

Holding animals in enclosures that block emigration causes demographic abnormalities called "fence effects." Experimenters have built exits that require animals to move through unfavorable conditions to leave enclosures. There are doubts about whether individuals that cross these challenging exits are true emigrants. We tested whether an exit that required house mice (Mus musculus) to swim through a water-filled trough was used only by mice triggered to emigrate from an experimental enclosure. Also, we examined the responses of mice to the availability of resources and the presence of conspecific adult animals in a small enclosure with an exit and in an enclosure made by joining two single enclosures. All mice left a barren enclosure within 12 h but no mice left during 7-day trials in a resource-rich enclosure during spring and summer. At the end of trials with repeated introduction of pairs of mice, about 85% of resident mice were the first mice added. Nearly all mice added later left the enclosure. A relatively constant number of mice became residents in small enclosures and about 2.3 times as many mice resided in double enclosures. Mice readily found and used exits when motivated to leave and did not accidentally pass through exits during routine exploration. Thus, mice that stayed in enclosures were not "fenced in" by the water-filled exit and exhibited residency as in nature. Tests of exits should give ecologists confidence that animals can display normal residency and emigration behaviors in experimental settings. The defense of resources by residents and the emigration of excess animals resulted in a consistent limit to the number of animals able to reside in enclosures.

Behavioral phenotyping of a murine model of Alzheimer’s disease in a seminaturalistic environment using RFID tracking

“…A total of 4 subdominant males (2 transgenic and 2 wild-type) and 1 wild-type female emigrated from the SNE. These animals were between 6 and 15 weeks of age, a time at which emigration in feral house mice has been previously described (Gerlach, 1996;Nelson, Johnson, Matter, & Mannan, 2002). The 35 mice that reached an age of 150 days comprised 11 wild-type and 6 transgenic females and 15 wild-type but only 3 transgenic males.…”

Linking habitat selection, emigration and population dynamics of freshwater fishes: a synthesis of ideas and approaches

“…Thus, emigration events are likely to occur when environments that lack adequate resources (or access thereof) trigger continued exploration until animals eventually emigrate from an area in search of suitable conditions elsewhere. Experiments with several different animals support this hypothesis (Matter et al 1989;Nelson et al 2002). Viewed in this way, the decision to stay in an area or emigrate represents two ends of a continuum of complementary behavioural responses that may be elicited from any individual of a mobile animal species in response to the adequacy of the site currently occupied.…”

“…In our model, individual differences in access to resources or changes in environmental or physiological requirements could elicit variation in movement among individuals from very limited to very mobile, thereby accounting for the wide variation in movement observed both within and among fish populations (Smithson & Johnston 1999;Gowan & Fausch 2002;Rodríguez 2002;Hilderbrand & Kershner 2004). Experiments with fishes and other animals demonstrating that individual emigrants readily become residents when needed resources are supplied and that residents become emigrants when resources are limited (Matter et al 1989;Nelson et al 2002), lend support to this inherent flexibility in switching between residency and emigratory behaviour. We hypothesise that emigration is primarily an adaptive response to the inadequacy of conditions at the site of residency, and other benefits of movement to species persistence (risk spreading, gene flow, colonisation of open habitat, rescue effect in metapopulations) accrue largely as a by-product of the movement resulting from habitat selection decisions as portrayed in our model.…”

Population dynamics of house mice without mammalian predators and competitors

“…Nelson et al (2002) found that adult male house mice emigrated from experimental enclosures at a higher rate than adult females. Other habitat differences between our study blocks do not explain mouse body size differences between QH and MH, as mice in QH did not differ significantly in size from mice in ML, and forest composition in the two blocks is similar.…”

“…Body size and restricted emigration may lead to a 'partial fence effect' Because rodent population density often increases when dispersal is prevented by a fence enclosing the population, dispersal is thought to be necessary for normal rodent population regulation ('fence effect'; Krebs et al 1969;Nelson et al 2002;Krebs 2013). It is likely that at least some mice could emigrate over the mammal-resistant fences surrounding the 17 ha Q block and the 3400 ha main Maungatautari reserve (which contained M block), as these fences were not designed to contain mammals but to exclude them (Day & MacGibbon 2007;Connolly et al 2009).…”