Figure 32.1 Rats, like mice, are commensal, literally meaning “eating at the
same table.” Photo by M. Berdoy.R
ats and miceprovide the best examples of com-
mensal living between rodent and human societies.
First, as notorious pests, rats and mice have a sig-
nificant impact on the world economy. As the archetype
of commensal rodents (fig. 32.1), they have contributed to
famines and continue to be responsible for the loss, through
feeding or destruction, of about one fifth of the world’s har-
vest. While their impact is most crippling in developing
countries (Singleton et al. 1999), rats and mice continue to
have an impact even in the world’s most industrial cities
(Sullivan 2004). In this chapter we will refer to populations
living in close association with humans as urbanor com-
mensalas distinct from fieldor feralpopulations. As suc-
cessful invaders, rats and mice can also have a significant
effect on endemic species from invertebrates to other mam-
mals and birds through direct predation, competition, and
by modifying the physical environment (Atkinson 1985,
1996; Jones et al. 1997; Dickman 1999).
The very aspects of their biology that make rats and mice
such successful species (and indeed, competitors) have also
contributed to their use as laboratory animals. The Norway
rat (Rattus norvegicus) was the first species to be domesti-
cated for mammalian research (in the early nineteenth cen-
tury) and the first rat and mouse inbred strains were estab-
lished at the turn of the twentieth century (Lindsey 1979;
Hedrich 2000). One century later, hundreds of inbred
strains (see http://www.informatics.jax.org)) have revolutionized
experimental biomedical science (Krinke 2000; Festing et al.
2002); rats and mice now constitute about 80% of the spe-
cies used in the laboratory (European Commission 2003).
Although the transgenics revolution is starting to blur this
distinction, mice have traditionally been the model of choice