A pleasing consequence of Norway rat eradication: two shrew species recover

Abstract

Four to 10 years after the successful eradication of the Norway rat ( Rattus norvegicus ) from three islands of the Sept-Îles Archipelago and one in the Molène Archipelago (Brittany, France), the abundance index of the lesser white-toothed shrew ( Crocidura suaveolens ) increased by factors of 7-25, depending on the island and the year. Moreover, in the same region, the abundance index of the greater white-toothed shrew ( Crocidura russula ) on Tomé Island increased by factors of 9 and 17, one and two years after the Norway rat eradication, respectively.The maximum variation of the abundance index for the lesser white-toothed shrew during seven years on the rat-free island of Béniguet in the same region was a factor of only 2.5. Moreover, the distribution of the lesser white-toothed shrew on Bono island, restricted before the eradication to two steep areas with few rats, increased and encompassed virtually the entire island four years after rats disappeared.These results suggest strong detrimental interactions between the introduced Norway rat and the two Crocidura shrew species on temperate oceanic islands. However, our data do not indicate the ecological mechanisms at work in these interactions.The main reason this shrew recovery was detected after rat eradication was the inclusion in the eradication protocol of the evaluation of impacts on the local biota of eliminating alien species. The rigor of the sampling procedure was also crucial to this discovery. This example demonstrates that an eradication operation can be extremely useful for both scientists and managers if it is planned as a research project.

The relationships between Ixodes ricinus and small mammal species at the woodland–pasture interface

“…Questing tick distribution in the environment is the result of their location when they detached from hosts, of their survival capability, questing activity and lateral movements, although I. ricinus ticks are considered to move no more than a few meters (Gray 1985;Carroll and Schmidtmann 1996). The simultaneous observation of small mammals on the study sites led to an index of abundance rather small, but in accordance with the normal Xuctuation found in France (Le Louarn and Quéré 2003;Pascal et al 2005). Only one small mammal species, A. sylvaticus, used all three habitat types, woodland, hedgerow and grassland.…”

Review of negative effects of introduced rodents on small mammals on islands

“…Pre-to post-eradication changes in abundance provided evidence of R. rattus repression of the two Western Australian marsupials Bettongia lesueur (Boodie Island) and I. a. barrowensis (Middle Island) as well as the Anacapa deer mouse Peromyscus maniculatus anacapae of Anacapa Island, Southern California (Morris 2002;Gellerman 2007). Post-eradication expansion across entire islands strongly suggested that two species (C. suaveolens and B. lesueur) had been locally displaced by introduced Rattus species (Morris 2002; Pascal et al 2005). The possibility that C. suaveolens was actually absent from Les Mottes Islets (Brittany, France) and has recolonised from a neighbouring island since the eradication of R. norvegicus also supports this theory (Pascal et al 2005).…”

“…An increase in the abundance of C. suaveolens followed the eradication of R. norvegicus on four islands; three in the SeptÎles Archipelago and one in the Molène Archipelago (Brittany, France). Furthermore, the response to eradication can be separated from any effects of environmental variation by comparison to the population dynamics on rat-free Béniguet Island (Molène Archipelago) illustrating the value of comparative 'control' data (Pascal et al 2005). The repression of the dusky shrew S. monticolus was also lifted by the eradication of R. norvegicus on Langara Island, British Columbia (Canada).…”

“…Post-eradication expansion across entire islands strongly suggested that two species (C. suaveolens and B. lesueur) had been locally displaced by introduced Rattus species (Morris 2002; Pascal et al 2005). The possibility that C. suaveolens was actually absent from Les Mottes Islets (Brittany, France) and has recolonised from a neighbouring island since the eradication of R. norvegicus also supports this theory (Pascal et al 2005). Introduced rodent control programmes may also provide useful data as illustrated by the greater survival of the New Zealand long-tailed bat C. tuberculatus in R. rattuspoisoned colonies versus a control colony during a R. rattus irruption year.…”

Assessing range re-expansion and recolonization of human-impacted landscapes by threatened species: a case study of the otter (Lutra lutra) in Italy

“…A possible way to investigate these processes is by identifying spatio-temporal associations between species recolonization and decrease in human pressure, due to socioeconomic changes or conservation policies. At present, some studies document recolonizations by threatened species (Swenson et al 1998;Pacheco and McGregor 2004;Davies et al 2005;Pascal et al 2005), however, to our knowledge, no study has attempted to make a quantitative large-scale analysis of human impacts on species distribution at different times to investigate recolonization processes.…”