Abstract
On large inhabited islands where complete eradication of alien invasive rodents through the use of poison delivery is often not practical or acceptable, mechanical trapping may represent the only viable option to reduce their impact in areas of high biodiversity value. However, the feasibility of sustained rodent control by trapping remains uncertain under realistic operational constraints. This study aimed to assess the effectiveness of non-toxic rat control strategies through a combination of lethal and live-trapping experiments, and scenario modelling, using the example of a remote montane rainforest of New Caledonia. Rat densities, estimated with spatially-explicit capture-recapture models, fluctuated seasonally (9.5–33.6 ind.ha-1). Capture probability (.01–.25) and home range sizes (HR95, .23–.75 ha) varied greatly according to trapping session, age class, sex and species. Controlling rats through the use of lethal trapping allowed maintaining rat densities at ca. 8 ind.ha-1 over a seven-month period in a 5.5-ha montane forest. Simulation models based on field parameter estimates over a 200-ha pilot management area indicated that without any financial and social constraints, trapping grids with the finest mesh sizes achieved cumulative capture probabilities > .90 after 15 trapping days, but were difficult to implement and sustain with the local workforce. We evaluated the costs and effectiveness of alternative trapping strategies taking into account the prevailing set of local constraints, and identified those that were likely to be successful. Scenario modelling, informed by trapping experiments, is a flexible tool for informing the design of sustainable control programs of island-invasive rodent populations, under idiosyncratic local circumstances.
Highlights
Human activities, such as agriculture and international trade, modify habitats and disturb the composition, richness and diversity of animal and plant communities (Garrott et al 1993; Vitousek et al 1997)
0 0 probability of capture g0 was significantly lower for adult male R. rattus and higher for juvenile R. rattus than for R. exulans, whereas there was no significant difference in g0 between adult female R. rattus and R. exulans (Table 3)
This study demonstrates that mechanical trapping can help maintain rat densities at low levels on a 5.5-ha area despite challenging environmental, logistical and social conditions
Summary
Human activities, such as agriculture and international trade, modify habitats and disturb the composition, richness and diversity of animal and plant communities (Garrott et al 1993; Vitousek et al 1997). Alien invasive mammals cause detrimental ecological effects on native taxa through predation, competition and spread of diseases (Garrott et al 1993; Towns et al 2006; Wäber et al 2013; Medina et al 2014; Lieury et al 2015), and further alter ecosystem structure and functions through trophic cascades (Chollet and Martin 2013; Thoresen et al 2017). In areas where complete removal of invasive mammals is not feasible or appropriate due to technical, social or ethical issues, the permanent control of their populations is a widely used approach to restore degraded ecosystems (Goodrich and Buskirk 1995; Doherty and Ritchie 2017; Lambin et al 2020) and has proven successful in enhancing the recovery of a wide range of endangered taxa (Fletcher et al 2010; Smith et al 2010; Jones et al 2016). A fundamental applied question is how to identify control strategies that deliver maximal benefits to biodiversity, while reducing reinvasion risks and operational costs (Doherty and Ritchie 2017)
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