Individual study: Interference competition between introduced black rats and endemic Galapagos rice rats
Harris D.B. & Macdonald D.W. (2007) Interference competition between introduced black rats and endemic Galapagos rice rats. Ecology, 88, 2330-2344
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Remove/control non-native mammals
A randomized, replicated, controlled, before-and-after study in 2002–2003 in arid shrubland on an island in Ecuador (Harris & Macdonald 2007) found that control of invasive black rats Rattus rattus reduced the rate of seasonal declines in the abundance of Santiago rice rats Nesoryzomys swarthi. Rice rat abundance declined in all sites regardless of black rat control (with control: from 11 to 8-9; without control: from 18-19 to 11-12 rats), but the rate of decline was slower in sites where black rats were controlled (data presented as statistical model outputs). The rate of immigrating female rice rats was higher where black rats were controlled (data presented as statistical model outputs). Black rat numbers decreased more in sites with black rat control (from 18 to 1 rat) compared to sites without black rat control (from 14 to 3 rats). Three sites were selected in Santiago Island, Galapagos. In each site, two trapping grids were set up (98 traps set in pairs at 30 m intervals), in one grid all black rats caught were euthanised and in the other black rats were released after capture. Six trapping sessions were carried out between December 2002 and September 2003 in which each site was trapped for five nights. Additional trapping was conducted 8–10 days after the normal trapping to remove “immigrant” black rats. Supplementary food (5 kg of rolled oats, 750 ml of vegetable oil and 600 g of peanut butter) was distributed in each site every six days.
(Summarised by Ricardo Rocha)