Land snail communities respond to control of invasive rats in New Zealand forests

Abstract

While invasive rats are demonstrably inimical to indigenous vertebrate species, there has not been unequivocal evidence of benefit to invertebrate communities from management of these invasive mammals in New Zealand forest systems. The present study examined the response of land snail communities to intensive management of ship and Norway rats by sampling paired rainforest blocks, one block of which had been subject to intensive management of rats, while the other block had been without management of invasive rats and thus subject to ambient rodent infestations. Rat tracking index data indicated rat management regimes were generally effective in reducing rat abundance relative to non-treated forest blocks. At the whole community level there was little evidence that forest management regime influenced the structure of land snail communities. However, when only the larger-shelled (≥4 mm maximum shell dimension) component of the communities was considered, strong effects of rat management regime were evident with increased land snail abundances, species richness and functional trait values. These results are discussed in relation to potential direct and indirect of effects of management regimes that reduce rat abundance.