Direct and indirect effects of rats: does rat eradication restore ecosystem functioning of New Zealand seabird islands?

Abstract

Introduced rats (Rattus spp.) can affect island vegetation structure and ecosystem functioning, both directly and indirectly (through the reduction of seabird populations). The extent to which structure and function of islands where rats have been eradicated will converge on uninvaded islands remains unclear. We compared three groups of islands in New Zealand: islands never invaded by rats, islands with rats, and islands on which rats have been controlled. Differences between island groups in soil and leaf chemistry and leaf production were largely explained by burrow densities. Community structure of woody seedlings differed by rat history and burrow density. Plots on islands with high seabird densities had the most non-native plant species. Since most impacts of rats were mediated through seabird density, the removal of rats without seabird recolonization is unlikely to result in a reversal of these processes. Even if seabirds return, a novel plant community may emerge.

Seabird islands take mere decades to recover following rat eradication

“…Although my present study focused only on islands previously invaded by R. exulans, evidence suggests the other invasive rat species have similar effects on island nutrient dynamics through their predation on seabirds (see Fukami et al 2006, Mulder et al 2009, Jones 2010. Thus, the island nutrient-recovery patterns investigated here are not unique to R. exulans and likely apply to all seabird islands that have been impacted by invasive rats.…”

“…1). Nine of the islands had rats removed between 12 and 22 years ago, another two continue to have rats (positive controls), and four islands have never had rats (controls [sensu Mulder et al 2009]; Table 1). Seabird effects to island nutrient dynamics are likely to diminish as island size increases but the chosen study islands are well within the range of seabird-influenced island size (Mulder et al 2011).…”

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

“…Not only do they have direct effects on other species, both as predators (e.g. [24]) and prey [52], but also through these strong direct effects they have cascading top-down indirect effects on other ecosystem components, such as invertebrates [53] and plants [54]. The magnitude of these indirect effects can also vary spatially [8].…”

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…With the strong climbing capabilities of R. rattus, few predators pose a greater threat to insular forest birds. Some seabirds are also at risk from R. rattus, particularly at the egg and chick life stages, yet many other vertebrate predators also threaten seabirds of all life stages and these other species can be more successful seabird predators than rats (see Mulder et al 2011).…”