Effect of pest–management operations on the abundance and size–frequency distribution of the New Zealand endemic frogLeiopelma hochstetteri

Abstract

in New Zealand, introduced mammals, especially rats, have been considered a primary factor in the extinction of amphibians. Leiopelma hochstetteri is a riparian frog, and is the most widespread of the surviving species of native frogs in New Zealand. at present, all populations of this frog species coexist with introduced mammals, which in some cases have been subject to pest-management operations without monitoring the potential benefits or damage to the frogs. We investigated the influence of a 7-year rat management operation on frog abundance in the Waitakere Ranges, New Zealand. We identified which habitat characteristics had significant influence on frog abundance; confirmed that the study areas represented similar habitats both inside and outside the pest-managed area, and finally evaluated the effects of the pest-management activities. frog abundance was positively correlated with percentage area covered by boulders and percentage area covered by water. Since the study sites were similar in terms of those variables, we could make a reliable comparison of frog abundance in relation to pest management. Presence/absence of pest-management operations did not have any significant effect on frog abundance. Size-frequency distribution data suggest that there has been recruitment of young frogs both inside and outside pest-management areas in the past 7 years.

Habitat-use model for the New Zealand endemic frog Leiopelma hochstetteri

“…According to the New Zealand River Environment Classification (MfE 2004), the channels of erosive streams with volcanic acidic geology tend to be steep and covered by coarse substrates (i.e. boulders and cobbles); steep-sloped stream channels covered by coarse substrates have been found to be positively associated with frog abundance (Nájera-Hillman et al 2009a), and this study indicates that they are also positively associated with frog distribution. Furthermore, it has been noted that L. hochstetteri is vulnerable to any disturbance that affects substratum stability (Tessier et al 1991), particularly, severe storms that cause sudden flooding (McLennan 1985); streams with small catchment areas are less susceptible to flooding than those with large catchment areas (Gregory et al 1991).…”

“…ship rats) and disease (Towns & Daugherty 1994, Baber et al 2006, Bishop et al 2009). However, Nájera-Hillman et al (2009a) did not find conclusive evidence that ship rats are a threat, and, despite extensive surveys, the amphibian disease caused by the fungus Batrachochytrium dendrobatidis has not been detected in L. hochstetteri (Bishop et al 2009). …”

“…The abundance and distribution of Leiopelma hochstetteri in the Waitakere Ranges have been surveyed (Ziegler 1999, Bradfield 2005 and its habitat has been described as wet, alongside shaded streams and seepages (McLennan 1985, Bell et al 2004, where the species' abundance is positively associated with the amount of coarse substrates in the stream channel (Nájera-Hillman et al 2009a). However, the links between L. hochstetteri distribution and its habitat characteristics have not been quantitatively investigated.…”

Differential population responses of native and alien rodents to an invasive predator, habitat alteration and plant masting

“…Often, a non-native predator may interact with both non-native and native prey within an ecosystem [8]. In such a situation, predicting which type of prey will dominate following the removal of the non-native predator is crucial [8][9][10][11], because the response of the prey community to the predator removal is contextdependent [12][13][14]. Theoretical studies have indicated that eradicating non-native apex predators results in the outbreak of non-native prey and induces severe declines in native prey populations if the non-native prey are either superior competitors or are mesopredators of the native prey (termed the mesopredator release effect) [9].…”

Hochstetter's frog (Leiopelma hochstetteri) egg, mobile larvae and froglet development

“…al. 1991;Whitaker & Alspach 1999;Na´jera-Hillman et al 2009). Only a few surveys have included seeps and river banks (McLennan 1985), and no survey work has specifically targeted seeps and stream emergence sites.…”