Modelling Endemic and Invasive Species' Biodiversity Corridors in the Southern North Island of Aotearoa New Zealand

Abstract

<p>Habitat loss and invasive species threaten endemic species and the habitats they maintain. Landscape corridors or ecological corridors are strips of vegetation that provide an opportunity to preserve endemic populations by connecting habitats which may be too small on their own to sustain a population and/or by promoting exchange of individuals and their genes which can help maintain overall genetic diversity and population health. Corridor mapping can also improve our understanding of invasive predator pathways and may allow for more efficient control. Finally, corridors can be designed to contribute towards ecosystem services that may make their construction more appealing to landholders. However, restoration with the goal of improving connectivity for native species has not been well evaluated for its impacts on invasive species or ecosystem services. Agricultural regions provide an opportunity to coordinate corridors through restoration, as these regions often contain piecemeal strips of marginal land. In this study, connectivity for multiple species in the Greater Wellington region of New Zealand was evaluated using connectivity models via Linkage Mapper opensource software. I posed three questions: (1) What are the baseline corridors and relative connectivity for multiple species in the study region? (2) What is the relationship between endemic species corridors and those of invasive predators? (3) How does connectivity in the study region change following hypothetical stream restoration aimed at improving water quality? Current landscapes and future scenario landscapes were evaluated for their potential to provide corridors based on known and inferred behaviours of species with contrasting dispersal abilities, represented by ngahere gecko (Mokopirirakau “southern North Island”) rifleman/tītipounamu (Acanthisitta chloris), kākā (Nestor meridionalis), and common brushtail possum (Trichosurus vulpecula). Corridors were successfully modelled in the landscape for all species. Ngahere gecko and tītipounamu exhibited limited presence of corridors that would enable them to traverse between areas of available and protected habitat. Kākā and brushtail possum showed extensive corridors that were concentrated along waterways but spanned the study region. The relationships between corridors for endemic species and invasive predators show there is a convergent spatial relationship between the two. Furthermore, following hypothetical restoration of streams within our modelling software specific responses by our study species were found. Ngahere gecko and tītipounamu showed improved connectivity throughout the region while kākā and brushtail possum had little change in connectivity under the stream restoration scenario. This knowledge may contribute towards more efficient predator control throughout the region as well as improved restoration design.</p>

Improving Urban Habitat Connectivity for Native Birds: Using Least-Cost Path Analyses to Design Urban Green Infrastructure Networks

“…The four study species have no established resistance values for different landscape elements. Therefore, the resistance values were approximated based on previous Linkage Mapper research for other native bird species [67]; the presence and distribution of the study species in central Wellington from the government-funded international database Global Biodiversity Information Facility (GBIF) [60][61][62][63]; and descriptions of their size, flight patterns, and habitat preferences [50][51][52][53][54] (Table 1). The landscape features included in the resistance rasters for the four study species were ground elevation, roads, and land cover (Figure 3).…”

“…Habitat needs and preferences are species-specific; therefore, land cover is important to consider in least-cost analyses because habitat type can significantly impact how easy or difficult it is to transverse landscapes based on the resources and risks they contain [82,83]. The land cover raster was created using the New Zealand Land Cover Database version 5.0 [64], which is the standard national land cover file used in ecological and habitat connectivity research in Aotearoa New Zealand, including in key references used to determine species resistance values for this research [47,51,67]. The land cover file was cross-checked with site visits to improve its accuracy.…”

“…There are a few examples where Linkage Mapper has been used to identify important ecological corridors [33,34], including two examples where it was used specifically for native Aotearoa New Zealand bird species [67,89]. However, this is the first study to use Linkage Mapper to design an urban green roof network and assess its impact on species dispersal.…”