Abstract
Urbanisation is one of the most prominent examples of habitat loss caused by anthropogenic activities. The net migration of humans from rural to urbanised areas resulted in the rapid growth of cities, and the degradation of biodiversity in these landscapes, as well as ecosystem services. Nature in cities has become highly fragmented, is found in different sized patches of different habitat types, and is distributed throughout areas of intense urbanisation. Publicly accessible parks and private gardens are two common types of urban green spaces that serve various ecological and social purposes. Parks can take the form of large forest remnants, amenity areas, or a combination of the two, and provide habitat for urban species. Gardens are often smaller patches of habitat within residential properties; however, they cumulatively comprise a significant proportion of the total city area and green space. Compared to other countries, New Zealand has a high proportion of green spaces. Recognition of the need to increase this biodiversity within all aspects of urban green spaces will improve the future sustainability of cities globally. This study used invertebrates as bioindicator taxa as they are an important contributor to ecosystem functioning and represent a diverse and abundant taxonomic group that responds to the negative impacts of human activities.
The first aim of this research was to investigate factors influencing Coleoptera and invertebrate abundance, richness, and diversity present in parks situated across a gradient of urbanisation intensity. The surrounding level of urbanisation intensity was associated with a significant decline in Coleoptera and other invertebrate groups; Dunedin parks situated within higher levels of urbanisation intensity had lower levels of invertebrate richness and to some extent diversity compared to parks surrounded by lower levels of urbanisation intensity. Abundance of invertebrates did not differ between urbanisation level of parks. Richness and abundance of
invertebrates collected in lawns was highest in parks surrounded by lower urbanisation intensities. Additionally, the taxonomic richness of invertebrates in lawn-dominated parks was lower compared to shrub-dominated parks. Parks closer to an urban green space greater than 30 hectares showed increased abundance of invertebrate taxa sampled from lawns.
The second aim was to investigate factors influencing Coleoptera and invertebrates in private gardens in relation to the extent of native vegetation. Contrary to predictions, there was no relationship between the extent of native vegetation and Coleoptera or invertebrate richness, abundance, or diversity collected in lawn or shrub vegetation. Gardens are typically more species-rich in terms of vegetation than other urban green spaces. This diversity of vegetation present in gardens likely explains the lack of statistical significance between gardens dominated by native or non-native vegetation. The abundance of invertebrates found in lawns was highest when gardens were closest to a surrounding green space,
This study indicates that parks and gardens support important diversity of invertebrate taxa in cities. Diversity could be further supported by increasing resource and niche availability through the diversification of vegetation present within urban green spaces. The negative effects of urbanisation on invertebrates could be mitigated through future diversification of existing urban green spaces.