Urban aliens and threatened near-naturals: Land-cover affects the species richness of alien- and threatened species in an urban-rural setting

Tanja K Petersen,James D M Speed,Vidar Grøtan,Gunnar Austrheim

doi:10.1038/s41598-020-65459-2

Abstract

Urbanisation has strong effects on biodiversity patterns, but impacts vary among species groups and across spatial scales. From a local biodiversity management perspective, a more general understanding of species richness across taxonomic groups is required. This study aims to investigate how fine-scale land-cover variables influence species richness patterns of locally threatened and alien species. The study was performed in Trondheim, Norway, covering a steep urbanisation gradient. Spatially correlated Generalised Linear Mixed Effects Models predicting the number of all-, threatened-and alien species by taxon, habitat, habitat heterogeneity and mean aspect within 500 m×500 m grid cells were constructed. The habitat categories were based on detailed land-cover maps. The highest number of threatened species was found in habitats relatively less affected by humans, whereas the number of alien species were only dependent on taxonomic group and spatial correlation. It is shown that land-cover variables within an administrative border can be used to make predictions on species richness within overarching species groups. Recommendations to biodiversity management agencies are to ensure protection of natural habitats to favour locally threatened species, and closely monitor urban areas to mitigate the introduction and spread of alien species.

Highlights

Urbanisation has strong effects on biodiversity patterns, but impacts vary among species groups and across spatial scales
We did so by constructing spatially correlated Generalised Linear Mixed Effects Models based on habitat, habitat heterogeneity, aspect and taxonomic group within 500 m × 500 m grid cells across the Trondheim municipality, selecting the best models based on ∆AIC
Overall, threatened- and alien species richness are not determined by the same land-cover variables

Summary

Introduction

Urbanisation has strong effects on biodiversity patterns, but impacts vary among species groups and across spatial scales. This study aims to investigate how finescale land-cover variables influence species richness patterns of locally threatened and alien species. The highest number of threatened species was found in habitats relatively less affected by humans, whereas the number of alien species were only dependent on taxonomic group and spatial correlation. Recommendations to biodiversity management agencies are to ensure protection of natural habitats to favour locally threatened species, and closely monitor urban areas to mitigate the introduction and spread of alien species. Cities are frequently located in biodiversity hotspots, and increases in urban areas inevitably will happen at the cost of other habitats important for biodiversity[3,4,5,6] This calls for studies detailing how to manage biodiversity efficiently and properly in urban areas. Knowledge of how broad land-cover variables affect the distribution and richness of these groups could help guide decisions on city development and biodiversity management on municipality level. Threatened and alien species have rarely been investigated simultaneously (but see Deutschewitz et al (2003)[29], Kühn et al (2004)[16] and Matthies et al (2017)[30]

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Discussion

Conclusion