# Ecology and Diversity of Urban Drosophila Species Communities as Potential Indicators of Biodiversity Decline

## TL;DR

This study shows that urban fruit fly communities in Vienna have declined significantly over 30 years, with new invasive species replacing native ones, suggesting broader biodiversity loss in cities.

## Contribution

The study provides novel evidence of biodiversity decline in urban areas using Drosophila as an indicator and identifies two new species records for Austria.

## Key findings

- Species richness in Vienna's Drosophila communities has declined by over 50% compared to 30 years ago.
- Non-indigenous species like D. mercatorum are replacing formerly common native species in urban areas.
- D. mercatorum is highly synanthropic, thriving in urban areas with high impervious surfaces.

## Abstract

Understanding the impact of ecological factors on biodiversity is central in the context of accelerating climate change and biodiversity loss. Urban areas, as landscapes under particularly strong anthropogenic influence, are undergoing rapid ecological change, yet the consequences for urban biodiversity and ecosystem functioning remain poorly understood. In this study, we focused on fruit flies of the genus Drosophila—a diverse group of dipterans with variable ecological niches and degrees of synanthropy, i.e., the adaptation to human‐modified habitats. We investigated species composition and community ecology in the metropolitan area of Vienna, Austria. With the help of numerous citizen scientists, we have collected approximately 18,000 specimens through dense spatio‐temporal sampling both indoors and outdoors of human dwellings. A total of 13 Drosophila species were identified, with communities dominated by widespread cosmopolitan synanthropic species. Among these,
D. mercatorum
and
D. virilis
represent novel records for Austria. Comparisons to a previous study from more than 30 years ago revealed that the species richness in Vienna was more than 50% lower than before and showed that formerly common species were potentially replaced by non‐indigenous drosophilids (neobiota). We further assessed ecological niches by intersecting species abundance data with high‐dimensional, high‐resolution earth observation datasets, which revealed distinct ecological preferences among species. In particular, the neozoan
D. mercatorum
emerged as a highly synanthropic species, tightly confined to urban areas with high levels of imperviousness. In summary, our study underpins the versatility of the Drosophila system as an indicator of biodiversity loss in a rapidly changing world.

We investigated urban Drosophila communities in Vienna using ~18,000 specimens collected with citizen scientists, identifying 13 species including two new records for Austria (
D. mercatorum
and
D. virilis
). Compared to surveys 30 years ago, species richness has declined by more than 50%, with formerly common species replaced by neobiotic taxa. Linking species abundances to environmental data showed distinct ecological preferences, with
D. mercatorum
emerging as a highly synanthropic urban specialist, highlighting fruit flies as indicators of biodiversity turnover in cities.