Europe is increasingly urban, with roughly 17% of land classified as cities and urban areas housing about 75% of the population. As urban expansion reshapes climate and habitats, researchers warn that terrestrial life, including the smallest invertebrates, is shifting in response to these changes.
In light of this, Austrian researchers began exploring how urban ecosystems influence biodiversity, focusing on arthropods whose presence supports higher trophic levels, such as birds. The study was published in a peer-reviewed journal on the topic of ecology and evolution.
Fieldwork spanned 180 sites arranged in an urban mosaic around Innsbruck, Austria. At every site, insect sampling targeted three micro-habitats: the treetop, the bark, and the shrub layer. Researchers analyzed arthropod abundance, richness, and diversity across three urban radii—100, 500 and 1,000 meters—to determine how varying degrees of urbanization shape these communities.
Safe in the bark of trees
The study found that urbanization tends to reduce both the richness and diversity of arthropod communities in the tree canopy and the undergrowth. In particular, flightless species, including certain web spiders and bowtails, were often displaced as landscapes became more urbanized.
Urbanization affects different arthropods differently and is vividly captured in a photo credit: Urbanization affects different arthropods differently, Holger Kleine.
Regarding the tree bark, richness and diversity showed little change as urban pressure rose. Researchers attribute this stability to the bark’s relative shade and its role as a shield against the urban heat island effect, offering shelter where sun exposure is limited.
The study also noted higher abundances of bark lice and crab spiders in denser, vegetated pockets, particularly in more settled areas. Urban shrubs seemed to yield higher productivity, offering nutritious leaves and supporting more herbivores in settings with greater tree cover, compared with sun-limited substrates. Additional groups—aphids, mealybugs, and flies—also appeared in larger numbers.
Some species regress and others develop
The findings suggest that while urban environments suppress flightless arthropods, flying insects can colonize and thrive in cities. Fragmentation of habitat within urban matrices acts as a key driver behind this selective process, since organisms with limited dispersal abilities struggle to reach and establish in such fragmented spaces.
A butterfly photograph marks another visual reminder of urban biodiversity patterns.
The researchers conclude that shifts in arthropod availability, which form the backbone of many food webs, could alter how higher-tister species forage. Birds, for instance, may adjust their diets or search more widely for food, potentially impacting their nutritional status and foraging strategies in urban landscapes.
The implications extend to urban planning and conservation, underscoring the need to preserve or create habitat features that support a broader range of arthropod life and, by extension, the wildlife that depends on them for food.
Note on the research and sources: the study aligns with contemporary work in urban ecology and was published to share insights about how city life reshapes ecological networks. Ongoing investigations continue to refine our understanding of urban biodiversity and its cascading effects on ecosystem services.
Marked in Ecology and Evolution, 2023, study on urban effects on arthropod biodiversity and trophic interactions. Additional discussion and data interpretations are available through scholarly summaries and science outreach materials.
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This article is intended for readers seeking an accessible overview of how urbanization can shift the balance of life at ground level and above, highlighting the resilience and vulnerabilities of different arthropod groups in city environments.