They identify which insects thrive and which recede in built-up areas

Currently in Europe, 17% of the land surface is urban areas that are home to 75% of the population, according to data from Eurostat and the OECD. Beyond the effects of urbanization on climate change, it also imbalances have occurred in terrestrial life, including the smallest invertebrates.

With this premise, researchers from Austria launched to investigate how urban ecosystems have altered biodiversity, focusing, in this case, on the arthropods, on which the success of other species located a few steps higher in the trophic chain depends, such as birds. The results of his study have been published in the journal Frontiers in Ecology and Evolution.

Thus, samples of arthropods were collected in 180 sites within an urban mosaic in the city of Innsbruck, Austria, and at each point insects were collected in three microhabitats: tree crown, bark, and shrub layer. Taking into account the level of urbanization in a radius of 100, 500 and 1,000 meters around the sampling locations, Abundance (how many arthropods), richness (how many different types) and diversity (all species) were analyzed.

Safe in the bark of trees

The investigation concluded that urbanization negatively affects both richness and diversity of arthropods, both in the tree canopy and shrub layerespecially in flightless species such as web spiders and springtails, which are often displaced by flightless ones.

Regarding the bark of the trees, no changes were detected as the level of urbanization increased, neither in richness nor in diversity.. The researchers explain this fact by saying that it is a part of the tree less exposed to solar radiation and, furthermore, it is a good refuge against the urban ‘heat island’ effect.

The study also points to a particular abundance of bark lice and crab spiders on shrubs, more intense in more built-up areas. “Shrubs in urban areas can be more productive, produce more nutritious leaves and support higher numbers of herbivores compared to the often light-limited understory in areas with greater tree cover,” the paper indicates. Other groups detected in greater quantities were aphids, mealybugs and flies.

Some species regress and others thrive

“This result strongly suggests that urbanization negatively affects flightless arthropods, while flying insects manage to colonize and thrive in urban areas. Habitat fragmentation in urban areas is undoubtedly the main driver of this filtering pattern, since species with low dispersal abilities (here without wings) can hardly colonize such habitats,” he continues.

The researchers conclude that this alteration in the presence of arthropods, key prey in the food chain for species at higher trophic levelscan mean a change in the foraging behavior of birds, which may be forced to change the diet or increase the search effort, with direct consequences on their nutritional status.

Reference study: https://www.frontiersin.org/articles/10.3389/fevo.2023.980387/full#h6