Urbanisation drivers and underlying mechanisms of terrestrial insect diversity loss in cities

Abstract

1. Urbanisation is one of the main land-use changes behind global insect collapse. Despite that previous studies have described the negative effects of urbanisation on insect communities, so far there is no synthesis that considers multiple urban drivers, their combined effects, and the role of species traits altogether.2. Here we developed an integrative framework of the underlying mechanisms behind terrestrial insect species loss in cities by exploring five leading drivers: impervious surfaces, habitat fragmentation, urban heat island, pollution, and exotic plants. For each driver, we identified the main direct and indirect (mediated through species interactions or changes in resources) effects on insect populations and communities, emphasising the role of species traits as moderators of such effects.3. Body size, mobility, and oviposition/nesting requirements were the traits that frequently defined insect vulnerability to urban drivers. Urban heat island and pollution deserve further research from a community-level approach. Direct effects of drivers dominated the literature, while most indirect paths were mediated by changes in resources rather than species interactions.4. In conclusion, our review showed the challenges of recognising particular effects and mechanisms for each urban driver and their combined effects. By doing so, we intended to encourage researchers to address some of the gaps we noticed in order to fully understand how urbanisation is affecting insect communities. Finally, we outlined the main recent urban planning strategies and future challenges in order to successfully conserve urban insect biodiversity.

Differences in Life History Traits in Rural vs. Urban Populations of a Specialist Ground Beetle, Carabus convexus

“…Therefore, to preserve a self-sustaining population of the studied large sized, forest specialist species with limited dispersal power, adverse environmental changes by urbanization should be prevented or mitigated. To realize these goals, multi-scale greenspace planning and management schemes are needed [7,13].…”

“…Our results show that despite the higher fecundity of urban females, the studied ground beetle species had significantly lower abundance in urban forest fragments than in rural forest stands. Altered habitat characteristics, environmental parameters, fragmentation, and isolation effects by urbanization could be the main reasons for this low abundance [7,13,27]. Therefore, intense urban habitat management (frequent mowing, strong thinning and pruning, and removal of decaying wood) should be eased or abandoned.…”

“…Positive effects of adopting soft management practices on ground beetles are well documented [69]. Mitigating the effects of fragmentation and isolation, the maintenance and/or restoration of source habitats, and the preservation or creation of corridors or stepping stones are key issues for promoting species dispersal between urban fragments and species survival in these patches [7,13,70]. Thus, to conserve and restore biodiversity in urbanized areas, a holistic, multi-scale management and planning scheme is urgently needed [7,71].…”

“…Urbanization is a human niche-creating activity, resulting in land take, resource concentration, and modulated environmental and ecological processes, from climatic regimes [5] to hydrological cycles [6] and biodiversity [7]. Many of the resulting effects are, however, detrimental to humans, directly or indirectly, including deposition of pollutants [8], reducing biodiversity [9], and/or various biological processes, like decomposition [10] or gene flow [11].…”

Insect extinction: introduction to special issue

“…Rocha-Ortega et al (2021) analysed the literature to determine the extent of biases (including taxonomic and geographic biases) that inform our assessment of insect decline, and detail how just scattered insect records are. Similarly, Fenoglio et al (2021) carried out a systematic review and evaluated the drivers of insect diversity loss in urban settings via the scientific literature.…”