Effects of urbanization on Arthropod communities

Feb 9, 2021   5:30pm IST

   As per the data collected in 2020, the human population is increasing at a rate of 1.05% and is estimated to increase by 81 million people per year [1]. In order to meet the needs of the ever-growing population, the forests and grasslands are being turned into fields and cities at an alarming rate. The current deforestation rate is estimated to be about 13 million hectares per year, and only half of this area is compensated by the growth of the new forest. This regular loss of flora and the conversion of wildlands into crop fields are two of the four major factors contributing to biodiversity loss along with habitat loss and habitat fragmentation.

Animals lose the natural habitat that they thrive in and it’s often noticed that the animal population gradually declines due to the shortage of flora that they are dependent on. Records of extinction due to deforestation are very rare since most of the smaller animals and plants have not been discovered and studied yet. Many plant and animal species have adapted to live in urban areas along with human civilizations, but not efficiently. Changes in habitat would affect their population rates, may trigger ecological disbalance, and eventually lead to an ecosystem collapse in the future.

Arthropods are one of the most diverse and abundant creatures that coexist with humans and urbanization has had significant effects on them.

The urban settlements consist of a collection of fragmented habitats ranging from parking lots to remnant patches of wildland and even your homes which are inhabited by a variety of these insects. Although some insects like ants started to flourish well in these heterogeneous urban habitats, most arthropod species are affected adversely by these rapid anthropogenic alterations.

Various studies have proven that the arthropod population, especially pollinators, declines with decreasing distance from a city center. It is observed that the flying arthropods have a significant drawback from tall buildings and urbanized lands. The skyscrapers prevent the movement of flying insects from one place to another and also prevent them from reaching flora which is essential for their survival. Urbanization has also affected and restricted their predation on other small animals [2].

Ground dwelling arthropods are also drastically affected by urbanization; with changes in landscape and fragmentation of their habitat, their feeding grounds get depleted. Thus, ground-dwelling arthropods are very rarely found in cities. After reaching a certain threshold of about 50-70% urbanization, a drastic decrease in ground-dwelling arthropods is observed. Various studies have shown that urbanization harms the dispersal of such flightless species. Forest specialist species in rural areas are being replaced by species that can thrive well in the changed conditions of urbanized lands.[3]

It is of great importance to understand that the stability of an ecosystem is highly dependent upon biodiversity. Therefore, an increasing rate of decline of species due to urbanization in a particular area is a major concern. However, it must also be understood that not all species are equally affected by these changing conditions. Where groups like Coleoptera (beetles) and Lepidoptera (butterflies and moths) are very critically affected, Hymenoptera (ants) and Araneae (spiders) thrive well in urbanized regions.[4]

These problems can be solved by early planning or slight changes in maps of cities or towns, or can even be implemented at an individual level. Some methods which have been experimentally proved to be beneficial for local flora and fauna in an urban settlement are:

• While planning the urbanized regions, it must be taken into account that the threshold (50-70%) should not be crossed.
• The quality of urban green spaces should be improved, which can be done by replacing piles of dead wood[5].
• Arthropods require litter to find their prey and hide from predators. Therefore, litter removal should be limited, and small litter patches can be kept to support the local diversity of organisms.
• Promote the dispersal of species- more corridors could be built in urban green networks which will allow species with low dispersal capabilities to reach green spaces and flourish.

References:

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1. Human population growth rate  
2. Lagucki, E., Burdine, J. D., & McCluney, K. E. (2017). Urbanization alters communities of flying arthropods in parks and gardens of a medium-sized city. PeerJ, 5, e3620.   
3. Vergnes, A., Pellissier, V., Lemperiere, G., Rollard, C., & Clergeau, P. (2014). Urban densification causes the decline of ground-dwelling arthropods. Biodiversity and Conservation, 23(8), 1859–1877.   
4. Ward, E. B., Doroski, D. A., Felson, A. J., Hallett, R. A., Oldfield, E. E., Kuebbing, S. E., & Bradford, M. A. (2021). Positive long‐term impacts of restoration on soils in an experimental urban forest. Ecological Applications, 31(5).   
5. Ward, E. B., Doroski, D. A., Felson, A. J., Hallett, R. A., Oldfield, E. E., Kuebbing, S. E., & Bradford, M. A. (2021). Positive long‐term impacts of restoration on soils in an experimental urban forest. Ecological Applications, 31(5).