In recent years, ecologists have begun to take a second look at plants and animals appearing in cities. There seems to be more ‘nature’ in urban areas than one would expect. Cities are supposed to be human territories—steel, brick and concrete—not exactly welcoming to wildlife. But urban places display a variety of species and habitats – biodiversity—in places we did not plan for them.
This makes us ask some questions:
Why are these plants and animals surviving in human settlements while others disappear? How and when did they move in? How many of them can survive in our cities?
Urbanized areas often share characteristics like:
- hard surfaces (roads, pavement)
- roads and buildings that break up natural, vegetated spaces
- bright light at night, loud sounds, water and soil pollution
All of these are known to make it difficult for ‘natural’ habitats to survive near cities.
But there are also ‘built’ green spaces like public parks and private gardens that cultivate a wide range of native and exotic plants. These can form the bases of food chains that attract consumers (like ants, grasshoppers, bees, beetle, squirrels) and their predators (lizards, birds, and monkeys), without our approval. If left uninterrupted, patches of wild ecosystems can be established within these built spaces.
But exactly which species of birds, bees and trees settle in cities? Where in a city are you more likely to come across wildlife? And, how come I can see kingfishers in one district but not another?
Another attribute of cities is the diversity of the habitats (or shelters) they can, unintentionally, form. Within one city, you can find
- abandoned lots-turned-grasslands
- old buildings that create dark and cool shelters
- long stretches of roadside vegetation
- food gardens
- golf courses
- remnant forests
Each of these will have unique structural features, creating different kinds of habitats.
For instance, reptiles that inhabit open spaces within their original forest habitats will probably adapt well to places in cities that have widely spaced trees and vegetation.
Wildflowers too benefit from the abundant sunlight and absence of competition (bigger plants) in urban patches. These are conditions not found beneath dense, natural forest canopies.
A more familiar example is the ubiquitous city pigeon. Have you ever wondered why this bird in particular flocks in cities worldwide? One reason might be the similarity between its original habitat – rocky cliffs – and the hard, ledged surfaces of city buildings that offer it space for nesting.
There is also another feature of cities that might be important for supporting biodiversity – the greater amount of food available. For species that are not very particular about their diet, gardens, cafeterias, litter, bird feeders, ornamental trees and nutrient-rich waterways offer abundant food resources.
So what does this mean for us?
One reason that ecologists are interested in urban wildlife is the benefits associated with biodiversity.
In natural ecosystems, there is abundant tree and vegetation cover, and processes like pollination, seed dispersal and decomposition that are carried out by large and small animals. All of these contribute services like food production, climate and water supply regulation.
These benefits (also known as ecosystem services) are important for us. If cities can support biodiversity, then they can help in species conservation and contribute these services that keep our environment healthy.
Urban biodiversity still poses many questions for ecologists to explore.
- How much green space is enough for biodiversity conservation?
- What ecosystem services can we expect from urban biodiversity?
- How are urban plants and animals different from those in natural habitats?
- How and why do biodiversity patterns vary among cities and geographical regions?
Answering these questions will take time and require that we pay closer attention to the other lives unfolding parallel to ours.
Resources for further reading:
Müller, N., Ignatieva, M., Nilon, C. H., Werner, P., & Zipperer, W. C. (2013). Patterns and trends in urban biodiversity and landscape design. In Urbanization, biodiversity and ecosystem services: Challenges and opportunities (pp. 123-174). Springer, Dordrecht.
Schilthuizen, M. (2019). Darwin comes to town: How the urban jungle drives evolution. Picador.