The effect of urbanisation on biodiversity in space and time

Urbanisation is one of the most pervasive forms of habitat change. More than half of the world’s human population now resides in urban areas, and urban land cover is projected to triple between 2000 and 2030. Anthropogenically-driven land conversion from a natural or semi-natural state to intensive agriculture and urban built environment poses a major threat not only to particular species, but also to biodiversity.

Anthropogenic land use varies considerably in time and space, making it a key challenge to account for both dimensions in our attempts to understand how biodiversity changes as a result of urbanisation. Urban sprawl typically results in habitat fragmentation at the transition zone between urban and rural areas. As this process unfolds, two competing forces are at play: habitat fragmentation makes populations less viable, potentially leading to extinctions that negatively impact biodiversity; conversely, the landscape becomes more diverse, potentially opening up new niches at the fringes of urban development. Later, habitat homogenisation through in-filling of previously spared tracts of land would be expected to decrease biodiversity. All these processes can vary in their speed and spatial extent, and can even be reversed if urban areas become depopulated.

Existing research on the relationship between biodiversity and urbanisation is inconclusive. A substantial body of work has suggested that urbanisation leads to biodiversity loss through biotic homogenisation of animal communities. Some of these studies provide evidence for a hump-shaped relationship with urbanisation. More recent work suggests that when green spaces are provided, cities, suburban areas and intensively cultivated rural land can host a considerable proportion of regional biodiversity. However, to date, research has focused on rural-urban gradients across space, with little consideration of changes over time. This is a critical knowledge gap, potentially leading to biases in the interpretation of previous results, especially if there is a time lag in the response of biodiversity to land use change. Moreover, previous studies have generally been conducted at small spatial scales, making it difficult to generalise observed relationships.
This project seeks to understand the relationship between biodiversity and urbanisation in space and time. The ultimate aim of this project is to develop quantitative methods that will transform the way we investigate the effect of urbanisation on biodiversity and provide the vital scientific information required to build cities that promote sustainable urban ecosystems.

Specifically, the project asks:

1) What are the characteristics of an urban habitat that can sustain high levels of biodiversity?

2) Is there a stage of urban sprawl at which biodiversity declines sharply?

3) How does the past ecological state (climatic, environmental, land use, species richness/evenness) of an area affect its capacity to buffer against urbanisation?

We will integrate bird biodiversity data collected over at least two decades in the US with environmental and land use data over the same time period. Both datasets are freely available for download, and demonstrates a number of characteristics of relevance for this project: the data cover an extremely large area (given the scale of the US) with large latitudinal and longitudinal gradients, and a substantial period of time during which significant urbanisation has taken place; further, the avian data are based on dense bird monitoring network that passes close to or through urban areas. We will model both temporal and spatial effects of urbanisation on biodiversity, largely using Bayesian models. This will allow us to fully characterise the roles of time, space and other explanatory variables, permitting future biodiversity projections and interpolations to non-censused areas. The project is in collaboration with Dr Clare Rowland, and expert in remote sensing, land-use data and urbanisation, at the Centre for Ecology and Hydrology.