The effects of housing density and the trade-off between housing density and sprawl area on breeding birds and carabid beetles

Given that urban populations are projected to increase well into the future, to be accompanied by rapid and dramatic changes to landscapes over broad spatial scales, an important question is how do we mitigate the impacts of this future growth on biodiversity? Specifically, how best can we accommodate a given human population in a given landscape to minimize its impacts on biodiversity? For a given human population, it is unclear whether the impacts on biodiversity are less where housing density is high and sprawl area is small or where housing density is low and sprawl area is large. In this thesis, I addressed the question 'at what housing density are the impacts of a given human population on biodiversity minimized?' using breeding birds (Chapter 1) and carabid beetles (Chapter 2). I empirically sampled both taxa in sites representing a gradient in housing density. I then estimated breeding bird and carabid beetle abundance and species richness in four hypothetical development scenarios representing the housing density/sprawl area trade-off: Undeveloped, Dispersed, Semi-compact and Compact. My results suggest that clustering development at a high housing density minimizes the impacts of a given human population on forest bird and forest beetle diversity. In Chapter 3, I used the empirical data I collected in the sites described above to determine if breeding bird responses to urbanization were indicative of those of carabid beetles. My results indicate that breeding birds and carabid beetles do not respond similarly to increasing housing density and I report novel patterns of response of the latter taxon to urbanization. The conservation implications of forest birds and forest beetles exhibiting high diversity in compact development are profound, particularly if all forest taxa share this response. If future development is compact rather than dispersed, the amount of habitat spared for forest taxa would potentially be enormous. Many questions in addition to those I addressed in this thesis remain to be answered in the field of urban ecology to further our understanding of the effects of urbanization and to identify the manner in which we may mitigate these effects on biological diversity.