How are birds communities structured in urban green areas : a perspective from Montréal island

Background/Question/Methods

Metacommunity concepts have been well documented and studied theoretically and through experiments. They have also been studied in natural systems as well, but to a lesser extent. However, few studies have studied how metacommunity theory applies in urban ecosystems. With the rapid expansion of cities around the globe, it becomes more and more important to address the impact of urbanization on species distribution and metacommunity theory could serve as a valuable framework to build upon. In addition, urban environments are surprisingly well adapted to study metacommunity empirically because of the fragmented nature of urban landscapes. As such, a better understanding of the structure of urban metacommunities could help provide insights for future conservation policies, management plans, and urban landscaping. The goal of this study is to understand how an urban metacommunity of resident passerine birds sampled in green zones (e.g. parks, conservation areas) in Montréal are structured by the environment (green zone area size, heat island, tree cover and building density), space (spatial eigenfunctions) and other factors affecting species co-distribution. More specifically, we focused on studying how the metacommunity structure differs between the mating and non-mating seasons. To analyze these data, we used joint species distribution models and variation partitioning.

Results/Conclusions

Although we expected dispersal to be higher in the non-breeding season since birds do not need to defend a territory, we found that, as a group, birds behave roughly the same way. However, the behaviour of some individual passerine bird species sometimes changes importantly between the breeding and non-breeding season. For example, during the non-breeding period, spatially structured environmental variables are important drivers structuring the distribution of red-winged blackbird (Agelaius phoeniceus) while during the breeding period the presence of other bird species seem to have a more important impact on the distribution of the red-winged blackbird. In addition, we also found that generalists and specialists bird species behave differently with regards to environment, space and the occurrence of other bird species. Generalists have greater amount of variance explained by spatial effects and co-distribution as opposed to specialists which tend to show stronger associations with environment and space. In addition of showing that recent development in metacommunity theory can directly be applied to learn more about urban ecosystems, the results we obtained have direct implications for understanding the underlying structure of metacommunities in an urban environment.