The luxury effect in urban aquatic ecosystems: exploring drivers of change

The ecological condition and biodiversity of urban ecosystems is influenced by multiple factors. In addition to environmental, socioeconomic processes, such as wealth, determines pollution, thus biodiversity in cities. Wealthier neighborhoods tend to have better ecological condition with higher biodiversity than less affluent neighborhoods, which is referred to as the Luxury Effect. Most often, household income is the single indicator of wealth in studies on the Luxury Effect. However, other socioeconomic factors, such as distribution of green spaces, can also affect ecological condition and biodiversity in cities. Evidence for the Luxury Effect comes primarily from studies in terrestrial ecosystems, while urban aquatic ecosystems are often overlooked. Here, we assess the effect of different wealth indicators (i.e. income and impervious area, which are related to placement of green spaces) on the biotic integrity and biodiversity of two aquatic taxa (macroinvertebrates, fishes) in urban streams in the Greater Toronto Area, Canada. We found that the relationship between wealth and biotic integrity / biodiversity change based on the wealth indicator and taxa considered. The biotic integrity and biodiversity of macroinvertebrate are negatively and often more strongly related to impervious area than income, while the biotic integrity and biodiversity of fish are positively related to income only. Our results suggest different mechanisms can determine the effect of wealth on biotic integrity and biodiversity, thus shaping the expression of the Luxury Effect. Understanding the mechanisms through which wealth influences aquatic biodiversity can allow us to advance towards management and planning decisions that acknowledges multiple socioeconomic realities within cities.