Aquatic communities in urban microecosystems

More and more people live in cities and urban areas are growing. Still, a large number of animals and plants can live in cities, too. While many studies have investigated birds and plants in cities, we know very little about the species that live in urban waters. Especially small water systems such as water-filled tree holes, graveyard vases and flower pots in peoples gardens have rarely been studied. These communities in aquatic microecosystems in cities consist largely of insect larvae but we do not know what determines which species live there, what the influence of different degrees of urbanization are on these communities and on the functions they perform. These habitats also provide breeding sites for mosquitoes, some of which are invasive species and may carry diseases dangerous to humans. These aspects have been studied very little in European cities but with climate change and ongoing movement of goods and people, they may become very relevant. Here, we propose to study these aquatic microecosystems in urban areas in order to understand the structure, diversity, functions and ecosystem services and disservices of these systems and how they are affected by various aspects of urbanization. We will use methods established in previous projects to achieve these aims. In particular, we will survey the biodiversity living in water-filled tree holes, graveyard vases and other systems and measure decomposition and the output of insects. We will use stable isotopes to identify predators in the communities that may help to reduce mosquito numbers. In addition, we will install wildlife cameras to understand how birds and small mammals such as mice, martens and hedgehogs use water-filled microecosystems for drinking, bathing and feeding. We will run some of our projects as Citizen-Science projects where people will host aquatic microecosystems (graveyard vases) in their gardens. This will benefit the project because more data can be gathered. In addition, citizens will be involved in the scientific process, will learn about ecological communities in urban areas and will communicate this knowledge further. We will also collaborate with several colleagues to run a similar project using graveyard vases in different European cities (Munich, Zurich, London, Berlin, Vienna, Salzburg) to investigate if our results apply in larger cities with different climates. At the end of the project we will understand the diversity and functioning of communities in water-filled microecosystems better and will be able to predict how these communities are affected by further urbanization. The results are interesting to answer fundamental ecological questions regarding the coexistence of species and functioning of ecosystems. In addition, they will help to address more applied issues, such as the conservation of urban diversity and the biocontrol of potential disease-carrying species.

Many plant and animal species live in cities. The urban species richness can sometimes exceed the levels of biodiversity found in rural landscapes because some urban habitats, such as private gardens, can offer a range of different living conditions. Some of this urban biodiversity is relatively well known to people living in cities, e.g. people appreciate the bird communities in their gardens and parks. However, there is also a large part of urban biodiversity that is scientifically understudied and often very inconspicuous. In this project we investigated the freshwater insect communities of small aquatic habitats in cities. These habitats included natural waterfilled tree holes (they are called "phytotelmata", so waterfilled plant parts), that also occur outside cities, as well so-called "anthrotelmata", man-made structures such as buckets, flower vases and plant containers that fill up with water and offer fish-free living conditions for aquatic life stages of certain insect species such as beetles, midges and flies. With several sub-projects that also included Citizen Science aspects, we studied the diversity and factors that determine the structure of such aquatic insect communities in cities. We found that quite a lot of standing water is available in cities, depending on the cities' structure (e.g. private gardens vs. parks or inner-city areas) and that the habitats were colonized by a broad range of species in Salzburg but also in other European cities (and one Canadian city). Local factors such as food availability partly explained the abundance of insect larvae, but also larger-scale factors, such as indices that measure the strength of urbanization (imperviousness and human population density) affected insect community structure. We also specifically addressed mosquito communities and described some of the parameters that drive their larval abundances, in order to support the development of potential measures for their control. In a further sub-project, we studied other animals besides insects that may use these habitats temporarily and found that a large number of bird and mammal species use small aquatic habitats for drinking, bathing and also feeding. In an additional project we focused entirely on the bird communities in Salzburg and found that these were negatively influenced by building cover but positively by grass cover, the number of trees and number of native tree species, with certain bird species-specific responses. In conclusions, our study shows that urban biodiversity can be high, even in little known habitats such as man-made structures that harbour aquatic organisms, however, that many aspects of urbanization affect the diversity and structure of these communities. These results may also help to design and implement management strategies for urban biodiversity.