Urban pollinators: their ecology and conservation

In this project a multidisciplinary team of ecologists, conservation practitioners and taxonomists will use a systems approach to study the impact of land use change on pollinators. The mathematics that predicts the system’s response to change are models that predict the robustness of the community to environmental change. There are three stages to our research programme:

STAGE 1: While there is a growing appreciation of the value of urban habitats to pollinators, in reality we do not know their worth in comparison to other habitats. Here, we will sample replicate urban habitats, agro-ecosystems and nature reserves for pollinators and their interactions with plants. Our replicate networks will be used to identify the factors and processes that act as filters following land use changes due to urbanization.

STAGE 2: We will identify the hot spots of pollinator abundance and diversity in urban habitats by constructing spatially explicit plant-pollinator networks for four cities. We will combine these data with estimates of pollinator dispersal from the literature, this providing us with plant-pollinator meta-communities. We will then simulate the effect of habitat loss on these meta-communities.

STAGE 3: Working closely with our practitioner collaborators, we will add urban equivalents of the nectar mixes used in agri-environmental schemes to the four cities as pollinator conservation measure. We will use a stratified, randomized design with urban margins added to increasingly urbanized zones.

There are two schools of thought concerning the effect of urbanization on pollinating insects. On one hand, urbanization is considered to be one of the major causes of insect decline, in particular through the alteration of ecological features important to pollinators, such as food and nesting sites. On the other hand, some urban habitats are remarkably good for pollinators: 35% of hoverfly species known from the UK were recorded in a single garden in Leicester, and urban habitats are one of the few habitats where bumblebees are not declining.
Our research will start by asking where pollinators are found in the UK landscape, by comparing pollinator diversity in three habitats: cities, farmland and nature reserves. Rather than just counting species though, we will use a systems approach to study the network of interactions between plants and their pollinators, as these interactions have a profound impact on a community’s response to species loss, stress and ecological restoration.
In the second stage of the proposed research, we will look in detail at the pollinator fauna of four cities (Bristol, Reading, Leeds and Edinburgh), with the aim of quantifying the value for pollinators of various city habitats. While ecologists know a little about the value of urban gardens for pollinators, practically nothing is known about the value of industrial estates, school grounds, allotments, graveyards and the many other habitats found in cities. Our pilot data suggest that some habitats can be remarkably good for pollinators, or can be managed to be so. Again a network approach will be used, and the impact of change will be predicted using an entirely new mathematical tool – one which combines data on the network of interactions linking pollinators to flowers with data on meta-community ecology (how the whole system of local pollination networks responds to species loss and species dispersal).
In the final stage of our proposed research, we ask whether we can improve conditions for urban pollinators. We will use a large-scale field experiment, replicated in four cities, in which we will manipulate pollinator food supplies by introducing an urban version of the field margins sown with ‘nectar flower mixtures’ on farmland to conserve pollinators. Our plant mixes will be chosen to provide pollinator food, be low-maintenance, and look attractive to the human eye. Working with local professional conservation practitioners in each city (seven of these are named collaborators on the proposal), treatments will be implemented in a bold experimental design in four cities.

Provisional and unpublished conclusions:
1. Urban habitats support significant numbers of species and individuals of pollinating insects. For some groups - such as bees, numbers in urban habitats can match those in agricultural habitats and nature reserves.
2. Pollinator diversity is not uniformly distributed in urban habitats - richness and diversity are particularly high in allotments, gardens and cemeteries, and low over manmade surfaces and amenity grassland.
3. Planting of wildflower meadows in urban parks significantly elevates local pollinator richness and abundance in comparison to amenity grassland controls.