Urbanization has opposite effects on the predatory activity of birds, depending on the latitude of the cities, a new study in Ecology and Evolution finds. This information can be used for future predictions of crop pests and pest control. Environmental geographer Juan Antonio Hernández-Agüero co-authored the article.
Juan Antonio Hernández-Agüero and Inés María Alonso-Crespo (Leuphana Universität Lüneburg) selected forests near two cities with three degrees of latitude difference in Germany: Hamburg and Frankfurt. Their aim was to study how urbanization affects the way species interact with each other. Specifically, the researchers studied herbivory carried out by insects on beech leaves, and the predation of insectivorous birds on artificial caterpillars.
Opposite effects
Insectivorous birds attacked caterpillars placed in forests closer to the city of Frankfurt more than those placed in forests further away. However, in the city of Hamburg, with a higher latitude, the opposite happened: the most affected caterpillars were those closest to populated areas.
Environmental changes
According to the authors, these opposite effects can be explained by environmental changes because of urbanization. An example of this is the urban heat island, which causes cities to have higher temperatures than their non-urbanized environment. A higher temperature in lower latitudes (in this case Frankfurt) can cause lower survival of fauna than in natural areas. At higher latitudes (in this case Hamburg), the same environmental changes, with higher temperatures inside cities compared to surrounding areas, may be facilitating the presence of animals that would normally be forced to migrate or simply would not survive the low winter temperatures.
Herbivory
The researchers also studied herbivory by insects on beech leaves at different distances from the city centers of Hamburg and Frankfurt. Here, they found no effects of urbanization. They did, however, detect effects of latitude. There was a higher rate of herbivory at the lowest latitude (Frankfurt) than at the highest (Hamburg). More stable environmental conditions at lower latitudes, with more benign climatic conditions, facilitate the survival of greater biological diversity, which is ultimately reflected in greater herbivory.
Living laboratories
The climatic conditions of cities can serve as living laboratories of climate change. Due to the urban heat island effect, urban areas are currently experiencing temperatures similar to predicted future temperatures if climate change is not stopped. The results of the article, published in Ecology and Evolution, can therefore be used to predict the future of herbivory interactions (such as crop pests) and predation (such as pest control).