Valentin Cabon, Hervé Quénol, Benoît Deletre, Louis Copin, Vincent Dubreuil, Benjamin Bergerot
This is a plain language summary of a Functional Ecology research article which can be found here.
In cities, the climate varies from the countryside to the centre, with temperature inside the city often higher on average, a phenomenon called the urban heat island (UHI) effect. Temperature variations at the scale of an entire city, or at the scale of a microhabitat can affect urban-dwelling animals. Among them, arthropods are likely to be strongly impacted by urban heat islands, since their bodies rely on external temperatures. Body size is a widely used metric to study how animals react to temperature change. Arthropods harbour highly diversified ecological strategies and the way temperature affects them may depend on characteristics such as mobility or development time. Therefore, comparing size-temperature relationships among species belonging to a specific arthropod group could help to predict which species may be particularly impacted by climate change based on their ecological characteristics.
To find out how body size relates to urban temperature and compare relationships among several species, we measured the size of 2283 spiders captured on 36 grasslands with varying heat levels in Rennes (France). The tested spiders belonged to 11 common species, with contrasting ecological characteristics. We found that two spider species were impacted by temperature: Pardosa prativaga was positively linked to UHI and Pardosa pullata negatively to the microhabitat temperature, whereas no clear relationships were observed in other species. These two spiders shared the particularity to belong to the wolf spider family (Lycosidae) and were characterised by large bodies (relative to the other tested species), limited dispersal capacities and a single generation per year. We also noticed that male and female spiders reacted differently to heat, with only females being affected. Our results therefore suggest that bigger spiders that are less mobile and have only one generation per year are more sensitive to warming than smaller spiders that can travel long distance through the air (ballooning) and have shorter generation times.
These findings suggest that accounting for the ecological characteristics of species from species-rich arthropod groups is important to understand how they are affected by a changing climate. This information could be crucial for understanding how other arthropods might change as cities get warmer.
Functional Ecology: Plain Language Summaries 