Urban colonies are less aggressive but forage more than their forest counterparts in the ant Temnothorax nylanderi
L Jacquier, M Molet, C Doums
Abstract
Urbanization imposes new constraints on organisms, leading to changes in various traits including behaviour. In particular, foraging and aggressive behaviours are often affected by urbanization. In eusocial species, behaviour can be defined at the individual level but also at the group level (colony), and only a few studies have investigated how urbanization may affect colony level behaviours. In this study, we compared the aggressive and foraging behaviours at the colony level between urban and forest populations of the ant species Temnothorax nylanderi. We collected colonies in three urban parks and in three forests. After acclimation to laboratory conditions, we investigated foraging traits (the mean number of foragers feeding on the food, the food discovery time and the number of food-to-nest trips) by introducing food in the foraging area. After the foraging experiment, the level of aggressiveness was measured for the same colonies by introducing the body of a frost-killed conspecific into the nest. We found no differences between urban and forest colonies for the mean number of foragers and the discovery time. However, we found that urban colonies performed more foraging trips than forest colonies and were less aggressive. Interestingly, foraging and aggressive behaviours were positively correlated in urban but not in forest colonies. This study is one of the few addressing the question of behavioural divergence at the group level in response to urbanization in ants. It corroborates what was found at the individual level in nonsocial species.
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