Summary1. Network analyses provide insights into the diversity and complexity of ecological interactions and have motivated conclusions about community stability and co-evolution. However, biological traits and mechanisms such as chemical signals regulating the interactions between individual species -the microstructure of a network -are poorly understood. 2. We linked the responses of receivers (flower visitors) towards signals (flower scent) to the structure of a highly diverse natural flower-insect network. For each interaction, we define link temperature -a newly developed metric -as the deviation of the observed interaction strength from neutrality, assuming that animals randomly interact with flowers. 3. Link temperature was positively correlated to the specific visitors' responses to floral scents, experimentally examined in a mobile olfactometer. Thus, communication between plants and consumers via phytochemical signals reflects a significant part of the microstructure in a complex network. Negative as well as positive responses towards floral scents contributed to these results, where individual experience was important apart from innate behaviour. 4. Our results indicate that: (1) biological mechanisms have a profound impact on the microstructure of complex networks that underlies the outcome of aggregate statistics, and (2) floral scents act as a filter, promoting the visitation of some flower visitors, but also inhibiting the visitation of others.

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Citation: Hö cherl, N., and J. Tautz. 2015. Nesting behavior of the paper wasp Polistes dominula in Central Europe-a flexible system for expanding into new areas. Ecosphere 6(12):262. http://dx.doi.org/10.1890/ES15-00254.1Abstract. In North America, Polistes dominula causes a stir because it spreads very fast in this region upon its recent introduction. Many different explanations are presented in the literature why P. dominula is such a good invader. In Europe, the invasion of this species into northern regions is also on the rise. Since little is known about the nesting behavior of P. dominula in Central Europe, we investigated basic principles about nesting in Germany (latitude 498). We found out that foundress groups (one to four foundresses) and nests are smaller and that the nesting season is shorter than in other regions. The mean size of newly founded nests was 83 cells and we recorded an average length of nesting season of 4.6 months. The queens neither preferred single (54%) nor multiple founding (46%). The major benefit of multiple founding is an increased rate of survival. Only 47% of single-foundress colonies survived, whereas 100% of colonies that were built by more than two queens, survived. However, there was no impact of the number of foundresses on the productivity of colonies in terms of number of cells and pupae per nest. Furthermore, we observed that the length of the nesting season as well as the nest sizes varied greatly in three consecutive years depending on the climatic conditions of the preceding winter. These results imply that P. dominula is remarkably flexible and reacts very quickly to outside conditions. This adaptation could be one explanation for the rapid spread of this species into colder areas.

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Paper wasps, like Polistes dominula, are considered as primitively eusocial. Hence, they are often used as model species for studies about the evolution of eusociality and dominance hierarchies. However, our knowledge about basic physiological processes in these wasps remains limited. In particular, the thermoregulation of individual wasps in their natural habitat has not yet been investigated in detail. We conducted a comprehensive field study to test their ability to respond to external hazards with elevated thorax temperatures. We presented artificial threats by applying smoke or carbon dioxide simulating fire and predator attacks, respectively, and monitored the thorax temperature of wasps on the nest using infrared thermography. We found that P. dominula workers recognized smoke and CO2 and reacted almost instantaneously and simultaneously with an increase of their thorax temperature. The maximal thorax temperature was reached about 65 s after the application of both stressors, but subsequently, the wasps showed a different behaviour pattern. No rise of the thorax temperature was detectable after an air blast was applied or in wasps resting on the nest. These observations provide evidence that P. dominula is able to heat up its thorax and that thermoregulation is employed in escape and defence reactions. Additionally, we investigated the thorax temperatures of queens during dominance battles. We found that the thorax temperature of the dominant queens rose up to 5 °C compared to that of subordinate queens that attacked the former, suggesting that the dominant queen defends herself as well as her nest.