Humans usually assess things not according to their absolute value, but relative to reference points – a main tenant of Prospect Theory. For example, people rate a new salary relative to previous salaries and salaries of their peers, rather than absolute income. We demonstrate a similar effect in an insect: ants expecting to find low-quality food showed higher acceptance of medium-quality food than ants expecting medium quality, and vice versa for high expectations. Further experiments demonstrate that these contrast effects arise from cognitive rather than mere sensory or pre-cognitive perceptual causes. Social information gained inside the nest can also serve as a reference point: the quality of food received from other ants affected the perceived value of food found later. Value judgement is a key element in decision making, and thus relative value perception strongly influences which option is chosen and ultimately how all animals make decisions.

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In order to make effective collective decisions, ants lay pheromone trails to lead nest-mates to acceptable food sources. The strength of a trail informs other ants about the quality of a food source, allowing colonies to exploit the most profitable resources. However, recruiting too many ants to a single food source can lead to over-exploitation, queuing, and thus decreased food intake for the colony. The nonlinear nature of pheromonal recruitment can also lead colonies to become trapped in suboptimal decisions, if the environment changes. Negative feedback systems can ameliorate these problems. We investigated a potential source of negative feedback: whether the presence of nest-mates makes food sources more or less attractive. Lasius niger workers were trained to food sources of identical quality, scented with different odours. Ants fed alone at one odour. At the other odour ants fed either with other feeding nest-mates, or with dummy ants (black surface lipid-coated glass beads). Ants tended to avoid food sources at which other nest-mates were present. They also deposited less pheromone to occupied food sources, suggesting an active avoidance behaviour, and potentiating negative feedback. This effect may prevent crowding at a single food source when other profitable food sources are available elsewhere, leading to a higher collective food intake. It could also potentially protect colonies from becoming trapped in local feeding optima. However, ants did not avoid the food associated with dummy ants, suggesting that surface lipids and static visual cues alone may not be sufficient for nest-mate recognition in this context.

Plant-soil microbial interactions have moved into focus as an important mechanism for understanding plant coexistence and composition of communities. Both arbuscular mycorrhizal (AM) as well as other root endophytic fungi co-occur in plant roots, and therefore have the potential to influence relative abundances of plant species in local assemblages. However, no study has experimentally examined how these key root endosymbiont groups might interact and affect plant community composition. Here, using an assemblage of five plant species in mesocosms in a fully factorial experiment, we added an assemblage of AM fungi and/or a mixture of root endophytic fungal isolates, all obtained from the same grassland field site. The results demonstrate that the AM fungi and root endophytes interact to affect plant community composition by changing relative species abundance, and consequently aboveground productivity. Our study highlights the need to explicitly consider interactions of root-inhabiting fungal groups in studies of plant assemblages.

Often, the first option is not the best. Self-control can allow humans and animals to improve resource intake under such conditions. Self-control in animals is often investigated using intertemporal choice tasks-choosing a smaller reward immediately or a larger reward after a delay. However, intertemporal choice tasks may underestimate self-control, as test subjects may not fully understand the task. Vertebrates show much greater apparent self-control in more natural foraging contexts and spatial discounting tasks than in intertemporal choice tasks. However, little is still known about self-control in invertebrates. Here, we investigate self-control in the black garden ant We confront individual workers with a spatial discounting task, offering a high-quality reward far from the nest and a poor-quality reward closer to the nest. Most ants (69%) successfully ignored the closer, poorer reward in favour of the further, better one. However, when both the far and the close rewards were of the same quality, most ants (83%) chose the closer feeder, indicating that the ants were indeed exercising self-control, as opposed to a fixation on an already known food source.