Socio-ecological factors shaping mixed-species groups

Thesis

Understanding why individuals form groups that are strikingly diversein their organisation is a central focus in evolutionary ecology. Although mixed-species groups, where members of different species interact and move together, are common across animal taxa, inter-species interactions have often been a point of secondary interest in the study of animal sociality.Using mixed-species flocks of individually marked tits (Paridae) as a model system, I investigate how individuals make adaptive decisions in their multi-species social environment. First, I investigated the role of social information in facilitating mixed-species groups. I developed a frameworkthat is based on concepts of optimality to link processes of group formation to signalling theory and information use. I found that tits actively produce recruitment calls to form foraging flocks, but socialcontext mediates the strategies for recruiting group members (Chapter 2). Further, I showed that social information about food transmits through heterospecific social connections and that adaptive social learning strategies prevent birds from being trapped in maladaptive behaviour when wrong information is being provided (Chapter 3). In the second part of my thesis, I addressed whether flock formation is a result of preferential interspecies interactions. I found that active preference for foraging with heterospecifics can enhance social cohesion amongindividuals, which presumably provides members of mixed-species groups with additional social benefits to single-species grouping (Chapter 4). Separating the influence of spatial environmental patterns, such as resource distribution, from active social preferences is challenging, but comparing observational interaction data to null models using permutations tests, enables to separate the effect of spatial pattern and social preferences. Applying this approach to a large long-term observational data set of heterospecific interactions, I demonstrate that individuals differ consistently in their propensity to associate with heterospecifics (Chapter 5).The work presented in this thesis demonstrates that individuals consider both their social and non-social environment when making decisions in their natural, multi-species environment. Participation in mixed-species flocks appears to be a complex balance of competition cost and grouping benefits, mediated by both individual phenotype and environmental conditions.The work presented in this thesis supports previous notions that mixed-species flocking is a mutualistic relationship between participating species. This thesis contributes experimental evidence for the importance of positive interactions in community ecology, and justifies recent advances of linking individual behaviour to community processes.

Authors: Hillemann, F

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: interspecific social behaviour; economic decision-making; collective animal behaviour; mixed-species group; foraging; paridae; social information; social network
• Subjects: behavioural ecology