The Allee effect corresponds to a positive relationship between population size and individual fitness. This positive relationship can cause thresholds, that is, critical population sizes below which the population becomes extinct. For species submitted to the Allee effect, the formation and cohesion of groups is therefore crucial to survival. Animals can achieve this collective behaviour through local interactions. Each individual interacts locally with conspecifics and, at the scale of the group, a unity of behaviour emerges: the animals move together, rest in the same place, or choose the same habitat patch to settle on. <p><p>We use a combination of mathematical modelling and experimental work to study certain mechanisms of collective behaviour. In particular we assess the extent to which different individual interactions can induce collective patterns and thereby influence the dynamics of dispersal and settlement of populations. First, we study the collective settlement induced by the arresting effect of a marker secreted by conspecifics. Then, two potential mechanisms for collective movement are examined: following the conspecifics and following a trail laid by conspecifics. Finally, we integrate explicit mechanisms of dispersal behaviour in a dynamic model involving a set of interconnected populations. This allows the study of the interplay between collective movements and Allee effects at the scale of the metapopulation.<p><p>Our work is inspired by the lifestyle of the two-spotted spider mite, Tetranychus urticae, a phytophagous pest of recognised agricultural importance. These subsocial mites live in aggregates on the leaf surface, protected by a collectively spun silk web. Experimental evidence suggests that its population dynamics are subject to the Allee effect. Moreover, these mites show a tendency to migrate collectively, which makes them an appropriate biological model. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished