title: Sensitivity of density-dependent threshold to species composition in arthropod aggregates.
abstract: How mixed-species groups perform collective behaviours provides unique insights into the mechanisms that drive social interactions. Herein, we followed the aggregation process of two isopod species under monospecific and heterospecific conditions at three population densities. Our experimental results show that the formation of both the monospecific and heterospecific groups responds to a similar threshold function. Furthermore, the two species contribute equally to the mixed-species aggregate growth and are not spatiotemporally segregated. However, we show that the cohesion is weaker and the probability of forming aggregations is lower in heterospecific groups than in monospecific populations. Thus, our results show that amplification processes are shared between species, but that the weighting given to conspecific and heterospecific information differs. We develop a theoretical model to test this hypothesis. The model reproduces our experimental data and shows that a relatively low level of inter-attractions between species is able to generate mixed-species aggregates. Moreover the greater the total population, the lower this parameter value is needed to observe aggregation in both species. This highlights the importance to study not only qualitatively but also quantitatively the heterospecific interactions in mixed-species groups. Finally, the patterns observed could be biologically relevant in favouring the association between species.
authors: Unit of Social Ecology, Université Libre de Bruxelles, Campus de la Plaine, 1050 Bruxelles, Belgium.
authors: Broly
authors: B
authors: Pierre
authors: Unit of Social Ecology, Université Libre de Bruxelles, Campus de la Plaine, 1050 Bruxelles, Belgium.
authors: Ectors
authors: E
authors: Quentin
authors: Unit of Social Ecology, Université Libre de Bruxelles, Campus de la Plaine, 1050 Bruxelles, Belgium.
authors: Decuyper
authors: D
authors: Geoffrey
authors: Unit of Social Ecology, Université Libre de Bruxelles, Campus de la Plaine, 1050 Bruxelles, Belgium.
authors: Stamatios C
authors: SC
authors: Nicolis
authors: Unit of Social Ecology, Université Libre de Bruxelles, Campus de la Plaine, 1050 Bruxelles, Belgium.
authors: Deneubourg
authors: D
authors: Jean-Louis
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D033321:Isopoda / Q000502:physiology*; D015233:Models, Statistical; D011156:Population Density; D013045:Species Specificity