Abstract
In fragmented landscape, individuals have to cope with the fragmentation level in order to aggregate in the same patch and take advantage of group-living. Aggregation results from responses to environmental heterogeneities and/or positive influence of the presence of congeners. In this context, the fragmentation of resting sites highlights how individuals make a compromise between two individual preferences: (1) being aggregated with conspecifics and (2) having access to these resting sites. As in previous studies, when the carrying capacity of available resting sites is large enough to contain the entire group, a single aggregation site is collectively selected. In this study, we have uncoupled fragmentation and habitat loss: the population size and total surface of the resting sites are maintained at a constant value, an increase in fragmentation implies a decrease in the carrying capacity of each shelter. For our model organism, Blattella germanica, our experimental and theoretical approach shows that, for low fragmentation level, a single resting site is collectively selected. However, for higher level of fragmentation, individuals are randomly distributed between fragments and the total sheltered population decreases. In the latter case, social amplification process is not activated and consequently, consensual decision making cannot emerge and the distribution of individuals among sites is only driven by their individual propensity to find a site. This intimate relation between aggregation pattern and landscape patchiness described in our theoretical model is generic for several gregarious species. We expect that any group-living species showing the same structure of interactions should present the same type of dispersion-aggregation response to fragmentation regardless of their level of social complexity.
Highlights
Living in groups is most likely the most common collective behavior among organisms, in vertebrates, invertebrates and unicellular organisms [1,2,3,4,5,6]
Considering the ability of most of the cockroach species to aggregate under shelters [22,51,52], we sought to assess the response of a group to habitat fragmentation and a consequent increase in the number of resting sites
We subjected a group of cockroaches to different fragmentation levels without habitat loss, with the total shelter area remaining constant: the number of shelters increases while the carrying capacity of each decreases
Summary
Living in groups is most likely the most common collective behavior among organisms, in vertebrates, invertebrates and unicellular organisms [1,2,3,4,5,6]. The benefits of group living are numerous [2]: reduction in predation risk by dilution or confusion [8], facilitation of foraging [9], and water loss regulation and thermoregulation [10,11]. These benefits reflect different underlying Allee effects [12,13] and are largely dependent on environmental characteristics. At any given time, the size of a group results from a balance between benefits and costs, such as the sharing of food resources [14,15], intensification of competition between sex partners [16], and increased epidemic risks [17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
