Impending extinction of the world’s primates due to human activities; immediate global attention is needed to reverse the trend.

Mixed‐species animal groups (MSGs) are widely acknowledged to increase predator avoidance and foraging efficiency, among other benefits, and thereby increase participants' fitness. Diversity in MSG composition ranges from two to 70 species of very similar or completely different phenotypes. Yet consistency in organization is also observable in that one or a few species usually have disproportionate importance for MSG formation and/or maintenance. We propose a two‐dimensional framework for understanding this diversity and consistency, concentrating on the types of interactions possible between two individuals, usually of different species. One axis represents the similarity of benefit types traded between the individuals, while the second axis expresses asymmetry in the relative amount of benefits/costs accrued. Considering benefit types, one extreme represents the case of single‐species groups wherein all individuals obtain the same supplementary, group‐size‐related benefits, and the other extreme comprises associations of very different, but complementary species (e.g. one partner creates access to food while the other provides vigilance). The relevance of social information and the matching of activities (e.g. speed of movement) are highest for relationships on the supplementary side of this axis, but so is competition; relationships between species will occur at points along this gradient where the benefits outweigh the costs. Considering benefit amounts given or received, extreme asymmetry occurs when one species is exclusively a benefit provider and the other a benefit user. Within this parameter space, some MSG systems are constrained to one kind of interaction, such as shoals of fish of similar species or leader–follower interactions in fish and other taxa. Other MSGs, such as terrestrial bird flocks, can simultaneously include a variety of supplementary and complementary interactions. We review the benefits that species obtain across the diversity of MSG types, and argue that the degree and nature of asymmetry between benefit providers and users should be measured and not just assumed. We then discuss evolutionary shifts in MSG types, focusing on drivers towards similarity in group composition, and selection on benefit providers to enhance the benefits they can receive from other species. Finally, we conclude by considering how individual and collective behaviour in MSGs may influence both the structure and processes of communities.

This review summarizes information on the behavioural ecology of mixed-species troops (interspecific associations) formed by different species of callitrichines, small New World monkeys, in western and central Amazonia. The formation of mixed-species troops is an integral part of the biology of several species of this subfamily. Niche separation between associated species is obtained through vertical segregation which results in differences in the prey spectrum. The degree of niche separation is a predictor for the stability of mixed-species troops. Individuals may benefit from the formation of mixed-species troops through increased safety from predators, increased foraging efficiency, and/or increased resource defence. Costs of mixed-species troop formation are probably very low and mainly relate to patterns of interspecific behavioural interactions. We point to gaps in our knowledge and suggest pathways for future research into mixed-species troops.

The sleeping habits of moustached tamarins, Saguinus mystax, and saddle‐back tamarins, Saguinus fuscicollis, were studied in northeastern Peru. Five types of sleeping sites were distinguished: 1) Jessenia bataua palms; 2) tree hollows; 3) dense tangles of vegetation; 4) crotches; 5) open horizontal branches. Both tamarin species used Jesseniu‐palms most frequently. Tree hollows ranked second in the saddle‐back tamarins, but were never used by moustached tamarins. Sleeping sites of moustached tamarins were located significantly higher than those of saddle‐back tamarins. Jessenia‐palms used by moustached tamarins were significantly higher than palms from a random transect sample, but this was not the case for Jessenia‐palms used by saddle‐back tamarins. For both species, concealment seems to be more important than height above ground. The maximum number of subsequent nights spent in the same sleeping site was two in moustached tamarins and six in saddle‐back tamarins. The two tamarin species did not compete for sleeping sites. While the general pattern of sleeping site selection conforms to hypotheses predicting safety from predators as a major factor, differences between the two tamarin species reflect general niche differences between them. Most sleeping sites are located in exclusively used parts of the home range. Moustached tamarins generally use sleeping sites that are close to the last feeding site of the afternoon. The distance between simultaneously used sleeping sites of moustached and saddle‐back tamarins are generally close together, which helps to minimize time spent out of interspecific association.

Russell A. Mittermeier, Janette Wallis, Anthony B. Rylands, Jörg U. Ganzhorn, John F. Oates, Elizabeth A. Williamson, Erwin Palacios, Eckhard W. Heymann, M. Cecília M. Kierulff, Long Yongcheng, Jatna Supriatna, Christian Roos, Sally Walker, Liliana Cortés-Ortiz, and Christoph Schwitzer (2009) Primates in Peril: The World's 25 Most Endangered Primates 2008–2010. Primate Conservation: Vol. 24, No. 1, pp. 1-57. https://doi.org/10.1896/052.024.0101