Behavioral Flexibility and the Evolution of Primate Social States

Comparative approaches to the evolution of primate social behavior have typically involved two distinct lines of inquiry. One has focused on phylogenetic analyses that treat social traits as static, species-specific characteristics; the other has focused on understanding the behavioral flexibility of particular populations or species in response to local ecological or demographic variables. Here, we combine these approaches by distinguishing between constraining traits such as dispersal regimes (male, female, or bi-sexual), which are relatively invariant, and responding traits such as grouping patterns (stable, fission-fusion, sometimes fission-fusion), which can reflect rapid adjustments to current conditions. Using long-term and cross-sectional data from 29 studies of 22 species of wild primates, we confirm that dispersal regime exhibits a strong phylogenetic signal in our sample. We then show that primate species with high variation in group size and adult sex ratios exhibit variability in grouping pattern (i.e., sometimes fission-fusion) with dispersal regime constraining the grouping response. When assessing demographic variation, we found a strong positive relationship between the variability in group size over time and the number of observation years, which further illustrates the importance of long-term demographic data to interpretations of social behavior. Our approach complements other comparative efforts to understand the role of behavioral flexibility by distinguishing between constraining and responding traits, and incorporating these distinctions into analyses of social states over evolutionary and ecological time

Fission-fusion dynamics: New research frameworks

Renewed interest in fission-fusion dynamics is due to the recognition that such dynamics may create unique challenges for social interaction and distinctive selective pressures acting on underlying communicative and cognitive abilities. New frameworks for integrating current knowledge on fission-fusion dynamics emerge from a fundamental rethinking of the term "fission-fusion" away from its current general use as a label for a particular modal type of social system (i.e., "fission-fusion societies"). Specifically, because the degree of spatial and temporal cohesion of group members varies both within and across taxa, any social system can be described in terms of the extent to which it expresses fission-fusion dynamics. This perspective has implications for socioecology, communication, cognitive demands, and human social evolution

News and Perspectives: Words matter in primatology

Postings on social media on Twitter (now X), BioAnthropology News (Facebook), and other venues, as well as recent publications in prominent journals, show that primatologists, ecologists, and other researchers are questioning the terms “Old World” and “New World” due to their colonial implications and history. The terms are offensive if they result in erasing Indigenous voices and history, ignoring the fact that Indigenous peoples were in the Americas long before European colonization. Language use is not without context, but alternative terminology is not always obvious and available. In this perspective, we share opinions expressed by an international group of primatologists who considered questions about the use of these terms, whether primatologists should adjust language use, and how to move forward. The diversity of opinions provides insight into how conventional terms used in primatological research and conservation may impact our effectiveness in these domains

Genetic Diversity and Population History of a Critically Endangered Primate, the Northern Muriqui (Brachyteles hypoxanthus)

Social, ecological, and historical processes affect the genetic structure of primate populations, and therefore have key implications for the conservation of endangered species. The northern muriqui (Brachyteles hypoxanthus) is a critically endangered New World monkey and a flagship species for the conservation of the Atlantic Forest hotspot. Yet, like other neotropical primates, little is known about its population history and the genetic structure of remnant populations. We analyzed the mitochondrial DNA control region of 152 northern muriquis, or 17.6% of the 864 northern muriquis from 8 of the 12 known extant populations and found no evidence of phylogeographic partitions or past population shrinkage/expansion. Bayesian and classic analyses show that this finding may be attributed to the joint contribution of female-biased dispersal, demographic stability, and a relatively large historic population size. Past population stability is consistent with a central Atlantic Forest Pleistocene refuge. In addition, the best scenario supported by an Approximate Bayesian Computation analysis, significant fixation indices (ΦST = 0.49, ΦCT = 0.24), and population-specific haplotypes, coupled with the extirpation of intermediate populations, are indicative of a recent geographic structuring of genetic diversity during the Holocene. Genetic diversity is higher in populations living in larger areas (>2,000 hectares), but it is remarkably low in the species overall (θ = 0.018). Three populations occurring in protected reserves and one fragmented population inhabiting private lands harbor 22 out of 23 haplotypes, most of which are population-exclusive, and therefore represent patchy repositories of the species' genetic diversity. We suggest that these populations be treated as discrete units for conservation management purposes

Effects of local habitat variation on the behavioral ecology of two sympatric groups of brown howler monkey (alouatta clamitans)

Although the brown howler monkey (Alouatta clamitans) is a relatively well-studied Neotropical primate, its behavioral and dietary flexibility at the intra-population level remains poorly documented. This study presents data collected on the behavior and ecology of two closely located groups of brown howlers during the same period at the RPPN Feliciano Miguel Abdala in southeastern Brazil. One group occupied a primary valley habitat, henceforth the Valley Group (VG), and the other group occupied a regenerating hillside habitat, the Hill Group (HG). We hypothesized differences in the behavior and ecological parameters between these sympatric groups due to the predicted harsher conditions on the hillside, compared to the valley. We measured several habitat parameters within the home range of both groups and collected data on the activity budget, diet and day range lengths, from August to November 2005, between dawn and dusk. In total, behavioral data were collected for 26 (318 h) and 28 (308 h) sampling days for VG and HG, respectively. As we predicted, HG spent significantly more time feeding and consumed less fruit and more leaves than VG, consistent with our finding that the hillside habitat was of lower quality. However, HG also spent less time resting and more time travelling than VG, suggesting that the monkeys had to expend more time and energy to obtain high-energy foods, such as fruits and flowers that were more widely spaced in their hill habitat. Our results revealed that different locations in this forest vary in quality and raise the question of how different groups secure their home ranges. Fine-grained comparisons such as this are important to prioritize conservation and management areas within a reserve

Tropical field stations yield high conservation return on investment

Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km2 than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly

News and Perspectives: Words matter in primatology

Postings on social media on Twitter (now X), BioAnthropology News (Facebook), and other venues, as well as recent publications in prominent journals, show that primatologists, ecologists, and other researchers are questioning the terms “Old World” and “New World” due to their colonial implications and history. The terms are offensive if they result in erasing Indigenous voices and history, ignoring the fact that Indigenous peoples were in the Americas long before European colonization. Language use is not without context, but alternative terminology is not always obvious and available. In this perspective, we share opinions expressed by an international group of primatologists who considered questions about the use of these terms, whether primatologists should adjust language use, and how to move forward. The diversity of opinions provides insight into how conventional terms used in primatological research and conservation may impact our effectiveness in these domains

Tropical field stations yield high conservation return on investment

Conservation funding is currently limited; cost-effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID-19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km2 than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly.Additional co-authors: Ekwoge Abwe, Tanvir Ahmed, Marc Ancrenaz, Raphali R. Andriantsimanarilafy, Andie Ang, Filippo Aureli, Louise Barrett, Jacinta C. Beehner, Marcela E. Benítez, Bruna M. Bezerra, Júlio César Bicca-Marques, Dominique Bikaba, Robert Bitariho, Christophe Boesch, Laura M. Bolt, Ramesh Boonratana, Thomas M. Butynski, Gustavo R. Canale, Susana Carvalho, Colin A. Chapman, Dilip Chetry, Susan M. Cheyne, Marina Cords, Fanny M. Cornejo, Liliana Cortés-Ortiz, Camille N. Z. Coudrat, Margaret C. Crofoot, Drew T. Cronin, Alvine Dadjo, S. Chrystelle Dakpogan, Emmanuel Danquah, Tim R. B. Davenport, Yvonne A. de Jong, Stella de la Torre, Andrea Dempsey, Judeline C. Dimalibot, Rainer Dolch, Giuseppe Donati, Alejandro Estrada, Rassina A. Farassi, Peter J. Fashing, Eduardo Fernandez-Duque, Maria J. Ferreira da Silva, Julia Fischer, César F. Flores-Negrón, Barbara Fruth, Terence Fuh Neba, Lief Erikson Gamalo, Jörg U. Ganzhorn, Paul A. Garber, Smitha D. Gnanaolivu, Mary Katherine Gonder, Sery Ernest Gonedelé Bi, Benoit Goossens, Marcelo Gordo, Juan M. Guayasamin, Diana C. Guzmán-Caro, Andrew R. Halloran, Jessica A. Hartel, Eckhard W. Heymann, Russell A. Hill, Kimberley J. Hockings, Gottfried Hohmann, Naven Hon, Mariano G. Houngbédji, Michael A. Huffman, Rachel A. Ikemeh, Inaoyom Imong, Mitchell T. Irwin, Patrícia Izar, Leandro Jerusalinsky, Gladys Kalema-Zikusoka, Beth A. Kaplin, Peter M. Kappeler, Stanislaus M. Kivai, Cheryl D. Knott, Intanon Kolasartsanee, Kathelijne Koops, Martin M. Kowalewski, Deo Kujirakwinja, Ajith Kumar, Quyet K. Le, Rebecca J. Lewis, Aung Ko Lin, Andrés Link, Luz I. Loría, Menladi M. Lormie, Edward E. Louis Jr., Ngwe Lwin, Suchinda Malaivijitnond, Lesley Marisa, Gráinne M. McCabe, W. Scott McGraw, Addisu Mekonnen, Pedro G. Méndez-Carvajal, Tânia Minhós, David M. Montgomery, Citlalli Morelos-Juárez, David Morgan, Amancio Motove Etingüe, Papa Ibnou Ndiaye, K. Anne-Isola Nekaris, Nga Nguyen, Vincent Nijman, Radar Nishuli, Marilyn A. Norconk, Luciana I. Oklander, Rahayu Oktaviani, Julia Ostner, Emily Otali, Susan E. Perry, Eduardo J. Pinel Ramos, Leila M. Porter, Jill D. Pruetz, Anne E. Pusey, Helder L. Queiroz, Mónica A. Ramírez, Guy Hermas Randriatahina, Hoby Rasoanaivo, Jonah Ratsimbazafy, Joelisoa Ratsirarson, Josia Razafindramanana, Onja H. Razafindratsima, Vernon Reynolds, Rizaldi Rizaldi, Martha M. Robbins, Melissa E. Rodríguez, Marleny Rosales-Meda, Crickette M. Sanz, Dipto Sarkar, Anne Savage, Amy L. Schreier, Oliver Schülke, Gabriel H. Segniagbeto, Juan Carlos Serio-Silva, Arif Setiawan, John Seyjagat, Felipe E. Silva, Elizabeth M. Sinclair, Rebecca L. Smith, Denise Spaan, Fiona A. Stewart, Shirley C. Strum, Martin Surbeck, Magdalena S. Svensson, Mauricio Talebi, Luc Roscelin Tédonzong, Bernardo Urbani, João Valsecchi, Natalie Vasey, Erin R. Vogel, Robert B. Wallace, Janette Wallis, Siân Waters, Roman M. Wittig, Richard W. Wrangham, Patricia C. Wright, Russell A. Mittermeie

Reproductive inequality in humans and other mammals

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women’s fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species—including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms

Tropical field stations yield high conservation return on investment

Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km$^{2}$ than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly