Altruism in Forest Chimpanzees: The Case of Adoption

In recent years, extended altruism towards unrelated group members has been proposed to be a unique characteristic of human societies. Support for this proposal seemingly came from experimental studies on captive chimpanzees that showed that individuals were limited in the ways they shared or cooperated with others. This dichotomy between humans and chimpanzees was proposed to indicate an important difference between the two species, and one study concluded that “chimpanzees are indifferent to the welfare of unrelated group members”. In strong contrast with these captive studies, consistent observations of potentially altruistic behaviors in different populations of wild chimpanzees have been reported in such different domains as food sharing, regular use of coalitions, cooperative hunting and border patrolling. This begs the question of what socio-ecological factors favor the evolution of altruism. Here we report 18 cases of adoption, a highly costly behavior, of orphaned youngsters by group members in Taï forest chimpanzees. Half of the adoptions were done by males and remarkably only one of these proved to be the father. Such adoptions by adults can last for years and thus imply extensive care towards the orphans. These observations reveal that, under the appropriate socio-ecologic conditions, chimpanzees do care for the welfare of other unrelated group members and that altruism is more extensive in wild populations than was suggested by captive studies

Predicting range shifts of African apes under global change scenarios

Aim: Modelling African great ape distribution has until now focused on current or past conditions, while future scenarios remain scarcely explored. Using an ensemble forecasting approach, we predicted changes in taxon-specific distribution under future scenarios of climate, land use and human populations for (1) areas outside protected areas (PAs) only (assuming complete management effectiveness of PAs), (2) the entire study region and (3) interspecies range overlap. Location: Tropical Africa. Methods: We compiled occurrence data (n = 5,203) on African apes from the IUCN A.P.E.S. database and extracted relevant climate-, habitat- and human-related predictors representing current and future (2050) conditions to predict taxon-specific range change under a best- and a worst-case scenario, using ensemble forecasting. Results: The predictive performance of the models varied across taxa. Synergistic interactions between predictors are shaping African ape distribution, particularly human-related variables. On average across taxa, a range decline of 50% is expected outside PAs under the best scenario if no dispersal occurs (61% in worst scenario). Otherwise, an 85% range reduction is predicted to occur across study regions (94% worst). However, range gains are predicted outside PAs if dispersal occurs (52% best, 21% worst), with a slight increase in gains expected across study regions (66% best, 24% worst). Moreover, more than half of range losses and gains are predicted to occur outside PAs where interspecific ranges overlap. Main Conclusions: Massive range decline is expected by 2050, but range gain is uncertain as African apes will not be able to occupy these new areas immediately due to their limited dispersal capacity, migration lag and ecological constraints. Given that most future range changes are predicted outside PAs, Africa\u27s current PA network is likely to be insufficient for preserving suitable habitats and maintaining connected ape populations. Thus, conservation planners urgently need to integrate land use planning and climate change mitigation measures at all decision-making levels both in range countries and abroad

Successful adoptions of orphaned infants in three communities of Taï chimpanzees.

<p>quick  =  adoption occurred within days after the death of the mother.</p><p>* =  Bonnie was first identified when she had already been adopted by her suspected brother, Clyde.</p><p>** =  Yayo has been observed to be carried by 4 other adult males of the East Group during the 4 months of his adoption, but Fredy was the main adopter.</p>d1<p> =  adoption interrupted by the death of the orphan.</p>d2<p> =  adoption interrupted by the death of adopter.</p>i<p> =  adoption actively interrupted by adopter.</p><p><u>Relation</u>: Sister/Brother =  older sibling of the orphan, Friend =  A♀ was a friend of the deceased mother, NR =  confirmed as not related following genetic testing, uk = unknown.</p

The presence of a close kin does not increase the likelihood of adoption in Taï chimpanzees (Fisher exact test: p = 0.463).

<p>The presence of a close kin does not increase the likelihood of adoption in Taï chimpanzees (Fisher exact test: p = 0.463).</p

The adult male Porthos with his adopted female infant Gia.

<p>A) Porthos cracking and sharing nuts with Gia, B) Porthos carrying Gia on his back.</p

The adult male Porthos carrying on his back the adopted female infant Gia.

<p>The adult male Porthos carrying on his back the adopted female infant Gia.</p

Number of orphans and adoptions seen in the 27 years of observation of three study groups of the Taï chimpanzee project.

<p>Number of orphans and adoptions seen in the 27 years of observation of three study groups of the Taï chimpanzee project.</p

Orphans adopted do not present higher likelihood of surviving for 2 years the death of their mother than non-adopted orphans in Taï chimpanzees (X2 = 0.37, df = 1, p = 0.54).

<p>Orphans adopted do not present higher likelihood of surviving for 2 years the death of their mother than non-adopted orphans in Taï chimpanzees (X2 = 0.37, df = 1, p = 0.54).</p