Home‐range use and intergroup encounters in western gorillas (Gorilla g. gorilla) at Lossi forest, North Congo

Abstract

I present data on home-range use and types of intergroup encounters for one group (Apollo) of western gorillas (Gorilla gorilla gorilla) from a new study site in the Republic of Congo. The total home-range size of the focal group, which I calculated by superimposing a 100 m x 100 m grid over the mapped daily path traveled, was 11 km2. The majority (73%) of the group's home range was used exclusively, although at the periphery it overlapped with the ranges of three other groups. Most encounters (86%) with other groups (n = 14) took place in the periphery of the home range, and appeared to involve access to fruit trees. The focal group silverback's encounters with solitary silverbacks occurred throughout the focal group's home range, did not involve access to fruit, and typically resulted in aggressive or avoidance behavior. The focal group silverback's response to other group males was more varied: it included tolerance (64%), avoidance (14%), and aggression (21%), and was dependent upon the identity of the extragroup male. The focal group exhibited an unusual form of tolerant behavior toward some other groups by occasionally forming "nesting supergroups" (two groups nested together overnight at distances of 30-50 m). The western gorillas at Lossi were somewhat fluid in their grouping. Subgrouping and supergrouping occurred, although more infrequently than reported previously, and with a new twist: subgrouping did not necessarily require a silverback's presence. I stress the need for intraspecific comparisons and more complete data sets on western gorilla social organization.

Noninvasive Follow-Up of Simian Immunodeficiency Virus Infection in Wild-Living Nonhabituated Western Lowland Gorillas in Cameroon

“…We determined the SIV infection rates (13 to 29%) in four identified nonhabituated social groups. We were also able to identify a single adult male (ID38) infected with SIV, illustrating that migrating individuals infected with SIVgor can be responsible for the spread of viruses in the area by fighting for a dominant position or by other routes while transferring to a new gorilla social group (2,29,43). Despite previous studies reporting that the use of RNAlater is not optimal for DNA analyses (36), we obtained a microsatellite amplification success rate comparable to those in previous studies on noninvasive samples, showing that storage of fecal samples in RNAlater allows for combined studies on the host and its pathogens.…”

“…The Campo-Ma'an National Park was created in 2000 and covers 2,640 km 2 of primary and mangrove forests in southwestern Cameroon, spanning an area from the Atlantic coast to roughly 100 km inland (62). We conducted our follow-up study in an area of approximately 200 km 2 at the center of the Campo-Ma'an National Park (CP), where previous surveys showed a relatively high rate of SIVgor infection in wild gorillas (34). In this follow-up study, the three previously described zones of collection (CP-GR, CP-OV, and CP-MV) were pooled together and were considered a single site, as they are located less than 10 km from each other and SIVgor-positive individuals were identified at all three locations.…”

Origin and Biology of Simian Immunodeficiency Virus in Wild-Living Western Gorillas

“…Adolescent males typically leave their natal groups and become solitary (and highly mobile) until they form their own harems (23), while females also transfer between groups (63). Individual groups have home ranges of about 15 to 20 km 2 (8,22,47), which often overlap, resulting in frequent encounters of neighboring groups (8,17,22,67). Thus, gorilla mating and social networks provide ample opportunity for a newly introduced SIV to spread, both within and between neighboring communities.…”

Origin of the HIV-1 group O epidemic in western lowland gorillas

“…Alternatively, it is possible that following its introduction, SIVgor may have not yet spread beyond southern Cameroon. The home ranges of gorilla groups are small compared with chimpanzees, and their movements, as inferred from gene flow, are influenced by both major and smaller rivers, perhaps more so than the migration of chimpanzees (28)(29)(30). It has been estimated that SIVgor sequence distances reflect at least 100-200 y of diversification (15).…”