Organization

Ring-tailed lemurs live in complex social units called troops. Troops usually have an average of 14 individuals consisting of males, females and juveniles. Troops function as nurseries, feeding cooperatives, and defense guilds (Jolly 1988).

One of the most interesting aspects of a ring-tailed lemur troop is the noted female dominance. Troops are matriarchial in nature and females are dominant over males. Daughters will remain in their natal troops with their mother and aunts, while males leave the troop at adolescence, wandering from troop to troop (Jolly 1966).

Photo courtesy of Guenther Eichhorn (gei@cfa.harvard.edu)

Social Interactions

Social interactions among lemurs include grooming, play and spats. Lemurs often sit together on a branch in as much contact as possible and will purr with bouts of clicks as they groom (Jolly 1966). Lemurs preferentially groom the parts of the body on others that they can't reach during self-grooming (Chalmers 1980). In greeting, one lemur approaching another or passing will briefly touch the tip of its nose to the other lemur's nose. Agonistic behavior includes staring (one animal will look away), swaggering (one male towards another), cuffing (one animal swats with a hand at another's face), feinting (lunging forward with shoulders but staying in the same place, used to warn of an inferior), biting (this does a lot of damage), stink fighting and chase and jump fighting (happens during breeding season) (Jolly 1966). Stink fights consist of a long series of tail-marking and tail-weaving between males and can last from 10 minutes to an hour. Tail marking occurs when a male rubs its two main external glands (antebrachial and brachial) together, stands on all fours with its tail arched over its back, and quivers the tail violently while shaking the odor forward. This is always directed towards another male and is consistered very aggressive (Jolly 1966). Eventually one male will break down and run away (Haring 2004).

Since dominance hierarchies among males constantly change (especially during the mating season), driving away solitary males during the non-breeding season does not lead to increased reproductive success. Aggressiveness towards solitary males is therefore advantageous not only to the aggressor but also to other resident males because this prevents solitary males from joining the troop and keeping them away from females. Resident males are likely to drive away solitary males regardless of their dominance rank (Miller 2002).

A study done by Kappeler, 1993, examined post-conflict behavior in ring-tailed lemurs, and the effects of conflicts on the probability of subsequent affinitive and agonistic interactions with former opponents and other group members. Suprisingly, no evidence was found for an increase in post-conflict affinitive interactions between former opponents. In fact, ring-tailed lemurs had a tendency towards renewed conflict in the post-conflict period. In red-fronted lemurs, which do not have clear dominance relations, reconciliation was observed. According to the reconciled hierarchy model, species with a pronounced dominance hierarchy and kinship structure normally demonstrate reconciliation after conflict, so the results of this study were suprising. Ring-tailed lemurs therefore demonstrate that it is possible to live in a cohesive social group despite a lack of reconciliation behavior and with frequent agonistic encounters (Kappeler 1993). I personally believe that these results are not entirely suprising, based on the constantly-changing nature of the dominance relations in a ring-tailed lemur troop. Were the dominance hierarchy (among both males and females) more rigid, reconciliation after conflict might play a more pronounced role in social relations. However, since dominance relations do change constantly, it is more feasible that conflict would be followed up with renewed conflict rather than reconciliation.

Why Female Dominance?

Female dominance is a rare phenomena in mammals. It is more common to find male dominance because of the sexual dimorphism in most mammal species, males being normally larger than females (Case 2004). It has been suggested that perhaps female dominance has evolved in ring-tailed lemurs because of their extremely short breeding season (See Mating and Sexual Behavior). Males exert incredible amounts of energy during the breeding season as they fight for mates; thus they need to "lay low" throughout the rest of the year to conserve their energy (Jolly 1985). Males are less aggressive than females and are very laid-back during the non-breeding season (Haring 2004). This has probably allowed females to become dominant.

Why Large, Multi-Male Groups?

A group of males may intimidate predators, and because of this terrestrial primates are more likely to have multi-male groups. Also, when troop ranges overlap (as in ring-tailed lemurs), the largest troop is usually dominant and can force the smaller troop to retreat during an encounter. Since more males can oust less males, the optimum troop size is small enough to find food within a feasible home range and large enough to be the "biggest in the neighborhood" (Jolly 1985). It is also advantageous for ring-tailed lemurs to live in large groups due to their foraging habits. Since they subsist on a 'fruit-flower-shoot' diet, they will be less likely to waste energy looking for food when they can feed and move with a group. Members of a large group will also be better able to communicate food presence (Chalmers 1980).

Photo courtesy of Tony Northrup (www.northrup.org)

Social Spacing

Home Range

Ring-tailed lemurs have very large home ranges (17-32 ha.). Home ranges in riverine forests have been found to be smaller (17 ha) in riverine forest and larger in dryer, more sparsely vegetated areas (32 ha) (Gould et. al 2003). Ring-tailed lemurs usually live in fairly dense populations and home ranges tend to overlap considerably with troops' home ranges, so there are no areas of exclusive use (Jolly 1966). Thus encounters between troops are frequent and lemurs from one troop are accustomed to seeing lemurs from neighboring troops (troops are well aquainted). While there is no evidence of territorial defense, in general troops do not mix. When troops do meet, they usually approach each other with "ordinary intra-troop aggressive gestures" and do not demonstrate ritualized forms of hostility. According to Jolly, 1966, ringed-tailed lemurs are extremely active and will visit all parts of their range within a week to 10 days (this is necessary due to scarce, clumped food distribution). Ring-tailed lemurs are among the primates with the highest ratio of day range to home range diameter (Pride 1999). Home ranges seem to amply satisfy the troops needs and are large enough to contain enough food to support many individuals (Chalmers 1980).

It has been shown that most troops retain the same core area from year to year, and intertroop antagonism may reflect the benefits of long-term area control. A study done by Pride, 1999 found that in a region of rapdily growing population, troops originated from the ejection of females from a group through targeted aggression, or by the division of a large group that had already begun ranging as two separate groups. Once established as a multi-male/multi-female group, the new troop would continue to have aggressive encounters with its neighbors, especially its sister troop. The sisters troops would typically range in parallel. As the new troop grew it would eventually begin to subdivide, starting the cycle over again. This study also showed that home ranges are stable but not rigidly fixed. Lemurs would make brief excursions to specific flowering trees outside their usual area about once every two weeks. It is suggested that in ranges dense enough for a parent troop to divide, intimate knowledge of the range, its resources and social challenges outweighs the cost of a newly independent troop having to fight for a foothold, and that there may be some benefit to living next to one's female kin (Pride 1999).

A study was done by Allison Jolly (1985) on ring-tailed lemur habitats in which one troop had a small riverside habitat (8 ha) with prime resources while another group had a larger (23 ha) inland habitat with very sparse resources. Suprisingly, the troops with the smaller habitat ranged farther throughout the day. This is because the inland troop's movements were fixed by a 600 m hike to a scrub area for succulent water plants with little movement at either end and little energy to spare. This shorter day range was therefore a reaction to resource distribution. Minimum length was determined by the distance between patches of food and cover in the riverside troop and the patches of water of water source in the dry inland troop. It can be concluded that a large home range is not a function of sparse food supply but is a stepwise function of the need to include patches of different resources (also food may be abundant in certain areas but these areas could be separated by long distances) (Jolly 1985).

Defense?

If there are intruders from another troop, it is always the female that will defend the range. Opposing groups of females will run at each other and utter threatening calls (San Francisco Zoo 2004). Males rarely take part in intertroop confrontation; their role in the troop is not about holding troop range. Having a core area is important only to females, as it ensures resources not only for the individual females but also as inheritance for their daughters and grand-daughters (Pride 1999). This relates to the fact that females remain in their natal troop (thus all females in a troop are related) while males leave the natal troop at adolescence.

Photo courtesy of Guenther Eichhorn (gei@cfa.harvard.edu)