AIM
To establish
the dominance style of the Buton macaque for the purpose of comparison with other
macaque species, in particular the Sulawesi macaques.
1)
To collect dominance interaction data from two habituated troupes of
Buton macaques in order to classify the social structure of this sub species as
either nepotistic-despotic (e.g. Macaca fuscata) or nepotistic- tolerant
(e.g. Sulawesi spp, Macaca nigra) and to determine whether dominance rank
has an effect on behavioural repertoire.
2)
To evaluate grooming interactions in relation to biological market theory
thus determining whether grooming is exchange using a ‘tit for tat’ strategy
or whether grooming is exchanged for other commodities.
Although all
macaque species have dominance relationships between individuals, research has
indicated that considerable variation can be found in the dominance ‘style’
of different species. Van Schaik (1989), building on Wrangham (1980) explained
primate dominance style as a product of the type of intergroup competition
(contest or scramble), the intensity of intergroup contest competition and the
adaptive significance of group life as a method of reducing predation rate. If
between-group competition is low, or predation risk is high, then dominants have
more freedom in despotically appropriating resources. In these circumstances,
group members should exhibit little tolerance towards subordinate conspecifics,
resulting in a strict dominance hierarchy and a generally despotic society. If
however, between-group competition is high and the predation risk associated
with changing groups is low, then dominant individuals will need to be more
tolerant of subordinates, so to prevent them from defecting to another group.
This mitigated competitiveness results in a more tolerant society and more
egalitarian dominance relationships (van Schaik, 1989).
Characteristics
of a despotic macaque society (e.g. Japanese macaque Macaca fuscata)
include a generally linear dominance hierarchy with few reversals in rank
position. The dominance gradient is steep, producing marked asymmetries in power
between dominant and subordinate individuals, thus governing partner choice for
social interactions. This also leads to a high rate of spontaneously submissive
behaviour from subordinates and uni-directional and intense aggression (de Waal
& Luttrell, 1989; Thierry et al, 1997). For this reason, rank
distance has been cited as a central feature of despotic societies, with closely
ranked individuals interacting more frequently than individuals with a large
rank distance. The frequency and intensity of aggressive behaviour in despotic
macaque species have also been found to correlate with rank distance, as when
rank distance is large, the subordinate will submit or flee rather than engage
in aggression (de Waal, 1991).
The Buton
macaque (Macaca ochreata brunnescens), a sub species of the booted
macaque (Macaca ochreata ochreata), confined to the islands of Buton and
Muna off the south east coast of Sulawesi, has provisionally been classified as
nepotistic- tolerant. This sub-species is yet to be studied in any detail so
classification has been based on the pattern exhibited by the remaining macaque
species endemic to Sulawesi. These macaques exhibit a less linear dominance
hierarchy with notable less asymmetry in power between dominants and
subordinates (Thierry, 1985, 2000; de Waal & Luttrell, 1989; Matsumara,
1991; Petit et al, 1997). Affiliative behaviours such as social grooming
occur at a higher rate in these ‘tolerant’ macaques and aggressive episodes
are less severe than in the more despotic species, as biting is neither frequent
nor injurious. When aggression does occur, greater symmetry in contests can be
observed with the majority of attacks inducing counterattacks from the target
(Thierry, 1985; Petit & Thierry, 1994; Petit et al, 1997). In
contrast to the despotic macaques, no correlation has been found between
dominance rank/rank distance and social behaviour for the Sulawesi species
(Chaffin, 1995; O’Brien & Kinnaird, 1997).
Species
dominance style has also been found to have an effect on affiliative behaviour
such as social grooming. Social grooming in primates has been described as an
altruistic behaviour (Trivers, 1971) in which the groomer (altruist) provides
the groomee (recipient) with benefits such as removal of ectoparasites and the
release of β-endorphins (Keverne et al, 1989). It has been
hypothesised that dyadic grooming bouts are exchanged reciprocally using a
‘tit for tat’ reciprocity strategy (Seyfarth, 1977). Social grooming could
therefore be exchanged for itself, such that grooming bouts are time-matched for
both members of the dyad (e.g. Macaca fuscata, Muroyama, 1991), or for
another commodity such as coalitionary support (Packer, 1977), allomothering (Muroyama,
1994) or tolerance at feeding sites (Seyfarth & Cheney, 1984). When grooming
exchanges involve other commodities the exchange may be affected by the
dominance ranks of the dyad members, as dominant individuals will presumably
make more powerful allies than subordinates will. Low-ranking individuals are
therefore believed to compete for access to higher-ranking conspecifics,
resulting in a positive correlation between dominance rank and the frequency and
duration of grooming received (Seyfarth, 1977; Silk, 1982). Grooming exchanges
may also be effected by the ‘trade value’ of the commodity in question. For
example in an exchange of grooming from subordinates for tolerance at feeding
sites from dominants, the exchange rate given for the grooming bout may be
influenced by the dominants resource holding potential (RHP – their ability to
monopolise the food source) and food availability (Noë & Hammerstein,
1995).
Work was
expected to be conducted on two troupes from 01/06/2002 to 23/08/2002,
unfortunately, as a result of poison placed in local farms, both study groups
had depleted in numbers by observation week three. Group 1 was the most heavily
effected and were no longer included in the study. All subsequent research was
conducted on group 2.
Each
individual within the troop was identified. Scan instantaneous samples were
conducted at 20 minute intervals for the behavioural categories; resting,
locomotion, foraging, feeding, self grooming, allogrooming, aggression, and
social, to give an overall indication of the activity budget of each individual.
All occurrences of dominance interactions (threat, chase, contact and
displacement) were recorded, noting the individuals involved and the cause of
the incident if known (food, allomothering, infants, coalitionary support). The
direction of these dominance interactions may then be used to calculate the
dominance hierarchy using Landau’s index of linearity and Appleby’s
probability test for linearity. The calculated dominance hierarchy and the rates
and intensity of aggressive episodes recorded for the Buton macaque may then be
compared to the social structures of nepotistic-despotic and nepotistic-tolerant
macaque species. Once rank positions are known it is then possible to combine
this data with the scan samples to determine the effect of rank position on
daily activity budget.
In addition
to scan samples, 15-minute focal animal continuous samples were conducted during
rest bouts for each adult member of the group for the behavioural categories
previously outlined, with the additional categories: eye gaze, approach,
solicit, grooming, terminate grooming, and allomothering, all of which may be
given or received. This data provides an indication of both the frequency and
duration of grooming bouts and which individuals have chosen to initiate and
terminate each bout. As grooming duration is provided it is possible to
determine if grooming bouts are time-matched between dyad members (suggesting
‘tit for tat’) or if time discrepancies occur (suggesting biological
markets). These data can then be related back to the dominance ranks of the
individuals involved to determine if rank or rank distance effects the amount of
grooming received.
Due to the
extensive loss of individuals to both the study groups and the ongoing period of
instability that ensued, the data produced from this research should not be
considered as representative of the social behaviour of the Buton macaque.
Further research will therefore need to be conducted and comparisons made with
this year’s data to provide confirmation of any findings.
The majority
of results may not be determined until the dominance hierarchy within the group
has been calculated. However, preliminary results have suggested that the rate
and intensity of aggression was generally low and retaliation occurred in the
majority of episodes. No significant effect was found between dominance rank or
rank distance and the frequency and duration of grooming received. These results
would suggest that the Buton macaque should be classified as
nepotistic-tolerant. However, time discrepancies were observed between young
nulliparous females and adult females with infants. Allomothering was also
observed between these dyads thus suggesting that grooming may be exchanged for
allomothering in the Buton macaque.
A
report entitled The
dominance style of the Buton macaque (Macaca ochreata brunnescens) will be
produced by Kathryn Slater, Liverpool University by November 2002.
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