Materials and Methods

Materials and Methods

Materials

A survey of the literature was undertaken with the aim of examining potential causes of dispersal patterns of primate species living in multi-male, multi-female groups. Species absent from the Macaca and Papio groupings, specifically the Guinea baboon (Papio papio), Assam macaque (Macaca assamensis), Moor macaque (Macaca maura), Black macaque (Macaca nigrescens), the Tibetan macaque (Macaca thibetana), the Formosan macaque (Macaca cyclopsis) and the Tonkean macaque (Macaca tonkeana), were all excluded due to a paucity of available data.

Table one- Species

Common name	Linnean classification
Olive baboon	Papio anubis
Yellow baboon	Papio cynocephalus
Hamadryas baboon	Papio hamadryas
Chacma baboon	Papio ursinus
Stump-tailed macaque	Macaca arctoides
Crab-eating macaque	Macaca fascicularis
Japanese macaque	Macaca fuscata
Rhesus macaque	Macaca mulatta
Pig-Tail macaque	Macaca nemestrina
Celebes macaque	Macaca nigra
Bonnet macaque	Macaca radiata
Lion-tailed macaque	Macaca silenus
Toque macaque	Macaca sinica
Barbary macaque	Macaca sylvanus
Mountain gorilla	Gorilla gorilla berengei
Bonobo	Pan paniscus
Chimpanzee	Pan troglodytes
Red Colobus	Colobus badius
Vervet monkey	Cercopithecus aethiops

Variables were chosen to elucidate which of two competing hypotheses, inbreeding avoidance or intra-sexual competition, was better supported. The parameters shown in table two were investigated for the 20 species detailed below. Sources of information are detailed in table three.

Table Two - Variables

Variable	Range	Coding
Female age at sexual maturity	2.5 - 10	Years
Male age at sexual maturity	3.2 - 13	Years
Female age at first conception	3.72 - 12.25	Years
Earliest age at natal dispersal	2.38 - 9	Years
Latest age at natal dispersal	5 - 12.4	Years
Average age at natal dispersal	3.5 - 11	Years
Average male tenure (either in group or as a male)	1.5 - 7.8	Years
Inter-Birth Interval	1.1 - 5	Months
Mating System (Multi- or single- mount)	1 - 2	1=Multi-Mount, 2=Single-Mount
Lifespan	18 - 44.5	Years
Average group size	7.3 - 57.07	Number of individuals
Average number of adult males in a group	1 - 16	Number of individuals
Average number of adult females in a group	1.9 - 24	Number of individuals
Evidence of infanticide	1 - 2	1=Infanticidal, 2=Non-infanticidal

Table Three - Sources of data

Species	Source of data
Papio anubis	Bercovitch and Strum 1993; Harvey and Clutton-Brock 1985; Manzolillo 1983; Melnick and; Packer 1979; Pearl 1987;Smith 1992.
Papio cynocephalus	Alberts and Altmann 1995; Altmann et al 1996; Bentley-Condit and Smith 1997; Glassman et al 1984; Rasmussen 1981; Smith 1992; Smuts and Nicolson 1989.
Papio hamadryas	Abegglen 1984; Harvey and Clutton-Brock 1985; Crawford and O’Rourke 1978; Kummer 1968; Phillips-Conroy et al 1992; Sigg and Stolba 1981; Sigg et al 1982; Zinner et al 1994.
Papio ursinus	Bulger and Hamilton 1988; Devore and Hall 1965; Melnick and Pearl 1987; Sapolsky 1996; Seyfarth 1976; Smith 1992.
Macaca arctoides	Bauers and Hearns 1994; Harvey and Clutton-Brock 1985; Faucheux et al 1978; Fooden 1990; Hadidian and Bernstein 1979; Harvey and Rhine 1983; Melnick and Pearl 1987; Ross 1992.
Macaca fascicularis	Berkson 1968; Harvey and Clutton-Brock 1985; Harvey and Rhine 1983; Kawamoto et al 1984; Nomura et al 1972; van Noordwijk and van Schaik 1985, 1999; Ross 1992; de Ruiter and van Hooff 1993; de Ruiter et al 1994; Suhana et al 1999.
Macaca fuscata	Harvey and Clutton-Brock 1985; Itoigawa et al 1992; Matsumura 1993; Nigi 1976; Scucchi 1984; Sprague 1992, 1998; Sprague et al 1998; Sugiyama 1976; Suzuki et al 1998; Takahata et al 1995.
Macaca mulatta	Berard 1999; Boelkins and Wilson 1972; Bourne 1975; Chepko-Sade and Olivier 1979; Harvey and Clutton-Brock 1985; Colvin 1988; Drickamer and Vessey 1973; Melnick et al 1984 a,b; Missakian 1983; Perry and Manson 1995; Wilson et al 1984.
Macaca nemestrina	Caldecott 1988; Harvey and Clutton-Brock 1985; Hadidian and Bernstein 1979; Melnick and Pearl 1987; Ross 1992; Sackett et al 1979.
Macaca nigra	Caldecott 1988; Harvey and Clutton-Brock 1985; Melnick and Pearl 1987; Rogers 1992; Ross 1992.
Macaca radiata	Harvey and Clutton-Brock 1985; Melnick and Pearl 1987; Rosenblum and Smiley 1980; Ross 1992; Silk 1998, 1990.
Macaca silenus	Harvey and Clutton-Brock 1985; Green and Minowski 1977; Lindberg and Lasley 1985; Melnick and Pearl 1987; Ross 1992.
Macaca sinica	Harvey and Clutton-Brock 1985; Dittus 1975, 1977, 1979; Keane et al 1997; Melnick and Pearl 1987; Ross 1992.
Macaca sylvanus	Harvey and Clutton-Brock 1985; Deag and Crook 1971; Kuester and Paul 1984, 1999; Kuester et al 1994; Martin and von Segesser 1998; Paul and Kuester 1985; Paul et al 1993; von Segesser et al 1992, 1999; Taub 1980;
Gorilla gorilla berengei	Harvey and Clutton-Brock 1985; Harcourt 1978; Robbins 1995; Sicotte 1993; Watts 1990, 1991, 1994 a,b; Yamagiwa 1999;
Pan paniscus	Hasmimoto 1997; Idani 1991; Ihobe 1992; Uehara 1988;.
Pan troglodytes	Harvey and Clutton-Brock 1985; Fragazy and Bard 1997; Hamada et al 1996; Pusey 1979, 1980; Sakura 1994; Takahata et al 1995; Yamagiwa 1999.
Colobus badius	Harvey and Clutton-Brock 1985; Marsh 1979; Stanford 1995; Struhsaker 1969, 1977; Struhsaker and Leland 1979, 1987.
Cercopithecus aethiops	Cheney 1981; Cheney and Seyfarth 1983; Cheney et al 1988; Harvey and Clutton-Brock 1985; Henzi and Lucas 1980; Whitten 1982.

Methods

Data consolidation

The data was entered into an SPSS database with each study entered seperately. Examination of the initial data set thus created revealed that despite the large number of studies examined no-one study contained all the variables necessary for a complete analysis. Indeed, most studies revealed only three or four variables at most. Given the difficulties this data set would present to any meaningful analytical approach, the decision was taken to reduce the data to an average value for each species. In order to avoid biasing these average values laboratory studies were excluded on the grounds that data obtained from such sources would likely no be reflective of the natural condition of the species concerned

Missing data

Missing data was one problem in the Macaque data set. To avoid the assumptions inherent in the exclusion of variables during analysis, an average value was inserted using the sub-groupings of Macaca species reported by Caldecott (1988).

Data manipulation

When the normality of the data set was explored, three of the fourteen variables were found to be significantly skewed in their distribution. Following the protocols set out in Fowler and Cohen (1993) these variables were transformed to normality via a log₁₀ computation. The variables thus transformed were: female age at sexual maturity; average male tenure and average age at natal dispersal. Due to the Macaque data points outnumbering other genera, the data set was weighted according to species type in order to avoid any subsequent biasing of analysis.

Data analysis

Initially the data set was analysed through a series of bivariate correlations, in an attempt to discern any immediately obvious relationships. To probe the findings further the data was re-examined using partial correlation analysis, controlling for each variable in turn. All statistical analyses were performed using SPSS

Due to the continuous nature of all but two of the variables, linear regression was the most powerful analytical method available. Using the stepwise method the data set was examined first as a whole then subsequently sub-divided according to species and then by mating system. Comparisons were made between the species types, between mating systems and between male dispersal and female dispersal.To further investigate why there are species differences in which sex disperses logistic regression analysis was employed to evaluate the relative importance of the contributing factors.