The basic prediction from sexual selection theory is male dominance. Males usually win conflicts and have priority of access to food, etc. Why? This goes back to sexual selection;
Because of sexual selection, you get sexual dimorphism; males are bigger and have more weaponry. When they come into conflict with females, it's usually the male who wins. In this sense, male dominance is kind of a byproduct of competition between males. Sexual selection shapes males physically but also mentally- they tend to be more aggressive and more competitive. There are cases where males and females are equal but there are very few instances where females are dominant.

Examples of species with male dominance: brown capuchins, baboons, langurs, orangutans, chimps.

All early studies in primatology focused on male dominance. One reason is that it's more visible and exciting. Also, they were all men and probably had a cultural bias that made it easier for them to see the male dominance. After a while, though, they began to see that females formed social bonds and could gang up on males. Through the 80's all serious work on female dominance was done by women primatologists.

"To a greater or lesser extent, females in these species take priority at feeding sites and control social access to other group members. An offending male who comes too close to a female or her infant is cuffed in the face or chased away, and in some cases males are relegated tot eh outskirts of the troops. These species stand in contrast to television narratives about 'central male hierarchies' and 'dominant male leaders' - Sarah Hrdy 1981, pg 59, describing female dominance

Most female dominance species are in the prosimians, especially the prosimians of Madagascar. Ring-tailed lemur, sifakas (propithecus), and the indriis who are monogamous.

There are also a few cases outside of Madagascar; squirrel monkey (evidence not quite so clear cut), and the talapon which is a small cercopithecus. In apes, some newer research on bonobos shows that by forming alliances with each other, the females are able to socially dominate the males.

Female dominance in prosimians

For a while it looked like the whole lemuridae family was female dominant, but it turned out that that's not the case- a 1990 comparative study of ring-tailed lemurs, crowned lemurs, and brown lemurs found that females were dominant in the ring tailed and the crowned lemur, but not in the brown lemur. Therefore, we can't just write it off as a characteristic of lemurs.

Patterns

Most research has involved conflict over food, mainly because it's more dramatic and easier to collect data on. If you look at % of encounters between males and females, in the sifaka about 70% are over food, but in the ring-tailed lemur only about half are over food.

If you look at % of encounters where females win in ring-tails, olfactory disputes, sexual disputes, and grooming disputes are all 100% female-won. Feeding and spatial (supplanting) disputes are won over 90% by the female, and agonistic disputes are won by the female about 60% of the time.

• very short breeding seasons
  
• small and monomorphic body size

Why? Two Hypotheses...

The male perspective

Males defer to females in order to conserve energy for the brief, but energetically costly, annual mating season. Think about it- male competition is all about mating access, but if for most of the time there are no receptive females since the breeding system is so short, then what's the point of wasting energy being dominant?

The female perspective

Environmental or metabolic factors combine to increase the costs of reproduction for females. Given these circumstances, females win competitive interactions because the benefits they gain are greater than those derived by males. Basically, females are harder-pressed to get enough food.

Data that supports or harms these theories:

Female dominant systems indeed have much shorter breeding systems than male dominant systems. Female dominant species' breeding season is about 50 days, while male dominant species' breeding season is about 220 days- like 2/3 of the year. However, the correlation is not perfect: brown lemurs have a very short mating system, about 14 days, so they should be female dominant but they're not.

Madagascar is more seasonal than most primate habitats. It's also got a pretty short season of plenty and they can't complete their whole reproductive cycle during the season, so the food goes away before they're done gestating and lactating. Note that there's no good data to back up this theory; no one has gone out and measured food availability and energy costs etc.

Smaller animals have higher metabolic rates. Are female dominant species unusually small? Yeah, they're smaller but it's not so dramatic. It's not statistically significant. The standards of deviations are pretty large.

If some species are producing more or larger infants, then that's going to increase the nutritional stress on the moms. Data? Female dominant species' neonate:mom weight ratio is .12, while in regular primates it's .72. So, indeed, female dominant species are having bigger kids. (This is total litter weight; may be because they have more kids or may be because they have heavier kids.)

After they're born do the kids grow up faster? If they do, then their nutritional needs are greater. The rate of infant growth shows how great the stress is on the mom. Data for this is weaning data compared to female weight; you look at whether they're being weaned early or late for their moms size. You see that female dominant species fall below the line- they're weaning before you'd expect; so their babies are growing up faster. This is definitely a trend, but it's not super dramatic.

If you plot life span vs birthrate, species that reproduce at higher rates tend to be those who die younger- this may have to do with the costs of reproduction. When you control for the lifespan of species, you find that female dominant species are above the line- they're reproducing offspring at a higher rate and they're dying earlier. All of which suggests their costs of reproduction are higher.

Propithecines show higher mortality rates for females than males for all age classes- life is harder on them for some reason, so they're more nutritionally stressed, so they die more.

To sum up;