Spacing Patterns and Territoriality

Also relevant to this lecture is ch. 22 in Smuts et al. which this lecture is partially based on.

The Use of Space

Most animals, besides our fun-loving friend the barnacle, move around and use space. If you were an animal, there are several spatial-use categories you might fall under.

You might wander nomadically, like the cedar waxwing. They don't often come back to same place twice. This type of spatial use is rare; most animals don't do that. Why? Because it's safer when you know territory, otherwise you'll waste energy looking for food, water, and safe spots. Most animals who wander nomadically do so 'cause they have to 'cause there's limited resources.

You might wander seasonally. This is seen in African ungulates like the zebra, for example, and also birds of course. You may ask, "Why bother? Migration is dangerous, difficult, and expensive in terms of energy." (Or you might not ask but I'll tell you anyway.) They do it because of seasonal changes; habitats become too cold or too dry, and food availability varies. Primates don't do this too much 'cause they're in the tropics so they're not too affected by seasonality.

Most animals stick in one place. The advantage to this is local knowledge. You know where the dangers are, where the food and water are, when and where not to go, and you also know other individuals or groups of the same species in the area. (Don't confuse staying in one place with the issue of dispersal; to avoid inbreeding, at least one sex must move once in its life, but just because a species disperses doesn't mean that they're nomadic. But dispersal comes later.)

What do primates need to have in their home range to be able to stick around? Food is always good. Water is, for some species. Some who live in the tropical rainforest can lick the dew off leaves, but in arid areas it's really important to have a water source. Shelter is not an issue for some species like ones who live in rainforest canopy, but for baboons who sleep on sleeping cliffs to escape from predators, their possible ranges are affected by the availability of cliffs. Also, the last thing you need are mates! You've got to be around the other sex or your territory will be uninhabited within one generation.

A Reminder on Terminology:

day range: The distance a group or individual moves in a day.
home range: The area it stays within during a set period of time like a year.
core area: The part of its home range that it stays in mostly. The definition of a core area is a little less precise than the others- there are no rules on measuring how long or how much they have to use it for it to be a core.

This brings us to the question, How long is long enough to watch a group? How do you make your recommendation measurable? You could watch them until they don't go anywhere new anymore, but that's a little imprecise. A more consistent way is to call it at a year. This is good 'cause sometimes there's seasonal variation.


Once you've decided to be an animal who stays in one place, how do you deal with other groups who want to go where you are? You might want to defend your space and its resources. This behavior is called territoriality.
Note that an animal or group's "area of exclusive use" isn't the same as area that they range over- ranges can overlap a lot or they can overlap hardly at all.

Four examples: Vervets, Gibbons, Mangabeys, and Gorillas

Vervets: They're terrestrial savannah dwellers with small territories. When groups meet, there's sometimes friendly interactions especially involving juveniles, but usually aggressive defense. Females take an active role in conflict. They have a special call for group-group conflicts. Conflicts involve chases, hitting, and sometimes biting.

Gibbons: Monogamous groups with small territories. They have aggressive defense involving displays, chases, and fights. They sing to defend their territory. When two couples meet up, they'll display, sing, and chase. Between-group aggression is sex-specific; males fight males, and the females fight females.

Mangabey: (cercocebus) Large home ranges with almost complete overlap but exclusively-used core areas. Males utter a distinct call upon contact and groups mutually avoid each other. They use a call called a whoop gobble to let others know they're there. If someone hears it, they move away and they all avoid each other. This is unless there is a specific resource that they might all want to feed at like a good fruit tree.

Gorillas: Large home ranges with almost complete overlap.
Adult males are the primary participants in aggression. Males initiate aggressive displays including chest-beating, branch-breaking, and charges. The females and young are rarely involved in conflicts. Our professor says that while he has never seen an adult male charging and displaying, everyone else who has agrees that it's quite intimidating!

What causes variations in...

...home range size?

Remember some things which affect home range size; the group size affects how much resources they need available. Also the quality of their food and how available it is. If you eat leaves, you don't need to look so hard for them so you don't need so much space. An example of this is seen when you compare orangutans and gibbons. They're good to compare 'cause they live in pretty much the same habitat and both eat the same type of food. However, orangutans' body size is much larger. Gibbons have smaller home rages because they just don't need as much space to find their food. Also, compare mangabeys; different kinds have different sized groups. Their body sizes are pretty constant but there's a strong correlation between group size and home range size. You can also compare colobines; the black and white colobus is pretty much folivorous and has a small home range but the red colobus, who lives in a similar habitat but includes more fruit in its diet, tends to have larger home ranges.

...encounters between groups?

Let's say your group has a set home range. When other primates are encountered, what do you do? Some groups do have encounters without conflict, like squirrel monkeys or colobus monkeys. Sometimes maybe they'll even play together, but since resources are often limited, they're competing so there's conflict. There are different ways to do this. One way is to set up a territory and defend it. In this system, who wins and who loses depends not so much on the characteristics of the group but where the conflict took place- the home team usually wins. Four representatives (one from each group of primates) who exhibit this kind of territoriality are: prosimian- indri; new world monkey- titi monkey; old world monkey- vervet; and ape- gibbon. Also, chimps defend community boundaries which are a little different.

Why don't all primates defend territory? It seems pretty nice since you get exclusive use and all, right? As long as there is competition for resources, there is the potential for territory defense but the problem is, it has to be economically defendable; the benefits of defense must outweigh the costs.

Check out the diagram from Krebs and Davies on home range size plotted against the costs and benefits. Costs increase linearly as the home range size increases, but benefits are a curve which will level off eventually. This is because you only need so much; getting more access to food won't mean anything if that's all you can eat. So, eventually the two lines cross. In the region where the benefits are greater than costs, that's where you'd expect defense of territory to happen. However, if benefits are always lower than costs then you don't expect territory defense to happen. People in primatology don't really use this type of approach quantitatively since in primates it's all too complex and too hard to measure well, but it is useful conceptually to help you think about relative costs and benefits.

One obvious cost for primate territoriality is related to the necessary size of home range for your food type. If it needs to be huge then it's too hard to defend it, but if you only need a smaller one then its easier to defend. Another factor is how hard it is to get around in your habitat. If you're a quick animal then maybe it's practical for you to defend your territory, but if you are really slow then don't even bother.

Some guy said, if d=diameter of home range and drl=day range length, you'll see territoriality when drl > d. In other words, if you can cross your whole territory in a day, then you'll defend it 'cause it won't cost you too much energy and time, but if it takes a long time to get through your territory then you won't.

Variation in intergroup behavior


Ok, let's say we're in a place that is not beneficial to defend. We encounter another group; what type of conflict will there be? Usually one group will be dominant over another- the outcome will not depend on the location of conflict, but on the competitors. In a number of encounters between the same two groups, one will usually win in every encounter.

Intergroup dominance

What determines which group is dominant? Generally it is the size of the group or the size of the fighters. It might also depend on the fighting abilities of the group members, but usually it's group size and number of adult males. An example of this is the macaques- the outcome of macaque conflicts depends on group dominance.

Mutual avoidance

In other species there's another solution- if groups are constantly encountering each other it will take a lot of energy fighting and chasing so if they could avoid it all, it would be better for everyone. Instead, some species use loud calls for mutual avoidance. A prime example of this is the howler monkey. When they get up, before they go anywhere they sit around and howl really loud and listen to who else is yelling. Then they go off for the day's foraging in a direction where there wasn't anyone yelling back. Likewise, the mangabeys' give out whoop-gobble to warn other groups of their presence, and they listen to whoop-gobbles to avoid others. This has been proven in playback experiments. Scientists recorded whoop-gobbles and then set up speakers. They played it back at different distances from groups of howlers. When the speakers were close to the group, they moved away, but when they were farther away, 200 meters or more, then they didn't do anything.

Individual differences in intergroup behavior

May be caused by difference in locale, since there is variation in geography. However, within the same location there's a lot of difference among individuals; sometimes even when the adults are going to fight, the kids get together first and play. If you think this is weird, remember that one sex is going to have to disperse, so this way they get to know people from the neighboring groups that maybe they're going to have to join when they hit puberty.

Intergroup behavior also varies between the sexes. We will do more on this later, but males and females have different agendas; A female's output is limited by access to food/resources, while males are limited only by access to mates. This means that females only fight when resources are limited and defendable. Depending on the situation, sometimes they'll fight and sometimes they won't fight. Female participation depends also on the composition of group. In some species, the females stay where they're born, but in others they disperse and live with strangers. So the females who stay make a sharp distinction between members of their groups and nonmembers so they fight more. In dispersing species, the females could care less if someone is attacking the group. Thus, both ecology and population structure both predict whether females will join in the fight.

For males, however, it always pays off to get more female access, so they always have conflict. This is very consistent. You can make a reliable prediction that males will fight other males.