--A territory is an area occupied more or less exclusively by an animal or group, and is defended by overt aggression or advertisement.

--There is lots of variation across species in whether they defend a territory. Many species only defend a territory for part of the year.

Territories may be held for many different reasons.

--Some territories, such as birds on winter feeding grounds, are just for feeding.

--Other territories, such as leks, are just for mating.

--All-purpose territories are used for feeding, breeding, raising young.

Territories are costly to hold.

--The boundaries have to be patrolled, and intruders have to be dealt with, either by displays or by fights.

Holding a territory also provides benefits. These might include:

--a longer-lasting food supply that is shared with fewer individuals

--increased access to mates

--better conditions for offspring

--familiarity with the territory. There is some evidence that animals practice escape routes; knowing the area is helpful in escaping predators.

Territories should only be held when they are economically defendable.

--The benefits of holding a territory should be outweighed by the costs.

Factors that influence the economic defendability of a territory:

1. Is there competition for the resource?

-- If no one else wants the resource, it is not necessary to defend a territory.

--If competitors are really numerous, it may not be possible to exclude others--you would spend all your time fighting.

2. How is the resource distributed in space?

--The easiest resource to defend is clumped. If resources are spread out over a large area, they are harder to defend.

3. How is the resource distributed in time?

--Predictably occurring patches are easier to defend.

Let’s look at a graphical picture of territoriality.

--In this example, we can think of the costs and benefits of maintaining a territory as being in units of energy.

--As territory size increases, the costs of defense increases. Why would this be so?

--As territory size increases, the benefits begin to level out.

Territory size. Sunbirds defend winter feeding patches. They drink nectar from flowers.

--When nectar levels were very low, they abandoned their territories because they could not gain enough energy to balance the cost of defense.

--When nectar levels were very high, the cost of depletion of nectar was low, so intruders onto the territories were tolerated.

--The birds always defended around 1600 flowers, even though the area of the territory varied about 300 fold.

When should owners allow satellites onto their territories?

--Satellites are other individuals that are allowed to use a territory.

--Example: Pied wagtails are birds that feed along a river bank, eating insects that have washed up on shore. Birds take, on average, about 40 min to complete a circuit.

--When food resources are very high, the territory owner allowed a satellite to walk the territory too. This meant that the food available to the owner was reduced by one half, but the cost of territory defense against other birds was shared by the satellite.

--Often, the owner of the territory, the resident, wins.

--Why might intruders win so often?

Hypothesis 1: They are better fighters. This idea was introduced back in game theory: the idea of resource holding potential, or RHP. That might be how they got ownership in the first place!

Hypothesis 2: They have more to gain from a fight and are therefore prepared to fight harder. Territory owners might find the territory more valuable than intruders, because they already know the location of good feeding and nesting sites.

Hypothesis 3: Maybe this is an arbitrary rule that serves to decrease the costs of fighting for both parties.

Territory size. Sunbirds defend winter feeding patches. They eat nectar from flowers.

--When nectar levels were very low, they abandoned their territories because they could not gain enough energy to balance the cost of defense.

--When nectar levels were very high, the cost of depletion of nectar was low, so intruders onto the territories were tolerated.

--The birds always defended around 1600 flowers, even though the area of the territory varied about 300 fold.

When should owners allow satellites onto their territories?

--Satellites are other individuals that are allowed to use a territory.

--Example: Pied wagtails are birds that feed along a river bank, eating insects that have washed up on shore. Birds take, on average, about 40 min to complete a circuit.

--When food resources are very high, the territory owner allowed a satellite to walk the territory too. This meant that the food available to the owner was reduced by one half, but the cost of territory defense against other birds was shared by the satellite.

What happens when territory owners are challenged?

--Often, the owner of the territory, the resident, wins.

--Why might residents win so often?

Hypothesis 1: They are better fighters. This idea was introduced back in game theory: the idea of resource holding potential, or RHP. That might be how they got ownership in the first place!

Hypothesis 2: They have more to gain from a fight and are therefore prepared to fight harder. Territory owners might find the territory more valuable than intruders, because they already know the location of good feeding and nesting sites.