Do land animals claim territory to prevent large oscillations in population?

I was watching my dog claiming territory the other day, and it occurred to me : why does the species Canidae spend all this energy marking and defending areas of land?

Well, I had a bit of insight. On average, in a given biome on earth, each square kilometer of land area produces X amount of biomass from fixing carbon. There’s roughly a factor of 10 difference with each layer in a food web, so the herbivores that eat the plants are about 0.1X in total biomass per square kilometer. The predators that feed on them, such as wolves, are 1/10 of that.

In short, each square kilometer can support over the long term a finite number of dogs. So each member of the species marks out a range big enough to ensure it has enough land area to survive. Whenever 2 members of the species want the same territory, the 2 animals compare each other to see which animal is better fed and healthier.

The comparisons measure muscle strength, total bulk (fat + muscle), and CNS coordination. That’s why it looks like a nipping and wresting match. It isn’t like that because it’s fun, it works that way because it measures the most important variables.

The losing animal goes off to find unclaimed territory or starve (I suspect the loser starves most often in the equilibrium situation). The reason animals respect each other’s territory once a comparison happens is because the species as a whole benefits if the loser goes off and dies. This is the same reason the animals try to avoid injuring each other during a battle for territory : from an individual utility perspective, it’s optimal for the losing animal to at least attempt to kill the bigger animal instead of retreating and dying for certain.

The reason all this is necessary is that if the animals just bred out of control without bothering to claim territory, in the short term this would work fine. There would be more and more animals in a given area of land and in the short term they would find sufficient food. The problem is that once the predators eat not only the weaker members of a herd, but all the breeders as well, the population of prey will crash to nearly nothing as the predators eat them all. This in turn means the predator population will crash as well. Genetic drift from the small number of remaining predators and small number of remaining prey will send both species to the edge of extinction. Presumably, in a given area, the predators will become locally extinct, the prey will repopulate, and then the oscillations start all over again.

So it’s really a control system that is underdamped.

I learned recently that male dogs aren’t so much ‘marking their territory’ as sending coded messages to other dogs. Someone more cleaver than me named it ‘pee-mail’.

One dog leaves a message on the side of a tree that communicates their state of aggressiveness and sexual readiness etc., and another dog comes along, decodes the message, and leaves their own message, and so on.

I think most young male animals will wander off at certain age to seek territory that is underpopulated, and this natural dispersal reduces the chance of overpopulation. Adult males may also chase off younger males which will reduce the chance of interbreeding and sexual competition.

True in principle, although the actual percentage can vary. Warm-blooded herbivores and predators, for example, have a lower ratio than cold-blooded animals since they use more energy per unit mass.

Again, true in principle, but this requires that the resource in question be economically defensible. It may not work for migratory herd animals, or animals too spread out to be easily defensible.

In most animals, combat is geared to test who will win an encounter without becoming lethal. This is of benefit to both the winner and the loser. The winner undergoes more risk of injury if he tries to kill his rival, while the loser, by giving up instead of fighting to the death, will live to fight another day (when he may be bigger and stronger or his rival older and weaker).

In general, biologists try to avoid explanations invoking “for the good of the species.” These behaviors can be explained in terms of individual selection rather than in terms of what’s good for the species. In fact, it may work out that way, but that’s not why it evolved.