Pheidole

A pheidologist and his exploration of a hyperdiverse myrmicine clade

Behavioral dominance vs Numerical Dominance vs Ecological Dominance

During my readings on ant behavior, there were some terms that cropped up that I was not quite sure about. Unfortunately, most of the papers seemed to assume reader familiarity with them, but my background is not ecology, so I had to search for some clarification. In the interest of perhaps helping those who also stumble on the meanings of the various types of dominance, here’s what I understand about them.

In any population of ants at a location, there is usually a dominance hierarchy among the species when it comes to obtaining and competing for resources like food.



In general, species that are more aggressive or are larger or have better weaponry tend to be able to procure the food. This is an example of behavioral dominance, where the behavior of the species is the main factor on whether it can dominate resources. Where I am right now in Central Florida, both Pheidole megacephala and Solenopsis invicta are aggressive competitors and are able to hold off or even push out competing ants from food baits. I have seen S. invicta take over baits surrounded by masses of ants simply by having their larger workers run right at the group. In the case of P. megacephala, a group of majors called up by the minors is usually enough to drive off pesky Brachymyrmex spp, Paratrechina spp, or Nylanderia spp. I have even seen them push out S. invicta workers that had already taken control of a bait.



Another way a species can dominate an area is via numerical dominance, which is simply when they can field significantly more workers in the field against competitors. This is because, other things being equal, the species that can harness more individuals normally will discover food faster, and be able to exclude other ants from the food simply due to their sheer mass. Unicolonial ants like P. megacephala, Linepithema humile and the like exhibit very strong numerical dominance due to the fact they do not form separate competing colonies.

An example of how numerical superiority can be a major factor during competition was in clear view to me when a Solenopsis invicta colony tried to push out a Pheidole megacephala peripheral node that I was studying. The larger individual fire ants with their potent stings were more than a match for even individual P. megacephala soldiers, but instead of absconding, the P. megacephala simply kept sending reinforcements to the front until the sheer mass of combatants overwhelmed the ability of the fire ants to push them out.

Finally, ecological dominance is the overall ability of a species to dominate an environment due to a combination of behavioral and numerical dominance. Many unicolonial ant species exhibit both and are thus ecologically dominant in many areas where they occur, and this includes P. megacephala, Wasmannia auropunctata, and Linepithema humile.

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