Maybe sympatry can work for you. It's a general and debated concept not really describing aspects related with limited resources, but with sharing and directly interacting in a common ecosystem. You could probably search for a concept among coevolutionary theory (have a look in The Coevolutionary process, by John N. Thompson)

Did you consider a temporal niche differentation? I am working mainly with beetles, but it could be possible to applied it also for mammals.

 Interference competitors may exist spatially together when they are segregated temporally and this provides a base for their co-existence. Further findings can be found here. http://onlinelibrary.wiley.com/doi/10.1046/j.1472-4642.2000.00069.x/abstract 

There is a concept on the basic niche, actually, in the nature, a lot of species had the overlap niches in every aspect. But you could divide them, if you had the enough data.There is an obvious fact, that means, the subject that you focused, they all lived in the same one habitat. 

You may want to investigate logisitic competition theory which predicts coexistence between species based on resource consumption. David Tilman conducted a lot of work on this subject. Good luck.

I want to make a point "large overlp territories" does not always means competitors. First of all, you should investigate from your data, if there are, if the species is really have "niche overlap" ... See for data needed on package spaa in R or EcoSimR...If you have data hat fit these packages, you can explore first how far these species are really in competition...

Hope this helps

Remember, if resources are not LIMITING (that is, one or both species suffer in some way at the expense of the other) then there is no competition. In your case, both populations could be well below their carrying capacities and therefore, they do not compete because the resource is not that which limits them. While these two species may interfere with each other, it does not mean that they actually cause a reduction in survival or reproduction as a consequence. Be careful not to DEFINE your situation in such a way that makes competition seem inevitable.

Thanks all your responses!! These are delicate concepts, which I'm trying to use carefully...   thanks for your inputs!

As Fathul suggests spatial processes can mediate competition in a number of different ways to facilitate coexistence. There is an excellent review of theory and data here: http://onlinelibrary.wiley.com/doi/10.1046/j.1461-0248.2003.00530.x/full, free pdf here: http://izt.ciens.ucv.ve/ecologia/Archivos/ECOLOGIA_DE%20_POBLACIONES_Hasta%202004/ECOL_POBLAC_Hasta%202004_(A-G)/Amarasekare%202003.pdf.

Why not propose a concept/framework for the phenomenon, as I haven’t heard of such a concept succinctly coined in the terminology?

We have found something similar to what you describe but for termites (whole paper attached):

“The spatial distribution of all termite mound

populations was aggregated, which represents by

far the most common pattern of spatial distribution

(Odum 1971). Random distribution is

relatively rare in nature and occurs where the

environment is homogeneous and where many

minor factors act together on the population.

When a few major factors dominate, as is usually

the case, there is a tendency to aggregate. Uniform

distributions prevail when competition is severe

or where there is positive antagonism, promoting

even-spacing.

In the northern KNP, there was no evidence of

severe competition during comparisons of both

active and inactive mounds involving all termite

colonies, colonies of Macrotermes only, or colonies

of the two dominant species of Macrotermes (only

active mounds). Studies in West Africa by Collins

(1981) and Lepage (1984) revealed that mounds of

M. bellicosus were distributed randomly, from

which they concluded that intraspecific competition

was not a key factor in regulating distribution.

Studies by Eggleton et al. (1996) in Cameroon

revealed that, in all cases, termite abundance was

highly clumped. The tendency of mounds to be

aggregated in the northern KNP therefore

suggests that a few major factors (presumably

topography, geology and soil) are dominant in

regulating their distribution.”  [Afr. Ent. 7:129]

Maybe from this and the references (esp. Odum and others) you might be able to glean something useful...

Article Distribution and density of termite mounds in the northern K...

Hello Francisca,

I've been working with such a system where competitors coexist. This phenomenon is well studied and proposed as a theory called "intraguild predation". This suggests that species with a considerable niche overlap in the same guild (with similar ecological requirements) can co-exist due to reciprocal predation on various life stages of the interacting species. For an example in a simple system with A and B species, adult A may prey upon juvenile Bs and Adult Bs may prey upon adult As, promoting a delicate balance between the population dynamics of both species. I have listed a couple of pioneering publications below and attached one of my recent publications for your reference. All the best.

Polis, G.A., & Holt, R.D. (1992) Intraguild predation: The dynamics of complex trophic interactions. Trends in Ecology & Evolution, 7, 151-154.

Polis, G.A., Myers, C.A., & Holt, R.D. (1989) The ecology and evolution of intraguild predation: potential competitors that eat each other. Annual Reviews of Ecology &. Systematics, 20, 297-330.

Hi Marcel! I have spatial data form camera traps, from which I know that within my study area they have 30% of overlap. I also worked in ecological niche modelling (using NDVI), from which I also assessed niche overlap. I know one species is avoiding the other one... that's why I thought they were not going to overlap that much... so I guess there is "something" that is forcing the subordinate species to take the risk and coexist with the dominant... maybe resources limitation? (prey scarcity?)....

A study by a fellow RG member that might interest you...

Article Population Dynamics Models Based on Cellular Automata that i...

Just because two species interfere with one another does not suggest that they should also not coexist. Hummingbirds, for example, often coexist while when at a particular flower, they will interact (interfere). It is simply that resources are abundant enough that they can't be defended EXCEPT at each particular point source of the resource, and even then, only while exploiting it.

On termites: the random versus clumped pattern, at first look, could be an artifact of the scale of observation; the random example seems a relative small, homogenous area, the clumped occurrence, large.  Wherever I saw termite mounds in Africa, their spatial distribution seemed random when observed on foot or wheels; over larger areas, studied on aerial photography, the mounds would be clumped, that is restricted to specific landscapes (e.g. Kafue Flats in profile);.

Competing, spatially co-existing carnivore pairs seem common, bear-wolf in the temperate zone (see profile); lion-cheetah (Namib desert) and many others; the spatial overlap is relatively easy to establish, the competition for prey, or mutual predation of juveniles more difficult. Bear and wolf may chase one another from prey and carrion; the outcome is difficult to predict; I have not seen reports on mutual predation of bear and wolf; lion killing cheetah has been recorded. There are several theories trying to explain such phenomena, spatial co-existence combined with temporal avoidance (diurnal; seasonal), specialization on different prey. 

Spatially co-existing herbivores are common as well in the savannas of East and Southern Africa, blue wildebeest-zebra may even migrate together; specialization on different plant species,phenology or parts seems the going theory.

We could look at (herbivore) humans and elephant from the same perspective; the crop farmer and the elephant share space and their  taste for maize as well as fruit  trees and water. Diurnal and seasonal avoidance are observed (see elephant papers in profile). Gorilla and people may share bamboo in diurnal or seasonal sequence (see profile).

Anyhow, spatial co-existence of  related mammals with similar ranges seems the rule; may the exception is the anomaly that needs explanation.

Plants are another story. Why are so many grasses co-existing in the same site and trees in the forest. Why does biodiversity prevails over dominance or vice versa.

Coexistence may explain this mainly because of limited resources. To put it simply, these species can be within a same area in order to both utilize the little resources available and maintain fitness.