There are a few papers about feral and wild cats in the same habitats. Some of them are based on the PhD thesis of Zsolt Biró from Hungary (https://szie.hu//file/tti/archivum/Biro_Zsolt_thesis_szie_.pdf). There is also an older PhD from Scotland on this topic (Corbett, L.K. (1979) Feeding ecology and social organization of wildcats (Felis silvestris) and domestic cats (Felis catus) in Scotland. PhD Thesis. University of Aberdeen, Aberdeen, UK. ).

Some papers:

Biró et al. 2005: Feeding habits of feral domestic cats (Felis catus), wild cats (Felis silvestris) and their hybrids: trophic niche overlap among cat groups in Hungary. J. Zool. 266: 187–196.

Daniels et al. 2001: Ecology and genetics of wild-living cats in the north-east of Scotland and the implications for the conservation of the wildcat. J. Appl. Ecol. 38: 146-161.

I myself did a small study on the prey of feral cats in Germany and I am currently working on a big stomach anlysis of wild cats.

Maybe some wildlife institute in Scotland could help you. They have both feral and wild cats living in the same surroundings. I do not have ane address ready for hand, but you might find it yourself.

If you are interested only in competition with other European predators, it seems dificult to find writen information. On the other hand, there are some papers dealing with competition of feral cats with indiginous predators in Australia, New Zealand and other islands. For example: 

Glen, A. S. and Dickman, C. R. (2005), Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management. Biological Reviews, 80: 387–401. doi: 10.1017/S1464793105006718

Here is another paper discussing interspecific competition within a mesocarnivore guild in Australia, including feral cats:

Brawata, R. L. and T. Neeman (2011). "Is water the key? Dingo management, intraguild interactions and predator distribution around water points in arid Australia." Wildlife Research 38(5): 426-436

Below is a paper discussing interspecific interactions between kit foxes, skunks, and feral cats:

Harrison, S. W. R., B. L. Cypher, S. Bremner-Harrison and C. L. V. H. Job (2011). "Resource use overlap between urban carnivores: Implications for endangered San Joaquin kit foxes (Vulpes macrotis mutica)." Urban Ecosystems 14(2): 303-311.

There is a paper by Krauze-Gryz et al. (2012). The good, the bad, and the ugly: space use and intraguild interactions among three opportunistic predators—cat (Felis catus), dog (Canis lupus familiaris), and red fox (Vulpes vulpes)—under human pressure. Canadian Journal of Zoology 90: 1402-1413. DOI: 10.1139/cjz-2012-0072.

Another piece of interesting research is the paper by colleagues Katherine Moseby, her husband John Read, and others, entitled:

Moseby, K. E., Neilly, H., Read, J. L. and Crisp, H. A. (2012). Interactions between a top order predator and exotic mesopredators in the Australian rangelands. International Journal of Ecology 2012, 1-15.

Dingoes killed all seven red foxes within 17 days. Feral cats survived longer.

The telemetry data from this project was recently analysed by University of Adelaide Honours student Tina Schroeder:

Schroeder, T. (2013). Spatial and temporal interactions of apex- and introduced mesopredators in the Australian arid zone. Spatial Information Group, School of Earth and Environmental Sciences. Adelaide, SA, The University of Adelaide. Bachelor of Science (Honours).

One of Tina's findings (p. 22) was: "The data presented here suggests that dingoes and cats and dingoes and foxes neither avoid nor attract each other at a short temporal scale (dynamic interaction) but there is a strong micro-spatial avoidance pattern, showing that cats and foxes are avoiding high use areas of the dingo (static interaction)."

Colleague and I have just published a large paper which records predation by feral cats (and a few red fox accounts) on our native dasyurid carnivorous quolls. We think the historical accounts primarily describe predation on Dasyurus viverrinus, though we currently have it happening on reintroduced D. geoffroii, so we have cats killing and eating c. 800-1600g dasyurid carnivores. Paper is:

Peacock, D. and I. Abbott (2014). "When the "native cat" would "plague": historical hyper-abundance in the quoll (Marsupialia: Dasyuridae) and an assessment of the role of disease, cats and foxes in its curtailment." Australian Journal of Zoology 61(3): 206-280.

Thank you very much to all colleagues. About my question, I think there are two methodological problems that overlap: the difficulty of estimating populations and how to evaluate the interaction. Has anyone used a procedure of spatial segregation study?

Yes - see Tina's thesis, as previously discussed. I have a copy please email me ([email protected]) and I can send it to you.