Circa a week ago, I read that Jackals now vastly outnumber Europe’s wolves, totaling at most 117000 by the latest official estimate. By contrast, a high estimate of Europe’s wolves is about 17,000. Slovenia itself has somewhere between 200 and 400 jackals, Dr. Krofel estimated, and about 75 wolves.
Being exact, according strictly to LCIE (Large Carnivore Initiative in Europe) experts - golden jackal distribution in Europe hesitates within a range of 97000-117000 while European wolf population counts 17000 individuals (incl. 13000-14000 within EU area, where Canis lupus species remains under protection). General conclusion stays permanent - current jackal population in Europe is 4-5 times larger than the wolf one.
Looks like the native to the Middle East and southern Asia, Canis aureus species found its new ecological niche, spreading all over the continent, locally between European regions.
- food resources aspect
Golden jackal's diet is mesocarnivore - it should consist at least 30-70% meat. Its diet flexibility was confirmed scientifically as diversified, regarding regional preferences. Jackals eat mainly multiple small vertebrate animals (up to 90%, depending on habitat), invertebrates and plants (omnivorously - grapes, nuts, watermelons). In Europe, the rapidly expansive brown hare overmatches as preyed animal. Anyway, living in wolf-alike family-based groups (4-6 per a pack) led by monogamous parental pair, hunting jackals can sporadically manage to attack larger ungulates like roe deer, red deer or a farming animal (sheep, lamb, goat), if not protected enough, properly or just not protected at all. Some plants of jackal diet can be forest biocenosis element same as part of agriculture.
The species could be recognized as invasive - it reached the southern edge of Central and Eastern Europe in early Holocene, however, its appearance was not established as its relative North American coyote (Canis latrans). It wasn't introduced by human as well.
Due to overlapped diet, increased jackal distribution could suppress European red fox.
- a safety/hazard avoidance (reproduction as the result)
In the context of the wild ecosystem, mesopredatory jackal avoids the wolf as an apex predator (mesopredator abundance reduction). It means that both of species are able to coexist (if wolves are not in the middle of hunt process and/or they've got enough preyed animals to eat on their territory) and even feed side by side - some jackals scavenging on wolf kills were reported. It means also that jackal population - if that species inhabits selected environment - manages rising where the wolf one declines (and inversely) if prey distribution remains reachable. The Eurasian wolf-jackal interactions pattern in Europe can be ecologically equivalent to Timber wolf-coyote ones observed in North America where in wildlife wolves manage coyote population at large spatial scales, coexisting simultaneously (vide coyotes scavenging on wolf hunt leftovers).
Jackal's similarity to wolf in behavioral aspect, makes it adaptive to migrate. Climate changes/global warming generally do not matter in so far as some factors don't make jackal's mobility simpler - evolutionary not living in locations where snow lays on the ground more then 100 days a year, modern golden jackal would gain by snow cover decrease.
Thomas Newsome, environmentalist, Australian dingo ecology expert, researched both of genus Canis representatives in the human-dominated landscapes of Europe testing the hypothesis that the range expansion of golden jackals (Canis aureus) was triggered by intensive persecution and resulting decline of the apex predator, the grey wolf (Canis lupus). In their group study, Thomas Newsome and company, point on the human factor influence as the trigger to the jackal expansion throughout Europe - the negative wolf portrayal caused by the lack of knowledge and/or education about that species; and shooting wolves in distal conclusion, as the so called "wolf population management". Humans exert strong pressures on apex predators by direct persecution, modifying habitats and depleting prey, often leading to changes in interspecific interactions among predators - they report, hypothesizing about two main factors as reasons.
- human garbage in the vicinity of human settlements
Mesopredatory omnivorous diet is way more adaptable than predatory carnivorous, does not require prey hunting to survive. Human food leftovers were reported as part of golden jackal diet in Europe (same as red fox).
- human-altered habitats
If reachable, being preferred by mesopredators in case of avoiding apex predators (to survive) - apex predatory animals inhabit remote, as less as possible human-degraded territories (to survive).
Historically, golden jackal remained limited to the Mediterranean and Black sea coastal regions until 20th century. Currently, it reached Switzerland, Germany, Poland, and the Baltic sea coast. Basing on survey data from hunting statistics, scientists report that the number of jackals hunted by humans increased from around 40 per year in the 1940s to almost 30000 nowadays.
Although apex predators are often severely reduced or even completely exterminated in such environments, many parts of Europe are recently experiencing recoveries of apex predators, despite high human densities - researchers suggest. Miha Krofel (University of Ljubljana, Department of Forestry) is Slovenian golden jackal specialist, who among the rest of scientists, was a prelegent of the 2nd Jackal Symposium in Greece giving a lecture about the Golden jackal expansion across Europe: causes and consequences. He also considers jackal expansion and wolf eradication being connected to each other (golden jackals avoid gray wolves in wildlife), even more than food resources influence - associated with human activity in land-use (agriculture, urban areas, a garbage).
Golden jackal expansion in Europe: a case of mesopredator release triggered by continent-wide wolf persecution? (2017); study by group work (incl. Thomas M. Newsome)
 citation after Rise of the Golden Jackal via The New York Times (Jan.14th, 2019)