Foreign mammals endanger native species

A LEADING wildlife researcher has called for joint action by governments, North and South, to protect some of our native wild animals from foreign species which have been introduced here.

Professor Ian Montgomery, lead researcher at the School of Biological Sciences at Queen’s University, Belfast, believes a stage has been reached in relation to threats posed to Irish mammals by invasive species where both governments should work together.

Some of our oldest inhabitants are facing serious dangers and possible extinction because of foreign species, according to researchers at Queen’s. And, it’s not a question of spending money, but of making decisions and coming up with agri-environmental schemes, such as planting more woodland, Prof Montgomery emphasises.

Also, a different approach could be taken to the management of hedgerows. “Habitat which is favourable to native species and not so favourable to introduced species should be preserved,” he maintains.

The red squirrel, Irish hare and red deer are just some native species which are under threat as a result of the introduction of foreign species. A new study, conducted over the last two years, looked at the impact of two introduced species — the bank vole and greater white toothed shrew — on two native small mammals, the wood mouse and the pygmy shrew.

If the present rate of invasion continues throughout the island of Ireland, native small mammals will die out in at least 80% of their available habitat, Prof Montgomery warns.

The study, published in the international journal Biological Invasions, found that in the recent past, the pygmy shrew has completely vanished in parts of Ireland where both invasive small mammals are found. Wood mouse numbers have decreased by more than 50% in areas where the bank vole is longest established.

Carried out in Munster, mainly Co Tipperary, the study found that wood mice in hedgerows were down by up to 90%. The pygmy shrew has become extinct in parts of Tipperary.

At the same time, the bank vole is extending its range along a line from north of Galway to Waterford, at a rate of 2km to 3km per year and is expected to reach Dublin in a couple of decades.

The greater white toothed shrew also appeared to be moving and has been seen in counties Limerick, Cork and Waterford.

The bank vole, Prof Montgomery thinks, may have been brought in from Germany during the construction of the hydro- electric scheme on the Shannon in the 1920’s, while the shrew could have come into Tipperary in containers of fruit and vegetables from southern France.

Small mammals occupy central positions in food webs, so major changes in species composition, which are already occurring, will have effects in the ecosystem. Bird and mammal predators as well as seeds and seedlings that small rodents and insect eaters feed on will be affected.

“The introduction of alien mammals to Ireland over the last 100 years has had major detrimental effects, threatening our indigenous habitats and species,” the professor says.

“The American grey squirrel, for example, passes a deadly virus to native red squirrels, whilst European hares threaten the ecological and genetic integrity of the native Irish hare through competition and interbreeding.”

Calling on the governments to work together, he says it is essential to understand both the mechanisms of invasion and the impacts of these aliens. It is no longer tenable to treat each invasive species as an isolated case.

“We should establish a realistic plan identifying the mammal species that are key to maintaining our unique biodiversity and ecology and those that we should eliminate or control,” he stresses.

The new study is believed to be the first of its kind to analyse the effects of invasive species on native species. Such a process is known as ‘invasional meltdown’.

Interestingly, Prof Montgomery refers to the importance of hedgerows for wildlife. The Celtic Tiger era, however, has taken a huge toll, resulting in the destruction of countless thousands of kilometers of hedgerows to make way for roads, housing estates, private houses, shopping centres and other development.

As Ireland has so little native woodland, hedgerows have become vital nature reserves and corridors for wildlife.

The rural landscape has changed almost beyond recognition in the last 40 years.

Most hedgerows began as earthen banks and a means of land division, in the 17th and 18th centuries. Whitethorn was often planted on top of the banks and, to a lesser extent, trees such as oak and ash and beech. The result, over time, was that wild plants and animals began to colonise the ditches which have been obliterated in recent decades.