• Adrian J. Boas

On Invasion and Demography

Mynah Bird (T G Santosh [CC BY-SA 3.0 (])

The debate over what to do about invasive species has been much in the media of late. It seems that climate change is partly, perhaps largely the cause, and most views appear to align on the side that regards changes to what we have long been used to as being a bad thing. It seems to me unfair that just because one species is more adaptable than others it should be condemned, and I would like to be devil’s advocate and defend those much-maligned plants and animals that are being censored merely because they know best how to survive. The difficulty of taking on that role is in that in many instances the success of the new arrivals appears to be the result of their aggressive behaviour. More than once I have observed Indian mynah birds forming a gang, like so many nasty little gangsters, jointly attacking a perfectly innocent crow twice their size that had been minding its own business and forcing it to make an embarrassing retreat. That sort of behaviour does not make it easy to come to their defence. And if we are to say that the success of these creatures and plants is due to their genetic superiority we come perilously close to being condemned as supporters of a Herrenvolk-like ideology for flora and fauna.

And to be fair, it is not difficult to understand why, in places where the so-called "native" animals and plants are distinctive, unique and iconic, the rampant spread of new breeds ignites hostility, as they are seen to be pushing out old favourites. The spread of American grey squirrels in Europe at the expense of the European red and the rampant plagues of rabbits and prickly pears in Australia are examples of invasions that have aroused understandable opposition. But in many cases the position of the opposing camp is not really all that strong. Here in Israel it is the fate of the garden birds like the sparrow, the bulbul (Alophoixus phaeocephalus) and the warbler (Prinia gracilis) that causes the most concern. But, delightful as these creatures indeed are, are they really natives? Those who would have us believe so should keep in mind that in this country the environment has radically changed over the twentieth century. When it was largely desolate, prior to the establishment and expansion of cities and the accompanying suburban spread with its gardens of primarily non-indigenous plants and trees (which, by the way, nobody seems to condemn), many of the so-called “natives” either did not exist or were present in only very small numbers and in limited regions.

One of my favourite trees here, and I recall it also from my Australian childhood, is the Ailanthus altissima, very aptly, in my opinion, known as the “Tree of Heaven” (its appearance certainly warrants the name, though it might be justifiably argued that its scent is something less than heavenly - it is popularly known as the “Stinking Sumac”). The Ailanthus is so successful in propagating itself that it is regarded in most places as a weed. It grows rapidly and tolerates drought and poor soils. Like the mynah it might fairly be regarded as aggressive in that it produces chemicals that suppress the growth of neighbouring plants. As a result, it has spread from China where it appears to have originated, thorough many parts of the world and all continents except the Antarctic. And indeed, what is wrong with that? We should be the last to condemn successful breeding. There is no creature on the planet more invasive than a certain African ape known as Homo sapiens.

Invasions can begin on a minute scale and go unnoticed for a long while until, at a certain point they break through an unseen barrier and become noticed, and eventually overwhelming. So it is with cancerous cells in the human body, and so it is with many animal and plant invasions. But invasions can also be a sudden from the outset and large, even massive in scale, like the abrupt appearance of a locust plague.

Although the First Crusade was no blitzkrieg and by modern warfare standards would be regarded as a protracted event, by medieval ones it was sudden, sudden enough to catch the Muslims pretty much unprepared. They knew the crusade was on its way, but they seem to have taken few measures to prevent it. With this type of invasion, if the invading force is not substantial enough initial successes are often followed by collapse, or at least decline when the demographic handicap of the invaders begins to play a role. Because the number of participants in First Crusade was substantial, the decline of the Frankish enclaves in the Levant took a while to come about, basically about eight decades. But decline was inevitable. We don't know how many crusaders set out, how many others came in their wake, or indeed how many reached the Holy Land, and we cannot really rely on the numbers given in contemporary accounts. Nor do we know how many Franks remained in the East and settled in the towns and countryside. But, however many tens of thousands of Europeans participated, the advantage remained well and truly on the side of the Muslims.

Demography was what shaped the nature of the Frankish settlement in the Levant, urban and rural, their actions in the battlefield, the way they defended their cities, developed their weapons and armour, the construction of their fortresses, and much else. Had there been less of a disparity in the numbers they would not have even needed the castles and city fortifications. They would have settled the countryside more thoroughly, they may have been successful at their several attempts at conquering their prime adversary - Egypt, and they might still be here today - a somewhat daunting thought! But such speculation is perhaps as pointless as wondering what type of avian life will be here eight hundred years hence.