Human as a Non-native Species
Scientific name: Homo sapiens sapiens
Modern men are not quite as distinct from the rest of the animal kingdom as we may think. It is likely that over half of the genes of humans are identical with many of the invertebrate species, and our genes are 99% identical with that of our close relatives, the Apes. However our impact on the planet have exceeded in some ways that presented by natural phenomenon such as climatic change, meteorite impact and tectonic movements, in terms of novelty and abruptness --- one could argue that humans are an extreme natural phenomenon, but there is no escape from facing the drawbacks deriving from the injustices the race has done to the environment whether or not we are defined as such.
Humans are an introduced species. This definition is most ambiguous if due consideration is given to the statement; we have breached the natural rules of range determination, and yet it could be viewed as the exemption of our race from the set of constraints, as our ancestors purportedly have naturally evolved on the planet, under the unconscious guidance of natural selection. We have, in a way, been selected as a superior race ecologically; we had the ability, above all, to conduct sophisticated thinking, learning, and developed culture of late, which is the fundamental notion that separated us from the rest of the world of organisms. We have, in the process of such development, defied nature, exploited it with our ignorance and transforming it to our whim, in perfect misconception about how the world worked for a long time --- what could have been described as the Dark Era in the history of earth still being extended without prospect of reaching the bounds; hapless is life, including ourselves, and strikingly similar we have been, and still are, to many of the NNS we have looked at in the previous section, we must call ourselves the ultimate NNS that has led to all that we are coerced to face and accept. It is most lugubrious that the human race has benefited not fellow organisms, in a way that the maudlin may approve; would the naturalist, on the other hand, refrain from accepting it as a fact of life? Not imaginably!
Humans have occasionally led to increase in the number of certain species, the commensals of men, which generally leads to localized ecological imbalance; the negative impacts of the human race on the planet and its organisms merit separate treatment in a much wider context; but we will point out the relevant ideas that qualify humans, ironically, as a "NNS" --- a self-introduced species that is more influential than all the other NNS combined. Firstly, we will think about how we have introduced ourselves all over the world.
Our ancestors came from Africa, where the graduate transition from forest habitat to savanna --- open, dry grassland --- assisted in the development of a range of skills. Leading an arboreal lifestyle certainly requires good coordination between the hand and the brain, and presumably the ability to use tools was selected for, so that life on the plains, as the early hominids had to embark upon when the forests shrunk, is less hazardous than would have been with all the big predators around; the use of tools allowed early men to use spears and other weapons to hunt, build their own shelters and cultivate subsequently, so that survival rate and standard of living both rose. Homo sapiens migrated out of Africa, and spread to Europe, Asia and the Indonesian Islands to Australia, North America across the Bering land bridge as the sea level transiently dropped, and eventually reached South America. More recently, still around 5000 BC, islanders have found their way to New Zealand, Hawaii, and various other oceanic islands, almost completing the conquest of the world, which their descendants achieved perhaps in a much too repugnant manner, inflicting many negative impacts on the environment.
1. Habitat Degradation
This is the number-one threat to the world's ecosystems through human activities. No organism on earth has had such a radical effect on such a wide range of ecosystems before, and certainly many have found it very difficult to cope with this relentless pace of change.
Habitats are destroyed or degraded in a multitude of ways. From our centre of dispersion relatively little has been detected till of late, when huge herds of livestock are reared so that the land is overgrazed, occurring when the natural replenishment of grass stock is not rapid enough to counteract the intensive violent feeding of the livestock. Tropical forests are logged all along the equator, and there the extinction rate may be over 100 species daily with many inconspicuous insects and plants disappearing well before they are known to science. Many of these cannot stand the loss of primary forests upon which they have evolved in. Temperate forests are also under siege, with perhaps as much as 80% of them having already succumbed to widespread burning and logging to empty land for pastures, arable land, urban construction, and so on. Grassland and savanna are used directly as pastures and agricultural land, changing the species composition of these rich habitats to perhaps three or four species of food crops, and conceivably decreasing biodiversity. Urban areas tolerate far fewer species than many habitats as food is scarce and human disturbance is frequent. Wetlands are deliberately drained to give farmland, and drained wetlands can perform no ecological function as they have previously. Mudflats are reclaimed as they look derelict, as are heaths, bogs and estuaries; these are in fact centres of the terrestrial biodiversity and wetland drainage jeopardize all life forms from migratory birds to subterranean invertebrates. Lakes, rivers and other freshwater systems are disrupted with the construction of dams, dykes, reservoirs and canals, which sweep the muddy or sandy riverbed away to give concrete barriers that support no life; the oceans now may contain so many drift nets that locally these may be killing off seabirds, turtles, sharks and other top pelagic predators, severing affecting the relative abundance of some food items that may outcompete linked relatives and eliminate their predators as well. Almost all the lowlands have been colonized or affected by men in some way, with the original landscape altered so much that wildlife could not tolerate. The rate of loss of many unaffected habitats are still on the increase however, as the population puts not only pressure on space for settlements but mining, extensive farming, large-scale fishing and logging compounded with side-effects as soil erosion, water quality degradation, leaching and land pollution that decreases available space for wildlife to thrive in are all occurring at accelerating rates and there is little control measures that are applicable and effective.
2. Agent of Introduction
The whole idea of NNS is that humans have played an instigating part in assisting the unhealthy success of few organisms, which is not in favour of the majority that suffers under the pressure of voracious invasions. Stowaways in the cargo ships, airplanes, trains, even human passengers in the case of microorganisms, have been dispersed. The NNS are locally transported further through degraded environments whereby they reach the pristine areas and in many cases penetrate them to affect the natives that have been forced to crowd in sanctuaries. The carrying capacity of the ecosystem is largely undermined and we will look at the collective effects in the next section closely.
As technology advances, sources of energy other than that from food are required by numerous human activities. Electricity is now a necessity in much of the developed world. We have been drawing upon the exhaustible petroleum reserves for about a century, and the combustion of fossil fuels produce huge amounts of carbon dioxide and other toxic chemicals that are literally poisoning the world.
Carbon dioxide is naturally present in the atmosphere and is vital for all life as plants obtain their source of carbon from atmospheric carbon dioxide; however these gas molecules can trap heat around the atmosphere, creating a greenhouse effect that keeps the temperature on earth high enough to sustain life. There are signs that the balance is tipping towards the hot side as more carbon dioxide is released than is absorbed. As a result of this, sea level may rise and eliminate many coastal ecosystems. Other pollutants include sulphur dioxide and nitrous oxides that form acidic rain in air and kill trees and other plants when precipitated. They have contaminated thousands of lakes in Scandinavia, rendering them devoid of fish and other aquatic life.
Factories have also poured large amounts of heavy metals, cyanides and acidic or alkaline chemicals into aquatic environments, and many of the poisonous substances cannot be metabolized. Pesticides such as DDT and aerosol constituents like CFCs have contributed to the reduction of birds of prey by affecting reproductive success and created increments in global temperatures in recent years. These have degraded the landscape of the planet in general, even affecting the air and water sources upon which many species rely on survival, including ourselves.
Humans are predators. We are omnivorous, but no less avaricious; and as our population surged beyond manipulation from both nature and ourselves, we as a whole require more food to sustain the ever-increasing population. Early in the Pleistocene (around 15000 to 10000 years ago) there has been signs of “Megafauna” extinctions that could be linked to increasing hunting pressures from the early humans (Megafauna meaning the large mammals that have evolved during the ice ages), whence the Mammoth, Woolly Rhinoceros and Irish Elk disappeared. The hunting never ceased. Humans directly lived off wild animals in large numbers; in Europe, where early in history settlements have concentrated, many wild animals such as Bison, Wolf, Spanish Lynx and others have been culled to very low numbers. All across the world, animals are hunted for food, pleasure as in game shooting, and collection of valued body parts. In Asia, Tigers are driven towards the brink of extinction due to their beautifully patterned hide, bones that allegedly have powerful medicinal uses, and due to potential hazard on livestock. Passenger Pigeons, once the most abundant bird in North America, have been shot to extinction in half a century. North Pacific Albatrosses have been hunted for their plumes and at one time the Short-tailed Albatross has only 100 remaining breeding pairs. Over-harvesting of the ocean is not new; all large Baleen Whales have been reduced by whaling activities with such severity that they may not be capable of recovery, and numbers stay low, about 10000 individuals for some species over their huge range. Herrings, Tunas, Salmons, Sardines, Cods, and many important commercial fish have been found to exist in stocks short of what people had expected to be sustainable perhaps as recently as a few years prior to that, but fishing pressure seemed not to have relented. As we directly live off the top layer of the ecological pyramid we are disfiguring the intricate links among organisms whose interactions help sustain the environment in which we rely upon. Overharvesting is lethal compounded with the effects of habitat destruction mentioned above, and recently the slaughtering of wild animals and plants seemed to have been alleviated. However, convalescence may not be feasible in some fish stocks, whales and restricted-range species as some island birds and small mammals.
Ordinary control methods for this species do not seem to be applicable at all. Conservation efforts stemming from the society have aided the recovery of many ecosystems and species, and special reserves are now set aside, into which human access is limited, so that wildlife can benefit from the least disturbance. Education to the public is necessary for instilling environmentally friendly concepts into new generations, as this may be critical to the future survival of not only Homo sapiens sapiens, but also all the other organisms with which we share the world.
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