Biodiversity Loss and the Fragmentation of the Wild
Throughout the earth wild habitats are being cut up, cut down and cut off. One inevitable result of this is fragmentation. By neglect, chance or design the conversion of wild habitat to human-dominated land leaves islands of wild habitat in an ever-rising sea of inhospitable terrain. The result is a very quiet, but huge, profound and disastrous effect on the world's terrestrial ecosystems and the species they contain.
This article will firstly take a quick look at the theory of why habitat islands and real islands have far fewer species than more continuous tracts of land. Secondly I look at three examples of the serious fragmentation of the wild and resulting species loss from the UK, USA and Brazil. Finally I will look at what environmental groups (FoE, Greenpeace and EF!) should be doing.
Islands can be thought of as one of three different types:
- Oceanic islands: Those that have nearly always been islands, like the Seychelles and all those other 'idyllic' faraway holiday islands.
- Land-bridge islands: Those that used to be attached to larger land areas (usually several thousand years ago, e.g. Britain).
- Habitat islands: Those 'natural' or 'semi-natural' habitats surrounded by a sea of human dominated landscape, like a copse of woodland surrounded by farming fields or meadows surrounded by housing and road developments.
All three types act in very similar ways.
- The smaller the island, the less species are present on it: see Figure 1.
- The further away from a source of colonising species, the less species are to be found on the island: see Figure 2.
- The longer the length of time they have been islands reduces the number of species found on the island. This point is controversial but the few studies done and the general theory seem to support it.
To account for these striking pattems seen over the whole globe, with virtually any plant or animal group, two groups of theories have been put forward. The first was proposed by the two mega-ecologists MacArthur and Wilson in 1967 in their seminal work "The Theory of Island Biogeography"  (which is still used widely today by those responsible for drawing up the National Park/Reserve guidelines etc.). They proposed that the area of the island sets limits on the number of individuals an island can support . They then said that the probability (chance) of a species becoming extinct on an island increases as the number of that species decreases.
Figure 1. The number of different species of amphibians and reptiles found on seven different-sized islands in the West Indies. (MacArthur & Wilson 1967)
This is entirely sensible if you imagine having a square of forest surrounded by fields and you then decide to chop half of it down; the number of trees, birds, beetles or whatever will be reduced; while the population of an individual species will also be reduced (not enough food, lack of breeding sites, fewer places to hide from predators). Some of this extinction is balanced by colonisation - new species arriving on the island - like insects blown in the wind, wind blown seeds, birds flying, fungi spores in the air and other more chancey events.
Figure 2. The number of land and freshwater bird species on various islands and archipelagos in the Pacific Ocean. ‘Near’ islands (open circles) are those less than 500 miles from a colonisation source (New Guinea). ‘Far’ islands (squares) are those greater than 2,000 miles from a colonisation source. Dots without circles or squares are islands of intermediate distance. (1) Wake, (2) Henderson, (3) Line, (4) Kusaie, (5) Tua Motu, (6) Marquesas, (7) Society, (8) Ponape, (9) Marianas, (10) Tonga, (1]) Carolines, (12) Palau, (13) Santa Cruz, (14) Renell, (]5) Samoa, (16) Kei, (17) Louisiade, (18) D’ Entrecasteaux, (19) Tanimbar (20) Hawaii, (21) Fiji, (22) New Hebrides, (23) Buru, (24) Ceram, (25) Solomons. (From MacArthur and Wilson, 1963.)
The colonisation of the island by new species is reduced the further the island is away from a source of colonising species (another island, or the ‘mainland’). The most important point about this theory is that the island reaches a new balance where it is stable but with a lot less species.
Figure 3. An example of a species-area relation: The number of breeding bird species in different size plots of North American deciduous forest. (Data from Preston, 1960)
So thinking back to our imaginary forest island, the smaller our island gets (mavbe some is taken for a new road-building scheme) the more species we will lose from our island by increasing the probability of each species going extinct. Our forest island could also end up with less species if sources of colonizing species are removed, i.e. our island will act a lot more like a far away island with less species present This means that destroying habitat islands affects other habitat islands that could be quite some distance away by removing sources of colonizing species With little or no colonization the vast majority of species could be lost from that particular island. Unfortunately this is precisely the direction we are racing towards in the late 20th century.
The second group of theories are known as Species-area theories. These have sprung up to explain the relationship between the area of a given place and the number of species found there . This relationship is amazing as it is seen from ants through to zooplankton and from the tropics to the arctic. The question then is why does area equal more species? There are three basic theories:
- Species numbers should increase because larger areas will contain more types of habitat. A pretty obvious conclusion, as most species are highly specialised in at least some of their requirements for life . If we go back to our imaginary island, the larger our forest is the more likely it is that it will be growing upon more than one soil type which will mean different (more) plant species will grow with new specialised insects living on them, with different birds living off the insects, and so on.
- A bigger population of each species (more woodpeckers or red admiral butterflies) leads to a decreased chance of extinction This is really just part of the MacArthur and Wilson theory described above.
- Some have said that this striking relationship between area and species numbers is nothing more than an artifact of the way in which we study nature i.e. there is no meaningful relationship between area and the number of species present.
All the theories are plausible, with supporting evidence for each. The real world probably shows a mish-mash of them all though in my opinion the MacArthur and Wilson theory and the increasing number of habitats in a given area probably account for most of the differences seen between ‘mainland’ and island ecosystems.
So to summarise this section: making habitat islands by the expansion of agriculture, dam building, housing developments, industrial expansion and road building reduces the number of species by:
- Excluding some from the area that remains particularly if rarely or patchily distributed.
- Increasing the likelihood of extinction of the species left in the new island habitat because of reduced population sizes.
- Decreasing or eliminating sources of colonisation for other areas left intact.
- Removing resources outside the area left that species inside that area may depend upon for their long-term survival.
- By the process of secondary extinction's, these are dependant upon the ecological imbalances resulting from factors a-d.
The question then becomes, yes reducing the world to a series of fragments will lose a huge number of species, but how widespread is the fragmentation and isolation? The short answer to that is VERY. Think about the average nature reserve or national park, an area of natural habitat surrounded by anything but natural habitat up to the park’s edge! Outside National Parks and reserves there seems even less of the natural world left. In an increasingly commercialised and industrial (for developing countries) world with ever more people to feed and multinational companies growing ever bigger and more powerful, the clamour for land gets greater year by year - big business wants it for its dividends for share holders, and peasants want it for subsistence. The natural world becomes excluded. Where the pillage of land means wealth and power, the natural world is in real trouble. In the near future it is expected that the only areas of natural habitat left will be in Nature Reserves, indigenous reserves and National Parks.
When was the last time you saw a few thousand or even a few hundred acres of fairly undisturbed British woodland? Well it is no surprise that there are NO large wild mammals in the U.K - perhaps it is because all of the fragments left in the U.K. are too small to support viable populations of them. Is this also one of the reasons why 40% of British insect species are poised for local extinction from the U.K, and our bird species see a decline in numbers each year?
See figure 4 showing the fragmentation and isolation of the Poole basin, Dorset, England, which between 1759 and 1978 lost 86% of its heathland (400,000 ha - 6,000 ha), a change from 10 large blocks separated by rivers to 1084 pieces with nearly half of these being less than one hectare, with only 14 sites bigger than 100 hectares.
Figure 4. Fragmentation and isolation of Poole Basin, Dorset, England. Between 1759 and 1978 it lost 86% of its heathland (40,000 ha to 6,000 ha), a change from 10 large blocks separated bv rivers to 1084 pieces, nearly half of these being less than 1 hectare, with only 14 sites bigger than 100 hectares. (From Webb and Haskins 1980.)
Figure 5 shows the reduction of tropical moist forest in Sao Paulo State in Brazil, which is about the size of Germany. In 1500 it had 81.8% forest cover. By 1973 it had 8.3% with only 3% to be left in 3 years time. The havoc this has wreaked on the flora and fauna of the area is mostly undocumented, although figure 7 gives a pretty good, but shocking idea.
Figure 5. Reduction of tropical forest in Sao Paulo state, Brazil, from year 1500 with 81.8% forest coverage to year 1973 with 8.3% forest coverage. By the year 2000, only 3% forest cover is projected. Sao Paulo state is about the size of West Germany or the state of Oregon. (From Oedekoven, 1980.)
Figure 6. Percentage of apparent extinctions during roughly the last century, based on presumed initial bird species composition in three Brazilian forest tracts in the State of Sao Paulo. It is not known when the forest tracts became isolated from the formerly continous forest, though it could have been as recently as a few decades ago. Note that all three tracts seem to have lost species, the smallest at the quickest rate. (From Terborgh & Winter 1980, based on data of Willis 1979.)
Figure 7 shows the impact on the forests of Green County, Wisconsin, North America. The continuous forest in 1773, was by 1978 (not in figure) reduced to 111 forest islands with an average size of 0.09km.
Figure 7. The fragmentation of forest in Cadiz Township (94.93 km sq.) Green Country, Wisconsin, into habitat ‘islands’ during the period of European settlement. The almost continous expanse of forest in 1831 was fragmented into 55 small forest islands by 1950. There were 111 forest islands by 1978 averaging 0.009 km sq. in size. (Sharpe et al. 1987). (From Curtis 1956.)
Obviously the fragmentation of the natural world is well under way and we can expect that only areas where serious exploitation is strictly prohibited will survive the next few decades unfragmented. What will happen to these areas? Will they survive and constantly lose species or will they 'collapse’.
To look at what the future may have in store I will look at the islands of Bomeo, Sumatra, Java and Bali in Southem Asia These islands were connected to the continental shelf up until about 10,000 years ago.
Therefore by estimating the number of species that have been lost since they became islands we can gain at least some idea of the fate of any natural habitat surviving well into the future. The method is simple in theory, but difficult to do in practice; firstly assume that when the island was connected to the mainland it had the same number of species of a given group that the mainland has today. Secondly, go out and find out how many species of that group there are on the mainland and how many on the island now. Finally compare the species lists - any differences should be due to extinctions because of fragmentation and isolation. The results are summarised in table 1. This shows for mammals, Borneo - the world's second largest island - lost 20% (1 in 5) of its mammal species in 10,000 years. Not bad, until you realise there is only one National Park in the world that is significantly bigger than Borneo. The unfortunate fact is that 97.9% of reserves are less than 10,000km squared and 84.7% are less than 1,000km squared. This puts the vast majority of reserves on a par with Bali which in this study lost 71% (almost three-quarters) of its mammal species in 10,000 years. If, according to MacArthur and Wilson's theory, all species are roughlyequal, then the small reserves can expect to lose over half their plant, insect, bird, fungi and reptile faunas - to name but a few - within the next thousand years as area effects kick in.
The ecologist Michael Soule (who has been called the father of conservation biology) looked at this ‘faunal collapse’ for East African parks and came to the conclusion that for the average reserve which has 48 large mammal species and an area of 4000km squared, it will lose 11% of these in 50 years, 44% in 500 years and 77% in 5,000 years.
The ‘biological meltdown’ could then actually become a reality - especially since all the above extrapolation and speculation does not include factors such as: ‘secondary extinctions’, effects of climate change, hunting, pollution or further area reductions. ‘Secondary extinctions’ are probably best thought of as the rippIes given off within the ecosystem when a species becomes extinct. These ripples if large enough cause further extinctions. A general example might be a host specific parasite - once the host (e.g. bird, beaver, or bee) becomes extinct, so does the parasite as it has nothing to live on. A classic specific example concerns the famous dodo bird, killed off by excess hunting. Now a tree species is going extinct as its seeds must pass through the gut of the dodo before they will germinate. This new extinction will then cause further ripples - any insects specialised to live only on that tree will also become extinct. This brings us on to a very important point. We are not seeing species going extinct in their droves yet as there is often, as in the case of the dodo, a long time lag - a long slow decline before extinction. Therefore the rampant fragmentation and isolation going on now is stirring up serious trouble for the future - even if the ecosystems do not seem ‘too bad’ at present.
This interdependence of species on each other may bring whole suites of species crashing down to extinction. The trouble is these ‘secondary’ extinctions are at present unpredictable, unforeseen and may or may not be of major importance to the future. But if the words of the eminent ecologist John Terborgh are anything to go by we should be mighty careful. He has said that the removal of half a dozen carefully chosen tree species (mostly figs) from the Amazon Basin could cause most of the rainforest and its species to ‘collapse’.
This is not to say that there will be no nature in the future. There most certainly will be. Nature is above all resilient, but it will be less varied, less exciting, less diverse, and possibly less stable. This coupled with climate change, industrial pollution (e.g. acid rain), rising human population and ‘Western’ lifestyles may leave us in a difficult and severely unpleasant world, but it will almost certainly do away with between a half and a third of all species we cohabit this planet with.
If this is not bad enough Michael Soule and Bruce Wilcox have a dire and scary prediction.
"The green mantle of the earth is now being ravaged and pillaged ins frenzy of exploitation by a mushrooming mass of humans and bulldozers. Never in 500 million years of terrestrial evolution has this mantle we call the biosphere been under such a savage attack. Certainly there have been 'crises' of extinction in the past, but the rate of decay of biological diversity during these crises is sluggish compared to the galloping pace of habitat destruction today.
"Perhaps the hardest to grasp is the geological and historical uniqueness of the next few decades. There is simply 110 precedent for what is happening to the biological fabric of this planet and there are no words to express the horror of those who love nature... the relentless harrowing of habitats particularly in the tropics, will reduce rainforests, reefs and savannas to vulnerable and senescent vestiges of their former grandeur and subtlety. But the loss of habitat and the loss of species is not the whole disaster. Perhaps more shocking than the unprecedented wave of extinction is the cessation of significant evolution of new species of large plants and animals. Death is one thing - an end to birth is something else, and nature reserves are too small (not to mention, impermanent) to gestate new species of vertebrates. There is no escaping the conclusion that in our lifetime, this planet will see a suspension, if not an end, to many ecological and evolutionary processes which have been uninterrupted since the beginning of palaeontological time.
"We hope it is only a suspension-that the horrible onslaught can be stopped before the regenerative powers of ecosystems are also destroyed... This is the challenge of the millennium. For centuries to come, our descendants will damn us or eulogise us, depending on our Integrity and the integrity of the green mantle they inherit."
That is to say we're well on the way, if we don't drastically change our behaviour, to drawing evolution, at least for larger species, to a close. Not only are we killing species off in their droves, we are virtually stopping any opportunity for the evolution of new species. In other words, we are participating in the largest, fastest and most severe mass-extermination episode the earth has ever seen.
Why aren't Greenpeace, Friends of the Earth and many within the EF! movement tackling what is arguably the issue of our time. They can't because the issues around habitat loss, fragmentation and isolation are so large, complex and mutually reinforcing that to accept and take action upon them would be a blatant attack upon the whole of the society they live within; the whole concept of 'owning' land, of industrialisation, of the false separation between humanity and all other life. The only act that would do any thing to avert this catastrophe would be the complete overthrow and dissolution of the industrial-military machine we live in, a complete change in the way humans relate to other forms of life and indeed to each other. We are talking about opening a very big can of worms here that could well alienate subscribers, funders and supporters and probably the majority of the Western public. If FoE etc brought up these issues they would be labelled 'extremists' and 'Out of touch with the real world' The measures required to tackle a problem of this scale and magnitude are massive; large scale land reform in both the developed and developing world, the cessation of activities that reduce natural habitat and the large scale ecological restoration of this entire ravaged earth. Which ever way you look at it unfortunately it is going to take heroic and drastic action to curb the threat of the virtual termination of much of the evolutionary process- the mainstream environmental organisations are not prepared to get involved.
This is where Earth First! should come in. We should be taking action against the real problems we face-however unpalatable it may be to admit what they are. Earth First! and other broadly similar groups should be at the forefront; they should:
- Get across the ecological issues of our time; 3 parts per million too much lead in 10% of the UK's drinking water is not a major issue, and certainly shouldn't be one of FoE's main campaigns. What is important is that today there are over 100 less species on this planet than there were yesterday and a few thousand acres more forest was wrestled from indigenous peoples by Trans-National Corporations. FE! needs to tell it how it is-however unpleasant.
- In a region such as Britain which is severely fragmented already, all habitat left becomes of serious value; be it a tiny piece of woodland on the M11 or habitat threatened by the expansion of a quarry. The removal of even hedgerows around fields can remove important 'wildlife corridors' between bits of woodland. Resistance to the further 'development' of the UK by the government and business is crucial.
- Earth First! should constantly address the place of humanity within nature. This is probably the most fundamental problem with the mainstream organisations. Their cry is 'exploit, exploit, but exploit sustainably and leave plenty of nature reserves for us to manage.' This is not good enough. FE! and others need to push the idea of humanity as part of nature-inextricably linked. We evolved as part of nature and we now divorce ourselves from it. We rely on nature ultimately for our economic, social, psychological and spiritual well-being. If we contribute to the loss of species and habitats, we destroy our own roots. With this view the conventional 'parks centred' view of nature develops several serious problems perfectly described by Western et al (3).
"Protected areas area seductively simple way to save nature from humanity. But sanctuaries admit a failure to save wildlife and natural habitat where they overlap with human interest, and that means 95% or more of the earth's surface. Conservation by segregation is the Noah's Ark solution, a belief that wildlife should be con-signed to tiny land parcels for its own good and because it has no place in our world. The flaw in this view is obvious: those land parcels are not big enough to avert catastrophic species extinction by insularization or safe enough to protect resources from the poor and the greedy. Simply put, if we can't save nature outside protected areas, not much will survive inside; if we can, protected areas will cease to be arks."
To finish this article which has focused primarily on biodiversity it is probably most fitting to finish with a quote from the man who coined the term: Ed. Wilson.
"What event likely to happen during the next few years will our descendants most regret? Everyone agrees... that the worst thing possible is global nuclear war... With this terrible truism acknowledged, it must be added that no country pulls the trigger the worse thing that will probably happen - in fact is already well underway - is not energy depletion, conventional war, or even expansion of totalitarian governments. As tragic as these catastrophes would be for us, they can be repaired within a few generations. The one process now going on that will take millions of years to correct is the loss to the genetic and species diversity by the destruction of natural habitats. That is the folly our descendants are least likely to forgive us"
Earth First! should strive to get these ideas across and intensify its struggle. We should build a movement that can destroy the processes and institutions that are responsible for this huge attack on the life support systems of the earth.
- Macarthur, R.H and E.O. Wilson, 1967, 'The Theory of Island biogeography'. Princeton University Press.
- Soule M.E and B.A. Wilcox (eds), 'Conservation Biology: An evolutionary-Ecological perspective'.
- Westem D. and Pearl. M, 1989, p304-323, 'Conservation for the Twenty First Century', Oxford University Press.
- Wilson. E.O, 1984, 'Biophilia', Harvard University Press.