Islands within Islands
Oceanic islands are paradigms for geographical entities ranging in size from tiny habitat patches to continents or even the entire earth. It is almost a platitude that Darwin’s observations in the Galapagos Archipelago and Wallace’s in the Malay Archipelago crystallized the then nascent concept of organic evolution by natural selection and many other classical advances in the theory of evolution rest originally in responses to visiting islands.
1 Islands in a sea of bracken
Skomer Island's six central fields as delineated by John Sadd in 1947. His sketch map of the distribution of vegetation is the heading of this page. Black areas are dominated by bracken, speckled areas are rock outcrops)
Sadd's survey is available as a pdf file below. It is about 100mb and will take time to download.
Islands are systems that are closed and bounded in many respects and thus present a manageable unit of scientific study. These same properties present island populations with the challenges of limited resource availability, tenuous resource security and limited natural carrying capacity. As habitat destruction continues to pose a growing threat to biodiversity, many mainland habitats are beginning to resemble islands, with isolated pockets of wildlife separated by degraded or developed lands. Thus, island species may serve as a model for understanding how mainland species will adapt to the rapidly changing environmental conditions brought on by habitat destruction and climate change. It appears that some common mainland species are already responding like island species. The evolution of the Skomer vole is just one example of an island phenomenon which has been observed as a relationship between fragmented mainland habitats and changes in body size in 25 European mammals over the past 200 years.
Classical island theory is an appropriate tool to study diversity patterns in fragmented habitats, providing allowances are made for spill-over colonization of ‘islands’ from the ‘sea matrix’. Skomer is isolated from the mainland biodiversity matrix and thereby provides a valuable resource for research into island biogeography. Also, its use by human communities over a period of at least 3,000 years has left behind an ecological patchiness visible in the landscape as abandoned walled fields. A set of these old field patches with the potential to function as outdoor laboratories for investigating the ecological theories of island biodiversity comprise six abandoned fields in the centre of the island. These were laid out in the 19th century as a commercial investment from the mainland to establish a 'modern' farm to be worked on scientific agricultural principles. These fields are prominent in the botanical map of Skomer, which was made by J Sadd as a contribution to the first field survey of the island carried out in 1946. A sketch map of the six fields clustered around the farmhouse (Fig 1) has been taken from Sadd's vegetation map of the whole island. At that time, the fields numbered 1, 3 and 5 were being cultivated for potatoes. Historically this was the final attempt to produce an agricultural crop for the mainland market. Since then these arable fields have been colonised by rabbits and one of them, Field 1, also called Calves Park, was enclosed with a rabbit-proof fence and used to study the population dynamics of rabbits in relation to the field's botanical diversity.
2 Beauty of the mundane
A commentary on 'Flora of Skomer '(Chapter 4 from 'Island of Skomer', Buxton & Lockley,m 1950)
Complexity is a term generally used to indicate a quality where many aspects or parts of specific entities or systems interact or form patterns with each other in varying ways. Observing and assessing these patterns of relationships are the focus of diverse scientific and mathematical studies of complex systems.
Psychologist Mihaly Csikszentmihalyi breaks down the beauty of complexity by stating that complexity is the result of two broad processes: differentiation and integration. Differentiation implies a movement toward uniqueness, towards separation from others. Integration refers to its opposite: a union with other entities. A complex system is one that succeeds in combining these opposite tendencies.
Mihaly uses the idea of an engine to make this point. In order to work, each part is highly differentiated but only works effectively in union with the other parts. Alone each part is useless to a large extent. It's function is limited if it operates exclusively in differentiation. But if its differentiation is appreciated in union with the other parts, it has value. It was the complexity of rabbirt-grazed grassland that impressed the botanists of Skomer when they wrote:
‘The dry, short, rabbit-nibbled pastures, so springy and pleasant to walk over, even on mornings of heavy dew, are broken up by the protrusions of rock on higher ground, and only drought-resisting plants survive here. This is a region largely dominated by ling and heather, but only in very few areas is this heath partnership a pure one. Usually it is shared with other plants of dry situations. Patches of sweet-smelling wild thyme delight the strolling botanist, who observes that it is associated with such other low-growing sun-loving species as English stonecrop, scarlet pimpernel, lesser skullcap, pearlwort, rock-spurrey and occasional colonies of bird's-foot trefoil. But the region of heath is so mixed in topographical character that any attempt to classify the whole into strict ecological communities breaks down; rather it is, like so much of Skomer, a patchwork of minute consociations in which, here and there, the observer finds the same pattern appearing.
Thus in a few slightly damper parts of the heath some of the species of the drier ground exist side by side with louse-wort, wood-sage, Yorkshire fog, red fescue and the sorrels. And again, where the rock thrusts clear to the surface, with only shallow pockets of earth to give roothold to the ling and heather, we find wall pennywort, buck's-horn plantain, sea stork's bill, and in the autumn the sheep's bit scabious. Some of the heath extends almost into the marshy areas of the centralvvalleys; some merges into the grassy plateaux above and towards the cliffs,vwhere the fescue grasses fringe the areas of thrift. This high ground has few showy plants except in spring, when the charming vernal squill, a species sufficiently rare in England to make it a special object for English visitors to see, is a common flower on Skomer in such situations.
We are used to fast and easy laboratory tools making the job in a couple of minutes what a few years ago was taking weeks to complete. It's because somebody before us has turned complexity into simplicity. This is the beauty of science; making the impossible possible and turning difficult into easy. In discussing the beauty of biology, Maura Flannery notes that "rhythm, form, order, of a pattern are themes that constantly recur from a molecular to the ecological level". Order dominates randomness and finds expression in its focus on symmetry, order, pattern repetition, and the elegance that comes from visual simplicity.
An ecological system as it develops is one of most fascinating complex entities in the world. A continuous change in form that takes place from week to week puzzles us by its very simplicity. The geometric patterns that present themselves at every turn invite mathematical analysis. The constancy, the orderliness of a whole series of events, repeating themselves thousandfold year by year, assures us of a causal sequence conspiring to create an object whose plans are adjusted to make a machine of extraordinary complexity.
On Skomer this is expressed as a mundane botanical pageant, which, once we become aware, makes an irresistible appeal to the emotional and artistic sides an our human nature. Hence it is not without feeling of regret that the ecologist sees these gems in nature committed to quadrats and computers to disturb their arrangements, to microdissecting instruments to pick them to pieces, of endless tortures by alterations in environment to disturb the orderly, normal course of events. Yet we feel, too, that if a mystery that surrounds the generation of the landscape microcosm is ever to come within our comprehension, we must have recourse to other means than description of a passing show, and the recompense will be to substitute a more deeper interest in an older emotional visual response to the order in nature.
3 Should rabbits be managed?
In many ways this wiki is the outcome of revisiting a research project dating from the early 1970s which was designed to study the long-term impact of Skomer's rabbits on vegetation. After the island became a nature reserve in 1959, there were big changes in the rabbit population. First came a ban on rabbit catching and then there was the arrival of rabbit hemorrhagic disease, Both events affected the island’s grassy habitats.. By the 1970s when the rabbit population was recovering from the myxamatosis pandemic, there was talk of a management plan to maintain the visually attractive maritime grassland cover of the central fields.
The rabbit work was started in 1979. After 13 seasons of data gathering by students and two PhD programmes the answer was that rabbits and vegetation have likely to have always been in a dynamic equilibrium. They have evolved together over at least a thousand years since rabbits had first been introduced and is no need for any human interference.
On the journey to this conclusion it became clear that the increased presence of woodsage, a rabbit-resistant species. made a significant contribution to nectar-feeding insects. Another positive impact of a large rabbit population was the provision of nesting burrows for shearwaters and puffins. The only conservation negative was that the rabbits of the western coastal slopes had destroyed large swathes of peaty Festuca mattress. This had actually reduced nesting opportunities for shearwaters. These conclusions were practical conservation outcomes, but the work also had an important bearing on what is regarded as the most important question of ecology, namely the generation and maintenance of biodiversity.
Applied challenges to biodiversity, such as the prediction of the ecological causes and consequences of global climate change, require the interfacing of phenomena that occur on very different scales of space, time, and ecological organization. The value of rabbits as a window into the mechanisms by which diversity is generated and maintained is evident when it is realised that their behaviour, in conjunction with climate, affects the scenic appearance ot the island’s landscape from season to season and year to year. Their visible presence, unconstrained, and their botanical impact contributes to the concept of the island being a wild, heterogenous place in the eyes of visitors.
A report on the rabbit work was produced in 1992, but the follow up has continued intermittently to the present.
4 A grassland microcosm
A visitor walking the island’s footpaths is oblivious to the highly ordered patterns of botanical biodiversity in the central fields. To appreciate this phenomenon is a ‘hands and knees job’ because it is a small scale characteristic of the closely grazed grassy sword, sometimes described as a ‘rabbit lawn’. Depending on the grazing pressure these grassy ecosystems can support about a dozen dicots and several mosses. These are mixed in with grasses that are cropped and trampled by rabbits to a few centimetres in height. To study this widespread feature of Skomer’s biodiversity requires skills to identify their dwarfed non-flowering parts.
Broadly speaking, the rabbit habitat of the central fields is defined by three visual elements characterised by the dominant plant species; bracken, woodsage and grass. The first two are not eaten by rabbits and it is the distribution of all three elements in time and space that produces the rabbit’s ecological landscape imprint.
It is at the landscape level that the problem of pattern and scale emerges as the central problem in ecology, unifying population biology, ecosystems science and marrying basic and applied ecology. In the wider scheme of things, the problem of ecological pattern is inseparable from the problem of the generation and maintenance of diversity. Not only is the heterogeneity of the environment often essential to the coexistence of species, but the very description of the spatial and temporal distributions of species is a description of patterns of diversity. Thus, an understanding of botanical pattern in the landscape over several magnitudes of scale, its causes and its consequences, is central to understanding evolutionary processes such as speciation, as well as ecological processes such as succession, community development, and the spread and persistence of individual species. The behaviour of rabbits in the grassland microcosm of Skomer's central fields holds the key to the existence of a range of mechanisms for generating pattern.
5 Population dynamics
Fig 1
Fig 2
6 Space time and scale
Fig 3 Helicopter view of five warren entrances, marked (W) in the eastern part of the Field 1 enclosure: shot from a helicopter with a hand-held camera in 1982.
Fig 4
An example of a coarse pattern of vegetation is presented in Fig 3. It was obtained by walking Field 1 in 2005 guided by a permanent grid that was originally created to measure the rabbit population. In each grid square a quadrat (0.5 x 0.5m) was thrown at random and the patch of vegetation enclosed by the quadrat was categorised by eye into one of the three ecological elements defined above.
Fig 5 Distribution of the three major botanical pattern-forming elements in Field 1, also known as ‘Calves Park’ (2005)
An example of digital colour enhancement of part of Field 1 can be seen in Fig 4. The site of the warren in Fig 2 is marked (W) in Fig 3.
Fig 5 This image was produced from the Google satellite image of Skomer using the enhancement tools of Corel PaintShop Pro5X for adjusting saturation and hue and then applying the topography tool
Comparison of the detail in the three images demonstrates that here is no single natural scale at which ecological phenomena should be studied; systems generally show characteristic variability on a range of spatial, temporal, and organizational scales. The observer and his or her method imposes a perceptual bias, a filter through which the system is viewed. This has fundamental evolutionary significance, since every organism is an "observer" of the environment, and life historical adaptations, such as dispersal and dormancy, alter the perceptual scales of the species, and the observed variability. This has fundamental significance for the study of ecological systems, since the patterns that are unique to any range of scales will have unique causes and biological consequences.
The key to predicting and understanding long term ecological changes lies in the elucidation of mechanisms underlying an observed pattern. Typically, these mechanisms operate at different scales than those on which the patterns are observed. In some cases, the patterns must be understood as emerging from the collective behaviors of large ensembles of smaller scale units. In other cases, the pattern is imposed by larger scale constraints. Examination of such phenomena requires the study of how pattern and variability change with the scale and time of description, and the development of investigative procedures for simplification, aggregation, and scaling. Ideally, such an analysis should begin with the finest scale of recording possible. It is here that enhancement of digital images from satellite or aerial surveys can be of help in highlighting patterns that can then be checked out for meaning with a ground survey using a hand-held GPS mapping device.
7 A campfire meditation
The distinctive feature of indigenous belief systems is that they are ways of life with the purpose of ordering human relationships with our fellow non-human beings, both spiritual and physical. At the root of it, a belief system is a quest for harmony between an individual, and his or her imaginings about nature and society. Thus, the unseen world of the imagination is as much a part of reality as that which is seen. In other words, the spiritual is as much a part of reality as the material. In fact, there is a complementary relationship between the two, with the imaginative being more powerful than the material. Also, the community is of the dead as well as the living. And in nature, behind visible objects lie essences, or powers of the imagination, which constitute the true nature of those objects.
So it is when visitors to an island face up to the physical marks left by previous visitors. Imagination is also brought into play when mainlanders meet up with the conceptual mapping of the survival strategies and discoveries of past islanders depicted in words, maps and pictures. From the latter point of view, a visitor becomes an islander through the very act of conceptualising their experiences. Take for example, the essence of the next sentence
“The first test of a visitor to Skomer Island is to make sense of ‘the Harold Stone’ situated above the landing in the context of it establishing a connection between the prehistoric community of the island and the Neolithic mainland culture expressed in a scattering of up-ended stones stretching as far east as Stonehenge’.
For ever more, you, dear reader, will always have to consider the truth or falsehood of this concept where there can be no resort to hard facts
We’re hearing so much about Indigenous knowledge lately
Knowledge about the natural world We want to know that knowledge
To understand what we’ve done wrong To make things better
But knowledge alone won’t do that for us Stories we hear
From indigenous mouths Are not stories of
Knowledge of place alone They are stories of
Sense of place Not what to know about
A place you live in But how to live in A place you know
Not just Humans in nature but Nature in humans
Stories not of Knowledge alone
But of wisdom which is Lessons we draw from knowledge
Information alone is nothing if There’s no lesson to draw
Tucson, April 1996
8 Additional web references
__http://www.esa.org/history/Awards/papers/Levin_SA_MA.pdf__
Appendix 1
Enhancement of digital images: using tools in Corel PaintShop ProX5
1 Adjusting saturation and hue
Saturation is the purity or vividness of a colour, expressed as the absence of white. A colour with 100% saturation contains no white. A colour with 0% saturation corresponds to a shade of gray.
A hue is the property that defines a particular colour. For example, blue, green, and red are all hues.
Hue refers to the actual colour (such as red or yellow). Saturation is the vividness of the colour. Imagine bright orange, which is a highly saturated colour. As the saturation is reduced (keeping the hue and lightness unchanged), the orange colour becomes brownish, then taupe, and finally a middle neutral gray (after the saturation has been reduced to zero). Reducing the saturation drains the colour away, leaving just the grayscale component. Taupe and mauve are low-saturation colours because they are quite neutral, with just a touch of colour. Apple red and banana yellow are high-saturation colours. Saturation is a measure of how different a colour is from a neutral gray of the same brightness.
In digital images, increasing the saturation can give the image brilliant colour and "punch," but too much saturation distorts colours and causes problems such as unnatural-looking skin tones. You can use the Vibrancy control to target only those areas that are low on saturation without affecting the rest of the image. For example, you can boost colour in less saturated parts of an image without significantly altering other
Corel PaintShop Pro gives you four ways to alter the hue and saturation of a selection or of an entire image:
2 Trace contour
The Trace Contour effect traces a series of single-pixel lines around areas of contrast and turns the remaining pixels white
3 Topography
The Topography effect gives an image a three-dimensional look so that the image appears to have been created from a system of terraces. You can access the Topography dialogue box by choosing Effects Artistic Effects Topography.
The Topography dialog box contains the following controls:
- Width - controls the size of each terrace or layer
- Density - sets the number of terraces
- Angle - affects which edges appear light and shadowed. The needle points to the direction of the light source, measured in degrees of rotation around the circle. To set the value, you can click in the circle, drag the needle, or set or type a number in the control.
- Colour - lets you choose a color for the light shining on the sides of the terraces. To change the light colour, you can click a colour in the original image, click the colour box to access the Colour dialogue box, or right-click the colour box to access the Recent Colours dialogue box.