An Investigation into Species Diversity with distance along a Pingo.

Authors Avatar

Homaira Ahmad UVI_URQ/BED

An Investigation into Species Diversity with distance along a Pingo

Aim:

The aim of this investigation is to identify the relationship between species diversity and distance along a pingo.  This will be achieved by identifying the number of different species along the profile of a pingo in Foulden Common, Norfolk.  Statistical tests will be done on the data to test the results’ significance.  Two abiotic factors will be investigated; including edaphic factors, in particular soil moisture and pH, and the effect of climate; light intensity at each zone will be measured to see the effect it has on the vegetation growth of the area.  

Introduction:

Foulden Common is situated in Norfolk.  It is classified as ancient chalk grassland and for that reason is a Site of Special Scientific Interest.  It is diverse is species and topography, containing pingoes, anthills, open pasture and set aside.  My study will focus on the pingoes, and the vegetation they are home to.  

The pingoes found on the Common are relic glacial landforms.  They are likely to have formed during the Pleistocene (the last Ice age about 2 million years ago).  There are two different types of pingo; a closed-system pingo and an open-system pingo.  The closed-system pingo forms from a local supply of water, they often form on the sites of small lakes.  Initially the water would insulate the underlying sediments, however in time sediment would be deposited on the bed, decreasing the depth of the lake, thus allowing winter freezing to extend to the bed.  The underlying sediment would no longer be insulated and would in turn freeze as the permafrost (permanently frozen soil i.e. all moisture within the soil is frozen) advanced from both sides.  The advance of the permafrost would exert a pressure onto the water within the sediment to push upward.  Doming occurs on the surface and the water remaining inside the mound is converted into an ice core.  

The open-system pingo forms as a result of water from a distant elevated source infiltrating the soil and mixing with the unfrozen sediments of the upper layers of the ground.  The water then freezes and as it does so expands to form localised masses of ice.  The ice forces the overlying sediment into a dome-shaped feature.  A body of water is trapped under ground after this freezing occurs; pressure from the surrounding permafrost forces the water upwards.  The water eventually freezes into an ice core, which results in further doming of the land.  Ground water under pressure continues to feed the ice core, ensuing larger mounds.  

As the surface of a pingo is stretched the summit may rupture and crack (due to increased pressure from the permafrost) and subsequent freezing of water beneath and sediments erupted out.  If the ice core melts, as in the case of the pingoes in Foulden Common, the dome may collapse leaving a hollow.  The pingoes in Foulden Common are likely to be open-system pingoes, which although are characteristic of valley bottoms, are situated where the permafrost was thin.  Closed-system pingoes on the other hand, whilst occurring in low-lying flat areas, occurred where permafrost was continuous i.e. around the poles where the climate was most severe.  

There are a large number of pingoes in the Common, the largest being approximately 2m deep and 10-15m in diameter.  Since the ice age there has been a build up of organic material in the bottom of the pingoes, thus increasing the fertility and quality of the soil.  Because of the varied terrain cause by the pingo the Common cannot be ploughed on, instead it is grazed.  Originally there two sources of grazing, firstly rabbits and secondly, by the local people of Foulden, who had grazing rights and so would tether their animals in the Common allowing them to graze.  However this phased out in the first half of the twentieth century, probably due to the First World War.  The rabbit population also fell due to myxomatosis in the 1950s.  The decline in grazing has encouraged natural succession converting the grassland into scrub and woodland.  Recently the rabbit population has begun to recover and cattle have also been introduced onto the Common to maintain the rare grassland habitat.  

Hypotheses:

It is hypothesised that water content, pH and light intensity will change with distance from the top of the pingo.  Changes in the water content, pH and light intensity will influence the species diversity along the pingo.  

Prediction:

‘Species diversity’ is a measure of the different species of vegetation found in an area.  The amount of different species in an area is dependent on various factors.  The main factor affecting species abundance is the carrying capacity of the environment.  Carrying capacity is “the maximum size of a population that can be supported sustainably in a particular habitat” (Cambridge, Biology 2).  The carrying capacity is not a set level and fluctuates with the population level of a species.  A population will flourish if the carrying capacity is high and will fall if the carrying capacity decreases.  

The carrying capacity is controlled by several abiotic factors combined with biotic factors.  Biotic factors include competition, density and predation.  It also includes and amount of waste produced by the populations, however this is not really applicable to vegetation.  Abiotic factors include temperature, light intensity, topography, and edaphic factors (moisture content, pH, depth, organic content and compaction).

All ecosystems are subject to intraspecific competition within a species and interspecific competition between species.  The species will compete for space, light and nutrients amongst other things.  Both types of competition will affect the species diversity and abundance along the pingo.  As the density of vegetation increases and the roots take up most of the nitrates and water, the carrying capacity for each population will decrease.  As this happens the environment will no longer be able to sustain as many species and they will begin to die.    It is this competition that leads to adaptations in plants so that they are best suited to survive in specific conditions.

Plants, being autotrophs are producers.  They therefore make up the initial stages of food chains, producing their own food and energy by photosynthesis.  W D Phillips and T J Chilton, in A-Level Biology define photosynthesis as “the process by which green plants trap light energy from the sun and transform it into chemical energy stored in molecules of carbohydrate”, whereas Jones and Gregory in Biology 2 further define it as “the fixation of carbon from carbon dioxide into organic molecules using light energy”.  Plants therefore require sunlight in order to photosynthesis and produce its own food.  The equation for photosynthesis is as follows;

6CO2 + 6H2O

Sunlight of the appropriate wavelength is absorbed by the photosytems within the thylakoid membranes of the chloroplast.  Light of 680nm is absorbed by photosystem II and light of 700nm is absorbed through photosystem I.  The photons of light are funnelled onto special molecules of chlorophyll a known as the ‘reaction centre’.  The main use of light in photosynthesis is in the ‘light stage’ where it is used in the photolysis of water.  Photosystem II contains a water splitting enzyme which together with the energy from sunlight, split water into 2H+, 2e- and ½ O2.  Energy from sunlight is then used to boost the electrons to higher energy levels, both in photosystem II and photosystem I.  After being initially boosted to a higher energy level (at photosystem II) the electron is accepted by an electron acceptor.  It then travels to photosystem I, as it does the electron is passed through a series of electron carriers.  The energy lost by the electron in the carrier system is captured by converting ADP and an inorganic phosphate into ATP.  Thereby converting light energy into chemical energy.  Photosystem I then uses light on 700nm to boost the electrons to a higher energy level, are accepted by an electron acceptor, some then take part in cyclic phosphoryllation whilst other electrons combine with 2H+ (from the photolysis of water) to form 2H, which is then used to reduce NADP.  Sunlight will therefore have a substantial impact on the species diversity of an area.  The more sunlight there is, the greater the rate and amount of photosynthesis and growth.  Therefore where there is most sunlight, there will be more plants.  There will be both interspecific and intraspecific competition for light, which will effect, which plants grow in which areas along the pingo.  

The leaf structure of plants is adapted in order to penetrate the most sunlight.  The upper layer of cells, the epidermis (which is coated by a waxy cuticle) is a colourless layer of closely fitting cells.  It contains no pigment and therefore sunlight is allowed to pass through without interruption.  The palisade mesophyll is the next layer.  The palisade cells are vertically arranged and are again closely fitting so that the rays of light are fully penetrated by the chloroplasts in the cell.  The palisade cells have many chloroplasts, containing chlorophyll in the cell cytoplasm.  These trap then sunlight for use in photosynthesis.  The spongy mesophyll contains many air spaces for gaseous exchange, i.e. for CO2 to reach the cells for photosynthesis and for O2 to be used in respiration and excess to leave via the stomata.  

Sunlight of a different wavelength (to that accepted by the chlorophyll) will simply pass through the leaf.

The leaves of different plants vary greatly.  The greater the surface area the greater the amount of sunlight will be able to be absorbed by the leaf.  Therefore plants with large leaves will have an advantage over those with smaller leaves for they have a larger surface area to absorb sunlight.  

Enzymes are involved in the photolysis of water in photosynthesis.  Enzymes are globular proteins.  They are biological catalysts, which act to speed up reactions whilst remaining unchanged themselves.  The enzymes achieve this by lowering the activation energy, which needs to be overcome before any reaction can take place.  The temperature of the environment will also therefore be a factor affecting plant growth, as temperature has a great effect on the activity of enzymes.  At low temperatures experiments occur slowly, because the substrate and enzyme molecules have little energy and therefore move slowly.  As a result fewer substrate molecules, in this case the water molecules; will collide with the active sites of the enzyme molecule.  When they do collide they may not have enough energy for the collision to be strong enough to bind forming the enzyme-substrate complex.  As temperature increases the molecules gain more kinetic energy and move faster.  The substrate molecules therefore collide more frequently with the active sites of the enzymes.  As they do so they have more energy, which makes it easier for the bonds in the water molecules to be broken, and the reaction occurs at a faster rate.  As the temperature of the habitat continues to rise so does the enzyme activity, however this does not go on indefinitely.  If the temperature exceeds the optimum for the particular enzyme, the active site denatures, thus preventing the enzyme from working.  Denaturing causes the enzyme structure to break down, it occurs as the molecule vibrates so energetically that some bonds, in particular the hydrogen bonds of the active site, which hold the enzyme in its precise shape break.   This is often irreversible.  Different species of plants will be located where they are best suited, in terms of temperature, for the enzymes to work efficiently, if not at their optimum.  

The pH of the soil will also affect the vegetation growing in the pingo.  pH indicates the amount of H+ ions in a solution.  Foulden Common is chalk grassland.  Chalk is almost a pure form of calcium carbonate; because of this the soils are expected to have a pH of 7.4-8.5, as is the case for the soils of other chalk grasslands i.e. alkaline soils.  Not only will the plants be adapted to the pH, in this case the pingoes should be home to calcicoles, or lime-tolerant plant species, but the enzyme activity will also be affected, as the uptake of water, and other substances from the soil, will be of greater alkalinity.  Most enzymes have an optimum pH around neutral.  The hydrogen ions in any solution interact with the R-groups of the amino acids in the enzymes.  This interaction affects the way in which the R groups bond with one another, and subsequently effects the 3D arrangement of the active site.  Extreme pH values cause denaturing of the enzyme rendering it useless.    As the pingoes are expected to have alkaline soils it is expected that calcicoles will be present in abundance along the profile.  

Water is another molecule essential for plant growth and sustenance.  A thin film of moisture surrounds all soil particles.  Water enters the plant root by osmosis.  The soil, whilst has some inorganic ions has them dissolved in water, having a diluted effect.  The root cell sap and cytoplasm however, have many inorganic ions, which is relatively concentrated thus lowering the water potential inside the root.  Water therefore moves down the gradient into the roots by osmosis.  The roots have root hairs, which are long thin extensions, increasing the surface area of the root in contact with the soil, and thus in contact with the water.  The more water there is in the soil the greater the rate of osmosis will be.  Chalk grasslands however are very porous and contain little water.  The amount of water is dependent on the depth of the soil layer (on top of the bedrock).  If the soil layer is thin the water will drain through it easily, quickly, and run straight through the chalk.  If the soil layer is thick, on the other hand the soil will have a greater capacity to hold water, before it is drained through the chalk.  Pingoes are glacial features, which occur by the uplift of the land and subsequent collapse of a mound.  As a result the base of the pingo will have greater moisture content because the soil is closer to the water table.  The ‘water table’ is the level at which there is naturally occurring water in the soil.  The higher up the pingo you go, the smaller the amount of water because the soil and bedrock have been lifted up and away from the water table.

The roots of plants also therefore have to be adapted to the ecosystem.  If there is insufficient water the roots will have to be adapted to find water and compete with the other species in the environment for it.  The general adaptation for this can be seen in the root hair.  The root hair is ‘very thin extension of the cells that make up the outer layer or epidermis of a root’ (Cambridge, Biology 1). They increase the surface area of the root with the soil, so more water can be taken into the plant by osmosis.  However other adaptations also occur in certain plants, for example, in dry areas plants are found to have long taproots, which grow deep into the soil in search of water.  Thus they grow towards the water table, where there will be greater water availability.  Roots also branch across nearer the surface of the soil where they can quickly uptake moisture from precipitation.  An example of this is spring sedge where roots branch across from each tuft of grass to the next.  

Soil depth is also important because the deeper the soil the more water it will be able to hold.  The soil depth will be thickest where there are most plants.  This is because as the plants die, they decay to produce humus and improve the quality of the soil.  Some areas will be shallower than others due to compaction of soil by both humans and the grazing animals.  Compaction reduces the amount of air in the soil, therefore trampling will reduce the species diversity of an area by reducing the carrying capacity of the soil. The soil quality will also be enhanced due to the presence of cattle and rabbits grazing on the land.  They add nitrate to the soil as they excrete which decomposes to form ammonium in the soil.  The process of nitrogen fixation by rhizobium, lightning, free living bacteria in the soil convert nitrogen in the air into organic nitrogen in the soil, which decomposes to ammonium.  This ammonium is the nitrified by nitrosomonas and nitrobacter in the soil forming nitrates which are then taken up by plants.  However grazing also has the effect of trampling the vegetation, and is enforced to prevent the process of succession.  In effect it will reduce the species diversity of an area.

Where the soil is thin and water scarce, the vegetation will adapt to reduce water loss by transpiration.  Transpiration occurs from the plant leaves to the air.  The walls of the mesophyll are wet; some of this water evaporates into the air spaces in the mesophyll layer until they are saturated.  The water diffuses out of the stomata travelling down a water potential gradient, as the inside of the leaf is more saturated than outside.  Grasses/xerophytes are adapted to dry conditions, they curl inwards to create a humid microclimate and therefore reduce transpiration.  Other adaptations include hairs on the surface of the plant insulate the plant therefore protecting it against wind and reducing transpiration and some plants have extra thick waxy cuticle which acts to again reduce water loss.

Join now!

Succession is the process of change in a vegetation community over time.  There are several stages in succession known as invasion; the arrival of species, colonisation; the establishment of species, competition; the struggle for survival and dominance which sees the strongest species survive as they are best-adapted and continue to develop, pushing other species out of the area.  Succession can be seen across the pingo, where the vegetation changes from grasses and herbs to shrub and finally trees and woodland.  As succession occurs the number and type of species change, as does the complexity of species and vegetation height. ...

This is a preview of the whole essay