2.6.1 5 6 and7and some 2.5 gpp npp


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2.6.1 5 6 and7and some 2.5 gpp npp

  1. 1. 2.6 – Changes and some 2.5 Function 2.6.1 - 2.6.4 And 2.5.5 and 2.5.6 5/11/2013 IB/ESS Author-Guru Topic 2 – The Ecosystem 1
  2. 2. Specifications IB/ESS Author-Guru 2.6.2 – Describe and explain ‘S’ and ‘J’ population growth curves. Population curves should be sketched, described, interpreted and constructed from given data. 5/11/2013 2.6.1 – Explain the concepts of limiting factors and carrying capacity in the context of population growth. 2
  3. 3. Population Growth IB/ESS Author-Guru • Nearly 1.6 million people join the human population each week. • 84 million people join every year. • In three years the human population grows by an amount nearly equivalent to the entire U.S population. • By 2025 the world population could exceed 8 billion 5/11/2013 Some Facts 3
  4. 4. • We are going to concentrate on population control of ecosystems but these theories can also be applied to human populations. IB/ESS • Studies on both human populations and smaller ecosystem populations are carried out in depth. Author-Guru • The study of any population is an important aspect of science. 5/11/2013 Population Studies 4
  5. 5. • The factors affecting a population size may be biotic or abiotic. IB/ESS Author-Guru • By taking samples and counting the numbers of organisms in a particular habitat, ecologists can study the affects of any factor on the size of a population. 5/11/2013 Population Size • Together they affect the rate at which population grows, and also it’s final size. 5
  6. 6. IB/ESS • How many abiotic factors can you think of that might affect population size? Author-Guru • How many biotic factors can you think of that might affect population size? 5/11/2013 Biotic Factors Affecting Population Size 6
  7. 7. Biotic and Abiotic Factors 5/11/2013 1. Temperature – higher temperatures speed up enzyme-catalyzed reactions and increase growth. 2. Oxygen Availability – affect the rate of energy production by respiration. 3. Light Availability – for photosynthesis and breeding cycles in animals and plants. 4. Toxins and pollutants – tissue growth may be reduced. IB/ESS 1. Food – both quantity and quality of food are important. 2. Predators – refer back to predator prey relationships. 3. Competitors – other organisms may require the same resources from an environment. 4. Parasites – may cause disease and slow down the growth of an organism. Abiotic Author-Guru Biotic 7
  8. 8. 8 Author-Guru IB/ESS 5/11/2013
  9. 9. IB/ESS Author-Guru All of these things come under the category of ‘Limiting Factors’ 5/11/2013 Biotic and Abiotic Factors 9
  10. 10. • Look at the graph of population growth. • This shows how population growth is eventually inhibited by environmental resistance and the environment reaches it’s carrying capacity. IB/ESS • This is usually because there is plenty of food and no accumulation of poisonous wastes. Author-Guru • When a small population grows in a particular environment, the environmental resistance is almost non-existent. 5/11/2013 Carrying Capacity 10
  11. 11. • Think of your brine shrimps!? IB/ESS • Once the carrying capacity is reached, unless the environmental resistance is changed, e.g. by a new disease, the size of the population will only fluctuate slightly. Author-Guru • The carrying capacity (K) is the maximum number of a species that the habitat can hold. 5/11/2013 Carrying Capacity 11
  12. 12. ‘S’ Curves IB/ESS Author-Guru • This is the type of graph that is almost always seen in nature. • As the energy resources become more scarce the population size levels off at the carrying capacity (K). 5/11/2013 • The graph we have just been looking at is an example of an ‘S’ curve. 12
  13. 13. Author-Guru IB/ESS 5/11/2013 ‘J’ Curves 13
  14. 14. • If the resources of the new habitat were endless then the population would continue to increase at this rate. IB/ESS • This type of growth produces a J shaped growth curve. Author-Guru • Just as in the ‘S’ curve example, a population establishing themselves in a new area will undergo rapid exponential growth. 5/11/2013 ‘J’ Curves 14
  15. 15. • Can you think of any examples where ‘J’ curve population growth would be extremely desirable. IB/ESS • Initially exponential growth will occur but eventually the increase in numbers will not be supported by the environment. Author-Guru • This type of population growth is rarely seen in nature. 5/11/2013 ‘J’ Curves 15
  16. 16. • It is very natural to ask the linked questions - does humanity have a carrying capacity and, if so, what is it - and when will we reach or overshoot this IB/ESS • Furthermore, experience with other species tells us that, ultimately, resource limitations and/or habitat degradation will force the human population curves to approach an upper limit - the carrying capacity, often symbolized as " K" by ecologists. Author-Guru • ‘As we have seen, the human population growth curve is currently following an exponential curve or a "J-shape”. Common sense tells us that such growth cannot continue otherwise within a few hundred years every square foot of the Earth's surface would be taken up by a human. 5/11/2013 Is there a Carrying Capacity for Homo sapiens? 16
  17. 17. Activity IB/ESS Author-Guru 2.6.3 – Describe the role of density-dependent and densityindependent factors, and internal and external factors, in the regulation of populations. 5/11/2013 • Complete the activity – The new zoos 17
  18. 18. • These factors exert their effect irrespective of the size of the population when the catastrophe struck. IB/ESS Author-Guru • The following factors are classed as densityindependent factors: • Drought • Freezes • Hurricanes • Floods • Forest Fires 5/11/2013 Density Independent Factors 18
  19. 19. The drought ended in 1978, but even with ample food once again available the finch population recovered only slowly. IB/ESS The decline (from 1400 to 200 individuals) occurred because of a severe drought that reduced the quantity of seeds on which this species feeds. Author-Guru This graph shows the decline in the population of one of Darwin's finches (Geospiza fortis) on Daphne Major, a tiny (100-acre) member of the Galapagos Islands. 5/11/2013 Density Independent Factors 19
  20. 20. • Many rodent populations (e.g., lemmings in the Arctic) also go through such boom-and-bust cycles. IB/ESS • Read the information about the gypsy moth. Author-Guru • Intraspecific Competition competition between members of the same species. 5/11/2013 Density Dependant Factors 20
  21. 21. • This occurs when two species share overlapping ecological niches, they may be forced into competition for the resource(s) of that niche. IB/ESS • This can include food, nesting sites, sunlight. Author-Guru • Interspecific Competition – this is competition between different species for different resources. 5/11/2013 Density Dependant Factors 21
  22. 22. Specifications Author-Guru IB/ESS 5/11/2013 • 2.6.4 – Describe the principles associated with survivorship curves including K- and r -strategists. 22
  23. 23. • Ragweed is well adapted to exploiting it’s environment in a hurry – before competitors can become established! IB/ESS Author-Guru • “I once ploughed up an old field and allowed it to lie fallow. In the first season it grew a large crop of ragweed.” 5/11/2013 R-Strategists 23
  24. 24. R-Strategists • Can you think of any other animals that may be r-strategists? IB/ESS Author-Guru • We say that they have a high value of ‘r’ • They are called r-strategists 5/11/2013 • Ragweed’s approach to continued survival is through rapid reproduction. 24
  25. 25. 2. 3. 4. 5. 6. 7. IB/ESS 1. In general, r-strategists share a number of features: Usually found in disturbed and/or transitory habitats Have short life spans Begin breeding early in life Have short gestation times Produce large numbers of offspring Take little care of their offspring (infant mortality large) Have efficient means of dispersal to new habitats Author-Guru • 5/11/2013 R-Strategists 25
  26. 26. • K-strategists have a stable population that is close to K. • There is nothing to be gained from a high r. • The species will benefit the most by a close adaptation to the conditions of the environment. IB/ESS Author-Guru • When a habitat become filled with a diverse collection of creatures competing with one another for resources, the advantage shifts to KStrategists 5/11/2013 K-Strategists 26
  27. 27. IB/ESS K-strategists share these qualities: Found in a stable habitat Long life spans Begin breeding later in life Long gestation times Produce small numbers of offspring Take good care of their young – infant mortality low 7. Have evolved to become increasingly efficient at exploiting an ever-narrower slice of their environment. Author-Guru • 1. 2. 3. 4. 5. 6. 5/11/2013 K-Strategists 27
  28. 28. Survivorship Curves Author-Guru IB/ESS 5/11/2013 • The graph shows 4 representative survivorship curves. 28
  29. 29. Survivorship Curves IB/ESS Author-Guru • Curve B – typical of populations in which factors such as starvation and disease inhibit the effects of aging and infant mortality is high. 5/11/2013 • Curve A – characteristic of organisms that have low mortality until late in life when aging takes its toll. • Curve C – a theoretical curve for an organism whereby the chance of death is equal at all stages • Curve D – typical of organisms that produce huge numbers of offspring accompanied by high rates of mortality. 29
  30. 30. Survivorship Curves • The Californian side-blotted lizard Author-Guru IB/ESS • R-strategists usually have D survivorship curves. 5/11/2013 • K-strategists usually have survivorship curves somewhere between A and C. 30
  31. 31. • 2.6.7 – Describe factors affecting the nature of climax communities. IB/ESS • 2.6.6 – Explain the changes in energy flows, gross and net productivity, diversity and mineral cycling in different stages of succession. Author-Guru • 2.6.5 – Describe the concept and processes of succession in a named habitat. 5/11/2013 Specifications 31
  32. 32. Succession – An intro • Succession takes places as a result of complex interactions of biotic and abiotic factors. • Early communities modify the physical environment causing it to change. • This in turn alters the biotic community which further alters the physical environment and so on. IB/ESS Author-Guru • A forest following a disturbance such as a fire. 5/11/2013 • The gradual process by which the species population of a community changes is called ecological succession. 32
  33. 33. Succession – What happens? IB/ESS Author-Guru • A succession (or sere) proceeds in seral stages, until the formation of a climax community is reached. 5/11/2013 • Each successive community makes the environment more favourable for the establishment of new species. 33
  34. 34. Primary Succession IB/ESS • You will be studying glacial moraines in detail as well as the succession occurring on bare rock. Author-Guru • Can you think of examples where this would occur? 5/11/2013 • Refers to colonization of regions where there is no pre-existing community. 34
  35. 35. Succession IB/ESS Author-Guru • Study the information on glacial moraines and answer the following questions: 5/11/2013 • Community changes on a glacial moraines 35
  36. 36. 1. 2. Explain what is meant by a climax community. Explain each of the following changes which occur during succession: Species diversity increases Gross production increases Stability of the ecosystem increases Give two reasons why farmland in the UK does not reach a climax community. a) b) c) 3. IB/ESS During succession there is a change in species composition of a community. There are also changes in species diversity, stability of the ecosystem, and in gross and net production until a climax community is reached. Author-Guru • 5/11/2013 Questions – Glacial Moraines 36
  37. 37. IB/ESS • Secondary Succession – occurs on sites that have previously supported a community of some sort. • Examples? Author-Guru • Primary Succession – occurs on newly formed habitats that have not previously supported a community. • Examples? 5/11/2013 Primary and Secondary Succession 37
  38. 38. Lichens, bryophytes and annual herbs After 100-200 years Slower growing broadleaf species e.g. oak Complex Community Fast growing trees e.g. Ash Author-Guru IB/ESS Bare Rock Mosses, Grasses and small shrubs 5/11/2013 Primary Succession – Bare Rock 38 Example for a Northern Hemisphere lithosere: a succession on bare rock
  39. 39. • As these species begin to grow well, they produce shade. Their own seedlings grow more poorly than shade-adapted plants. • Plants that grow well under full sun are replaced by plants that germinate and grow better in deeper shade. IB/ESS • Examples = lichens, grasses, herbs Author-Guru • These are usually fast growing plants that photosynthesize well in full sunlight. • We call these pioneer species making up the pioneer community 5/11/2013 In Summary - the 1st Invaders! 39
  40. 40. Secondary Succession • Humans may deflect the natural course of succession in these circumstances (e.g. by mowing or farming). • This leads to the development of a different climax community than would otherwise develop naturally. IB/ESS Author-Guru • These events do not involve loss of the soil. • Secondary succession therefore occurs more rapidly than primary succession. 5/11/2013 • This type of succession takes place after a land clearance (e.g. from fire or landslide). 40
  41. 41. 1-2 3-5 Young broad leaved woodland 31-150 Mature woodland: mainly oak Scrub: shrubs and small trees IB/ESS Time to develop: Years Grasses and low growing perennials Author-Guru Primary Bare Earth Open pioneer community (annual grasses) 5/11/2013 Secondary Succession – Cleared Land 16-30 41 150+ = climax community
  42. 42. Succession Continues • Animal species have a profound affect on the plant species occurring within a habitat. • Changing conditions in the present community allows for new species to become established (the future community). • Succession continues until the climax community is reached. IB/ESS Author-Guru • Decomposers will join the community as well as animal species. 5/11/2013 • As the plant community changes, the soil will also undergo changes (abiotic factors will change). 42
  43. 43. Wetland Succession 5/11/2013 • Wetland areas present a special case of ecological succession. Open water Plant invasion Siltation and Infilling Author-Guru IB/ESS • Wetlands are constantly changing: • Wetland ecosystem may develop in a variety of ways: 43
  44. 44. Wetland Succession • In special circumstances, a an acid peat bog may develop. (may take 5000+ years). IB/ESS Author-Guru • In non-acidic, poorly drained areas, a swamp will eventually develop into a fen. 5/11/2013 • In well drained areas, pasture or heath may develop as a result of succession from fresh water to dry land. 44
  45. 45. IB/ESS • This is called productivity Author-Guru • Think back to the work on food webs/chains • It is often useful to know how much energy is passing through a trophic level over a period of time. 5/11/2013 Productivity • Productivity is a measure of the amount of energy incorporated into the organisms in a trophic level, in an area, over a certain period of time. 45
  46. 46. IB/ESS • 2.5.6 – Define and Calculate the values of gross and net productivity from given data Author-Guru • 2.5.5 – Define the terms gross productivity, net productivity, primary productivity, secondary productivity, gross primary productivity and net primary productivity. 5/11/2013 Specifications 46
  47. 47. Productivity • The rate at which producers convert light energy into chemical energy is called primary productivity. IB/ESS Author-Guru • It is therefore measured in units of kilojoules per square metre per year (kJm-2year-1) 5/11/2013 • The area is normally one square metre and the time is usually one year. 47
  48. 48. Gross Productivity • The producers use some of this energy during respiration and energy needs which is eventually lost to the environment as heat. • The remaining energy is available to the herbivores and is known as net primary productivity (NPP) IB/ESS • It is related to the total amount of chemical energy incorporated into the producers. Author-Guru • This is sometimes shown as GPP – Gross Primary Productivity 5/11/2013 • Gross Productivity (GP) – is the total gain in energy or biomass per unit time. 48
  49. 49. Recap of Definitions! • Gross Productivity (GP) = the total gain in energy/biomass per unit time. • Gross Primary Productivity (GPP) = the total gain in energy of the producers. • Net Productivity (NP) = the gain in energy/biomass per unit time remaining after allowing for respiration (R) loses. • Net Primary Productivity (NPP) = the gain in energy/biomass per unit time remaining after allowing for respiration loses which is passed onto the herbivores. IB/ESS • Secondary Productivity = The rate at which primary material is synthesised into animal tissue per unit area in a given time. Author-Guru • Primary Productivity = The rate at which energy/biomass is formed through photosynthesis 5/11/2013 • Productivity = production per unit time 49
  50. 50. IB/ESS • The rate at which plants can convert light energy into chemical energy is affected by many factors: • Sunlight • Water • Temperature • Amount of nutrients Author-Guru • Primary productivity varies greatly in different environments. 5/11/2013 Environmental Productivity 50
  51. 51. Environmental Productivity • In the oceans however, the most productive areas are in cold regions due to the up-welling of water bringing plant nutrients with it. IB/ESS Author-Guru • This is due to good light levels and high temperatures in the tropics. 5/11/2013 • In natural ecosystems primary productivity tends to be highest in tropical regions. 51
  52. 52. IB/ESS • We can calculate NPP for both producers and consumers as: NPP = GPP – energy used in respiration Author-Guru • We can calculate GPP as follows: GPP = NPP + R 5/11/2013 Important Calculations • In addition, the equation for consumers only is: GP = food eaten – faecal losses 52
  53. 53. Calculating Productivity Values • What is the GPP of an ecosystem if the NPP is 1660 kJm2yr-1 and the energy lost during respiration is 573 kJm-2yr1? • What is the NPP if the GPP is 2700 kJm-2yr-1 and the energy used in respiration is 1850 kJm-2yr-1? IB/ESS Author-Guru • What is the % energy from sunlight that is fixed as GPP if the total energy from the sun in 3 x 106 and the gross primary productivity = 2.8 x 104? 5/11/2013 • Some easy ones to start you off! 53
  54. 54. IB/ESS Author-Guru Now for some slightly harder ones! 5/11/2013 Calculating Productivity Values 54
  55. 55. Therefore, for photoautotrophs, photosynthetic efficiency is determined as: Photosynthetic Efficiency = Net production ÷ Light Energy Absorbed IB/ESS Ecological Efficiency is the net production of new biomass at each trophic level as a percentage of the total energy flowing through that trophic level Author-Guru Energy flow diagrams illustrate energy flow through communities and include values for respiratory losses and energy flow through the decomposers Information from energy flow diagrams can be used to calculate ecological efficiencies 5/11/2013 Energy Flow Diagrams 55
  56. 56. 5/11/2013 IB/ESS Author-Guru Use information from the energy flow diagram to: • Explain the meaning of the term Gross Primary Production • Explain the meaning of the term Net Primary Production • Calculate the Photosynthetic Efficiency of the phytoplankton 56
  57. 57. 5/11/2013 IB/ESS Author-Guru Gross Primary Production is the total energy fixed by photoautotrophs during photosynthesis Net Primary Production is the energy stored as biomass (gross production – energy lost as heat in respiration) Photosynthetic Efficiency = 57 3.7 x 104 ------------ x 100 172 x 104 = 2.15%
  58. 58. 58 Author-Guru IB/ESS 5/11/2013
  59. 59. 114 x 103 kJ m-2year-1 NPP = 69.7 x 103 kJ m-2year-1 NPP = 200 kJ m-2year-1 Author-Guru GPP = 24 x106 kJ m-2year-1 IB/ESS 5/11/2013 Photosynthetic efficiency = 1.3% NPP = 800 kJ m-2year-1 59
  60. 60. • This is because climax communities are better adapted to an efficient rate of utilisation of their resources. • They become stable. IB/ESS • As ecosystems become more diverse, the overall GPP is also going to increase. Author-Guru • The NPP and GPP of any ecosystem is going to fluctuate. This is especially the case during each seral stage. 5/11/2013 Finally Back To Succession! 60
  61. 61. The Early Stages • This is due to low respiration rates of the initial producers and therefore a lot of energy available to be passed on. • This allows the system to grow and biomass to accumulate. IB/ESS • Net Productivity = High Author-Guru • This is due to the initial conditions and the relatively low density of producers. 5/11/2013 • Gross Productivity = Low 61
  62. 62. The Later Stages • Net Productivity = Low • Increased rates of respiration and other energy sapping activities by consumers means that NP will begin approaching zero. IB/ESS Author-Guru • This is due to an increase in the consumer community who can synthesise a lot of energy from the food they eat. 5/11/2013 • Gross Productivity = High 62
  63. 63. • Ultimately, the climate will be responsible for affecting the nature of the climax community unless human or other factors maintain an equilibrium at a sub-climax community. IB/ESS • Climax communities are more stable that the seral stages that preceded them. Author-Guru • Succession comes to an end with the establishment of a mature, relatively stable community – the climax 5/11/2013 The Climax 63