Bio 208

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Bio 208
2012-12-10 13:20:45
Landscape Ecosystem Ecology

Unit 5
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  1. Succession
    Sequential, directional, and relatively predictable change through time in community composition, and associated abiotic properties, following disturbance
  2. Climax community
    • The ultimate association of species after succession
    • ...but don't take too literally - so-called climax communities are usually in a state of dynamic equilibrium...succesion in an outcome (of all other interactions)
  3. Disclimax communities
    require continual disturbance to persist
  4. Primary succession
    Succession on newly formed or eposed sites, which lack previous biotic influences -> no organic matter, and typically no soil.
  5. Secondary succession
    Succession after an existing ecosystem is distrubed (previous ecosystem (soil, seed bank...) influences subsequent processes
  6. Reasons for secondary succession
    • Species with fast growth and heavy seed production likely to "find" newly opened habitats first
    • Slower growing, more shade tolerant species increase in # after ~50 years and outcompete pioneers
    • Outbreaks of natural enimies regulate some species, while even more shade tolerant (=most competitive) species eventually dominate
  7. Primary succession at Glacier Bay
    • 1. Pioneer species (0-10 years)
    • 2. Within 10 years: small shrubs
    • 3. 10-50 year: importance of Alder
    • 4. 100-200 years: spruce displaces Alder
    • 5. 200-500 years: Hemlock -> spruce
    • Richness is increased rapidly at first, then more slowly
    • Timing of maximum species richness differs among plant groups
    • Climax community reached in approx. 500-1000 years
  8. Autogenic changes
    • Environment chages brought about by organisms within the community -> a common feature of terrestrial succession
    • colonization alters the environment; eg. light, soil, nutrients...
    • May make environment more or less suitable...
  9. Succession and allocation
    • Pioneer species = good colonizers, fast growth, but often shade intolerant...
    • Often change the systems in favou of other species, not themselves...
    • Neither Alder nor Spruce germinates well in the stage where it's dominant
  10. Key differences between primary and secondary succesion
    • Secondary
    • soil typically contains organic matter and can support a variety of species; may already contain a diverse seed bank ->succession may be faster
    • Disturbance is an opportunity: eg. more light and space, less competition from previously dominant species, etc
    • Immediate beneficiaries are species that can disperse over long distances and/or grow quickly; no explicit need for pioneer species
    • Primary
    • Substrate, if present at all, contains no organic nutrients (eg. N)-> most species can't survive, regardless of dispersal ability
    • Pioneer species that help to creat soil must colonize first, before other species can colonize (many fix nitrogen, etc.) ->slow process
    • Succession follows a slow path from pioneer to (dis)climax community
  11. Primary species
    "create" soil
  12. Succession in Aquatics
    • Aquatic communities are subject to both primary (beaver making a dam) and secondary (sedementation) succession
    • Sedmentation (usually in shallow ponds/lakes) may eventually result in disappearance of the lake!
  13. BACI design
    Before, After, Contol, Impact
  14. Hubbard Brook ecosystem study
    • Experimental deforestation: how do forests affect nutrient loss/retention?
    • BACI design
    • Studies nutrients in 2 streams 3 years before treatments
    • Clear cut 1 catchment (impact); other left as control
    • Herbicides used to supress growth/recovery
    • Then let succession proceed (after)
    • -after clear cutting, more calcium, potassium, and nitrate lost relative to control (high spikes, then slowly decline)
    • After herbicide stopped, nutrient loss declines (as succession is allowed)
    • Nutrient retention because: runoff water slowed, transpiration means less water left, soil not lost as easily, and many nutrients are taken up by forest species and held in biomass
  15. Flashback: Clements and Gleason
    • Clements: communities are discrete groups of interdependent organisms (more then the sum of its parts -> "superoranism") (implies that communities can be classified: "pine forest", "peat bog", etc
    • Gleason: species respond to the environment independly; no larger-scale "organization" - species present depend on... chance: who arrives first or at the right time -> dispersal ability: Tolerance: who can survive once there.
    • Outcome of succession not predicatable; dependent on local interactions and conditions. Succession may not result in the same climax community even under similar conditions
  16. Current Understanding of succession conters around 3 mechanisms
    • Facilitation; Only certain (pioneer) species can surive successional stages
    • These species modify the environment ->less suitable for theselves, but more suitable for species characteristic of later successional changes
    • Earlier successional species die out as they make the environment less and less suitable for themselves, and are replaced... eventaully this leads to a climax community when there are no other species that can replace the existing ones.
    • Tolerance: Any species, not just pioneers, can colonize in early succession
    • Early species do not improve the environment for later species, they simly change it
    • Later species are those that can better tolerate the changes to the environment, and the climax community is reached when there are no more species taht are more tolerant than the existing ones
    • Inhibition: Any species, not just pioneers, can colonize in early succession
    • Early species inhibit colonization by later species...
    • Later species can only colonize if a space opens up (disturbance)
    • Climax community consists of species that dominate simply because they live longer and can resist damage/disturbance
  17. Ecosystem changes
    Because this is ecology, no single mechanism fits all cases, a combination of factors usually govern succession.  Surrent research suggests that, depending on many factors, there may be several possible climax communities, and that any climax community is still dynamic
  18. Ecosystem changes during succession
    • 1. Changes in species composition
    • 2. Increased complexity (structure) of soils, habitat structure... herbs to shrubs to tress..
    • 3. Increased complexity (function) food web and energy flow: more energy used for maintenence of existing biomass over time, less energy used for production of new biomass.
    • 4. Increased biomass: more standing biomass ( not necessarily production)
    • 5. Increased nutrient conservation: early; soils leach nutrients, later; more nutrients tied up in living biomass; also more soil organics
    • 6. Ecosystem reaches stability
  19. Stability
    • Absence of change
    • can be a lack of disturbance, or resistance and resilience
    • Overall stability is an "average" of all species abundances
    • May also have several states that it is stable in (alternative stable states)
  20. Resistance
    • Ability to maintain community structure/function in the face of disturbance.
    • Theory predicts that more diverse communities will be more resistant to disturbance
    • Invasion resistance: less available niche space and more effective use of resources
    • Averaging effect: averaged responses of many species will act as a buffer against disturbance
    • Insurance effect: many species mean more reduandancy in the community
    • Disease/pest resistance: harder for the disease/pest to specialize
    • This is one reason that preserving biodiversity is a major goal of conservation
  21. Resilience
    • Ability to return of original structure/function after disturbance
    • Some factors to consider:
    • Lattitude: how much can a community be changed before it can't recover
    • Precariousness: how close is the community to that point?
    • Resistance: how much does the community resist change?
  22. Alternative stable states
    Communities that are stable in one of several states (grasshopper, spiders, and a dominant plant...)
  23. Stability can be caused by many things
    • Temporally by...
    • species composition/diversity
    • interaction between those species
    • climate/weather

    • Spatially by...
    • physical environment
    • climate/weather
  24. Communities not static
    Disturbance and succession are part of many communities, so should disturbances by "conserved" too???
  25. Biogeochemistry
    Raw materials for the ecosystem
  26. Energy
    Needed to convert raw materials into life forms
  27. Organisms
    Energy input lets them exist; in turn, they participate in energy flow and nutrient recycling (food webs)
  28. Main components of an ecosystem
    • Biogeochemistry
    • Energy
    • Organisms
  29. Trophic classification (Elton)
    • Simpl summary of feeding interactions within the ecosystem
    • Basic description of ecosystem structure: numbers, biomass, or energy at each level
    • Suffests transfer of energy
    • Trophic structure focusses on the functinal role of organisms, not on their individual indentities
  30. Linear food chain
    Simplest abstraction of trophic relationships within a community
  31. Food webs
    • Feeding relationships usually are more complex then "linear"
    • These contain trophic levels
  32. Energetic hypothesis
    Length of food chain is limited by ineffeciency of energ transfer (ie, essentially by productivity)
  33. Gross primary production (GPP)
    Total assimilation of energy by autotrophs, regardless of costs
  34. Net primary production (NPP)
    Energy available after respiration... ie. the amount of energy left over after the autotrophs have met their own needs

    NPP = GPP - respiration

    • This is the amount of energy actually available to consumers in the ecosystem
    • Energy flow in ecosystems startw with autotrophs usually harnessing solar energy (photosynthesis)
    • Primary production supplies carbohydrates (chemical energy) needed to build tissues, function, and reproduce
  35. What controls productivity?
    • Light: length...depth in aquatic systems...
    • Climate: termperature, moisture, actual evaportranspiration (integrates temp and moisture)
    • Nutrients: availability influences uptake, photosynthesis, plant growth: N,P,&K most often limiting
    • Temporal variation in PP: seasonal, annual climate variation, age or plant/forest stand
  36. Trophic cascade (Mary Power)
    • When affects of predation extend (indirectly) to lower trophic level
    • Bottom-up control: when lower trophic levels (or nutrients) determin "size" of levels below
    • Top-down control: when higher trophic levels determine "size" of levels below
    • Structure: Primary producer, herbivore, primary carnivore, secondary carnivore
  37. 2 fates of NPP
    • 1. Consumption by herbivores
    • 2. Death & degradation
  38. Secondary production and ecological efficiency
    • of ingested NPP (I), some is assimlated (A), and some is egested (W)
    • of assimilated, (A=I-W), some is respired (R)
    • Remaining NPP is available for growth and reproductios
    • P = I - W - R = A - R
    • Same process occurs at each higher trophic level
  39. Production efficiency of plants
    • NPP/GPP * 100%
    • -> 30-85%, higher when rapidly growing
    • 2nd law of thermodynamics: when energy is transferred, some is lost to entropy (heat)
  40. Ecological efficiency of Energy Transfer
    • Net production efficiency
    • 1-6% for endotherms; up to 75% for ectotherms
    • Assimilation efficiency: the proportion of consumed energy that is actually assimilated (can actually be used)
    • 10-80% for herbivores (browers'grazers'granivores)
    • 60-90% for carnivores
    • Meat is assimilated more easily than plants: in plants, seeds>leaves>grass
  41. Trophic pyramids
    • General consequence: decrease in biomass with each extra trophic level=biomass pyramid
    • In some ecosystems, the biomass pyramid may be inverted...
    • But the energy pyramid can never be inverted
    • Rule of thumb is 10% is passed on to next level, but highly variable....
  42. Two major food chains in ecosystems
    • Grazing food chain: herbivores feed on living plant biomass
    • Detrital food chain: source of energy is dead organic matter
    • These are linked: detritus waste from grazing chain contributes to detrital chain. Carnivores may not discriminate prey from either chain
    • Relevant importance of the 2 chains varies among ecosystems
    • In many, detrital is major route of energy
  43. Decomposers
    Bacteria, fungi, worms, insectséother arthropods
  44. Detritvores:
    A sub-group that can ingest larger chunks of matter
  45. Exploitation efficiency
    • The efficiency with which the biological production of a trophic level is consumed
    • =prey biomass eaten/prey biomass produced
  46. Assimilation efficiency
    • The proportion of consumed energy that is actually assimilated (can actually be used)
    • =assimilation/inegestion
  47. Net production efficiency
    • The efficiency with which assimilated energy is incorporated into growth, storage & repro
    • =production (growth and repro)/assimilation
  48. Growth production efficiency
    • The overall efficiency of biomass production within a trophic level
    • =assimilation efficiency * net production efficiency
    • =production/ingestion
  49. Ecological efficiency
    • The % of energy actually transferred from one trophic level to the next
    • =assimilation efficiency*exploitation efficiency*net production efficiency
    • =Pn/Pn-1
  50. Time and energy flow
    • Food chain efficiencies indicate how much energy eventually reaches each trophic level, but the rate of energy transfer provides another index of ecosystem energy dynamics
    • Residence time
  51. Residence time
    • How long does it take for energy to move through trophic levels?
    • =energy stored in biomass/NPP
    • or
    • =actual standing biomass/biomass produced each year
    • Longer residence time = more energy accumulation
    • Aquatic systems generally have much quicker turn over times
  52. Influences on production
    • Abiotic: temperature, nitrogen mineralization, percipitation, age
    • Biotic: trophic cascades (sometimes consumption increases productivity: compensatory growth), biodiversity
  53. Ecosystems: nutrient cycling
    • Remember, energy is essentially on a one-way trip through ecosystem
    • On the other hand, many nutrients and elements are recycled
  54. General global ecosystems model
    • Nutrients reside in compartments (can be biotic or abiotic)
    • Compartments contain a pool of a given nutrient
    • Nutrients move between compartments; rate of movement = flux
  55. Geochemical cycle
    Geologic, slow, less intense
  56. Biochemical cycle
    biological, faster
  57. Biogeochemistry
    • biotic and abiotic components of the ecosystems are linked
    • Nutrients required bor biota, could not be maintained without recycling (which involves biota): cycles involve biotic and abiotic components: cycles are driven by energy flow...
  58. Local ecosystem model: nutirent inputs and losses
    • Gains - nutrients with a gaseous cycle enter via the atmosphere
    • -nutrients with a sedimentary cycle enter via weathering of rocks -> soil formation
    • Losses - to atmosphere via respiration
    • -transport via biota
    • -leaching from soil/sediment/detritus
    • -erosion, harvesting, fire
  59. Global H2O cycle driven by soalr radiation
    • Main processes: evaporation, transpiration, and precipitation
    • Driven by solar radiation: ~1/4 ot total solar energy used in cycle
    • Major pools: ocean (97%), glaciers (2%), groundwater (0.6%)
    • Surface water, soils, biota and especially atmosphere: small pools but relatively large fluxes
  60. Nutrient cycles
    • All common elements cycle...
    • Depending on element, may take minutes, years, or millennia
    • 3 nutrient cycles that are particularly important: phosphorus, nitrogen, and carbon
  61. Phosphorus
    • Not especially common in usable forms, but very important (ATP, DNA, etc)
    • Major pools are mineral, not atmospheric
    • Lots of P in bottom of ocean (mineral form)
  62. Nitrogen
    • Also relatively uncommon, but necessary for many organism structures and functions (DNA) (most significant effect in ocean and primary producers is to add nitrogen)
    • Immobilization: conversion of mineral forms of nitrogen (ammonia & nitrate) into organic forms (protein) eating
    • Mineralization: conversion of organic forms of nitrogen into mineral forms dying
    • Nitrogen fixation: conversion of atmospheric N2 into ammonia (NH3), usually by bacteria or lightning
    • Ammonification: release of ammonium, NH4+ -> nitrate, NO3-
    • Both ammonium and nitrate are useable by many plants and others...
    • major pools is atmospheric
  63. Carbon
    • DNA, phospholipids, etc.
    • More CO2 then ever before
    • Major pools: 1 carbonate rock, 2 ocean, 3 Hydrocarbons, 4 Organic material in sediments/soils, 5 Plants (especially forests)
  64. 3 major processes in the carbon cycle
    • 1. Assimilation (usually photosynthesis) and dissimilation (respiration) by organisms
    • 2. Diffusion (exchange between atmosphere and ocean)
    • 3. Dissolution and sedimentation in aquatics
    • Now we can add a fourth major process: combustion
  65. Decomposition
    • Nutrients such as nitrogen and phosphorus are made available to the primary producers of terrestrial ecosystems via mineralization
    • -mineralization occurs during decomposition
    • -decomposition is influenced by temperature, moisture, and the composition of stuff being decomposed
    • In other words, nutrient cycling is affected by climate and chemistry
  66. Decomposition in a changing climate
    • Arctic and subarctic have deep, organic soil
    • 20-60% of soil-based C on earth is there
    • Much more than C from fossil fuels & deforestation
  67. Biotubation
    • Prevents stratification of nutrients
    • More vertical homogeneity: more horizontal heterogeneity
    • Gophers, roots and earthworms do this...
  68. Nutrient cycling: land versus water
    • Similar, just different proportions
    • Terrestrial tends to have more decomposition
    • Aquatic has less primary producer biomass present and more herbivores, just smaller
  69. Lakes, rivers, and wetland
    • ~0.01% of water
    • 87-88% in significant lakes
    • 11% wetlands
    • 2% rivers
  70. Nutrient cycling
    • aspects of the ecosystem are moving downstream due to current
    • Spiraling length = velocity*cycle time
    • Nutrient retentiveness
    • short spiralling length: high retentiveness
    • long spiralling length: low retentiveness
    • Organisms can also increase cycling time and slow downstream movement of nutrients if they travel upstream
  71. Limits the primary production of many aquatic systems
  72. Aquatic disturbance
    Variation in water level and inputs such as leaf litter may overwhelm the normal balance between nutrient input and losses
  73. Disturbances adn nutrients
    • Vegetation slows/prevents nutrient loss from ecosystems - especially important where rates of decomposition are high (warm and wet)
    • Remember, N limites terrestrail primary productivity
  74. Atmospheric cells and biomes
    • Polar cell, Ferrel Cell, Hadley cell
    • Tundra, boreal forest, temperate forest, desert, tropical savanna, tropical rain forest
  75. Thermohaline
    salt and temperature gradients driver deeper circulation
  76. Wind and thermohaline
    circulation combine to create ocean currents which moderate regional climate
  77. El Nino
    Surface water temp around south america changes (warms), no up-whelming of cold water, bringing up nutrients, feeding primary producers
  78. North Atlantic Oscillation
    • zone of high pressure moving from east to west
    • Positive - southern post colder then usual, arctic drier then usual: plants flower earlier, ungulate reproduce more than normal
  79. Pacific Decadal Oscilation
    takes into account many cycles and puts them together, intenisty felt more in some areas then others, mostly around Calgary
  80. Human effects on planet
    • directly use ~50% of global productivity, and have altered ~50% of all land
    • 40% of land used for argiculture, plus 10% of all freshwater
    • Can't forget "secondary" effects: albedo, burning, edge effects, etc.
  81. Local (alpha) richness (Salpha)
    Number of species in a small area of uniform habitat
  82. Regional (gamma) richness
    Total number of species within the region, minus species common to two or more patches (don't want to count same species more than once)
  83. Beta diversity
    • degree of difference in species (turnover) among patches
    • -compare the number of species that are unique to each patch: measure variablity
    • beta = gamma/average alpha
    • beta at 1 means no variability, larger than one means variability
  84. Factors that might cause diversity gradients
    • History: time and area (more time and area creates more diversity)
    • Spatial heterogeneity- physical and biological complex habitats usually result in more species
    • Biotic interactions - Predation reduces/prevents competitive exclusion, competition affects niche width and overlap (tropical species more specialized)
    • Climate and climatic variability
  85. Large-scale patterns in species diversity related to
    • Lattitudinal gradient
    • Topographic relief
    • Fronts of abrupt change
    • Peninsular decreases
    • Larger area = more species
  86. Biodiversity
    The degree of variation in life forms... or the number of biological elements... in a defined area (usually large)
  87. Islands as useful models
    • Commonly used to understand fundamental ecological and evolutionary process eg. the relationsihp between geographical patterns and biological processes
    • relatively small
    • Quaite common
    • Varying degrees of isolation/size
    • Often, relatively simple communities
  88. Island
    • Isolated bits of favourable habiat in a "sea" of different of nfavourable habitat
    • True islands have fewer species than comparable mainland areas. New colonists displace existing species = balance in species #, but lots of turnover
  89. Island species richness affected by
    • Area of island
    • Distance from source (of imigration)
    • Dispersal mechanism of species can reduce or eliminate the isolation effect
  90. Landscape ecology
    • The study of the relationship between spatial heterogeneity and ecological processes across multiple spatial scales
    • Size, shape, composition, # and position of different elements in a landscape mosaic (landscape structure)
  91. Corriors
    Physical connection between patches may inrease movement, gene flow, (re)colonization, species diversity, etc.