Bio 208

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Bio 208
2012-12-04 13:54:23
Community Ecology

Unit 4
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  1. Ecology
    The scientific study of the distributions and abundance of organisms and the interactions that determine destribution and abundance
  2. Intraspecific interactions, types
    Classified by the benefits or harm that interacting species recieve (Birth rate? Death rate? Growth? K? ....?)
  3. Mutualism
    • (+/+)
    • Often the product of intimate coevolutionary relationships (symbiosis)
    • May be obligate (cannot live without each other) or faculitative (convenient but can life without one another)
  4. Commensalism
    • (+/0)
    • One species benefits and the other is unaffected
    • eg. Big fish who moves stones to eat and little fish benefit as well, one organism who use other organism for transport (cows and ergots)
  5. Neutralism
    • (0/0)
    • Species totally unaffected by each other
    • Not very common
  6. Exploitation: Predation
    • (+/-): Predation
    • One species is kills and consumes another (usually animals)
  7. Exploitation: Herbivory/grazing
    • (+/-)
    • One species, usually an animal, consumes all or part of a plant
  8. Exploitation: Parasitism
    • (+/-)
    • One species "takes advantage" of another organism without killing it
  9. Exploitation: Parasitoidism
    • (+/-)
    • One species feeds on another organism, ultimately killing it
  10. Amensalism
    • (0/-)
    • One species is unaffected, and the other is affected negatibely
  11. Competition; interference
    • (-/-)
    • Interference competition: interacting species interfere directly with each other
    • One competitor is denied access to a resource by the other(s)
    • eg. elk fighting, one wins, one leaves
  12. Competition; exploitative
    • Exploitative competition: interacting species interfere with each other through competition for the same limiting resource
    • Both species have access to the resource, so the outcome depends on how effective each speicies is at using the resource
    • -> lowers performance of competing organisms
    • -->one species is able to get to the resource first and use it up
    • -->In nature, the presence of one species often restricts the distribution/abundance of other species in that habitat
  13. Competition; intraspecific
    • Intraspecific competition: within the same species
    • Remember density dependence
    • Results from a decrease inper capita resources (among other things)
    • eg. planthoppers: increase the density of planthoppers, they are smaller and mature slower
    • Self thinning, as plants grow bigger, the less plants survive, when plants are small there may be more biomass as more plants actually present, as they are larger, fewer plants survive at the expense of all the other ones.
  14. Competition: interspecicies
    • Interspecific competition: between two or more species
    • Generally similar effect interspecifically as intraspecificaly if two species use the same resource
    • The less efficient species may be eliminated due to competition
    • -> Competition MAY play a role in determining community composition
  15. Competition exclusion prinsiple (Gause's principle)
    Two species exploiting the same resources -ie., having the same niches - cannot coexist in the same habitat indefinitely
  16. Unstable equilibrium
    OUtcome can go either way... winner depends on speicific condition for the species
  17. Resource partitioning
    sufficiently different niches to prevent exclusion
  18. 3 main outcomes of comptition
    • Exclusion: one species always wins, the second species goes locally extinct (expiratated)
    • -most likely to occur in simple, stable, homogeneous environments between ecologically similar species
    • 2. Unstable equilbrium: either species can win, depends on ecological conditions of the moment
    • -Variation in the environment or individual competitive abilities may allow each species a spatially or temporally specific advantage (=refuge)
    • 3. Stable coexistance: neither wins, the species coexist and "share" resources between them
    • -most likely to occur where species' niches allow paritioning of resources
  19. Degree of coexistance
    Likely related to degree of similarity between niches
  20. Lotka-Volterra models of competition
    Competition coefficient (alpha): a mathematical modifier to express the effect of one individual of species 1 on the population growth of species 2
  21. G.E.Hutchinson
    • Niche guy
    • Partial competitive exclusion is common
  22. Can we measure competition coefficient in the field?
    Alpha is related to niche overlap (not the same thing, but related)
  23. Fundamental niche
    Total range of environmental conditions/resources under which a species can maintain itself
  24. Realized niche
    The environmental conditions/resources under which a speies actually exists in the presence of competitors, predators, etc
  25. Gause's principle
    If the overlap of realized niches is too high, exclusion is likely
  26. Many coexisting species have overlapping niches: how without violating Gause's principle?
    • Minimize overlap of their realized niches
    • ->specialize on resources not used by other competitors - resource partitioning
    • -avoids exclusion
    • -allows coexistence
    • -shaped communities
  27. Evaluating competition in nature
    If competition is an important force, then potential competitors should display resource partitioning to minimize negative consequences
  28. MacArthur's warblers:resource partitioning
    • Each species:
    • -concentrated feeding in different parts of trees
    • -used different foraging methods
    • was in contact with, and consumed different prey
    • -bred at slightly different times (different times of max resource requirements)
    • MacArthur:these differences (resource partitioning) are sufficient to explain coexistence
  29. 3 main niche axes
    • Habitat
    • Food
    • Time
  30. Character displacement
    Evolutionary seperation of two species in morphology, physiology, etc. when in sympatry vs. allopatry
  31. Predation
    The consumption of one organism by another, where the prey was alive when first attacked
  32. Potential importance of predation
    • -Affects population dynamics of the prey species
    • -Affects the realized niche of the prey species
    • -Influences community structure and organization
    • -It's a major selective (evolutionary) force
  33. True predators
    Kill prey ~immediately after attack, and kill several prey over lifetime
  34. Grazers
    Attack many prey, but consume only part of each; rarely lethal
  35. Parasites
    Consume only a part of their prey (host); rarely lethal; attack concentrated on one or few prey during lifetime
  36. Parasitoids
    Free living as adults; eggs laid in, or, or near prey. Larvae develop within the host, which dies sooner or later
  37. Simple model of predation (Lotka and Volterra)
    • Explicity links predator and prey populations
    • -predators regulate the growth of prey populations->density-dependent mortality
    • -prey influence growth of predator populations (or death rate)
    • -->model predicts stable oscillations

    Problem is stable cycle not inherent property of predator-prey system...requires constant source of "disturbance"
  38. Predators can determine prey abundance, and vice-versa.. but stable predator-prey systems may require
    • External disturbance (immigration)
    • Complex environment (refuges)
    • Co-evolution (cuckoo)
  39. How do predators respond to an increase in prey density?
    • 1. Predators can increase in number
    • 2. Each predator can eat more prey -> functional response
  40. Type 1 functional response
    • -#prey eaten increases linearly (until satiation)
    • -implies mortality is density independent
  41. Type 2 functional response
    • -# prey eaten increases but at a decreasing rate, and eventually reaches an asymptote
    • -% of prey population killed decreases as prey density increases-> density dependent
    • -due to limitations of handling time and satiation
  42. Type 3 functional response
    • -# prey eaten increases in a sigmoid fashion before reaching asymptote
    • -% of prey population killed increases at first, then decreases as prey density increases

    Due to: limited prey refuge; search image and "learning"; prey switching
  43. Prey refuge
    • Physical space or environment
    • Numbers (large or small)
    • Time
    • Size (big or small)
  44. Total (combined) response
    Numerical (# predators) * functional (#prey/predator) = # prey eaten/time
  45. Endemic
    • % losses of prey increase as functional (maybe numerical) response increases
    • can slow or stop prey population growth
  46. Epidemic
    • As predator responses level off, predators cause less % loss of prey as prey numbers increase
    • Prey escape control by predators
  47. Mullerian mimicry
    Poisonous prey look like each other ->reinforces the "message" for predator
  48. Batesian mimicry
    An edible mimc looks like a poisonous one -> predator is decieved
  49. Evolved defenses against predation
    • Life history
    • Chemical defense
    • Cryptic colouration
  50. Overcompensation of plants
    • Grazing can result in icrased production by plants, by removing old, unproductive parts and increasing light available to growing parts
    • Grazers convert biomass into useable nutrients
    • Grazing early in the season allowed plants to recover and re-grow
  51. Grazers usually eat a small amount.  Why?
    • Self regulation of herbivores (unlikely)
    • Other mechanisms (eg predation) regulate herbivores
    • Plants have good defences (may be constitiutive or induced); physical, chemical, or biological 
  52. Predaion Models (Lotka & Volterra)
    • Start by assuming that the prey species is capable of exponential growth in the absence of predators
    • Next we add a "brake" on prey population by factoring in predation
    • Now we have to consider predator population growth.  Here we assume that predator growth is related to the rate of "converting" prey into predators, minus the predator's per-capita death rate
    • We can use these 0-vaules to make isoclines of zero population growth.
  53. Simple model of predation (Lotka & Volterra)
    • Explicitly links predators and prey populations
    • Predators regulate the growth of prey populations ->density-dependent mortality
    • Prey Influence growth of predator populations (or death rate)
    • --> model predicts stable oscillations
  54. The ecology of fear
    • Predators do more than simply consume prey.
    • Consumptive effects: being eaten
    • Non-consumptive effects: fear of being eaten.

    This changes the behaviour of the prey due to a predator's presence
  55. Plant defenses
    • High C:N ration - bad food for many animals
    • Handling time - Requires extensive food processing
    • -chewing, digestion (processing cellulose and other "indigestible" matter, detoxification of chemicals, ~80% of consumed material not absorbed
    • Sheer volume of plant matter to be consumed
  56. Physical Plant defenses
    • Spines, trichomes, arumour
    • These are consitutive
  57. Chemical Plant defenses
    • can produce cyinide in pockets, when chewed, all components come together, producing hydrogen cyinide
    • Tea, eat too much and digestion is slowed considerably
  58. Mimicry & mutualism
    • Plants that mimic spots as though eggs are already laid
    • Ruminants use mutualism to be able to digest the plants...
  59. Symbiosis
    • Organisms live in close proximity
    • May show adaptations for living in proximity

    May be obligat (need each other) or facultative (can live without each other)
  60. Ectoparasites
    Parasites that live on, or exploit, the surface of the host organism
  61. Endoparasite
    • Parasites that live in the host's body
    • Intercellular: between cells
    • or Intracellular: inside cells (tends to be smaller)
  62. Symbiotic relationships
    May arise through coevolution or by chance, and their relative costs/benefits may vary with the environment
  63. Disease
    • Many diseases caused by intracellular endoparasites
    • Facultative: some bacteria: Brucella, Listerica and others
    • Obligate: Bacteria Riskettsia, Chlamydia and many others; Viruses
    • Growth of disease-causing organisms is subject to natural selection and constrains on population growth just like other organisms
    • -> biggest difference is that "growth" can occur both within and between hosts
    • -->Interactions between diseases and hosts are ecological interactions
  64. Vaccination and Herd immunity
    • The purpose of vaccination is to slow the growth rate of a taget disease
    • Not every person needs to be vaccinated to achieve herd immunity, the point at which the disease's growth rate declines to the point of extirpation from the target population
  65. Resource-resource Mutualisms
    • Each part gains resources
    • Legumes and Rhizobia bacteria
    • -legumes recieve nitrogen from bacteria
    • -Bacteria recieve carbohydrates from roots
  66. Resource-service mutualism
    • One gains resources, the other gains a service
    • Ants and Aphids
    • -ants recieve honeydew from aphids
    • -aphids receive protection from ants
  67. Service-service mutualisms
    • Exchange services
    • Clownfish and anemones:
    • -Clownfish receive protection from the anemones
    • -anemone receives protection from clownfish
  68. Complex Mutualisms
    • LIchens: mutualism between fungus and algae or cyanobacterium
    • Corals: mutualism between an Anthozoan and a zooxanthella
  69. Cheating in Mutualism
    • Mutualism involves an ingerent conflict among participants that may lead to cheating.
    • An increase in the fitness of one participant will likely come at the expense of the other participant
    • Cheating may be apative, so lone as it remains relatively uncommon
  70. Community
    An association of interacting populations in a given area of habitat during a given period of time
  71. Assemblage
    A taxonomically related group that occurs in the same area
  72. Guild
    A group taht uses resources in the same manner, without regard to taxonomic relatedness
  73. Community ecology
    The study of patterns and processes at the community level of organization

    • Are there repeated, integrated entities seperated by clear boundaries?
    • If so, what processes produce and maintain those entities?
    • Is a community an organized system or recurrent species? Or is it a haphazard collection of populations with minimal integration?
  74. Clements
    • Communities are discrete groups of interdependent organisms
    • -Community = more than the sum of its parts-> "superorganism"
    • -Implies that communities can be classified: "pine forest", "peat bog" etc
  75. Closed community
    • A natural ecological unit
    • Distinct boundaries
    • Fixed, limited "membership"
  76. Gleason
    • Species repond to the environment independently; 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
  77. Open community
    • No distinct boundaries
    • Independent distribution
    • Membership no fixed
  78. Ecotones
    • A gradient of species replacement
    • -physical change in the environment
    • -edge of the range of a highly dominant species

    In closed communities, shapr ecotones, in open, no clear ecotones
  79. Ecotones and Fragmentation
    • Fragmentation results in less core, and more edge -> more ectones
    • Where dispersal links the fragments, may result in a metacommunity
    • -->more likely, rare species will be extirpated from patches
  80. Community Structure
    • Community composition and biodiversity
    • Relative species abundance and dominance
    • Species role
    • Trophic structure (eg. food webs)
  81. Community Organization
    • What processes shape observed community structure?
    • How do communities respond to change?
  82. Dominant species
    • Are substantially more common then others
    • Determined by counting individuals, biomass estimation, or area occupied
  83. Indicator species
    • One or a few species that reflect the "health" of a commuity
    • Specialized to one habitat type or set of conditions
    • Closely associated with other taxa
    • Easily surveyed and well-known
  84. Richness, evenness
    • Richness is number of species present
    • Evenness is relative abundance of those species
  85. Diversity indices
    Simpson index (D)

    Shannon-Wiener index (H')
  86. Membership in plant comunities
    Likely defined by dispersal and tolerance
  87. Environmental Heterogeneity
    • Although there are other factors, heterogeneity of the environment accounts from much of the diversity in plants and algae
    • --> plant diversity, in turn, explains much of animal diversity
  88. Animals: Coexistance
    • Coexistance: avoidance of compeitive exclusion
    • Breadth (or width): the range of resources exploited by a species
    • Overlap: the proportion of a resource, or niche, shared with a 2nd species
  89. Community richness in relation to niche space
    community richness depends on average niche width and on total niche space available.
  90. Ecological release
    Expanded niche breadth in the absence of competitors
  91. Niche shift
    Change in niche breadth or position due to the presence of competitiors or other factors. Most are shifts in habitat; shifts in diet and time are less common
  92. Niche complementarity
    Ecologically similar species often show non-overlapping distributions when co-occuring -> ie, divide total niche space
  93. Checker boards distributions
    • Mutually exclusive distributions amoungst pairs of eologically similar species
    • Always involve the most ecologically similar guild members
    • these result from mutual competitive exclusion
  94. Hutcinson
    Computed size ratios of adjacent seabird secies pair, finding the average size ratio to be ~1.3 for the necesseary difference for two species to co-occur
  95. Gause's principle
    If resources are limited, extensive overlap of realized niches should lead to exclusion in the zone of overlap. To coexist, competing species must shift realized niches to limit their degree of overlap. Ecological release (niche expansion) expected when competitiors are absent. If resource use is reflected in morphology, limiting similarity will structure size distribution patterns within guilds/assemblages due to the effects of competition
  96. Disturbance
    • Any relatively discrete event in time that distrubutes an ecosystem, community or population structure and changes resources, substrate availability, or the physical environment
    • A discrete, puctuated killing, displacement, or damaging of one or more idividuals that directly or indirectly creates an opportunity for new individuals to become established
    • Characteristics: frequency; mean # of events per unit time
    • Size or scale: spatial extent of disturbance, relative to "target"
    • Intensity or severity: the force of the disturbance and its effet on the community (eg. % biomass removed)
  97. Consequences of Disturbance
    Creates gaps, renews limiting resources, generates heterogeneity
  98. Principle of allocation
    • Adaption involves copromises (costs/benefits)
    • Trade-offs between traits; eg. competition vs. colonization
  99. Frequent/intense disturbance:
    Community will contain only species that colonize and complete their life cycles between disturbances
  100. Rare/minor distubance
    Community will contain only species that are very effictive competitors
  101. Intermediate disturbance
    • Sufficient time between disturbaces to allow colonization by many speicies
    • Insufficient time between disturbances to allow competitive exclusion
  102. Ecological networks (trophic or symbiotic)
    • Trophic: who eats whom
    • Symbiotic: who helps/hurts whom
  103. Species interactions properties
    • Complexity: how many links per species?
    • Connectance: what proportion of potential connections are realized?
    • Clustering: are many links aimed at one or a few fcal species?
    • Compartmentalization: is the network "subdivided" into relatively distinct sub-units?
    • And lots more!
  104. Competitive heirarchies
    • Transitive: If A > B = D > C, then A>D, B>C etc
    • Intransitive: even A>B=D>C, A vs D, B vs. C A vs. C are independent
  105. "centrifugal" (competitive asymmertry)
    species organization around a core habitat
  106. Keystone species
    • A keystone species is a species whose activities play a major role in determining community level patterns
    • importance>biomass
    • -- > frequently a predator
    • Ecosystem engineers
    • Mutualistic keystones
    • Invasive species
    • Humans are a keystone species
  107. Alternative stable states
    either population could exist, but once one has been established, it will likely stay that way.
  108. Mutualistic keystone
    Trees that can flower in really dry seasons, when no other plants do... Feeding honey bees that pollinate all other plants
  109. Autogenic engineers
    Change their environment via their physical structure: ecosystem engineers
  110. Allogenic engineers
    change their environment through action: ecosystem engineers
  111. Invasive species
    • species that establish a new range in which they proliferate, spread, and persist to the detriment of the environment (many are ecosystem engineers)
    • Rapid growth and reproduction
    • High dispersal ability: potentially, assocation with humans
    • Tolerance of a wide range of conditions/generalist
  112. Elton (invasive species)
    • Communities with high speicies diversity should be harder to invade --> high diversity = most niche space already occupied... no more room!
    • Seems to be more a matter of scale
    • small - interactions are strong and diversity reduces invasion
    • larger, species interactions are weak and diversity higher, invsive species may simply be responding to resource availability