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    Organismal Ecology:
    Individual vs. Environment

    Organismal Ecology is the study of how an individual organism's morphology, physiology, and behavior
    allow it to meet the challenges posed by its environment.

    Homeostasis is common to all living things.

    An organism's reproductive success (the keystone of natural selection) depends on its ability to maintain homeostasis in the face of environmental changes.

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    Internal and External Environments

    The conditions experienced by cells and tissues include
    • temperature
    • pH
    • water content
    • ion concentrations
    • etc.

    Most of a multicellular organism's cells are surrounded by other cells, and do not directly contact the external environment.

    Most experience only the internal environment

  • A sensed (regulated) variable is kept within a limited range by physiological mechanisms responding to feedback from a sensor.

  • A controlled (non-regulated) variable is kept within a limited range by the organism's systems in the absence of sensors.

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    Species differ widely in their ability to keep their controlled variables different from external environmental conditions.

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Evolutionary Adaptation: Crypsis

    Evolutionary Adaptation

    • Evolutionary adaptation is a genetic change affecting the physiology, biochemistry, or morphology of a species in response to natural selection.

      It occurs over generations, and does not occur in an individual.

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Individual Adaptation: Defense
(click on pic for source)

    Individual Adaptation

  • Individual adaptation is a short-term response to environmental change.

    • physiological
        Some species are able to gradually change their physiological tolerance levels in a slowly changing environment. This ability, too, is controlled by genes that have been selected over evolutionary time.

    • morphological
    • behavioral
        Behavioral adaptations allow an animal to respond relatively quickly to environmental challenge.

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    Individual Adaptation: Acclimatization

    Acclimatization is a physiological, biochemical, or anatomical change that occurs within the lifetime of an individual organism.

    Acclimatization results from chronic exposure to a naturally occurring environmental challenge.

    It usually involves a change in gene expression, reflected in phenotype.

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    Individual Adaptation: Acclimation

    Acclimation is a physiological, biochemical, or anatomical
    change that occurs in an invidual organism
    in a manipulated situation.

    Acclimation results from relatively short-term exposure
    to environmental change in a laboratory
    or other controlled situation.

    The various aspects of an organism's
    environmental tolerances help determine its ecological niche.

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    Regulators and Conformers

  • A regulator uses metabolic means to maintain homeostasis
    in response to environmental changes.
    A regulator can control the value of a controlled variable.

  • A conformer is less able to metabolically maintain homeostasis.
    The environment controls the value of a controlled variable.

    A species may be a regulator with respect to some controlled variables,
    and a conformer with respect to others.

    View the figure at the left.

    • Is the salmon a conformer or a regulator with respect to temperature?

    • Is the salmon a conformer or a regulator with respect to chloride ion concentration in its tissues?

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catadromous: Anguilla anguilla (Freshwater Eel)

anadromous: Salmo salmo (Atlantic Salmon)

    Regulation vs. Conformity: Osmoregulation

  • Anadromous fish migrate from marine to freshwater to breed.

  • Catadromous fish migrate from freshwater to marine to breed.

    Both types of fish have sophisticated osmoregulatory systems
    that maintain constant internal salt balance when they move
    from one habitat to another.

    They are osmoregulators

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conformers: Echninoderms

    Regulation vs. Conformity: Osmoconformity

    Echinoderms have a vestigial excretory system.
    Nitrogenous waste (ammonia) leaves the body via diffusion.

    Echinoderms have very little control over their internal salt and water balance.
    They are thus strictly limited to marine environments.
    Their tissues have essentially the same salinity as sea water.

    They are osmoconformers

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    Regulation vs. Conformity: Thermoregulation

    Interaction between an organism and its temperature environment affects
    • its metabolic rate
    • its species' geographical distribution

  • Heat Source terms:

    • ectotherm - main heat source is the external environment
    • endotherm - main heat source is internal metabolic reactions

  • Temperature Regulation terms:

    • poikilotherm - temperature regulated primarily by environment
      (from the Greek poikilo meaning "variable")
    • homeotherm - temperature regulated primarily by metabolism
      (from the Greek homeo meaning "constant")

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    The Key to Homeostasis in Regulators is Feedback

    Feedback from a controlled variable is facilitated
    by communication between body systems.

    An animal body constantly sends itself messages about its internal state.

    If an internal variable changes, metabolism is altered to achieve homeostasis.

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    Negative Feedback

    Negative feedback occurs when the system responds to changes in a controlled variable by bringing the variable back to its set point.

    Negative feedback, nearly synonymous with homeostasis, is the most common in living systems.

    • A stimulus produces a change to a variable ( regulated factor).
    • A receptor monitoring the controlled variable detects the change.
    • INPUT travels away from the receptor to the...
        control center, which determines the appropriate response.
    • OUTPUT from the control center travels to the...
        effector, which delivers the response.

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    Set Point

    The set point of a controlled variable
    is the level of that variable required for normal function.

    Feedback from the controlled variable tells the body
    whether the variable needs to be regulated in some way.

    Example: A horse's normal body temperature range is ~37.5 - 38.5oC
    If the horse's body temperature exceeds normal

    • Skin and brain receptors inform the brain.
    • Brain informs cooling effectors
      • sweat glands activate
      • blood vessels in skin and extremities diilate

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    Positive Feedback

    Positive feedback occurs when the system
    reinforces changes in a controlled variable.

    Positive feedback is less common than negative.
    However, it is critical for normal

    • nerve impulse transmission
    • digestion processes
    • reproductive processes

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Limits of Tolerance

Even regulators do not have an unlimited capacity to maintain their controlled variables.

    Environment is Relative

    An animal's environment comprises the collective physical, chemical and biological components its surroundings.

    An environment cannot be defined without considering the organism.

    • What is your current environment?
    • What will be your environment after class?
    • Are you alone in there?

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    Limits of Tolerance
    Determine Biogeography

    Abiotic factors that affect organismal ecology include
    • temperature
    • oxygen levels
    • water and humidity
    • ionic composition and concentrations

    Tolerance to various environmental challenges depends on
    • species
    • natural history/evolution
    • biogeography

    Swallowtail butterflies are more diverse at warmer latitudes.

    • species temperature tolerances differ
    • host plant diversity is lower at higher latitudes

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Eury- vs. Steno-

Beyond specific levels of any given factor, a lethal range exists.
This may differ significantly among species.

Outside the lethal range, an individual can adjust its metabolism or behavior to tolerate a challenging environmental stimulus.

For example...

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(photo by B. Wursten)

    Community Ecology:
    Species Interactions

    Communities of organisms interact in many possible ways.

    One can categorize these interactions (<-- required link) on the basis of the effect on each of the two interacting populations.

    • obligate mutualism
    • protocooperation
    • commensalism
    • competition
    • amensalism

    • predation
    • parasitism
    • parasitoidism
    • neutralism

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    Species Interactions and Symbioses

    Symbiosis (from the Greek sym, meaning "together" and bios, meaning "life")
    is two different species engaging in interaction that affects each
    population both ecologically and evolutionarily.

    When two species evolve in response to each other's activities,
    the process is known as coevolution.

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Ecosystem Ecology

Ecology at the level of the ecosystem involves
study of the flow of energy and matter among ecosystems.

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    Energy Flow through Ecosystems

    Energy Flow begins with primary productivity, the amount of light energy converted to chemical energy (organic matter) by community autotrophs over a given period of time.

    • Energy makes a one-way trip through ecosystems
      as it increases entropy.
      (Second Law of Thermodynamics)

    • Matter is continually recycled through ecosystems.
      (Law of Conservation of Mass)

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    The Ecological Niche

    The sum of a species' use of the biotic and abiotic resources in its environment--as dictated by its evolutionary adaptations--is called that species' ecological niche.

    The ecological niche includes that species:

    • range of tolerance to physical extremes (heat, salinity, pH, etc.)
    • use of resources (food, space, etc.)
    • physical use of habitat
    • Circadian rhythm
    • interactions with other species, etc.

    Everything a species is and does determines its ecological niche,
    which can be considered its ecological position relative to
    other species in the same ecosystem
    .

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(click on pic for source)

    Who's Eating Whom?

    An autotroph (Greek auto, "self" and troph, "feeding")
    is an organism that makes its own organic food
    via photosynthesis.

    • Autotrophs are also known as producers.

    A heterotroph (Greek hetero, "other" and troph, "feeding")
    is an organism that feeds on other organisms for its energy.

    • Heterotrophs are also known as consumers.

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    Trophic Structure

    The structure and dynamics of a community are largely determined
    by the feeding relationships among its species.

    This is the community's trophic structure.

    The transfer of energy

    • from primary producers (photosynthetic organisms)
    • x to primary (1o) consumers (feed on producers)
    • xx to secondary (2o) consumers (feed on 1o consumers)
    • xxx to tertiary (3o) consumers (feed on 2o consumers)
    • xxxx to decomposers (feed on dead everyone else)

      ... is known as a food chain.

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    Food Webs

    Energy transfer in real ecosystems
    is almost never a simple chain.

    Most organisms feed on (or are eaten by)
    more than one other type of organism.

    The multiple, interweaving food chains create
    a complex food web.

    Food Webs drive the flow of energy and nutrients
    through ecosystems.

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    Productivity

    Biomass
    • is the total dry weight of organisms in a given area.
    • can be calculated for an entire community
    • is more usually expressed for a species or organism type (e.g., vegetation)

    Standing crop biomass
    • is the dry weight of given organisms in an ecosystem
    • at any given "snapshot moment" in time

    Productivity can be expressed as either

    • energy/unit area/unit time (e.g., Joules/m2/year)
    • biomass/unit area/unit time (e.g., kg/m2/year).

    • Gross Primary Productivity (GPP) = total primary productivity
    • Net Primary Productivity (NPP) = GPP - Erespiration

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    Measuring Productivity

    Energy transfer efficiency can be expressed as

      E = Pt/Pt-1

    where
    • Pt = productivity at level t (e.g., primary consumers)
    • Pt-1 = productivity at the trophic level just below t (e.g., primary producers)

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    Energy Transfer Efficiency: Example

    Copepods feed on crunchy phytoplankton.
    In a system where...

    • standing crop biomass of copepods is 25g/m3
    • standing crop biomass of the phytoplankton is 150g/m3

    ...then the transfer efficiency of that part of the system is:

    25g/m3 / 150g/m3 = 0.17

    The efficiency of that trophic level is 17%.

    This means that 17% of the phytoplankton biomass
    is converted into copepod biomass.


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    Efficiency of Energy Transfer

    Food chains generally tend not to be
    longer than three to four steps.

    Animals are not efficient at utilizing
    the energy in the food they eat.

    The inefficiency of energy transfer
    between trophic levels
    limits the length of the food chain.

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    Energy Pyramid

    Efficiency with which trophic levels convert energy from the previous trophic levels varies across ecosystems, ranging between 5% - 20%.

    General Rule of Thumb:

      Only 10% of the energy in organisms
      eaten by those in the next trophic level
      is converted to the higher-level consumer's biomass.

    The reduction in available energy at higher trophic level can be expressed with a trophic energy pyramid.

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    Standing Crop Biomass Shrinks
    with Higher Trophic Level

    The Energy Pyramid is reflected in the
    standing crop biomass of each trophic level.

    The higher the trophic level, the lower the biomass.

    In general:
    the higher the trophic level, the fewer the individuals.

    More individuals can exist at lower trophic levels.
    When humans eat lower on the food chain,

    • energy loss is reduced
    • more energy is available
    • more individuals can be fed

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    Biogeochemical Cycles

    Trophic interactions result in a cycling of energy and nutrients through the biosphere in systems we call biogeochemical cycles.

    A generalized cycle can be superimposed on Biogeochemical Cycles for many different nutrients

    Our everyday activities have profound effects on these cycles.

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    Species Diversity

    The variety of species found in an ecosystem
    comprise that ecosystem's species diversity.

    Species diversity has two components:

    • species richness
        the number of different species
        in the community

    • relative abundance
        the proportion of the community
        represented by each species

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    Species Richness vs.
    Relative Abundance

    The two forest communities shown have

    • the same species richness

    • different relative abundances of each species

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(click on pic for source)

    Diversity Confers Resistance

    Communities with high species diversity tend to be more resistant
    to disruption by invasive exotic species than less diverse communities.

  • Diverse species have diverse ecological requirements.
  • Resident species use greater diversity of available resources.
  • Fewer resources are available for incoming invasives.
  • This is especially true of exotics with specific ecological needs.
  • Greater diversity of potential predators and pathogens also may protect the community.

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    High Impact Species

    The dominant species in a community are the most numerous or have the highest total biomass in that community.

    They tend to exert a strong influence on community structure and dynamics.

      Example: Sugar Maples typically form dense stands that affect
      soil nutrient composition and shade habitat.
      This affects which other plant species (and hence, animal species)
      can live in the forest.

    Why does a species become dominant?
    • better at competing for limited resources
    • better at avoiding predation or pathogens (Why are exotic invasive species so invasive? (Hypothesize!)

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(click on pic for source)<./a>

    Keystone Species

    A keystone species exerts strong influence on a community
    by means of its ecological role in that community.

    Example:

    The Saguaro Cactus (Carnegiea gigantea) provides
    food and shelter for many desert animals.

    These resources allow greater diversity of animal species.

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(photo by Phil McLean/Minden Pictures)


Greasewood, Sarcobatus vermiculatus
(click on pic for source and more info)

    Indicator Species

    An indicator species demonstrates, by its
    • presence
    • abundance
    • lack of abundance
    • chemical composition
    ...some distinctive aspect
    of the character or quality of an environment
    .

  • Greasewood indicates alkaline, saline soil.
  • Mosses often indicate acid soil.
  • Lichens indicate good air quality.
  • Plant tissue analysis can reveal soil chemical composition.

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(click on pic for source)

    Foundation Species

    A foundation species is sometimes called an "ecosystem engineer".

    An ecosystem engineer causes dramatic, fundamental alterations to the habitat, thus affecting community structure and diversity.

    The effect can be positive on some species, and negative on others, depending on those other species' ecological requirements.

    Sea oats (Uniola paniculata have deep root systems that hold dunes together, preventing erosion.

    This provides solid habitat for many other seaside species of plants and animals to flourish.

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(click on pic for source)

    Exotic Species

    An exotic species is a species that has been introduced
    by humans to an area where it did not evolve.

    Many ornamental plants fall into this category.
    As long as they do not escape cultivation
    and invade native ecosystems,
    they are not problematic.

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(click on pic for source)

    Invasive Exotic Species

    An invasive exotic species is an exotic species
    that aggressively displaces native species.

    Southern Florida is a hotbed of invasive exotics
    such as the Brazilian Pepper (Schinus terebinthifolius).

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    Diversity Changes:
    Ecological Succession

    Species interactions can drive change in species diversity over time.

    Ecological Succession is the process of change in community structure of an ecosystem over time.

    It generally begins with some type of disturbance

    • wildfire
    • volcanic eruption
    • anthropogenic ecosystem disruption

    ... and can take decades to hundreds of years
    to reach a climax community state.

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    Primary and Secondary Succession

    Succession can be
    • primary (starting from scratch)
    • secondary (replacing a damaged system)

    Human activity has driven a lot of succession
    since the Industrial Revolution.

    Can ecosystems always recover?

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    It's Up to Us

    Understanding the components of ecosystems
    and their interactions will ultimately help humanity
    make the right choices to preserve the beauty and utility of the biosphere.

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