Ecology by yurtgc548



      Topic 5.1, 5.2, 5.3
Option G1, G2, G3, G4, and G5
 Ecology is the study of how organisms interact with their
  environment and each other.
• This interaction of organisms is a two-way interaction. Organisms are
   affected by their environment, but by their activities they also change
   the environment.
Levels of Organization
• Ecology is studied on several levels:
  – Organism
      • Ecologists may examine how one kind of organism meets the challenges of its environment,
         either through its physiology or behavior.
   – Population
     • Group of individuals of the same species living in a particular geographic area.
   – Community
     • Consists of all the populations of different species that inhabit a particular area.
   – Ecosystem
     • Includes all forms of life in a certain area and all the nonliving factors as well.
   – Biosphere
     • The global ecosystem; the sum of all the planet’s ecosystems.
     • Most complex level in ecology, including the atmosphere to an altitude of several
        kilometers, the land down to and including water-bearing rocks under 3,000 m under
        Earth’s surface, lakes and streams, caves, and the oceans to a depth of several kilometers.
     • It is self contained, or closed, except that its photosynthesizers derive energy from sunlight,
        and it loses heat to space.
Levels of Organization
Abiotic vs. Biotic
 Abiotic components
   Temperature, forms of energy, water, inorganic nutrients, and
    other chemicals.
 Biotic components
   Organisms making up the community
  Habitat-
    The specific environment in which an organism lives in.
    Each habitat can be described by characteristic abiotic factors.
Abiotic Factors
 Physical and chemical factors (abiotic) affecting the
  organisms living in a particular ecosystem:
   Solar energy
   Water
   Temperature
   Wind
   Soil composition
   Unpredictable disturbances
Abiotic Factors- Solar Energy
  Powers nearly all terrestrial and shallow-water
  In aquatic environments that sunlight reaches,
   the availability of light has a significant effect
   on the growth and distribution of
   photosynthetic bacteria and algae.
    Most photosynthesis occurs near the surface of
     a body of water.
  In terrestrial environments, light is often not
   the most important factor limiting plant
    In many forests, however, shading by trees
     creates intense competition for light at ground
Abiotic Factors- Water
 Essential to all life.
 Aquatic organisms have a seemingly
  unlimited supply of water, but they face
  problems of water balance if their own
  solute concentrations does not match that
  of their surroundings.
   These organisms confront solute conc. in
    freshwater lakes and streams that are very
    different from those in the sea.
 For a terrestrial organism, the main water
  problem is the threat of drying out.
   Many land species have watertight coverings
    that reduce water loss.
   Most terrestrial animals have kidneys that
    save water by excreting very concentrated
Abiotic Factors- Temperature
  An important abiotic factor because of its effect on metabolism.
  Few organisms can maintain a sufficient active metabolism at
   temperatures close to 0 degrees Celsius, and temperatures above 45
   degrees Celsius destroy the enzymes of most organisms.
  Extraordinary adaptations enable some species to live outside this
   temperature range.
    For example, some of the frogs and turtles living the northern United
     States and Canada can freeze during winter months and still survive,
     and bacteria living in hydrothermal vents and hot springs have enzymes
     that function optimally at extremely high temperatures.
    Mammals and birds can remain considerably warmer than their
     surroundings and can be active in a fairly wide range of temperatures,
     but even these animals function best at certain temperatures.
Abiotic Factors- Wind
 An important abiotic factor for several reasons. Local wind damage
  often creates openings in forests, contributing to patchiness in
 Wind also increases an organism’s rate of water loss by
   The resulting increase in evaporative cooling can be advantageous on a
    hot summer day, but it can cause dangerous wind chill in the winter.
Abiotic Factors- Soil composition
 Most soils are complex combinations of inorganic nutrients,
  organic materials in various stages of decomposition, water, and
 Such variables as soil structures, pH, and nutrient content often
  play major roles in determining the distribution of organisms.
Abiotic Factors- Unpredicatable
 Include fires, hurricanes, tornadoes, tsunamis, and volcanic
 Fire occurs frequently enough in some communities,
  however, that many plants have adapted to this periodic
Natural Selection and Abiotic Factors
 Organisms are adapted to abiotic and biotic factors by natural
 An organism’s ability to survive and reproduce in a particular
  environment is a result of natural selection.
 By eliminating the least fit individuals in populations,
  environmental forces help adapt species to the mix of abiotic and
  biotic factors that they encounter.
 The presence of a species in a particular place can come about it
  two ways:
   The species may evolve in that location.
   The species may disperse to that location and be able to survive.
 Biomes- A large ecosystem that is usually determined by
  climate and categorized by the available producers and other
  organisms that adapted to the particular environment.
 The major terrestrial biomes are named after the climatic
  conditions and the vegetation, however, their microbial
  organisms, fungi, and animals are also important.
 Climatograms
   Used to compare the annual precipitation and annual
    temperature in various biomes.
Biomes- Tropical Rainforest
 Temperature is warm all year long and has about 11-12 hours of
 Plenty of rain (200-400 cm per year) results in fast
  decomposition, as a result the soil is very thin.
 Very complex species diversity
 Vegetation includes trees, vines, and epiphytes. Very rich animal
Biomes- Shrublands (savanna,
 Lower rainfall (30-50 cm a year) and warm temperatures year
 The plants are fire adapted because of the frequent fires.
 Typical plants are grasses with scattered trees and shrubs.
 Grazing animals, insects, birds, large predators.
Biomes- Deserts
 Very dry areas with less than 2 cm of yearly rainfall, very large
  temperature fluctuations.
 They can grow some deep rooted shrubs, cacti, and other
  succulent plants, annual plants with very fast growing period
 Adaptations to extreme dry conditions.
Biomes- Temperate Deciduous Forests
 Warm summers, cold winters.
 Fairly even annual rainfall (60-150 cm)
 Dominant species are various broad leaf trees, such as oak, maple,
  hickory, birch, etch.
 Various shrubs and annuals are found in the broad leaf regions.
Biomes- Taiga
 Long, cold winters and short, wet summers that are sometimes
 Soil is acidic and nutrient-poor, not fit for many plants.
Biomes- Tundra
 Bitter cold winters, high winds and low precipitation (15-25 cm).
 Because the soil is constantly frozen, the temperatures are low and the
  evaporation is also low, the soil is constantly saturated with water.
 Vegetation includes dwarf shrubs, grasses, mosses, and lichens.
 Characterized by permafrost, continuously frozen subsoil.
 A biological community is an assemblage of all the populations
  of organisms living close enough together for potential
 Key characteristics of a community:
   1.Species diversity
   2.Dominant species
   3.Response to disturbances
   4.Trophic structure
   5. Community interactions
 1.Species diversity
    The variety of different kinds of organisms that make it up,
    Has two components:
       1. species richness
          The total number of different species in the community.
          The more species present in a sample, the 'richer' the sample.
            Species richness as a measure on its own takes no account of the number of individuals of each
             species present. It gives as much weight to those species which have very few individuals as to
             those which have many individuals. Thus, one daisy has as much influence on the richness of an
            area as 1000 buttercups.
       2. species abundance (sometimes referred to as “evenness”)
         a measure of the relative abundance of the different species making up the richness of
            an area.
            To give an example, we might have sampled two different fields for wildflowers. The sample from
             the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from
             the second field comprises 20 daisies, 49 dandelions and 931 buttercups (see the table below).
             Both samples have the same richness (3 species) and the same total number of individuals (1000).
             However, the first sample has more evenness than the second. This is because the total number of
             individuals in the sample is quite evenly distributed between the three species. In the second
             sample, most of the individuals are buttercups, with only a few daisies and dandelions present.
             Sample 2 is therefore considered to be less diverse than sample 1.
 1.Species diversity (continued)
   A community dominated by one or two species is considered to be
    less diverse than one in which several different species have a similar
   As species richness and evenness increase, so diversity increases.
   Simpson's Diversity Index is a measure of diversity which takes
    into account both richness and evenness.

 n = the total number of organisms of a particular species
 N = the total number of organisms of all species
 The value of D ranges between 0 and 1. With this index, 1
  represents infinite diversity and 0, no diversity.
 2.Dominant species
   In general, a small number of species exert strong control over a
    community’s composition and diversity.
   In terrestrial situations, the dominant species is usually the most
    prevalent form of vegetation.
     For example, wildflowers are the dominant species in some communities.
     The types and structural features of plants largely determine the kinds of animals
      that live in a community.
   Keystone species is a species that exerts strong control on
    community structure because of its ecological role, or niche.
     For example, a seastar of the genus Pisaster is a keystone predator that reduces the
      density of the strongest competitors in the community, thus preventing the
      competitive exclusion of weaker competitors.
       In an experiment on the Washington coast, Pisaster was removed from the
        community. The results was that the Pisaster’s main prey, a mussel of the genus
        Mytillus, outcompeted many of the other shoreline organisms reducing the
        number of organisms from over 15 species to under 5 species.
  2.Dominant species (continued…)
    Keystone species (continued…)
      Also, sea otters are a keystone predator in the North Pacific. Sea otters feed on
       sea urchins, and sea urchins feed mainly on kelp, a large seaweed. In areas where
       sea otters are abundant, sea urchins are rare and kelp forests are well developed.
       Where sea otters are rare, sea urchins are common and kelp is almost absent.
         During the last 20 years, sea otters have declined dramatically in large areas
          off the coast of western Alaska. The loss of this keystone species has allowed
          sea urchin populations to increase, resulting in the destruction of kelp forests.
         Killer whales are the cause of the sea otter decline, which is probably because
          their previous prey of the whales, mainly seals and sea lions, have declined in
         The decline of these prey species reflects a decline in the populations of fish
          species that the seals and sea lions eat.
         And, all of these changes in the Alaskan marine communities are probably
          related to human overfishing in the North Pacific
 3. Response to Disturbances
   Events such as storms, fire, floods, droughts, overgrazing, or human activity that damage
      biological communities, remove organisms from them, and alter the availability of resources.
     The types of disturbances and their frequency and severity vary from community to
     Small-scale disturbance often have positive effects. For example, when a large tree falls in a
      windstorm, it disturbs the immediate surroundings, but it also creates new habitats.
     For instance, more light may now reach the forest floor, giving small seedlings the
      opportunity to grow; or the depression left by its roots may fill with water and be used as
      egg-laying sites by frogs, salamanders, and numerous insects. Small-scale disturbances may
      enhance environmental patchiness, which can contribute to species diversity in a community.
     Communities change drastically following a severe disturbance that strips away vegetation
      and even soil. The disturbed area may be colonized by a variety of species, which are
      gradually replaced by a succession of other species, in a process called ecological
  3. Response to Disturbance (continued)…
    Early successional communities are characterized by a low species
     diversity, simple structure and broad niches
    The succession proceeds in stages until the formation of a climax
      The most stable community in the given environment until some disturbance
    Two types of Ecological Succesion:
      Primary Succession
      Secondary Succession
 3. Response to Disturbances (continued…)
   Primary succession
     When ecological succession begins in a virtually lifeless area with no soil.
     Usually takes hundreds or thousands of years.
     For example, new volcanic islands or rubble left by a retreating glacier. Often the
       only life-forms initially present are autotrophic bacteria. Lichens and mosses are
       commonly the first large photosynthesizers to colonize the area. Soil develops
       gradually as rocks weather and organic matter accumulates from the decomposed
       remains of the early colonizers. Lichens and mosses are gradually overgrown by
       grasses and shrubs that sprout from seeds blow in from nearby areas or carried in
       by animals. Eventually, the area is colonized by plants that become the community’s
       prevalent form of vegetations.
   Secondary succession
     Occurs when a disturbance has destroyed an existing community but left the soil
     For example, forested areas that are cleared for farming, areas impacted by fire or
 3. Response to Disturbances (continued…)
 Primary Succession
    Example: autotrophic prokaryoteslichens,
     mossesgrassesshrubstreesclimax communty

 Secondary Succession
    Example: herbaceous plants woody shrubs trees climax community
 4. Trophic structure
   The feeding relationships among the various species making up the
   A community’s trophic structure determines the passage of energy
    and nutrients from plants and other photosynthetic organisms to
    herbivores and then to carnivores.
   The sequence of food transfer up the trophic levels is known as a
    food chain
     Trophic levels are arranged vertically, and the names of the levels appear in
      colored boxes.
     The arrows connecting the organisms point from the food to consumer. This
      transfer of food moves chemical nutrients and energy from the producers up
      though the trophic levels in a community.
 4. Trophic Structure (continued…)
   At the bottom, the trophic level that supports all others consists of
    autotrophs, called producers.
     Photosynthetic producers use light energy to power the synthesis of organic
      compounds. Plants are the main producers on land. In water, the producers are
      mainly photosynthetic protists and cyanobacteria, collectively called
      phytoplankton. Multicellular algae and aquatic plants are also important
      producers in shallow waters.
   All organisms in trophic levels about the producers are heterotrophs,
    or consumers, and all consumers are directly or indirectly
    dependent on the output of producers.
 4.Trophic Structure (continued…)
   Trophic Levels:
   Primary producers
      Mostly photosynthetic plants or algae
   Primary consumers
      Herbivores, which eat plants, algae, or phytoplankton.
      On land include grasshoppers and many insects, snails, and certain vertebrates
      like grazing mammals and birds that eat seeds and fruits
     aquatic environments include a variety of zooplankton (mainly protists and
      microscopic animals such as small shrimp) that eat phytoplankton.
   Secondary consumers
     Include many small mammals, such as a mouse, a great variety of small birds,
      frogs, and spiders, as well as lions and other large carnivores that eat grazers.
     In aquatic ecosystems, mainly small fishes that eat zooplankton
   Tertiary consumers
      Snakes that eat mice and other secondary consumers.
   Quaternary consumers
      Include hawks in terrestrial environments and killer whales in marine environment.
 4.Trophic Structure (continued…)
   Another trophic level of consumers are called detrivores which derive their energy
    from detritus, the dead material produced at all the trophic levels.
      Detritus includes animal wastes, plant litter, and all sorts of dead organisms.
        Most organic matter eventually becomes detritus and is consumed by
        A great variety of animals, often called scavengers, eat detritus. For instance,
          earthworms, many rodents, and insects eat fallen leaves and other detritus.
          Other scavengers include crayfish, catfish, crows, and vultures.
      A community’s main detritivores are the prokaryotes and fungi, also called
       decomposers, or saprotrophs, which secrete enzymes that digest organic
       material and then absorb the breakdown products.
        Enormous numbers of microscopic fungi and prokaryotes in the soil and in mud
          at the bottom of lakes and oceans convert (recycle) most of the community’s
          organic materials to inorganic compounds that plants or phytoplankton can use.
        The breakdown of organic materials to inorganic ones is called
 4.Trophic Structure (continued…)
   A more realistic view of the trophic structure of a community is a
    food web, a network of interconnecting food chains.
   Food webs, like food chains, do not typically show detrivores, which
    consume dead organic material from all trophic levels.
 5. Community Interactions
   Interspecific competition:
      If two different species are competing for the same resource.
      Causes the growth of one or both populations may be inhibited.
      May play a major role in structuring a community.
      Weeds growing in a garden compete with garden plants for nutrients and water.
      Lynx and foxes compete for prey such as snowshoe hares in northern forests.
 5. Community Interactions (continued…)
 Competitive exclusion principle
   In 1934, Russian ecologist Gause studied the effects of interspecific
    competition in laboratory experiments with two closely related species
    of Paramecium.
     Gause cultured these protists under stable conditions with a constant amount of
      food added every day.
     When he grew the two species in separate cultures, each population grew rapidly
      and then leveled off at what was apparently carrying capacity of the culture.
     But when Gause cultured the two species together, one species was driven to
   Gause concluded that two species so similar that they compete the
    same limited resources cannot coexist in the same place. One will use
    the resources more efficiently and thus reproduce more rapidly than
    the other. Even a slight reproductive advantage will eventually lead to
    local elimination of the inferior competitor.
 5. Community Interactions (continued…)
   The competitive exclusion principle applies to what is called a
    species’ niche.
     In ecology, a niche is a species’ role in its community, or the sum total of its use
        of the biotic and abiotic resources of its habitat.
       For example, the attachment sites on intertidal rocks, the amount of exposure to
        seawater and air, and the food it consumes are some of the aspects of each
        barnacle’s niche.
       The fundamental niche of a species is the potential mode of existence, given
        the adaptations of the species.
       The realized niche of a species is the actual mode of existence, which results
        from its adaptations and competition with other species.
       Combining the niche concept with the competitive exclusion principle, we
        might predict that two species cannot coexist in a community if their niches are
 5. Community Interactions (continued…)
   There are two possible outcomes of competition between
   species having identical niches: Either the less competitive
   species will be driven to local extinction, or one of the species
   may evolve enough through natural selection to use a different
   set of resources.
     This differentiation of niches that enables similar species to coexist in a
      community is called resource partioning.
 5. Community Interactions (continued…)
   Predation is an interaction between species in which one species,
    the predator, kills and eats another, the prey.
   Because eating and avoiding being eaten are prerequisites to
    reproductive success, the adaptations of both predators and prey tend
    to be refined through natural selection.
   Examples of prey capturing strategies:
     Most predators have acute senses enable them to locate prey.
     In addition, adaptations such as claws, teeth, fangs, stingers, or poisons
      help catch and subdue prey.
     Predators are generally fast and agile, whereas those that lie in ambush are
      often camouflaged in their environments.
     Predators may also use mimicry; some snapping turtles have a tongue that
      resembles a wriggling worm, thus luring small fish.
Camouflage   Chemical Defense
 5. Community Interactions (continued…)
   Predator defenses:
     Mechanical defenses: such as the porcupine’s sharp quills or the hard shells of
      clams and oysters.
     Chemical defenses: animals are often bright colored, a warning to predators; like
      a poison arrow-frog or a skunk.
     Batesian mimicry: a palatable or harmless species mimics an unpalatable or
      harmful one; like the king snake mimics the poisonous coral snake
     Mullerian mimicry: two unpalatable species that inhabit the same community
      mimic each other; like bees and wasps                  Mullerian Mimicry

         Batesian Mimicry
  5. Community Interactions (continued…)
    Herbivory
      Animals that eat plants or algae
      Aquatic herbivores include sea urchins, snails, and some fishes.
      Terrestrial herbivores include cattle, sheep, and deer, and small insects.
      Herbivorous insects may locate food by using chemical sensors on their feet,
       and their mouthparts are adapted for shredding tough vegetation or sucking
       plant juices.
      Herbivorous vertebrates may have specialized teeth or digestive systems
       adapted for processing vegetation. They may also use their sense of smell to
       identify food plants.
      Because plants cannot run away from herbivores, chemical toxins, often in
       combination with various kinds of anti-predator spines and thorns, are their
       main weapons against being eaten.
 5. Community Interactions (continued…)
 Herbivory
   Some herbivore-plant interactions illustrate the concept of coevolution, a series of
    reciprocal evolutionary adaptations in two species.
         Coevolution occurs when a change in one species acts as a new selective force
          on another species, and counteradaptation of the second species in turn affects
          the selection of individuals in the first species.
         For example: an herbivorous insect (the caterpillar of the butterfly Heliconius,
          top left) and a plant (the passionflower Passiflora, a tropical vine). Passiflora
          produces toxic chemicals that protect its leaves from most insects, but
          Heliconius caterpillars have digestive enzymes that break down the toxins. As a
          result, Heliconius gains access to a food source that few other insects can eat.
           o The Passiflora plants have evolved defenses against the Heliconius insect. The
             leaves of the plant produce yellow sugar deposits that look like Heliconius
             eggs. Therefore, female butterflies avoid laying their eggs on the leaves to
             ensure that only a few caterpillars will hatch and feed on any one leaf.
             Because of this, the Passiflora species with the yellow deposits are less likely
             to be eaten.
 5. Community Interactions (continued…)
   Symbiotic Relationships are interactions between two or more
   species that live together in direct contact.
    Three main types:
       Parasitism
       Commensalism
       Mutualism
       *Parasitism and mutualism can be key factors in community
 5. Community Interactions (continued…)
   Parasitism
    A parasite lives on or in its host and obtains its nourishment from the host.
    For example: A tapeworm is an internal parasite that lives inside the intestines of
     a larger animal and absorbs nutrients from its hosts.
    Another example: Ticks, which suck blood from animals, and aphids, which tap
     into the sap of plants, are examples of external parasites.
    Natural selection favors the parasites that are best able to find and feed on hosts.
    Natural selection also favors the evolution of host defenses.
       For example, the immune system of vertebrates provides a multiprolonged
         defense against specific internal parasites. With natural selection working on
         both host and parasite, the eventual outcome is often a relatively stable
         relationship in which the host is not usually killed.

   Tapeworm in small intestine                           Tick on dog
 5. Community Interactions (continued…)
   Commensalism
     One partner benefits without significantly affecting the other.
     Few cases of absolute commensalism have been documented, because it is unlikely that
      one partner will be completely unaffected.
     For example: algae that grow on the shells of sea turtles, barnacles that attach to whales,
      and birds that feed on insects flushed out of the grass by grazing cattle.

        Algae on Sea Turtle                              Barnacles on Whale
 5. Community Interactions (continued…)
   Mutualism
    Benefits both partners in the relationship.
    For example: the association of legume plants and nitrogen-fixing bacteria.
      Bacteria turn nitrogen in the air to nitrates that the plants can use
    Another example: Acacia trees and the predaceous ants they attract.
      Tree provides room and board for ants
      Ants benefit the tree by attacking virtually anything that touches it.

                           Acacia Trees and Ants
 An ecosystem consists of all the organisms in a community as well as the abiotic
  environment with which the organisms interact.
 Ecosystems can range from a microcosm such as a terrarium to a large area such as a
 Regardless of an ecosystem’s size, its dynamics involve two processes- energy flow
  and chemical cycling.
 Energy flow: the passage of energy through the components of the ecosystem.
    For most ecosystems, the sun is the energy source, but exceptions include several
     unusual kinds of ecosystems powered by chemical energy obtained from inorganic
    For example, an a terrarium, energy enters in the form of sunlight.
       Plants (producers) convert the light energy to chemical energy.
       Animals (consumers) take in some of this chemical energy in the form of organic compounds when
        they eat the plants.
       Detrivores, such as bacteria and fungi in the soil, obtain chemical energy when they decompose the
        dead remains of plants and animals.
       Every use of chemical energy by organisms involves a loss of some energy to the surroundings in the
        form of heat.
       Eventually, therefore, the ecosystem would run out of energy if it were not powered by a continuous
        inflow of energy from an outside source.
 Chemical cycling: involves the transfer of materials within the
   An ecosystem is more or less self-contained in terms of matter.
   Chemical elements such as carbon and nitrogen are cycled between
    abiotic components (air, water, and soil) and biotic components of
    the ecosystem.
   The plants acquire these elements in inorganic form from the air and
    soil and fix them into organic molecules, some of which animals
   Detrivores return most of the elements in inorganic form to the soil
    and air.
   Some elements are also returned as the by-products of plant and
    animal metabolism.
 Biomass is the term ecologist use to refer to the amount, or mass,
  of living organic material in an ecosystem.
 Primary production is the amount of solar energy converted to
  chemical energy (organic compounds) by an ecosystem’s producers
  for a given area and during a give time period.
   It can be expressed in units of energy or of mass.
   The primary production of the entire biosphere is 170 billion tons of
    biomass per year.
   Different ecosystems vary considerably in their primary production as
    well as in their contribution to the total production of the biosphere.
   Net primary production refers to the amount of biomass produced
    minus the amount used by producers as fuel for their own cellular
     Gross production- respiration = net production (GP-R=NP)

•Tropical rainforests are                                   •Even though the open
                             •Coral reefs also have         ocean has very low
among the most               very high production, but
productive terrestrial                                      production, it
                             their contribution to global   contributes the most to
ecosystems and               production is small
contribute a large portion                                  Earth’s total net primary
                             because they cover such        production because of
of the planet’s overall      a small area.
production of biomass.                                      its huge size- it covers
                                                            65% of Earth’s surface
 Pyramid of Production
   Illustrates the cumulative loss of energy with each transfer in a food
   Each tier of the pyramid represents one trophic level, and the width of
    each tier indicates how much of the chemical energy of the tier below
    is actually incorported into the organic matter of that trophic level.
   Note that producers convert only about 1% of the energy in the
    sunlight available to them to primary production.
   In this idealized pyramid, 10% of the energy available at each trophic
    level becomes incorporated into the next higher level.
   The efficiencies of energy transfer usually range from 5 to 20%.
   In other words, 80 to 95% of the energy at one trophic level never
    transfers to the next.
 Pyramid of Production
   An important implication of the stepwise decline of energy in a
    trophic structure is that the amount of energy available to top-level
    consumers is small compared with that available to lower-level
   Only a tiny fraction of the energy stored by photosynthesis flows
    through a food chain to a tertiary consumer, such as a snake feeding
    on a mouse.
   This explains why top-level consumers such as lions and hawks
    require so much geographic territory; it takes a lot of vegetation to
    support trophic levels so many steps removed from photosynthetic
   This also explains why there is less biomass and fewer numbers of
    organisms in higher trophic levels.
 Life depends on the recycling of chemicals. Because chemical
  cycles involve both biotic and abiotic components, they are called
  biogeochemical cycles.
 General scheme for the cycling of a nutrient within an ecosystem:
   1. Producers incorporate chemicals from the abiotic reservoir into
    organic compounds.
   2. Consumers feed on the producers, incorporating some of the
    chemicals into their own bodies.
   3. Both producers and consumers release some chemicals back to the
    environment in waster products (CO2 and nitrogen wastes of
   4. Detritivores play a central role. As organisms die, these
    decomposers return chemicals in inorganic form to the soil, water,
    and air. The producers gain a renewed supply of raw materials, and
    the cycle continues.
  Biogeochemical cycles:
    Water cycle
    Carbon cycle
    Nitrogen cycle
    Phosphorous cycle
 Carbon cycle:
   Carbon is the major ingredient of all organic molecules. Like water, the element
    carbon has an atmospheric reservoir and cycles globally. Other abiotic reservoirs
    of carbon include fossil fuels, dissolved carbon compounds in the oceans, and
    sedimentary rocks such as limestone.
   The reciprocal metabolic processes of photosynthesis and cellular respiration are
    mainly responsible for the cycle of carbon between the biotic and abiotic worlds.
   Carbon compounds in detritus-animal wastes, plant litter, and dead organisms of
    all kinds—are consumed and decomposed by detrivores, and detritivore
    respiration, along with that of plants, animals, and other organisms, returns CO2
    to the atmosphere.
   On a global scale, the return of CO2 to the atmosphere by respiration closely
    balances its removal by photosynthesis. However, the increased burning of wood
    and fossil fuels (coal and petroleum) is raising the level of CO2 in the atmosphere.
    This is appears to be leading to the significant problem of global warming.
The Greenhouse Effect
 Greenhouse Effect: a natural phenomenon caused by the release
    of greenhouse gases, which act as a thermal blanket in the
    atmosphere, letting in sunlight, but trapping the heat that would
    normally radiate back into space
   About 75% of the natural greenhouse effect is due to water vapor.
   The next most significant contributor is carbon dioxide.
   In the past, our climate has shifted between periods of stable
    warm conditions to cycles of ice ages and “interglacials.”
   The current period of warming is explained in part by recovery
    after the last ice age 10,000 years ago. However there are many
    indications that climate warming is accelerting and that this
    acceleration is partly the result of human activity, in particular, the
    release of greenhouse gases into the atmosphere.
The Greenhouse Effect
 Sources of Greenhouse Gases:
   Carbon dioxide
     Exhaust from cars, combustion of coal, wood, oil, and burning rainforests
   Methane
     Plant debris and growing vegetation, bleching and flatus of cows
   Chloro-fluoro-carbons (CFCs)
     Leaking coolant from refrigerators and air conditioners
   Nitrous oxide
     Car exhaust
   Tropospheric ozone (found in the lower atmosphere)
     Triggered by car exhaust (smog)
The Greenhouse Effect
 What are the consequences?
   Recent data from the UN Environment Programme, based on
    studies of glaciers across nine mountain ranges, indicates that
    average glacial shrinkage is accelerating.
   Moreover, the rates of summer melting of Arctic ice are
    exceeding early predictions, leading to new forecasts predicting
    an ice-free Arctic by as early as 2013.
   Ice sheet shrinkage has a feedback effect too, because ice
    increases the amount of heat reflected back from the Earth.
   The effect of global warming on the Earth’s systems is likely to
    be considerable.
The Greenhouse Effect
 Potential Effects of Global Warming
   Sea levels
     Expected to rise by 50 cm by the year 2100
     Result of the thermal expansion of ocean water and melting glaciers and ice
     Warming may also expand habitat for many pests, e.g. mosquitoes, shifting the
      range of infectious disease.
   Forests
     Higher temps and precipitation changes could increase forest susceptibility to
      fire, disease, and insect damage.
     Forest fires release more carbon into the atmosphere and reduces the size of
      carbon sinks.
     A richer CO2 atmosphere will reduce transpiration in plants.
   Weather patterns
     May cause regional changes in weather patterns such as El Nino and La Nina, as
      well as affecting the intensity and frequency of storms. Driven by higher ocean
      surface temperatures, high intensity hurricanes no occur more frequently.
The Greenhouse Effect
   Water resources
     Changes in precipitation and increased evaporation will affect the water
      availability for irrigation, industrial use, drinking, and electricity generation.
   Agriculture
     Climate change may threaten the viability of important crop-growing regions.
     Paradoxically, climate change can cause both too much and too little rain.
   The ice-albedo effect
     Ice has a stabilizing effect on global climate, reflecting nearly all the sun’s energy
      that hits it.
     As polar ice melts, more of that energy is absorbed by the Earth.
The Greenhouse Effect
 The Precautionary Principle
   states that if an action or policy has a suspected risk of causing harm to
    the public or to the environment, in the absence of scientific
    consensus that the action or policy is harmful, the burden of proof
    that it is not harmful falls on those taking the action.
   allows policy makers to make discretionary decisions in situations
    where there is the possibility of harm from taking a particular course
    or making a certain decision when extensive scientific knowledge on
    the matter is lacking.
   implies that there is a social responsibility to protect the public from
    exposure to harm, when scientific investigation has found a plausible
   These protections can be relaxed only if further scientific findings
    emerge that provide sound evidence that no harm will result.
The Greenhouse Effect
 The Precautionary Principle (continued):
   “In order to protect the environment, the precautionary approach
    shall be widely applied by States according to their capabilities.
    Where there are threats of serious or irreversible damage, lack of
    full scientific certainty shall not be used as a reason for postponing
    cost-effective measures to prevent environmental
    degradation”~United Nations Conference on Environment
    and Development
   Should the health and wealth of future human generations be
   Is it right to knowingly damage the habitat of, and possibly drive to
    extinction, species other than humans?
 Population: a group of individuals of a single species that
  occupy the same general area.
   These individuals rely on the same resources, are influenced by the
    same environmental factors, and have a high likelihood of interacting
    and breeding with one another.
   Most of our knowledge of population dynamics comes from studies
    of much smaller groups that are confined by more restricted
    geographic boundaries—for instance, a population of binds on an
    island, or fish in a lake, or protists in a laboratory culture.
 Population density is the number of individuals of a species per
  unit area or volume. For example, the number of oak trees per
  square kilometer (km2) in a forest, or the number of earthworms
  per cubic meter (m3) in forest soil.
 To measure population density, ecologists use a variety of
  sampling techniques to estimate population densities. In most
  cases, it is impractical or impossible to count all individuals of a
 Sampling Techniques:
   Point Sampling
   Transect Sampling
   Quadrat Sampling
   Mark and recapture (capture-recapture)
  Mark and recapture (capture-recapture)
    Animals are captured, marked, and then released. After a suitable
     time period, the population is resampled. The number of marked
     animals recaptured in a second sample is recorded as a proportion
     of the total.
      Useful for: determining total population density for highly mobile species in
       a certain area (e.g. butterflies). Movements of individuals in the population can
       be tracked (especially when used in conjunction with electronic tracking
      Considerations: time consuming to do well. Not suitable for immobile
       species. Population should have a finite boundary. Period between samplings
       must allow for redistribution of marked animals in the population. Marking
       should present little disturbance and should not affect behavior.
 Mark and recapture (capture-recapture) Steps:
   1. The population is sampled by capturing as many of the individuals as possible and
     2. Each animal is marked in a way to distinguish it from unmarked animals (unique
      mark for each individual not required).
     3. Return the animals to their habitat and leave them for a long enough period for
      complete mixing with the rest of the population to take place.
     4. Take another sample of the population (this does not need to be the same sample
      size as the first sample, but it does have to be large enough to be valid).
     5. Determine the numbers of marked to unmarked animals in the second sample.
      Use the following equation (The Lincoln Index) to estimate the size of the overall
        Population size= (n1 x n2)/n3
        n1= number of individuals initially caught, marked, and released
        n2=total number of individuals caught in the second sample
        n3= number of marked individuals in the second sample.
 Within a population’s geographic range, local densities may vary
 The dispersion pattern of a population refers to the way
  individuals are spaced within their area.
 These patterns are important characteristics for an ecologist to
  study, since they provide insights into the environmental effects
  and social interactions in the population.
   Clumped
   Uniform
   Random
 Clumped pattern
   Most common in nature
   Individuals are aggregated in patches
   Often results from an unequal distribution of resources in the
     For example, plants or fungi may be clumped in areas where soil conditions and
      other factors favor germination and growth.
   Clumping of animals is often associated with uneven food distribution
    or with mating or other social behavior.
     For example, fish are often clumped in schools, which may reduce predation
      risks and increase feeding efficiency. Mosquitoes often swarm in great numbers,
      increasing their chances for mating.
  Uniform, or even, pattern
    Pattern of dispersion often results from interactions between the
     individuals of a population.
      For example, some plants secrete chemicals that inhibit the germination and
       growth of nearby plants that could compete for resources.
    Animals may exhibit uniform dispersion as a result of territorial
      For example, penguins and humans
 Random dispersion
   Individuals in a population are spaced in a patternless,
    unpredictable way.
     For example, clams living in a coastal mudflat might be randomly dispersed at
      times of the year when they are not breeding and when resources are plentiful
      and do not affect their distribution.
   Varying habitat conditions and social interactions make random
    dispersion rare.
 Population size
   The number of individuals comprising a population may fluctuate
    over time. These changes make populations dynamic.
   A population in equilibrium has no net change in its abundance.
   Population Growth = B – D + I – E
 • Factors that influence the number of individuals in a population:
    – Birth (B) also known as natality
    – Death (D) also known as mortality
    – Immigration (I)
    – Emigration (E)
 Life Tables
   Used to determine the average lifespan of various plants and animal
    species to study the dynamics of population growth.
 Survivorship curves
   Graphs generated from life tables to make the data easier to
   Plot the proportion of individuals alive at each age.
    • Type 1- produce few offspring, take care of their young, many survive into
    • Type 2- intermediate, more constant mortality over the entire life span.
    • Type 3- high death rates for the very young, mature individuals survive longer,
      usually involves very large # of offspring with little or no parent care
          Three types of survivorship curves
 The Exponential Growth Model
   The rate of population increase under ideal conditions.
    (High Birth Rate, Low Death Rate)
   Gives an idealized picture of unregulated population
    growth; no population can grow exponentially
   The whole population multiplies by a constant factor
    during each time interval.
   The simple equation G=rN describes this J-shaped curve
     G : growth rate of the population (the number of new individuals
      added per time interval)
     N: stands for the population size (the number of individuals in the
      population at a particular time)
     r: intrinsic rate of increase; remains constant (maximum capacity
      of members that population to reproduce)
 Logistic Growth Model
   A description of idealized population growth that is slowed by
    limiting factors as the population size increases.
   Limiting factors are environmental factors that restrict population
   G=rN(K-N)/K
     K= carrying capacity (maximum population size that a particular
       environment can support or “carry”).
   S-shape curve
     1. Exponential Growth Phase-When the population first starts growing, N
       is very small compared to the carrying capacity K. Population growth is close to
       exponential growth; (K-N)/K nearly equals K/K or 1
     2. Transitional Phase- The population growth starts to slow; N gets closer to
       carrying capacity, the term (K-N)/K becomes an increasingly smaller fraction.
     3. Plateau Phase- Carrying capacity is reached and the population is as big as
       it can theoretically get in its environment; N=K, therefore (K-N)/N=0,
       therefore G=O.
          Logistic Growth Curves
 What does the logistic growth model suggest to us about real
  populations in nature?
   Model predicts that a population’s growth rate will be small when
    the population size is either small or large, and highest when the
    population is at an intermediate level relative to the carrying
     Small Population: resources are abundant, and the population is able to grow
      nearly exponentially. The increase is small because N is small.
     Large Population: limiting factors strongly oppose the population’s potential to
      increase. These limiting factors cause the birth rates to decrease, the death rate
      to increase, or both. Eventually, the population stabilizes at the carrying
      capacity (K), when the birth rate equals the death rate.

    **It is important to realize that this is a mathematical model…no natural
      populations fit perfectly!**
 Factors that appear to regulate growth in natural populations:
   Density-dependent factors:
     Competition among members of a growing population for limited resources,
      like food or territory.
     Health of organisms
     Predation
     Physiological factors (reproduction, growth, hormone changes)
   Density independent factors
    • Regardless of population density, these factors affect individuals to the same
      – Weather conditions
      – Acidity
      – Salinity
      – Fires
      – Catastrophies
  Life History is the series of events from birth through
   reproduction to death.
  For a given population in a particular environment, natural
   selection will favor the combination of life history traits that
   maximizes an individual’s output of viable, fertile offspring.
  Key life history traits:
    Age at which reproduction first occurs
    Frequency of reproduction
    Number of offspring
    Amount of parental care given.
 Life History (continued)
   Some ecologists hypothesize that different life history patterns are favored under
    different population densities and conditions.
   r-selection (r-strategies)
     Individuals mature early
     produce a large number of offspring at a time. Usually only reproduce once.
     Have a small body size
     Have a short life span
     For example, insects and weeds
   K-selection (K-strategies)
     Typically larger-bodied
     Long life span, late maturity
     Reproduction occurs at a later age with the production of a few, well-cared for
        offspring. Usually reproduce more than once.
     Common in populations that live at densities close to the carrying capacity (K) of
        their environment.
     Example: many large terrestrial vertebrates
 Life history (continued)
   There are organisms that display either extreme r- or K- strategies,
    but most organisms have life histories that are intermediate on the
   Some organisms such as Drosophila switch strategies depending on
    environmental conditions:
     In a predictable environment
        In order to maximize fitness, it pays to invest resources in long-term
         development and long life (K-strategy)
     In an unstable environment
        It is better to produce as many offspring as quickly as possible (r-strategy)
        *ecological disruption favors r-strategists such as pathogens and pest species
Impacts of Humans on Ecosystems
 Statospheric Ozone Depletion
 Loss of biodiversity
 Endangered Species
 Impact of Alien Species
 Fisheries Management
Impacts of Humans on Ecosystems
 Stratospheric Ozone Depletion
   Ozone (O3) is found in a band of the upper stratosphere as a
    renewable thin veil.
   It absorbs about 99% of the harmful incoming UV radiation from the
    sun and prevents it from reaching the Earth’s surface.
   An increase in UV-B radiation is likely to cause immune system
    suppression in animals, lower crop yields, a decline in the
    productivity of forests and surface dwelling plankton, more smog,
    changes in the global climate, increasingly severe sunburns, increase
    in skin cancers, and more cataracts of the eye.
   Ozone is being depleted by a handful of human-produced chemicals:
     CFCs appear to be the primary cause for ozone depletion. UV light hits a CFC
      molecule and releases a chlorine atom. Chlorine reacts with ozone, forming a
      Chlorine oxide molecule. This interferes with ozones ability to renew itself,
      causing holes in the ozone layer.
Impacts of Humans on Ecosystems
Impacts of Humans on Ecosystems
 Loss of Biodiversity
   Biodiversity is measured by species. It is not distributed evenly on
    Earth, being consistently richer in the tropics and concentrated more
    in some areas than in others.
   Biodiversity hotspots are located in the tropics and most are forests.
   Loss of biodiversity reduces the stability and resilience of natural
    ecosystems and decreases the ability of their communities to adapt to
    changing environmental conditions.
Impacts of Humans on Ecosystems
 Endangered Species
   Species under threat of severe population loss or extinction are
    classified as either endangered or threatened.
   An endangered species is one with so few individuals that it is at high
    risk of local extinction, while a threatened (or vulnerable) species is
    likely to become endangered in the near future.
     For example, hunting and collecting are one cause of species decline. Black
      Rhinoceros were once plentiful throughout much of Africa. Now, only remnant
      populations remain. In Kenya, 98% of the population was lost in only 17 years.
      Conservationists suspect that a trader with a large stockpile of horn is trying to
      cause rhinoceros extinction in order to increase the horn’s value. 
Conservation of Biodiversity

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