BW EssentialCh04Lecture by HC11112501231

VIEWS: 15 PAGES: 100

									     Ecology and evolution:
    Populations, communities,
        and biodiversity

This lecture will help you understand:

• How evolution generates
• Speciation, extinction, and
  the ―biodiversity crisis‖
• Population ecology
• Community ecology
• Species interactions
• Conservation challenges
• Evolution by natural
 Key Words
adaptation               density dependent          host
adaptive trait           detritivores               immigration
age distribution         ectoparasites              interspecific competition
age structure            Emigration                 intraspecific competition
age structure diagrams   endemic                    invasive species
allopatric speciation    endoparasites              keystone species
anthropogenic            environmental resistance   K-strategist
artificial selection     evolution                  limiting factors
biodiversity             exponential growth         logistic growth
biological diversity     extinction                 mass extinction
biosphere                food chain                 mutations
biotic potential         food web                   mutualism
carnivores               fossil                     natural selection
carrying capacity        fossil record              niche
climax community         growth rate                omnivores
clumped distribution     habitat selection          parasite
community                habitats                   parasitism
competition              herbivores
decomposers              heritable
Key Words
 phylogenetic trees         sex ratio
 pioneer species            speciation
 pollination                species
 population density         succession
 population dispersion      symbioses
 population distribution    tertiary consumers
 population growth curves   trophic levels
 population size            uniform distribution
 primary consumers
 primary succession
 random distribution
 resource partitioning
 secondary consumers
 secondary succession
Central Case: Striking Gold in a Costa Rican
Cloud Forest

• The golden toad of Monteverde, discovered in 1964, had
  disappeared 25 years later.
• Researchers determined that warming and drying of the forest was
  most likely responsible for its extinction.
• As the global climate changes, more such events can be expected.

Biodiversity, or biological diversity, is the sum of an
area’s organisms, considering the diversity of species, their
genes, their populations, and their communities.

A species is a particular type of organism; a population or
group of populations whose members share certain
characteristics and can freely breed with one another and
produce fertile offspring.

Costa Rica’s Monteverde cloud forest is home to many
species and possesses great biodiversity.
                                                       Figure 5.1
Natural selection

Natural selection rests on three indisputable facts:

   • Organisms produce more offspring than can survive.
   • Individuals vary in their characteristics.
   • Many characteristics are inherited by offspring from
Natural selection

THEREFORE, logically…

     • Some individuals will be better suited to their
       environment; they will survive and reproduce
       more successfully.
     • These individuals will transmit more genes to
       future generations.
     • Future generations will thus contain more genes
       from better-suited individuals.
     • Thus, characteristics will evolve over time to
       resemble those of the better-suited ancestors.
Natural selection

Fitness = the likelihood that an individual will reproduce
          the number of offspring an individual
          produces over its lifetime

Adaptive trait,
or adaptation = a trait that increases an individual’s
Natural selection

Evidence of natural
selection is all around us:

In nature …

Diverse bills have
evolved among species of
Hawaiian honeycreepers.

                              Figure 4.23a
Beak Types Resulting From Natural Selection
         Fruit and seed eaters   Insect and nectar eaters
          Greater Koa-finch
                                        Kuai Akialoa
          Kona Grosbeak

                                 Crested Honeycreeper

          Maui Parrotbill                  Apapane

                       Unknown finch ancestor
Natural selection

Evidence of
selection is all
around us:

… and in our
                   Dog breeds, types of cattle, improved
                   crop plants—all result from artificial
                   selection (natural selection conducted
                   by human breeders).
                                                     Figure 4.23b

The process by which new species come into being

Speciation is an evolutionary process that has given Earth
its current species richness—more than 1.5 million
described species and likely many million more not yet
described by science.

Allopatric speciation is considered the dominant mode of
speciation, and sympatric speciation also occurs.
Allopatric speciation

                        1. Single interbreeding

                        2. Population divided by a
                           barrier; subpopulations

                                              Figure 5.2
Allopatric speciation

                        3. The two populations
                           evolve independently,
                           diverge in their traits.

                        4. Populations reunited
                           when barrier removed,
                           but are now different
                           enough that they don’t

                                               Figure 5.2
Allopatric speciation
Many geological and climatic events can serve as barriers
separating populations and causing speciation.
                            Chemical Evolution
                              (1 billion years)

 Formation               Small               Large                    First
   of the               organic              organic                protocells
   earth’s             molecules           molecules                 form in
    early               form in          (biopolymers)              the seas
 crust and             the seas              form in
atmosphere                                  the seas

                            Biological Evolution
                              (3.7 billion years)

         Single-cell           Single-cell           Variety of
        prokaryotes            eukaryotes           multicellular
           form in               form in             organisms
          the seas              the seas             form, first
                                                    in the seas
                                                      and later
                                                      on land
Stanley Miller's experiment animation.

            Click to view
Stabilizing Selection

                   Click to view
Disruptive Selection

                  Click to view
                   Niches and Natural Selection

Number of individuals


                                                                       Generalist species
                        Specialist species                             with a broad niche
                        with a narrow niche

                                                    Region of
                                                    niche overlap

                                              Resource use
  Various Niches and Their Adaptations

                                                                                                                  Herring gull is a
                                                                                                                  tireless scavenger

 Black skimmer                                Brown pelican dives for fish,             Dowitcher probes deeply
                                              which it locates from the air                                               Ruddy turnstone
 seizes small fish                                                                      into mud in search of             searches
 at water surface    Scaup and other                     Avocet sweeps bill through     snails, marine worms,             under shells and
                     diving ducks feed on                mud and surface water in       and small crustaceans             pebbles for small
                     mollusks, crustaceans,              search of small crustaceans,                                     invertebrates
                     and aquatic vegetation              insects, and seeds

feeds on                                                                  Oystercatcher feeds on       Knot (a sandpiper) picks up
minute                                                                    clams, mussels, and          worms and small crustaceans
organisms                                      Louisiana heron wades into other shellfish into which   left by receding tide
in mud
                                               water to seize small fish  it pries its narrow beak

                                                                                                                           Piping plover feeds
                                                                                                                           on insects and tiny
                                                                                                                           crustaceans on
                                                                                                                           sandy beaches
Geographic Separation
                                                     Arctic Fox


             northward                                       Adapted to cold through
                         Different environmental
             and                                             heavier fur, short ears,
Early fox                conditions lead to different
                                                             short legs, short nose.
population   southward   selective pressures and evolution
                                                             White fur matches
             and         into two different species.
                                                             snow for camouflage.

                                                       Gray Fox

                                                             Adapted to heat
                                                             through lightweight
                                                             fur and long ears,
                                                             legs, and nose, which
                                                             give off more heat.

Span worm          Wandering leaf insect      Bombardier beetle       Foul-tasting monarch

Poison dart frog   Viceroy butterfly mimics                           When touched, the
                                              Hind wings of io moth   snake caterpillar
                   monarch butterfly
                                              resemble eyes of a      changes shape to look
                                              much larger animal      like the head of a snake
Phylogenetic trees

Life’s diversification results from countless speciation
events over vast spans of time.

Evolutionary history of divergence is shown with diagrams
called phylogenetic trees.

Similar to family genealogies, these show relationships
among organisms.
Phylogenetic trees
These trees are constructed by analyzing patterns of
similarity among present-day organisms.

This tree shows all of life’s major groups.

                                                       Figure 5.4
Phylogenetic trees

Within the group Animals in the previous slide, one can
infer a tree of the major animal groups.

                                                          Figure 5.4
Phylogenetic trees

And within the group Vertebrates in the previous slide, one
can infer relationships of the major vertebrate groups, and
so on…
                                                       Figure 5.4

Extinction is the disappearance of an entire species from
the face of the Earth.

Average time for a species on Earth is ~1–10 million years.
Species currently on Earth = the number formed by
speciation minus the number removed by extinction.

Some species are more vulnerable to extinction than others:

      • Species in small populations

      • Species adapted to a narrowly specialized resource
        or way of life

Monteverde’s golden toad was apparently such a specialist,
and lived in small numbers in a small area.

Some species are more vulnerable to extinction than others:

      • Species in small populations

      • Species adapted to a narrowly specialized resource
        or way of life

Monteverde’s golden toad was apparently such a specialist,
and lived in small numbers in a small area.
Life’s hierarchy of levels

                             Life occurs in levels:

                             from the atom up to
                               the molecule to
                                 the cell to
                                   the tissues to
                                     the organs to
                                      the organism…

                                                      Figure 5.7
Life’s hierarchy of levels

                         … and from the organism
                          to the population to
                           the community to
                            the ecosystem to
                              the biosphere.

                         Ecology deals with these
                         levels, from the organism
                         up to the biosphere.

                                                Figure 5.7
The study of:

      the distribution and abundance of organisms,

      the interactions among them,

      and the interactions between organisms and
      their abiotic environments

Ecology is NOT environmental advocacy!
            (= a common MISUSE of the term)
Habitat and niche
Habitat = the specific environment where an organism
lives (including living and nonliving elements: rocks, soil,
plants, etc.)

Habitat selection = the process by which organisms choose
habitats among the options encountered

Niche = an organism’s functional role in a community
(feeding, flow of energy and matter, interactions with other
organisms, etc.)
Population ecology
Population = a group of individuals of a species that live in
a particular area

Several attributes help predict population dynamics
(changes in population):

                • Population size
                • Population density
                • Population distribution
                • Age structure
                • Sex ratio
 Population size

Number of individuals present at a given time

Population size for the golden toad was 1,500+ in 1987,
and zero a few years later.
 Population density

Number of individuals per unit area or,
Number of individuals per unit volume

Population density for the harlequin frog increased locally
as streams dried and frogs clustered in splash zones.
Population distribution

Spatial arrangement of individuals



                                                     Figure 5.8
Age structure

Or age distribution =
relative numbers of
individuals of each age or
age class in a population

Age structure diagrams,
or age pyramids, show
this information.

                             Figure 5.9
Age structure

Pyramid weighted     Pyramid weighted
toward young:        toward old: population
population growing   declining
                                        Figure 5.9
Sex ratio

Ratio of males to females in
a population
Even ratios (near 50/50) are
most common.

Fewer females causes slower
population growth.

   Note human sex ratio
   biased toward females at
   oldest ages.
Population growth

Populations grow, shrink, or remain stable,
      depending on rates of birth, death, immigration,
            and emigration.

      (birth rate + immigration rate) –
                   (death rate + emigration rate)
                                = population growth rate
Exponential growth

Unregulated populations increase by exponential growth:

Growth by a fixed
percentage, rather
than a fixed amount.

Similar to growth
of money in a
savings account
Exponential growth in a growth curve

growth curves
show change in
population size
over time.

Scots pine shows

                                       Figure 5.10
Limits on growth

Limiting factors restrain exponential population growth,
slowing the growth rate down.

Population growth levels off at a carrying capacity—the
maximum population size of a given species an
environment can sustain.

Initial exponential growth, slowing, and stabilizing at
carrying capacity is shown by a logistic growth curve.
Logistic growth curve

                        Figure 5.11
Population growth: Logistic growth

Logistic growth (shown here in yeast from the lab) is only
one type of growth curve, however.

                                                      Figure 5.12a
Population growth: Oscillations

Some populations fluctuate continually above and below
carrying capacity, as with this mite.

                                                   Figure 5.12b
Population growth: Dampening oscillations

In some populations, oscillations dampen, as population
size settles toward carrying capacity, as with this beetle.

                                                         Figure 5.12c
Population growth: Crashes

Some populations that rise too fast and deplete resources
may then crash, as with reindeer on St. Paul Island.

                                                      Figure 5.12d
Density dependence

Often, survival or reproduction lessens as populations
become more dense.

Density-dependent factors (disease, predation, etc.)
account for the logistic growth curve.
Biotic potential and reproductive strategies

Species differ in strategies for producing young.

Species producing lots of young (insects, fish, frogs, plants)
have high biotic potential.

Others, such as mammals and birds, produce few young.

However, those with few young give them more care,
resulting in better survival.
                                           POPULATION SIZE

Biotic Potential

                Growth factors                             Decrease factors
               (biotic potential)                     (environmental resistance)
                    Abiotic                                    Abiotic
                                                     Too much or too little light
         Favorable light                             Temperature too high or too low
         Favorable temperature                       Unfavorable chemical environment
         Favorable chemical environment                (too much or too little of critical
          (optimal level of critical nutrients)        nutrients)
                      Biotic                                        Biotic
         High reproductive rate                      Low reproductive rate
         Generalized niche                           Specialized niche
         Adequate food supply                        Inadequate food supply
         Suitable habitat                            Unsuitable or destroyed habitat
         Ability to compete for resources            Too many competitors
         Ability to hide from or defend              Insufficient ability to hide from or defend
          against predators                            against predators
         Ability to resist diseases and parasites    Inability to resist diseases and parasites
         Ability to migrate and live in other        Inability to migrate and live in other
          habitats                                   habitats
         Ability to adapt to environmental           Inability to adapt to environmental
          change                                       change

                                                Late loss
  Percentage surviving (log scale)



                                           Early loss
                                                K-Selected Species

Terms come from:                  Elephant

                             Fewer, larger offspring
K = symbol for carrying
                             High parental care and protection of offspring
capacity. (Populations
                             Later reproductive age
tend to stabilize near K.)
                             Most offspring survive to reproductive age
                             Larger adults
                             Adapted to stable climate and environmental conditions
                             Lower population growth rate (r)
                             Population size fairly stable and usually close to
                             carrying capacity (K)
                             Specialist niche
                             High ability to compete
                             Late successional species
r-Selected                                  r-Selected Species



                         Many small offspring
r = intrinsic rate of    Little or no parental care and protection of offspring
population increase.     Early reproductive age
(Populations can         Most offspring die before reaching reproductive age
potentially grow fast,   Small adults

have high r.)            Adapted to unstable climate and environmental
                         High population growth rate (r)
                         Population size fluctuates wildly above and below
                         carrying capacity (K)
                         Generalist niche
                         Low ability to compete
                         Early successional species
Community ecology

Ecologists interested in how populations or species interact
with one another study community ecology.

Community = a group of populations of different species
that live in the same place at the same time

 e.g., Monteverde cloud forest community–golden
 toads, quetzals, trees, ferns, soil microbes, etc.
Roles in communities: Producers
By eating different foods, organisms are at different trophic
levels, and play different roles, in the community

Plants and other photosynthetic organisms are producers.

                                                      Figure 5.14b
Primary consumers

Animals that eat plants are primary consumers, or
herbivores, and are at the second trophic level.

                                                    Figure 5.14b
Secondary consumers

Animals that eat herbivores are secondary consumers, at
the third trophic level.

                                                  Figure 5.14b
Detritivores and decomposers

                        Detritivores and
                        decomposers eat
                        nonliving organic
                        matter; they recycle

                                         Figure 5.14b
Trophic levels
Together these comprise trophic levels.

                                          Figure 5.14b
Food chains and webs

We can represent feeding interactions (and thus energy
transfer) in a community:

   Food chain: Simplified linear diagram of who eats

   Food web: Complex network of who eats whom
Food web for an eastern deciduous forest

                                     Figure 5.14a
Keystone species

Species that have especially great impacts on other
community members and on the community’s identity

If keystone species are removed, communities
change greatly.

             A ―keystone‖ holds an arch together.
                                                      Figure 5.15a
Keystone species
When the keystone sea otter is removed, sea urchins
overgraze kelp and destroy the kelp forest community.

                                                        Figure 5.15b
Balance of Life

(a) Southern sea otter   (b) Sea Urchin   (c) Kelp bed

One species, the predator, hunts, kills, and consumes the
other, its prey.

                                                      Figure 5.16
Predation drives adaptations in prey

Cryptic coloration:   Warning coloration:   Mimicry:
Camouflage to hide    Bright colors warn    Fool predators
from predators        that prey is toxic    (here,
                                            mimics snake)
                                                    Figure 5.18

When multiple species seek the same limited resource

   Interspecific competition is between two or
   more species.

   Intraspecific competition is within a species.

Usually does not involve active fighting, but subtle contests
to procure resources.
Interspecific competition

Different outcomes:

   Competitive exclusion = one species excludes the other
   from a resource.

   Species coexistence = both species coexist at a ratio of
   population sizes, or stable equilibrium.
Competitive Exclusion Principle

                  Click to view
Interspecific competition

Adjusting resource use, habitat use, or way of life over
evolutionary time leads to:

   Resource partitioning = species specialize in different
   ways of exploiting a resource.

   Character displacement = physical characters evolve
   to become different to better differentiate resource use.
Resource partitioning

Tree-climbing bird
species exploit
insect resources in
different ways.

                        Figure 5.20

One species, the parasite,
exploits the other species,
the host, gaining benefits
and doing harm.

                              Figure 5.21
             Both species benefit one another.
Hummingbird pollinates flower while gaining nectar for itself.

                                                          Figure 5.22

    Oxpeckers and black rhinoceros   Clown fish and sea anemone

     Mycorrhizae fungi on juniper     Lack of mycorrhizae fungi on
     seedlings in normal soil         juniper seedlings in sterilized soil

A series of regular, predictable, quantifiable changes
through which communities go

      • Primary succession: Pioneer species colonize a
        newly exposed area (lava flows, glacial retreat,
        dried lake bed).

      • Secondary succession: The community changes
        following a disturbance (fire, hurricane, logging).
Primary aquatic succession

1. Open pond

2. Plants begin to cover
   surface; sediment

3. Pond filled by sediment;
   vegetation grows over
                              Figure 5.24
Secondary terrestrial succession

                                   Figure 5.23

             Click to view
Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession

                               Immature Ecosystem                       Immature Ecosystem
Characteristic                 (Early Successional Stage)               (Late Successional Stage)

Ecosystem Structure
                               Small                                    Large
Plant size
                               Low                                      High
Species diversity
                               Mostly producers, few decomposers        Mixture of producers, consumers,
Trophic structure
                                                                        and decomposers
                               Few, mostly generalized
Ecological niches                                                       Many, mostly specialized
Community organization                                                  High
(number of interconnecting

Ecosystem Function
                               Low                                      High
                               High                                     Low
Net primary productivity
                               Simple, mostly plant         herbivore   Complex, dominated by
Food chains and webs
                               with few decomposers                     decomposers
Efficiency of nutrient recycling Low                                    High
Efficiency of energy use       Low                                      High
Invasive species

A species that spreads widely and rapidly becomes
dominant in a community, changing the community’s
normal functioning

Many invasive species
are non-native, introduced
from other areas.

Purple loosestrife invades
a wetland.

                                                    Figure 5.25
Climate change and Monteverde

Monteverde’s cloud forest become drier in the 1970s–

       Number of dry days rose     Stream flow fell

                                        From The Science behind the Stories
Climate change and Monteverde

                           Cool ocean; low
                           clouds; mountains
                           receive moisture

                           Warm ocean; high
                           clouds; mountains
                           get less moisture

                           From The Science behind the Stories
Viewpoints: Conservation of Monteverde?

                Robert                Nathaniel
                Lawton                Wheelwright

―A few committed people          ―Whatever negative local impact
can have an impact.              the steady onslaught of ecotourists
Conservation efforts must        may have on resplendent quetzals
take into account local social   and howler monkeys, it is more
aspirations. Conservation        than compensated for by inspiring
can lead to economic             people to appreciate tropical forests
success. But local               and their own natural heritage.‖
conservation is not enough.‖
                                                            From Viewpoints
Conclusions: Challenges

Earth’s biodiversity faces a mass extinction event caused by
human actions.
Climate change may alter communities and cause species
Invasive species pose a new threat to community stability.
Conservation efforts need to consider local economies and
social conditions in order to succeed.
Evolution and natural selection provide a strong explanation
for how Earth’s life diversified.
Conclusions: Solutions

There is still time to avoid most species extinctions
threatened by human actions.
Studies like those at Monteverde are clarifying the effects of
climate change.
Ecological restoration efforts can remove invasive species
and restore original communities.
Many conservation efforts today are locally run or promote
local economies.

Allopatric speciation requires…?

        a. Natural selection
        b. More than two populations
        c. Some kind of barrier separating populations
        d. Sex ratio bias in one population

Which is a K-strategist?

        a. A dragonfly that lays 300 eggs and flies away
        b. An oak tree that drops its acorns each year
        c. A bamboo plant that flowers only once every 20
        d. A human who raises three children
        e. A fish on the second trophic level

Which of the following lists of trophic levels is in the
correct order?

         a. Producer, secondary consumer, herbivore
         b. Producer, herbivore, secondary consumer
         c. Secondary consumer, producer, detritivore
         d. Herbivore, carnivore, producer

Primary succession would take place on all of the following

        a. The slopes of a Hawaiian volcano’s new lava
        b. A South Carolina coastal forest after a hurricane
        c. Alaskan land just uncovered as a glacier melts
        d. A new island formed by falling levels of a
           reservoir in Ohio
QUESTION: Weighing the Issues

Can we continue raising the Earth’s carrying capacity for
humans by developing technology and using resources more

        a. Yes, our growth can continue indefinitely.
        b. Our growth can continue some more, but will
           eventually be halted by limiting factors.
        c. No, we cannot raise Earth’s carrying capacity
           for ourselves any longer.
QUESTION: Weighing the Issues
Are national parks and preserves the best way to conserve

        a. Yes, because species depend on their habitats
           and intact communities being protected.
        b. No, because climate change can ruin
           conservation efforts if it changes conditions
           inside preserves.
        c. Ecotourism and encouraging local interest in
           conservation is more important than
           establishing parks.
QUESTION: Interpreting Graphs and Data
You would expect this population to be…?

                               a. Growing rapidly
                               b. Shrinking rapidly
                               c. Stable in size
                               d. Oscillating in size

Figure 5.9
QUESTION: Interpreting Graphs and Data
How can you tell that this population growth curve shows exponential
                                     a. Population is increasing.
                                     b. Data points match curve
                                     c. Population is rising by the
                                        same number during each
                                     d. Population is rising by the
                                        same percentage during each

Figure 5.10
QUESTION: Interpreting Graphs and Data
This shows     growth ending at a(n)              .
                                       a. exponential… carrying
                                       b. intrinsic… equilibrium
                                       c. logistic… carrying
                                       d. runaway…
                                       e. logistic… extinction

Figure 5.12a
QUESTION: Viewpoints

What is the most important lesson we can learn from the
Monteverde preserve?

        a. Preserves do little good if species can become
           extinct inside them.
        b. Climate change means that we will need more
           than preserves to save all species.
        c. Ecotourism and local participation can make for
           successful conservation.

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