Key Points:

▪ A community's structure can be described by its species

richness and species diversity.

▪ Species Richness – number of species present in an

ecosystem.
▪ Species Diversity – measure of both species richness
and species evenness (relative numbers).

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Key Points:
▪ Community structure is influenced by many
factors, including
✓abiotic factors
✓species interactions
✓level of disturbance
✓chance events

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Key Points:

▪ Some species, such as foundation species and

keystone species, play particularly important
roles in determining their communities'
structure.

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▪ Different ecological communities can be pretty different in
terms of the types and numbers of species they contain.

Arctic Community

Tropical Rainforest Community

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Community Structure
▪ Community structure is essentially the composition of
a community, including the number of species in that
community and their relative numbers.
▪ It can also be interpreted more broadly, to include all
of the patterns of interaction between these
different species

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How do we measure Community
Structure?

▪ Species Richness!
▪ Species Diversity!

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 Species Richness
▪ Species richness is the number of different species
in a particular community.

For example:
▪ If we found 30 species in one community, and 300
species in another, the second community would have
much higher species richness than the first.

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▪ Communities with the highest species richness tend to
be found in areas near the equator, which have lots of
solar energy (supporting high primary productivity),
warm temperatures, large amounts of rainfall, and little
seasonal change.
▪ Communities with the lowest species richness lie near
the poles, which get less solar energy and are colder,
drier, and less amenable to life.

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Jamalia M. Macatanong, CAS, IMCC 9/15/2019 12
Species Diversity
▪ Species diversity is a measure of community complexity.
▪ It is a function of both the number of different species in
the community (species richness) and their relative
abundances (species evenness).

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 Species Diversity
▪ Larger numbers of species and more even abundances of
species lead to higher species diversity.

Example:
▪ A forest community with 20 different kinds of trees would have greater
species diversity than a forest community with only 55 kinds of trees
(assuming that the tree species were even in abundance in both cases).
▪ A forest community with 20 different kinds of trees in even abundances
would have greater species diversity than a forest community with the
same number of species in very uneven abundances (for instance, with
90\%90% of the trees belonging to a single species).

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In general, ecologists think that more diverse ecological communities are
more stable (that is, more able to recover after a disturbance) than less diverse
communities.

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 ▪ Define Species Richness
▪ Define Species Diversity

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 Between these two communities, which is more likely to be
resilient against disturbances? Why?
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Community Community
A B

Which has a higher species richness? Why?

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Community Community
A B

Which has a higher species abundance? Why?

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What factors shape community
structure?
1. The climate patterns of the community's location.
2. The geography of the community's location.
3. The heterogeneity (patchiness) of the environment.
4. The frequency of disturbances, or disruptive events.
5. Interactions between organisms.

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Foundation and Keystone species
▪ Some species have unusually strong impacts on
community structure, preserving the balance of the
community or even making its existence possible.

❖Foundation species
❖Keystone species

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 Foundation species
▪ A foundation species plays a unique, essential role in
creating and defining a community.
▪ Foundation species act by modifying the environment
so that it can support the other organisms that form
the community.

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 Kelp Forest
Kelps create environments that
allow the survival of other
organisms that make up the
kelp forest community.

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 Beavers, which modify their environment by building dams,
can also be seen as a foundation species

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▪ A keystone species is a species that has a disproportionately large
effect on community structure relative to its biomass or abundance.

▪ Keystone species differ from foundation species in two main ways:

1) They are more likely to belong to higher trophic levels (to be top
predators).
2) They act in more diverse ways than foundation species, which
tend to modify their environment.

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▪ The intertidal sea star Pisaster ochraceus, which is
found in the northwestern United States, is perhaps
the most famous example of a keystone species.
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Philippine Eagle – topmost predator in Philippine old-growth lowland forests

They feed mostly on flying lemurs (also called kagwang), snakes, palm civets, flying
squirrels, giant cloud rats and occasional monkeys.

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▪ Define Keystone Species and provide example.
▪ What is a Foundation Species?
▪ Give 3 possible impacts of loss of a keystone species.

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31

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 ▪ Invasive species are species that have been
introduced into areas outside their native
range and can cause—or have caused—harm in
their new area.
▪ Invasive species may outcompete native
species for resources or habitat, altering
community structure and potentially leading to
extinctions.

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There are many ways in which the introduction of non-native
or exotic species negatively affects our environment and
the diversity of life on our planet:

1. Compared to other threats to biodiversity, invasive introduced

species rank second only to habitat destruction, such as forest
clearing.
2. Introduced species are a greater threat to native biodiversity
than pollution, harvest, and disease combined.
3. Introduced species inflict an enormous economic cost.
4. Of course, some introduced species (such as most of our food crops
and pets) are beneficial. However, others are very damaging.

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 Exotic species are NOT
good guests!
▪ The greatest impact is caused by introduced species
that change an entire habitat, because many native
species thrive only in a particular habitat.
▪ Other invaders, though they do not change a habitat,
endanger single species or even entire groups of them
in various ways.

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 Lake Lanao Endemic Cyprinids (Ismail, 2011)

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 Barbodes tumba (Macatanong, et al., 2017)

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▪ How do you address our growing problem
with exotic species in the Philippines?
▪ Cite your solutions in detail for preventing entry and
addressing exotic species that are already in the
country.
▪ Provide realistic examples in your solutions… e.g. for
exotic plant species and exotic animals.

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 Which is better?

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 Which is better?

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 Which is better?

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Biodiversity
▪ Biological diversity, or biodiversity, is the variety of:

▪ the earth’s species,

▪ the genes they contain,
▪ the ecosystems in which they live, and
▪ the ecosystem processes such as energy flow and
nutrient cycling that sustain all life

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Jamalia M. Macatanong, CAS, IMCC 9/15/2019 46
Functional Diversity
The biological and
chemical processes such
as energy flow and matter
recycling needed for the
survival of species,
communities, and
ecosystems.

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 Genetic Diversity
The variety of genetic
material within a species
or a population.

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 Ecological Diversity
The variety of terrestrial
and aquatic ecosystems
found in an area or on
the earth.

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 Species Diversity
The number and
abundance of species
present in different
communities

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▪ Can introduced species be invasive? (Yes or No) Why?
▪ How did exotic species prevailed in the Philippines?
▪ What are the components of biodiversity?
▪ Importance of genetic diversity?

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 Where do Species Come From?

▪ Biological evolution by
natural selection explains
how life changes over time.

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 Where do Species Come From?

Father of evolution

Charles Darwin:
Galapagos Islands
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 Where do Species Come From?

Alfred Russel Wallace:

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Malay Peninsula 9/15/2019 55
 Darwin and Wallace’s Findings:

• Darwin and Wallace

observed that organisms
must constantly struggle to
obtain enough food and
other resources to survive
and reproduce.

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 Darwin and Wallace’s Findings:

• They also observed that individuals in a population with a specific

advantage over other individuals are more likely to survive,
reproduce, and have offspring with similar survival skills.

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 Darwin and Wallace’s Findings:

• Darwin and Wallace

concluded that these
survival traits would
become more prevalent in
future populations of the
species through a process
called natural selection.

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▪ Fossils provide physical evidence of ancient
organisms and reveal what their internal structures
looked like.
▪ The world’s cumulative body of fossils found is called
the fossil record.
▪ This record is uneven and incomplete.

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The Genetic Makeup
of a Population Can Change
▪ The process of biological evolution by natural selection involves
changes in a population’s genetic makeup through successive
generations.
➢Note that populations—not individuals—evolve by becoming
genetically different.

▪ The first step in this process is the development of genetic

variability in a population.
➢Mutations

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▪ The next step in biological evolution is natural
selection
➢ Occurs when some individuals of a population have
genetically based traits (resulting from mutations)
that enhance their ability to survive and produce
offspring with these traits.

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▪Adaptation, or Adaptive trait – is any heritable
trait that enables an individual organism to survive through
natural selection and to reproduce more than other
individuals under prevailing environmental conditions.

▪ For Natural Selection to occur:

▪ A trait should be heritable.
▪ Inherited trait must lead to differential reproduction
▪ Organisms must have Genetic Resistance.

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Example:
Antidrug resistant bacteria
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▪ Note that natural selection acts on individuals,
but evolution occurs in populations.

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 ▪ Biological Evolution by Natural Selection Summary:

▪ Genes mutate,
▪ individuals are selected
▪ populations evolve that
are better adapted to
survive and reproduce
under existing
environmental
conditions

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When environmental conditions
change, a population of a species
faces three possible futures:

1. Adapt to the new conditions through natural

selection,
2. Migrate (if possible) to an area with more
favorable conditions,
3. or become extinct.
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 Biogeography of the
Philippines

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▪ Father of Evolution?
▪ Contribution of Alfred Russel Wallace to evolution?
▪ 3 important things needed for Natural Selection to
occur?
▪ Impact of the Philippine’s geographical location to its
biodiversity?

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 See you next meeting!

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