Transcript evolution, biological communities, & species

EVOLUTION, BIOLOGICAL
COMMUNITIES, & SPECIES
INTERACTIONS
CHAPTERS 6 and 7
What are we learning about in this
chapter?
• We will examine specific ways organisms are
limited by the physical aspects of their
environment.
• We will discuss how members of a biological
community interact.
• We will answer questions like why does a
particular species live where it does? How is it
able to live there? How does it deal with the
physical resources of its environment? How
does it interact with others? What gives one
species an edge over another?
Lamark’s Theory of Evolution
• Believed that organisms
acquired characteristics
throughout life and then
passed these onto their
offspring.
• “Inheritance of acquired
characteristics”
• If giraffes stretch during life
to reach trees, then their
offspring will have long
necks.
• Does a body builder produce
a baby with bulky muscles?
Darwin’s Theory of Evolution
• Collected specimens on voyage of
the Beagle.
• Returned to England & over 40
years developed his theories on
natural selection & evolution.
• Used Thomas Malthus’ Essay on
the Principle of Population to help
him develop his theories.
• His theory of evolution by natural
selection is…
– Most organisms produce more
offspring than can survive.
– Those with better attributes will
survive, others will die
– Those that survive pass on fit traits
to offspring resulting in entire
population with that fit trait.
• Presented his theory in book, On
the Origin of Species in 1859.
How would Darwin describe Giraffe
evolution?
• Some giraffes had
long necks, some
short
• Those with long
necks reached the
food, those with short
starved
• Long necks mate and
produce population of
long necked giraffes.
What do Darwin’s theories
assume?
• Different traits or
properties must be
present in a population
• These traits must affect
reproductive success
• The traits must be genetic
• Some selective pressure
must favor these traits
differently.
• We now know that these
traits can be the result of
mutations in DNA
What types of selective pressures
can influence a population?
•
Limiting factors determine distribution
and population size of different species
– Temperature, moisture, nutrient supply,
soil, water chemistry, predation,
competition
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Tolerance limits- minimum & maximum
limits for an organism
Critical factor- usually one specific
limiting factor that limits populations
– Ex: Saguaro cactus very sensitive to
low temperatures.
•
Many species of plants & animals are
so sensitive to environmental change,
they can be used as environmental
indicators to determine health or
components of an ecosystem
– Ex: trout sensitive to pollution so
presence or absence of them indicates
water quality; Lichens indicate air
pollution/acid rain problems
Can evolution be forced by
humans?
• Selective breeding for
traits in plants &
animals
• Pesticide usage has
led to the rapid
evolution of
resistance in insects
• Overuse of antibiotics
has led to evolution of
microbes
Now that we know why organisms
are different, lets discuss how they
interact…
• Everything has a habitat- place
where it lives.
• Everything has a niche- or role
in its habitat. How it gets food,
interacts with other
populations, or service it
provides to community.
• Generalists- wide range of
food & habitats (raccoons,
cockroaches)
• Specialists- specific food
sources & habitats (pandas);
less resilient to changes in
environment
What is the Law of Competitive
Exclusion?
• No two species will occupy
the same niche and compete
for exactly the same
resources in the same
habitat for very long.
• Eventually, one species will
outcompete the other and
push the weaker species out
of the habitat, or cause its
extinction.
• Could result in two
insectivores feeding in same
tree, just at different times of
the day.
More on competition…
• Compete for food, chemical nutrients in
soil, space, mates, etc.
• Intraspecific- competition within a species
– Trees provide shade so their own
seedlings can’t grow underneath them
so no competition for sun
– Caterpillars eat leaves while adult
butterflies eat nectar. Reduces
competition for food sources
– Some create a territory to prevent
competition
• Interspecific- competition between two
different species
– Ex: when different weeds produce
numerous seeds & race to cover most
ground
– secrete substance that inhibits root
growth
– different herbivores on savanna
compete for grasses
Besides competition, how else do
species interact?
• PREDATOR-PREY
• Predator- an organism
that feeds directly upon
another living organism,
may or may not kill prey
• Includes herbivores,
carnivores, omnivores
• Help force evolution of
prey species
• Leads to coevolutionexert selective pressure
on each other- evolve in
response to each other
How else do species interact?
• PARASITE-HOST
• Parasites feed directly
on another living thing
but do not kill it in the
process.
• Ex: ticks suck blood
from dog
How else do species interact?
• COMMENSALISM
• one member benefits, the
other is not substantially
benefited or harmed.
• Ex:
– cattle egrets feed on
insects stirred up by
grazing cattle
– Clownfish gets protection
from sea anemone which is
not helped or harmed by
fish.
– Bromeliads grow on tree
branches to reach sunlight
How else do species interact?
• MUTUALISM
• Both members benefit
significantly from the
relationship
• Ex:
– Lichens- combo of fungus
(provides water & place for
algae to grow) and algae
(provides food for both)
– Insects & their pollinators
– Ants and acacia trees
How else do species interact?
• KEYSTONE SPECIES
• A species or group of species whose
impact on a community are much
larger than would be expected from
mere abundance.
• Ex: sea otters & kelp beds; tropical figs
& frugivores (fruit eaters)
• http://www.grinningplanet.com/2004/06
-22/keystone-species-article.htm
• Keystone species increase niche
diversity because without them other
species cannot survive- may either
move to new habitat or become locally
extirpated
How do organisms defend themselves
against predation & parasitism?
• Chemical defense- smell bad
or taste bad
• Batesian mimicry
– Harmless species mimics
harmful
– Ex: monarch butterfly &
viceroy butterfly; moth has
eyespots, looks like owl
• Mullerian mimicry
– Two species that are harmful
develop same patterns/colors
– Most wasps have yellow/black
banding patterns
• Camouflage- look like dead
leaves or twigs or even bird
poop
What are some fundamental properties
of biological communities?
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Productivity
Diversity
Complexity
Resilience
Stability
Structure
Productivity
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Rate of biomass production which
indicates the rate of conversion
from sun to food.
Energy left after respiration
(breaking down food to get
energy) is called net primary
productivity
Needs for productivity:
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High light levels
High temperature
High moisture
High nutrient availability
See Figure 4.18
Tropical rainforests, estuaries, and
coral reefs all have high levels of
productivity because all have met
requirements listed above.
Abundance & Diversity
• Abundance- total # of
organisms in a biological
community
• Diversity- # of different
species in a community.
• Usually this is an inverse
relationship…
• Rainforest is very diverse,
but only a few individuals
of each species.
• Tundra is overflowing
with flying insects, but
usually only a couple of
different species.
Complexity
• Number of species at each
trophic level and number of
trophic levels in a community
• Diverse community may not be
complex if all species are
located at 1 or 2 trophic levels
• Some complex communities
have specially adapted
populations which helps to
reduce competition
– Ex: herbivores are grouped
based on what part of plant
they eat- fruit, seed, root, leaf
Resilience & Stability
• 3 kinds
– Constancy- lack of fluctuation
– Inertia- resistance to change
– Renewal- ability to repair
damage after disturbance
• The more complex &
interconnected a community is,
the more stable and resilient it
will be when faced with a
disturbance. Should be able to
recover easily from
disturbance.
• Can diversity make an
ecosystem less resilient rather
than more?
Community Structure
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Structure- spatial distribution of
individuals & populations & how they
relate to environment
Random distribution– Live where resources are available
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Clumped distribution
– Populations are clustered
– Protection, reproduction, mutual
assistance
– Ex: hunt in packs, schools of fish,
mating season causes clumping
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Uniform distribution
– Usually result of competition &
territoriality; nesting sites, roots of
sagebrush release toxins to keep other
plants away from it
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Vertical distribution
– Animals feed at different levels to
reduce competition
– Tropical rainforest, African savanna,
aquatic ecosystems
Community Structure
• Ecotones- boundary
between one habitat
and another.
• From forest moving
toward field- closed
community
• If edge is less distinct,
animals move in & out
of each habitat- open
community
Community Structure
• Shape of environment is
as important as size.
• Some animals need a
large “core” for protection,
establish territories,
feeding, etc.
• Some environments are
irregularly shapedfragmented- which
reduces cover for animals
How do communities come to
exist?
• Succession- process
by which organisms
occupy a site and
gradually change
environmental
conditions by creating
soil, shade, shelter, or
increasing humidity.
Primary Succession
• Occurs when a
community begins to
develop on a site
previously unoccupied by
living organisms
• Ex: volcanic island,
glacier retreating
• Pioneer species- lichens,
moss, microbes that don’t
need soil to grow.
Secondary Succession
• When an existing
community is
disrupted and a new
one develops at the
site
• Ex: deforestation,
fire, flooding, mining,
natural disaster,
fallow crop land
• Pioneer speciesgrasses, annuals
Primary vs. Secondary
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Primary succession
– Lichens, mosses, break down rocks
create soil
– Annuals, wildflowers that have
lightweight seeds, tolerate sun &
exposed soil, soil thickens
– Perennials, grasses, shrubs,
outcompete annuals which die, soil
thickens
– Sun-loving evergreen trees move in,
outcompete grasses for sun, soil
thickens
– Evergreen seedlings cannot compete
with parent trees, shade-loving
deciduous trees move in, outcompete
evergreens and take over.
– Climax community- community that
resists change; has all plants & animals
can hold.
– Takes a long time because soil has to
be established
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Secondary Succession
– Soil already established
– Annuals, wildflowers that have
lightweight seeds, tolerate sun &
exposed soil, soil thickens
– Perennials, grasses, shrubs,
outcompete annuals which die, soil
thickens
– Sun-loving evergreen trees move in,
outcompete grasses for sun, soil
thickens
– Evergreen seedlings cannot compete
with parent trees, shade-loving
deciduous trees move in, outcompete
evergreens and take over.
– Climax community- community that
resists change; has all plants & animals
can hold.
– Takes less time- soil is already formed
Abiotic factors & succession
• As plants move in, the abiotic
factors within an ecosystem
change- this leads to
changes in more biotic
factors.
• Biomass accumulates & the
ecosystem becomes more
rich, able to capture more
moisture, sheltered from
wind/climate, biologically
more complex.
• As plants colonize, animals
are attracted.
Fire-climax community
• Community that is
shaped or maintained
by fires
• Grasslands,
chaparral, coniferous
forests
• Often called
equilibrium
communities or
disclimax
communities
How are organisms adapted to fire
climax communities?
• Resistant to some
degree to fire
• Reseed quickly after
fire
• Need fire to pop open
seed coating (jack
pine)
• Reduces competition
What can threaten biological
diversity?
• Introduced speciesspecies not native to
a particular area.
• Usually outcompete
or prey on native
species
• Usually do not have a
natural predator to
limit their populations.
Introduced Species
• Sometimes escape from
ships onto islands…
• Livestock outcompete
native animals & plants
• Trample & compact soil
• Native island organisms
have not evolved
defensive mechanisms
against predators
• EX: goats, cats invading
bird nests, pigs & rats
digging up sea turtle
eggs, invade nests
In Hawaii, Silversword plant became
endangered when feral pigs, goats, &
sheep overconsumed the plant
Introduced Species
• Sometimes introduced to
solve problems in an
ecosystem- but cause
problems instead.
• Mongoose introduced in
Hawaii to kill rats, rats are
nocturnal, mongoose is
diurnal so they did not
interact. Instead
mongoose contributed to
problem by killing native
birds instead of rats.
Introduced Species
Cane Toads• Introduced in Australia to
control sugar cane
beetles in 1935
• Prolific breeder
• Has poison glands so kills
or sickens anything that
might prey on it.
• Has outcompeted native
amphibians, killed native
predators.
Zebra mussels
covering crayfish
Other invasive
species…
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Zebra mussels
Snakehead fish
Kudzu
Dandelions