Transcript HETEROTROPHS

OUTLINE
• Heterotrophs
• Chemical composition and nutrient
requirements
• Defenses of the plants
• Mimicry
• Evolution in defense mechanisms
and what they lead
HETEROTROPHS
Heterotrophic organisms use
organic molecules both as a source
of carbon and as an energy source.
Major groups of heterotrophs:
Herbivores
Carnivores
Detritivores
 All these three groups face
problems
CHEMICAL COMPOSITION
AND
NUTRIENT REQUIREMENTS
• Elemental composition of the
organisms
• C:N ratio in organisms
• Additional nutrients
• How do plants and animals supply
their nutrient requirements?
HERBIVORES
• Herbivores are the organisms that
eat plant.
• Problems that the herbivores face defense mechanisms of the plants:
1. physical defenses
2. chemical defenses
• toxins
• digestion-reducing substances
1. Physical Defenses
• Thorns
• Abrasive silica in the tissues
• Toughened tissues with cellulose
and lignin
2.Chemical Defenses
• Increased C:N
ratio due to the
cellulose and
lignin content
results in a
carbon-rich;
nutrient poor
plant.
• If a pine tree is
considered; tree
trunks occupy
most of the area,
creating a biomass
that has a C:N
ratio of 300.1.
• What is more, most of the animals
cannot digest cellulose or lignin.
• These animals overcome this
problem by the help of the bacteria,
fungi or protists that live in their
digestive tract.
• The further chemical defenses are
grouped as toxins and digestionreducing substances.
• Toxins: kill, impair, repel most of
the would-be consumers.
• Digestion reducing substances:
compounds that bind to plant
proteins, inhibiting their
breakdown by enzymes and further
reducing the nitrogen availability
which is already low.
• Chemists have
isolated thousands
of species and
draw a conclusion:
more tropical
plants contain
toxic alkaloids
than do temperate
species.
• Although plants have evolved
higher levels of chemical defenses,
herbivores can still consume
approximately %11-%48 of the leaf
biomass in tropical forests.
• Despite the fact that the plants in
temperate forest have lower levels
of chemical defenses, herbivores
only consume %7 of the leaf
biomass.
• Conclusion: Natural selection for
chemical defense is more intense in
tropical plant populations.
Experiment:
Generalization about high
levels of chemical defense
among plants
Robin Bolser, Mark Hay (1996)
• Hypothesis: Tropical seaweeds have
more chemical defenses than
temperate seaweeds.
• They collected several species of
seaweeds from:
North Carolina (temperate species)
Bahama Islands (tropical species)
• Same species or at least, species
that belong to same genus were
taken.
• Palatability of the seaweeds was
tested using temperate and tropical
sea urchins.
• Results:
– Clear preference for temperate species
of seaweeds.
– Both temperate and tropical sea urchin
species preferred temperate species of
seaweeds.
– Additional tests showed that tropical
seaweed species possessed more
intense chemical defense.
No defense is perfect…
• Most defenses of the plants work,
but not all.
• The tobacco plant uses nicotine to
repel herbivorous insects, which
suddenly die after ingesting
nicotine.
• However, some species can excrete
nicotine or convert it to non-toxic
molecules.
• Spotted
cucumber
beetle is
attracted by
the toxins and
repellents
unlike other
insects.
• Some
specialized
herbivores can
even use toxins
as a source of
nutrition.
DETRITIVORES
• Detritivores (detrius feeders or
saprophages) feed on nonliving
organic matter.
• They obtain nutrients by consuming
detrius.
• They play a crucial role in nutrient
cycling.
• They consume carbon and energy
rich, but nitrogen poor food.
• Plants already have low nitrogen
content. When their leaves are cast off,
they contain even lower amounts of
nitrogen.
• Low nitrogen content of the detritus
results in nitrogen poor food for
detritivores.
• Average nitrogen contents of the living
and nonliving leaves from tropical rain
forests through deserts and temperate
forests showed that living leaves contain
about twice the nitrogen as dead leaves.
CARNIVORES
• Carnivores mainly feed on animal
flesh.
• Their prey are nutritionally rich.
• Their problems about nourishment:
– They cannot go out from their
environment
– They do not choose prey at will
– Prey usually have good defense
mechanisms
Defense mechanisms of prey
• Basic defense: camouflage.
• Anatomical defenses: spines, shells,
repellents, poisons.
• Behavioral defenses: flight, taking
refuge in burrows, banding together
in groups, playing dead, fighting,
flashing bright colors, spitting,
hissing, screaming at predators.
Aposematic coloration:
“think twice before feeding on
me”
• Aposematic:
Conspicious, bright
colors that warns
predators about the
possibility of poison.
• Aposematic
coloration is usually
consists of
contrasting patches
of orange, yellow and
black.
MIMICRY
• Mimicry: similarity in appearance.
– Müllerian mimicry : Among noxious
species. (stinging bees, wasps,
poisonous snakes, butterflies)
– Batesian mimicry : Harmless species
mimic noxious species, taking them as
a model.
The monarch butterfly (the
model) contains noxious
chemicals in its tissues.
The viceroy butterfly
(harmless species) mimics
monarch butterfly.
How have prey populations
evolved their defenses?
• H. Kettlewell (1959) found that predation
by birds favors camouflage.
• Birds choose conspicuous members,
leave better camouflaged ones. Namely,
predators eliminate poorly defended
prey and leave the well defended ones.
• Conclusion: average level of defense
increases with time.
White and black peppered
moths.
Birds eat conspicuous
members of the pepper
moths.
• As a consequence of good prey
defenses, prey capture rate by
predators is low.
• Observations about bald-faced
hornets showed that they rapidly
pounce on inanimate objects as they
may be prey. Their prey capture
rate was found to be less than %1.
(Bernd Heinrich, 1984)
Carnivor preys usually
similar in nutrient content
• Carnivores are widely distributed
geographically; their diets can vary
from one place to other.
• Variety in prey is related with the
availability of the prey.
Size-Selective
Predation
• Predators must catch
and subdue their prey.
• It’s most common in
solitary predators; like
Puma concolor.
• Puma size changes
depending on the
latitudinal gradient; and
prey size is directly
proportional with the
predator size.
Size selective
predation has
two reasons:
1. Large prey is
hard to subdue
and may even
injure the
predator; small
prey is difficult to
find or catch.
2. Energetic basis.
Results of predator-prey
relationships
• Predators consume nutritionally rich
prey but face with well defended and
strong prey.
• Predators eliminate poorly defended
members, leading average prey defenses
improve.
• Improvement in average prey defenses
make poor predators be eliminated and
leave fewer offspring.
• Improvement in hunting skills lead
further natural selection.