outline heterotrophs chemical composition and nutrient requirements defenses of the plants mimicry...
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OUTLINE
• Heterotrophs• Chemical composition and
nutrient requirements• Defenses of the plants• Mimicry• Evolution in defense mechanisms
and what they lead
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HETEROTROPHS
Heterotrophic organisms use organic molecules both as a source of carbon and as an energy source.
Major groups of heterotrophs:HerbivoresCarnivoresDetritivores
All these three groups face problems
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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?
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HERBIVORES• Herbivores are the organisms that
eat plant.• Problems that the herbivores face
- defense mechanisms of the
plants:1. physical defenses2. chemical defenses
• toxins•digestion-reducing substances
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1. Physical Defenses
• Thorns• Abrasive silica in the tissues• Toughened tissues with
cellulose and lignin
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2.Chemical Defenses
• Increased C:N ratio due to the cellulose and lignin content results in a carbon-rich; nutrient poor plant.
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• 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.
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• 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.
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• The further chemical defenses are grouped as toxins and digestion-reducing 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.
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• Chemists have isolated thousands of species and draw a conclusion: more tropical plants contain toxic alkaloids than do temperate species.
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• 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.
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Experiment: Generalization about high levels of chemical defense
among plantsRobin Bolser, Mark Hay
(1996)• Hypothesis: Tropical seaweeds
have more chemical defenses than temperate seaweeds.
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• 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.
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• 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.
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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.
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• 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.
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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.
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• 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.
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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
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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.
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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.
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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.
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The monarch butterfly (the model) contains noxious chemicals in its tissues.
The viceroy butterfly (harmless species) mimics monarch butterfly.
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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.
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White and black peppered moths.
Birds eat conspicuous members of the pepper moths.
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• 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)
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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.
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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.
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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.
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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.