Transcript Herbivory and Plant Defenses - Powerpoint for Oct. 19.

Herbivory
Monarch caterpillar and Milkweed leaf
Plant Resource Defense
• Qualitative defense - highly toxic substances,
small doses of which can kill predators
• high nutrient environment/fast growth (high
turnover in plants) - use toxins (plant
secondary compounds) that often require N,
expensive to make (must be replaced often),
but can be made rapidly - cyanide compounds,
cardiac glycosides, alkaloids - small molecules
Plant Resource Defense
• Quantitative defense - substances that
gradually build up inside an herbivore as it eats
and prevent digestion of food
• low nutrient environment/slow growth (low
turnover in plants) - primarily use carbon
structures - wood, cellulose, lignin, tannins large molecules - makes plant hard or
unpleasant to eat (woodiness, silica), but plants
are slow to make these defenses
Evolutionary “Arms” Races
Monarch and milkweed
Evolutionary “Arms” Races
Evolutionary “Arms” Races
California garter snake
Pacific newt
Other Plant Defenses Include:
• mechanical defenses - plant thorns and spines deter
many vertebrate herbivores, but may not help much
against invertebrate herbivores
• failure to attract predators - plants somehow avoid
making chemicals which attract predators
• reproductive inhibition - some plants such as firs
(Abies) have insect hormone derivatives which if
digested, prevent successful metamorphosis of insect
juveniles
• masting - the synchronous production of very large
numbers of progeny (seeds) by trees of one species in
certain years
Traumatic Resin Ducts –
Norway Spruce
Produces terpene containing resins to inhibit feeding
Eurasian Jay with Acorn
Masting
Masting
Fagus sylvaticus – European Beech
Dipterocarp distribution
Dipterocarp trees
Dipterocarp seeds
Beech seeds and boring moth
Lyme’s disease life cycle
Masting and Human Health
- Lyme’s Disease
Induced Defenses
• Another aspect of plant defenses is that plants
do not always have tissues loaded with
defensive chemicals - in many plants,
defensive chemicals are only produced when
they are needed, usually after the plant has
experienced some herbivory - this is an
induced defense
Impact of Herbivores Is Not
Uniformly Experienced
Aphids attacking Alfalfa
Spotted Alfalfa Aphid
Induced defenses in Birch Trees
Induced defenses in Birch Trees
Induced defenses in Birch Trees
Rubus prickles
Acacia depanolobium
Giraffe and Acacia
Plant defenses are developed at a cost
to fitness when:
1. Organisms evolve more defenses if they are exposed
to much damage and fewer defenses if cost of defense
is high
2. More defenses are allocated within an organism to
valuable tissues that are at risk
3. Defense mechanisms are reduced when enemies are
absent and increased when plants are attacked mostly true for chemicals not structures
4. Defense mechanisms are costly and cannot be
maintained if plants are severely stressed by
environmental factors
Plant defenses are developed at a cost
to fitness when:
1. Organisms evolve more defenses if they are exposed
to much damage and fewer defenses if cost of defense
is high
2. More defenses are allocated within an organism to
valuable tissues that are at risk
3. Defense mechanisms are reduced when enemies are
absent and increased when plants are attacked mostly true for chemicals not structures
4. Defense mechanisms are costly and cannot be
maintained if plants are severely stressed by
environmental factors
Pine beetle infestation – British Columbia
Pine Beetle and Pitch Tube
Serengeti Grazing System
Serengeti Grazing System
Serengeti Grazing System
•
•
•
•
•
1 million wildebeest
600,000 Thompson’s gazelles
200,000 zebra
65,000 Cape buffalo
Unknown numbers of 20 other species of large
grazing mammals
• 36 species of rodents
• 38 species of grasshoppers
• Area of about 23,000 square kilometers
Serengeti Grazing System
Grazing facilitation
• Grazing facilitation occurs when the feeding
activity of one herbivore species improves the
food supply for a second species
Opuntia stricta – prickly pear
Prickly pear infestation in Australia
Area infested with prickly pear before biocontrol
Same area after biocontrol
Biocontrol Agent – Cactoblastis cactorum
Symbiosis
Symbiosis
• Symbioses - species living in close
association
• Parasitism +,- parasite benefits, host
harmed
• Commensalism +,0 or 0,0 can have
positive effect for one species or for
neither
• Mutualism +,+ both species benefit
Gopher Tortoise – Commensal Host
Gopher Tortoise Distribution
Epiphytes
Bird’s Nest
Fern
Nalini Nadkarni
studying
epiphytes
Epiphytes
Figure 1: Hypothetical tree illustrating how
vascular epiphytes in humid forests tend to
partition substrates illustrating sensitivity to
micro climate, particularly humidity, and
associated development of the organic rooting
media required by some populations.
Parasitism and Disease
Lyme Disease Cycle in the UK
Parasitism
• Parasitism - intimate association between two
species in which the parasite obtains its
nutrients from a host - parasite usually causes
some degree of harm to its host - either
reduced growth or reproduction
• Pathogen – disease causing agent
• Disease – abnormal condition of host due to
infection by a pathogen that impairs
physiological functioning