Download Lect 04 The Evolution

Lect 04 The Evolution-Ecology
Connection
Some Plant and Animal Adaptations
to Environmental Factors
Plant and Animal Adaptations to Environmental
Conditions - Terrestrial Environments
• *Temperature Extremes
• *Water Issues
– Desiccation ------ Excesses
• Reproduction
• Competition for:
– Light
– Nutrients
– Pollen transfer
Temperature and Thermoregulation: Warmblooded vs. cold blooded
• Homotherms: constant body temperature
• Energetically expensive in cold temps
• Activity over broad range of temps
• Heterotherms: tend to maintain constant body
temperature when active – but due to size may
allow temp. to drop when inactive
– Examples: daily temp. cycles assoc. with small
mammals, birds
– Seasonal – true hibernators
• Poikliotherms: body temperature varies
• Loss of activity with cold temps
• Tend to employ behavioral strategies to maintain
temperature
Thermoregulation
• An animal must balance heat gain and loss to maintain its
core body temperature
– The core exchanges heat with the surface area by
conduction
– Influenced by thickness/conductivity of fat, movement of blood to
surface
– The surface layer exchanges heat with the environment
via convection, conduction, radiation, and evaporation
• Terrestrial animals face more extreme
(and dangerous) changes in thermal
environment than aquatic animals
• Aquatic animals live in a more stable
energy environment
Hstored = Hmetabolism + Hconduction + Hconvection +
Hradiation + Hevaporation
– The heat energy from metabolic processes
(Hmetabolism) is always positive
– The heat energy from conduction, convection,
radiation, and evaporation can be positive or
negative
heat of
Body heat = metabolic
activities
heat gained/lost
+/- from various
sources
• Endothermy: the process of generating body
heat through metabolic processes
• assumes sufficient nutrients can be obtained to
maintain body temperature
• Metabolically/energetically expensive
• Relied on heavily by homotherms/heterotherms
• Ectothermy: process of gathering heat energy
from the environment
• Energetically inexpensive
• Major means of thermoregulation by
poiklotherms
• What allows some poikliotherms to function over a broad range
of temperatures?
Acetylcholinesterase
in a Poikilotherm:
Rainbow Trout
• Degrades
acetylcholine –
neurotransmitter
• Two forms
– 2 C - winter form
– 17 C – summer form
Counter-current heat
exchange ~ Poikilotherm
• Thermo-regulation of
swim muscle in Tuna and
Sharks
• Warm blood leaving
muscles warms blood
entering
Homotherms and the Thermoneutral Zone:
• Temperature range over which metabolic rate does not
change – basal metabolic rate maintained
• Outside of this range maintenance of body temperature
comes with a metabolic cost
• The thermoneutral zone is a range of environmental
temperatures within which the metabolic rates are minimal
• Metabolic rate increases beyond the critical temperatures
above and below the thermoneutral zone
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Mechanisms/Adaptations impacting TMZ
Behaviorial traits
Insulation
Countercurrent heat exchange mechanisms
Vasoconstriction/vasodilation effects
Bird on Ice: thermal
regulation via heat
exchange
• Blood entering feet
warms blood
returning
• Other mechanisms
– Cutaneous circulation
reduced with cold
temps
• Raynaud’s syndrom – an example of a faulty
thermoregulatory process
Cooling in homotherms:
• Perspiration
• Shading
• Panting
• Vasoconstriction/vasodilation
• Countercurrent circulatory mechanisms –
redirecting of blood flow
• Behavior
• Radiating surfaces
• Keeping heat out
– The oryx cools the
brain by cooling
venous blood via
evaporation in the
sinus cavity
Heterotherms – regulate temp
when active – but may allow
temp to fall otherwise
Hibernation:
• Period of reduced metabolic
rate
• Fat reserves provide energy
Torpor: esp in small creatures
• Enter torpor if food
unavailable
• Torpor  low metabolic
rate, even at high temps
Temperature optima
• Mesophiles: optimal growth 20-45C
• Thermophilic – adapted to high temperature
• Psychrophilic – adapted to cold environment
• Acclimation – physiologic adaptations
– Physiological change
Decreasing Water Loss from
Foliage – Different
Approaches:
• Summer Deciduous: Loose
leaves during warm/dry
season
• Geophytes: retain food &
water in subterranean bulb
during dry months
• Annuals: complete life
cycle before dry season
begins – over-summer as
seed
More Drought
Evasion
Strategies
• Low growth habit
(reduced wind
exposure)
• Hirsute leaves
• Leaf size/shape
• Leaf coloration
CO2 necessary for photosynthesis
enters passively
stomata have to be open for long
periods of time
Water loss a serious
problem in low RH
climates
Strategies for decreasing water loss via leaves:
• Protect stomata:
– Strategies:
• sunken in pits or grooves
• Obstructed by hairs, wax tubules
• More frequently found on undersides of leaves
• Develop small, thickened, wax coated leaves –
sclerophyllous
– Typically evergreen – most photosynthesis during
spring/autumn
– Tough/fibrous, poor nutritional quality, aromatic
oils act as defense
Roots with different water seeking strategies in dry
climates
• Dual root systems:
– Thick taproot –
– Mat of fine roots close to soil surface
• Coast Redwood
– Shallow root system
• Ca 6 ft. from surface
– Reliance on summer
fog drip limits range
Survival Following Fire: Sprouters and Seeders
• Sprouters: develop from burls or root crown
(lignotuber)
– May also develop from bud wood protected
beneath bark (redwoods do this for example)
• Seeders:
– Refractory seed survive prolonged fire
– Germination stimulated by heat, volatile smoke
related chemicals
– Fire followers
– Ashes of fire provide nutrients
Adaptations of Plants in CA
Chaparral:
• Tiered root system with
high root system: foliage
ratio
• Sclerophyllous, small
leaves
• Regeneration following
fire
Wetland Environments Present Unique
Constraints on Plant Adaptations
• Too much water can stress plants as much as
too little water
– The symptoms of excess water are similar to
symptoms of not enough water!
• Plants need sufficient water and rapid gas
exchange with their environment
– Much of this exchange occurs in the soil
– When soil pores are filled with water, roots are
essentially drowned as they switch to anaerobic
respiration
• In the response to anaerobic or flooded
conditions
– Some plants accumulate ethylene in their roots
– Stimulates cells to self-destruct and form gas-filled
chambers called aerenchyma
– Flooded roots die and adventitious roots emerge
above where oxygen is available
– Shallow root systems develop in poorly drained
soils
– Pneumatophores are specialized growths of the
root systems of plants growing where the water
table fluctuates
Salts
Hyperosmotic or Hypertonic – more dissolved substances
outside cell
water leaves the cell  crenation (like a pickle)
Hypoosmotic or Hypotonic – less dissolved substances outside
water enters the cell  cell swells and bursts
Isoosmotic or Isotonic – same concentration inside and out,
the cell is at dynamic equilibrium
Wetland Environments Present
Unique Constraints on Plant
Adaptations
• Halophytes are plants that take in water
containing high levels of solutes
• For a halophyte to maintain a water potential
gradient, they:
– Accumulate high levels of ions within their cells
(especially leaves)
– Dilute solutes with stored water
– Secrete salt onto the leaf surface to be washed away
by rainwater
• The degree of salt tolerance varies greatly in
different halophytes
• Pickle Weed: adaptations to salty
environments
• Concentrates salt – thus water is absorbed
from brackish waters