Part I: Study questions
for Chapter 3 (covers Wed & Fri): page 110: 1,2 (3 in leture), 4-7,10
Part II: Temperature considerations
To put the topic of this lecture in perspective..
STUDY LOOKS AT TEMPERATURE CHANGES
A temperature change of only a few degrees can disrupt
a community of animals, according to a researcher who studied how hot and
cold affects the delicate balance of starfish and mussels in Oregon's tidal
waters. Eric Sanford of Oregon State University said his study, published
in the journal Science, suggests that if a key species in a community of animals
is particularly sensitive to temperatures, a slight warming or cooling can
start a whole cascade of rapid changes affecting every animal in an ecosystem.
Sanford found a 5-degree change in temperature is enough
to change dramatically the feeding habits of the starfish, a five-armed creature
that feeds mainly on mussels and is common along the Pacific coast of the
United States. The finding, said Sanford, has important implications for understanding
the effects of global warming.
"Many people have assumed that the effects of climate change would be gradual,"
the researcher said in an interview. "But this shows that if an important
species in a community is highly sensitive to temperature, then the effects
of a small temperature change can happen rapidly."
In his study, Sanford tracked the feeding
patterns of starfish kept in the laboratory at different temperatures. He
checked his results by manipulating the population of starfish and mussels
in two areas along the Oregon coast.
Sanford found that a temperature drop
of 5 degrees caused the starfish to virtually stop feeding on the mussels.
This allows the mussels to rapidly expand in population. Conversely, when
the water temperature was increased by 5 degrees, Sanford said starfish
went on a feeding binge,quickly reducing the population of mussels. Either
way, he said, there are dramatic changes in the tidal community of animals.
When mussels are not controlled by starfish,
said Sanford, their population explodes. The mussels attach themselves
to every surface in the near-shore tidal zone, crowding out barnacles, algae
and other organisms. "If you take away the sea stars, then you go from an
ecosystem with a diverse population of species to a system where there is
essentially only one species," Sanford said.
When starfish eat too much, he said, the reef-like
mussel communities quickly start falling apart. These reefs, Sanford said,
are homes for crab, sea cucumbers and worms, all important parts of the ecosystem.
Temperatures along the Oregon coast are affected by upwelling, cold deep waters
surging to the surface. The frequency of upwellings, said Sanford, is determined
by winds that, in turn, are affected by global temperatures. If cold upwellings
become less frequent, starfish may eat more mussels, said Sanford; if the
upwellings happen more often, thus cooling the tidal waters, starfish will
eat less, allowing the mussel population to suddenly explode.
Today will concentrate on how an organism controls its body temperature in
relation to ambient conditions....given that organisms can't always control
the external temperature.. how is it that they can at least maintain their
own body temperatures-
The following 'processes' are used by most all
organisms to regulate their body temperature:
I. Direct solar radiation: how can this lizard
or any organism control the amount of solar inception? look carefully at the
diagram... how can changes in:
maximize or minimize solar interception?
II. Conduction is the transfer of heat through bodily contact with
rocks, vegetation. How can this process be controlled by an organism?
| 
|
Lizard..... here I am
contented lizard
I spend my days
belly to the sun
stretching out
without fearing
the dagger of my imperfections
(M. Sanchez)
What is the significance of this poem to a lizard? go back after discussing
the following section on strategies.
|
III. Infrared radiation: what wavelengths are we talking about here?
not the high (UV) but low energy range we perceive as 'heat'
IV. Convection: +/- transfer from object to fluid where a fluid can
refer to water or air...( a non-solid )
The rate of transfer to a fluid from a form or vis versa is a function of
the difference in temperature between the 2 media.
Factors which affect flow or exchange of heat: shape, velocity of fluid, physical
properties of fluid.
How would a ball shape organism respond differently than a linear shaped organism?
V. Metabolic internal generation of heat. What is the expense of heat
generation?
VI. Evaporation:
1. Lungs: try a simple experiment - exhale onto to the palm of your hand.
What is the temperature of the exhaled air? where did this heat come from?
also consider the vapor -- water converted to gaseous form. Now consider how
much air you exhale during a day and then figure the heat loss via breathing.
Volume of air x (difference between 100% saturated incoming air) x latent
heat of vaporization ( 1 gm of H20 into vapor)
2. Sweating: loss of heat through same process via the eyes, ears, skin. Again,
how can a body control this loss? If you know all these values you can predict
the climate space of an individual
In spite of all the ways a lizard can gain or lose heat, the variance in
lizard body temperature may be as little as 4-5 C
Strategies of dealing with temperature
I. Non-regulators:
no control via physiological controls; instead they use behavioral
modifications to alter body temperature.
Ex burrowing in ground, nocturnal as we discussed in previous lecture
| - Costs? limited environment in which they
can survive & reproduce - the soil can't be too cool or too hot.
Fortunately in the temperate climates most soils deeper down stay
a near constant 50-55 F year round.
|
| + Gain? more efficient use of food . How
important is this? consider the loss of calories by a mammal- it may
be as high as 80-90% for metabolic costs, whereas a nonregulator may
only lose 60% or less to metabolism. How much more food does one have
to search for to compensate? |
II. Heliotherms:
maintain near constant temperature by
primarily regulating the amount of solar radiation input along with control
other vectors (conductance etc.)
Ex. lizard
| - Costs: |
+ Gains: |
| *except in tropics must remain relatively
small in size (remember surface area to volume considerations): too
large a lizard could not absorb enough heat to warm a high volume
area.
|
*biomass is cheap to sustain;
|
| *can be active only at certain times of
day, seasons-If not careful may be unable to move when they need to.
Dead snakes and alligators on the road are often due to staying too
late on the road, cooling down too fast and not having enough energy
to get back off the road before being hit. |
*less time foraging for food which means
less exposure to potential predators.
|
| *limited environmental expansion
|
*reduced metabolic rate may increase longevity |
| *activity may be short-lived; can easily
become anaerobic as enzymes necessary for metabolism only function
within a certain temp range. |
|
III. Endotherms:
metabolism produces heat to maintain constant body temperature; Blood flow,
breathing, sweating, insulation all help in regulating body temp
Ex. mammals, birds
| - Costs: |
|
+Gains:
instant control of body temperature means they
can live in many environments |
| *expensive to burn off calories so must
forage a lot.. which then forces them to be exposed a longer time
period to predators.
|
| *high oxygen demand - must get enough oxygen
for production of ATP
*some size considerations- more efficient with
a larger body- too small, lose heat to readily- small mammals have
high metabolism to compensate. Little mice lose so much heat due to
shape, and must burn so many calories that it shortens their live
span. Generally the higher the metabolic rate the shorter the life
span as with metabolism comes the production of some toxic by productions. |
| |
Basal metabolism and whales...from (http://216.239.41.104/search?q=cache:pFXlOxzgWRYJ:www.phys.virginia.edu/classes/304/scaling.pdf+Klieber%E2%80%99s+Law&hl=en&ie=UTF-8)
" What determines the ultimate length a whale can grow to? Several factors
combine to limit its size (which may be the largest possible size for any mammal):
the need for oxygen and food increases as the cube of its length, but the generation
of energy to sustain life also means the production of waste heat. The surface
of a whale must be sleek
so it can swim rapidly. This means it can not have projecting radiator fins
(other than its swimming apparatus, of course). But then the whale’s ability
to get rid of its excess body heat, even in very cold water, is limited by the
surface area, which increases only as the square of its length. Basal metabolism
of mammals (that is, the minimum rate of energy generation of an organism) has
long been known to scale empirically as
B=dQ/dt =const. (Mass)3⁄4
.
The origin of this relation, sometimes called Kleiber’s Law, has been
explained by West, et al.in terms of optimizing the pumping efficiency for fluid
flow in the circulatory and pulmonary systems of mammals. They notethat the
terminus of a capillary or alveolar duct must necessarily be of constant size,
independent of animal mass. Since the arterial network and bronchial systems
each have a tree- like structure, and since the sub sections of the tree are
self-similar (“fractal”) what determines the size of the entry—the
aorta or the trachea, respectively—is the ratio of branch diameter to
branch length, and the fact that the branches are (almost)
always bifurcations When this ratio is chosen to minimize resistance to flow,
hence pumping power, Klieber’s Law emerges. The largest whales are certainly
at the ragged edge, maintaining a precarious balance between energy
production and heat dissipation. When a whale dies (by being killed by hunters,
e.g.) and its heart
stops circulating the blood (which acts like the coolant in a radiator), its
flesh actually cooks within its jacket of blubber because the residual metabolic
heat production has no way to escape. The temperature rises, therefore (the
onset of decay from bacterial action accelerates this process). Some of the
old-time whalers apparently enjoyed whale meat “cooked” in this
fashion"
IV. Heterotherms: use multiple strategies
-->Helio when solar conditions are good
-->Endo ( metabolic) when solar conditions are poor ( early am) 1
Ex. adult insects, some fish, some birds will warm-up and shiver to generate
heat for flight, then use solar energy as becomes available.
Torpor and hibernation
Torpor: bats, hummingbirds will go to ambient T
when resting to conserve metabolic losses.
Hibernation: as CO2 levels in body increase -->
respiratory acidosis --> reduced metabolic rate and lowered cellular processes.
Few animals go through true hibernation. Why not?
V. Considering thermal regulation in the
past: Use the concepts above and the reading below to explain
which side of the controversy you are.. Do you believe dinosaurs were ecto or
endo thermic? substantiate your decision with concrete observations.
Were dinosaurs cold blooded?
BY BRENDAN I. KOERNER
The dinosaurs most of us over the age of 20 grew up with were plodding beasts
with pea-size brains. In textbooks and schlocky B films, they were portrayed
as little more than souped-up crocodiles, lurching lethargically about on
splayed-out legs, hunched over like Quasimodo. Like the modern-day reptiles
they were thought to resemble, dinosaurs were cold blooded: unable to self-regulate
their body temperatures and dependent on the sun alone for warmth.
The budding paleontologists of today's kindergarten set are being raised on
a very different crop of "terrible lizards." Bipedal carnivores,
clever and fleet-footed, zip around children's literature in voracious packs.
Ninety-foot-long sauropods gracefully rear up on their hind legs in coloring
books. And the fierce velociraptors of Jurassic Park are able to fog up a
window with their steamy breath;a sure-fire sign of a warm-blooded
animal's ability to regulate its internal thermostat under almost any condition.
It is that last revisionist detail that has divided the paleontological world
into rival camps. For some, endothermy, is the only way to explain the dinosaurs'
evolutionary success. Without the ability to keep their bodies at optimum
temperatures regardless of their surroundings, they argue, dinosaurs could
never have dominated the globe for 160 million years.
Skeptics counter that ectothermy, was the logical strategy for dinosaurs living
in the Mesozoic Era's generally sweltering heat;and, this group claims, the
only option that is supported by physiological, rather than circumstantial,
evidence.
The revisionist view that has so captured the public imagination has long
been led by Robert Bakker,who has defended dinosaur warm bloodedness. As a
Yale undergraduate in the late 1960s, he assisted the legendary paleontologist
John Ostrom in his landmark research on Deinonychus, an agile carnivore whose
sleek skeleton seemed built for a life of speed more be fitting a warm-blooded
bird than a cold-blooded reptile.
Bakker went on to become paleontology's enfant terrible, a crusader against
slow-moving, dimwitted, crocodilian dinosaurs-. He proposed such self-described
"heretical" ideas as a 10-ton triceratops that could gallop past
a charging rhino, and brontosaurs that gave birth to live, 500-pound young.
Above all, he painted a picture of dinosaurs that were every bit as endothermic
as humans, who manage to keep their body temperature around 98.6 degrees Fahrenheit
night and day, winter and summer. Instead of spending their days lazily basking
in the sun and occasionally trudging along at a torpid pace, Bakker's dinosaurs;which
he wryly termed "nature's special effects";moved at constant
speeds, their postures fully erect in the manner of birds and mammals. "Meat-eating
dinosaurs related to Tyrannosaurus rex cruised at 3 to 4 miles an hour,"
claims Bakker, who bases his conclusion on fossilized footprints. "No
turtle anywhere cruises at 3 to 4 miles an hour."
Bakker and his acolytes also point to dinosaurs' relatively fast growth as
evidence of endothermy. Mammals and birds, which develop quickly compared
with ectothermic reptiles, have bones characterized by microscopic channels
that appear complex and crystal-like under the microscope. These elegant patterns
form when growing bone meets and meshes with connective tissue, capturing
blood vessels in dense, woven structures called Haversian canals. Armand de
Ricqles, a University of Paris anatomist, found that dinosaur bones exhibited
those same intricate channels rather than the simpler, less dense structures
common to reptiles. "We see the same well-vascularized bone in mammals
but not in turtles and crocodiles," says Kevin Padian, a paleontologist
at the University of Calif-Berkley; ``The way the bones ,;grew, dinosaurs
seem to have been active all the time." That pace of activity, argue
Bakker and his cohorts, is the telltale sign of warm bloodedness. With Bakker's
charisma and de Ricqles's bone histology work, endothermic dinosaurs quickly
became the rage. Books were revised, natural-history museums scrambled to
accommodate the shift, and Bakker became a dinosaur superstar, commanding
speaking fees of up to $10,000.
. Although the public fell head over heels for the warm-blooded dinosaurs,
many within the scientific community remain wary of Bakker's claims. Since
measurements show that endotherms require up to 20 times more food than ectotherms,
some question how the gigantic dinosaurs could possibly have eaten enough
if they were warm blooded . "Can you imagine if a herd of brontosaurs
were endothermic?" asks Frank Paladino, a physiologist at Indiana-Purdue
University~v "They would have eaten through North America in a couple
of weeks." The problem would have been worse for endothermic carnivores,
for, as James Farlow of Indiana-Purdue notes, "there's a lot less meat
on the hoof than plant on the stem."
Bakker has tried to explain away this by asserting that predators were very
rare and thus able to feast on ample prey. But, as Paul Sereno of the University
of Chicago. notes, an incomplete fossil record has made it "very, very
difficult to reconstruct the number of predators and prey." ~
The evidence based on bone structures has come under fire too. Tomasz Owerkowicz,
a young Harvard University red searcher, has asserted that the dense canals
that de Ricqles detected could have resulted from physical exertion rather
than endothermy. In an ingenious experiment, Owerkowicz gave. cold-blooded
monitor lizards regular treadmill workouts and then compared their bones with
those of nonaerobicized contemporaries. The well-exercised group showed the
same kind of complex channels characteristic of mammals, birds, and dinosaurs,
suggesting that Haversian canals a causally linked to an active lifestyle
rather the warm bloodedness. South African histologist Anusuya Chinsamy has
also countered some of the bone structure arguments contending that dinosaur
bones exhibit bands called lines of arrested growth.-These are characteristic
of modern-day ectotherms, whose growth rate speeds up and slows down according
to seasonal temperature fluctuations. Chinsamy concluded that dinosaurs grew
at a more reptilian pace than envisioned by the Bakkerites.
Rather than just playing spoilsport, the ectothermic side has sought to boost
its case with hard physiological evidence. John Ruben, a physiologist at Oregon
State University, believes he may have found the answer in turbinates, tiny
whisps of bone or cartilage deep inside the nasal cavities of mammals and
birds. These structures make warm bloodedness possible by limiting water loss.
When warm, moist air is exhaled, the water condenses on the turbinates; the
next breath brings water vapor back into the lungs. "If [endotherms]
didn't have respiratory turbinates, there is no way they could lose that much
water" and survive, says Terry Jones, one of Ruben's assistants. Turbinates
have never been found in living ectotherms;nor in dinosaurs.
Although Ruben's team believes they finally have the proof to cool down dinosaurs
for good, they deny that they're trying to drag the animals back into lethargy.
"Cold blooded doesn't necessarily mean slow and sluggish," says
Jones. The Komodo dragon, the world's largest living lizard, hunts deer. "And
deer are pretty active," he says. Paladino agrees: "Ectotherms can
do some pretty amazing things," he says. "If I put you on a beach
with a 15-foot crocodile and you try to get away, I'll put my 10 bucks on
the crocodile.
Many on the cold-blooded side now use the term "gigantothermy" to
describe the unique energetics of large dinosaurs. Being huge is one way to
maintain a relatively constant body temperature despite cold bloodedness:
Large things;which have a lot of bulk in relation to their skin
area;lose heat to the outside world much more slowly than do small
things. Had they been endothermic, argues James Spotila, a biologist at Drexel
University, the large dinosaurs would have experienced a "meltdown,"
as they would be unable to dissipate internally generated heat at a fast enough
rate. However, if they were indeed cold blooded, the slow heat loss associated
with gigantothermy would allow them to stay relatively warm;and
thus avoid a reptilian torpor;when confronted by the night or an
overcast day.
In the generally tropical climate of the Mesozoic, ectothermy may have given
dinosaurs an edge over warm-blooded mammals, which had to spend a great deal
of energy thermoregulating themselves. Since ectotherms require so much less
energy than do birds and mammals, "it's a very, very nice way to make
a living if you're in an equitable climate," says Ruben. Contrary to
the popular belief that warm bloodedness is always the superior strategy,
ectothermy might have been key to the dinosaurs' long reign . Saying that
endothermy is superior, says Peter Dodson, a paleontologist at the University
of Pennsylvania, is just evolutionary "chauvinism."
The warm-blooded camp, however, is unconvinced by the new set of evidence.
Bakker says that Ruben's turbinate research doesn't take into account the
possibility that dinosaurs could have utilized an alternative, as yet unknown
structure to limit water loss. "Ruben's argument is like an expert on
piston-driven airplanes looking at a jet and saying you don't have a propeller,"
he says. Berkeley's Padian, who notes that "behavior precedes hardware
in evolution," says dinosaurs may have managed warm bloodedness using
mechanisms far different from those found in contemporary animals. Bakker
believes that chambers found in Tyrannosaurus skulls may have acted as water-loss
regulators in place of nasal turbinates.
Bakker also points to fossils that have been found in Alaska and Australia;two
of the very few Mesozoic locales where the mercury occasionally dipped below
freezing;as chinks in the seemingly ironclad case for ectothermy.
"You don't have Komodo dragons in Seattle, walking into Starbucks,"
he says. Adverse weather would have particularly affected the smallest of
dinosaurs;some of which ranged down to chicken size;who
couldn't limit their heat loss through gigantothermy. Cold-blooded advocates
have contended that hibernation or migration would have been viable alternatives,
but those explanations remain in the realm of conjecture.
Unless time machines or Jurassic Park's DNA cloning technique miraculously
become realities, the controversy can never be definitively resolved. "I
would never say we know for sure, because we can't' admits Ruben. But although
the debate will probably never end, there is little doubt as to which side
has more ominous implications for our own species: If dinosaurs were indeed
endothermic, then their sudden disappearance 65 million years ago may bode
ill for a human race that seems to consider itself invincible. "Maybe
we have to rethink our nonvulnerability to global change," explains William
Showers, a geochemist at North Carolina State University. 'We can't take comfort
in being warm blooded if the dinosaurs were warm blooded, too."