Transcript Elephants - Wofford College

Order Proboscidea: the
Elephants
One living Family, two living genera, 2 living species.
For most of our species-existence, most people have
lived with elephants. As we move through the 21st
century, this co-existence is becoming increasingly
difficult!
The plan for the day:
• Ancestry and evolution
• Range and Status
• Anatomy
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Size
Legs
Trunk (including some weird speculation on evolutionary origins)
Tusks & skull
Cheek teeth
Basic ecology (eating even the worst plants)
Metabolism (be big)
Social organization (center on females)
Specifics on Asian elephants (including conservation)
Conservation of African elephants
Ancestry and Evolution
• Elephants should probably be considered part
of the Afrotheria. Closest living relatives are
seacows and hyraxes (see next slide).
• Earliest proboscideans were tapir-like.
• Evolutionary trends were deepening the teeth,
shortening skull, lengthening trunk and legs.
• Elephas & Mammuthus evolved in Africa; they
were most modern elephants, invading Eurasia,
North America and finally South America.
• Loxodonta, more primitive, survived in Africa.
They may not look like elephants, but…
• An ancient branch of the Afrotheria evolved to exploit “lowquality” vegetation.
• One “twig” of the branch became aquatic (seacows, upper left).
• Another “twig” invaded xeric habitats (hyraxes; upper right;
once some types were much bigger).
• The third “twig” exploited intermediate habitats and became
elephants.
New dates:
1 7.6MYBP
2 6.7MYBP
2
1
• Note the
complexity of
the
Proboscidean
tree.
• Many
taxonomists
would show
Mammuthus
branching
even later
from Elephas.
• Note that
Mammut,
Mammuthus,
and Stegodon
survived until
relatively
recent times.
Range and status today
• Loxodonta: Once pan-African, now intra-tropical.
– In plains and savannas, African elephants are now largely
restricted to hunting preserves and national parks.
– In thick forest, status less well known (but may be common).
• Elephas: Once widely distributed from India
throughout continental S.E. Asia and into southern
China. Now very rare.
– Working elephants in Myanmar; tourist elephants elsewhere.
– Wild elephants in Indian national parks– and a few are
widely scattered in some other national parks.
• Almost everywhere they occur, elephants are often
considered more valuable (or less trouble) dead than
alive. Nowadays, people have the equipment to make
‘em that way.
Dimensions of
Elephants
African elephant:
Shoulder height:
XX: 2.4-3.4m
XY: 3.0-4.0m
Mass:
XX: 2400-3500kg
XY: 4000-6300kg
Asian Elephant:
Shoulder ht: 2.5-3.0m
Mass: 3500-5000kg
Elephant legs are
graviportal.
• Bones are large and
“stacked.”
• Elephant walks on 5
toes & heel pad.
• Elephants move long
distances– for food,
for water, for sex,
maybe for fun.
• Elephants don’t run:
– Typical elephant walk
is like brisk human
walk.
– Fastest walk is like
top human sprint.
Evolutionary
elongation of the
trunk
The conventional history of elephant
evolution: Terrestrial ancestor of
Afrotherian megavertebrates gives rise
to elephants, seacows, and hyraxes.
The trunk of elephant ancestor
lengthens in accompaniment with
lengthening legs.
• Apparent paradox:
– Short trunk is useless to
tall grazer
– Evolving structure must
be useful at all stages.
• Ancient elephants:
relatively short legs &
trunk that reached
ground.
• Intermediate elephants:
longer legs, longer skull,
longer jaws, longer
trunk– that reached
ground.
• …then trunk stays on
the ground as skull and
jaw shortened.
• But
A Garrettian (=
wild-ass,
contrarian)
trunk-centered
hypothesis on
elephant
evolution
• The structure of elephant lungs and
thoracic cavity suggests adaptation for
snorkeling.
– Anatomical adaptations are numerous and
profound.
– These adaptations cannot easily be
accounted for by use of the trunk for
terrestrial drinking.
• Did snorkeling adaptations occur early?
– Identical structures exist in Asian and African
elephants.
• Early snorkeling adaptations would
suggest that elephants evolved from
aquatic animals.
– The logical candidate would be some
ancestor shared w/ seacows (conventional).
– The question is, was that ancestor aquatic?
– If so, the lengthening of the trunk might have
preceded the lengthening of the legs, which
would have occurred after an invasion of the
land, contrary to the conventional wisdom.
The snorkeling-elephant conundrum
(Note: We’re talking about
systemic circulation to
parietal pleura; pulmonary
circulation is protected by
“Zone 2 Phenomenon.”)
Anatomy suggests
that snorkeling
adaptations may
have been
fundamental.
Remember: The origin of
these adaptations must be
more than 7.6MYBP.
• The vulnerable pleural
membranes are replaced by
thick plates of dense
connective tissue.
• The “pleural cavity” itself is
filled with loose connective
tissue.
• The diaphragm is much
thicker than would be
expected for an animal of
elephant size.
• All these adaptations (and
others) are observable early
in embryonic development.
• But we’ve digressed long
enough; back to the trunk
Uses of the trunk
• As a tool
– Grazing & browsing
– Manipulating objects
– Moving water
• As a sense organ
– Touch
– Smell
• As a social-signaling organ
– A trumpet that amplifies vocalizations
– A bearer of visual signals
Tusks are next 
– A touch-communicator
Remember: The
trunk helps
maintain contact
with the ground
as the legs
lengthen.
Evolution of tusks & skull
• Tusks are second upper
incisors. Tusks typically
emerge in XY & XX African
but only in XY Asian adults.
• Tusks’ utility and social
importance are enormous.
• Evolutionary tendency for
skull to shorten & tusks to
lengthen.
• The conservation
significance of tusks &
ivory….
• Now: Other teeth
Cheek teeth
Elephant or mammoth
Mastodon
Not a member of the Elephantidae.
• Shredding in
living sps &
mammoths;
crush-grinding
in mastodons.
• 6 molarform
teeth per jawquadrant
• 1 functioning
tooth per
quadrant; loss
in front;
magazine
replacement
from rear (see
next 2 slides).
Elephant teeth & their replacement
To know about
elephant teeth is to
know about elephant
demography.
Schedule of Tooth Replacement
Tooth
M1
M2
M3
M4
M5
M6
Ages of
use,
African
0-1
1-2
years years
2-6
years
6-15
years
15-28
years
28-47
years
Ages of
use,
Asian
0-1
1-6
years years
6-8.5
years
8.5-22.5
years
22.5-40
years
40-70
years
Note: African-elephant data are from wild animals; Asian-elephant
data are from captive, working animals.
Next, ecology
Basic ecological strategy
• Elephants grow very large, thereby decreasing
surface-to-volume ratio.
• This reduces per-kg thermoregulatory expenses and
therefore the amount of calories needed per kg body
mass. (See next slide for Kleiber Curve)
• Vast variety of plants eaten (Kibale, Uganda: 227 of
255 known species) but most food is usually from few
species.
• Absorptive efficiency is low, and elephants meet
minimal nutritional needs by eating large quantities of
OK food or vast quantities of wretched food.
• Elephants have the capacity to alter an environment–
and the mobility to move into a new area.
Elephant Metabolism
(C is “caloric expenses”; M is “Mass”; α & M are fitted constants)
• Some general principles
(Kleiber Curve):
• C = αMβ
• β is always < 1 (0.75+/-)
• Now figure expense/size
C/M = (αM0.75)/M
C/M = α/M0.25
• That is, expenses per kg
decline with increases in
body size.
• That is, elephants’ main
metabolic specialization
is to be BIG.
• Some elephant specifics:
• “Small” stomach, large
caecum.
• Feeding per day:
– 10-18 hours
– 150-250kg (c. 5% mass)
• Throughput time c. 1126 hours.
• Defecation per day: 150250kg
• Assimilation efficiency:
– Elephant: 44%
– Cow: 66%
Social organization
(Most data are from African elephants.)
• A baby elephant is born into a matriarchy after 2122mo. gestation. It receives much education, and
interbirth interval is typically 4-6 years.
– For 1st 6months, baby is watched all the time.
– Baby is weaned at 6-18 months (occasionally later).
– Until it’s almost 10 years old, juvenile spends c. 50% of its
time within 5m of its mother (closer in moments of danger).
• XX’s stay in natal group, cementing relationships
w/mothers, grandmas, sisters, aunts, XX cousins….
• Between ages 8-20yrs, XY’s think increasingly of sex
& become such pests that XX’s run them out of herd.
Thereafter they join bachelor society (next slide).
The machismo of
bachelor society
• Young males entering elephant
bachelor society learn their
places– or else.
• Size is the major factor in
establishing dominance.
• Mutsch temporarily over-rides
other considerations.
– Temporal glands drain, penis drips,
testosterone levels soar.
– Temper, temper….
• Skull structure cushions headbashing (pneumatic skull).
• Use of tusks is dangerous.
• Biggest XY occasionally return to
XX groups.
• Now, back to the more important
considerations of XX groups!
Long-lasting female groups form the
nucleus around which all elephant
society is organized!
Female groups & elephant commo
• Oldest XX is matriarch
– She knows the area & the elephants.
– She outlives repro years (only elephants and people); why?
• Interaction & commo holds group together
–
–
–
–
Lots of touching and signaling
Trunk-in-mouth greeting ceremony
Low-frequency sounds
Play builds tightest bonds among young XX cousins
• Courtship can be dramatic
– XX receptive for only a day or two (but she courts longer)
– Many XY’s may follow a receptive XX, but in a typical
elephant population, only a few become fathers.
The sociology and physiology of (African)
elephant ears: looking big and cooling off!
• Elephant social
processes are
mediated by size.
Threat or dominance
position has ears
extended.
• Ears also serve as
radiators.
– Each is right triangle,
1.5mX2m; total
surface is 6m2, or
about 20% of total.
– Mass of each ear is
about 20kg, or < 1%
of total.
– Blood-flow through
ears can be > 1000
liters/hr.
Next: A little on the sociality of Asian elephants
A few social specifics
on Asian elephants
• Lots like Loxodonta, but
haven’t shared common
ancestor for about 7.6MY
(people-chimps separation
is about 5MY.).
• Are Asian XY’s more
connected w/XX groups?
• It’s reported that Asian
XX’s may form communal
nursery groups. (Is this
true? If so, does this occur
in African elephants too?).
Uh, how do you tell an Asian elephant
from an African elephant?
• Well, if you’re in
Africa….
• Otherwise,
Even with
these babies,
can’t you tell
which is which?
– African has larger ears.
– Asian has convex spinal
line; African has concave
spinal line.
– Two-lip trunk in African
elephant; Asian elephant
has single trunk-lip.
– Asian elephant usually
smaller.
– African XX usually have
emergent tusks.
A general note on S.E. Asian conservation
• Although not particularly urban, S.E. Asia is
the most crowded area in the world.
• Intensive agriculture covers almost every
available hectare of reasonably flat land.
• Most vertebrate wildlife survives only in national
parks, many of which are also under threat.
• In 1975, Vietnam was thought to have many
hundreds, perhaps thousands, of elephants.
• Today population is probably < 100, in widely
separated small groups.
• Elephants interfere with local people.
Conservation of African elephants
• The subject is much more complex than most
“experts” would like to admit!
• Elephant demography makes harvest
potentially damaging to elephant populations.
• Prior to international ivory ban (enforced by
1989), different countries had experienced
different results with their management plans.
• Conservation decisions, which should have
been made on a biological basis, were driven
by largely political concerns.
• The arrogance of the “developed” world was
demonstrated yet again.
Elephant
conservation:
How does one
act responsibly
in a world of
limited
resources,
inequitably
distributed?
Conservation? In January 2008 the Philadelphia Zoo
announced that it would breed its African elephants to
help with species-conservation. The zoo also announced
the construction of a $27 million elephant exhibit. One
baby might be produced by 2010. Meanwhile, RSA will
start killing thousands of elephants in May 2008, and the
per-capita income in Zimbabwe is < $1/day.
For 2010,
cut by 50%
The future of elephants
• Elephants are not an
evolutionary deadend, not a taxon that
has outlived its
ecological capacity.
• Elephants are smart,
adaptable, modern–
and can live almost
anywhere on almost
any plant food.
• BUT more than any
other large mammal,
elephants are efficient
competitors with
people!