Presentation on theme: "Order Proboscidea: the Elephants One living Family, two living genera, 2 living species. For most of our species-existence, most people have lived with."— Presentation transcript:
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 21 st century, this co-existence is becoming increasingly difficult!
The plan for the day: Ancestry and evolution Range and Status Anatomy 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 “low- quality” 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.
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. 11 2 New dates: 1 7.6MYBP 2 6.7MYBP
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.
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 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 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.
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. 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 Remember: The origin of these adaptations must be more than 7.6MYBP.
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 –A touch-communicator Tusks are next
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 Remember: The trunk helps maintain contact with the ground as the legs lengthen.
Cheek teeth Shredding in living sps & mammoths; crush-grinding in mastodons. 6 molarform teeth per jaw- quadrant 1 functioning tooth per quadrant; loss in front; magazine replacement from rear (see next 2 slides). Elephant or mammoth Mastodon Not a member of the Elephantidae.
Elephant teeth & their replacement To know about elephant teeth is to know about elephant demography.
Schedule of Tooth Replacement Tooth M1M2M3M4M5M6 Ages of use, African 0-1 years 1-2 years 2-6 years 6-15 years 15-28 years 28-47 years Ages of use, Asian 0-1 years 1-6 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 = αM β β is always < 1 (0.75+/-) Now figure expense/size C/M = (αM 0.75 )/M C/M = α/M 0.25 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. 11- 26 hours. Defecation per day: 150- 250kg Assimilation efficiency: –Elephant: 44% –Cow: 66%
Social organization (Most data are from African elephants.) A baby elephant is born into a matriarchy after 21- 22mo. gestation. It receives much education, and interbirth interval is typically 4-6 years. –For 1 st 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 head- bashing (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 6m 2, 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, –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. Even with these babies, can’t you tell which is which ?
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.
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% Elephant conservation: How does one act responsibly in a world of limited resources, inequitably distributed?
The future of elephants Elephants are not an evolutionary dead- end, 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!