3-5 1 4-5 3 3-4 1 4-5 3 = 44-54 __________ 5 1 3 4 4 1 3 4 ________ = 50.
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Transcript of 3-5 1 4-5 3 3-4 1 4-5 3 = 44-54 __________ 5 1 3 4 4 1 3 4 ________ = 50.
3-5 1 4-5 33-4 1 4-5 3
= 44-54__________5 1 3 44 1 3 4
________ = 50
Marsupial – Eutherian differencesTrophoblast and Placenta
Chorio-vitellinePlacenta
(most marsupials)
Chorio-Allantoic placenta
(eutharians)
Trophoblast(eutharians only)
Costs of pregnancy vs. lactation
Offspring: number vs. size
Marsupial reproduction & developmental constraints
Neonatal movement to the pouch necessitates forelimb function
http://www.arkive.org/species/GES/mammals/Macrotis_lagotis/Macrotis_lagotis_09c.html?movietype=wmMed
from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial shoulder girdles. Evolution 58:2353-2370
Marsupial developmental constraints
from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial shoulder girdles. Evolution 58:2353-2370
Marsupial – Placental Forelimb development
Marsupial female reproductive cycles
Macropod marsupialsReproductive flexibility
MARSUPIAL-PLACENTAL CONVERGENCE
Gliders
Burrowers
MARSUPIAL-PLACENTAL CONVERGENCE
Arboreal folivores
Ant-termite feeding
MARSUPIAL-PLACENTAL CONVERGENCECursorial hind limbs
MARSUPIAL-PLACENTAL CONVERGENCECarnivory
http://www.naturalworlds.org/thylacine/films/java/film3/film_3.htm
Thylacine vs. Dingo ecological replacement?
AUSTRALIAN MARSUPIALS Conservation issues
Disproportionate percentage of affected taxa are small- to medium-sized and ground dwelling.
Omnivores & herbivores affected more than carnivores.
Multiple factors involved:
1) Changes in plant community structure due to: a) browsing and grazing by exotic placentals (livestock, rabbits) b) altered fire ecology (decreased frequency and increased severity of fires)
2) Introduced predators (dogs, cats, red fox)
3) Exotic diseases
a) Koala – sexually transmitted Chlamydia causing infertility and other problems b) Tasmanian Devil – facial tumor disease
c) Thylacine -- distemper virus implicated in decline
4) Direct hunting (extinction of thylacine on Tasmania)
MARSUPIAL-PLACENTAL COMPETITION
Predomonance of eutherians on northern continents
Contemporary Asian origin of marsupials and placentals; more rapid spread of marsupials into southern continents
American faunal exchange (late Pliocene- Pleistocene)
Evolutionary dominance of placentals
Extinction of a much larger number of S. American placental groupsNorthern invasion and continued spread of didelphid marsupials
Placental carnivores replaced S. American “marsupicarnivores”
Prehistoric extinctions of Australian marsupials
Late Pleistocene extinction of most large-bodied marsupials,possibly through human hunting or by predation/competionfrom introduced dogs.
Extinctions may have been due to global climate change.Comparable levels of extinction seen for placentals onother continents.
Historic decline & extinction of Australian marsupials
A disproportionate percentage of historic mammal extinctions have involved Australian marsupials. Competition from exotic placentals has been directly implicated in some cases.
Native Australian placentals (rodents) show same dramatic level of decline and extinction. Competition with exotic placentals is only one of many factors endangering marsupials.