BIO120H1 Lecture Notes - Lecture 4: Succulent Plant, Convergent Evolution, Continental Drift
19 Jan 2017
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CHAPTER 4
Juan Fernandez archipelago – islands most famous for their isolation
o Today, these islands are a living museum of rare and exotic plants and animals with many species that are
endemic (found nowhere else in the world)
o The island is also notable for what it is missing – it does not have a single native species of amphibian,
reptile or mammal -> this pattern gives evidence for evolution
Biogeography – the study of the distribution of species on earth; the roots lie deep in religion
Theory that multiple reatios ere distriuted aross the earth’s surfae arose
o Some biologists proposed that all the continents were once connected by giant land bridges -> no evidence
for this
o Darwin proposed his own theory which states that the distributions of species were explained by evolution,
not by creation – plants/animals had a way of dispersing and could evolve into new species -> he was right
to a certain extent
2 developments:
o Continental drift
o Molecular taxonomy
Evolutionary theory predicts that as species diverge from their common ancestors, their DNA sequences change in a
straight-line fashion with time -> e a use this oleular lok to estiate diergee of tie of speies ad
match the evolutionary relationships between species with the known movements of the continents/glaciers and
formation of land bridges -> tells us whether the origins of species are concurrent with the origin of new
continents/habitats
Continents
2 distant areas that have similar climate and terrain -> have different types of life
o Ex: succulents in deserts – different deserts have different types of succulents; can tell the different
between the 2 types by their flowers and sap
Marsupial mammals and placental mammals – different species filling similar roles
o These 2 groups show anatomical differences in their reproductive systems – marsupials have pouches and
placentals have placentas
Evolution explains the patterns for why different types of animals have similar forms in different places through a
process called convergent evolution – species that live in similar habitats will experience similar selection pressures
from their environment therefore evolving similar adaptations
Convergent evolution demonstrates 3 parts of evolutionary theory working together:
o Common ancestry – why some species share similar features
o Speciation – the process by which each common ancestor gives rise to many different descendants
o Natural selection – makes each species well adapted to its environment
The co-occurrence of fossil ancestors leads to one of the most famous predictions in the history of evolutionary
biology -> Dari’s hypothesis that huas eoled i Afria
o The profusion of ape-human transitional fossils were found in Africa
The evidence for evolution from patterns of life on continents is strong but that from life on islands is even stronger
Islands
2 types of islands:
o Continental islands: once connected to a continent but later separated either by rising sea levels that
flooded former land bridges or by moving continental plates
o Oceanic islands – never connected to a continent but instead arose from the seafloor; missing many types
of native species that we see on both continents and continental islands -> disparity is hard to explain
Mammals, amphibians, freshwater fish and reptiles often do very well when humans introduce them to oceanic
islands -> often take over, wiping out native species
Although oceanic islands lack many basic kinds of animals, the types that are found are often present in profusion,
comprising many similar species
o Galapagos – comprised of 13 islands that have 28 species of birds where 14 belong to a specific group of
closely related birds, the Galapagos finches -> ecologically diverse
Oceanic islands – missing many groups of species that live on continents and continental islands and the groups that
are found on oceanic islands are replete with many similar species -> show that life on oceanic islands is unbalanced
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Document Summary
Biogeography the study of the distribution of species on earth; the roots lie deep in religion. 2 developments: continental drift, molecular taxonomy. Marsupial mammals and placental mammals different species filling similar roles: these 2 groups show anatomical differences in their reproductive systems marsupials have pouches and placentals have placentas. The co-occurrence of fossil ancestors leads to one of the most famous predictions in the history of evolutionary biology -> dar(cid:449)i(cid:374)"s hypothesis that hu(cid:373)a(cid:374)s e(cid:448)ol(cid:448)ed i(cid:374) afri(cid:272)a: the profusion of ape-human transitional fossils were found in africa. The evidence for evolution from patterns of life on continents is strong but that from life on islands is even stronger. Mammals, amphibians, freshwater fish and reptiles often do very well when humans introduce them to oceanic islands -> often take over, wiping out native species. Plants, birds, insects/other anthropods can colonize an oceanic island through long-distance dispersal.
