Chapter 21: Human Evolution
Humans are Primates:
-
Primates are mammals adapted to living in trees
-
Although humans (unlike
monkeys and many apes) do not live in
trees, many human characteristics can be explained on the basis of adaptation
to an arboreal (tree-dwelling) existence
Primate characteristics:
-
³opposable² thumbs
(& sometimes big toes) (i.e.:
thumbs can touch each of the other digits (fingers))
-
nails (instead of claws)
-
single birth
-
expanded forebrain
-
stereoscopic vision
(depth perception)
-
extended period of
parental care
-
emphasis on learned
behavior
Order Primates: 2
suborders
-
Prosimians: believed
to be first primates
- large eyes, small (resemble mice,
squirrels)
- includes tarsiers, lemurs, and lorises
-
Anthropoids:
surviving species divided into 3 superfamilies
-
New World
monkeys: long tails & flat noses
- includes spider monkeys & capuchins (organ-grinder monkeys)
- Old
World monkeys: no long tails (often ground dwellers);
protruding noses
- includes baboons & rhesus monkeys
- Hominoids:
includes all apes and humans
-
Apelike hominoid Proconsul (lived during Miocene epoch (6-24 million years ago)) is believed to be the
common ancestor to all apes and humans
-
According to the
³molecular clock² approach, using similarities in DNA sequences among primates
to estimate divergence from the primate line of descent:
- monkeys diverged about 33 million years ago (MYA)
- orangutans diverged about 10 MYA
- African apes and humans split about 6 MYA
-
Differences between apes and hominids
(family Hominidae, includes
humans) include mode of locomotion, shape of jaw, and brain size
Following split of modern
African apes and hominids (about 6 MYA), genus Australopithecus (australopithecines) is believed to have evolved in Eastern Africa, and split from genus Homo about 3.5 MYA
-
the common ancestor between australopithecines and genus Homo is believed to be Australopithecus afarensis (the much studied ³Lucy² fossil)
-
evolutionary theory
predicts that genus Australopithecus became extinct about 1 MYA, while genus Homo continued to evolve to become modern humans
-
cranial capacity (brain
size) continued to steadily increase during the evolution of genus Homo, from the 500 cc (cubic centimeter) capacity of australopithecines to 1,360 cc of modern humans (Homo sapiens)
-
Homo species which are believed to have evolved from Australopithecus
afarensis include Homo habilis, Homo erectus, the Neanderthals, the Cro-Magnons, and Homo sapiens
-
Homo habilis: believed to have evolved from australopithecines about
2 MYA
-
the first hominid to make tools; hunted for food, and probably
could speak
-
Homo erectus:
evolutionary theory predicts this species evolved from Homo habilis about 0.5 to 1.9 MYA
-
some theories predict Homo
erectus migrated out of Africa, and were
big game hunters with advanced tools;
may have been the first hominids to use fire
- Neanderthals: archaic Homo sapiens species (Homo sapiens neanderthalensis); not considered to be on the main line of descent to modern humans (may have evolved separately)
- fossils found in Neander Valley in Germany about 200,000 years ago
- Cro-Magnons (Homo sapiens sapiens): modern humans; predicted to have migrated to Eurasia about 100,000 years ago
- Cro-Magnons: believed to be skilled hunters (made advanced stone tools; spears) with language & art (culture)
- thought by many to be the link between Homo erectus and Homo sapiens
2 hypothesis for migration
of Homo species:
-
Out-of-Africa
hypothesis: modern humans evolved in Africa, and later migrated to Europe and Asia, perhaps replacing the
Neanderthals
-
Modern humans evolved
separately in Africa, Europe, &
Asia
The main line of hominid
descent is now believed to include: Australopithecus ramidus,
Australopithecus afarensis, Homo habilis, Homo erectus, and Cro-Magnons
Chapter 23: Ecology of Populations
Ecology: the
study of the interactions of organisms with other organisms and with the
physical environment (Ernst Haeckel)
-
Ecology &
evolution intertwined: ecological interactions are selective pressures that
result in evolution, and evolution affects ecological interactions
-
Ecological interactions
determine the distribution & abundance of organisms in a particular region
and across all the earth
Ecological terms:
-
Habitat: the
place where an organism lives
-
Population: all
organisms of a given species in a particular habitat
-
Community: all the
populations of organisms interacting in a particular region
-
Ecosystem: a
community of populations and the abiotic environment (earth, atmosphere, sun)
-
Biosphere: that
portion of the surface of the earth occupied by living things
Characteristics of populations:
Population density: the
number of individuals per unit area or volume
Population distribution: the pattern of dispersal of individuals in a given
area
-
limiting factors:
determine whether an organism lives in an area
(e.g.:
atmosphere, water supply, temperature & climate)
Population size: the
number of individuals contributing to the populationıs gene pool
Net reproductive rate
(r): birthrate death rate
-
used to determine the population
growth rate
-
Exponential growth: # of new
individuals in a population increases as the total # of females increases
- exhibits biotic potential: maximum
population growth under ideal conditions
-
Logistic growth:
population size stabilizes (stops growing) when the carrying capacity (K,
maximum # of individuals of a given species an environment can support) is
reached
-
exhibits environmental resistance: limits in an environment
that prevent further population growth
Regulation of Population
Size:
-
Life history
strategies:
- r-strategist: small individuals with short life span; produce many offspring that mature rapidly & receive little or no care
- K-strategist: large individuals with long life span; produce few offspring that mature slowly & receive extended care
Human population: humans
are generally considered K-strategists, but in many less-developed countries, the growth rate approaches
exponential growth (0.1%/year for more-developed countries vs. up to 2.5%/year
for less-developed countries; in the U.S., it is estimated at 0.6%)
-
currently, the estimated
doubling time for the worldıs
population is 47 years
-
perhaps without stabilization of the net reproductive rate by
some combination of means, the carrying capacity of the earth may be determined
in the all too near future
Chapter 24: Community Ecology
Community Organization:
-
Ecological
Niche: the role an organism plays in its community, including
its habitat & interactions with other organisms
- includes the resources an organism uses to meet its energy, nutrient & survival demands
-
fundamental (potential) niche vs. realized (actual) niche
- Competition between populations:
- Interspecific competition: members of different species compete for the same limited resource
- Competitive exclusion principle: no 2 species can occupy the same ecological niche at the same time
- Resource
partitioning: often results from interspecific
competition; physical separation of a
necessary resource
- Character
displacement: tendency for characteristics to be more divergent in
populations sharing a community than when isolated
- evidence for competition & resource partitioning
Predator-Prey interactions:
Predation:
one living organism, the predator, feeds on another, the prey
-
presence of predators in an ecosystem can decrease
prey densities, and vice-versa
Prey defenses:
- Camouflage: adaptation (coloring or resemblance to another object that allows blending of an organism with its environment
- Alarming appearance or defense mechanism (e.g.: spines or quills of porcupine; illusion of increased size)
- Association with other prey (safety in groups)
- Mimicry: resemblance to (mimic) the appearance of another animal with a strong defense mechanism
Symbiotic
relationships:
Symbiosis: a close relationship between organisms of different species
- Parasitism: 1 organism is harmed, the other benefits (e.g.: bacteria, tapeworms, roundworms)
- Commensalism: 1 organism benefits, the other is neither harmed nor benefits (e.g.: epiphytes, barnacles & whales/crabs)
- Mutualism: both organisms benefit (e.g.: lichens, ants & acacias, termites & cellulose-digesting protozoa)
Chapter 25: Ecosystems
The nature of ecosystems:
Biosphere: the part of the atmosphere, hydrosphere, and lithosphere that contains living things
- Atmosphere: extends from the earthıs surface to 1,000 kilometers above the earthıs surface
- contains carbon dioxide, nitrogen, oxygen, and water vapor
- Hydrosphere: all water on earth; covers three fourths of the earthıs surface
- Lithosphere: extends from the earthıs surface to 100 kilometers deep (below the earthıs surface)
- contains minerals and decaying organic material (humus)
Biotic components of an ecosystem:
Autotrophs: producers (produce their own food through photosynthesis or nitrogen fixation)
- Photoautotrophs: (e.g.: plants, algae, and photosynthetic bacteria); carry out photosynthesis to produce most of the organic nutrients for the biosphere
- Chemoautotrophs: bacteria that obtain energy by oxidizing inorganic compounds such as ammonia, nitrites, and sulfides, and use this energy to produce carbohydrates
Heterotrophs: consumers (consume food from producers or other consumers)
- Herbivores: feed on plants or algae
- Carnivores: feed on other animals (consumers)
- Omnivores: feed on both plants and animals
- Detrivores: feed on detritus (decomposing organic material) (e.g.: earthworms, termites, maggots)
- Decomposers: carry out decomposition (breakdown of dead organic material) (e.g.: fungi, nonphotosynthetic bacteria)
Energy
Flow & Nutrient Cycling:
Primary productivity: the total amount of energy an ecosystemıs producers capture within plant material over a certain length of time
- Energy flows through an
ecosystem; nutrients cycle within and among ecosystems