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93 Cards in this Set
- Front
- Back
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• Relationship of humans to African and Asian apes
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Darwin was correct that humans are more closely related to African apes (gorillas and chimps) than Asian apes (orangatangs and gibbons). Evolutionary systems put all apes on one branch and humans on another but those systems were wrong.
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• Distinguishing features of primates:
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binocular vision and prehensile hands with opposable thumbs
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• Prosimii, Tarsiiformes and Anthropoidea
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Three suborders of primates:
- Prosimii: lemurs, galagos and lorises (retain ancestral, elongated faces) - Tarsiiformes: tarsiers (shortened snout and more forward-pointing eyes) - Anthropoidea: monkeys, apes and humans (larger brains) |
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• Hominoidea (Apes): who are they and what are their shared, derived characters?
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Better known as apes
• Includes gibbons, orangutan, gorillas and chimpanzees (closest relative to the humans) • Shared, derived characters of the Hominoidea are: - reduction (loss) of tail - evolution of shoulder blades enabling swinging from branch to branch |
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• Primate genome sequencing: why is macaque genome important?
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Humans and chimps share 98.7% genome although primitive versus derived genomes cannot be distinguihed. The Rhesus macaque was the most recent genome to be mapped in April of 2007.
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• Chimpanzee versus Bonobo social systems
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• Chimpanzee
- Male dominated and aggressive - Females disperse but males remain in natal territories so males tend to be related - Males conduct murderous raids on neighboring communities • Bonobo - Female dominated and conciliatory - Sex is used as a greeting and as a means of conflict resolution - Sexual and social bonding in females prevents male domination - Individuals prefer sexual contact within group over violent confrontations with outsiders |
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• Punctuated equilibrium: what is it, how can it be explained and its relevance to human evolution
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Puncuated equilibirium is long periods of morphological stasis followed by rapid
bursts of evolutionary change. Once an evolutionary equilibrium is reached, why should there be evolutionary change? • Often rapid evolutionary change is associated with major geological events and climatic changes. Punctuated environmental changes due to geological events and climate • Reorganization of the phenotype due to changes in timing and rate of developmental processes (heterochrony). Major transitions in human evolution associated with dramatic changes in global climate - evolution of bipedalism 6 to 7 mya - split between Australopithecus and Homo 2.5 to 3 mya |
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• Heterochrony and differential growth rate in human evolution
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- change in timing of
developmental events, leading to alterations of size and shape - fetal head shapes in human and chimp very similar - changes in small number of regulatory genes affecting relative growth rates can dramatically affect adult phenotype |
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• Subfamily Hominini (lineage leading to modern humans after split from chimpanzee)
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• Lineage leading to modern
humans is subfamily Hominini • Molecular estimates indicate human-chimp split at 6.5 million years ago • Oldest fossil hominin is Sahelanthropus tchadensis, estimated to be 6 -7 million years old • Best known early hominin is Australopithecus afarensis • Last hominin to go extinct was Homo neanderthalensis, 28,000 years ago |
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• Sahelanthropus tchadensis: oldest hominin
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Earliest known Hominini,
Sahelanthropus tchadensis • Found in Chad (reported in Nature, July 2002) • Estimated to be 6–7 million years old • Fossil consists of cranium, jaw fragment and several teeth • Mixture of chimp & australopithecine features |
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• Orbital plane, foramen magnum evidence for bipedalism in Sahelanthropus tchadensis
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Skull revelations
• Chimpanzee - walks on all fours (knucklewalking quadraped) - quadrapedalism reflected in anatomy of head - acute angle (650) between foramen magnum and orbital plane • Human - bipedal - spinal cord enters brain on nearly vertical line - creates larger angle with orbital plane (1030) - indicates head held upright • Sahelanthropus – 950 angle suggests that species held head upright and was bipedal |
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• Ardipithecus: where found and how old
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Known primarily from dental
structures and fragmented skeletal remains • Ardipithecus kadabba - Ethiopia - 5.2 to 5.8 mya - jawbone, teeth, arm fragments, collarbone and toe bone - form of toe bone suggests upright posture • Ardipithecus ramidus - Ethiopia - 4.4 to 4.5 mya - jawbone, teeth and arm fragments 16 Best known, early Hominini |
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• Australopithecus afarensis (Lucy and the Dikika baby)
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Australopithecus afarensis
• Taken from sites in Ethiopia (Hadar) dated at 2.9 to 3.5 mya and 3.6 mya in Tanzania (Laetoli) • Best preserved specimen was Lucy from Hadar - skeleton 40% complete • Site in Tanzania - famous because skeletal remains found in association with 3.6 myo footprints - proves A. afarensis was bipedal |
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• Mosaic evolution in Australopithecus afarensis
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Mosaic evolution
• Morphologically intermediate between human and ape • Bipedalism clearly indicated by pelvic structure • Small-brained (slightly larger than chimp) • Intermediate dentition – reduced canines – shortened jaw – herbivorous diet |
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• Hypotheses for bipedalism: which is best supported and most parsimonious?
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Hypotheses for bipedalism
• Man the hunter • Man the scavenger • Woman the gatherer • Man the provisioner Most parsimonious explanation was that Bipedalism was fueled by fragmentation of the forest. |
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• Differences between the genera Australopithecus + Paranthropus versus Homo: encephalization and dentition
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Between 2 and 3 m.y.a., 4 to 5 species of hominins co occurred in Africa
• Small brains, large cheek teeth -- Genera Australopithecus and Paranthropus • Large brained, small cheek teeth -- Genus Homo Robust australopithecines (also called Paranthropus) • Adapted for feeding on tough plant foods – enormous cheek teeth – robust jaws – massive jaw muscles anchored to bony crest at top of skull – nicknamed “the nutcracker man” • All extinct by 1 m.y.a. |
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• Homo habilis/rudolfensis
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Homo habilis/rudolfensis
• First Homo species (2.4 - 1.6 mya) • Transition from Australopithecus to Homo involved increased encephalization and decreased dentition • First big-brained hominin - brain size of 750 cm3 (Gorilla 400 cm3; Australopithecines 500 cm3; human 1350 cm3) • Definitely used stone tools - unclear whether australopithecines used tools - oldest stone tools dated at 2.4 mya • Strongly sexually-dimorphic |
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• Hominid and ape brain/body size allometry
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• Comparisons of
brain sizes should correct for differences in body size • Genus Homo – abrupt increase in ratio of brain to body size |
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• Homo ergaster/erectus
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• Evolved in Africa 1.8 mya (H. ergaster)
• Populations spread to Middle East, Asia and Europe • Went extinct between 50,000 and 100,00 years ago • First appearance outside Africa (H. erectus) • First appearance of systematic hunting • Well-defined home bases • Advanced tools, e.g., axes • Use of fire • Brain size ranged between 850-1100 cm3 Turkana boy • Discovered in 1984 at Lake Turkana, northern Kenya • Virtually complete specimen of Homo erectus boy • Well-dated deposits 1.6 mya • Compared to modern humans - thick cranial bone - prominent brow ridges - low, flat forehead - thick femur - heavy musculature - thinner spinal cord |
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• Homo floresiensis
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From Indonesian island of
Flores • Fossils dated at 18,000 years old • 1 to 1.5 m tall • Bipedal • Found with stone tools, dwarf elephants and Komodo dragons • Mosaic of primitive and derived traits • Brain size and stature of Australopithecus • Facial and dental morphology of Homo |
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• Origin of modern humans: Candelabra versus Multiregional versus Out-of-
Africa models |
Candelabra model
• Proposed that three geographic populations of H. erectus independently evolved into H. sapiens Multiregional Model • Argues for a geographically widespread transformation from Homo erectus to modern Homo sapiens with some gene flow between populations Out of Africa = African Replacement = Uniregional Model • Argues for a geographically discrete origin of H. sapiens in Africa followed by migration and replacement of H. erectus populations |
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• Mitochondrial Eve hypothesis
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• Based on study of human mitochondrial DNA by Cann et al. (1987)
• Phylogenetic analysis indicated that base of tree consisted entirely of mitochondrial haplotypes(genotypes) from Africa • Proposed that all current human mitochondrial haplotypes could be traced back to mitochondria of a single female in Africa 200,000 years ago - Mitochondrial Eve hypothesis Does not mean that only one female existed at that time - only that other mitochondrial lineages have since gone extinct Mitochondrial Eve hypothesis explained: • Mitochondrial DNA study did not demonstrate existence of an Eve (a single female alive 200,000 years ago) • Does indicate that most recent common ancestor (MRCA) of all humanity via mitochondrial pathway existed in Africa 200,000 years ago • Based on coalescent theory for mtDNA - concept that all maternal lineages trace back to single mother in ancestral population - only females transmit mitochondria to offspring - each generation, some women have no children and others have only sons - working backwards towards common ancestor, this reduces number of women who have contributed mitochondria to current population until only one remains - consequently, all men and women carry mitochondria inherited from single woman - nuclear genes from many contemporary women of Mitochondrial Eve are present in today's population, but mitochondrial DNA from them is not |
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Origin of Homo sapiens: mtDNA perspective
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Limitations of Cann et al. (1987)
• Based on outdated method of inferring mitochondrial DNA sequence (restriction fragment length polymorphisms, or RFLPs) • Did not use outgroup to root tree More recently • Ingman et al. (2000) repeated study using 53 complete sequences of mitochondrial genome • Chimpanzee used as outgroup • Cann et al. (1987) were right! • All men and women carry same mtDNA derived from Mitochondrial Eve 171,500 years ago • Over time, mtDNA has accumulated different mutations • First three branches (L0, L1 and L2) contain only sub-Saharan sequences • All women outside Africa descend from M or N, two daughter lineages of L2 |
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• Y-chromosomal Adam perspective on human origins
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• Only men have Y chromosome
which does not recombine with X • Each generation, some men have no children and others only daughters - sexual selection on males increases variation between individuals in number of offspring produced - reduces coalescence time of Y chromosome compared to that of mitochondria • Working backwards towards common ancestor, this reduces number of males contributing Y chromosomes to current population until only one remains • Consequently, all men carry Y chromosome inherited from a single individual, the Ychromosomal Adam • Although all men carry Y chromosome from same ancestor, different mutations have gradually accumulated • First two branches in Y-tree are sub-Saharan • All male lineages outside sub-Saharan Africa carry derived M168 mutation • Coalescent theory: all extant human Y chromosomes descended from single man, Y-chromosomal Adam, who lived in Africa 90,000 years ago • Again, name incorrectly implies that Ychromosomal Adam was only living male of his time - he was not - autosomal genes from many contemporary men of Y-chromosomal Adam are present in today's population - however, only Y-chromosomal Adam produced unbroken line of male descendants carrying his Y chromosome |
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• Newly discovered AMHS fossils from Ethiopia (160,000 years BP)
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Africa
- oldest anatomically modern Homo sapiens (AMHS) fossils recently discovered in Ethiopia - dated at 160,000 years ago • Middle East - next oldest AMHS - Qafzeh site in Israel - dated at 90,000 years ago • Asia/Australia - precise dates controversial - 40,000 to 50,000 years ago • Europe - dominated by Neanderthals until 30,000 years ago - AMHS do not appear in eastern Europe until 40,000 years ago - AMHS do not appear in western Europe until 32,000 years ago • Fossil evidence also supports Outof- Africa hypothesis |
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• Consensus view of genetic and fossil evidence for Multiregional versus Out-of-
Africa models |
Fossil evidence consistent with Out-of-Africa model
• Molecular evidence based on mitochondrial DNA, Y-chromosomal DNA and autosomal DNA all support relatively recent origin of Homo sapiens in Africa • Analyses of DNA sequences from MHC loci, mitochondria and Y-chromosomes all indicate that genetic diversity is greatest in Africa • Most probable scenario is that modern Homo sapiens are derived from geographically discrete population that evolved in Africa 150,000 to 200,000 years ago |
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• Pattern of exodus of Homo sapiens from Africa: when and to where?
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conditions, sea level
230 feet lower than now • Humans crossed Red Sea, gradually expanding along the the coast in east/southeasterly direction • Arrived in Australia by 45,000 years ago • This pattern of migration explains existence of darkskinned, aboriginal peoples in New Guinea and Australia Why exodus via the southern route? • Migration into Europe not achieved until 35,000 to 40,000 years ago |
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• Neanderthal: historical duration, geographic distribution and molecular
evidence of relationship to Homo sapiens |
• Dominant hominin fossil in
Europe and Middle East between 300,000 and 30,000 years ago • Coexisted w/ Homo sapiens (Cro-Magnon man) in Europe between 40,000 and 30,000 years ago • Extinct by 28,000 years ago • Stocky, barrel-chested and very muscular • Remains include many broken and healed bones • Evidence of cannibalism - cut and burned bones at several sites • In 1997, Krings et al. succeeded in sequencing 360 bp of mitochondrial DNA from the femur of the Neanderthal type specimen • The average pair-wise divergence between human-Neanderthal is 27 substitutions compared to an average of 8 differences between geographic populations of Homo sapiens |
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• Neanderthal genome sequencing project
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The Neanderthal Genome Sequencing Project
• Neanderthal Genome Sequencing Project (NGSP) based on a new sequencing technology developed by 454 Life Sciences • Sequences genome in small fragments which is ideal for ‘dead DNA’ • Only 6% of DNA extracted from Neanderthal fossils belongs to Neanderthal |
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• FOXP2 gene and human spoken language: insights from comparative genomics and studies of human disease
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Evolution of complex
spoken language • Evolved in ancestral Homo sapiens population in Africa • Enabled greater integration within social groups, more complex culture and more efficient cultural inheritance • Provided competitive edge in competition with Neanderthal? A. Structure of FOXP2 gene showing mutations that cause verbal dyspraxia B. Phylogenetic analysis indicating high rate of amino acid substitution in human FOXP2 since divergence from human-chimp ancestor C. Humans with verbal dyspraxia exhibit abnormality in brain function during speech |
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• Ethology versus psychology
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Ethology
• The study of animal behavior in relation to the natural environment • The ecology and evolution of animal behavior • Pioneering ethologists – Konrad Lorenz, Niko Tinbergen and Karl von Frisch – first and only animal behaviorists to win Nobel prize (in physiology and medicine, 1973) Psychology • The study of how behavior is modified by experience through learning and memory |
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• Proximate questions versus ultimate questions
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• How Questions = Proximate Questions
– What are the mechanisms underlying behavior? – How is the nervous system wired? – What stimuli elicit a behavior? – How do hormonal levels influence the development and expression of the behavior? • Why Questions = Ultimate Questions = Evolutionary Questions – What is the purpose or function of a behavior? – How does the behavior affect the probability of survival and/or reproduction of an individual? – What was the original step in the historical process that led to the existence of a behavior? – How has the behavior evolved and how has it changed over evolutionary time? |
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• Instinctive behavior = Fixed action pattern = innate behavior
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Instinctive behaviors
• Behaviors that appear in fully functional form the first time they are performed – term “genetically-determined” is somewhat misleading • Called Fixed action patterns (FAPs) by ethologists – web-building in spiders – egg-rolling in geese – pecking response in gull chicks |
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• Learned behaviors
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• Involve the durable modification of
behavior in response to experience |
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• Testis-determining factor (TDF): effects on male brain development and behavior
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Primary sex-determining
signal stems from testis determining factor (TDF) on Y • Organizational effect – affects development of brain when the animal is very young • Activational effect – high concentration of hormone triggers sexual behavior |
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• Estrogens, estradiol
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• In absence of TDF,
ovaries develop and testes regress • Female fetus develops under the influence of estrogens (estradiol) • Brain develops estrogen receptors • Maturing brain develops mechanisms for mating and maternal behavior |
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• Intrauterine position effects on male behavior
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• Rats are multiparous
• Gender of neighboring fetuses influences uterine environment • 2M males – male fetus develops between two brothers – low estradiol • 0M males – male fetus develops between two sisters – high estradiol • Genetically identical 2M males much more aggressive that 0M males |
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• Deprivation experiments as tools for studying instinctive versus learned behavior
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Many studies in
laboratory – rear individuals in isolation to see if they still exhibit the behavior |
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• Alarm call versus contact call in galah parrots reared by pink cockatoos
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• Both species nest in tree holes in Australia
• Sometimes larger cockatoos eject adult galahs from nest after galahs have laid eggs • Cockatoos become foster parents of galah chicks • Provides natural experiment to investigate instinctive versus learned behaviors • Galah chicks learn contact call of cockatoos • By contrast, galah chicks give galah alarm and begging calls despite having been completely isolated from other galahs |
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• Twin concordance studies: identical twin versus fraternal twin comparisons
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• Concordance: presence of a
given trait in both members of a pair of twins • If genes influence probability of exhibiting a trait, identical twin pairs will be highly concordant • Fraternal twin pairs – no more similar genetically than non-twin siblings – less concordant - more pairs in which one twin exhibits the trait and other does not • Comparison of degree of concordance in identical and fraternal twins provides estimate of extent to which genes influence trait expression • Cognitive and personality traits influenced by both genes and the environment • Heritability of behavioral traits similar to that of cardiovascular risk factors • However, most complex behaviors influenced by many genes |
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• Reverse genetics
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Classical genetics
• Observe phenotype • Infer genetic basis from breeding experiments or twin studies Reverse Genetics • Manipulate gene – insert genetically engineered mutant version of gene – silence gene by interference RNA or similar method • Examine phenotypic consequences of genetic manipulation |
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• fruitless gene and male courtship in Drosophila
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Male courtship
• Requires products of fruitless (fru) gene • Gene spliced differently in males and females • Alleles of fru constructed so male splicing pattern occurs in both sexes • Male splicing essential for male courtship behavior and sexual orientation • Male splicing also sufficient to generate male behavior in otherwise normal females • Splicing of single neuronal gene thus specifies essentially all aspects of complex innate behavior: Cell, 121: 785–794 (2005) |
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• Factors favoring instinctive over learned behaviors
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• Short generation time
and absence of parental care – insects, spiders, etc. – no time for learning • Expression of behavior is appropriate in almost every context – pecking response is "feed me" • Expression of behavior has to be right the first time – alarm calls – predator avoidance in kangaroo rats |
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• Releasers (and examples)
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Releaser: specific stimulus
required to elicit a FAP • Red underside acts as releaser of male aggressive behavior in sticklebacks – realistic stickleback model without red elicits no response – any of models with red underside elicit strong aggressive response • Red bill spot in gulls – only a red spot on an elongate rod is needed to elicit pecking response in chicks |
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• Super-releasers in brood parasites
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Duped by a super-releaser
• Cuckoos are brood parasites on several bird species including reed warbler • Female cuckoo lays eggs in nest of host species • Cuckoo chick hatches first and literally kicks out eggs of host species • Gaping beak of comparatively huge cuckoo acts as super-releaser of feeding behavior in reed warbler adoptive parent |
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• Instinctive behaviors in humans: smiling, flirtatious behavior and eyebrow flash
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Study of possible FAPs pioneered by German
ethologist, Irenaeus Eibl-Eibesfeldt • Filmed people across range of cultures with right-angle reflex lens camera • Human universals: smiling, flirtatious behavior and the “eyebrow flash” |
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• What is learning?
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Learning: the durable modification of
behavior in response to experience |
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• Classical conditioning
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Studied by Pavlov
• Involuntary activity becomes associated with stimulus • Animal learns to associate involuntary activity with stimulus • Repeated association of stimulus with reward or punishment causes stimulus alone to elicit response • Turn on light, give dog meat powder, dog salivates • Eventually light alone causes dog to salivate • Occurs in organisms ranging from roundworms to humans |
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• Operant conditioning (trial and error learning)
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Animal learns to associate voluntary behavior with a stimulus
• Trial and error learning • Skinner boxes |
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• Skinner box
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Contains one or more levers which
animal can press • One or more stimulus lights and one or more places in which reinforcement stimuli such as food can be delivered • Presses on levers can be detected and recorded and delivery of reinforcement can be set up to operate automatically • Also possible to deliver other reinforcement stimuli such as water • Or to deliver punishment such as electric shock through the floor of the chamber 24 B.F. Skinner: an evil mad scientist? Thought much of human behavior could be reduced to operant conditioning Legend • Skinner raised own daughter (Deborah) in a "Skinner box” • As a result, she grew up psychologically damaged, sued her father, and committed suicide Fact • Constructed crib similar to large hospital incubator - tall box with door at base and a glass window in front • “Baby tender" provided Deborah with place to sleep without need for layers of clothing and blankets • Deborah slept in baby tender until two and a half years old and grew up a healthy child |
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• Behavioral imprinting
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Behavioral imprinting
• Pioneered by Konrad Lorenz • Form of learning in which individuals exposed to certain key stimuli very early in development form a lifelong association with the object |
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• Imprinting and the domestication of the Paca
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Paca (Agouti paca)
• One of largest rodents in the world • Prized by hunters throughout Central and South America • Weighs up to 30 lbs and is “muy sabroso” Nick Smythe • Former staff scientist at Smithsonian Tropical Research Institute in Panama • Paca as ecologically friendly alternative to cattle • By imprinting newborns on large social groups, able to domesticate paca within just a few generations |
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• Population density, biomass and spacing
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• Population density
– number of individuals of a species per unit area (terrestrial) – number of individuals of a species per unit or volume (aquatic) • Biomass – total mass of all individuals of a species – usually expressed per unit area or volume – corrects for size differences between species • Spacing – the distribution pattern of individuals across space |
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• Clumped versus random versus uniform distribution
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Patterns of spacing
Dispersion • How individuals are distributed over space • Can provide insights into processes that shape group structure Three types of patterns • Clumped (or aggregated) – social behavior – heterogeneous environment • Uniform – usually indicates intraspecific competition • Random – passive dispersal combined with weak interactions between individuals – combined effects of environmental heterogeneity and competition |
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• Population dynamics and demographic processes
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Population dynamics
• Describes whether a population is increasing, decreasing or staying the same size • Depends on demographic processes • Demographic Processes – births – deaths – immigration – emigration |
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• Exponential population growth (recognize equation, graph and know terms in equation)
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• Asexually reproducing
organism that divides in two every 20 min (e.g., E. coli) • In technical terms, a discrete generation, pure birth process model of population growth Exponential growth • occurs when birth rate and death rate do not change with population size; assumes resources are unlimited dN/dt = rate of population change b = average birth rate per individual (per capita) d = average death rate per individual (per capita) N = number of individuals in population (= population size) b-d = rmax • r is called the "intrinsic rate of increase” • per capita rate of population growth If b > d, population will grow exponentially |
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• Carrying capacity
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Carrying capacity (K)
• maximum number of individuals of a species that can be supported by a particular environment Population size is limited by • food • nest sites • disease • predators • social interactions |
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• Logistic population growth (recognize equation, graph and know terms)
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S-shaped growth curve
• dN/dt = rate of population change • N = population size • r = per capita rate of population growth (a constant) • K = carrying capacity |
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• Density dependent versus density independent population regulation
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Density dependent
• Per capita birth or death rate depends on the population density • Usually biotic factors – increased competition for food or space – increased risk of disease or predator attack Density independent • Per capita birth or death rate does not vary with density • Usually abiotic factors – hurricane induced mortality – frost damage from cold spell Equilibrium is reached when birth rate and death rate are equal If birth rate or death rate or both are density dependent, population fluctuates around an equilibrium size, the carrying capacity (K) |
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• Maximum sustained yield
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Maximum sustained yield
• Population size at which the harvest rate is maximized – occurs where dN/dt is at a maximum • For the logistic curve – occurs at the inflection point (K/2) – that is, at half the carrying capacity |
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• Over-harvesting: consequences and examples
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Over-harvesting
• reducing population levels below K/2 • results in low harvest rate • high probability of population extinction • has occurred with many fisheries |
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• Technical solution and tragedy of the commons
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• Technical Solution
• one that requires change only in techniques of natural sciences, and no change in human values or ideas of morality (Hardin 1968) • Over-harvesting and human population growth cannot be addressed with a technical solution The collapse of California’s sardine industry, once the largest fishery in the world, was triggered by overharvesting 16 Over-harvesting of whales • Sequential over-harvesting of whale species has driven several them to the brink of extinction • Classic example of Tragedy of the Commons |
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• How do we calculate doubling time?
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Nt=N0rt
2N0=N0rt ln 2= rt t = ln2/r = 0.693/r |
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• Human population growth: birth versus death rate control
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I. Decrease birth rate
• Natural controls – Low food supply inhibits pregnancy or increases risk of spontaneous abortion • Voluntary family planning – Abstinence – Rhythm method – Artificial contraception – Abortion • Involuntary family planning – Restrictions or fines limiting reproduction, e.g., China – Forced sterilization II. Increase death rate Natural Controls • Infectious disease – AIDS 40% of young adult population HIV positive in some African countries • Mass starvation – Ethiopia, Somalia Genocide/War • Nazi Germany, Liberia, Cambodia, Rwanda, Darfur |
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• Demographic transition
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In industrialized societies
• changing roles of women in society resulted in natural decline in birth rate in association with a decline in death rate In developing countries • public health measures result in rapid decline in death rate without concomitantly rapid decline in birth rate |
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• Life history, life table and cohort
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• Life History
– the stages of growth, reproduction and dispersal that an individual passes through during its life from birth to death • Life Tables – summarize the schedule of births, deaths and reproduction through the life history of an organism • Cohort – a group of individuals born at the same time – used to calculate life tables |
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• Semelparity versus iteroparity
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Semelparity is reproductive event only at one point in time. Iteroparity is both seasonal and continuous reproductive events.
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• Type I, II and III survivorship curves
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• Note: Y-axis (number surviving) is on log-scale
• Type 1: nearly all individuals survive potential life span then die almost simultaneously – annual plants – semelparous, big bang reproducers – approximated by human populations in industrialized societies • Type 2: constant survivorship throughout life span – song birds • Type 3: survivorship very low for young individuals but high for adults – marine organisms with planktonic larvae, e.g., oysters |
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• Ageing versus senescence
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• Ageing
– all time-dependent changes that occur in molecules, cells and tissues of an organism • Senescence – progressive loss of function accompanied by decreasing fertility and increasing mortality with advancing age – subset of aging-related changes that negatively affect the functions of an organism |
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• How can life history theory explain aging?
– Force of natural selection declines with age and late-onset diseases have been invisible to selection throughout much of human evolution. |
Early (incorrect) evolutionary explanations for aging
• Senescence is programmed in order to limit population size or accelerate turnover of populations, thereby aiding adaptation to changing environments (altruism, group selection) • Flaw in argument – Scant evidence that senescence contributes significantly to mortality in the wild Extrinsic mortality in wild environments occurs to an extent that senescentassociated mortality is rare, undermining idea that genes specifically for aging have evolved Evolutionary explanations for senescence I: Mutation/selection balance • Genetic variation maintained by balance between – input of variation from mutation at many loci, and – loss of variation due to selection • Because selection is weaker at older ages, there is higher equilibrium level of deleterious mutations that exert their effects at later ages compared to mutations that exert their effects early in life Evidence for mutation/selection balance • Adaptations that reduce extrinsic mortality (e.g., wings, shells, large brains) are linked to increased longevity • Aging should occur more rapidly in hazardous environments • Populations of opossums on mainland versus islands – On mainland, predation is high aging is faster – On islands, predation much lower aging is slower Evolutionary explanations for senescence II. Antagonistic pleiotropy theory • Senescence occurs because of pleiotropic effects of genes • Selection for alleles that enhance survivorship and/or reproduction at early ages may simultaneously lower survivorship and reproduction at later ages • There is a tradeoff (antagonism) between fitness components early in life and later in life • Because contribution to fitness depends on both strength of gene effect and probability of surviving to be affected, small beneficial effect early in life outweighs large, deleterious effect late in life Evidence for Antagonistic Pleiotropy • Protein p53 is a tumor suppressor gene that restrains uncontrolled growth in cancer • P53 mediates trade-off between cancer risk and rate of aging a. p53 +/+ mouse (wild-type) • High cancer • Slow aging b. p53 +/m mouse (p53 overexpressed) • Low cancer • Rapid aging |
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• Types of species interactions:
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competition, predator/prey
parasitoid/host, parasite/host and mutualism |
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• Resource/exploitation competition versus interference competition
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Resource competition = Exploitation competition
• Two or more species exploit same limiting resource – food, nest sites, settling space in rocky intertidal • Each species depresses population growth rate of the other • Ecological niche – ecological role of a species in a community – range of physical conditions and resources required by a species |
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• Ecological niche: fundamental versus realized niche
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Fundamental niche
• an n-dimensional hypervolume describing range of physical conditions that can be occupied by a species Realized niche • subset of fundamental niche that is actually occupied in presence of other species including predators and competitors Fundamental and realized niches in barnacles • Intertidal zone is an ideal environment for studying relationship between fundamental and realized niche • Characterized by steep environmental gradients • The barnacle, Chthamalus, occupies only small subset of its fundamental niche due to presence of Semibalanus |
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• Gause’s Competitive Exclusion Principle
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• Competitive exclusion principle
(1934) – no two species can occupy the same ecological niche – in a homogeneous environment, one species always drives the other to extinction • Based on experiments with Paramecium aurelia and P. caudatum Gause showed that competitive coexistence could be maintained in heterogeneous environments in which each species does better than the other in one of the “sub-environments” |
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• Competitive coexistence: environmental heterogeneity and disturbance
(biotic and abiotic) |
• Paramecium aurelia and
P. caudatum both predators on yeast and bacteria • Both species grew well in culture tubes by themselves and exhibited logistic growth • When grown together, P. caudatum always declined to extinction • Concluded that no two species with same niche can coexist when resources are limiting |
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• How does environmental heterogeneity enable competitive coexistence
between Chthamalus and Semibalanus? |
In nature, competitive coexistence is
achieved by • Environmental heterogeneity – natural selection favors resource partitioning • Disturbance or predation – prevents competitive exclusion by restricting population growth of the competitively dominant species • Semibalanus is distributed over a broad range of depths but is more sensitive to desiccation • Chthamalus is more desiccation tolerant but is out-competed by Semibalanus lower in the intertidal zone |
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• Resource partitioning, character displacement and ecological release
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Resource partitioning
• dividing of scarce resources so that species with similar requirements can use resources in different ways, in different places, and at different times • the ghost of competition past • indirect evidence of earlier competition resolved by evolution of niche differentiation Anolis lizards on Caribbean islands a. Canopy species b. Twigs on periphery c. Base of trunk d. Open, grassy areas on ground Character displacement • Tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species Ecological release • a species expands its resource use when a competitor species is absent |
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• Correlative versus experimental evidence for competition
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Most direct method of assessing
competition • Remove individuals of species A and measure response of species B • Removal treatments easy to carry out on sessile species • Connell’s hypothesis – Chthamalus competitively excluded from lower intertidal by Semibalanus • Transplanted rocks from high intertidal to low intertidal • Experimentally removed Semibalanus from one side of rock and left other side as control • Monitored survival of Chthamalus on both sides of rocks |
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• Predator-mediated coexistence and keystone species: Pisaster example
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• Sea star (Pisaster) is
predator of mussels (Mytilus californianus) • Mussels are competitive dominant species along rocky shores of Pacific northwest • In absence of Pisaster, mussels monopolize space • Pisaster lowers population density of Mytilus, preventing competitive exclusion • Pisaster is keystone species |
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• Interference competition: examples
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• One species directly
interferes with another to prevent it from using a resource • Lions kill cheetah cubs but don’t eat them • Lions kill hyenas but don’t eat them • Common in sessile marine invertebrates that compete for space – anemones sting each other – corals chemically digest their competitors |
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• Predator/prey versus parasitoid/host versus parasite/host
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One species benefits, other
is harmed • Predator/Prey: predator benefits, prey is harmed • True predation: predator kills prey in a single act • Predator/prey interactions characterized by oscillations in predator/prey numbers Parasitoid/host and parasite/host Again, one species benefits, other is harmed • Parasitoid/host: larvae of parasitoid slowly consume host and kill it – 60,000 species of parasitoid wasps in family Ichneumonidae – Cotesia congregata injects both eggs and polydnavirus into host, the tobacco hornworm – virus causes host immunosuppression, allowing parasitoids to mature without invoking strong host immune response • Parasite/host: parasite garners resources from host but doesn't necessarily kill host |
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• Mutualism: examples
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Both species benefit from the
interaction • Flowering plants and animal pollinators • Corals and zooxanthellae • Ruminants (cows, sheep, goats, etc.) and endosymbiotic bacteria – mutualism enables digestion of cellulose • Termites and intestinal endosymbionts |
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• Mimicry: Mullerian versus Batesian mimicry
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Mullerian mimicry
• Similarity in appearance between two or more distantly-related noxious or dangerous species • Both species benefit from this convergent similarity Batesian mimicry • Form of mimicry in which an innocuous mimic species gains protection by resembling noxious or dangerous model species • Mimic species benefits • Model species may be slightly harmed |
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• Biodiversity
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Biodiversity: biological
diversity at the level of the • Gene • Population/species • Community/Ecosystem |
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• Conservation biology
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• Goal is to understand causes
and consequences of biodiversity in order to develop scientifically-sound principles for maximizing its preservation |
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• Mutational meltdown/extinction vortex
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• Selection not strong
enough to override genetic drift in small populations |
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• Evolutionarily significant unit (ESU): 3 definitions
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The agony of choice
• More biodiversity for the dollar Evolutionarily significant unit (ESU) • A unique group of organisms that should be managed separately • A population reproductively isolated from other conspecific population units and representing an important evolutionary legacy of the species |
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• Reciprocally monophyletic
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• ESU should be reciprocally monophyletic for mitochondrial
DNA – all alleles in each population genealogically closer to one another than to any alleles in the other population |
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• Dusky Seaside Sparrow: lessons from molecular systematics
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• Dusky Ammodramus maritimus
nigrescens was phenotypically divergent from other subspecies - darker head and back • Faced with extinction due to loss of wetland habitat in NE Florida • Last two males crossed with females from Gulf coast subspecies (A. m. peninsulae) – crosses unsuccessful • Post-extinction mitochondrial DNA sequencing revealed that – Dusky differed little from other Atlantic coast subspecies – subspecies A. m. peninsulae geographically close but genetically very different |
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• Two views of the Tropics
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• Tropics as a
fascinating repository of biological diversity – Charles Darwin on the Tropics – Alfred Russell Wallace on the Tropics • Tropics as a hostile and dangerous place that should be tamed and exploited for human development – Beyond the Chagres |
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• Where are tropical rain forests?
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• 6% of land surface or about 8.5 million km2
• About 2/3 of rain forest area in South America (Amazonia); remainder in Asia (Indonesia and New Guinea) and Africa (Congo Basin & Zaire) • High productivity • Rapid decomposition • Low volume of nutrients in soil • Acidic soils |
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• Seasonality and distance from the equator in tropical rain forests
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• French Guiana
– 40 N latitude – 2.5 month continuous dry season • Panama – 90 N – 4 month continuous dry season • Belize – 150 N – 5 month continuous dry season |
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• Tropical forest types: how defined and which is most and which is least diverse?
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Lowland Forest
• To 1000 m elevation • Canopy height 45 m • Highest total diversity Montane forest • 1000 m to 3000 m elevation • Canopy 2 to 15 m • Abundant epiphytes Mangroves • Estuarine • Low diversity but high productivity • Most genera distributed worldwide Flooded Forests of the Amazon • Terrestrial communities submerged for much of rainy season • Soil instability favors stilt roots and flying buttresses • Fish important in seed dispersal • Harsh conditions and low species diversity |
