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Chapter 09- From Tree Shrew to Ape.pdf

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McMaster University

Chapter 10: From Tree Shrew to Ape Bernard Ho - during Permian and early Triassic periods, much of the world’s fauna was dominated by therapsids, a diverse group of reptiles - at end of Triassic, most therapsid groups disappeared, and dinosaurs radiated most lands - at end of Mesozoic, placental and marsupial mammals dominated - modern humans have many complex adaptations, like grasping hands, bipedal locomotion (walking upright on two legs), tool-making, language, and cooperation Continental Drift and Climate Change - evolution produces adaptation, but what is adaptive in one environment may not be adaptive in another environment - if environment varied over time, then evolution would have to track a moving target instead of moving towards a fixed goal - the positions of the continents have changed relative to each other and to the poles - one factor that has caused the world to change a lot is the movement of continents, or continental drift - continents are not fixed, but are enormous, relatively light plates of rock that make up the continents slowly wander around the glove, floating on the denser rock that forms the floor of the deep ocean - about 200 mya, all the land that exists today was once a giant landmass called Pangaea - about 125 mya, Pangaea broke off into a northern half, called Laurasia (North America and Eurasia minus India), and a southern half, called Gondwanaland - Gondwanaland separated into Africa and India - India headed north and crashed into Eurasia - continental drift is important in the history of human lineage because: 1. oceans serve as barriers that isolate certain species from others, so the position of the continents plays an important role in the evolution of species 2. continental drift is one of the engines of climate change, and climate change has fundamentally influenced human evolution - size and orientation of continents have effects on climate o very large continents tend have severe weather The Methods of Paleontology - much of our knowledge of history of life comes from study of fossils, the mineralized bones of dead organisms - bones of dead organisms may be preserved long enough for the organic material in the bones to be replaced by minerals (mineralized) from surrounding rock o natural copies of bones are called fossils - there are several radiometric methods of estimating the age of fossils - radiometric methods provide one of the most important ways to date fossils 1 1. potassium-argon dating  used to date age of volcanic rocks found in association with fossil material  molten rock emerges from volcano at high temperatures  all of argon gas is boiled out of rock  any argon present in rock must be due to decay of potassium  ratio of potassium to argon can be used to date volcanic rock  argon-argon dating  allows more accurate dating of single rock crystals 2. carbon-14 dating (radiocarbon dating)  based on unstable isotope of carbon that living animals and plants incorporate into their cells  measure ratio of unstable carbon-14 to the stable isotope carbon-12  once animal dies, carbon-14 decays into carbon-12 at a constant rate 3. thermoluminescence dating  based on an effect of high-energy nuclear particles traveling through rock  particles come from decay of radioactive material in and around the rock and from cosmic rays that bombard the Earth from outer space  heating a rock relaxes bonds holding that atoms in the crystal lattice together  all trapped electrons are recaptured by their respective atoms, giving off light  possible to estimate number of trapped electrons in these flints of heating them in laboratory and measuring amount of light given off 4. electron-spin-resonance dating  used to determine age of apatite crystals, an inorganic component of tooth enamel  crystals are preserved in fossil teeth and are bombarded by a flow of high-energy particles that generate trapped electrons in the crystal lattice  scientists estimate number of trapped electrons by subjecting teeth to a variable magnetic field (using a technique called “electron spin resonance”) - methods based on isotopes that decay very slowly, such as potassium-40, work well for fossils from distant past - potassium-argon cannot be used to date samples less than about 500 000 years old - carbon-14 can be used only to date sites that are less than about 40 000 years old - absolute radiometric dating is supplemented by relative dating methods based on magnetic reversals and comparison with other fossil assemblages - radiometric dating methods are problematic for two reasons: 1. a particular site may not always contain material that is appropriate for radiometric dating 2. radiometric methods have relatively large margins for error - relative methods are used to supplement these absolute methods: 2 1. based on remarkable fact that, every once in a while, the Earth’s magnetic field reverse itself 2. make use of fact that sometimes the fossils of interest are found in association with fossils of other organisms that existed for only a limited period of time The Evolution of Early Primates - evolution of flowering plants created a new set of ecological niches o primates were among the animals that evolved to fill these niches - during first two-thirds of Mesozoic, forest of world were dominated by gymnosperms - breakup of Pangaea during Cretaceous gave rise to flowering plants, called angiosperms - angiosperms depend on animals pollinating them - ancestors of modern primates were small-bodied nocturnal quadrupeds much like contemporary shrews - the plesiadapiforms give us information what earliest primates were like o from Paleocene epoch, 65-54 mya o varied from tiny, shrew-sized creatures to animals as big as a marmot o well-developed sense of smell o probably terrestrial - Carpolestes simpsoni had an opposable big toe with a flat nail, but claws on its other digits o claws and hands helped it climb large-diameter tree trunks o had low-crowned molars, which are suited for eating fruit o possess some but not all of the traits that characterize modern primates  argued that forward-facing eyes that provide binocular stereoscopic vision, grasping hands and feet, and nails on the toes and fingers all evolved together to enhance visually directed predation on insects in branches of trees  discovery that grasping hand and feet evolved in a frugivorous plesidapiform species before eyes shifted forward presents problems in this hypothesis - discovery of C. simpsoni helps explain why natural selection favored the basic features of primate morphology - another scientist proposed that grasping hands and feet allowed early primates to forage on fruit, flowers, and nectar in the terminal branches of angiosperms - eyes were shifted forward to facilitate visually directed predation on insects - Eocene epoch (54-34 mya) was even wetter and warmer than preceding Paleocene - Eocene primates were highly successful and diverse group, occupying a range of ecological niches - it is in these Eocene primates that we see at least the beginning of all the features that define modern primates o they had grasping hands and feet with nails instead of claws, hindlimb- dominated posture, shorter snouts, eyes moved forward in the head and encased in a bony orbit, and relatively large brains - Eocene primates are classified into two families: Omomyidae and Adapidae 3 - some omomyids had huge eye orbits, like modern tarsiers o suggests they were nocturnal because nocturnal primates do not have tapeta o tapetum is a reflecting layer behind the retina that increase the light-capturing capacity of the eye o some seem to have been adapted for frugivory, and others for more insectivorous diets o some have elongated calcaneus bones in feet, and may have been able to leap from branch to branch - adapids had smaller eye orbits and were likely diurnal o resemble living lemurs in their teeth, skull, nasal, and auditory regions o however, unlike lemurs, they do not display tooth comb, a specialized formation of incisors used for grooming o diets range from insects to fruits o generally larger than omomyids, and their postcranial bones (bones that make up skeleton below neck) The First Anthropoids - primates similar to modern monkeys may have first evolved during the Eocene, but they radiated during the Oligocene - origins of anthropoids extend back into Eocene epoch - earliest unambiguous anthropoid fossils are found at a site in the Fayum Depression of Egypt - the Fayum is now one of the driest places on Earth, but it was once a warm, wet and somewhat seasonal habitat - evidence suggest that the Fayum was a swamp during the Oligocene - the Fayum contains one of the most diverse primate communities ever documented o includes at least five groups of prosimians, one group of omomyids, and three groups of anthropoid primates: the oligopithecids, parapithecids, and proliopithecids - parapithecids were a very diverse group; currently divided into four genera and eight species o many aspects of parapithecid teeth and postcranial anatomy are also primitive, suggesting that they may have been the unspecialized ancestors both of more derived Old World monkey lineages and of the New World monkeys - the proliopithecids are represented by two genera and five species o largest and most famous of the proliopithecids is named Aegyptopithecus Zeuxis, who is known from several skulls and a number of postcranial bones o A. zeuxis was a medium-sized monkey  relatively small brain  shape and size of teeth suggest that it ate mainly fruit  males larger than females, indicating that they probably lived in nonmonogamous social groups - third group of Fayum antrhopoids, the oligopithecids, were among the earliest Fayum monkeys 4 o share many primitive features with Eocene prosimians o also share some derived features with contemporary anthropoids o dental formula of some oligopithecids was the same as the modern Old World monkeys and apes o oldest New World monkey fossils come from a late-Oligocene site in Bolivia  monkeys at this site have three premolars like modern New World monkeys and were about size of owl monkeys  shape of molars suggests they were frugivores - absence of Oligocene primate fossils in North America and the many similarities between New World monkeys and the Fayum primates suggest to many scientists that the ancestor of the New World monkeys came from Africa o problem is that scientists don’t know how they could have gotten from Africa to South America since the two continents were separated by at least 3000 km - other researchers suggest that New World monkeys descended from a North American primate o two problems with this:  although there is evidence of Eurasian prosimians reaching North America earlier, there are no known anthropoid fossils from North America for that time  North America did not join South America until 5 mya  this scenario requires also requires the anthropoid ancestor to have made an ocean voyage The Emergence of the Hominoids - apes and monkeys differ in some features of their skeletal anatomy, dentition, brain size, and life history patterns - some of anatomical features that distinguish living apes from Old world monkeys are related to their locomotor behavior - monkeys climb along on tops of branches, using their hands and feet to grip branches and use their tail for support - apes make much more use of suspensory postures during feeding and locomotion o swing from branch to branch as they move through trees and often hang from branches while feeding o compared to monkey’s, apes have relatively short trunks, broad chests, long arms, and flexible shoulder joints; and have no tails - fossils that are now assigned to species Morotopithecus bishop were first collected at site in Uganda and were classified as hominoids - a number of skeletal features claimed that it moved like an ape, not like a monkey o femur suggests that it might have climbed slowly and cautiously, and the shape of the scapula indicates that it could have hung by its arms and brachiated slowly through trees - before appearance of Moropithecus, most paleontologists believed that oldest hominoids were members of family Proconsulidae 5 - Proconsul share several derived features with living apes and humans that we don’t see in anthropoid primates o don’t have tails and did not have fleshy sitting pads that Old World monkeys and gibbons have o also had larger brains in relationship to body size than similarly sized monkeys had o teeth had thin enamel, which is consistent with a frugivorous diet o postcranial anatomy was like that of quadrupedal monkeys, but certain features of feet and lower legs were more apelike o had an opposable thumb - evolutionary history of apes of Miocene is poorly understood - no clear candidates for ancestors of any modern apes, except the orangutan, who shares a number of derived skull features with Sivapithecus of the middle Miocene - we can be certain that earliest hominins evolved from some type of Miocene ape - apes flourished during Miocene, but all but a few genera and species eventually became extinct - number of living monkey species greatly exceeds number of extinct monkey species 6 Chapter 11: From Hominoid to Hominin Bernard Ho - during Miocene, Earth’s temperature began to fall because: o total amount of rain declined each year o rainfall became more seasonal, so there were several months each year when no rain fell - some animals failed to adapt and became extinct - spread of woodland and savanna led to evolution of first hominins about 6 mya - hominins were different from any of the Miocene apes in two ways: 1. they walk upright  bipedal locomotion led to major morphological changes in bodies 2. in new savanna and woodland habitats, new kinds of food became available  caused changes in teeth, jaws, and skulls - 5 categories distinguish modern humans from contemporary apes: 1. We habitually walk bipedally. 2. Our dentition and jaw musculature are different from those of apes in a number of ways. 3. We have much larger brains in relation to our body size. 4. We develop slowly, with long juvenile period. 5. We depend on an elaborate, highly variable material and symbolic culture, transmitted in part through spoken language. - hominins are not included in the same genus (Homo) as modern humans At the Beginning - last common ancestor of humans and chimpanzees lived between 7 and 5 mya - Ardipithecus ramidus, Orrorin tugenensis, and Sahelanthropus tchadensis have begun to shed light in history of human lineage Ardipithecus - genus Ardipithecus include two species (A. ramidus and A. kadabba) and both have similarities to both humans and chimpanzees - several features suggest that A. ramidus was a hominin o opening on bottom of skull through which spinal cord passes (foramen magnum) is located forward under the skull, as it is in humans o forward placement of foramen magnum is associated with bipedal locomotion o were smaller, more incisorlike canine teeth that are not sharpened by the lower premolar, unlike apes, which have relatively large canines o enamel is thinner than in other early hominins, and the canines are smaller than in chimpanzees and gorillas but larger than in later hominins o seemed to have lived in a forested environment  based on fossils of wood and seeds found at site - unclear whether Ardipithecus is related more closely to humans or to chimpanzees 7 Orrorin tugenensis - second early fossil with similarities to humans - incisors, canines, and one of the premolars are more like with the teeth of chimpanzees than of later hominins - arm and finger bones have features that are believed to be adaptations for climbing - thigh bones are more similar to those of later hominins than to those of apes - habitat was a mix of woodland and savanna Sahelanthropus tchadensis - fossil consists of a nearly complete cranium, two fragments of lower jaw, and several teeth - fossil shook paleontological community because: 1. it came from an unexpected place  most work on human evolution has focused on East Africa and South Africa, but this specimen comes from the middle of Africa  suggests that hominins had a larger range than believed 2. this fossil is surprisingly old  geology of site does not allow radiometric or paleomagnetic dating  oldest hominin cranium 3. possesses a very surprising mix of anatomical features  face is relatively flat and massive browridge over eyes The Hominin Community Diversifies - a number of hominin species lived in Africa between 4 to 2 mya o they are divided into three genera: Australopithecus, Paranthropus, and Kenyanthropus 1. Australopithecus o includes 6 species: A. anamensis, A. afarensis, A. africanus, A. garhi, A. habilis, and A. rudolfensis o the australopithecines had small bipeds with teeth, skull, and jaws adapted to a generalized diet 2. Paranthropus o includes 3 species: P. aethiopicus, P. robustus, and P. boisei o similar to the australopithecines from neck down, but had massive teeth and jaws adapted to heavy chewing of tough plant materials, and a skull modified to carry enormous muscles necessary to power chewing apparatus 3. Kenyanthropus o includes 1 species: K. platyops o distinguished by a flattened face and small teeth Australopithecus - A. anamensis o bipedal, but had a more apelike skull than later australopithecines had o found near Kenya o found parts of upper and lower jaw (part of tibia- larger of two bones in lower leg) and numerous teeth 8 o large molars with thick enamel and smaller canines, and the shapes of knee and ankle joints strongly indicate it was bipedal o arm bones suggest that it retained adaptations for life in trees o ear holes are small and shaped like ellipses, as they are in living apes, but ear holes of later australopithecines are larger and more rounded o dental arcade is more like U shape (seen in chimpanzees and gorillas), unlike the V-shaped dental arcade seen in later australopithecines o lived in a mixture of habitats including dry woodlands and gallery forest along rivers - A. afarensis o most extensive fossil collections come from several sites in Ethiopia o found bones of a 3 million year old knee joint that showed striking similarities to a modern human knee o also discovered fossils in Tanzania o habitats ranging from woodland to dry savanna o cranium (skull minus lower jawbone) is quite apelike o its endocranial volume (capacity of brain cavity) is small  about size of modern chimpanzee o front of case below the nose is pushed out- a condition known as subnasal prognathism o jaw point is shallow o teeth and jaws are intermediate between those of apes and humans 1. dental arcade of A. afarensishas an intermediate V shape, the canines are medium-sized, and the diastema (space between teeth and jaw) is modest 2. in its canines, A. afarensis displays less sexual dimorphism than chimpanzees but more than modern humans 3. first lower premolar has a small inner cusp and a larger outer cusp  chimpanzees have a single cusp, whereas humans have two cusps of approximately equal size o was bipedal Cranium of A. afarensis 9 Teeth and Jaws of Australopithecus afarensis Pelvis of A. afarensis 10 Schematic Diagram of Lower Body at Point of Stride o although they are bipedal, it is not clear whether this hominin had same striding pattern as modern humans because many features in the pelvis and legs are different than those from modern humans o have shorter legs than modern humans o pelvis is much wider, which means minimized vertical motion of body during walking o probably spent a good deal of time in trees o traits of feet, hands, wrists, and shoulder joints suggest that they were partly arboreal o variation in size of A. afarensis adults  could represent sexual dimorphism  could also represent two different species  bigger one could have adapted to savanna and smaller one could have adapted between tree climbing and walking - A. africanus o base of skull has fewer air pockets, face is shorter and less protruding below the nose, the canines are less dimorphic, and the base of cranium is bent further upward, or flexed o molars are quite big, and lower jaw is larger and sturdier than in modern humans o matured rapidly, unlike humans o if we know rate at which teeth developed in extinct hominins, we can estimate how rapidly they developed overall  enamel is secreted as teeth grow o developed faster than chimpanzees, not slowly like humans  these results show that australopithecine infants did not have as long a period of dependency as human children do 11 - A. garhi o lived about 2.5 mya in East Africa o discovered a number of postcranial bones and partial skeleton of one individual in Ethiopia o later discovered pieces of skull, maxilla (upper jaw), and teeth come from the same stratigraphic level as postcranial remains o had small brains, like A. afarensis and A. africanus o canines, premolars, and molars were generally large o also had a sagittal crest, a fin of bone that runs along the centerline of the skull (like a Mohawk haircut) o do not reveal some interesting developments in hominin lineage o resembles chimpanzees in proportions of bones (humerus, the radius and ulna (the lower bones of arm), and femur are about same length) - A. habilis/ rudolfensis o cranial bones indicated that it had a much larger brain than Austalopithecus had, and small, more humanlike teeth o nicknamed “handy man” because it was believed that they were found responsible for making simple, flaked-stone tools that were discovered nearby o had a much larger brain than any known australopithecine had o had a relatively large, australopithecine-like face o skulls and teeth of fossils were variable o analysis of layering of dental enamel indicates that specimens assigned to the species habilis and rudolfensis had rapid apelike developmental patterns, like other australopithecines o fossils assigned to habilis and rudolfensis were classified members of genus Homo because: 1. brain of these fossils is bigger than that of any of the australopithecines 2. teeth are smaller and have thinner enamel, and the dental arcade is more parabolic, than in australopithecines o scientists argued that these fossils do not elong in Homo but should be included in the genus Australopithecus Paranthropus - skull has a distinct black colour - lived about 2.5 mya - similar to A. afarensis o same jaw structure o sexually dimorphic o equipped with relatively small brains in relation to body size - skull is very different than australopithecines - molars are enormous, lower jaw is very large, and entire skull has been reorganized to support massive chewing apparatus o has pronounced sagittal crest, which enlarges surface area of bone available for attaching the temporalis muscle, one of muscles that works the jaw 12 - has large teeth, which requires even more space for muscle attachment, and the sagittal crest served this function - cheekbones are flared outward to make room for enlarged temporalis muscle - P. robustus o appeared about 1.8 mya and disappeared about 1 mya o brains averaged about 530 cc o postcranial anatomy shows that they were undoubtedly bipedal o it is unclear what the paranthropines were doing with this massive chewing apparatus  animals with large teeth are associated with a diet of tough plant materials, and omnivorous animals typically have relatively large canines and incisors - Paranthropus boisei o large molars o even more robust than P. robustus o body is somewhat larger than body of P. robustus, and its molars are larger than those of P. robustus o skulls are even more specialized for heavy chewing Kenyanthropus - Kenyanthropus platyops is a recently discovered species that lived in East Africa between 3.5 and 3.2 mya - cranium has a small ear hole - like most of early hominins, it has a chimpanzee-sized braincase and thick enamel on its molars - molars are substantially smaller than those of any other early hominin except A. ramidus - broad and very flat face - fossils found in association with cranium suggest that they lived in a mix of woodland and savanna Hominin Phylogenies - hard to construct phylogenetic tree because there is extensive convergence and parallelism in hominin evolution The Evolution of Early Hominin Morphology and Behaviour - although there are many gaps in fossil record, we know several important things - human lineage is derived from a small biped who was adept in trees o its teeth and jaws were suited for a generalized diet o males were considerably larger than females, their brains were the same size as those of modern apes, and their offspring developed rapidly like modern apes The Evolution of Bipedalism - walking on two legs is an efficient form of locomotion on the ground 13 o Rodman and McHenry at UC Davis found that bipedal and quadrupedal locomotion are more or less equivalent in efficiency - why did humans become bipedal when they left trees? o ancestors of terrestrial monkeys were arboreal quadrupeds who fed on tops of branches, but ancestor of hominins were suspensory feeders (hanging below branches to feed, as modern orangutans do) o selection might have favored quadrupedalism among aniamls descended from above-the-branch feeders and favored bipedalism among animals descended from suspensory feeders - erect posture allowed hominins to keep cool o heat stress is a more serious problem in the hot savanna than in the shade of forest o most savanna creatures have adaptations that allow their body tempeatures to rise during the day and to cool at night o also have adaptations that keep the temperature of blood in their brain well below temperature of blood in rest of their bodies  however, this is not available to hominins o instead, humans have evolved a system of evaporative cooling: sweating o erect posture helps reduce heat stress and lessens amount of water necessary for evaporative cooling in three different ways 1. sun strikes a much smaller fraction of body of an erect hominin than a quadrupedal animal of same size 2. air is warmer near the ground than it is higher up 3. wind velocities are higher 2 m off ground than they are 1 m off ground  moving air increases efficiency of evaporative cooling - bipedal locomotion leaves hands free to carry things o quadrupeds can’t carry things in hands without interfering with their ability to walk and to climb  must carry things in their mouths o bipedal hominins can carry larger quantities of food in their hands and arms - bipedal posture allows efficient harvesting of fruit from small trees o allows efficient harvesting of fruit of small trees that predominate in African woodlands Early Hominin Subsistence - increased seasonality in rainfall favors a greater dependence on foods available during dry season: corms, tubers, and meat - little competition during rainy season because of abundance of food; however there is a lot of competition during dry season - Rob Foley, from Cambridge University, suggested that hominin lineage may have adapted to increased seasonality in two different ways 1. robust hominins in genus Paranthropus, with huge jaws and chewing muscles, may have specialized in processing tough plants 2. less robust species may have shifted to a more omnivorous diet and relied more heavily on meat 14 - many anthropologists thought it was unlikely that the early hominins ate very much meat because hunting requires careful planning and subtle coordination o small-brained hominin must have lacked necessary cognitive and linguistic skills o however, chimpanzees have shown to ambush animals on the forest floor - earliest identifiable tools first appear about 2.5 mya, and it is possible that one of the species discussed manufactured these tools - chimpanzees make and use tools to perform a wide variety of tasks o use branches, vines, sticks, and twigs to poke into ant nests and termite mounds o are toolmakers and toolusers o use stone hammers and anvils to crack open hard-shelled nuts o approximately half of the tasks for which chimpanzees manufacture and use tools are related to food processing and food acquisition - McGrew argues that the reason chimpanzees don’t make greater use of tools is because they can’t transport them easily o that’s why it doesn’t pay off for chimpanzees to put a lot of effort into making tools Early Hominin Social Organization - unlike most primates, chimpanzees frequently share food - mothers regularly share with their infants, and adults share food with each other under certain circumstances - mothers are most likely to share foods that are difficult for infants to obtain or to process independently - more often, kills are retained by captor and shared with others who cluster closely around - males, who are generally the ones who control the kills, share food with other males, adult females, juveniles, and infants - fossils give evidence that hominins lived in large groups o sexual dimorphism in body size is consistent with formation of multimale or one- male groups - analysis indicates that terrestrial primates usually live in bigger groups, on average, than arboreal primates do o large groups may be used for defense against terrestrial predators - large groups tend to contain several adult males because it is difficult for a single male to maintain exclusive access to a large number of females 15 Chapter 12: Oldowan Toolmakers and the Origin of Human Life History Bernard Ho The Oldowan Toolmakers - the earliest identifiable stone tools are from about 2.5 mya - at sites about 2.3 mya, researchers found an extensive array of stone artifacts, including flakes (small, sharp chips), cores, hammer stones, and debris from manufacturing - these artifacts, collectively are called Oldowan tool industry, are very simple o round stones that have been chipped o artifacts are quite variable in shape and size o made from different raw materials o tool industries are collections of tools that are found in a particular region and time - we do not know which hominin species were responsible for making tools - it is also possible that earliest stone tools were made by species that do not appear until later in the fossil record - stone tools are more durable than bones, so the archaeological record is usually more complete than the fossil record Complex Foraging Shapes Human Life Story - anthropologists divide foods acquired by forages into three types according to the amount of knowledge and skill required to obtain them o these are, in order of increasing difficulty of acquisition, collected food, extracted foods, and hunted foods 1. collected foods can be simply collected from the environment and eaten 2. extracted foods come from things that don’t move but are protected in some way  these things must be processed before food can be eaten 3. hunted foods come from things that run away, and thus must be caught or trapped  may also need to be extracted or processed before consumption Chimp Humans Collected 96% 10% Extracted 4% 30% Hunted 2% 60% - humans depend on hard-to-learn skills to acquire food - contemporary foraging peoples depend on extracted and hunted foods to a much greater extent than chimpanzees do - unlike other predators, humans must learn a very diverse set of hunting skills - most large mammalian predators use one of two methods: wait in ambush, or combine a stealthy approach with fast pursuit 16 - efficient extraction of resources requires considerable skill - Blurton and Jones (both from UCLA) discovered digging up deeply buried tubers from rock soil as a complex mining operation involving much clever engineering of braces and levers - reliance on hunting and extractive foraging favors food sharing and division of labour in contemporary foraging groups - usually, men take primary responsibility for hunting large game, and women take primary responsibility for extractive foraging - division of labour makes sense on two grounds: 1. hard-to-learn techniques reward specialization  takes a long time to be good hunter, and it takes a long time to learn how to dig tubers 2. because child care is more compatible with gathering than with hunting, and lactation commits women to child care for a substantial portion of their adult lives, it makes sense that men specialize in hunting - reliance on meat eating favours evolution of food sharing o if several hunters share catch, chance of starvation is much lower - food sharing and division of labour lead to extensive flows of food between people of different ages and sexes - selection may have favoured larger brains, a prolonged juvenile period, and a longer life span because these traits make it easier to learn complex foraging methods - complex, learned foraging techniques allow humans to acquire highly valuable or otherwise inaccessible food resources - meat is a much better source of nutrients that animals need than is the usual primate fare of leaves and ripe fruit o meat is high in protein, lipids, and is rich in energy - humans were able to access a large supply of food by learning how to use tools to dig them up - if learning is valuable, natural selection will favour adaptations that make a better learner o favour larger brains and greater intelligence o reliance on complex learned foraging skills would also favour the evolution of a prolonged juvenile period  this will generate longer life span  longer life span is costly, but added time allows learning that produces more capable adults - food sharing and vision of labour lead to reduced competition between males and reduced sexual dimorphism o when males invest in offspring, there is less male-male competition and reduced sexual dimorphism Evidence for Complex Foraging by Oldowan Toolmakers 17 - Oldowan toolmakers are plausible candidates for species that links early apelike hominins to later hominins, who have more humanlike life history patterns - contemporary foragers rely on complex, hard-to-learn foraging techniques to a much greater extent than other primates do, and this shift can explain evolution of main features of human life history - contemporary experiments suggest that Oldowan tools could be used for a variety of tasks, including the butchery of large animals o Schick and Toth found that stone flakes struck from cobble cores can be used for many tasks, including butchering large animals like elephants o cores can be used for a more limited number of jobs, such as chopping down a tree to making a stick or spear - wear patterns on bone tools from South Africa suggest that they were used to excavate termite mounds o extractive foraging (commonly done with wooden sticks) is likely to leave traces in archaeological record o evidence suggests that hominins from this period were extractive foragers o found number of broken bones that had wear patterns suggesting that they had been used as tools o analysis shows that the fossil tools were used for digging in termite mounds Archaeological Evidence for Meat Eating - at several archaeological sites in East Africa, Oldowan tools have been found along with dense concentrations of animal bones - bones found belong to a wide range of animal species (pigs, horses, elephants, hippopotamuses, rhinoceroses, and a variety of carnivores) - along with these bones, Leakey found several kinds of stone artifacts: cores, flakes, battered rocks that may have been used as hammers or anvils, and some stones that show no signs of human modification or use - association of hominin tools and animal bones does not necessarily mean that early hominins were responsible for these bone accumulations - there are other possibilities for the accumulation of bones o bones may have been deposited there by moving water or by other carnivores o maybe animals died of natural causes - study of taphonomy provides one means to resolve questions about what happened at sites o taphonomy is the study of the processes that produce archaeological sites  examine characteristics of contemporary kill sites (spots where animals were killed, processed, and eaten) - taphonomic analyses at Olduvai Gorge suggest that bones at most of these sites were not accumulated by natural causes - sediments surrounding Olduvai sites do not show any of the features characteristic of sediments deposited by rapidly moving water - concentrations of bones were not due to deaths of a large number of animals at one spot 18 - taphonomic analyses suggest that hominins were active at a number of the Olduvai sites and used tools at these sites to process carcasses - bones at these sites provide direct evidence of hominin activity - teeth and tools leave characteristic marks and grooves in ground Hunters or Scavengers? - there has been controversy about whether the Oldowan hominins were hunters or scavengers - we assume they ate meat because of the bones at archaeological sites - eating meat does not imply hunting - for most contemporary carnivores, scavenging is as difficult and dangerous as hunting - scavengers must be brave enough to snatch kills from jaws of hungry competitors, shrewed enough to hang back in shadows until kill is momentarily left unguarded, or patient enough to follow herds and take advantage of natural mortality - most large mammalian carnivores practice both hunting and scavenging - taphonomic evidence suggests that early hominins acquired meat both by scavenging and by hunting - an animal that tries to defend its kill risks losing it to scavengers, so some animals drag their kill into trees and eat their meat in safety - this means that limb bones usually disappear from a kill site first, and less meaty bones (vertebrae and skull) disappear later or remain at the kill site - if hominins obtained food from scavenging, we would expect to find cut marks made by tools mainly on bones typically left at kill sites by predators - if hominins obtained food from own kills, we would expect to see cut marks mainly on large bones, like limb bones - at Olduvaie Gorge, cut marks appear on all kinds of bones, meaning that sometimes hominins stole kills or that sometimes they killed the preys themselves Domestic Lives of Oldowan Toolmakers - evidence shows that Oldowan toolmakers used their tools for extractive foraging and to process prey carcasses - obtained carcasses through mix of hunting and scavenging - nearly all contemporary foraging peoples establish a temporary camp (home base), where food is shared, processed, cooked, and eaten - camp is also place where people weave nets, manufacture arrows, sharpen digging sticks, string bows, make plans, resolve disputes, tell stories, and sing songs - has huts and shelters - some archaeologists have interpreted dense accumulations of stones and bones as home bases, much like those of modern foragers, but this view is not consistent with some of the evidence - dense collections of bones and artifacts were thought to b the result of prolonged occupation of home base 19 - there is even a circle of stones that is similar to circles of stones anchoring walls of simple huts - however there are some inconsistencies: 1. both hominins and nonhminin carnivores were active at Olduvai sites  most bone marks were gnawed by nonhominin carnivores 2. hominins and nonhominin carnivores apparently competed over kills  perhaps carnivores were killed (and eaten) when attempting to scavenge hominin kills or when hominins attempted to scavenge their kills 3. modern kill sites are often scene of violent conflict among carnivores  conflict occurs among members of different species as well as same species  kill attracts many other animals 4. bones accumulated at Olduvai sites are weathered  bones that lie on surface get cracked and peeled  the longer they remain exposed on surface, the greater the extent of weathering 5. Olduvai sites do not show evidence of intensive bone processing  bones at these sites show cut marks and tooth marks, and many bones were apparently smashed with stone hammers to remove marrow - it is hard to imagine that early hominins could have occupied these sites if lions, hyenas, and saber-toothed cats were regular visitors - bones at Olduvai sites appear to have accumulated over a period of years - fossilized bones found at Olduvai were not processed as thoroughly as modern foragers process their kills - hominins may have brought carcasses to these sites and processed the carcasses with flakes made from previously cached stones - Potts (anthropologist at Smithsonian Insitution) gugests that these sites were butchery sites- places where hominins worked but did not live o believes sites are where hominins brought their kills to and dismembered their carcasses there  would explain why bones accumulated over such a long time o processed kills at sites because there were their tools at the sites  it was also safe to process food at sites; scavengers did not have to steal kills Back to the Future: The Transition to Modern Human Life Stories - Oldowan toolmakers were extractive foragers, hunters, and scavengers of meat - reduced sexual dimorphism and delayed maturation characterize hominins - seems likely that these morphological and developmental features, which also characterize modern humans, represent adaptations to this new way of life 20 Chapter 12: Introduction: - About 1.8 mya, Homo ergaster appeared - First hominin to make its way out of Africa - They were much more like modern humans than the apelike hominins who preceded them were - They developed slowly and their infants were largely helpless at birth - They had large, robust bodies with long legs and short arms, telling us that they were fully committed to life on the ground - The males were only slightly larger than the females - They invented a new kind of tool technology and probably learned to master fire and hunt large game - They may have coexisted with H. habilis in Kenya Homo ergaster: - Ancestral features include narrowing of braincase behind the eyes, receding forehead, no chin - Derived features include shorter nose, less prognathic face, taller skull, smaller jaws and molars, occipital torus, large browridges; many of these traits are probably related to diet - Anatomical suite of characteristics indicates H. ergaster was fully adapted for terrestrial life, without the adaptations for arboreal life seen in earlier hominins - Less sexual dimorphism than in other hominins - There is no evidence that there was spoken language - More rapid juvenile development than humans, but slower than earlier hominins - Tools and survival: o Homo ergaster made fancier tools than earlier hominins had made o Between 1.6 and 1.4 mya, H. ergaster improved on Oldowan tools and added the stone biface- a Mode 2 technological innovation that was part of the Acheulean industry o To make a biface, the toolmaker strikes, the toolmaker strikes a large piece of rock from a boulder to make a core, and then flakes this core on all sides to create a flattened form with a sharp point at the narrow end o Axes could have been used to butcher animals, to dig up tubers or water, to strip bark from trees, as projectiles to hurl at animals or people or to generate flake tools o Evidence that H. ergaster ate meat includes the abnormality of the bones of a H. ergaster woman, the ubiquity of hand axes, cut marks in animal bones from stone tools, the dental morphology of H. ergaster and intestinal parasites o One of the most compelling pieces of evidence that these hominins ate meat comes from the skeleton of an H. ergaster woman whose long bones were covered with a thick layer of abnormal bone tissue o They found that this kind of bone growth is symptomatic of vitamin A poisoning- the only way she could have got the poisoning was by eating the liver of a large prey o Whether meat for consumption came from hunting or scavenging is unknown - H. ergaster may have controlled fire - Archaeologists found baked earth beside stone tools at a site dated to about 1.6 mya Summary: - H. ergaster represented a marked departure from its predecessors - Shared important adaptive traits with modern humans: terrestrial life, complex foraging technology, slow development, reduced sexual dimorphism and probably extensive paternal investment in offspring 21 - Because we share these features, it is classified in the same genus as us - With its smaller brain and relatively static and inflexible technology however, it was still quite different from modern humans Leaving Africa - Between 1.8 and 1.2 mya, H. ergaster started to leave Africa and migrated as far as the Caucasus Mountains - During glacial period, the world was dry and Africa and Eurasia were isolated from each other by a massive desert - During interglacial periods the world was much wetter, and animals moved from Africa to Eurasia - The Georgian site of Dmanisi revealed fossils as well as stone tools from this species Homo erectus: - Found in Java, Indonesia, dating to between 1.8 and 1.6 mya - The main morphological differences between H. erectus and H. ergaster lie in the skull - In Homo erectus: o The skull is thicker o The browridges are more pronounced o The sides of the skull slope more steeply o Lower, less domed cranium o More massive face o More pronounced occipital torus o Sagittal keel o Shorter and stockier Tool Use: - Homo erectus was associated with Mode 1 tools - Acheulean tools are rarely found in eastern Asia - A lack of Mode 2 tools could be related to different cognitive abilities compared to H. ergaster or to a difference in materials available for toolmaking Middle Pleistocene Climate - Long, cold glacial periods and short, warm interglacial periods dominated this epoch - Temperature fluctuations affected the distribution of the world’s biological habitats, which in turn affected the dispersal of hominins Homo heidelbergensis (Archaic H. sapiens) - Hominins with substantially larger brains, between 1200 and 1300 cc and more modern skulls appeared in Africa and western Eurasia during the first half of the Middle Pleistocene - Probably present between 800 to 500 kya - Derived cranial features included vertical sides, high foreheads and a more rounded occipital bone - Ancestral features included a long, low skull, thick cranial bones, prognatic face, no chin and large browridges - Fossil evidence comes from areas as diverse as Spain and Zambia - Possibly coexisted with H. erectus in east Asia 22 Tools and Subsistence: - Tool kits are dominated by Mode 2 Acheulean tools - There is solid evidence for hunting big game o The remains of a large number of fossilized bones from mammoths and woolly rhinoceroses have been found at the base of a cliff o Some of the bones come from adults which were too big to be vulnerable to most predators o The carcasses clearly have been butchered with stone tools o Suggests that H. heidelbergensis drove the animals over the headland, butchered the carcasses and ate the meat - About 300 kya, hominins in Africa shifted to a new stone tool kit - Hand axes became much less common and were replaced by tools that were manufactured by the production of sizable flakes, which were then further shaped or retouched - These tools were made from large, symmetrical, regular flakes via complicated techniques - The individuals probably used the Levallois technique which is a Mode 3 technology Homo floresiensis - H. erectus evolved into a tiny, small-brained hominin called Homo floresiensis on a small Indonesian island - Only about 3 feet tall - Had very small brains, around 380 cc - Lived between 35 and 12 kya - Some researchers think these were descendants of H. erectus that became isolated and evolved different characteristics because of natural selection - Others think that these individuals made up a modern human population with a small stature and microcephaly - Still, others suggest that these speciments preceded H. erectus into Asia Neanderthals - H. heidelbergensis in Europe had begun to diverge from other hominin populations during the Middle Pleistocene - Appearance in western Eurasia around 130 kya - Species existed from about 127 to 30 kya in Europe and western Asia - Faces that bulge in the middle - Double-arched browridges - Rounded back of the skull - Large cranial capacity, around 1400 cc - Small back teeth and large front teeth - Robust, heavily muscled bodies - Language capabilities unknown - There is lots of evidence that Neanderthals made Mode 3 tools and hunted large game - Mode 3 tools are characterized by flakes struck from prepared cores - Neanderthal sites are littered with stone tools and the bones of red deer, fallow deer, bison, aurochs, wild sheep, wild goats and horses - There is little evidence for shelters or even organized camps at Neanderthal sites - Neanderthals probably purposefully buried their dead - Evidence of this comes from the abundance of complete Neanderthal skeletons 23 - Burial protects the corpse from dismemberment by scavengers and preserves the skeleton intact Sources of Change: - The changes in hominin morphology and technology may be the product of a number of different kinds of processes - It is likely that Africa has been occupied continuously by members of the genus Homo - This means that the makers of Mode 1 tools evolved slowly into the makers of Mode 2 tools and the makers of Mode 2 tools evolved into the maker of Mode 3 tools - There was continuous occupation and in-place evolution - It is also possible that some of the changes in the fossil record are the product of the replacement of one population of hominins by another - The technological shifts seen in Eurasia were associated with the migration of hominins from Africa during interglacial periods - Possible that hominins staged repeated invasions of Eurasia during each of these warm interglacial periods, bringing new technologies with them Lumpers and Splitters: - Hominins in Africa and Eurasia were one, single interbreeding population throughout the Pleistocene - Hominins split into several new species as they migrated out of Africa during the Pleistocene 24 Chapter 50: An Introduction to Ecology Bernard Ho March 17, 2011  Ecology is the study of how organisms interact with their environment Areas of Ecological Study  Organismal Ecology o How individuals interact with each other and their physical environment o Researchers explore the morphological, physiological and behavioural adaptations that allow individuals to live successfully in a particular area o Also focuses on physiological adaptations that allow individuals to thrive in heat, drought, cold or other demanding physical conditions o Ex. Sockeye Salmon  After spending four or five years feeding and growing in the ocean, salmon travel long distances to return to stream where they hatched  Females create nests in the gravel stream bottom and lay eggs  Nearby males compete for the chance to fertilize eggs as they are laid  When breeding is finished, all adults die o Biologists want to know how these individuals interact with their physical surroundings and with other organisms in and around the stream  Which females get best nesting sites and lay most eggs  Which males are most successful in fertilizing eggs  How do individuals cope with transition from living in saltwater to living in freshwater  Population Ecology o A population is a group of individuals of the same species that live in the same area at the same time o Biologists focus on how the number of individuals in a population change over time o Mathematical models of population growth have been used to predict the future of particular salmon populations o Many salmon populations have declined as their habitats have become dammed or polluted o If the factors that affect population size can be described accurately enough, mathematical models can assess the impact of proposed dams, changes in weather patterns, altered harvest levels or specific types of protection efforts  Community Ecology o A biological community consists of the species that interact with each other within a particular area o Researchers ask how species interact with each other and the consequences of those interactions  May concentrate on predation, parasitism or competition 25 o Biologists might also analyze how groups of species respond to disturbances such as fires, floods and volcanic eruptions o Ex. When they are at sea, salmon eat smaller fish and are themselves hunted and eaten by orcas, sea lions, humans and other mammals  When they return to freshwater to breed, they are preyed on by bears and bald eagles  In both habitats, they are subject to parasitism and disease  Ecosystem Ecology o An ecosystem consists of all the organisms in a particular region along with non- living components o These physical or abiotic components include air, water and soil o Biologists study how energy and nutrients cycle through the environment o Ex. Salmon form a link between marine and freshwater ecosystems  They harvest nutrients in the ocean and when they die and decompose, they transport these molecules to streams  In this way, salmon transport chemical energy and nutrients from one habitat to another  Conservation biology is the effort to study, preserve and restore threatened populations, communities and ecosystems  Ecologists study how interactions between organisms and their environments result in a particular species being found in a particular area at a particular population size  Conservation biologists apply these data to preserve species and restore environments Types of Aquatic Ecosystems  An organism’s environment has both physical and biological components  The abiotic or physical components include temperature, precipitation, sunlight and wind  The biotic components consist of other members of the organism’s own species as well as individuals of other species  In aquatic ecosystems, water depth and rate of water movement qualify as key physical factors that shape the environment  Water depth dictates how much light reaches the organisms that live in a particular region  Water movement presents a physical challenge, it can sweep organisms off their feet  Freshwater Environments o Lakes and Ponds  Ponds are small, lakes are large enough that the water in them can be mixed by wind and wave action  Most occur in northern latitudes, formed in depressions that were created by the scouring action of glaciers thousands of years ago  Water depth  Littoral zone consists of the shallow waters along the shore, where flowering plants are rooted 26  Limnetic zone is offshore and comprises water that receives enough light to support photosynthesis  Benthic zone is made up of the substrate  Regions of the littoral, limnetic and benthic zones that receive sunlight are part of the photic zone  Portions of a lake or pond that do not receive sunlight make up the aphotic zone  Water flow  Driven by wind and temperature  Littoral and limnetic zones typically much warmer and better oxygenated than benthic zone  Benthic zone is relatively nutrient rich because dead and decomposing bodies sink and accumulate there  Water from different depths can mix  Organisms  Plankton (cyanobacteria, algae) live in photic zone, as do fish that eat them  Detritus (animals that consume dead organism) are common in benthic zone o Wetlands  Shallow-water habitats where the soil is saturated with water for at least part of the year  Water Depth  Only have shallow water and have emergent vegetation, meaning plants grow above the surface of the water  All or most of water in wetlands receive sunlight and emergent plants capture sunlight before it strikes the water  Water Flow  Freshwater marshes and swamps are wetland types characterized by a slow, but steady flow of water  Bogs in contrast, develop in depressions where water flow is low or non-existent  If water is stagnant, oxygen is used up during the decomposition of dead organic matter faster than it enters via diffusion from atmosphere  As a result, bog water is oxygen poor and once oxygen is depleted, decomposition slows  Organic acids and other acids build up, lowering pH of water  At low pH, nitrogen becomes unavailable to plants  Organisms 27  Combination of acidity, lack of available nitrogen and anoxic conditions makes bogs extremely unproductive habitats  Plants in bogs are carnivorous  Marshes and swamps offer ample supplies of oxygenated water and sunlight and are very productive  Marshes lack tress and typically feature grasses (productive)  Swamps are dominated by trees and shrubs (productive) o Streams  Bodies of water that move constantly in one direction  Creeks are small streams, rivers are large  Water Depth  Most streams are shallow enough that sunlight reaches the bottom  Availability of sunlight is usually not a limiting factor for organisms  Water Flow  When it originates at a mountain glacier, lake or spring, it tends to be cold, narrow and fast  As it descends towards a lake, ocean or larger river, it accepts water from tributaries and becomes larger, warmer, slower  Oxygen levels tend to be high in fast-moving streams because water droplets are exposed to atmosphere when moving water splashes over rocks and other obstacles  Slow-moving streams tend to become relatively oxygen poor  Cold water holds more oxygen than warm water does  Organisms  Rare to find photosynthetic organisms in small, fast-moving streams  Nutrient levels tend to be low and most of organic matter present consists of leaves and other materials that fall into water from outside stream  As stream widens and slows down, conditions become more favourable for growth of algae and plants and the amount of organic matter and nutrients increases o Estuaries  Form where river meets ocean (freshwater mixes with saltwater)  Salinity varies with changes in river flow and with proximity to ocean  Salinity has drastic effect on osmosis and water balance  Water Depth  Most are shallow enough that sunlight reaches substrate  May fluctuate in response to tides, storms, floods  Water Flow  Fluctuates daily and seasonally due to tides, storms, floods 28  Fluctuation is important because it alters salinity, which affects which types of organisms are present  Organisms  Because water is shallow and sunlit and because nutrients are constantly being replenished by incoming river water, most productive environments on Earth o Ocean  Water Depth  Intertidal zone consists of a rocky, sandy or muddy beach that is exposed to air at low tide, but submerged at high tide  Neritic zone extends from intertidal zone to depths of about 200 m o Outermost edge is defined by end of the continental shelf, gently sloping, submerged portion of a continental plate  Oceanic zone is the open ocean, deepwater region beyond continental shelft  Benthic zone is bottom of ocean  Photic zone is the intertidal and sunlit regions of neritic, oceanic and benthic zones  Areas that do not receive sunlight are in an aphotic zone  Water Flow  Dominated by different processes at different depths  In intertidal zone, tides and wave action are major influences  In neritic zone, currents that bring nutrient-rich water from benthic zone of deep ocean toward shore have heavy impact  Organisms  Each zone is populated by distinct species that are adapted to physical conditions present  Organisms that live in intertidal zone must be able to withstand physical pounding from waves and desiccation at low tide  Productivity is high due to availability of sunlight and nutrients contributed by estuaries as well as by currents that sweep in nutrient-laden sediments from offshore areas  Productivity is also high on outer edge of nerithic zone, due to nutrients contributed by upwellings at the edge of the continental plate Types of Terrestrial Ecosystems  Broad-leaved forests, deserts and grasslands are biomes, major groupings of plant and animal communities defined by a dominant vegetation type 29  Each biome found around the world is associated with a distinctive set of abiotic conditions  The type of biome present in a terrestrial region depends on climate, the prevailing, long-term weather conditions found in an area  Weather consists of the specific, short-term atmospheric conditions of temperature, moisture, sunlight and wind o Temperature is critical because enzymes that make life possible work at optimal efficiency only at narrow ranges of temperatures o Moisture is significant because it is required for life and because terrestrial organisms constantly lose water to the environment through evaporation o Sunlight is essential because it is required for photosynthesis o Wind is important because it exacerbates the effects of temperature and moisture  Of the four components, temperature and moisture are the most important to plants  The nature of biome that develops in a particular region is governed by o Average annual temperature and precipitation o Annual variation in temperature and precipitation  Each biome contains species that are adapted to a particular temperature and moisture regime  On land, photosynthesis and plant growth are maximized when temperatures are warm and conditions are wet  Conversely, photosynthesis cannot occur efficiently at low temperatures or under drought stress  Terrestrial Biomes o Tropical wet forest  Found in equatorial regions  Plants have broad leaves and are evergreen  No complete, seasonal loss of leaves  Temperature  High, with low variation  Precipitation  Very high with high variation  Vegetation  Very productive due to favourable year-round conditions  Renowned for species diversity o Subtropical deserts  Found 30 degrees latitude, both north and south  Temperature  High, with moderate variation  Precipitation  Very low, with low variation  Vegetation 30  Scarcity of water in deserts cannot support photosynthesis so productivity is low  Individual plants are widely spaced  Desert species adapt to extreme temperatures and aridity by growing at a low rate year-round or breaking dormancy and growing rapidly to any rainfall  Cacti are prominent o Temperate Grasslands  Found throughout central North America (prairies) and central Eurasia (steppes)  Temperature  Moderate, with moderate variation (temperate)  Precipitation  Low, with moderate variation  Vegetations  Grasses are dominant life-form because conditions are too dry to enable tree growth or encroaching trees are burned out by fires  Productivity generally lower than forest communities, but grassland soils are generally very fertile  Grassland soils retain nutrients so ideal for growing wheat, corn and other cultivated grass o Temperature forests  In temperate areas with relatively high precipitation, grasslands give way to forests  Common biome found in eastern North America, western Europe, east Asia, Chile and New Zealand  Temperature  Moderate, with moderate variation  Precipitation  Moderate, with low variation  Vegetation  Dominated by deciduous species  Needle-leaved evergreens are also common  In temperate forests of New Zealand and Chile, broad-leaved evergreens predominate  Most have high productivity levels that are lower than those of tropical forests, but higher than deserts or grasslands  Moderate level of diversity o Boreal forests  Because these regions are just south of Arctic Circle, are referred to as subarctic  Temperature  Low, with very high variation 31  Precipitation  Low, with low variation  Vegetation  Dominated by highly cold-tolerant conifers, including pines, spruce, fir and larch trees  Except for larches, these species are evergreen  Two hypotheses for evergreen o Evergreens can begin photosynthesizing early in spring, even before snow melts, when sunshine is intense enough to warm needles o Boreal forest oils tend to be acidic and lack nitrogen  Because leaves are nitrogen rich, species that produce an entirely new set of leaves each year might be at a disadvantage o Arctic Tundra  Found throughout arctic regions of Northern Hemisphere and in regions of Antarctica that are not covered in ice  Temperature  Very low, with high variation  Precipitation  Very low, with low variation  Vegetation  Treeless  Leading hypothesis is that growing season is too short and cool to support production of large amounts of non-photosynthetic tissue  Low species diversity, low productivity and low aboveground biomass  Most tundra soils are in a perennially frozen state called permafrost Role of Climate and Consequences of Climate Change  Why are the tropics warm and poles cold o Over the course of a year, regions at or near the equator receive much more sunlight per unit area and thus more energy in the form of heat, than regions that are closer to the poles o At the equator the Sun is directly overhead o As a result, sunlight strikes Earth there at or close to a 90 angle o At these angles, Earth receives a maximum amount of solar radiation per unit area o Because Earth’s surface slopes away from the equator, the Sun strikes the surface at lower and lower angles moving towards the poles  Why are tropics wet 32 o When average annual rainfall is mapped for regions around the globe, it is clear that areas along the equator receive the most moisture, while locations about 30 latitude north and south of the equator are among the driest on the planet o A major cycle in global air circulation, called a Hadley cell, is responsible for making the Amazon River basin wet and the Sahara Desert Dry o Air that is heated by the strong sunlight along the equator expands and rises o Warm air can hold a lot of moisture because warm water molecules tend to stay in vapour form instead of condensing into droplets o As the air rises, it radiates heat to space o It also expands into a larger volume of the upper atmosphere, which lowers its density and temperature (adiabatic cooling) o As rising air cools, its ability to hold water declines and the water condenses o The result is that high levels of precipitation occur along the equator o As more air is heated along the equator, the cooler “older” air above Earth’s surface is pushed poleward o When the air mass has cooled enough, its density increases and it begins to sink o As it sinks, it absorbs more solar radiation reflected from Earth’s surface and begins to warm o As air warms, it gains water-holding capacity o Thus, the air approaching the Earth holds on to its water and little rain occurs where it returns to the surface, so area bathed in warm, dry air Biogeography: Why Are Organisms Found Where They Are  The study of how organisms are distributed geographically is called biogeography  Do insect outbreaks contribute to global warming o The mountain pine beetle is native to the pine forests of western North America, where they attack mature lodgepole pine trees o A female MPB bores into the bark of a pine tree to reach the layer of vascular cambium, where she release a pheromone, a chemical signal to attract a mate o Once she has mated, the female beetle lays 40-50 eggs in long tunnels called egg galleries o 7-10 days later, the eggs hatch o The beetle larvae eat their way through the vascular cambial layer, eventually cutting off transport to water and minerals to the tree’s needles and transport of sugars from needles to non-photosynthetic parts of tree o Beetle is helped in its attack by a blue-stain fungus o Before adult beetles leave their natal tree, they actively gather fungal spores and store them in specialized pouches in their mouths o When a MPB colonizes a new tree, it releases the fungal spores o Blue-stain fungal hyphae grow along the walls of the egg galleries, invading the host’s phloem and xylem and helping the beetle to kill the tree, while serving as an additional food source for the beetle o Cold winters limit the survival of MPB and its fungal companion (beetles die in cold) 33 o Forest fires also act to reduce MPB populations, preventing severe outbreaks o MPB populations have exploded in BC forests o BC’s forests have traditionally functioned as a carbon sink, as the trees transform CO 2nto sugar by photosynthesis o With the explosive increase in MPB, these forests will change from a carbon sink to a major source of greenhouse gases o Increase due to warming trend of Earth (global warming) o Kurz suggests that the dead trees could be converted to biofuel, reducing the need for oil and gas o Dead forests will be replaced, planted with seedlings of various species to reduce the vulnerability of future forests to insect attack  Because of fitness trade-offs, organisms tend to be adapted to a limited set of physical conditions  Although some species have much broader geographic ranges than other species do, humans and bacteria that live in and on them may have the widest distribution of any species at present, no organism can live everywhere  To understand a species’ distribution thoroughly, it is essential to examine historical and biotic factors in addition to physical conditions present  The Role of History o Dispersal refers to the movement of an individual from the place of its birth, hatching or origin to the location where it lives and breeds as an adult o If a particular species is missing from an area, a physical barrier to dispersal may be present o Humans have transported thousands of seeds, birds, insects and other species across physical barriers to new locations, sometimes purposefully and sometimes by accident o One accidental introduction has had disastrous consequences for the arid shrublands and grasslands of the western US o A native plant of Eurasia called cheatgrass was accidentally introduced to western North America in a shipment of crop seeds o Cheatgrass is an annual plant with seeds that germinate over winter so that plants grow and set seed in early spring o As a result, cheatgrass seedlings get a “jump” on many North American plant species, which initiate growth later o Early growth allows cheatgrass to use more of the available water and nutrients o If an exotic species (one that is not native) is introduced into a new area, spreads rapidly and eliminates native species, it is said to be an invasive species  Biotic Factors o The distribution of a species is often limited by biotic factors, meaning interactions with other organisms o Ex. Townsend’s warblers and hermit warblers  Both live in evergreen forests 34  Male Townsend’s warblers directly attack male hermit warblers and evict them from breeding territories and historical data has been expanding steadily at the expense of hermit warblers  The results support the hypothesis that a biotic factor, competition with another species, is limiting the range of hermit warblers o Competition is not the only biotic factor to consider o In Africa, the range of domestic cattle is limited by the distribution of tsetse flies o The flies transmit a parasite that causes the disease trypanosomiasis, which is fatal in cattle o Also, yucca moths lay their eggs only in the flowers of yucca plants, so they cannot live where yucca plants are absent  Abiotic Factor o In many cases, introduced species may not become established in a region because of abiotic factors, particularly temperature and moisture o Ex. Even though the invasive plant kudzu grows throughout the southeastern United States, it is killed when the soil freezes to a depth of a foot or more o Often difficult to separate the effects of biotic and abiotic factors on a species range o Ex. Cheatgrass  Does not grow well in wet grasslands because it does not compete well against the tall species that thrive there  Has been able to invade two important types of biomes in North America, dry temperate grasslands and the arid, shrub-dominated habitats known as sage-steppe  Cheatgrass has been able to invade sage-steppe habitats because it is not affected by fire  Fire is an abiotic factor that can kill the shrubs that dominate sage-steppe  Because cheatgrass grows in dense beds and dies back in early spring, it actually leads to an increase in frequency and intensity of wildfires  Beds of cheatgrass offer a continuous source of fuel  However, fire does not affect cheatgrass for two reasons  Cheatgrass is annual so there is no living tissue exposed once growing season is over  Cheatgrass seeds sprout readily in soils that have been depleted of organic matter by fire  Because sagebrush and other shrubs are perennial, their tissues are heavily damaged or killed by hot fires  Presence of cheatgrass creates an environment that favours its spread  Prior to arrival of cheatgrass, grasslands in arid areas of American West were dominated by bunchgrasses  Bunchgrasses do not form a continuous sod, they grow in compact bunches  The space between these bunches are occupied by “black-soil crust”  Many of these species also fix nitrogen 35  Nitrogen becomes available to surrounding plants when microbial cells die and decompose  When European settlers arrived and began grazing cattle in this biome, both the black soils and bunchgrasses were affected  Cattle grazed on bunchgrasses until grasses died and their hooves compacted and disrupted the black soils  Neither component of the ecosystem was allowed to recover in part because of intensive grazing continued and in part because cheatgrass arrived  Cheatgrass shades out black-soil crust organisms  When black-soil crust is gone, the amount of nitrogen available to bunchgrasses is reduced  Cheatgrass also competes successfully with bunchgrasses for water and nutrients because it completes its growth early for water and nutrients, before native bunchgrasses have broken dormancy and begun to grow  Expansion of cheatgrass increased frequency and severity of fires, which further degraded integrity of black-soil crust communities  Cheatgrass has adapted to fire and can thrive in compromised soil Live Lecture  Slide 18 o How organisms interact with environment  Evolution of crypsis (tendency for organism to adjust its colouration to match its background)  Physiological acclimatization  Adjustment of fish to rising temperature in body of water (but gradual change) Chapter 50: An Introduction to Ecology Bernard Ho March 17, 2011  Ecology is the study of how organisms interact with their environment Areas of Ecological Study  Organismal Ecology o How individuals interact with each other and their physical environment o Researchers explore the morphological, physiological and behavioural adaptations that allow individuals to live successfully in a particular area o Also focuses on physiological adaptations that allow individuals to thrive in heat, drought, cold or other demanding physical conditions o Ex. Sockeye Salmon  After spending four or five years feeding and growing in the ocean, salmon travel long distances to return to stream where they hatched 36  Females create nests in the gravel stream bottom and lay eggs  Nearby males compete for the chance to fertilize eggs as they are laid  When breeding is finished, all adults die o Biologists want to know how these individuals interact with their physical surroundings and with other organisms in and around the stream  Which females get best nesting sites and lay most eggs  Which males are most successful in fertilizing eggs  How do individuals cope with transition from living in saltwater to living in freshwater  Population Ecology o A population is a group of individuals of the same species that live in the same area at the same time o Biologists focus on how the number of individuals in a population change over time o Mathematical models of population growth have been used to predict the future of particular salmon populations o Many salmon populations have declined as their habitats have become dammed or polluted o If the factors that affect population size can be described accurately enough, mathematical models can assess the impact of proposed dams, changes in weather patterns, altered harvest levels or specific types of protection efforts  Community Ecology o A biological community consists of the species that interact with each other within a particular area o Researchers ask how species interact with each other and the consequences of those interactions  May concentrate on predation, parasitism or competition o Biologists might also analyze how groups of species respond to disturbances such as fires, floods and volcanic eruptions o Ex. When they are at sea, salmon eat smaller fish and are themselves hunted and eaten by orcas, sea lions, humans and other mammals  When they return to freshwater to breed, they are preyed on by bears and bald eagles  In both habitats, they are subject to parasitism and disease  Ecosystem Ecology o An ecosystem consists of all the organisms in a particular region along with non- living components o These physical or abiotic components include air, water and soil o Biologists study how energy and nutrients cycle through the environment o Ex. Salmon form a link between marine and freshwater ecosystems  They harvest nutrients in the ocean and when they die and decompose, they transport these molecules to streams  In this way, salmon transport chemical energy and nutrients from one habitat to another 37
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