Ecology PDF

A History of Ecology Ecology’s Origins • Some of our earliest evidence for an interest in the study of ecology may be from the observations of Theophrastus, a student, friend and associate of Aristotle, who wrote about the interrelationships between plants and the environment (Enquiry Into Plants...

A History of Ecology Ecology’s Origins • Some of our earliest evidence for an interest in the study of ecology may be from the observations of Theophrastus, a student, friend and associate of Aristotle, who wrote about the interrelationships between plants and the environment (Enquiry Into Plants and On the Causes of Plants). He is widely considered to be the “Father of Botany”. Theophrastus (372-287 BC) Roots of Ecology • From the Greek “oikos”, meaning “of the family or household” – Same Latin root as economics • Ecology can be thought of as the study of “the economy of nature” – Cost versus benefits – Optimization – Resource allocation • In fact, the term home economics is believed to have originated from the term “oekology” used by the scientist Ellen Swallow Richards – Is an all-encompassing biological discipline • Large scale patterns have been investigated – Ecosystems – Landscapes – The Biosphere Ecology as a Discipline • Due to its broad definition, ecology has become an umbrella covering practically every type of biological investigation that has an organismic component: – Behavior (inter- and intraspecies interactions, and abiotic) – Physiology (interactions with abiotic and biotic environments) – Molecular biology • Population • Genetics • Selection (evolutionary ecology) – Symbioses Ecology, Defined • How can we define ecology? – The study of the interrelationships between organisms and their environment • First coined by Ernst Haeckel (1866) as “oekologie” – Defined as “the study of animals to their environment” – Suggested three kingdoms: animals, plants and protists (coined name) – He is possibly most famous for the biogenetic law, which suggests that “Ontogeny Recapitulates Phylogeny” – Responsible for drawings that suggested many organisms pass through similar embryonic stages, presupposing a commonality of origin – According to the Library of Congress, Haeckel “was known for his speculative approach to natural history and his frequent invention of new scientific terms” “Botanical Geography” • 18th and 19th centuries, maritime powers explored globe – Developed commerce, expanded spheres of influence – Identified and catalogued novel natural resources • Scientists and other specialists typically were part of crews – Identify new organisms, determine potential for new resources • Increased numbers of known plant species • 20K in 18th century • 40K in 19th century • ~400K presently • Alexander von Humboldt (1769-1859) – Correlated plant morphology with geography • Described vegetative zones by latitude and altitude (geobotany) • Check his Wikipedia page for a more exhaustive list of accomplishments • Book: Idea for a Plant Geography (1805) “Oekologie” • Term was not used in general until 1895 – Plantesamfund: Grundtrak af den Okologiske Planteografie*, by Johannes Warming • Warming established plant ecology as a division of botany. – The basis of his work was the interactions of plants with their environments and how these interactions affected their growth and survival. – He was very much interested in the “communal” existence of organisms in a habitat (what he considered an “ecology”), and the acclimation of organisms to a habitat (epharmosis). • Warming also was one of the first to introduce the idea of different successional stages, and the direct role plants played in defining them – Origin of ecology was as a fringe science • Became firmly entrenched in the public consciousness in the 60’s and 70’s as a result of the environmental movement • Eventually overshadowed by the molecular biology movement of the mid 20th C – Molecular techniques now used to elucidate ecological questions *Translated as: “Oecology of Plants: An Introduction to the Study of Plant Communities” Concept of Ecosystem, Biosphere • Roy Clapham (1930) first coined the term “ecosystem” – As “…the combined physical and biological components of environment” • Arthur Tansley (1935) refined ecosystem definition – Interactions of animal communities, physical components and ecotope (spatial dimensions) • “Biosphere” first proposed by Eduard Suess in 1875 – Considered it the conditions promoting life, such as those found on Earth, which includes flora, fauna, minerals, matter cycles, etc. – Observed that life develops/survives within limits (think tolerances) – Also first suggested the supercontinent Gondwana • Vladimir Vernadsky (1926): The Biosphere – Described principles of biogeochemical cycles • Thus coined the modern definition (sum of all earth’s ecosystems) – Thought of life as the geological force that shapes the earth The Biosphere The Biosphere "... one thing seems to be foreign on this large celestial body consisting of spheres, namely, organic life. But this life is limited to a determined zone at the surface of the lithosphere. The plant, whose deep roots plunge into the soil to feed, and which at the same time rises into the air to breathe, is a good illustration of organic life in the region of interaction between the upper sphere and the lithosphere, and on the surface of continents it is possible to single out an independent biosphere" - Eduard Suess (from: Das Antlitz der Erde) Foundations of Ecology • The field of ecology started with these European plant geographers. They noticed that plants from different parts of the world and from different habitats had different characteristics. But along with these differences were similarities. Let’s quickly look at some of these influential figures…. – Karl Willdenow (1765-1812) • – Friedrich Heinrich Alexander von Humboldt (1769-1859) • • • – Commissioned by the Hungarian government to describe the vegetation of E. Hungary and Transylvania. Described the concept of vegetational change through time (succession) in the book Plant Life of the Danube Basin Introduced the use of transplant gardens to study the responses of plants from different topographic regions Johannnes E. Warming (1841-1924) mentioned earlier • • • • – Studied the effects of environmental factors on plant distribution, particularly temperature. Came up with the idea of naming plant associations for dominant species Anton Kerner (1831-1898) • • • – Sponsored by King Carlos IV of Spain Spent 5 years exploring Mexico, Cuba, Venezuela, Peru and explored the Amazon and Orinoco rivers. Humboldt described vegetation in terms of physiognomy (correlating types with environmental factors) and is responsible for coining the phrase “association” as it applies to biological applications Joachim Frederik Schouw (1789-1852) • • – Similar climates support similar vegetation Followed Schouw at U of Copenhagen - first to teach a course in plant geography Studied the tropical vegetation of Brazil Advanced the idea of differing life forms and noted the influence of fire and time on changes in vegetative structure Don’t forget he wrote Plantesamfund and translated that volume into 4 languages (from German), including English. In it, Warming synthesized and unified plant morphology, physiology, taxonomy and biogeography into a coherent unit. This book was very influential to the development of ecology as a whole. Jozef Paczoski (1864-1941) • • • • University of Poznan (Poland?) Showed that plants modify the environment by creating microhabitats Introduced the concepts of shade tolerance, competition, competition, succession, the father of plant sociology. Unfortunately, since his book was published in Slavic, the influence of his book was minimal, because no one read it. More “Contemporary” Ecology Arthur Tansley George Evelyn Hutchinson • The scientists from the previous page yielded a foundation that provided the basis for modern ecology. They had a tremendous impact on the development of the European “plant sociology” movement. They also influenced the development of American plant biology, which at the time was led by: – Frederic E. Clements and his work in the area of vegetation dynamics. • – Arthur G. Tansley (Britain) • • • F.E. Clements A. Thinenmann (1931) – F.A. Forel (1901) • • – G.E. Hutchinson (1950’s), R.A. Lindeman (1940’s) Eugene Odum (1950’s)- also continued and expanded upon Tansley’s ecosystem concept J. Ovington (1965) Cannot not mention the impact of Darwin and Mendel – A. Lavoisier Wrote “The Lake as a Microcosm”, on food chains in lakes and the role selection plays in regulation populations of predators and prey. Nutrient Cycling – • Interested in physical parameters of lakes Described thermal stratification, and introduced the term “limnology” in his monograph on the natural history of Lake Leman Energy flow, food webs and budgets – – • Freshwater ecologist. Introduced the ideas of nutrient cycling, trophic levels and the usage of the terms “consumers” and “producers” Stephen A. Forbes (Illinois) • S.A. Forbes Expanded the term and concept of ecosystem Used an experimental approach to field ecology-esp. physiological ecology, life-histories and pop dynamics, rather than simple descriptions. Spearheaded the conservation movement in England. Truly a man ahead of his time, his thoughts on research and the future growth of ecology predated the actual research by decades, as much of it didn’t actually take place until the 1970’s. – • • Described the plants of NA (Nebraska), gave ecology a hierarchical framework, and suggested the concept of ecological indicators, and posited a theory of succession and plant associations that is still influential today. Believed that plants determine productivity of ecosystems and by extension the presence and types of animals found in particular habitats. Also chemists Lavoisier and de Saussure’s (posthumous) contributions regarding nitrogen cycle Eugene Odum Population Ecology R. Fisher S. Wright • Population genetics – Sewell Wright- role of inheritance in evolution – R.A. Fisher – J.B.S. Haldane • Population dynamics – P.F. Verhulst- Population growth in context of limited resources – A. Lotka, V. Volterra - founders of population ecology J. Haldane • Population growth in context of predation, competition, etc – G.F. Gause- tested the models of Lotka and Volterra • Also formulated the Competitive Exclusion Concept G. Gause A. Lotka Modern Ecology • The field of ecology has shifted along with and has been influenced by scientific advancements. It has evolved to become a catch-all for all types of biological studies that focus on the level of the organism (or above). – Ecology has moved from basic natural history to more mechanistic approaches – Advancements in molecular techniques have allowed us to look into patterns that previously were purely speculative – GIS and other large-scale methodologies allow us to investigate on the level of the ecosystem and above Broad Scale Ecology (Using Satellites) *G.I.S. As a Methodology for Ecological Study *G.I.S.: Geographic Information System Scientific Method and Experimental Design Ecology Defined, Again • Ecology is the study of the interactions of organisms and their environment(s) • Encompasses relationships ranging from single individuals up to those influencing the entire biosphere • Incredibly broad discipline: ecologists study everything from mating systems, population censuses, photosynthetic rates, and predator-prey co-evolution to theoretical computer models of long-term evolutionary processes Levels of Organization • Ecological studies are conducted within one of the following levels of organization (“focal units” of study): • Individual (single individual of a species) – Physiological and behavioral responses to environment (i.e., Bombus thermoregulation) • Population (conspecific group occupying an area) – Evolution, adaptation, population growth and extinction, demographics (e.g., cane toads in Australia) • Community (interacting species living in an area) – Predator/prey, mutualisms, interspecies competition, food webs (e.g., warbler guild, lynx and snowshoe hare population cycles) • Ecosystem (community interactions, including abiotic features) – Understanding the factors influencing nutrient cycling and energy flow (e.g., forest canopy productivity during droughts or flooding) • Landscape (several ecosystems sharing an area) – Exchange of species, genetic material, etc., between communities (e.g., island biogeography work of Simberloff and Wilson) Level of Understanding Decreases Levels of Organization • Ecological studies are conducted within one of the following levels of organization (“focal units” of study): • Individual (single individual of a species) – Physiological and behavioral responses to environment (i.e., Bombus thermoregulation) • Population (conspecific group occupying an area) – Evolution, adaptation, population growth and extinction, demographics (e.g., cane toads in Australia) • Community (interacting species living in an area) – Predator/prey, mutualisms, interspecies competition, food webs (e.g., warbler guild, lynx and snowshoe hare population cycles) • Ecosystem (community interactions, including abiotic features) – Understanding the factors influencing nutrient cycling and energy flow (e.g., forest canopy productivity during droughts or flooding) • Landscape (several ecosystems sharing an area) – Exchange of species, genetic material, etc., between communities (e.g., island biogeography work of Simberloff and Wilson) Ecological Approaches • There are 3 general “study modes” or “levels of analysis” – Descriptive- Natural history observations – Functional- Dynamics and relationships (“proximate”) – Evolutionary- Historical bases for observations (“ultimate”) Scientific Vocabulary • Fact – Particular, pragmatic truths of the natural world (can be checked and confirmed) • Hypothesis – Proposition that suggests an explanation for an observable situation or phenomenon • Experiment – Test of an hypothesis. Can be observational or manipulative • Principle – Accepted statements that are basically definitions • Model – Verbal or mathematical statement of an hypothesis • Theory – Set of hypotheses that when taken together explain a series of (empirical) observations • Law – Universal, deterministic statements so well corroborated that they are accepted. • There are no laws applicable to ecology, but there are in chemistry, physics, genetics The Scientific Process • Scientists attempt to answer questions about the natural world using a standard process called the “Scientific Method” • What exactly is the Scientific Method? • Steps: – – – – – Observation of some phenomenon Pose a question regarding the observation Hypothesize a possible explanation to the question (may, if/then) Prediction(s) of possible outcomes (sometimes included with hypothesis) Test hypothesis to ascertain whether to accept or reject hypothesis The Scientific Method Two Hypotheses The null hypothesis is a general statement or default position that there is nothing significantly different happening, like there is no association among groups or variables, or that there is no relationship between two measured phenomena. Null Hypothesis is Rejected at 0.95 CI Why do we use 95 confidence interval? This means that the observed phenomenon has a 5% chance of occurring randomly 0.025 The 95% confidence interval defines a range of values that you can be 95% certain contains the population mean. With large samples, you know that mean with much more precision than you do with small sample, so the confidence interval is quite narrow when computed from a large sample. 0.025 Experimentation • A fundamental feature of the scientific method is hypothesis testing – this is accomplished by performing an experiment • An experiment is an activity in which natural processes are allowed to occur under controlled conditions • There are two types of experiments, observational and manipulative. – Observational: basic natural history type experiments where an investigator collects data on/from a natural situation (mensurative). • Measurements made or taken at one or more points in space or time. Space or time is the only "experimental" variable or treatment. – Manipulative: the investigator alters the study system to determine causal relationships. • Always involve two or more treatments, can render ambiguous results unless care is taken in experimental design. Troubleshooting Experimental Design • Recognition of and statement of the problem. – – – Where should I take my samples? How should I collect data in space and time? How many species should I try to take? • Factors and levels – Selection of independent variables and/or factors to be investigated. • Selection of a response variable – – In choosing a response (or dependent variable) the experimenter must be certain that the response provides information about the study question How will the response variable be measured, and what is the probable accuracy of those measurements? • Choice of experimental design – – Important to keep the design and analysis as simple as possible Choose a balanced design based on a simple analysis. Experimental Design Goal: to gather ecological data from the real world to test predictions of hypotheses Experimental Design Caveats • Important considerations: – Control- treatment for which there is no manipulation, “normal” – Blindness- observer is unaware of different treatments – Treatment (variable under control of investigator [independent var]) • Dependent variable- variable for which a change can be observed – – – – Randomness or haphazardness Replication (exact copies of experiment run concurrently) Statistical analysis Appropriate data collection methodology (quantifiable?) • • • • Molecular markers Behaviors Growth parameters Variables Natural Selection and Evolution The Diversity of Life Plants • • • • Multicellular Autotrophic Cells with plasma membrane and cellulose cell walls Cells with chlorophylls A and B Animals • • • • Multicellular Heterotrophic Cells with plasma membranes and mitochondria Embryonic development Fungi • • • • Multi- or unicellular Heterotrophic Cells with plasma membranes and chitinous cell walls Functional units are hyphae, reproductive units are spores Description of a Tiger • • • • • Very large cats (males can weigh up to 500 lbs.) Orangish background with black stripes White undersides Small manes with white fur Huge paws But Among (Siberian) Tigers, Individuals Vary The Evolution of Natural Selection • The idea of intra species variation is not a recent one • Many ancient thinkers made observations suggesting this: – Aristotle (384-322 BC)- different forms arose in response to functional needs • Interjected the concept of heredity into his observations • Also conceded that new species can arise spontaneously, albeit rarely – Empedocles (490-430 BC)- organisms arose via heat and cold – Al-Jahiz (776-868)- environmental factors lead to “adaptations” – Al-Biruni (973-1048)- nature functions in a similar manner to artificial selection • Despite these and other stated observations and beliefs, the classical view of idealism of organisms held quite strongly until the early 19th C – Departures from the idealized type observed in nature were deemed to be relatively insignificant How Did Natural Selection and Evolution Evolve? • Again, leading to the 18th – 19th C, most held to the classical belief that each species was created separately and remained relatively unchanged through history • Scientific explorations suggested otherwise – Europeans saw strange plants and animals abroad • And many had structural differences that appeared to be correlated to environmental differences – This led to some serious questioning: • Why are there different plants and animals in different places? • Why are extinct animals different from extant ones? • How could a single anatomical plan be effective for different types of locomotion (vertebrates)? What Exactly Is Natural Selection? • Natural selection is the mechanism by which evolution occurs. These are the three criteria for natural selection: – There are heritable differences among individuals in populations – Many more offspring are produced than can possibly survive – There is differential survival among members of a population • It is important to note that natural selection is an individuallevel phenomenon, and does not act on populations as a whole Some Terms for Understanding Selection • Fitness- the ability of an organism to reproduce and to pass genes to future generations • Adaptation- traits that help an organism to survive • Population- single species interbreeding unit • Selective advantage- quality that provides an organism the increased likelihood of surviving relative to other individuals in a pop or community • Now, who were some important contributors to these concepts of natural selection and evolution? Jean Baptiste Lamarck (1744-1829) • Believed that species were created separately • But, he also believed that species were descended from older ones – Descent was based on natural laws, not supernatural • Two main points to Lamarck’s hypothesis: – Physical needs determine how an organism develops – Changes in structure caused by use were inherited – Called “Inheritance of acquired characteristics” • His ideas were influential at the time because they couldn’t be tested (and proven) experimentally. • When Mendel’s laws were established in the early 20th Century, Lamarck’s notions were finally and unequivocally disproven Lamarck’s Hypothesis – Acquired Characteristics Charles Darwin • Although we think of Charles Darwin as the “Father of Evolution”, he was not the only person to think that extant species evolved from ancestors. One of his contemporaries, Alfred Russell Wallace, independently theorized the process of evolution via natural selection. • Charles Darwin (1809-1882) – From wealthy family, studied to be clergyman at Cambridge • Found he wasn’t suited for a career in medicine or the church – After graduation, became the naturalist on HMS Beagle (1831) • • • • The Beagle was on a 5-year voyage to map the SA coastline Darwin investigated the mainland during stops Most significantly, Darwin visited the Galapagos Islands Among his observations, he noticed variance among – After return to UK, he procrastinated for a long while before formulating his theory of evolution by natural selection – Wrote On the Origin of Species… in 1859 Darwin’s Summary of Natural Selection • If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But, if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection. From: On The Origin Of Species, Chapter 4 Darwin’s Summary of Natural Selection • If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But, if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection. From: On The Origin Of Species, Chapter 4 Darwin And The Galapagos • Noticed that different islands had their own species suites (i.e., they had similar but slightly different assemblages or communities) – Hypothesized that islands were populated by species from the mainland – Most significantly, he surmised that the species changed from their original forms, adapting to the local conditions of the islands to which they moved – After his return to England, a major gap in his logic was bridged. Thomas Malthus’ model of population survival in the face of limited resources led Darwin to hypothesize that certain members in populations have a competitive advantage over others, and that these individuals’ traits would be retained and carried over to their offspring. Alfred Russel Wallace • Alfred Russell Wallace (1823-1913) – Originally worked as a land surveyor, then as a teacher • This outdoor experience introduced him to natural history • While at Collegiate School, he became friends with Henry Walter Bates – Entomologist who contributed the concept of Batesian mimicry – After his brother’s death, accompanied Bates to South America – Spent bulk of time collecting, observing along the Rio Negro – Later explored several Asian countries • While in Malaysia, formulated his concept of NS • Wallace became a significant figure in the scientific community – – – – – Introduced the idea of warning coloration (aposemitism) Wallace effect- selection encourages speciation via barriers to hybridization Wallace line, effect; is frequently called the “Father of Biogeography” His book, The Malay Archipelago, has never been out of print Wallace is frequently called the “Father of Biogeography” Wallace’s Line Asian Australian/Asian Darwin’s Evolutionary Thoughts… With a Sprinkling of Wallace From September 1854 I devoted my whole time to arranging my huge pile of notes, to observing, and to experimenting in relation to the transmutation of species. … early in the summer of 1858 Mr. Wallace, who was then in the Malay archipelago, sent me an essay "On the Tendency of Varieties to depart indefinitely from the Original Type;" and this essay contained exactly the same theory as mine. Mr. Wallace expressed the wish that if I thought well of his essay, I should sent it to Lyell for perusal. T. Malthus C. Lyell The extract from my MS. and the letter to Asa Gray* had neither been intended for publication, and were badly written. Mr. Wallace's essay, on the other hand, was admirably expressed and quite clear. Nevertheless, our joint productions excited very little attention, and the only published notice of them which I can remember was by Professor Haughton of Dublin, whose verdict was that all that was new in them was false, and what was true was old. It has sometimes been said that the success of the 'Origin' proved "that the subject was in the air," or "that men's minds were prepared for it." I do not think that this is strictly true, for I occasionally sounded not a few naturalists, and never happened to come across a single one who seemed to doubt about the permanence of species. Even Lyell and Hooker, though they would listen with interest to me, never seemed to agree. I tried once or twice to explain to able men what I meant by Natural Selection, but signally failed. *Asa Gray, a Harvard botanist at the time, was Darwin's friend and a confidant to whom he sent an abstract of his new theory in September 1857. A. Gray Other Natural Selection Theorists • Although we have discussed some of the better-known scientists who conceived ideas of Natural Selection, they are by no means the only ones. Here are two more • William Charles Wells (1757-1817) – May have made the first recognition of natural selection, though he did not widely publish it. Darwin, however, recognized him in the 3rd edition of On The Origin of Species. He used the idea of selection within the context of different skin colors among human races. He suggested that similar forces may govern other life forms as well. • His ideas were shared by William Lawrence and James Pritchard • Patrick Matthew (1790-1874) – Suggested that selecting particular trees for timber would produce stronger wood for ships. Extrapolated that to natural systems Darwin and Wallace – Natural Selection Natural Selection and Acquired Characteristics, Compared Acquired Characteristics Natural Selection Natural Selection As A Concept • Via Darwin ~1842 (first drafts); 1859 Origin of Species (published) – Heritable differences among individuals in a population – Offspring produced in excess – Some individuals have higher fitness than others • Remember, fitness refers to relative ability to survive and reproduce • Still a gap in his hypothesis: – How are advantageous characteristics passed on from parents to offspring? • Solution would not come until Gregor Mendel’s work with peas at the end of the 19th century Gregor Mendel • In short, Mendel’s work with peas, Pisum sativum, at two gene loci (seed texture: rough/smooth; plant height: short/tall) showed how characters are passed from parents to offspring. – – – – Alleles vs genes Dominant vs recessive Homozygosity vs heterozygosity Genotype vs phenotype • When combined with Darwin’s work, Mendel’s elucidation of the process of heredity revolutionized biology The Process of Natural Selection • In a nutshell, natural selection is the result of differences in fitness among different phenotypes – Biotic and abiotic selective factors affect survival and reproduction • How do these factors affect phenotypes? – How are phenotypes selected for or against? – Three modes of natural selection: • Directional Selection • Stabilizing Selection • Disruptive Selection Directional Selection • Selection favors characters at one end of the distribution continuum Selection Population Phenotype Stabilizing Selection • Selection favors intermediate phenotypic characters Selection Selection Population Phenotype Disruptive Selection • Selection favors traits at the ends of the distribution- discontinuous Selection Population Phenotype Review of Selection Modes Variation In Populations • Local environmental conditions combined with genetics are the main factors affecting variation in populations – Ecotypes-locally adapted and genetically distinct populations – Clausen et al. 1940, Potentilla glandulosa, different morphology in different habitats (low, mid-elev, and alpine) • Each ecotype grew best in own habitat Clausen et al. I 1 2 3 4 Clausen et al. II Stanford Mather Timberline Low (Stanford) 1 Low-Med (Mather) 2 Med-High (Mather) 3 High (Timberline) 4 Clausen’s Study, Reviewed Orcas Also Exhibit Different Ecotypes Variation In Populations II • Remember, local environmental conditions combined with genetics are the main factors affecting phenotypic variation – Case (1976), Sauromalus obesus, is a widely distributed herbivorous desert lizard. There are significant differences in rainfall across its range, both in terms of total amount and variation year to year. • Chuckwallas from higher elevation (more rain), were significantly larger (length and weight). – Follow-up common-garden study (Tracy [1999]) • Lizards from different habitats raised under identical conditions • S. obesus from lower elevations grew fastest to maturity • Those from higher grew to larger size and grew faster after maturity Heritability (h2) • The inheritance and continued passing of beneficial traits form parents to offspring is the basis of evolution via natural selection. • As we have already seen, variability is the result of both genetic and/or environmental factors. • Heritability is the proportion of phenotypic variation in a population that is attributable to genetic transmission. • Heritability analyses estimate the relative contributions of differences in genetic and non-genetic factors to the total phenotypic variance in a population. • In its simplest form, heritability can be expressed as: • h2 = VG/VP Where VG is genetic variance and VP is phenotypic variance Natural Selection Studies • Jonathan Losos et al. 1997, Anolis lizards – Morphological correlates with vegetation type (limb length) – Trade-off between speed and dexterity/balance – Lizards caught from one source were introduced to several different islands with different vegetative structures – Predictions: • Morphology of introduced lizards should differ from source – Differences should correlate with vegetative structure • Lizard pops should correlate between limb length and perch diameter – Lizards lived, undisturbed on islands for 10-14 years! Data collected supported their hypotheses: • Positive correlation between differences in vegetation and limb length • Hind limb length was positively correlated with perch width Variation in Caribbean Anoles Natural Selection Studies II • Soapberry bugs (Jadera haematoloma) (Carroll and Boyd 1992) – Example of host shifting from native plants to exotics • Feed on fruits by piercing with beak – Several species of Sapindaceae were introduced to southern US • Fruit sizes differ among species – Those introduced to FL have smaller fruits than native soapberry – Those introduced to South Central US have larger fruits than natives – Differences found in beak lengths for host shifting bugs • Those in Florida had shorter beaks than those feeding on natives • Those in South Central US had longer beaks than native feeders – Genetic changes between different forms • Reduced fitness for those that are moved back to native host and vice-versa Carroll et al. 1992 Natural Selection Leads To Evolution • The cumulative effects of natural selection on individuals in a population will yield a population comprised of individuals that possess certain traits • Over time, it is possible to see that the genetic composition of this population has changed (remember, the traits that affect survival are heritable). • This is evolution: The change in allele frequencies in a population over time Evolution - Supporting Evidence • Fossils- parts or impressions of living things from past geologic eras – The fossil record has bolstered evolution due to the following: • Showed that different organisms lived at different times • Organisms from the past were different than extant forms • Fossils from adjacent layers are more similar than those from non-adjacent layers • Intermediate “missing links” have been found to fill in some gaps • Older rock tends to have more primitive fossils than newer rock Evolution - Supporting Evidence II • Comparative Anatomy – Homology- structures that share a common origin • Forelimbs, e.g., fossils suggest that the mammal forelimb is derived from those from ancestral amphibians. • The basic structure, one bone in the upper part and two in the lower, and 5 digits is shared by all vertebrates with legs. • This arrangement is so unique that it is very unlikely that it could have evolved independently in each vertebrate lineage. • In addition, the suggestion that this arrangement is the optimal one for running, swimming, flying, handling is equally unlikely. Evolution - Supporting Evidence III • Vestigial Organs and Structures – Structures that have no apparent use in current organisms, but may have been important to ancestral forms – Examples: • Coccyx (tail bone), wisdom teeth in humans • Thigh- and hip bones in pythons • Pelvis and femur in whale: Evolution - Supporting Evidence IV • Molecular – All life on earth share the same components that make up their respective genetic material(s) • Four nucleotides (A, C, G, T) make up DNA • The same 20 amino acids are components of all proteins – Also, DNA has been used to show relationship patterns between extinct species and extant descendents • e.g., DNA from extinct termites is very similar to that of present-day species that shared certain morphological features. Other extant species that are morphologically distinct, however, are quite different at the DNA level. Evolution - Supporting Evidence V • Biogeography (geographic distribution of organisms) – Darwin’s and Wallace’s voyages to South America • Darwin noticed the diversity of orgs on Galapagos and compared them to those on Cape Verde (off African coast) – Despite their similarity in terms of soil, climate, etc, different taxa – No amphibians on Galapagos, why? – Different taxonomically-instead of being related to each other’s fauna, the animals on these islands were most similar to species living on the mainland (whose soils, etc were very different) – Darwin noticed morphologically similar unrelated organisms, and closely related species that were very distinct - environment effects – Convergence v.s. Parallel Evolution v.s. Co-Evolution Supporting Evidence Coda: Convergence Convergence is a process by which unrelated species living under similar conditions and with similar selective factors develop similar morphological adaptations. As a result, they can become quite similar in appearance and habits. Convergence I Convergence II