Chapter 20: Microevolution: Genetic Changes within Populations20.1: Variation in Natural Populations

Microevolution: heritable change in the genetics of a populationo Population: all individuals of a single species that live together in the same

place and time Phenotypic Variation: differences in appearance or function that are passed from

generation to generation Evolutionary biologists describe and quantify phenotypic variation:

o Most characters exhibit quantitative variation: Individuals differ in small, incremental ways

i.e. weight usually depicted in bar graph or with a curve (if sample is large

enough) width of curve is proportional to variability among

individuals mean describes the average value of the character

o Qualitative variation: Exist in two or more discrete states Intermediate forms are absent

i.e. either blue or white feathers Polymorphism: existence of discrete variants of a character

Such traits are polymorphic Described by calculating percentage or frequency of each

trait Phenotypic variation can have genetic and environmental causes

o Can be causes by genetic causes, environmental causes or an interaction of the two

Genetic and phenotypic variations may not be perfectly correlated Sometimes, organisms with different genotypes have same

phenotypeso Black mice in Arizona have different genotype than

black mice in New Mexico Sometimes, organisms with same genotype have different

phenotypeso Acidity in soil influences flower color in some

plants Important to distinguish if is genetic, environmental or both

because: Only genetically based variation is subject to evolutionary

change Practical applications (such as in agriculture)

How do we determine causation? Changing one environmental variable and measuring

effects Breeding experiments: Mendel

o Not always ethical or practical

Studying pedigreeso Provides poor results for analyses of complex traits

Several processes generate genetic variationo Two sources of genetic variation:

Production of new alleles: Most arise from small-scale mutations in DNA

Rearrangement of existing alleles: Results from larger scale changes in chromosome structure

or number o Several forms of genetic recombination

Crossing over between homologous chromosomes during meiosis

Independent assortment of nonhomologous chromosomes during meiosis

Random fertilizations between genetically different sperm and eggs

Populations often contain substantial genetic variationo Every locus exhibits some variability in its nucleotide sequence

Not every variation affects phenotype – Some do not change amino acid sequence of the protein for

which the genes code20.2: Population Genetics

All populations have a genetic structureo Populations are made up of individuals

Individuals each have their own genotypeo Gene Pool:

Sum of all gene copies at all gene loci in all individuals Diploid organisms:

o Individual’s genotype includes two copies of every gene

To describe structure of gene pool: First identify genotypes in a representative sample and

calculate genotype frequencieso Percentages of individuals possessing each

genotype Diploid organisms have two copies of each

gene Either same or different allele

Then calculate allelic frequencieso Percentages of alleles in gene pool

2 allelic frequencies and 3 gene frequencies for two alleles Hardy-Weinberg Principle is a Null Model that Defines How Evolution Does Not

Occuro Null models: conceptual models which predict what would happen if

particular factor had no effect

Theoretical reference point against which observations can be evaluated

o Hardy-Weinberg principle: Specifies conditions under which a population of diploid

organisms achieves genetic equilibrium Point at which neither allele frequencies nor genotype

frequencies change in succeeding generations Showed that dominant alleles need not replace recessive ones Shuffling of genes does not cause gene pool to change Genetic equilibrium is only possible is:

1. No mutations are occurring2. The population is closed to migration from other3. Population is infinite in size4. All genotypes in population survive and reproduce equally

well5. Individuals in population mate randomly with respect to

genotypes Null model that serves as reference point for evaluating the

circumstances under which evolution may occur20.3: The Agents of Microevolution

o Mutation creates new genetic variations Spontaneous and heritable change in DNA Rare events

Exert little to no immediate effect Accumulation over years is significant

Major source of heritable variation Animals: only mutations in germ line are heritable Plants: mutations can occur in meristem cells and be passed down Deleterious mutations: alter in a harmful way Lethal mutations: causes great harm to organism carrying them

If dominant, homo- and heterozygous carries will die from its effect

If recessive, kills only homozygous recessive individuals Death of individuals – removal of allele from gene pool

Neutral mutations: neither harmful nor helpful May not change phenotype (i.e. amino acid codons) May change phenotype in a way that neither aids nor harms May be beneficial later if environment changes

Advantageous mutation: confers dome benefit on an individual that carries it

Natural selection may preserve the mutationo Gene flow Introduces Novel Genetic Variants into Populations

Change in allele frequencies as individuals join a population and reproduce

Many animals migrate from population to population Plants: dispersal agents

Pollen-carrying wind or seed-carrying animals Evolutionary importance of gene flow depends on the degree of

genetic differentiation between populations and rate of gene flow between them

o Genetic drift reduces genetic variability within populations Chance events that cause allele frequencies to change

unpredictably Has dramatic effects on small populations

Generally leads to loss of alleles and reduced genetic variability Two general circumstances:

Population Bottlenecks:o External factor kills large proportion of individuals

in populationo Dramatic reduction in population size

Founder Effect:o Few individuals colonize a distant locality and start

a new populationo Carry only a small sample of the parent

population’s genetic variationo Some alleles are missing and some that were rare

may be emphasized Conservation Implications

o Endangered species experience severe population bottlenecks

Loss of genetic variabilityo Small number of individuals available for captive

breeding programs may not fully represent a species’ genetic diversity

o No matter how large population becomes, will be less resitant to diseases or less able to cope with environmental change

o Natural selection shapes genetic variability by favoring some traits over others

Process by which advantageous traits become more common in subsequent generations

BASED ON PHENOTYPE, NOT NECESSARILY GENOTYPE If phenotype is successful, genotype will be passed down

Relative fitness: number of surviving offspring that an individual produces compared with the number left by others in the population

More relative fitness, more an organism will reproduce, more that allele will be passed on

Has no bearing on traits that appear during postreproductive life i.e. Huntington’s

Three modes of natural selection:

Directional selection – individuals near one end of the phenotypic spectrum have the highest relative fitness

o Traits shift toward a favored extremeo Incredibly commono Frequently used in artificial selection

Stabilizing selection - Intermediate phenotypes have highest relative fitness

o Eliminates phenotypic extremeso Reduces genetic and phenotypic variationo Most common mode of natural selectiono Sometimes caused by opposing forces of directional

stabilization Disruptive selection – extreme phenotypes have higher

relative fitness than intermediate phenotypeso Promotes polymorphismo Much less common than directional and stabilizing

o Nonrandom mating – choice of mates based on their phenotypes and genotypes

Sexual selection: two related processes:

o Intersexual selection – selection based on interactions between males and females

o Intrasexual selection – based on interactions between members of same sex

Fostered evolution of showy structureso Most probable cause of sexual dimorphism –

differences in size or appearance of males and females

Pushes phenotypes toward one extreme Nonrandom mating – selecting a mate with a particular

phenotype (and underlying genotype)o Thus, more homozygous than heterozygous

offspring than would be predicted by Hardy-Weinberg

Inbreeding – genetically related individuals mate with each other

20.4: Maintaining Genetic and Phenotypic Variation Diploidy can hide recessive alleles from the action of natural selection

o Diploid condition prevents removal of harmful recessive alleles These are dangerous in homozygous state but have little to no

effect on heterozygotes Thus can be protected from natural selection because

PHENOTYPE is unaltered Even if we could eliminate homozygous mating:

As frequency of recessive allele decreases, increasing proportion of its remaining copies is hidden in heterozygotes

o Diploid state preserves recessive alleles at low frequencies in large populations

In small populations, a combination of natural selection and genetic drift eliminate recessive alleles that are harmful

Natural selection can maintain balanced polymorphismso Balanced polymorphisms: one in which two or more phenotypes are

maintained in fairly stable proportions over many generationso Natural selection preserves balanced polymorphisms when:

Heterozygote advantage: heterozygotes have higher relative fitness Heterozygotes have higher relative fitness than either

homozygoteo i.e. sickle cell anemia conferring immunity to

malaria Selection in varying environments: when different alleles are

favored in different environments at different times Populations that span several habitats, selection preserves

different alleles in different places, thus maintaining variability in the population as a whole

Frequency-dependent selection: rarity of a phenotype provides an advantage

Rare phenotypes have higher relative fitness than common phenotypes

Rare phenotype will increase in frequency until it becomes common enough to lose its advantage

Sometimes established by predator-prey interactions Some genetic variations may be selectively neutral

o Some genetic variation is neither preserve nor eliminated by natural selection

o Neutral Variation Hypothesis: some of the genetic variation at loci coding for enzymes and other soluble proteins is selectively neutral

Even if various alleles code for slightly different amino acid sequences in proteins, the different forms of the proteins may function equally well

Natural selection would not favor some alleles over other Therefore not every genetic variant that persists in a

population has been preserved by natural selection Small populations should have less genetic variation than larger

ones20.5: Adaptation and Evolutionary Constraints

Scientists construct hypotheses about the evolution of adaptive traitso Adaptive trait: any product of natural selection that increases relative

fitness of an organism in its environmento Adaptation: accumulation of adaptive traits over time

o Evolutionary biologists compare variations of a trait in closely related species living in different environemnts

o Traits observed today may have had different function in pasto Not all characteristics are necessarily adaptive

Some are product of chance events and genetic drift Others produced by alleles selected for unrelated reasons Some result from action of basic physical laws

Several factors constrain adaptive evolutiono Adaptive traits of most organisms are compromises produced by

competing selection pressureso No organism can be perfectly adapted to its environment because

environments change over time Adaptation always lag behinds environmental changes

o Natural selection works primarily with alleles that have been present for many generations

Adaptive changes in the morphology of an organism are almost inevitably based on small modification of existing structures

Chapter 21: Speciation21.1: What is a Species?

Speciation: the process of species formation Morphological Species Concept: all individuals of a species share measurable

traits that distinguish them from individuals of other specieso Practical applications: =

Used to identify the species of fossilized organisms Field guides to plants and animals use physical characteristics

o Problems: Variation in morphology Does not help with closely related species that are nearly identical

in appearance Tell us little about the evolutionary processes that produce new

species Biological Species Concept: based on reproductive characteristics

o If two members of two populations interbreed and produce fertile offspring under natural conditions, they are a species

o Defines species in terms of population genetics and evolutionary theoryo Explains why members of the same species looks similar: same gene poolo Problems:

Does not apply to asexual organisms Cannot be used on extinct organisms

Phylogenetic Species Concept:o Uses both morphological and genetic sequence data to define species as a

population that shares recent evolutionary historyo Advantages: can be used to any group of organisms (including asexual

and/or extinct one)o Problems: detailed evolutionary history described for few groups of

organisms, so can’t be applied to all forms of life yet Many species exhibit substantial geographical variation

o Subspecies: geographically separated populations that exhibit significant, easily recognized phenotypic variation

Usually interbreed where geographical distributions meet Offspring often exhibit intermediate phenotypes Race is shorthand for subspecies

o Two patterns: Ring species:

Ring-shaped geographical distribution that surrounds uninhabitable terrain

Adjacent populations can exchange genetic material directly

o Gene flow only occurs through intermediary populations

Clinal variation Species is distributed over a large, environmentally diverse

area, traits exhibit a cline

o Pattern of smooth variation along a geographical gradient

Results from gene flow between adjacent populations that are each adapting to slightly different conditions

21.2: Maintaining Reproductive Isolation Reproductive isolating mechanism: biological characteristic that prevents the gene

pool of two species from mixing Two categories:

o Prezygotic isolating mechanisms: Exert effects before the production of a zygote (fertilization)

o Postzygotic isolating mechanisms After zygote formation

Prezygotic isolating mechanisms prevent the production of hybrid individualso Five mechanisms:

Ecological Live in different habitats

Temporal Mate at different times of day or different times of year

Behavioral Signals used by one species are not recognized by another

o i.e. courtship displays Mechanical

Differences in structure of reproductive organs or other body parts

Gametic Incompatibility between sperm of one species and the eggs

of another Postzygotic isolating mechanisms reduce the success of hybrid individuals

o Offspring has lower fitness when hybrid than intraspecific matingso 3 mechanisms:

hybrid inviability: two sets of developmental instructions (one from each

parent) that do not interact properly for the successful completion of embryonic development

hybrid sterility: offspring is born and is healthy but cannot produce

functional gametes hybrid breakdown:

first generation is healthy and fertile but second generation has reduced survival or fertility

o little long term mixing of gene pools21.3: The Geography of Speciation

Three modes of speciation based on geographical relationship of populations as they become reproductively isolated

o Allopatric speciation – occur between geographically separated populations

Physical barrier subdivides a large population or a small population becomes separated from a species’ main geographical distribution

Occurs in two stages: Geographical separation – prevents gene flow between

them Populations experience distinct mutations as well as

different patterns of natural selection and genetic drift – accumulate genetic differences that isolate them reproductively

Sometimes a barrier divides a large population into two or more units, sometimes peripheral populations are isolated

Species cluster: group of closely related species recently descended from a common ancestor

Sometimes, reestablish contact when barrier is eliminated or breached: SECONDARY CONTACT

Provides test of whether or not populations have diverged into separate species

o Tests reproductive isolation In early stages of secondary contact: prezygotic isolation

may be incompleteo Some members of each population may mate with

individuals from other, producing viable and fertile offspring

Areas where this happens: hybrid zones Reinforcement: if postzygotic isolating mechanisms cause hybrid

offspring to have lower fitness than those produced within each population, natural selection will promote the evolution of prezygotic isolating mechanisms, favoring individuals that amte only with members of this phenomenon

o Parapatric speciation – occurs between adjacent populationso Distributed across a discontinuity in environmental conditions

Although organisms interbreed freely, natural selection favors different alleles on either side, thus limiting gene flow

Occurs if hybrid offspring have low relative fitness Can be argued that places with parapatric populations are hybrid

zones where allopatric populations established o Sympatric speciation – occurs in one continuously distributed population

Most likely in insects that feed on just one or two plant species Genetic mutations that change some insect’s hoice of host plant

could result in formation of ecological isolation New individuals would collectively form separate

subpopulation – host race Example: apple maggot Often occurs in plants through polyploidy

An individual receives one or more extra copies of the entire haploid complement of chromosomes

o Large-scale genetic changes - prevents polyploidy individuals from breeding with individuals of the parent species

Chapter 22: Paleobiology and Macroevolution 22.1: The Fossil Record

Fossils form when organisms are buried by sediments or preserved in oxygen-poor environments

o Most fossils form in sedimentary rock Rain and runoff erode land, fine particles of rock and soil

carried downstream, settle to bottom as sediments, form layers (strata)

Weight of newer layers compress old layers into solid matric and fossils form within the layers when remains are buried in accumulating sediments

Lowest strata: oldest Highest strata: newest

o Usually only details of hard structure are preserved Rest is consumed by scavengers or decomposed by

microorganismso Dissolved minerals replace some part – fossils becomes stoneo Some fossils form casts that are later transformed into solid rocko Some environments: near absence of oxygen prevents decomposition

and soft-bodied organisms are preserved Embedded in amber Glacial ice Coal Tar pits Acidic water of peat bogs

Fossil record provides an incomplete portrait of life in the pasto Less than 1% of all species described by fossil record:

Several factors: Soft-bodied organisms do not fossilize as readily as

species with hard body parts Unlikely to find fossilized remains of species that were

rare and locally distributed Fossils rarely form in habitats where sediments do not

accumulate Many fossils are deformed or destroyed

o Rain, wind, pressure, natural disaster Scientists assign relative and absolute dates to geological strata and the

fossils they containo Relative ages: sequence of fossils in the lowest (oldest) to the highest

(newest) strata Used to establish geological time scale Does not tell us how old, just tells us what is older

o Radiometric dating: correlating the breakdown of radioisotopes with age

Unaffected by chemical reactions or environmental conditions

Measure relative amounts of the parent radioisoptope and its breakdown products and compare ratio with half-life

Time it takes for half of given amount of radioisotope to decay

o Used to estimate absolute age of rock’ Works best with volcanic rocks – but most fossils are found in

sedimentary rocks Determine age of volcanic rocks from same stratum

Fossils that still contain organic matter – use carbon-dating Fossils provide abundant information about life in the past

o Only direct information about life in the past Size and appearance of ancient animals and plants How structures were modified as they became adapted for

specialized use Chronicle proliferation and extinction of evolutionary lineages

and provide data on their past geographical distributionso Provide indirect data about behavior, physiology and ecology

22.2: Earth History Continental drift has altered the configuration of landmasses and oceans

o Earth’s crust is constantly in motiono Theory of plate tectonics: earth’s crust is broken into irregularly shaped

plates of rocko Currents in mantle cause plates and continents on them to move:

continental drift 250 million years ago – Pangea

o widespread distribution of many terrestrial groups

Separated into Laurasia and Gondwana (northern and southern continents)

Broke into contienents we know today Organisms on southern continents (remnants of Gondwana)

very different from those that live on northern continents (remanants of Laurasia)

o Smaller landmasses produced by plate tectonics are surrounded by more extensive coastlines and shallow marine habitats than were large continents

Harbored tremendous biodiversity As continents separated, populations living in shallow sea became

geographically isolated from each other Locally distributed organisms diversified and differentiated

from those in other regions Today, shallow marine habitats in temperate zone have giant kelp

beds; those in tropics have coral reefs Geological processes and unpredictable events changed the environments where

organisms lived o Contintental drift affected climate, extent of glaciations, sea levels

o Changed physical environments where organisms live on local, regional and global scales

o Both sudden and incremental changes Climate, glaciations and sea level:

Environmental temperatures vary with latitudeo Shifting continents underwent changes in local

temperatures Sizes of landmasses also have an effect on their climates

o Coastal regions experience smaller daily and seasonal fluctuations in temperature

o Whenever landmasses were joined into large continents, vast expanses of the interior landscape must have experienced frigid winters and hot summers

o As landmasses broke up, larger fration of the land was close to sea (thus less fluctuation in climate)

Global temperature:o Shifted from warm and wet to cool and dry several

times Changing positions of continents – alters

flow of ocean currents ^ + small changes in Earth’s orbit around

sun = climatic shifts leads to ocean waves rising and

falling influences the evolution of living systems

Volcanic Eruptions and Asteroid Impacts: Volcanic Eruptions:

o Spew enormous quantities of ash and gaso Block incoming sunlighto May cause earth’s surface temperature to decrease

several degrees for as long as a year Asteroid strikes

o Have devastating effects of living systemso Obliterate gigantic area and throw massive amounts

of material into the atmosphere, blocking sunlight and altering climate

22.3: Historical Biogeography and Convergent Biotas: Historical biogeography explains the broad geographical distributions of

organismso Continuous and disjunct distributions:

Continuous distribution: live in suitable habitats throughout a geographical area

Disjunct distribution: closely related species live in widely-separated locations

Two phenomena create this:

o Dispersal: the movement of organisms away from their place of origin

Produce a disjunct distribution if new population becomes established on the far side of a geographical barrier

o Vicariance: fragmentation of once-continuous geographical distribution by external factors

How do we tell the difference: Analyze fossil record for a group of

organismso Biogeographical realms:

Breakup of Pangea vicariant experience Isolation of continents evolution of distinctive regional

biotas o All organisms living in a region)

Biotas used to define six biogeographical realms:o Nearctic, Neotropical, Ethiopian, Oriental,

Palearctic, Australian Australian and Neotropical reams – geographically isolated

since Mesozoico Contain many endemic species

Those that occur nowhere else on Eartho All of Australia’s mammalian fauna are entirely

unique Endemic marsupials: mammals that give

birth after short gestation period and then carry their young in a pouch

All placental mammals extinct Nearctic and Palearctic realms fairly similar

o Bering land bridge Evolution has produced convergent biotas in widely separated regions

o Distantly related species living in different biogeographical realms are sometimes very similar in appearance

Convergent evolution: evolution of similar adaptations in distantly related organisms that occupy similar environments

Fostered morphological simiarlities in distantly related animals that feed on similar foods and occupy similar habitats in widely separated geographic ranges

22.4: The History of Biodiversity Biodiversity – number of species living on Earth

o Changed over time as a result of adaptive radiations and extinctions Adaptive radiations are clusters of related species with diverse ecological

adaptationso Adaptive radiation:

Rapid speciation produces cluster of closely related species that occupy different habitats or consume different foods

Often occurs after an ancestral species moves into an unfilled adaptive zone (a general way of life)

Movement into a new adaptive zone – triggered by chance evolution of a key morphological innocation that allows it to use the environment in a unique way

Can also be triggered by demise of successful group Extinctions have been common in the history of life

o Adaptive radiation countered by extinction Death of last individual in a species or the last species in a lineage

o Two distinct patterns of extinction: Background extinction: as environments change, poorly adapted

organisms will not survive and reproduce We expect species to disappear at some low rate:

background extinction rate Mass extinction: large numbers of species and lineages died out

over relatively short periods of geological time Well above background rate

6 mass extinctions thus far (one of which is current times) Biodiversity has increased repeatedly over evolutionary history

o Mass extinctions temporarily reduce biodiversity But also create evolutionary opportunities

o Highly adapted species survive and grow Undergo adaptive radiation and fill adaptive zones made available

by mass extinctiono Sometimes success of one lineage comes at the expense of anothero 3 major periods of adaptive radiation:

Cambrian: animal phyla first appeared Many became extinct

Ordovician: established dominant Paleozoic fauna Permian extinction Neogene period – produced immediate ancestors of modern marine

animals Diversity of marine animals has increased constantly since

early Neogene o Because of continental drift – as continents and

shallow seas became increasingly isolated, regional biotas diversified independently of one another

Increased worldwide biodiversityo Evolution of ecological interactions may have led to historical increase in

biodiversity22.5: Interpreting Evolutionary Lineages

Modern horses are living representatives of a once-diverse lineageo When horses’ ancestral lineage discovered, believed that evolution was

gradual, directional evolution in several skeletal features Changes in legs and feet allowed horses allowed horses to run

more quickly

Changes in face and teeth accompanied a switch in diet from soft leaves to tough grasses

o As fossil record grew, became apparent that from a common ancestor, there were many branches, all of which differed

o All but one are extinct (Equus)o There is no linear evolutionary path

Tempo of morphological change varies among lineageso Phyletic gradualism hypothesis: most morphological change occurs

gradually over long periods of time Discovery of transitional fossils

o For most organisms, though, fossils record is not as complete Discovery of transitional fossils rare Most species appear suddenly in a particular layer, persist for soe

time with little change and then disappear from fossil record Replaced by another species with different traits higher in the

recordo Punctuated equilibrium hypothesis: explanation for absence of transitional

forms Speciation usually occurs in isolated populations at edge of

species’ geographical distribution Experience substantial genetic drift and distinctive patterns

of natural selection Therefore:

most species exhibit long periods of morphological equilibrium punctuated by brief periods of speciation and rapid morphological evoltuon

Transitional forms only live for short periods of geological time in small, localized populations – thus, no fossils

However: What is “rapid” change? – could be generations or

hundreds of thousands of years Is it stasis? – alternating periods of directional selection

could produce appearance of stasiso Evidence of both gradual and punctuated morphological changes have

been found As have some intermediate patterns

22.6: The Evolution of Morphological Novelties Differential growth of body parts and changes in the timing of developmental

events produce distinctive structureso Allometric growth: the differential growth of body parts

Sometimes causes change in morphology of individuals over time Can establish morphological differences in closely related species

Skulls of chimpanzees and humans are similar in newborns but markedly difference in adults

o Grow in different places at different rates

o May reflect changes in one or a few genes that regulate the pattern of growth

o Heterochrony: changes in timing of developmental events Paedomorphosis: the development of reproductive capability in an

organism with juvenile characteristics Common form of heterochrony

Morphological novelties often arise as modifications of existing structureso Original version: exaptation

A.k.a preadaptationo Natural selection may then exaggerate trait ot modify it to enhance new

functiono Never evolve in anticipation of future evolutionary needs or benefits

Evolutionary developmental biology may explain the sudden appearance of some morphological novelties

o Evolutionary developmental biology: how evolutionary changes in the genes regulating embryonic development can lead to the changes in body shape and form that foster adaptive radiations, increasing biodiversity over geological time

Developmental biologists study how regulatory genes control the development of phenotypes and their variations

Homeotic genes code for transcription factors that bind regulatory sites on DNA –

activate or repress the expression of other genes that contribute to an organism’s form

Most animals share genetic tool kit that regulates their developmento Comparisons of genome sequence data – most animals share a set of

several hundred homeotic genes that control their development Dubbed “genetic tool kit”

Govern the basic design of the body plan by controlling the activity of thousands of other genes

Do not differ structurally among the animals that possess them

o Generally play the same role in all species Evolutionary changes in developmental switches may account for much

evolutionary changeo If animals share the same tool-kit genes, why are there so many different

body plans? Morphological differences among species arise when mutations

alter the effects of developmental regulatory genes Varying comnbinations of took-kit gene may be expressed at

different times and in different body regions Several hundred tool-kit genes encode proteins that work as

either activators or repressors in a multitude of possible combinations

o Thus, can generate an unimaginably large number of different gene expression patterns

o Allometric growth, heterochrony and the tool kit suggest that morphological novelties arise when evolutionary changes in developmental switches alter the expression patterns of existing genes

Contrasts with explanation of modern synthesis: most morphological novelties arise as mutations that slowly

accumulate in the genes that carry blueprints for building particular structures

Chapter 23: Systematics and Phylogenetics: Revealing The Tree of Life23.1: Nomenclature and Classification

systematics: branch of biology that studies the diversity of life and its evolutionary relationships

o identify, describe, name and classify organisms in terms of evolutionary relationships

Taxonomy: science that identifies, names and classifies new species Linneaus developed system of binomial nomenclature

o Binomial nomenclature: species are assigned a binomial (Latinized two-part name):

First part: genus: group of species with similar characteristics Second part: specific epithet: species

Defined using morphological species concepto Provides unique name for every specieso Allows people everywhere to discuss organisms unambiguously (no

matter language or culture) Linnaeus Devised the Taxonomic Hierarchy to Organize Information about

Specieso Classification: conceptual filing system that arranges organisms into ever

more inclusive categories Called taxonomic hierarchy

Nested series of formal cetagories:o Domain, kingdom, phylum, class, order, family,

genus, species, subspecies Organisms included in any one category compose a taxon

o Taxons lower down tree share more similarities than taxons higher up in tree

23.2: Phylogenetic Trees Systematists adapted Linneaus’ approach to a Darwinian worldview

o Organisms in same genus generally share a fairly recent common ancestor while those into higher taxonomic categories share more distantones

o Phylogeny: evolutionary history of organisms Illustrated in phylogenetic trees:

Formal hypotheses that identify likely relationships among species and higher taxonomic groups

A phylogenetic tree depicts the evolutionary history of a group of organismso Trees can include anywhere from all organisms to a specific specieso All share structure, thougho Drawn along implicit or explicit time line

Common ancestor: root of the tree Anagenesis: slow accumulation of evolutionary changes as the

environment shift over time Development of a new species from an old one, but does

not increase biodiversity Illustrated by a straight line in phylogenetic tree

Cladogenesis: speciation where an ancestral species produces two descendent species – increases biodiversity

Each is morphologically distant from their common ancestor

Illustrated by branching points (nodes) in a phylogenetic tree

o Each new branch (clade) = a new species Each new species has potential to become

root of lineage that includes all of its descendants

Two clades that emerge from same node = sister cladeso Each other’s closest relatives

Two species that emerge from same node near top of tree = sister species

o Phylogenetic Tree Conventions: If explicit time axis:

position of nodes reveals when geological time scale two clades originated

length of vertical branch between nodes – how long an ancestral group persisted before diversification

if emerge from same node near top of tree – closely relatedif emerge from same node near bottom of tree – distantly related

Horizontal spacing is usually not significant unless specified Most nodes have two branches protruding from them

If third or more branches portrayed, biologists have not yet discovered that specific pattern

“unresolved” node Clades can be rotated around nodes without changing meaning of

tree Thus cladograms present same info as phylogenetic trees

Phylogenetic trees allow biologists to define evolutionary classificationso Monophyletic taxa: one clade – an ancestral species and all of its

descendants, but no other species Most useful in classification but requires more data

o Polyphyletic taxon: organisms from different clades, but not their common ancestor

o Paraphyletic tacon – includes an ancestor and some, but not all, of its descendents

23.3: Sources of Data for Phylogenetic Analyses Modern systematists infer that morphological differences serve as indicators of

underlying genetic differences between species and lineageso Any heritable trait that is intrinsic to the organism can be used in a

phylogenetic analysis (excluding phenotypic differences caused by environmental variation)

Analysis of homologous characters sheds light on evolutionary relationships

o Phenoyptic similarities between organisms reflect their underlying genetic similarities

Species that are morphologically similar have often inherited the genetic basis of their resemblance from a common ancestor

o Homologies: similarities that result from shared ancestry Homologous structures may differ greatly among species if

function has changed over timeo Homoplasies: phenotypic similarities that evolved independently in

different lineages Analogies/analogous characters – homoplastic characters that serve

similar functions in different specieso How do you determine homology v. homoplasy?

Homologous structure are similar in anatomical details and relationship to surrounding structures

Homoplastic structures have same function but different structure – are results of convergent evolution

In multicellular organisms – homologous characters grow from same embryonic tissues and in similar ways during development

Structure of phylogenetic tree can reveal if two or more species inherited specific similarities from a common ancestor

If they did, structures are homologous If not, homoplastic

Morphological characters provide abundant clues to evolutionary relationshipso Pros:

Morphological differences often reflect genetic differences Easy to measure in preserved or living specimens Clearly preserved in fossil record – allow comparison of living

species with extinct relativeso Cons:

Morphological traits that are useful in phylogenetic analyses vary from group to group (difficult to compare, say, dog to worm)

Morphological characters alone cannot reveal the details of all evolutionary relationships

Behavioral characters are useful when animal species are not morphologically distinct

o When organisms are very similar in appearance, their pre- and post-zygotic isolating mechanisms can differentiate them

Molecular sequences are now a commonly used source of phylogenetic datao Phylogenetic analysis often conducted using molecular characters:

Nucleotide base sequences of DNA and RNAo Polymerase Chain Reaction (PCR) makes it easy for researchers to

produce numerous copies of specific segments of DNA for analysis Allows scientists to sequence minute quantities of DNA taken

from dried or preserved specimens in museums and even from some fossils

o Advantages:

Provide abundant data Every base in nucleic acid serves as character for analysis

Genes have been conserved by evolution: molecular sequences can be compared between distantly related organisms that share no organismal characteristics

Can be used to study closely related species with only minor morphological differences

Not directly affected by the developmental or environmental factors that cause nongenetic morphological variations

o Drawbacks: Limited number of character states Often difficult to assess homology of nucleotide base substitution Molecular characters have no embryonic development Do not understand significance of many molecular differences Only recently developed techniques that allow them to sequence

DNA found in fossils23.4: Traditional Classification and Paraphyletic Groups

Traditional systematics: prior to theory of evolution – o constructed phylogenetic trees and classified organisms by:

assessing the amount of phenotypic divergence between lineages and patterns of branching evolution that had produced them

classifications used both anagenesis and cladogenesis did not always strictly reflect the patterns of branching

evolution Four classes of tetrapod vertebrates:

o Amphibiano Mammaliao Reptiliano Aves

Based both on evolution and morphology23.5: The Cladistics Revolution

Classification based both on branching evolution and morphological divergence (as in traditional systematics) deemed unclear

Thus, created cladistics: based solely on evolutionary relationshipso Produces phylogenetic hypotheses and classifications that reflect only the

branching pattern of evolutiono Ignores morphological divergence altogether

Cladistic analyses focus on recently evolved character stateso Analyzes evolutionary relationships among organisms by comparing their

organismal and genetic characteristics Each character can exist in two or more forms (character states) Evolutionary processes change cahracters over time from an

original, ancestral character state to a newer, derived character state

Derived character: apomorphy Derived character found in two or more species: synapomorphy

Presence of synapomorphy: may be members of same cladeo How to tell if ancestral or derived character:

Fossil record Outgroup comparison: compare character in ingroup (clade under

study) to a closely related species that is not a member of the clade (outgroup)

Character states observed in outgroup – ancestral Only in ingroup – derived

Cladistics uses synapomorphies to reconstruct evolutionary historyo Constructs phylogenetic trees by grouping together species that share

derived characters Ancestral characters are not useful in defining a clade

o Results of cladistric analysis: presented in cladogram Diagram illustrating distribution of character states in organisms

being studied and the hypothesized sequence of evolutionary branching that produced them

o PhyloCode: strictly phylogenetic system that identifies and names clades instead of using traditional taxonomic categories

Systematists use several techniques to identify an optimal cladogramo Parsimony approach:

Principle of parisomony: philosophical concept Simplest plausible explanation of any phenomenon is the

best Thus the best cladogram is that which hypothesizes the

smallest number of evolutionary changes needed to account for the distribution of character states within a clade

o Minimizes the number of homoplasieso Statistical approach:

Statistical models of evolutionary change that take into account variations in the evolutionary rates at different nucleotide positions or in different genes or species as well as changes in evolutionary rates over time

Maximum likelihood methods:o Alternative trees are compared with specific models

of evolutionary changeo Cladogram that is most likely to have produced

observed distribution of character states is identified as the best hypothesis

Bayesian methodo Determining the probability that is correct given the

distribution of character states and the assumptions of the evolutionary model

23.6: Phylogenetic Trees as Research Tools Molecular clocks estimate the time of evolutionary divergences

o Mutations that arise in non-coding regions of DNA do not affect protein structure

Not eliminated by natural selectiono If mutations accumulate in these segments at a reasonably constant rate,

differences in their DNA sequences can serve as a molecular clock Large difference: difference in distant past Small difference: more recent common ancestor

o Different molecules evolve at different rates: Mitochondrial DNA (mtDNA) – evolves relatively quickly

Useful for dating evolutionary divergences that occurred within the last few million years

Chloroplast DNA (cpDNA) and genes for ribosomal RNA evolve more slowly – provide information about divergences dating back hundreds of millions of years.

Phylogenetic trees allow biologists to propose and test hypotheseso Comparative method:

Researchers compare the characteristics of different species to assess the homology of their similarities and infer where on the phylogenetic tree a particular trait appeared

Example: most parsimonious explanation as to why both crocodilians and birds have high parental care – common ancestor had it

o True: non-avian dinosaur fossil discovered sitting on nest of eggs

Phylogenetic analyses help track the origin and spread of infectious diseaseo Some pathogenic organisms and viruses mutate as they proliferate

Establish derived character states that are ripe for phylogenetic analysis

23.7: Molecular Phylogenetic Analyses Molecular phylogenetics has identified the most ancestral angiosperm

(Amborella) Analyses of gene sequences have revealed the branching pattern of the entire tree

of lifeo Originally, living systems organized into five kingdoms:

Monera, Fungi, Plantae, Animalia, Protista Protista – polyphyletic “grab bag” of unicellular or cellular

organismso Now, due to molecular phylogenetics:

Use rRNA since it is similar in all forms of life Divides organisms into three primary lineages (domains):

Bacteria – prokaryotes; well-known microorganisms Archea – prokaryotes; extremophiles and other

microorganisms Eukarya – eukaryotes; familiar animals, plants and fungi +

some lineages from Protista Archea Eukarya more closely related than either is to Bacteria

Direct descent: transmission of derived traits from ancestors to descendantso The three domains have not evolved separate from one another, though

Horizontal gene transfer – movement of genetic material from one clade to another

o Transformation and transductiono Viral infectiono Incorporation of one organism into another

Chapter 30: Deuterostomes: Vertebrates and Their Closest Relatives30.12: Nonhuman Primates:

Primates: mammalian lineage that includes humans, apes, monkeys and their closet relatives

First Primates appeared in Eocene epoch – 55 million years ago Key derived traits enabled primates to become arboreal, diurnal and highly social

o Arboreal: live in trees instead of ground Primates have more erect posture than other mammals Flexible hip and shoulder joints Can grasps objects because have nails, not claws Fingertips have sensory nerves Opposable big toe

o Diurnal: active during daylight hours Rely more on vision than on sense of smell Have short snouts and small olfactory lobes Forward-facing eyes with overlapping fields of vision Color vision

o Social: Primate brains are large and complex

Have exceptional capacity to learn Live in social groups Lots of parental care

Living Primates Include Two Major Lineages:o Strepsirhini:

Possess many ancestral morphological traits: Moist, fleshy noses Eyes positioned laterally on their heads

Short gestation period Rapid menstruation Some arboreal Some spend substantial time on ground

o Haplorhini – familiar monkeys and apes Have derived primate characteristics:

Compact, dry noses Forward-facing eyes

o 130 or so species of monkeys + 13 species of apes + humans = monophyletic haplorhine lineage Anthropoidea

arose in Africao Continental drift then established long-term geographical and evolutionary

separation of anthropoids in the New and Old World By middle of Oligocene epoch – ancestors of New World monkeys arrived in

South America – 30 million years agoo Now live in Central and South America

Anthropoids in the Old World:o Gave rise to two lineages:

One ancestral to Old World monkeys Occupy habitats from tropical rain forests to deserts in

Africa and Asia Grow as large as 35 kg Sexually dimorphic Use all four limbs for locomotion

One ancestral to apes and humans Hominoidea

o Apes and humanso Monophyletico Climate of early Miocene – wetter than today

Extensive foresto Shift to cooler and drier climate in middle Miocene

converted dense forests into more open woodlands

Hominoids shift to adopt a more terrestrial existence and shifted their diets to include leaves and hard foods

Distinguishing features between Old World Monkeys and hominoids:

Apes lack a tail Great Apes are much larger than monkeys Posterior region of vertebral column is shorter and more

stable in apes Apes show more complex behavior Gibbons and siamangs: smallest of apes

o Brachiation: hand below branches and swing forward

Gorillas: largest of living primateso Knuckle-walking locomotiono Exclusively vegetarian

Chimpanzeeso Fprest-dwellingo Bipedal

30.13: The Evolution of Humans African hominoids diverged into several lineages between 10 million and 5

million years agoo One lineage: hominins – includes modern humans and bipedal ancestors

Hominins first walked upright in East Africa about 6 million years agoo Upright posture and bipedal locomotion – key adaptations that distinguish

hominins from apes

o FINISH THIS CHAPTER LATER ANJALI

Chapter 49: Ecology and the Biosphere49.1: The Science of Ecology

Ecology: study of interactions between organisms and their environments Biotic: biological components Abiotic: nonbiological components

o Three abiotic components: Hydrosphere – all water Lithosphere – rocks, sediments and soils Atmospheres – gases and airborne particulates

Two related disciplines: o Basic ecology: distribution and abundance of species and how they interct

with each other and the physical environmento Applied ecology: develop conservation plans and amelioration programs

to limit, repair and mitigate ecological damage caused by human activities Ecologists study levels of organization ranging from individual organisms to the

biosphereo Can be divided into five increasingly complex and inclusive levels of

organization: Organismal ecology:

Study genetic, biochemical, physiological, morphological and behavioral adaptations of organisms to the abiotic environment

Population ecology: focuses on populations Groups of individuals of the same species that live together Study how the size and other characteristics of populations

change in space and time Community ecology: examines groups of populations that occur

together in one area Study interactions between species, analyzing how

predation, competition and environmental disturbances influence a community’s development, organization and structure

Ecosystem ecology – explores cycling of nutrients and the flow of energy between the biotic components of an ecological community and the abiotic environment

Biosphere ecology – largest scale Ecologists test hypotheses with observational and experimental data

o Ecologists create hypothesis about ecological relationships and how they change through time or differ from place to place

o Formalize these ideas in mathematical models that express clearly defined, but hypothetical, relationships among important variables in a system

o Manipulation – allows for simulation of natural events and large-scale experiments before investing time, energy and money in field/lab work

49.2: Environmental Diversity of thr Biosphere Climate: weather conditions prevailing over an extended period of time

o Sunlight, temperature, humidity, wind speed, cloud cover and rainfall

Vary on global, regional and local scales Undergo seasonal changes almost everywhere

Variations in incoming solar radiation create global climate patternso Global pattern of environmental diversity results from:

Latitudinal variation in incoming solar radiation Earth’s rotation on its axis Orbit around the sun

o Solar Radiation: Earth’s spherical shape: intensity of incoming solar radiation varies

from equator to poles Equator: travels shortest possible distance through

radiation-absorbing atmosphere and falls on smallest possible surface area

o hotter Poles: arrives at oblique angel: travels longer distance and

shines on larger areao Rotation on axis: seasonality

Earth is tilted on angle Produces seasonal variation in duration and intensity of

incoming solar radiationo Northern hemisphere receives maximum

illumination on June solsticeo Southern on December solsticeo Twice a year (vernal and autumnal equinoxes)

Sun shines directly over the equator Tilt is permanent

Only tropics (latititudes between Tropics of Cancer and Capricorn) ever receive solar radiation from directly overhead

o Tropical regions experience only small seasonal changes in temperature and day length

Variation increases as head to poleso Air circulation:

Sunlight warms air masses Expand, lose pressure and rise in atmosphere

Unequal heating of air at different latittudes initiates global air movements

3 circulation cells in each hemisphere flow of air masses at low altitudes: creates winds near planet’s

surface surface rotates beneath atmosphere – moves rapidly near the

equator and slowly near poles Coriolis Effect: latititudinal variation in the speed of rotation

deflects movement of rising and sinking air masses from a strictly north-south path into belts of east-west winds

o Precipitation

Differences in solar radiation and global air circulation create latitudinal variations in rainfall

Warm air holds more water vapor than cool air: As air in equator heats up, absorbs water from oceans Air masses expand as they rise and heat energy is

distributed over larger volume, causing temperature to drop Adiabatic cooling: decrease in temperature without actual

loss of heat energy After cooling adiabatically, air masses release moisture as rain Cool, dry air masses descend at 30 degrees, absorb water (thus,

creating dry areas) Release this water at 60 degrees northern and southern

temperate zoneso Ocean Currents:

Solar radiation warms ocean’s surface water unevenly Volume of water increases as it warms: sea level is higher at

equator than at poles Slope is enough to cause movement of water in response to

gravity Aided by winds

Surface water flows in the direction of prevailing winds Form major currents

Also influenced by Earth’s rotation, position of landmasses and the shapes of ocean basins

Clockwise in Northern Hemisphere, counter in S. Regional and local effects overlay global climate patterns:

o Proximity to ocean: Continental climate: not moderated by the distant ocean Maritime climate: tempered by proximity to water

Currents running along seacoasts: exchange heat with air masses flowing above them

Moderate temperature over nearby land Breezes blow from sea land during day Land sea during night

Also influences rainfall Monsoon cycles: seasonal reversals of wind direction results in

torrential downpouro Effects of topography:

Mountains, valleys and other topographic fatures In North:

o South-facing slopes warmer and drier than north Receive more solar radiation

Mountains establish regional local rainfall patterns Rising to cross mountain: cools and releases water on

windward side

Descent: warms and forms rain shadow by absorbing moisture

o Microclimate: the abiotic conditions that immediately surround organisms Have greatest effect on survival and reproduction

49.3: Organismal Responses to Environmental Variation and Climate Change Organisms use homeostatic responses to cope with environmental variation

o Obligate: behavioral and physiological that must always be usedo Facultative: may be used or not as immediate conditions demand

Anolis lizards – bask more frequently at higher altitudes to make up for lower temperatures

Global climate change affects the ecology of many organismso Rising temperatures will affect the geographical distributions of

populations, species and communities Distributions of polar species – contract to higher latitudes Ranges of temperate and tropical species will expand or shift

toward the poles Lowland species will move to higher elevations Timings will be altered

Plants may flower earlier Migratory animals will migrate/mate earlier

Changing combinations of species that occur together within ecological communities

o Ocean temp. also rising reflected in the distributions of marine species 49.4: Terrestrial Biomes

biome: vegetation type + associated microorganisms, fungi and animals 8 major terrestrial biomes:

o tropical forestso savannaso desertso chaparralo temperate grasslandso temperature deciduous forestso evergreen coniferous forestso tundra

Environmental variations governs the distribution of terrestrial biomeso Climate: main determinant of biome distribution

Climograph: portrays particular combination of temperature and rainfall conditions where each terrestrial biome occurs

Provides general portrait of temperature and moisture conditions where different biomes occur

o Does not address details of environmental variation i.e. only has annual, doesn’t depict seasonal

changes does not show nonclimactic factors

distributions of biomes appear as bands

Tropical Forests: include Earth’s most species-rich communitieso Three types:

Rain forest Deciduous forest Montane forest

o In areas with intense solar radiation and heavy rainfallo Tropical rain forests:

High humidity and precipitation High annual temperature High productivity Rapid decomposition Trees replace leaves year round – produces continuous rain of

detritus – consumed by scavengers – decomposed – absorbed by vegation or washed away by rain

Thus, high vegetation but soil is nutrient poor Usually layered:

Dense canopy that blocks most sunlighto Shallow roots but wide buttresses (woodly lateral

extensions of trunks that stabilize them in the ground)

Shade tolerant shrubs and small trees: understory layers below canpy

Little sunlight reaches forest flooro Tropical deciduous forests:

Areas with pronounced summer rainy season and winter dry season

Winter drought reduces photosynthesis and most trees drop their leaves

o Tropical montane forests: High altitudes in the tropics Enveloped in mist Short trees Thrive in moisture-laden air Grow slowly because productivity is limited by low temperatures,

high humidity, sun-light blocking clouds Savannas – moderate rainfall is highly seasonal

o Grasslands with few treeso Grow adjacent to tropical deciduous forestso Seasonality determined by availability of water

Doughts last for montho Grasses successful in semiarid conditions: shallow roots harvest water

efficientlyo Home to large herbivorous mammalso Thorn forests: arid borders of true savanna where large mammals less

abundant Large underground root systems

Highly seasonal Deserts – little precipitation

o Rainfall averages less than 25 cm per yearo Extreme conditions:

Rainfall arrives infrequently in heavy, brief pulses Sudden runoff erode topsoil – high mineral content but little

organic mattero Dry air and scant cloud cover: most sunlight reaches ground

Very hot in day time Loses heat quickly – at night and in winter

o Vegetation sparse due to arid environments Perennial plants protect tissue from herbivores with spines or toxic

chemicals Many use CAM photosynthesis to conserve water

o Abundant animals – mostly small Seed-eating mammals – drink water extracted from food Insects, lizards and mammals – consume sparse vegetation Scorpions, lizards and bird – eat insects Snakes, owls, foxes – other animals

o Most animals avoid midday heat and dehydrating conditions Many retreat into underground burrows or are nocturnal

Chaparral – cool and wet winters, hot and dry summerso Narrow sections of coastal land between 30 and 40 degreeso 25-60cm rain per yearo dense shrubs with hard, tough, evergreen leaves

woody stems above ground and large root systems in soil many species produce toxic aromatic compounds that inhibit

germination and growth of other plantso After winter rains – shrubs covered with leaves and flowers

Many insects and birso Hot dry summers 00 most plants dormant

Lightning sparks frequent fires Aromatic oils make flammable – aboveground parts burn

swiftly but resprout quickly Temperate Grasslands are subject to periodic disturbance:

o Interior of continents Cold, snowy winters and warm, fairly dry summers

o Near constant state of flux: Seasonal drought Periodic fires Grazing by mammals

o Grassland is rich in organic matter – aboveground parts of most plants die and decompose annually

o North America: Shotgrass prairie in the west

Strong winds Light rainfall Rapid evaporation

Occupied by drought resistant plants and large grazing mammalso Temperate deciduous forests: seasonal dormancy

Temperate latitude Warm summers, cold winters Low to middle altitudes

Winter: low temps. Reduce photosynthetic rateso Snow and ice damage leaves

Most plants shed leaves and grow new ones in spring Thick layer of leaf litter which releases mineral nutrients as

it decomposeso Enrich soil

Slow decomposition Fewer species than tropical forests Canopy + woody shrub understory + ground layer of mosses

Flower early inn spring before sunlight blocked by leaves in canopy

o Evergreen coniferous forests: high northern latitudes Boreal forest or taiga

Circumpolar expanse of evergreen coniferous trees Snow blankets ground during long and cold winters Precipitation falls during short summer Plants grow quickly during long summer days Needle-shaped leaves dominate:

o Thick cuticle and recessed stomata that conserve water

Acidify the thin soil – speeds leaching of most nutrients

Lightning sparked fires – common Relatively undisturbed by humans

o Harbors native animals Large herbivores, small mammals, wolves,

lynx and wolverines, bears and insects Temperate rain forest: coniferous forest where winters are mild

and wet and summers are cool Supported by heavy rain and fog

o Tundra: vast, treeless plain in Northernmost habitats Treeless Spreads from boreal forests to polar ice cap Wind-swept and wet Winter temperature consistently below freezing 2-month summer – still cold

ground below perpetually frozeno permafrost

little rainfall: however, little evaporation and impermeability of permafrost leaves soil waterlogged

plants short – flower profusely during summer’s nearly continuous sunlight

some animals: herbivorous arctic hairs, lemmings predatory snowy owls, wolves, foxes, lynx migratory animals from boreal forests

Alpine Tundra: high mountaintops throughout world

49.5: Freshwater Environments Water with [salt] < 0.5%

o Lotic system: water flows through channelso Lentic system: water stands in an open basino Highly productive wetlands – occur at borders of freshwater environments

Streams and rivers carry water downhill to a lake or seao Flowing water environments:

Starts as seeps on high ground Water flow downhill – collects into narrow streams Merge to form wide rivers

Streams and rivers include 3 habitats:o Riffles: shallow, fast-moving, turbulent stretches

over a rough bottom of pebbles or rockso Pools: deep, slow-moving areas with a smooth sand

or mud bottomo Runs: deep, fast-moving stretches over smooth

bedrock or sand Steams: high flow rate, low volume, lots of riffles and

pools Rivers: flow rate lowers, flow volume increases, lots of

runs and pools Flow rate and volume vary seasonally with rate of water input

from rainfall and snowmelt and geographically with altitude and topography

[suspended particulate material] – low in streams, high in rivers temperature: rises as water flows downstream to warmer lowland

habitats oxygen more soluble in cold than warm water thus

[O2] higher in streams than rivers Erosion of streambed and surrounding land: provides solute

content of flowing water Lakes – bodies of standing water that accumulates in basins:

o Fed by rainfall and streams/rivers that carry water from surrounding landso Availability of light affects photosynthesis by a lake’s phytoplankton and

plants Photic zone: surface water that sunlight penetrates

Aphotic zone: deeper area that is darkero Lake zonation:

Defined by depth and distance from shore Littoral zone: shallow water near shore

Sunlight penetrates to bottom Enriched by nutrients made available by decomposers and

runoffo High photosynthetic activityo Occupied by many specieso Rooted and floating aquatic plants commono Submerged vegetation houses microorganismso Used by many animals for feeding and reproducing

Limnetic zone: sunlit water beyond littoral Supports plankton communities

o Primary photosynthesizers: phytoplanktono Eaten by zooplanktono Eaten by small fisho Eaten by larger fish

Profundal zone: perpetually dark water below limnetic zone Photosynthesis impossible Rain of detritus from limnetic zone support community of:

o Bacterial decmoposerso Animals that feed on dead or dying material

o Seasonal changes in temperate lakes Temperature variations induce changes in the vertical zonation of

lakes Ice floats on water Winter: ice forms on surface of lakes –

o Temperature varies from near freezing below ice to 4C at the bottom (density difference keeps ice afloat)

Spring: As ice melts, warmer, denser water sinks – surface temperature rises to 4C

Brief time: temperature uniform at all depths Winds create vertical currrents: spring

overturn – mixes surface water with deep water

O2 at surface moves to bottom Nutrients from bottom move to

surface Midsummer: sunlight heats top layer of limnetic zone

(epilimnion)o Hypolimnion: deep water in profundal zone

Temperature remains low

o Boundary between the two – temp. changes abruptly over a narrow depth range: thermocline

o Orevents vertical mixing because warm surface water floats above thermocline

Cool deep water says below it Summer: nutrient-rich detritus sinks to the bottom of the

lake – o Decomposition depletes O2 in hypolimnion

Autumn: declining sunlight + winds cause epilimnion coolo Water becomes densero Water sinkso Thermocline is eliminatedo Autumn overturn: equalizes dissolved substances at

all depths Photosynthetic Activity:

Spring: increased sunlight, warm temperatures and sudden availability of nutrients induce a bloom of photosynthesis and growth

As season progresses, nutrient levels reduce and thermocline prevents vertical mixing

Late summer: limit photosynthesis Autumn overturn – short burst of productivity Days get shorter – productivity remains low until spring

o Trophic nature of lakes Lakes classified by nutrient content and rates of photosynthetic

activity Oligotrophic lakes:

o Poor in nutrients and organic mattero Rich in oxygeno Crystal clear water (low productivity)

Eutrophic lakes:o Rich in nutrients and organic mattero Decomposition of organic matter depletes ocygen in

hypolimniono Highproductivity in epilimnion often chokes water

with seasonal blooms of cyanobacteria and filamentous algae

o Thick and soupy Over long periods of time, oligotrophic

lakes become eutrophic49.6: Marine Environments

[salt] averages about 3%o covers nearly 3.4 of Earth’s surface o accounts for a large fraction of its phytosynthetic activity

process large amounts of carbon dioxide

generate oxygen moderate major cause of global climate change

Depth and distance from shore govern the physical charactersitics of marine habitats

o Photic v. aphotico Pelagic province: the water

Neritic zone – shallow water above continental shelves Oceanic zone – deep water beyond them

o Benthic province: bottom sediments Intertidal zone: shoreline alternately submerged and exposed by

tides Abyssal zone: bottom sediments that lie permanently below deeper

watero Five marine environments:

Estuaries Rocky and sandy coasts Continental shelves and oceanic banks

Chapter 50: Population Ecology50.1: Population Characteristics50.2: Demography50.3: The Evolution of Life Histories50.4: Models of Population Growth50.5: Population Dynamics50.6: Human Population Growth

Chapter 51: Population Interactions and Community Ecology51.1: Population Interactions51.2: The Nature of Ecological Communities51.3: Community Characteristics51.4: Effects of Population Interactions on Community Characteristics51.5: Effects of Disturbance on Community Characteristics51.6: Ecological Succession: Responses to Disturbance51.7: Variations in Species Richness Among Communities

Chapter 52: Ecosystems52.1: Modeling Ecosystem Processes52.2: Energy Flow and Ecosystem Energetics52.3: Nutrient Cycling in Ecosystems52.4: Human Disruption of Ecosystem Processes

Chapter 53: Biodiversity and Conservation Biology53.1: The Biodiversity Crises on Land, in the Sea, and in River Systems53.2: Specific Threats to Biodiversity53.3: The Value of Biodiversity53.4: Where Biodiversity is Mostly Threatened53.5: Conservation Biology: Principles and Theories

Chapter 54: The Physiology and Genetics of Animal Behavior54.1: Genetic and Environmental Contributions to Behavior54.2: Instinctive Behaviors54.3: Learned Behaviors

Chapter 55: The Ecology and Evolution of Animal Behavior55.1: Migration and Wayfinding55.2: Habitat Selection and Territoriality55.3: The Evolution of Communication55.4: The Evolution of Reproductive Behavior and Mating Systems55.5: The Evolution of Social Behavior