Evolution, Natural Selection, and Evolution, Natural Selection, and CommunitiesCommunities

Topics And Objectives for the Topics And Objectives for the WeekWeek

Evolution by Natural SelectionEvolution by Natural Selection

CommunityCommunity

Species InteractionsSpecies Interactions

Species DiversitySpecies Diversity

SuccessionSuccession

Possible Exam QuestionsPossible Exam Questions

1. List and explain the four premises of evolution by natural selection as proposed by Charles Darwin.

2.2. Relate the concepts of niche, competitive Relate the concepts of niche, competitive exclusion, and resource partitioning.exclusion, and resource partitioning.

Evolution and Natural SelectionEvolution and Natural Selection

The Underlying Mechanisms of Species Diversity

Charles DarwinCharles Darwin

"There is grandeur in this view of "There is grandeur in this view of life, with its several powers, having life, with its several powers, having been originally breathed by the been originally breathed by the Creator into a few forms or into Creator into a few forms or into one; and that, whilst this planet has one; and that, whilst this planet has gone on cycling on according to the gone on cycling on according to the fixed law of gravity, from so simple fixed law of gravity, from so simple a beginning endless forms most a beginning endless forms most beautiful and most wonderful have beautiful and most wonderful have been, and are being evolved.“been, and are being evolved.“

--The Origin of Species--The Origin of Species

Charles DarwinCharles Darwin

Darwin was born into the Darwin was born into the family of a prominent family of a prominent physician on February 12, physician on February 12, 1809, in Shrewsbury, England. 1809, in Shrewsbury, England. His mother was the daughter of His mother was the daughter of Josiah Wedgewood, founder of Josiah Wedgewood, founder of the famous pottery firm. In the famous pottery firm. In 1825 Charles entered the 1825 Charles entered the University of Edinburgh to University of Edinburgh to become a physician. Two become a physician. Two years later he entered years later he entered Cambridge University to study Cambridge University to study for the clergy.for the clergy.

GranthamGrantham

Charles DarwinCharles DarwinIn 1831 Darwin joined the In 1831 Darwin joined the HMS Beagle HMS Beagle as the naturalist for a as the naturalist for a circumnavigation of the world; the voyage lasted five years. It was circumnavigation of the world; the voyage lasted five years. It was his observations from that trip that lead to his proposal of his observations from that trip that lead to his proposal of natural natural selectionselection to explain the diversity of organisms. to explain the diversity of organisms.

It was not until 1859 that Darwin finally published his It was not until 1859 that Darwin finally published his Origin of Origin of Species.Species.

Darwin’s FinchesDarwin’s Finches

""The most curious fact is the perfect The most curious fact is the perfect gradation in the size of the beaksgradation in the size of the beaks in the in the different species of Geospiza, from one as different species of Geospiza, from one as large as that of a hawfinch to that of a large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in chaffinch, and (if Mr. Gould is right in including in his sub-group, Certhidea, in the including in his sub-group, Certhidea, in the main group), even to that of a warbler. The main group), even to that of a warbler. The largest beak in the genus Geospiza is show inlargest beak in the genus Geospiza is show in Fig. 1Fig. 1, and the smallest in, and the smallest in Fig. 3 Fig. 3; but instead ; but instead of their being only one intermediate species, of their being only one intermediate species, with a beak of the size shown in with a beak of the size shown in Fig. 2Fig. 2, there , there are no less than six species with insensibly are no less than six species with insensibly graduated beaks. The beak of the sub-group graduated beaks. The beak of the sub-group Certhidea, is shown inCerthidea, is shown in Fig. 4 Fig. 4. The beak of . The beak of Cactornis is somewhat like that of a starling; Cactornis is somewhat like that of a starling; and that of the fourth sub-hroup, and that of the fourth sub-hroup, Camarhynchus, is slightly parrot-shaped. Camarhynchus, is slightly parrot-shaped. Seing this gradation and diversity of Seing this gradation and diversity of structure in one small, intimately related structure in one small, intimately related group of birds, one might really fancy that group of birds, one might really fancy that from an original paicity of birds in this from an original paicity of birds in this archipelago, one species had been taken archipelago, one species had been taken and modified for different endsand modified for different ends [ [stressstress added]." Charles R. Darwin, 1845, added]." Charles R. Darwin, 1845, The The Voyage of the BeagleVoyage of the Beagle [Edited by Leonard [Edited by Leonard Engel, 1962, NY: Doubleday], pages 380-Engel, 1962, NY: Doubleday], pages 380-381.381.

Darwins’s Four PremisesDarwins’s Four Premises

1.1. Each species produces more offspring than Each species produces more offspring than will survive to maturity.will survive to maturity.

2.2. Individuals in a population exhibit variation.Individuals in a population exhibit variation.

3.3. There are limits on population growth There are limits on population growth imposed by the environment.imposed by the environment.

4.4. There is differential reproductive success There is differential reproductive success among individuals within a population.among individuals within a population.

What is Evolution?What is Evolution?

• Descent with modification.Descent with modification.

• Change in the genetic structure of a Change in the genetic structure of a population.population.

Mechanisms That Change the Genetic Mechanisms That Change the Genetic Structure of a Population And Cause Structure of a Population And Cause

Evolutionary Change?Evolutionary Change?

1.1. Genetic mutationsGenetic mutations

2.2. Genetic drift (Isolation of populations and Genetic drift (Isolation of populations and different accumulations of mutations)different accumulations of mutations)

3.3. Founder effect (Small initial reproductive Founder effect (Small initial reproductive populations with limited genetic diversity)populations with limited genetic diversity)

4.4. Natural selection (Differential reproductive Natural selection (Differential reproductive potential)potential)

What Is Natural Selection?What Is Natural Selection?

• Differential survival and reproduction Differential survival and reproduction among individuals of a population.among individuals of a population.

• Response to selection pressures.Response to selection pressures.

Relationship of Evolution and Selection Relationship of Evolution and Selection Pressures to Environmental SciencePressures to Environmental Science

1.1. Biodiversity arises through evolution.Biodiversity arises through evolution.

2.2. Human disturbance changes selective Human disturbance changes selective pressures.pressures.

3.3. Conservation of individual species.Conservation of individual species.

Process of Evolution through Natural Process of Evolution through Natural SelectionSelection

1.1. OverproductionOverproduction

2.2. Resources limit population growthResources limit population growth

3.3. Heritable variation in traitsHeritable variation in traits..

4.4. Differential survival and/or reproductionDifferential survival and/or reproduction

Potential Selective PressuresPotential Selective Pressures

AbioticAbioticTemperatureTemperaturePrecipitationPrecipitationpH (acidity)

BioticBioticPredationPredationDiseaseDiseaseCompetitionCompetition

Types of SelectionTypes of Selection

Stabilizing SelectionStabilizing Selection

Directional SelectionDirectional Selection

Disruptive SelectionDisruptive Selection

Example of Natural Selection: Example of Natural Selection: Peppered MothPeppered Moth

Peppered MothsPeppered Moths

CommunityCommunity

Association of different Association of different populations of organisms that populations of organisms that live and interact together in the live and interact together in the same place at the same time.same place at the same time.

The Underlying Bases of The Underlying Bases of Community Structure is Community Structure is

Species InteractionsSpecies Interactions

And NUH is the letter I use to spell NutchesWho live in small caves, know as Nitches, for Nutches.

These Nutches have troubles, the biggest of which isThe fact that there are many more Nutches than Nitches.

Each Nutch in a Nitch knows that some other NutchWould like to move into his Nitch very much.

So each Nutch in a Nitch has to watch that small Nitchor Nutches who haven't got Nitches will snitch.

Dr. Suess (Geisel, 1955)

Interactions = Relationships or Interactions = Relationships or Associations Between Members of Associations Between Members of

Two or More Different SpeciesTwo or More Different Species

Type of Type of InteractionInteraction

Effect on Effect on Species 1Species 1

Effect on Effect on Species 2Species 2

CompetitionCompetition -- --

PredationPredation ++ --

HerbivoryHerbivory ++ --

ParasitismParasitism ++ --

MutualismMutualism ++ ++

CommensalismCommensalism ++ 00

NichesNiches• A niche is the way an organism interacts the way an organism interacts

with other living things and with its with other living things and with its physical environment.physical environment.

• AA fundamental niche fundamental niche = the roles/functions = the roles/functions that the organism could play (i.e., where that the organism could play (i.e., where could it live).could it live).

• A A realized nicherealized niche = the role/function that the = the role/function that the organism actually fulfills (i.e., where does it organism actually fulfills (i.e., where does it actually live).actually live).

Tidewater Tidewater NichesNiches

Factors That Restrict the Realized Factors That Restrict the Realized Niche of an OrganismNiche of an Organism

Limiting environmental factors may be:Limiting environmental factors may be:

1.1. The physical environmentThe physical environment

2.2. Biotic factors (e.g., competition)Biotic factors (e.g., competition)

Limiting FactorsLimiting Factors

Summary of Community StructureSummary of Community Structure

The numbers and types of organisms that exist in The numbers and types of organisms that exist in an ecological niche are dependent upon both the an ecological niche are dependent upon both the physiological resources available and the physiological resources available and the relationships between different species. relationships between different species.

Resources are limited in an ecosystem, and Resources are limited in an ecosystem, and species survive because of strategies that ensure species survive because of strategies that ensure adequate access to the resources and minimize adequate access to the resources and minimize competition for resources with other species. competition for resources with other species.

Summary of Community StructureSummary of Community Structure

As resources change and species interactions As resources change and species interactions change over time, those members of the species change over time, those members of the species best adapted to the new conditions are the best adapted to the new conditions are the individuals that live to reproduce and pass on individuals that live to reproduce and pass on their genetic information.their genetic information.

Thus, because of our ever changing world, over Thus, because of our ever changing world, over time there are changes in the gene pool of a time there are changes in the gene pool of a population (i.e., evolution). Evolution population (i.e., evolution). Evolution is notis not a a directed choice, it is the consequence of natural directed choice, it is the consequence of natural selection. In many cases natural selection leads selection. In many cases natural selection leads to the loss of an entire species (e.g., the dodo).to the loss of an entire species (e.g., the dodo).