Ecology Test # 1

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What are hypotheses?

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Hypotheses are possible causes

Hypotheses reflect past experiences

Hypotheses can be eliminated but never confirmed with absolute certainty

Hypotheses that have been tested and tested can become "theories"-- having a very high degree of certainty

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Ecology

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the scientific study of the interactions between organisms and their environment

the scientific study of how organisms interact with one another and with their physical and chemical environment

"environment" is a very broad concept that really is about everything that has some impact on an organism--both abiotic and biotic factors

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The study of ecology is usually at 4 levels

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1.) Population level- population is all of the organisms of the same species in a specified area

2.) Community level- community is made up of multiple populations in a specified area

3.) Ecosystem level- ecosystem is made up of the biotic and abiotic components of an area- the study of ecosystems is about how both interact

4.) Landscape to Biome to Biosphere level

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Ecology & Evolutionary Biology

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Events that occur in the framework of "ecological time" (minutes-year) translate into effects over the longer scale of evolutionary time (decades- millenia)

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"Finch Logic"

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If factors in the environment continue to "select" the most adaptive version of a trait, then the population will become one of mostly strong-billed birds.

The population is changing over generations and now shown by long term research on the finches.

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Artificial Selection

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A process selected traits based upon the desires of their breeder, leading to an increase in the frequency of one form of a trait in a captive population

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Natural Selection

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Darwin's idea of what occured in the finches in the Galapagos Islands

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Origin of Species (1859)

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Darwinism makes two assertions:

The idea that (1) diversity of life the product of evolution was accepted almost almost at once by most naturalists

But, Darwin's idea of (2) gradual evolution by natural selection was fiercely debated

It wasn't until the 1930s, when genetics clearly explained the process (now called "The New Synthesis"), that the biological community accepted evolution by natural selection

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Darwin's Observations

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Observation #1: All species have great potential fertility that their populations would increase exponentially if all survived.

Observation # 2: Populations tend to remain stable in size, except for seasonal fluctuations

Observation # 3: Environmental resources are limited

(Inference #1: Production of more individuals than the environment can support leads to struggle for existence, with only a fraction of offspring surviving each generation.)

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Darwin's Observations Continued

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Observation #4: Individuals of population vary extensively in their characteristics- no two individuals are exactly alike!

Observation #5: Much of this this variation is heritable.

(Inference #2: Survival is not random, but depends upon the hereditary constitution of the surviving individuals who likely leave leave more offspring.

Inference #3: This unequal ability to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations.)

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Darwin's Main Ideas

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Natural selection is differential success in reproduction

Natural selection occurs through an interaction between the environment and the variability among individuals that make up a population

The product of a natural selection is the adaptation of populations of organisms to their environment

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Evidence of Evolution

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Fossils

Evolution of insecticide-resistant insects

Evolution of antibiotic resistant bacteria

Homologous structures

Vestigial organs

Embryological homologies

Molecular simulates

Bio-geography

Convergent Evolution

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Evolution: "The New Synthesis"

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"Genetic change in a line of decent over generations of time"

"The chage in allele frequency in a population over time"

These definitions are from the level of where the action is - genes!

At some point, these changes do manifest themselves as morphological changes

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Microevolution

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Change at the species or sub-species level

it involves "population genetics"

Population- group of individuals of the same species occupying a given area

We know that individuals don't evolve (why?)- only populations can

Populations have characteristics (physiological, morphological, behavioral, genetic) that are quantifiable and generally heritable

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Characteristics of a Species

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A species is "a group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature"

Each species is distributed over a certain geographic range, but are concentrated in localized populations

A population may be isolated from other populations only rarely exchanging genetic material

A population has a characteristic "pool of genes" made up of the entire set of alleles in the populations

Each individual of a population has specific number of genes for the species but, the alleles could be different

If all members of populations are homozygous for the same allele- the allele is "fixed" in the gene pool

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Gene Pools

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Often, there are two or more alleles for each gene, each having a "frequency" in the pool

We can calculate the frequency of the possible allele types

If the sexual process maintains the same allele frequencies the gene pool is said to be in equilibrium- Hardy-Weinberg equilibrium- a non-evolving population

This idea by Hardy and Weinberg describes how the genetic system has no tendency to alter gene frequency

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Hardy-Weinberg Theorem

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Theorem States: Allele frequencies will stay the same through successive generations if (all of these conditions are met)

1.) T here is no mutation
2.) Have a very large population (no genetic drift)
3.) Population is isolated (no gene flow)
4.) Random mating ocurs
5.) All individuals survive and reproduce equally (no natural selection)

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Hardy Weingberg Theorem Cont'd

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Rarely, if ever, do all five conditions occur in a population in nature

Gene mutation is infrequent, but inevitable

Natural selection, gene flow, and genetic drift may drive the population away from genetic equilibrium, even in a few generations. And finally, mating is never random.

Be aware that the loci (gene points) on a chromosome may be at equilibrium while allele frequencies at other loci are changing

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Microevolution

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It is "small scale" changes in allele frequencies, as brought about by mutation, natural selection, gene flow, genetic drift and non-random mating

The two greatest causes of microevoloution are genetic drift and natural selection

Natural selection is the only cause of microevolution that generally adapts a population to its environment

The other 3 agents of microevolution (GD, GF, M) can affect populations in positive, negative, or neutral ways

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Genetic Drift

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A random change in allele frequencies over generations

Genetic drifts impact on the gene pool depends upon population size. The effect will be much quicker in small populations

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Natural Selection

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Natural selection is differential (reproductive) success in a population- that is, some individuals leave more offspring than others

Selection results in alleles being passed along to the next generation in numbers disproportionate to their relative frequencies

Natural selection accumulates and maintain favorable genotypes in a population. It and genetic drift cause most of the changes in allele frequencies that are observed in evolving populations

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Gene Flow

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But allele frequencies can also change by migration between populations (or by mutations)- called "gene flow"

When individuals of the same species move about over time, they can move their alleles between populations

Emigration and immigration cause loss or gain, respectively of alleles

"Gene flow" does counter genetic differences that arise by mutation, natural selection, ad genetic drift

Homogenizes population differences

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Mutation

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Mutation is defined as a chemical change in the gene-one kind is called a "point mutation" = AAT to AA

Each gene has "mutation rate"= probability of changing between DNA replications.In a single generation, about one sex cell in 100,000 to 1,000,000. has a new mutation at any given gene

A mutation that has severe effects on phenotype will result in death- lethal mutation

Neutral mutation don't have any discernible effects on chance of immediate survival (earlobe attachment)

Beneficial mutations and neutral ones have been accumulating in lineages for billions of years

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Modes of Selection

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1.) Directional Selection- allele frequencies that underlies some rage of variation in phenotypes shift in a consistent direction

2. Stabilizing Selection- intermediate forms of a trait are favored and alleles that specify extreme forms are eliminated from a population. It tends to counteract the effects of mutation, gene flow, and drift and to preserve the common genotypes.