Eco - Evolution and Ecology

trophy hunting and inadvertent evolution

• trophy hunting removes the largest and strongest males (the ones that would sire many healthy offspring

• the average size of males and their horns decreased over 30 years of study

• horn size in bighorn sheep is a heritable trait; trophy hunting selectively eliminates rams w/ large horn, thus favoring rams with genes for small horns

• trophy hunting is likely causing the genetic makeup of bighorn sheep populations to change, or evolve, over time

genes can have two or more forms called ____?

alleles

evolution

change in allele frequencies (proportions) in a population over time

• change in allele frequencies is a narrow (or strict) definition of evolution

natural selection

individuals with certain heritable traits survive and reproduce more successfully than other individuals

3 things that cause allele frequencies in a population to change over time

1. natural selection

2. genetic drift

3. gene flow

what do mutations result from

• copying errors during cell division

• mechanical damage

• exposure to chemicals (mutagens)

• high energy radiation

recombination

• produces different genotypes within a population

• rearranges the raw material into new combinations

directional selection

individuals at one phenotypic extreme (e.g., large size) are favored

• ex- in medium sized ground finches, drought favored large beak size for cracking hard seeds

stabilizing selection

individuals with an intermediate phenotype are favored

• ex- parasitic wasps prefer small gall size of Eurosta flies; while birds prefer large gall size; as a result, larvae in galls of intermediate size have an advantage

disruptive selection

individuals at both phenotypic extremes are favored

• ex- african seedcrackers (birds) have two food sources — hard seeds that require large beaks to crack, and smaller, softer seeds that smaller beaks are more suited to

fixation

the complete replacement of all alternative gene variants at a specific location in a DNA sequence, leaving every individual in a population with the exact same single variant

• gene frequency has hit 100% meaning genetic diversity for that specific trait is completely gone

genetic drift

occurs when chance events determine which alleles are passed to the next generation; significant only for small populations

do random events have a relatively larger impact on smaller or larger populations?

smaller populations

four effects that genetic drift has on small populations

1. it acts by chance alone - thus causing allele frequencies to fluctuate at random

2. because some alleles are lost, genetic variation of the population is reduced

3. frequency of harmful alleles can increase if the alleles have only mildly deleterious effects

4. difference between populations can increase - chance events may lead to allele fixation in one population and loss from another population

gene flow

alleles move between populations via movement of individuals or gametes

two effecs of gene flow

1. populations become more similar

2. new alleles can be introduced into a population

adaptaions

features of organisms that improve their ability to survive and reproduce

• include morphological and physiological features such as enzymes that function at high temperatures

acclimation vs adaptation

acclimation - a preconditioning to environmental conditions by prior experience of that individual; a trait that varies in response to the environment is plastic, such a trait demonstrates phenotypic plasticity

adaptation - noun; trait; a genetically determined characteristic that enhances the ability of an organism to cope with its environment

to adapt - verb; the process of becoming more fit; genetic change in a population that increases individual fitness to environmental conditions

type of change with acclimation and adaptation

acclimation = physiological change (within individual)

adaptation = genetic change (multiple generations)

adaptive evolution

• traits that confer advantages tend to increase in frequency over time

• caused by natural selection consistently favoring individuals with certain alleles

examples of apid adaptive evolution

• antibiotic resistance in bacteria

• insecticide resistance in insects

• drab coloration in guppies, making them harder for predators to see

• in Drosophila, change in frequency of the Adh^S allele in response to climate change

list three constraints on evolution

• lack of genetic variation

• evolutionary history

• ecological trade offs

evolution constraint - lack of genetic variation

if there is no beneficial allele, adaptive evolution at that gene cannot occur; advantageous alleles arise by chance, not “on demand”

• ex- initially, mosquito populations lacked alleles for pesticide resistance so the pesticides were effective

evolution constraint - evolutionary history

natural selection works on traits that already exist; organisms have certain characteristics and lack others because of their ancestry

• ex- dolphins evolved from terrestrial mammals; they have lungs and cannot “breathe” underwater

evolution constraint - ecological trade-offs

the ability to perform one function may reduce the ability to perform another function; adaptations represent compromises in the abilities of organisms to perform different and sometimes conflicting functions

what is adaptive evolution driven by

ecological interactions

when does speciation most commonly occur?

when a barrier (geographic or ecological) prevents gene flow between two or more populations of a species

the populations then diverge genetically over time

how goes gene flow affect speciation?

gene flow slows down or prevents speciation

how many mass extinction events does the fossil record document?

5 mass extinction events

adaptive radiation

• increased diversity of surviving groups after a mass extinction

• can also occur when a group evolves major new adaptations

what human made product is a strong source of directional selecion?

antibiotics - leads to evolution of antibiotic resistance in bacteria

reasons why Earth in undergoing a biodiversity crisis

• habit fragmentation

• pollution

• overharvesting

• introductions of invasive species