Bio 101 Exam 4

Evolution

 a unifying concept in biology, from the origin and diversification of life to understanding disease and behavior; change in allele frequencies in a population over time

looks at:

• changes in trait distributions

• why some individuals survive more than others

• how populations adapt (or don’t)

Ecology

takes biology from the level of cells and individuals to explain the complexity of interactions between organisms and their environments.

looks at:

• change in abundance (population)

• interactions b/w species

Ecosystem

a dynamic community of living organisms (biotic component) interacting with their non-living physical environment (abiotic component)

Uniformitarianism

change occurs through continuous, gradual processes over long periods of time

• small processes that accumulate

  • erosion, sedimentation, slow climate shifts, etc.

• long timescales

Catastrophism

change occurs through sudden, dramatic events that rapidly alter systems.

• large, intense events with immediate effect

  • volcanic eruptions, earthquakes, floods, glacial events, etc.

• short timescales

Trait

any measurable or observable characteristic of an organism.

• body size, coloration, growth rate, timing of reproduction, behavior, etc.

Fecundity

the number of offspring an individual can produce

Speciation

the evolutionary process by which populations evolve to become a distinct species

- can happen when gene flow is reduced/stopped

Biological Species concept

a group of individuals that have the potential to interbreed and produce fertile offspring

limitations: fossils, asexual reproduction, self-fertilization)

Gene flow

movement of genes between populations via migration

- followed by reproduction

- keeps populations genetically similar (when a yellow butterfly migrates towards an orange butterfly space, they then reproduce with orange butterflies, and both species become more similar).

- must be disrupted by reproductive barriers for speciation to occur

Prezygotic reproductive barriers (no mating attempted)

Temporal Isolation - they breed during different times of the year

Habitat Isolation - live in different habitats, so they never meet or breed

Behavioral Isolation - unique behaviors, i.e., mating calls

Prezygotic reproductive barriers (mating attempted)

Mechanical Isolation: morphological features prevent successful mating

Gametic isolation: gametes do not unite

Post-zygotic barriers

Hybrid inviability: hybrid development impaired

Hybrid sterility: hybrid cannot reproduce (mules)

Hybrid breakdown: 1st gen hybrids fertile + 2nd gen feeble/sterile

Allopatric speciation

occurs when populations are geographically separated; gene flow is interrupted by physical barriers

i.e., islands, glacial separation, habitat fragmentation

Sympatric speciation

occurs without geographic separation; due to behavioral differences, ecological specialization, and genetic changes (e.g., polyploidy).

Polyploidy

gametes with extra chromosomes due to an error in cell division

• change in # of chromosomes → new species

Natural Selection

a process where individuals with certain traits survive and reproduce more successfully than others.

Fitness

an organism’s relative ability to survive and reproduce

• high fitness → more offspring

• low fitness → fewer offspring

Genetic Variation

difference in genes among individuals in a population

• required for evolution

• w/o it → no differences in survival or reproduction

Genetic drift

chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next

- Founder effect: individuals isolated from the main population

- Bottleneck effect: population goes through a period in which its size decreases

• important in small populations

• can reduce/eliminate alleles (reduce genetic variation)

• may cause alleles to become fixed

Gene flow

genetic exchange due to the migration of fertile individuals or gametes between populations

• reduces genetic differences between populations

• increases genetic diversity within a population

• can increase/decrease the fitness of populations

Directional selection

favors individuals at one extreme of a phenotypic distribution

• population mean shifts in one direction

• one trait value is consistently favored

Stabilizing selection

favors individuals with intermediate phenotypes

• extremes selected against; good to be average. (high fitness)

• variation decreases

• population becomes more average

Disruptive selection

favors individuals with extreme phenotypes

• low / high = good; middle/average = bad

• population splits into two groups

• can lead to divergence

Balancing selection

• Frequency-dependent selection: the fitness of a phenotype depends on how common it is in the population

  • common = bad

  • maintains genetic diversity in population

• Heterozygote advantage: natural selection does not always cause the elimination of “weak” or less fit alleles

  • carrying the recessive gene for sickle cell can protect you from malaria.

Sexual selection

acts on traits that affect reproductive success

• mate choice (intersexual selection): one sex prefers certain traits

• competition (intrasexual selection)

• traits that increase mating success become more common

  • they may become exaggerated

Artificial selection

humans intentionally choose which individuals reproduce, favoring certain traits.

• traits that were beneficial where organisms were bred may not be ideal for the wild.

Macroevolution

major evolutionary changes over a longer period of time

• speciation, extinction, large-scale diversification

• occurs through extended microevolution over long time scales

Adaptive radiation

rapid diversification of a single ancestral species into multiple species adapted to different environments

• occurs when new habitats are available

• often follows environmental change

Gradualism

evolution occurs slowly and continuously over long periods of time

Punctuated equilibrium

evolution occurs in rapid bursts, separated by long periods of little change

Homologous structures

anatomical features in different species that share a common evolutionary ancestor

• used to reconstruct evolutionary relationships

• they are evidence of shared evolutionary history

Analogous structures

biological features in different species that share a similar function but evolved independently (not from a common ancestor)

Vestigial structures

reduced or non-functional features inherited from ancestors

• evidence of past environments and evolutionary history

Exponential growth

when resources are abundant and conditions are ideal

• population grows faster as it gets larger

Logistic Growth

growth of a population slows over time

• resources become limited

• competition increases

Carrying Capacity (K)

the maximum population size an environment can support