What is microevolution?
evolution at the population level
occurs mainly through selection (which results in adaptation) or drift
What is macroevolution?
evolutionary change above species level
origin of complex novel characteristics
appearance of higher taxa
mass extinctions
speciation
What is the biological species concept?
consists of a group of actually or potentially interbreeding individuals that are reproductively isolated from other such groups
What are four problems with the biological species concept?
- Only applies to sexually reproducing species (what about asexual species?)
- Suggests that two different species would never mate and produce offspring (what about successful hybrids?)
- Ecological species concept: species is a set of organisms adapted to a particular set of resources, called a niche, in the environment (at extremes of distributions “species” differs)
- Phylogenetic species concept: evolutionary history (some populations are more unique than rest)
What is reproductive isolation?
isolating mechanisms are required to maintain reproductive isolation between populations
pre-reproductive isolating mechanisms: prevent two individuals from forming a zygote, prezygotic
post-reproductive isolating mechanisms: occur after zygote has formed, postzyogotic
What are prezygotic isolation mechanisms?
ecological (habitat) selection: tree canopy vs grass
temporal isolation: different time of day/season
behavioral isolation: courtship patterns, pheromones
mechanical isolation: anatomically incompatible
gametic isolation: sperm and egg cannot fuse
What are postzygotic mechanisms?
zygote death
hybrid infertility: offspring of cannot reproduce
hybrid unviability: lower fitness, survival and/or reproduction
What is speciation?
the formation of new and distinct species in the course of evolution
the process by which one genetically-cohesive population splits into two or more reproductively-isolated populations
What is cladogensis?
the branching or splitting of a lineage (like a node on a cladogram)
What is anagenesis?
evolutionary change within a lineage, resulting in differences between sister lineages
What is allopatric speciation?
the first step toward reproductive isolation happens when a single population becomes subdivided by a geographical barrier(s)
examples: mountains, water, natural disasters, habitat fragmentation
What is sympatric speciation?
subgroups can form within a continuous habitat
if individuals in the subgroup stop mating with individuals of the larger population, they may eventually become a new species
How do species become reproductively isolated?
- A single population becomes subdivided (geographically, physically, or within a habitat)
- More likely to mate with individuals of their subgroup, gene flow is greatly reduced
- Meanwhile, microevolution (by natural selection, genetic drift, mutation, non-random mating) is independently working on the subgroups
- The separated groups eventually evolve and adapt to their local environment, becoming different in form, physiology, or behavior, so that mating no longer occurs between them
- Speciation event has occured
What are hybrids?
individual formed by mating between unlikely forms, usually genetically differentiated populations or species
if hybrid individuals are less viable or less reproductively successful than non-hybrid individuals, the two species are considered to be good (distinct) species
What is introgression?
incorporation of genes from other species into gene pool
What is a reinforcement change in hybrid zones over time?
hybrids are less fit than either purebred species, the species continue to diverge until hybridization can no longer occur
What is a fusion change in hybrid zones over time?
reproductive barriers weaken until the species become one
What is a stability change in hybrid zones over time?
fit hybrids continue to be produced
What is gradualism?
slow differentiation by natural selection over many generations
What is punctuated equilibrium?
speciation happens rapidly followed by relatively long periods of stasis (no change)
