Unit 1:part 2 (lesson 5+) Flashcards
speciation
the process by which one species splits into two or more species
- responsible for the diversity of life
- explains differences and similarities between species
microevolution
changes over time in allele frequencies in a population
macroevolution
broad pattern of evolution above the species level
biological species concept
says that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring-but do not produce such offspring with other species
reproductive isolation
the existence of biological factors that impede members of two species from interbreeding and producing viable, fertile offspring
- block gene flow between species
- limit hybrids
- types: prezygotic and postzygotic
hybrids
offspring that results from the mating of two individuals from different species
prezygotic barriers
block fertilization from occurring
types: habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation
postzygotic barriers
prevent a hybrid zygote from developing into viable, fertile adult
types: reduced hybrid viability, reduced hybrid fertility, hybrid breakdown
habitat isolation
- prezygotic barrier
- two species that occupy different habitats in the same area may encounter each other rarely
temporal isolation
- prezygotic barrier
- species breed at different times of day, different seasons, or different years
behavioral isolation
- prezygotic barrier
- courtship rituals that attract mates and other behaviors unique to a species may cause isolation
mechanical isolation
- prezygotic barrier
- mating is attempted but morphological differences prevent its successful completion
gametic isolation
- prezygotic barrier
- sperm of one species may not be able to fertilize the eggs of another species
reduced hybrid viability
- postzygotic barrier
- genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment.
reduced hybrid fertility
- postzygotic barrier
- hybrids are sterile
hybrid breakdown
-postzygotic barrier
some first generation hybrids are viable and fertile but their offspring are feeble and sterile.
limitations of the biological species concept
- can be applied only to a limited number of species
- does not apply to organisms that reproduce asexually - cannot evaluate fossils
- some species are morphologically and ecologically distinct but have gene flow
morphological species concept
characterizes a species by body shape and structural features
-distinguishes most species but can be subjective
ecological species concept
views species in terms of its ecological niche; the sum of how members interact with nonliving and living parts of their environment
phylogenetic species concept
defines a species as the smallest groups of individuals that share a common ancestor, forming one branch of the tree of life
-compares separate species
allopatric (other country) speciation
gene flow is interrupted when a population is divided into geographically isolated sub- populations
-once separation has occurred, different mutations arise and natural selection and genetic drift may alter allele frequencies
Evidence for allopatric speciation
- regions that are isolated or heavily subdivided typically have more species
- reproductive isolation between two populations generally increases as the distance between them increases
Sympatric (Same Country) Speciation
- speciation that occurs in populations that live in the same geographic area
- can result from polyploidy, habitat differentiation, or sexual selection
polyploidy
an accident during cell division that results in an extra set of chromosomes;
may allow a new species to originate
-most common in plants
-can result from non-disjunction
autopolyploid
an individual that has more than two chromosomes sets that are all derived from a single species
allopolyploid
has 2 or more chromosome sets as a result of 2 different species interbreeding
-can mate with each other but not parent species
habitat differentiation
genetic factors enable a sub-population to exploit a habitat or resource not used by the parent population
non-disjunction
when homologous chromosomes do not separate during meiosis, sex cell will contain too few or too many chromosomes
hybrid zone
a region in which members of different species meet and mate, producing at least some offspring of mixed ancestry
-form when 2 species lacking complete barriers to reproduction come into contact
reinforcement
strengthening of reproductive barriers
-can occur when hybrids are less fit than parent species
fusion
weakening reproductive barriers
-much gene flow occurs between two species, gene pools become increasingly alike and eventually fuse into a single species
Stability
continued formation of hybrid individuals
- sometimes hybrids are fitter
- sometimes hybrids are at disadvantage but a small hybrid zone with migration might occur
punctuated equilibria
In the fossil record, long periods of apparent stasis in which species undergo little or no morphological change interrupted by relatively brief periods of rapid speciation
Speciation Rates
- experiments and observations suggests that once the process of speciation begins, it can be completed rapidly
- on average, millions of years may pass before a newly formed species will give rise to another species
plate tectonics
continents are part of great plates on Earth’s crusts that essentially float on the mantle
-plates move over time
Consequences of Continental Drift
- alters habitats in which organisms live
- causes climate changes as continents shift location: organisms adapt, move, or become extinct
- promotes allopatric speciation (continents break apart)
- helps explain geographic distribution of extinct organisms.
Pangaea
supercontinent formed about 250 million years ago
- destroyed shallow water habitats, interior cold and dry
- caused extinction, new opportunities for surviving species
Mass Extinction
time in which large numbers of species became extinct
Permian Mass Extinction
- between paleozoic and mesozoic eras
- claimed 96% of marine species and many insect species
- enormous volcanic eruptions in Serbia 251 million years ago
- warmed atmosphere, oxygen levels dropped
Cretaceous mass extinction
- between Mesozoic and Cenozoic eras
- about 65.5. million years ago
- 50% of marine species and many terrestrial plants and animals extinguished
- hypothesized to have been caused by an asteroid striking the earth
Consequences of Mass Extinctions-
- reduces diversity of life
- changes types of organisms found in ecological communities
- can end lineages with highly advantageous features
- paves way for adaptive radiations
Adaptive Radiations
periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities
- often occur after mass extinctions
- organisms increase in diversity as they play new roles in the environment
- organisms that arise can serve as new food source
taxonomy
the scientific discipline of naming and classifying organisms
binomial nomenclature
names organisms using two part name
-genus name+ specific epithet
Hierarchical Classification
Domain Kingdom Phyla Class Order Family Genus Species
phylogenetic tree
a branching diagram that represents a hypothesis about the evolutionary history of a group of organisms
- Intended to show pattern of descent, not phenotypic similarity
- Sequence of branching in a tree does not necessarily indicate the actual age of a species
- Do not assume that a taxon evolved from a taxon next to it
PhyloCode
a system of classification that only names groups that include a common ancestor and all of its descendents
rooted
describes a phylogenetic tree that has a branch point that represents the most recent common ancestor of all taxa
polytomy
a branch point from which more than 2 descendent groups emerge
-signifies evolutionary relationships among taxa not yet clear
homoplasies
analogous structures that arose independently
molecular systematics
the discipline that uses data from DNA and other molecules to determine evolutionary relationships
cladistics
an approach to systematics that uses common ancestry as the primary criterion to classify organisms
clades
groups that include an ancestral species and all of its descendents
monophyletic
a group that consists of an ancestral species and all of its descendants
paraphyletic
consists of ancestral species and some of its descendents
polyphyletic
includes new taxa with different ancestors
shared ancestral characters
a character that originated in an ancestor of the taxon
shared derived characters
an evolutionary novelty unique to a clade
outgroup
a species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes the group we are studying
maximum parsimony
the principle that systematists should first investigate the simplest explanation that is consistent with all of the facts
- requires fewest evolutionary events, or fewest DNA base changes
maximum likelihood
given certain probability rules about how DNA sequences change over time, a tree can be found that reflects the most likely sequence of evolutionary events
