final Flashcards
basic principles of natural selection
- some of that variation is inherited
- populations generally remain fairly constant
- offspring that have inherited characteristics that best suit environmental conditions survive to reproduce
- the others die or at least contribute fewer individuals to the next generation
Natural Selection as a Process: Consequences
- Predictable within generation effect
- Predictable between generation effect
Natural Selection as a Process: given
- Variation in a trait or attribute
- A consistent relationship between the trait and survivorship or reproduction
- Inheritance of the trait (a consistent relationship between parents and their offspring)
Sexual Reproduction: Life Cycles
Three life cycle plans, with 1 common thread:
- Alternation of meiosis
- Net effect – new characteristics can appear (which may be advantageous)
Reproduction
- Variation is the “raw material” for natural selection
- Domestic animals: inbreeding leads to problems
Domestic Plant Crops
- Modern agriculture: prevention of the operation of natural selection
- Domestic crops – most would not survive in the wild; genetic diversity is very low
Reproduction affects
- Breeding system: cooperative polyandry
- Smaller islands: greater degree of inbreeding
- Parasite load is correlated with degree of inbreeding
- Innate immunity is lower in more inbred populations
Adaptation & Adaptedness
- A trait that increases the ability of an individual to survive or reproduce compared with individuals without the trait
- Any feature of an organism that substantially improves that organism’s ability to survive
A process of acquiring adaptedness
acquiring a collection of traits that together well suit an organism (or a population) for its environment
what is Adaptation?
- an evolutionary process – that changes traits (anatomy, physiology, or behaviour)
what does adaptation result in?
resulting in an increased ability of an organism
what does adaptation give?
- Some traits will give some individuals an advantage over others in the population
Acclimation
can refer to the changes in the form or behaviour of an organism during its life as a response to environmental stimuli
short-term acclimations eg
Acquisition of cold tolerance (resulting from prior exposure to lower temperatures)
Speciation
The process in which two or more contemporaneous species evolve from a single ancestor
Species
The fundamental taxonomic category for organisms; variously defined and diagnosed using different species concepts
Adaptive radiation
evolutionary divergence into a number of very different forms and lifestyles
what does Isolation result in ?
Many sub-populations, with local adaptations to local conditions
what can breeding and outbreeding do?
can lead to reduced fitness`
what happens if parents are too different?
hybrid offspring with intermediate characteristics are not favoured
Prezygotic mechanisms
blockages at different steps that prevent the formation of a zygote in the first place
- A combination of ecological and temporal separation
Ecological separation
failure to encounter because mating sites are different
Temporal separation
differences in the timing of fertile periods
Behavioural separation
Darwin’s finches recognize and respond to different songs, by-and-large preventing hybridization
Mechanical & physiological barriers
biochemical barriers to the formation of a pollen tube prevents fertilization
Post-zygotic mechanisms can act in these ways
- The zygote fails to develop properly and dies
- zygote lives but fails to reach maturity
- The zygote cannot produce viable gametes
- The zygote can produce gametes and/or offspring, but overall fertility is greatly reduced
Can two independent populations, which appear to be separate species, hybridize when they meet again?
it depends on
- time
- rate of genetic change
- degree of specialization
Mechanisms of Speciation (4)
Allopatric Speciation
Parapatric Speciation
Sympatric Speciation
Polyploidy
Allopatric Speciation
- The formation of new species that occurs when populations are geographically isolated
- Divergence of populations into separate species as a result of geographic isolation from one another
Allopatric Speciation: key points
- Geographic separation
- Spatial subdivision of populations
- Formation and colonization of new habitats
- Changes are driven by genetic drift and/or natural selection
Allopatric Speciation Via Vicariance
- Vicariance = splitting
- events that result in the geographic isolation of previously connected populations
TECO: TECTONIC, eustatic, climatic, or oceanographic
Isolation of a continental island by tectonic plate movements (Tectonic event)
TECO: tectonic, EUSTATIC, climatic, or oceanographic
Isolation of a continental island by rising sea levels (Eustatic event)
TECO: tectonic, eustatic, CIMATIC, or oceanographic
climatic events causing separation: flood, hurricane
TECO: tectonic, eustatic, climatic, or OCEANOGRAPHIC
Separation & isolation of ocean basins because of the drifting together of landmasses (Tectonic + Oceanographic
Peripatric Speciation
- Involves jump dispersal
- Involves very few individuals (or just 1 fruitfly)
- peripheral areas that were previously uninhabited
what 3 things are involved with Peripatric Speciation
the founder effect, selection, & genetic drift
The Founder Effect
- Small subset of individuals, not necessarily representative of whole original population
- New population has a quite different genetic makeup compared to original population
- New population is isolated from original population, and can evolve independently, based on selection pressures in new area
Founder Effect & Genetic Drift
- happen through random processes, chance events
- higher risk of loss of genetic diversity in small populations
the effects of genetic drift in small pop vs big pop
The effect of genetic drift is much larger in small populations than in large populations
Speciation: Founder Events
a sequence of temporally and spatially isolated founding events
outcome for founder events: Random dispersal of a few individuals to peripheral
- geographically isolated areas
- Each new population evolves independently
- meanwhile species a persists in original location
outcome for founder events: A few individuals colonize a nearby isolated area
A few individuals of species b colonize the next isolated area; these evolve into species
Parapatric Speciation
differentiation occurs when two populations have contiguous but narrowly overlapping ranges
- often representing two distinct habitat types
Parapatric Speciation: key points
- Range expansion into a new habitat
- Various subpopulations develop – and they become increasingly reproductively isolated
- Hybrids have reduced fitness
- Genetic drift and natural selection can both play roles
Sympatric Speciation
occurs within the area of distribution of the ancestral species
- differentiation of two reproductively isolated species from one initial population within the same local area
Sympatric Speciation: key points
- No geographic or spatial isolation
- Disruptive selection is most likely mechanism, coupled with assortative mating
Polyploidy
The doubling or multiplication of the whole set of chromosomes with the cells of an organism
why is Polyploidy important?
polyploidy has been an important mechanism for speciation
Ecological Divergence
that increased ecological divergence is associated with increased reproductive isolation
Ecotypes & Reproductive Isolation
Within-region same-ecotype compatibility was higher than between-regions same-ecotype compatibility
- indv of different ecotypes were not compatible
microevolution
Evolution (change) at the species level, within a single population
reasons for microevolution
Natural selection Sexual selection Mutation Migration Genetic drift Restrictions to gene flow
Macroevolution definition
Evolution (change) above the species level
Macroevolution key points
- Focuses on changes in morphological forms in the fossil record
- Often forms seem to have long periods of no change (stasis) interspersed with brief periods of rapid change (new species; punctuated equilibrium)
- Important patterns are stasis, evidence for character change, speciation, extinction
Microevolution: Outcomes
- A change in gene frequency
- Over time, changes in gene frequency can lead to changes in phenotypic expression
Macroevolution
Character change – can be quick, can be slow; can be directional – or not
Lineage-splitting & speciation
Extinction
Macroevolution: Punctuated-Gould, Eldredge
proposed that evolution can be punctuated – long periods of stasis followed by relatively rapid periods of considerable change
Macroevolution: Gradualistic- darwin
proposed that evolution takes place at a steady & gradual rate – this called gradualistic evolution
Punctuated reasons by Eldredge & G
- involves “bursts” of extinction & speciation, followed by stasis
- Species-level selection
Why Classify
to arrange in classes, to assign to a class
what is classification
a group of things having some characteristics in common
reason for classification
a human activity, based on recognition and description of characteristics deemed to be important, and used to organize and simplify complex information – into patterns that ‘make sense
Classification in Biogeography
- A system of identifying and naming entities, both extant and extinct, that mirrors their evolutionary relationships
- Recognition and naming of groups of organisms in specific environments
Linnaean System of Classification
- the system for naming, ranking and classifying organisms still used today
- original largely based on morphology
how does Linnaean System of Classification work?
- has a unique binomial, a generic name and a specific epithet
- Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
Classification & Phylogeny
- A hierarchical scheme
- capture degrees of relationship
Parallel Evolution
independent evolution of similar traits amongst non-related species in response to the SAME kinds of selection pressures, starting from a SIMILAR ancestral condition
Phylogenetic Systematics (cladistics)
to be quantitative, but also to include biological judgment on importance of particular traits
Key points in parallel evolution:
- Species in SIMILAR niches have surprisingly SIMILAR appearance
- Involves homologous structures
- Must consider: degree of “non-relatedness”
Convergent Evolution
Independent evolution of similar traits amongst non-related species in response to SIMILAR kinds of selection pressures, starting from a very DIFFERENT ancestral condition
Convergent Evolution:Key points
- the similar biological traits involve analogous structures
- non-relatedness is very clear
Island Types & Formation
Continental Islands•Island Arcs•Hotspot Islands•Terranes & Accretion
Continental Islands
Origin:Part of a continental landmass
Formation:Separated by rising ocean levels (e.g. Newfoundland),Separated by tectonic processes (e.g. Madagascar, New Zealand)
island arcs
origin: volcanic activity
formation: old ocean crust is subducted, causing stresses nearby on the overlying plate, volcanic eruptions build new islands that rise above the seafloor
Hotspot Islands & Seamounts
Origin: fixed “hotspots” scattered throughout the earths mantle (hawaii)
formation: volcanoes rise from the seafloor; plate moves creating islands
what does erosion do in Hotspot Islands & Seamounts
reduces islands to seamounts (guyots)
Formation of an Island Chain
- Erosion flattens the tops of the islands & seamounts
- Seamounts are “islands” of incredible biodiversity
- Seamounts are poorly known – and are being destroyed rapidly by deep-sea trawling
pacific islands
All three types of islands:
- Continental
- Island arc
- Hotspot Islands
Terranes
- terrane: a small area where geology is different from surrounding regions
Accretion
a landmass that originated as an island arc or a microcontinent that was later added onto a continent or other landmass
The Nature of Islands
- Well-defined boundaries
- Often relatively isolated
Study of Islands: Ecological Scale
- biotic and abiotic challenges and interactions
- Island “impoverishment” & species-area relationships
Study of Islands: Evolutionary Scale
- Islands and speciation
- The Equilibrium Theory of Island Biogeography (ETIB)
Island Biotas: Unique Properties
-community composition \+Ecological roles \+Niche breadth & differentiation \+Population densities -body size -growth form
Disharmonic Island Communities
If non-random processes – you would expect islands to differ from the mainland, and also from each other
Island Biota: Which Species?
Harmonic, or balanced – species composition similar to mainland composition•Disharmonic, or unbalanced – species composition is differentthan mainland composition
Harmonic biotas
species are ‘assembled’ randomly from mainland source pools
Disharmonic biotas
done so by non-random processes
Typical non-random processes
differential ability amongst taxa to migrate & colonize, or to persist once established
Differential Dispersal Abilities
- Active dispersal
- Passive dispersal
- Active dispersers
- Passive dispersers
Active dispersal
light, ability to cope with seawater
Passive dispersal
high altitude winds, high velocity winds, ocean currents, “hitch hiking” on
Active dispersers
bats, birds, insects
Passive dispersers
via spores (microbiota, fungi, ferns), via fruits and seeds (flowering plants), via egg masses (insects, some vertebrates)
Island Biota: Ecological Roles
Many island species are generalists rather than specialists
Species–Area Relationship for islands
- isolation
- that the number of species supported is less than the number in a comparable area of mainland – most islands suffer some degree of species impoverishment
reasons for Island Biota: Ecological Roles
- Role of resource limitations compared to mainland areas – “food” resources have lower standing stocks and renewal rates
- Organisms that have lower demands and are less “fussy” have a greater probability of establishing a persisting population
Advantages of Being a Small-Bodied Generalist
- Small animals need less
- Generalists use many different sources
- Small animals can maintain higher maximum population densities
Island Biota: Higher Densities
- Niche breadth & density both increase
- Similar trends seen for many birds on small islands
Density “overcompensation” on small islands is common
- Large vertebrates, top predators – tend to be absent
- Absence of congeners; absence of other members of the feeding guild; net result, reduced competition
- Absence of other predators and/or parasites
Body Size: the “Island Rule”
- A graded trend, within and among taxonomic groups
- The tendency for small animals to become bigger, and for big animals to become smaller
Island Biota: Body Size
Dwarfism:
‘Normally’ big animals became smaller
Gigantism:
‘Normally’ small animals became bigger; a trend very often seen for herbivores & seed eaters – e.g., rodents, iguanas, tortoises
ecological release
- Few or no predators, therefore little or no selective pressure for large size for protection
- More intense intraspecific competition for limited resources
immigration selection
- Biased initial breeding stock
- In absence of predators herbivores can feed more often & more rapidly
how might Isolation effect species richness?
- – as distance increases, non-volant mammal species richness decreases for islands
Temporal isolation
in the Gulf of California, so-called land-bridge islands that have been isolated for longer periods have fewer species
The ETIB: Background
Islands are recipients of species from a source pool of species living on a mainland area
The number of species received by an island depends on
- Island size (area)
- Island distance from mainland (isolation)
- The source pool of species & their characteristics
Why might distance matter?
- Takes more time & energy to reach a far island
- More likely to die before reach a far island
- Fewer individuals actually make it to the island
distance conclusion
islands that are far away have lower rates of immigration than islands that are closer to source pools of species
Why might area (size) matter?
- Greater variety of topography
- Greater variety of possible habitats
- Perhaps higher resource levels (larger islands “collect” more energy)
- Potentially larger populations
area conclusion
larger islands would have lower rates of extinction, smaller islands would have higher rates of extinction
MacArthur and Wilson 1967: main parameters
distance (isolation) affects the rate of immigration, size (area) affects the rate of extinction
MacArthur and Wilson 1967: Mechanism
balance between rates of immigration and rates of extinction, and development of “most probable curves”
Predictions at Equilibrium: Species #
at equilibrium, drop a perpendicular from crossing-points of “rates” to X-axis, Ŝ (S-hat)
Predictions at Equilibrium: Turn-over Rate
at equilibrium, draw a horizontal line from crossing-points of “rates” to Y-axis, T (T-hat)
Effect of Distance (Isolation): Two equal-sized islands
that differ in distance from the source pool have the same extinction rates, but different immigration
Effect of Island Area: Two different-sized islands
experience the same rate of immigration (colonization) (identical curves for I), but extinction rates are greater on the small island
ETIB: Assumptions
- New species immigrate and old species die out at random
- Immigration and extinction are independent processes; one does not influence the other
- The source of colonists is the mainland
ETIB: Overall Predictions 1.
The number of species on an island stabilizes at a constant value (an equilibrium)
ETIB: Overall Predictions 2.
The stabilized value is dynamic, because there is a continual turnover of species, due to immigrations and extinctions
ETIB: Overall Predictions 3.
If degree of isolation is the same, large islands will support more species than small islands, but small islands will return to equilibrium more quickly
ETIB: Overall Predictions 4.
If island size (area) is the same, the number of resident species will be higher on the nearby island, and the nearby island will return to equilibrium more quickly
What the ETIB Does Not Do
- identity
- timing of those changes
- relative species abundances
- speciation in the past, present or future
MacArthur on the ETIB
a theory is a lie which makes you see the truth
Effects of Scale: Size & Time
- sigmoidal, based on different scales of investigation
Very large islands
where in situ speciation becomes important (evolutionary forces become more important)
Very small islands
may be different (no species-area effect)
Intermediate islands
– the familiar species-area relationship (largely ecologically determined)
Modifying the ETIB
Non-interactive (1)
Interactive (2)
Assortative (3)
Evolutionary (4
Incidence & Assembly Rules
- Jared Diamond proposed communities & ecosystems are not randomly constructed
- Only some species combinations occur out of all possible combinations
what was Incidence & Assembly Rules theory based on
studies of bird communities of island archipelagos
Diamond’s Incidence Rules: A sedentary species
occurs only on species-rich islands (example, a cuckoo, Centropus violaceus)
Diamond’s Incidence Rules: An intermediate tramp species
occurs on a wider variety of islands, but still not on the species poor-islands
Diamond’s Incidence Rules: A supertramp species
is absent from species-rich islands; such a species occurs only on small, species-poor islands
Diamond’s Assembly Rules
- Some pairs of species are never found together
- Restriction on ‘allowed’species pairs – due to competition
main ETIB idea (species sorting hypothesis)
that compatible species, each with its distinctive and individual niche, become sorted over the course of time to assemble themselves into a stable equilibrium community
new theory should include
- evolution (speciation)
- immigration filters, geology, climate
- species-based (eg. dispersal)
- place-based eg. changes of the island
General Dynamic Model Approach-Whittaker & colleagues (2008)
for oceanic islands:
- geological life history
- biological life history
- Consequences for rates of immigration, colonization (carrying capacity), speciation, extinction
- The concept of Single-Island Endemics (SIEs)
geological “life history” of islands
role of erosion, subsidence, land slips
Early history
area & altitude increase to a maximum then decrease
Mid history
topographic complexity increases to some maximum value
Late history
area, altitude & topography all decrease
The biological “life history” of islands
- Habitat diversity – more opportunities, more niches
- Greater species diversity (dotted line, via immigration, via speciation)
In late biological stages
- Biotic interactions increase
- Opportunities decrease
- Effect of isolation decreases
overall General Dynamic Model
- With time, new species evolve
- With time, more of the biota of islands will consist of single-island endemics (SIEs)
- The number of SIEs should change in a predictable way over the life-time of an island
General Dynamic Model: letter chart
- K … carrying capacity
- I … immigration rate
- S … speciation rate
- R … realized species richness
- E … extinction rate
