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Evolution 2 Summary (B-B2EVO09)
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All material taught during the Evolution 2 course.
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Evolutie 2Chapter 18 The Geography of Evolution
Endemic species are species restricted to a particular geographic region. Cosmopolitan
species can be found worldwide.
Wallace’s line separates species by taxonomic composition into two groups, a group with
Asian families and genera and a group with Australian affinites.
- Wallace also designated several biogeographic realms, major regions that have
characteristic animal and plant taxa
- Palearctic, Nearctic, Neotropical, Ethiopian, Oriental and Australian
Some taxa have disjunct distributions, which means their geographical distributions have
gaps.
Three historical processes have impacted the current distribution of taxa:
1. Extinction: can reduce distributional ranges
2. Dispersal: movement of individuals can lead to expansion of distributions
3. Vicariance: the separation of populations of a widespread species by barriers arising
from changes in geology, climate, or habitat
There are several geographic range limiting factors:
1. Dispersal limitations: problems with obtaining mates or crossing barriers
2. Ecological niches
a. Fundamental ecological niche: the set of all those environmental conditions
in which a species can have positive population growth
b. Competitive exclusion principle: species that are too similar in their use of
food or other limiting resources cannot coexist indefinitely
i. Phylogenetic niche conservatism: similar ecological requirements
that they have inherited from their common ancestor
ii. Niche availability changes potential ranges
Phylogeography: principles and processes governing geographic distributions of
genealogical lineages, within and among closely related species, providing insight into past
movement and current distribution
Latitudinal diversity gradient: the number of species decline with increasing latitude, both
on land and in the ocean. Most taxa of terrestrial animals and plants are far more diverse in
tropical regions than in extra-tropical regions. There are three hypotheses about this
phenomenon:
1. Tropical locations can support a higher equilibrium number of species
2. The diversification rate might be higher in the tropics
3. Lineages diversify at the same rate, but started to diversify more recently in the
temperate zone than in the tropics
, Chapter 19 The Evolution of Biological Diversity
The rate of change in the number of species per unit of time is:
- dN/dt = (S-E)N = DN
- N = number of taxa
- dt = time period in which one species gives rise to another species
- S = speciation rate
- E = extinction rate
- D = net diversification rate (D = S - E)
- The number of species will on average increase if S is greater than E,
so if D > 1
Problems with estimating biodiversity:
1. Rare species more likely in large samples
2. Imprecise estimate of duration because of use geological stages
3. Fossil is minimum (origination) and maximum (extinction) age
4. Count of living species is more complete (pull of the recent)
5. Singletons
Diversity dependent factors are factors such as competition for food or space that become
more intense as the diversity of competing taxa increases.The diversity may then attain an
equilibrium at K species.
Pull of the Recent: the more recently a taxon arose, the more likely it is to still be extant,
diversity will seem to increase as we approach the present, even if it didn’t actually increase.
Background extinction: some lineages become extinct during every geological time
Mass extinction: dramatic crash in diversity
Why are extinction and origination rates correlated?
- Ecologically specialized species of mammals and other groups show higher
extinction rates than generalized species, because they are more vulnerable to
changes in their environment
- Species with a broad geographic ranges tend to have a lower rate of extinction
because they are not extinguished by local environment changes
Red Queen hypothesis: species have to evolve as fast as possible to survive, because its
competitors, predators and parasites also continue to evolve.
The tiers of evolutionary change:
1. Microevolutionary change within populations and species
2. Differential proliferation and extinction of species
3. Shaping of the biota by mass extinctions
Ecological opportunity: many open ecological niches
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