1 1 . Patterns of speciation and extinction - Description
The rise and fall of biodiversity. Four major mass extinctions of marine organisms:. End of Silurian Devonian, Permian, and Cretaceous). Rise in diversity during Cambrian, Silurian, Cretaceous, and Paleogene. ID: 547951 Download Presentation
The rise and fall of biodiversity. Four major mass extinctions of marine organisms:. End of Silurian Devonian, Permian, and Cretaceous). Rise in diversity during Cambrian, Silurian, Cretaceous, and Paleogene.
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11. Patterns of speciation and extinction
The rise and fall of biodiversity
Four major mass extinctions of marine organisms:
End of Silurian Devonian, Permian, and Cretaceous)Rise in diversity during Cambrian, Silurian, Cretaceous, and Paleogene
The rise and fall of biodiversity
Eliminating all groups known only from a single stage (5-6 mya):
Rise in diversity during
, and Ordovicium and in the Paleogene
Decline of longer lasting taxa from Ordovicium to Triassic
What is a species in the evolutionary context?
The biological species concept states that species are actually or potentially interbreeding natural populations that are genetically isolated from othersThe evolutionary species concept states that species are ancestor – descendent lineages of organisms that have their own evolutionary fate. The phylogenetic species concept states that a species is the smallest monophyletic group of organisms of common ancestry (a lineage from one node to another).The genetic species concept states that a species is a genetically sufficiently distinct group of organisms as identified by a genetic fingerprint.The ecological species concept states that a species is a group of organisms (population) that are ecologically distinct from other groups. The heuristic species concept states that a species is a group of organisms that are practically clustered together for the aims of a certain study.
8. Vegetarian tree finch (Platyspiza crassirostris)
9. Medium tree finch (Camarhynchus pauper)
10. Large tree finch (Camarhynchus psittacula)
11. Small tree finch (Camarhynchus parvulus)
12. Warbler finch (Certhidia olivacea)
13. Mangrove finch (Cactospiza heliobates
Speciation is the divergence of genetic structure between subpopulations until new separate populations emerge.
Any mechanism that promotes the emergence of sublineages is therefore a potential speciation mechanism
Premating examples are:spatial isolationbehavioural isolationtemporal isolation (separated generations)host switch in parasites and herbivoresselective habitat choice
Divergence can be triggered by premating and postmating mechanisms:Premating mechanisms are those that keep populations isolated before mating occurs.Postmating mechanisms prevent hybrids to develop or breed.
Postmating examples are:genetic incompatibilitymorphological incompatibilityearly death of hybridssterility
Speciation due to ecological or spatial or temporal isolation
Barriers of gene flow or genetical isolation
Sympatric lineage emergence
Genetic differences within the same geographical region result in genetic isolation and lineage divergence.
Parapatric lineage emergence
Differential selection pressures cause lineage divergence even within narrow spatial ranges.
Barriers of gene flow or genetic isolation
How fast is speciation?
Time to genetic isolation
It seems that evolutionary speed is not correlated with generation length
and body size
Are species reproductively independent lineages?
Many ‘species’ do not represent genetically isolated lineages. However ecological, morphological or spatial mating barriers exist
Time to ecological isolation
Adaptation or species selection?
Species selection means that evolution proceeds via differential extinction of species with certain characteristic features.
Adaptive trends imply differential speciation rates of better adapted lineages
Examples of fast evolutionary speed
Minotetrastichus frontalis (=ecus)
The Faroer Island house mouse origin
ed from the Western European House Mouse (Mus domesticus). During 250 years of colonization it has evolved three distinct isolated island populations. The Nólsoy House Mouse is a sub-species called (Mus musculus faeroensis) and the Mykines House Mouse is also a sub-species called (Mus musculus mykinessiensis). Its closest relative was the now extinct St Kilda House Mouse (Mus musculus muralis).
The Aesculus miner C. ohridella was first described in 1984 in Albania as a rare new species.Since then it colonized whole Europe and became a dominant mining species on Aesculus hippocastanus.It is unknown what caused the rapid spread.Nevertheless it is a good example how an evolutionary novelty can trigger dispersion. This dispersion initiated host switches and lineage divergence of its major parasite Minotetrastichus frontalis.
Natura non facit saltus?
Gradualism in Pliocene snails, 10 to 3 Mya.
means sudden rapid evolutionary change that is manifest in genetic isolation.
The classic view of speciation
Phyletic gradualism asserts that Species arise by the transformation of an ancestral population into its modified descendants. The transformation is even and slow. The transformation involves large numbers, usually the entire ancestral population. The transformation occurs over all or a large part of the ancestral species' geographic range
This implies thatIdeally, the fossil record for the origin of a new species should consist of a long sequence of continuous, insensibly graded intermediate forms linking ancestor and descendant. Morphological breaks in a postulated phyletic sequence are due to imperfections in the geological record.
Ernst Mayr, 1904-2005
Classical Darwinian selection implies a continuous (graduate) change in species characters.
The combination with population genetics gave rise to the neodarwinean synthetic theory of evolution formulated mainly by Ernst Mayr and J.B.S. Haldane.
John B. S. Haldane, 1892-1964
The theory of punctuated equilibrium of Niles Eldredge and Stephen Jay Gould states thatThe fossil record is relatively complete.Most speciation occurs via peripatric speciation. Widespread species usually change slowly, if at all, during their time of existence. Daughter species usually develop in a geographically limited region. Daughter species usually develop in a stratigraphically limited extent.Sampling of the fossil record will reveal a pattern of most species in stasis, with abrupt appearance of newly derived species being a consequence of ecological succession and dispersion. Adaptive change in lineages occurs mostly during periods of speciation. Trends in adaptation occur mostly through the mechanism of species selection.
Tempo and mode of evolution reconsidered
Stephen Jay Gould, 1941-2002
Niles Eldredge 1943-
Evolution is assumed to proceed via fast genetic transitions within an peripatric speciation framework.
Mean thorax width of Trilobite species
The evolution of man is a good example of punctuated equilibrium
Does evolution need hopeful monsters? Or evolution above the species level
Classical Darwinian theory assumes character evolution to be a gradual process.However higher taxa are of often distinguished without any intermediate fossils (fossil gaps).Did major evolutionary branches evolved very fast or is our fossil record too incomplete?
Goldschmidt assumed that major evolutionary transitions are caused by mutations in regulatory genes giving rise to major morphological changes.Most of these highly altered creatures have no chance to survive, but few succeed and are ‘hopeful monsters’ that are ancestors of new higher taxa.Punctuated equilibrium is a modern form of this saltationism.
The history of whales: Gradualism or saltationism?
The history of birds: Gradualism or saltationism?
Evolutionary trends and major questions
Major evolutionary trends
Rising number of genes across clades?Rising morphological complexity across clades?Rising hierarchical organization?Rising physiological and ecological flexibility?Rising efficiacy in design?Rising evolvability (the ability to cope with changing environmental conditions)?Decreasing evolvability due to trends for specialization?Rising complexity of ecological interactions?
What made vertebrates prone to evolve large brains?Why did insects never get large?Why did plants never evolve nerves and muscles?Why did Dinosaurs not become small? Why did marine taxa stop evolving since the Cambrian?Why did major taxa (phyla) only evolve in the late Proterozoic? Did life appear only once?
Discuss these questions using the many internet sources!
Trade off between extinction and speciation
The background extinction rate e(t) of marine taxa decreased!
Trade off between extinctions and speciations
Extinction and origination rates are connected.
Peaks in speciation of marine taxa occurred often after mass extinctions.
Mass extinctions might also change ecological dominance. Bivalvia raised after the mass extinction of the ecologically similar Brachiopoda.
Mass extinctions are not equally distributed among taxa.
Advanced species that are physiologically more buffered against environmental changes increased in frequency after mass extinctions
Motile species were often less affected than sessile species
Predator species richness increased after mass extinctions
Adaptation to herbivory and promiscuity might cause high rates of speciation
< 10000 species
> 200000 species
< 10000 species
> 300000 species
Birds of paradise
Change in feeding style
Change in mating system
The interplay between extinction and origination
Correlations between actual diversity and speciation r(D-
S) and extinction rates r(D-DE) (mid Jurassic to Neogene) show that high diversities were correlated with high extinction rates but not with high speciation rates. This points to a density dependent effect in speciation.
equilibrium number of species
Hence, the realized number of species is always lower than the maximum possible number.
Ecological systems cannot be saturated with species.
Data from Mc Peek, Brown (2007)
ss increases with taxon age.Speciation rates l are independent of species richness but decrease with taxon age.Younger taxa have higher speciation rates l.Total species richness is also determined by species survival rates.
Species richness and taxon age
Insecta and Vertebrata
Extinction rates seem to be pylogenetically clustered
From Roy et al. 2009)
Extinction rates of mesozoic Bivalvia were stable in time
Extinction rates were phylogenetically clustered in time
The Red Queen hypothesis
Extinction rates (probabilities) are roughly constant through time.One explanation for this is the Red Queen hypothesis (after Lewis Carroll’s Through the Looking Glass).Each species has to run as far as possible (to evolve continuously) only to stay in the same place.Its competitors, predators and parasites also evolve continuously. Under these circumstances extinction probabilities will remain roughly constant.
Leigh M. Van Valen 1935-
Survival times for extinct genera of Echinoidea (sea urchins).