1. Lecture 22: Coevolution reciprocally induced evolutionary Δ’s in 2 + spp. or pop’ns Mutualistic vs. Antagonistic typespecies 1species 2 commensalism+0 competition-- predation+- parasitism+- mutualism++

2. Mutualism e.g. C. Am. Acacias & Ants: Herbivory:  growth; permits competition from fast growing spp. 90% acacia spp: bitter alkaloids → prevent insect/mammal browsing 10% spp: lack alkaloids; have symbiotic ants

3. Acacias Ants swollen thorns (nest sites) petioles (nectaries) Beltian bodies (protein) attack herbivores remove fungal spores attack shading plants

4. Competition Anolis spp. spp. turnover (Caribbean islands) due to coevol’n carrying capacity of island is a function of body size: best body size for invading spp body size frequency

5. body size frequency body size After Invasion: - invader selected for smaller body size - competition displaces residents : body size ↓ Later: -invader evolves to optimum body size - eventually, resident driven to extinction frequency X

6. Sequential Evolution “tit for tat” e.g. plants & herbivorous insects (predation): plants : 2° metabolites to repel insects insects: detoxification (mixed function oxidases) e.g. nicotine: from a.a. or sugar pathway

7. Erlich & Raven (1964): 2° metabolites → new adaptive zones MFOs → new adaptive zones leads to cycle of adaptive radiations & ↑ diversity

8. speciation of plant → speciation of insect OR speciation of insect → speciation of plant Phylogenetic analysis of sequential evolution: e.g. pinworm parasites of primates: congruent phylogenies divergence in host → divergence of parasite not the other way around parasite/host interactions:host evolves defenses should parasite ↑ or ↓ virulence? depends!

9. Virulence 1)Transmission: Correlated w repro rate: NS ↑ virulence Requires live host: NS ↓ virulence (trade-off) e.g. Myxoma virus of rabbits 2) Coinfection 1 parasite : all offspring related kin selection: → ↓ virulence multiple infection : competition selection for ↑ repro rate → ↑ virulence

10. 3) Type of Transmission: Horizontal: ↑ virulence Vertical: ↓ virulence “Arms Race” : adaptive advances must be countered or face extinction!

11. e.g. “Brain Size Race” b/w Ungulates & Carnivores: a)Ungulate b)Carnivore archaic paleogene neogene recent Population dist’n Brain:Body size ratio

12. Conclusions Relative brain size ↑ through time Carnivores are “smarter” than ungulates Evidence for coevolution? Less evidence for coevol’n of running speed Why? costs of adaptation resistance to 1 pred. may ↑ vulnerability to others e.g. Cucurbitacins:protect from mites; attract beetles

13. Generally: Specialist predator; Single prey → coevol’n probable Multiple Interactions → coevol’n slow; sporadic How important is coevolution to pattern of diversity? taxonomic survival curves: used to determine if survival of taxon is age-independent

14. Taxonomic Survival Curves Does mortality (extinction) depend on age ? agespecies 1species 2 1 10001000 2 900740 3 810600 4 729580 5 656570 6 590560 7 531550 8 478540 9 430460 Sp. 1: 10% die yearly, regardless of age Sp. 2: mortality high for young & old; mortality low in middle age

15. Log - linear analysis : Age - independent mortality is linear

16. Taxonomic Survival Curves log (# of taxa surviving) vs. age of taxon for most taxa: linear → age - independent 2 interpretations: time a) constant rate of extinction b) variable rate of extinction independent of age

17. Extinction Probability of Extinction: New Taxa = Old Taxa What causes extinctions? Biotic factors: antagonistic interactions (pred’n, parasitism, compet’n) lag load: L = Diff’n b/w mean & optimum genotype L ↑ : rate of evolution ↑ Why? selection coefficient ↑ L ↑ : probability of extinction ↑ Why? falling behind in the “arms race”  opt -   opt

18. Lag-Load Models 1. Contractionary sp. w ↑ L : falls behind, goes extinct 2. Expansionary sp. w ↓ L : outcompetes; increases these 2 models are unstable may fluctuate between 1 & 2

19. 3. Stationary: all spp. L = 0 no change; no extinction perturbations; back to equilibrium extinctions not due to biotic factors 4. Dynamic Equilibrium: “Red Queen” hypothesis all spp. have ↑ L Env’t constantly deteriorating due to arms race “running as fast as they can to stay in the same place!”

20. Implications of Red Queen to TSCs older taxa same prob. of extinction as newer taxa log - linear survival curves are evidence for RQ Why?: “zero - sum game” : means L stays constant 2 versions of RQ: 1. Strong Abiotic factors negligible Extinctions due to spp. inter’ns improbable, but testable 2. Weak Abiotic & Biotic factors imp. likely true, but untestable

21. Testing RQ using TSCs: Evidence for Strong RQ: constant chance of going extinct b/c of spp. interactions - extinctions even in constant physical env’t ! Evidence for weak RQ?: -other mechanisms b/c extinction rates fluctuate over time

22. Lecture 23: Mass Extinctions Biodiversity: balance b/w spec’n & extinction > 99% of all species are extinct Because of: 1)Background extinctions: gen’lly due to biotic factors e.g. competition, predation etc.

23. Background Rate marine families: → relatively constant ~ 5 - 10 families / my mass extinctions e.g. Sepkoski & Raup (1982)

24. Ecological Significance of Mass Extinctions 1.Open up vast niche spaces 2.Lead to adaptive radiations e.g. mammals diversify after extinction of dinosaurs 3. Taxa can recover: e.g. ammonites decimated in Permian extinction; came back & diversified in Triassic

25. Mass Extinctions of the Phanerozoic: “The Big 5” 1.) Cambrian (540 - 510 mya): Explosion of diversification Marine; soft-bodied (few fossils) Evidence for ~ 4 separate events Trilobites, conodonts, brachiopods hit hard Cause: Glaciation: - sea level ↓ (locked in ice) - cold H 2 O upwelling & spread - ↓ O 2 levels?

26. 2.) Ordovician (510 - 438 mya) 2 nd most devastating to marine organisms Echinoderms, nautiloids, trilobites, reef - building corals Causes: Glaciation of Gondwanaland evidence in Saharan deposits drifted over N. pole (cooling) sea level ↓ losses correspond to start & retreat of glaciers

27. 3.) Devonian (408 - 360 mya) Terrestrial life starts & diversifies Extinctions over 0.5 - 15 my (peak ~ 365 mya) Marine more than terrestrial Brachiopods, ammonites, placoderms Causes: Glaciation of Gondwanaland evidence in Brazil Meteor impact?

28. 4.) Permian (286 - 245 mya) formation of Pangea: continental area > oceanic Devastation (~245 mya): ~96% marine spp; 75% terrestrial spp Causes: a) formation of Pangea? b) vulcanism? - basaltic flows in Siberia - sulphates in atmosphere → ash clouds c) glaciation at both poles: major climatic flux d) ↓ salinity of oceans?