Midterm Exam Review Questions

1. Midterm Exam Review Questions • Short essays (60-70% of exam) drawn from list of questions distributed Tuesday on the website • Stratified (although non-random) across the chapters • Address the question--no bonus for extraneous stuff • Only textbook and lecture material • Closed book exam without notes, etc.

2. Midterm Exam Review Session • Sunday, 1-4pm EST • 53 Church St., Room L01 • Bring photo ID for access to building • Email questions to Anne (ammcguir@fas.harvard.edu) • To access the live stream of the review sessions,students should go to http://cm.dce.harvard.edu/classroom/ and click on ENVR E-140 at around 12:55 p.m. on the day of the review. • A window will open with a button that says "Join". Students click on the button and join the classroom. There is a one or two second delay in the stream. • If the page opens to "No videos are available at this time" it means they're probably too early for the class. They'll need to refresh the page periodically until they get the "Join" button and then click on the "Join" button. • The sessions will also be added to the course video page.

3. OFT, Predator-Prey & Parasite-Host Relationships (continued from last lecture)

4. Habitat Preference and Switching • determined by relative profitabilities of encountering • and harvesting prey in different habitats

5. … but habitat preferences change when predator present -trade-off between foraging efficiency & predation risk

6. The Lotka-Volterra predator-prey model predicts coupled cycles in predator and prey abundance; - hare-lynx & hare-food oscillations linked together

7. But even in simple communities--- a complex web of interactions

8. Huffaker’s mites:a) herbivorous mite prey without its mite predatorb) simple system of coupled oscillationsc) complex environment (orange patches separated by complex travel routes)allows sustained oscillations …and snowshoe hares do not cycle in patchy habitats!

9. Disease transmission threshold & critical population size • Ro: basic reproduction rate = average number of new infections per infected host introduced into a susceptible population • Transmission threshold: infection will spread when Ro >= 1 • Ro increases with • L, the period of time host remains infected • S, number of susceptible individuals in population • B, transmission coefficient - • If microparasites are highly infectious (large B) or have long periods of infectiousness (large L) then: • have high Ro values • & small transmission thresholds of population size • If powerful immune response, so very transient in individuals (small L), then • Large critical population size (e.g., measles -= 300,000) • S drops during epidemic as susceptibles die or develop immunity

10. Disease dynamics and cycles: immunity & death reduces % of “susceptibles” & so lowers incidence; but then susceptibles increase through births & immigrants a) 1-2 year cycles in measles (pre-vaccination) b) 3-4 year cycles in whooping cough (mass vaccination > 1956) (England & Wales)

11. Epidemic Curves of Infection:parasite will spread if critical susceptible population is exceededa) Legionaire’s disease & b) foot-and-mouth disease (cattle & sheep)

12. Population ecology of parasites:- Density-dependent regulation of flea population on blue tits

13. - Density-dependent regulation of nematodes in eels

14. Predator-mediated coexistence of prey species:predation or grazing can interrupt competitive exclusion Ex.1: pigmy owls prevent competitive dominance of Coal Tits on Scandinavian islands Ex. 2 0= no grazing, 1=light, etc. 4=very heavy grazing

15. a) tide pools vs. b) emergent substrates Intermediate densities of periwinkles maintain high algal diversity in New England tide pools - Enteromorpha alga competitively exclude others at low densities- At high densities, periwinkles broaden diet- effect is due to preference for competitive dominant … but Carcinus crabs prey on periwinkle juveniles in Enteromorpha canopy…

16. Impact of parasites on community structure is underappreciated-Kevin Lafferty’s salt marsh food web

17. Coevolution & Mutualisms • (skip over chap 8.1-8.2 for now) • Coevolutionary arms races • Symbiosis: Mutualism and Parasitism • Mutualisms Interspecific Competition • Influence on Community Structure (chap 6.4) • Importance of Competition

18. Ecology of Mutualisms & Parasitism • Symbiosis: association between species in which one lives on or in the other • Parasite: lives intimately associated with host organism(s), deriving resources from and harming the host • The “habitat” of parasites are host organisms (egg or larval stages may use different host types or survive in the soil) • Microparasites: small, numerous and reproduce within host (bacteria, viruses, etc.) • Macroparasites: large, grow within host but produce infective stages that disperse to new hosts • Live on the host body or within body cavity • Parasitic worms, nematodes, etc. • Parasites harm the host: have negative effects on growth, reproduction and/or survivorship

19. Coevolutionary Arms Races- predator/prey-grazer/plant-specialists are more prone to arms racesa) specialists have lower mortality on toxic chemicalsb) generalists lower mortality on chemicals not provoking coevolutionary response(e.g., tannins, lignin)

20. Coevolutionary Arms Races- parasites & hosts- continual evolution of new influenza strains-Canadian Plains Indiansevolution of resistance to TB

21. Coevolution of host and parasite: Control of rabbits in Australia & Britain by selection for increased transmissibility in Myxoma virus strains (thereby lowering virulence)

22. Mutualists & Commensuals • Mutualism: association which benefits both species (have positive effects on growth, reproduction and/or survivorship for both populations) • Mutualisms are cases of reciprocal exploitation in which both partners have net benefit • mycorrhiza- associations between fungus and plant root that extracts soil nutrients • Pollination, seed dispersal, etc… • Commensuals are symbionts that have no measurable cost or benefit to host • Effects may depend on the “load” of parasites or commensuals and depend on nutritional status and health of host organism

23. Higher plants as specialized niches for arthropods, worms & protozoa - not shown are nematodes, bacteria & viruses (!)

24. Higher animals as specialized niches for arthropods, worms, protozoa, bacteria & virusesfungi- brownworms- bluearthropods- greenprotozoa-yellow

25. Mutualistic protectors: cleaner fishcleaner:Labroides dimidiatus client:Hemigymnus melapterus

26. Modified plant parts for mutualists:a) beltian bodies of bullhorn Acacia tended by antsb) hollow thorns enclosing colonies

27. Experimental removal of predatory symbiotic ants reveals mutualistic benefit in reducing herbivorytree: Tachigali myrmecophila ant: Pseudomyrmex concolor

28. Farming mutualisms in aphids & ants, cost of mutualism: a)ants lower predation on aphids, but b) if no predators, ant-excluded colonies lower aphid growth & reproductionTuberculatis quericola Formica yessensis

29. Pollination - reward is nectar or pollenspecialized (at least temporarily) to ensure pollen transfer to conspecificslimit production so visit sequential individualsSeed Dispersal- reward is pulp or seedsno need for temporal specialization, so can be generalists

30. Fig wasp symbiosis & fig tree phenology:- intraspecific randomized fruiting to maintain pollinating agaonid wasp species

31. Fruiting Phenology- as a result of coevolution with pollinating wasps, figs always available for vertebrate frugivores- figs are “keystone species” in rainforests Ficus subtenda 1 f-r--f-r-f-r-f-r--f-r---f-r 2 r--f-r-f-r-f-r--f-r-f-r--f-r 3 -f-r--f-r-f-r--f-r---f-r--f-r Ficus stupenda 1 f----r--f-----r----f-------r----f- 2--f-----r----f-----r---f------r--- 3-r---f-----r---f-----r--f------r--

32. Many symbiotic species (specialized) Complex life cycles (e.g., alternating hosts) Dispersal important (transmission & infection) Sex common to generate variation in evolutionary wars Few symbiotic (generalized; e.g., lichens, rhizobial bacteria) Simple life cycles Vectors for transmission rare Sex uncommon as evolutionary conflict reduced Parasites vs. Mutualists

33. Life cycle of the parasitic cestode worm Diphyllobothrium- birth rates determined by hosts

34. Life cycle of malaria-causing Plasmodium protozoa: from vertebrate red blood cells to mosquito gut to salivary glands

35. Behavioral responses of Hosts to Parasites: Manipulation to benefit the parasite-Anopheles mosquitos feed on more hosts when infected with the malaria parasite Plasmodium -Gall growth to harbor larvae induced by different species of Andricdus wasps

36. The vertebrate immune response changes habitat quality for specific parasites (and toxins); production of antigens promotes immunity to subsequent colonization attempts

37. Mutualistic microbiota in vertebrate guts- microbes (mostly protozoa & bacteria) receive plant foods & live in high pH, regulated shelters- vertebrate hosts receive food from otherwise indigestible leaves- food in form of short-chain fatty acids (SCFAs), protein & vitamins zebra kangaroo rabbit sheep

38. Corals contain photosynthetic algae called zooanthellae-intracellular symbionts that photosynthesize-expelled by stressed corals (bleaching)

39. the symbiotic, mutualistic nitrogen-fixing bacteria of Rhizobium, infecting root nodules (especially legumes) Legume trees are common on N-poor soils, and provide protein-rich leaves & seeds (Koompassia)

40. Effects of symbiotic Rhyzobium vs. N on soybeans & grass:change in competitive outcomes

41. Most mycorrhizas increase P & N uptake by host, but some may protect from pathogens: P uptake in HyacynthoidesVulpia protected from fungus by Glomus