1. Schedule changes 9Nov 5 Community EcologyT,B&H: chap. 9 Essay I: final version due 7 days after draft returned 10Nov 12 Sustainability/Human Population EcologyT,B&H: chap. 12 Essay II assigned to undergraduates Proposed term paper topics submitted by graduate students 11Nov 19 Resource & Energy Cycling & Anthropogenic PollutionT,B&H: chap. 11, 13 Nov 26 Thanksgiving Holiday Essay II draft due before this date 12Dec 3 Patterns & Determinants of Species RichnessT,B&H: chap. 10 Draft of term paper due from graduate students 13Dec 10 Conservation of BiodiversityT,B&H: chap. 14 Essay II final copy due from undergraduates Dec 13Sunday afternoon review session for final exam (1-4 pm) Dec 17Final Examination Final version of term paper due from graduate students

2. Midterm Exams Midterms handed back in class on Nov. 12th Grades will be emailed on the 13th to students not in class on the 12th If distance student based in USA and wish to receive midterm back, send mailing address to Julie If outside USA, inform Julie & we will try to fax or scan & email

3. Graduate term papers 3 items on the website now: –Term paper guidelines –Hints on choosing a topic –Previous good term papers as models Email Julie your term paper topic by Nov. 12th –Best is brief outline with a few references –But at very least a few sentences about one or more possible topics Initiate an email discussion with Julie & I early (before the 12th)!

4. Population Dynamics in Communities Multiple determinants of population abundance & dynamics Metapolution dynamics & dispersal among habitat patches Temporal patterns of community composition Food webs: direct vs. indirect effects & trophic cascades Community stability & food webs

5. Multiple Determinants of Abundance and Dynamics of Populations What factors determine population density over time? Why do populations vary from place to place? Depends on: –Physiocochemical conditions –Resource availability –Life cycle characteristics –Influence of competitors, parasites, predators & mutualists Effects of these factors on B, D, E & I Key-factor analysis to distinguish what determines and what regulates a population Dispersal, patches & metapopulation dynamics

6. Correlations can inform, but do not reveal mechanism + relationships between food availability and population growth rate … but growth rate reaches an asymptote---why? Red kangaroosBarn owls Wildebeest Feral pigs

7. Androsace population appears stable but this masks underlying dynamic processes - gains from seed germination of 150-1000 seedlings/m2 - 50-300 adults each yr Irruptive population of mice (Mus) in agricultural field, Australia

8. Possible patterns of population dynamics - dominated by: a)Pop growth after disasters b)Limited K with abundant resources c)Limited K (low K) d)Pop decline after colonization or recruitment

9. What determines abundance vs. what regulates abundance are different questions a) Population regulation with density-dependent birth or death rates b) equilibrium population size depends on site-specific death rates

10. Key factor analysis Distinguish factors that determine vs. regulate abundance Technique: calculate k-values for different phases in the life cycle of a population –Actually, identify key phases of life cycle! –K-values measure mortality (killing power) –Construct life table Answer: How much of total mortality occurs in each phase? Also, what is relative importance of each phase in determining year to year fluctuations in abundance? Key phases have mortality strongly related to overall mortality

11. What are most important mortality factors? k-values for Colorado potato beetle - identifies key phases that determine abundance - life table data for seven life stages; data for one year - k-values are differences in log N for successive phases

12. Which phases determine fluctuations in abundance? - examine regressions of phase mortality on total mortality across different years -largest regression coefficients associated with key phase causing population change -------> (summer adults, r=.906) regulation: strongest density-dependence Emigration of summer adults starvation of larvae

13. key-factor analysis of annual plant Androsace -key phase has largest regression coefficient (= seed failure to germinate in soil)

14. Population interactions & Lyme Disease How could a key-factor analysis be used to identify the important phases that determine risk of human disease? Gypsy moths prefer oak vs. maple Initial bull’s eye rash -facial nerve paralysis -Borrelia Lyme spirochetes - Ixodes deer tick & nymph stage -whitetail deer & deer mouse - acorn population control

15. How can we identify the “key phases” in determining disease risk? Modeling several populations and factors Hypothesis: acorn crop predicts Lyme disease intensity two years in future Information: - acorn production linked to mice, ticks, deer, gypsy moth & weather - tick larvae 8x greater following large acorn crop & 40% more ticks/mouse - in experimental plots, acorn availability correlated with mice density Which population density do we wish to understand? - Borellia bacterium - deer tick Passenger pigeons -major predators - deer mice (& deer)? on acorns; controlled deer mice? - acorns - gypsy moth Key-factor analysis identifies factors that determine density and its regulation Managing populations “causing”disease? - controlling deer mice population? - controlling acorn crops?

16. Metapopulations: Dispersal among habitat patches - some populations are fragmented and subpopulations have different dynamics c ) colonized: only 1990; e) extinct: only 1983; filled: present 1983 & 1990; open: present only 1990

17. Levin’s model: stable occupancy rate if rate of colonization > rate of extinction Many Melitea populations extinct in 1993, unrelated to N (!) - this is unusual Metapopulation abundance determined by: - Dynamics of populations within patches - Dynamics of patches (rates of colonization & extinction of patches) determine p(t), proportion occupied -Conservation importance: persistence through colonization of patches

18. Persistence in a metapopulation of Pika (Bodie, CA) - some populations are fragmented and subpopulations have different dynamics a) 3 patch clusters; 4 pop censuses, 1972-91 b) computer simulations without colonization c) with colonization between the 3 clusters North as “source”

19. Community Ecology Temporal patterns in community composition Community succession Food webs –Direct & indirect effects –Top down vs. bottom up control –Community stability Is community stability related to food web structure?

20. Temporal Patterns in Community Composition - patch dynamics: dispersal between patches & changes within patch - patches are “gaps” created by disturbance - two kinds of community organization: 1) founder-controlled: competitive lottery for living space species are: - good colonists - similar competitors Coral reef fish larvae; rainforest shade-tolerant seedlings

21. 2) dominance controlled communities: patch successions - early pioneers are replaced by competitive dominants - predictable sequence: fast-maturing, then longer-lived competitors - final, lower diversity stage of climax species - examples: rocky shoreline algae; rainforest trees

22. Succession on newly exposed landforms: Primary succession -lava flows: 100s of yrs N-fixing Alder colonization facilitated biomass-rich phase -marine subtidal rocks: a dozen yrs

23. Primary succession on coastal sand dunes (Lake Michigan) - compared 13 ridges of known age (30-400 yrs since formation) -experimental transplants showed All can colonize, if arrive, so… - sequence determined by differences in dispersal, rodent seed predation, and competition

24. -fugitive annuals - perennials germinate in shade - monolayered->multilayered Light saturation curves of early, mid & late successional plants: - photosynthetic rate vs. photosynthetically active radiation (PAR) Secondary succession: example- abandoned agricultural fields annual weeds -> perennials->shrubs-> early successional trees->late trees

25. Early successional species are fugitives that grow fast and reproduce through high rates of photosynthesis… then outcompeted

26. Old Field Succession in Minnesota (chap. 1.3.2) -natives replace introduced -perennials replace annuals -N increases Is convergence due to age or N? Experiment on 1968, 1957 & 1992 fields a)1982-92: 17 g N/m2 added b)If only 1 g N/m2 -less convergence

27. Intertidal mussel beds in Brazil - barnacle Chthamalus colonizes large gaps > 6 months - limpet Collisela colonizes small, peripheral gaps - mussel Brachiodontes dominates later -succession different in small vs. large, & center vs. periphery

28. Animal community succession usually passively follows plants: Temporal gradient of vegetative succession following disturbance

29. However, large animals can have profound effect on succession Elephant overcrowding drastically reduces tree cover in savanna environments -- debate over active management

30. Managing successional stages for conservation Endemic NZ giant weta Introduced gorse provides refuge from mammalian predators Management: Maintain cattle -cattle open pathways for goats -Goats graze gorse into dense spiny hedges

31. Predators Grazers Plants Community matrix of species interactions - predator-prey & competitive relationships Direct vs. Indirect Effects: - How can adding a competitor increase your abundance? - Can the loss of one of your predators reduce your abundance? -Trophic cascade: predator reduces prey abundance so that its food resources increase

32. Food webs: unexpected effects -If eliminate “superpredator” cats from islands with endangered birds… rats drive prey extinct … cats control “mesopredator” rats, reducing overall predation on birds

33. Direct & indirect effects in food webs: trophic cascade in birds, limpets & algae - experimental removals of shorebirds on NW Pacific intertidal community - Gulls & oystercatchers prefer the limpet L. pelta but L. digitalis increased! -L. strig. is competitively inferior, so declined when birds were excluded by wire cages -Birds also prefer gooseneck barnacles on which L. digitalis is cryptic, so it increased with > barnacles -Barnacles outcompete algae for space, so removing birds decreased their cover &diversity

34. Keystone Predators: Paine’s Pisaster starfish exclusion experiments Mytilus mussels outcompeted other space-holding spp, reducing species diversity from 15 -> 8 Starfish prefer to feed on the dominant mussels & barnacles

35. Top-down or Bottom-up control of Food Webs? Communities with 1, 2, 3 or 4 tropic levels (comp/pred = population dynamics determined by competition or predation) Control of community structure from: - Below (bottom-up): by nutrient or prey availability, so populations mostly affected by competition, or - Above (top-down): species abundance and number determined mostly by predators controlling prey 2-level web: Aldabra tortoise

36. A 3-trophic level system: Variation in the Great Salt Lake pelagic system Decreased salinity in 1985-6 allowed invasion of predatory insect Trichocorixa … reducing density of the grazer Artemia … and therefore the grazing rate …allowing density of phytoplankton to rise (as measured by chlorophyll a) … thus lowering water transparency (a green soup!)

37. Variation in four-level food webs by predator intensity a) NA stream community b) Bahamas: Top predators have stronger (weak omnivory or 2-level feeding) effects on herbivores, so functions as 3-level

38. Top-down or Bottom-up control of Food Webs? Why is the world green? Hairston: top-down control dominates- predators control herbivores Murdoch: the world (of plants) is prickly and tastes bad! But control can be switched! Low nutrients: trophic cascade- Insects> snails & algae dominate High nutrients: Larger snails dominate but plants high biomass (Murdoch)

39. Community Stability & Webs Stable because are either: –Resilient: returns rapidly to prior structure after disturbance –Resistant: undergoes little change when disturbed Are some food web structures more stable than others? Are some communities more fragile, and more in need of conservation? Initial hypothesis: Complexity begets stability –However models unkind: higher species richness decreases pop & comm stability! –Resilience decreases with connectance among pairs of species, & strength of interactions

40. a)40 webs: terrestrial, marine & freshwater (poor data!) b) 95 insect- dominated webs c) seasonal versions of a pond d) Venez. & C.R. swamps & streams Connectance & species richness in food webs - fraction of possible pairs of species that interact with one another - b-d: any possible relationship, so stability argument unsupported

41. Natural experiment: more diverse grassland communities resisted drought better (Yellowstone NP, USA) -high R indicates relative abundances & species composition changed little

42. …and NZ streams with more flow-related disturbance had simpler food webs… - both web size and connectedness decrease with disturbance But food web theory is poorly developed… -needs more good field studies before any generalizations