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Announcements

This announcement provides information about the midterm exam, a review session, and the topics covered in the section. It also explains the concept of niche and its importance in determining how organisms fit into their environment, as well as species interactions such as competition and mutualism.

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Announcements

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  1. Announcements • Midterm Exam: Wednesday, Nov 3rd • Review this week in section: • Bring questions to section

  2. Summary from Friday • Building a model to show population interactions • Age structure affects population • Life tables • static vs. cohort-based • Life strategies • opportunists vs. competitors • seasonal variation in life strategy within a species • Niche

  3. What is a niche? • A niche is the total of all biotic and abiotic factors that determine how an organism fits into its environment. • Where and how does an organism live and function? • habitat • role in community

  4. potential survival, but stressed potential survival, but stressed Success intolerant intolerant optimum Environmental variable (Temperature, for example)

  5. Niche in n-variable hyperspace

  6. Fundamental niche:where a species could live Realized niche:with competition from other species, where a species does live Fundamental vs. Realized Niche

  7. Niche Partitioning in Animals • Species divide up an apparent niche

  8. perennial grasses annual grasses

  9. Convergent Evolution • Organisms adapt to fill open niches • Organisms in two different environments that are not closely related may have the same “job” and similar anatomy

  10. Selection minimizes competition Two species living separately. Two species living together.

  11. Species interactions • Competition • Mutualism • both species benefit • Commensalism • one benefits, other is unaffected • Parasitism • one benefits, one loses • Predator-Prey

  12. Parasitism • microparasites vs. macroparasites • Biotropic • thrive on live hosts only • Necrotropic • can benefit even if host dies • Parasitoids • always kill their host

  13. Predator-Prey Relationships • Prey defenses • coevolution • as predator evolves, prey evolves to evade it

  14. Predator-Prey Relationships • Prey defenses • coevolution • as predator evolves, prey evolves to evade it • warning coloration and mimicry • aposematic “away signal” = bright red and yellow • some mimics very toxic, others harmless

  15. Predator-Prey Relationships • Prey defenses • coevolution • as predator evolves, prey evolves to evade it • warning coloration and mimicry • aposematic “away signal” = bright red and yellow • some mimics very toxic, others harmless • camouflage • blending in

  16. Predator-Prey Relationships • Prey defenses • coevolution • as predator evolves, prey evolves to evade it • warning coloration and mimicry • aposematic “away signal” = bright red and yellow • some mimics very toxic, others harmless • camouflage • blending in • moment-of-truth defenses • large or startling displays

  17. Predator-Prey Relationships • Optimal Foraging Theory- describes how prey are chosen • small prey provide little food, but they are easy to hunt • large prey provide a lot of food, but they are more difficult to hunt • Trophic Cascades • Food webs can be complex

  18. Prey Selection

  19. Trophic Cascade Eagles 4th trophic level predator/ tertiary consumer predator/ secondary consumer Foxes 3rd trophic level herbivore/ primary consumer 2nd trophic level Mice autotroph/ primary producer Plants 1st trophic level

  20. Trophic Cascade Eagles 4th trophic level if eagles go extinct, what could happen to… foxes? mice? plants? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  21. Trophic Cascade Eagles 4th trophic level If a new predator on mice is introduced, what could happen to… mice? foxes? plants? eagles? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  22. Trophic Cascade Eagles 4th trophic level If drought caused a dip in plant production, what would happen to… mice? foxes? eagles? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  23. Simplified Temperate Forest Food WebTo which trophic level do these organisms belong? Eagle Wolf Fox Shrews Deer Caterpillars Rabbit Oak seedling Grasses Herbs

  24. Optimal Foraging • Predators tend to target dominant prey • enhancement of diversity • What about herbivores? • don’t necessarily eat dominant plants • plants have secondary compounds and chemical toxins that taste bad herbivores may target tasty rare plants

  25. Community Ecology A community is a group of living organisms that occupy a certain area and interact with one another. • Niche partitioning • Species interactions • Food web dynamics • Environmental variation/disturbance • driver of diversity

  26. Do communities change? • What we see now wasn’t always here • communities do change • Spatial scale is important • global vs. local change • Time scale is important • long term change • measured in 10’s of thousands of years or more • short term change • measure on a decadal time scale

  27. Announcements • Look at course webpage for study guide • Read Enserink et al. articles “Biological Invasions Sweep In…” for section next week (after midterm) • Please let know today if you have special needs for the exam • Note on syllabus: problem set will be handed out Nov. 10th • Office hours: Monday after class

  28. Summary from Wednesday • Niche partitioning • Convergent evolution • Community ecology • Species interactions • Optimal foraging theory and prey selection • Herbivory and plant selection • Trophic cascades and food web dynamics • Change over time

  29. Sediment cores Ice cores Pollen records Fossil records Packrat middens Tree rings How do we detect long-term change?

  30. Isotopes • Isotope: element where atoms have a different # of neutrons O16 O18 Lighter and common Heavy and rare = proton = neutron

  31. Isotopes • Isotope: element where atoms have a different # of neutrons • Can be used to detect global-scale long-term change

  32. Isotopes • Isotope: element where atoms have a different # of neutrons • Can be used to detect global-scale long-term change • Total oxygen pool is composed of: • Mix ofO16and O18 • Fractionation during seawater evaporation • O16evaporates easily • O18gets left behind

  33. Isotopes in Sediment Cores • Sediment contains foraminiferans • microscopic sea creatures • O16/O18 in tests reflects that of seawater • live on sediment or sink to bottom when dead

  34. Isotopes in Sediment Cores • Sediment contains foraminiferans • microscopic sea creatures • O16/O18 in tests reflects that of seawater • live on sediment or sink to bottom when dead • If the climate cools… • ice sheets will expand • ice comes from rain from evaporated seawater • evaporated seawater is high in O16 • seawater left behind high in O18 • therefore, high O18 in ocean = cold conditions

  35. Variation in Ocean O18 more negative values: less O18 and warmer conditions less negative values: more O18 and colder conditions

  36. Ice core measurements: thickness of layers physical properties dust and silt conductivity trapped air (CO2, NOx, and O2) ions (K+, Ca2+, NO3-) isotopes

  37. Pollen records can be used to detect long term change on a regional scale. Trees can migrate 200-300 miles in 1000 years.

  38. Fossil Pollen – Silver Lake, OH J. G. Ogden III, 1966.

  39. Dendrochronology: exact calendar dating using annual growth rings in wood Dendroclimatology: using tree rings to look at past climate very old trees can be used to get the longest history Bristlecone pine (Pinus longaeva) White Mountains, CA ~5000 years old

  40. Soil development • Weathering of primary minerals • nutrients become more available • in old soils, the nutrients get leached out • Formation of clays • Accumulation of organic matter

  41. Long-Term Change Shifts in climate Change in vegetation Change in soil development Change in animal populations

  42. Long-Term Change Shifts in climate Change in vegetation Change in soil development Change in animal populations Community change

  43. Short-Term Change Succession Textbook definition: “a change in species that occupy a given area, with some species invading and becoming more numerous while others decline in population and disappear” Can be thought of as the replacement of one community by another

  44. Primary vs. Secondary Succession • Primary: • Community gets established on a new surface • Lava flow • River sandbar • Glacial moraine • Secondary: • Recovery following disturbance • Fire • Flood • Post-agriculture

  45. Primary Succession Can take hundreds to thousands of years Soil must develop New species must come from somewhere else Secondary Succession Faster

  46. Primary Succession Can take hundreds to thousands of years Soil must develop New species must come from somewhere else Secondary Succession Faster

  47. Early shade intolerant nutrient demanding short-lived poor competitors Late shade tolerant adapted to lower nutrient conditions long-lived good competitors Earlyvs. Late Succession Species

  48. Classic Succession Clements’ idea of “climax community” • eventually, a given system reaches a predictable steady-state • independent of the early succession community

  49. Mixed Beech-Maple Forest Oak forest Oak-Hickory Oak woodland Pine forest Willow shrub Sumac-Pine Poplars Cattail marsh Broomsedge Dune grass Aquatic plants Aster-Goldenrod Annual weeds Sand dune Swamp Old field

  50. Bird succession

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