1. Variation in the Physical Environment BIOL400 21 October 2015

2. Variation in Terrestrial Ecosystems

3. Air Temperature  Latitudinal Variation Sun strikes earth more obliquely at higher latitudes Sun strikes earth more obliquely at higher latitudes Solar equator—point of most direct sunlight (thus warmest) Solar equator—point of most direct sunlight (thus warmest) 0  latitude on 21 March and 21 September0  latitude on 21 March and 21 September 23.5  N on 21 June23.5  N on 21 June 23.5  S on 21 December23.5  S on 21 December Land masses at 0  are always close enough to solar equator to be warm Land masses at 0  are always close enough to solar equator to be warm

4. Fig. 6.1 p. 82

5. Air Temperature  Seasonality Occurs due to 23.5  tilt in earth's axis Occurs due to 23.5  tilt in earth's axis Reversed for Southern vs. Northern Hemispheres Reversed for Southern vs. Northern Hemispheres

6. HANDOUT

7. Air Temperature  Effect of elevation Temperature decreases at higher elevation Temperature decreases at higher elevation 1000 m rise in elevation = cooling by 6-10˚C 1000 m rise in elevation = cooling by 6-10˚C

8. Air Temperature  Proximity to a Large Body of Water Temperature fluctuations are minimized Temperature fluctuations are minimized Water takes far longer than air to heat or cool (higher specific heat), and exchanges heat with airWater takes far longer than air to heat or cool (higher specific heat), and exchanges heat with air Southern Hemisphere (20% land) experiences less annual variation in temperatures than Northern Hemisphere (40% land) Southern Hemisphere (20% land) experiences less annual variation in temperatures than Northern Hemisphere (40% land)

9. Fig. 6.2 p. 83

10. Precipitation  Latitudinal variation Air masses converge and rise at the [solar] equator, cooling and losing moisture as rain Air masses converge and rise at the [solar] equator, cooling and losing moisture as rain Returning to earth's surface at ~30  N and S [of the solar equator], arid air produces little precipitation and may in fact draw water by evaporation Returning to earth's surface at ~30  N and S [of the solar equator], arid air produces little precipitation and may in fact draw water by evaporation Deserts thus located at ~30  N and ~30˚SDeserts thus located at ~30  N and ~30˚S

11. Fig. 6.3 p. 84

12. Precipitation  Seasonality in wet-dry tropics Solar equator shifts point at which air masses meet Solar equator shifts point at which air masses meet Shifts zone of heaviest rainfall seasonally, relative to equator Shifts zone of heaviest rainfall seasonally, relative to equator North (northern summer)North (northern summer) South (northern winter)South (northern winter)

13. HANDOUT

14. Precipitation  Proximity to a Mountain Range Precipitation on leeward side is noticeably less than precipitation on windward side Precipitation on leeward side is noticeably less than precipitation on windward side Rising air masses cool, lose moisture Rising air masses cool, lose moisture May make for profound adaptations in a species as one crosses a mountain rangeMay make for profound adaptations in a species as one crosses a mountain range

15. Fig. 6.11 p. 91

16. Precipitation  “Lake Effect” Heavier precipitation on leeward side of large lake Heavier precipitation on leeward side of large lake Erie, Edinboro, Buffalo, etc.Erie, Edinboro, Buffalo, etc. Also true of coastal areas Also true of coastal areas Seattle, Portland, Louisiana in summer, etc.Seattle, Portland, Louisiana in summer, etc.

17. Variation in Aquatic Ecosystems

18. Lakes

19. Annual Lake Cycles  Stratification of water in summer and winter  Spring and fall overturn

20. HANDOUT—Water Density

21. Spring Overturn  Warming (toward 4˚C) surface water is denser and sinks, mixing waters  Wind increases mixing, bringing nutrients up from bottom and taking oxygen to depths

22. Lake in Summer  Thermocline separates lower zone of cold water from upper, heated water Strata above and below do not mix Strata above and below do not mix  Epilimnion— zone of primary production, thus well oxygenated; inorganic nutrients become limiting  Hypolimnion— becomes depleted of O 2 by consumers (mostly decomposers)

23. Fall Overturn  Surface layers cool rapidly, become denser, and sink  Mixing occurs

24. Streams

25. HANDOUT—Stream Order

26. River Continuum Model  Stream order determines: Productivity Productivity Reliance on autochthonous vs. allochthonous organic matter Reliance on autochthonous vs. allochthonous organic matter Autochthonous—produced in the streamAutochthonous—produced in the stream Allochthonous—produced outside the stream,Allochthonous—produced outside the stream, washed in from surrounding landscape or from upstream

27. River Continuum Model  Low Order (1st to 3rd): Headwater streams Headwater streams Primary production < Respiration Primary production < Respiration Autochthonous production fed by periphyton and some vascular plants Autochthonous production fed by periphyton and some vascular plants Allochthonous leaf fall is highly important and makes for rich communities of benthic invertebrates Allochthonous leaf fall is highly important and makes for rich communities of benthic invertebrates

28. River Continuum Model  Middle Order (4th to 6th): Large creeks and medium-sized rivers Large creeks and medium-sized rivers Primary production > Respiration Primary production > Respiration Production fed primarily by submerged macrophytes due to less shading in wider stream and clear water Production fed primarily by submerged macrophytes due to less shading in wider stream and clear water

29. River Continuum Model  High Order (7th to 12th): Large rivers Large rivers Primary production < Respiration Primary production < Respiration Greater current velocity makes water more turbid Greater current velocity makes water more turbid Community fed by Community fed by Upstream allochthonous productionUpstream allochthonous production PhytoplanktonPhytoplankton

30. Ward. 1992. A Mountain River, Chapter 23 in River Handbook, P. Calow and G.E. Petts, eds.

31. Riffle-Run Organization of a Stream  Most typical of medium- sized (4 th -6 th order) streams  High discharge scours sediments from pools, to accumulate in riffle zones  Pool—mud, silt, bedrock  Riffle—gravel, cobble Chunky River, Mississippi

32. River Bend  Steep, eroding outer bank  Sand deposits on flat inner bank  Differ in current, depth, and deadwood accumulation Upper Leaf River, Mississippi

33. Conecuh River Alabama Leaf River Mississippi

34. Oxbow Lake  Old river bed cut off from flow (except during floods)  Functionally very lake- or pond-like

35. Dammed Rivers: Reservoirs Mississippi River, Dubuque, IA

36. Reservoir  River-Lake Hybrid Model  Nutrients/sediments—highest at river end due to current velocity  Light penetration—Highest at lake end due to upstream turbidity  Productivity—highest in middle, transitional area Best combination, nutrients + light Best combination, nutrients + light

37. HANDOUT—Kimmel et al. 1990

38. Reservoir  River-Lake Hybrid Model  Transitional zone placement relative to dam depends on water’s residence time River-like reservoirs: River-like reservoirs: Short residenceShort residence TZ near damTZ near dam Lake-like reservoirs: Lake-like reservoirs: Long residenceLong residence TZ far upstreamTZ far upstream

39. Tombigbee River, Alabama

40. Satellite Image of Rhode Island