Bio 356 announcements. No lab this week. Climate diagrams due today Lab 7 due Wed Dec 4

Transcription

1 Bio 356 announcements No lab this week Climate diagrams due today Lab 7 due Wed Dec 4

2 Tropical wet forest Temperate grassland Temperate woodland Tropical dry forest Desert Tropical savanna Mediterranean shrub Tundra

3 Climate diagrams Why do different places on the planet differ in temperature and rainfall? What vegetation and adaptations characterize organisms in each biome? Compare sites in terms of how different the extremes are from average. Did any shift in biome?

4 Biology 356: Lecture #10 Ecosystem Ecology

5 Outline Introduction to disturbance and succession Mechanisms of succession Mechanisms of stability

6 Disturbance is any event, relatively discrete in time, that removes biomass. Succession refers to a (predictable) replacement of species in a particular place over time. It generally follows a disturbance.

7 Examples of ecological disturbance If disturbance eliminates vegetation and soil Primary succession Volcanos, glaciers If disturbance maintains soil Secondary succession Fire, hurricanes, old fields, logging, biotic disturbance

8 Natural disturbances: Fires, Glacial retreat Yellowstone fires, 1988 Glacier Bay, Alaska soil exposed <20 to 200 years Ecologists study chronosequence

9 Natural disturbance example: Volcano

10 May Magnitude 5.1 earthquake 400 m of peak lost in lateral blast Ash rose to 20 km above sea level, traveled 95 km/hr

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13 Pyroclastic flows

14 Debris avalanche hummocks 2.3 km 3, 240 km/hr

15 Mudflow

16 Lateral blast effects

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18 Human-caused disturbances: Agriculture, forestry

19 Hubbard Brook experiment = classic study on ecosystem response to deforestation Measure water flow and composition in stream exiting forested and deforested watershed

20 Disturbance: Elwha river dam removal Image credit: M. Black

21 Disturbance and succession: conclusions Disturbance removes biomass, and succession describes the patterns of change that follow disturbance. Disturbance regimes differ in area, frequency, and intensity. Primary and secondary succession differ with respect to soil structure remaining after disturbance. Humans have a profound impact on disturbance regimes.

22 Outline Introduction to disturbance and succession Patterns and mechanisms of succession Mechanisms of stability

23 Changes in ecosystem structure and function through succession Diversity Biomass or Production Nutrient cycling efficiency Time

24 Changes in ecosystem structure and function through succession Diversity Late-successional systems have more habitat complexity Time But competitively superior species may reduce diversity when particular resources are considered

25 Roger del Moral s photos

26 Roger del Moral s photos

27 Roger del Moral s photos

28 Roger del Moral s photos

29 Roger del Moral s photos

30 Roger del Moral s photos

31 Richness and diversity on Pumice Plains of Mt St Helens in 5 community types (del Moral et al. 2012)

32 New community types appear Vegetation cover on a barren plain of Mt St Helens (del Moral et al. 2010)

33 Changes in ecosystem structure and function through succession Nutrient use efficiency Time Late-successional systems have efficient nutrient cycling Therefore latesuccessional systems have low nutrient loss

34 High nutrient losses when vegetation was removed Red = deforested Purple = reference

35 Following a disturbance, species accumulate and then plateau, but this can happen at different temporal scales from days (Fig. 20.8) to months (Fig. 20.7) to thousands of years (Fig. 20.3).

36 Following disturbance, biomass tends to build up over time, including living biomass (Fig and Fig ) and organic material in soil (Fig ).

37 Through succession, all types of nutrients accumulate in abiotic components of the environment (Fig , 20.12, 20.13) because loss rates decline (Fig , 20.15) or retention increases (Fig ).

38 In terrestrial environments, early-successional species tend to be smaller or shorter than later-successional species (Fig. 20.3).

39 Mechanisms of succession Facilitation: few species can survive in early succession; these species then modify the environment, and promote the establishment of other species. Tolerance: all species can survive in early succession; species are slowly eliminated as the environment changes. Inhibition: all species can survive in early succession; the first species to arrive modify the environment and prevent the establishment of other species.

40 Examples After glaciers retreat, mosses and lichens are the first colonizers, and they build soil that is necessary for larger plants to grow. Mechanism = But in the rocky intertidal zone, leafy green algae colonize and grow rapidly, and they prevent establishment of other species until eaten by crabs. Mechanism =

41 Mechanisms of succession Colonizing (ruderal) species are replaced by competitive species through succession. At the community level, richness increases and then levels out (diversity may eventually decline). At the ecosystem level, biomass, production, respiration, and nutrient retention increase then level out. Whether later species are facilitated or inhibited by earlier species in succession, or simply better tolerate changing environmental conditions, can be tested by removal of early species.

42 Time 0 Time t Test for mechanism of succession: Remove early species Response: timing of dominance of later species

43 Time 0 Time t Test for mechanism of succession: Remove early species Response: timing of dominance of later species If successional sequence accelerates, then

44 Time 0 Time t Test for mechanism of succession: Remove early species Response: timing of dominance of later species If successional sequence accelerates, then If successional sequence is delayed, then

45 Time 0 Time t Test for mechanism of succession: Remove early species Response: timing of dominance of later species If successional sequence accelerates, then If successional sequence is delayed, then If successional sequence does not change, then

46 Time 0 Time t Test for mechanism of succession: Remove early species Response: timing of dominance of later species If successional sequence accelerates, then inhibition If successional sequence is delayed, then facilitation If successional sequence does not change, then tolerance

47 Following a volcanic eruption, an ecologist observes that species composition is dominated by species A for 10 years, but after that point species B is more common. Concurrently, the ecologist carries out an experiment in which species A is removed from some plots. If species B becomes common in the removal plots after 5 years, then tolerance succession is occurring at the site. If species B becomes common in the removal plots after 10 years, then primary succession is occurring at the site. If species B becomes common in the removal plots after 5 years, then facilitation succession is occuring at the site. If species B becomes common in the removal plots after 5 years, then inhibition succession is occurring at the site. If species B becomes common in the removal plots after 10 years, then tolerance succession is occurring. If species B becomes common in removal plots after 15 years, then inhibition succession is occurring.

48 Outline Introduction to disturbance and succession Patterns and mechanisms of succession Mechanisms of stability

49 Stability some definitions Climax communities infer some ecological goal for succession. Ecologists instead refer to late-successional or steady-state communities. These are stable due to low levels of disturbance. Resilient systems recover rapidly from disturbance. Resistant systems are little affected by disturbance generally because particular species tolerate disturbance.

50 Let s consider drought as a disturbance Updated at a.gov/oa/climate/res earch/prelim/drought /phdiimage.html

51 Biodiversity and stability studied in old fields in Minnesota species richness varied due to history of fertilization Low SR Moderate species richness Lowmoderate SR Moderatehigh SR Low SR High SR Plant biomass was measured annually at the end of the growing season How did biomass vary in a drought year across plots of different plant species richness?

52 Biodiversity promotes stability through the portfolio effect Resistance Tilman and Downing 1994 Particular species vary, but overall production remains more consistent because poor performance in one species is compensated by better performance in another

53 Biodiversity promotes stability through the portfolio effect Tilman and Downing 1994 Species-rich plots in 1993 were more similar to predrought biomass than were species-poor plots. (Resilience)

54 Rothamsted plotsfertilized grasslands also demonstrate stability at the level of functionally-similar species, although particular species vary more dramatically

55 Undisturbed, resistant, or resilient? Algal biomass rapidly increases in upwelling zones of a creek within 2 months of a flash flood removing most of the biomass. Saguaro cacti slowed their growth in a year of extreme drought, but did not die, thus contributing a large fraction of the plant biomass over a long time period. Prior to industrial forestry, large expanses of Washington contained similar species composition of trees because steady-state communities reflected broad temperature, moisture, and soil conditions.

56 Linear regression the basics Dependent variable Dependent variable Group A Group B T-tests: calculated t values express how much of the total variation comes from mean differences between two groups Continuous independent variable Regression: calculated t values express how much of the total variation comes from the slope of the line

57 Linear regression the basics Dependent variable Continuous independent variable Regression: best fit line minimizes the squared distances between each point and the line

58 REVIEW What are 4 major types of indirect effects? Design studies to test their importance in an interaction web. What is trophic efficiency in the following case? Plant production = 100 kj/area/time. Cows eat 20 kj/a/t. Cows defecate 16 kj/a/t. Cows produce 0.5 kj/a/t. Calculate connectance. Test mechanisms of succession among plant species Birds Grasshoppers Grass Wolves Cows Forb Legume Herb