Ecosystems Development and Productivity

1. Ecosystems Development and Productivity ENV 326 Lecture 14 2007 Erika Nowak

2. Ecosystem Development and Productivity: Definitions Ecosystem a more-or-less self-contained assemblage of all the organisms in an area (community), together with their physical environment, and including all the energetic interactions and material cycling that link organisms with one another and with their physical environment.

3. Definitions Tansley 1935 (Ecology): �... the biome, considered together with all the effective inorganic factors of its environment, is the ecosystem. In an ecosystem the organisms and the inorganic factors alike are components which are in relatively stable dynamic equilibrium...�

4. Definitions Ecosystem ecology moves beyond the consideration of individual organisms� All the interacting parts of the physical and biological worlds. -- Ricklefs 1990 The biological community in an area and the physical environment with which it interacts. -- Ehrlich and Roughgarden 1987

5. Ecosystem Ecology A thermodynamics perspective on ecosystems. Focuses on the movement and transformation of mass and energy.

6. Energy Flow Quick Review 1st law of thermodynamics:

7. Energy Flow Quick Review 1st law of thermodynamics: Energy conservation

8. Energy Flow Quick Review 2nd law of thermodynamics:

9. Energy Flow Quick Review 2nd law of thermodynamics: there is no �free lunch�, in terms of energetics universal law of increasing entropy �the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium� (Wikipedia)

10. Energy Flow in Ecosystems Energy flows through ecosystems; matter cycles Pools or Sinks are where matter is temporarily stored (assimilated) within the ecosystem, usually as biomass or organic matter. Flux = transfer from one pool to another (release of E) Budgets are an accounting of all sinks and fluxes of energy or a particular element

11. Energy Budgets Budgets are an accounting of all sinks and fluxes of energy or a particular element similar to a checking account (Ricklefs 1979) Income Expenditure Assimilated light energy Respiration (transported in) (transported out)

12. Ecosystem Productivity Gross Primary Productivity = Total amount of biomass produced by all autotrophs Net Primary Production (NPP) = Biomass left over after autotrophs have met their E needs (respiration) = Energy (as biomass) available to consumers You know that: 6CO2+ 6H2O ? C6H12O6+ 6O2 Provides (among other critical functions): Carbon sink O2 Food

13. Ecosystem Productivity How do you measure NPP? harvest and weight of biomass (Lindeman) gas exchange (respiration/assimilation) annual actual evapotranspiration, increases with temp and precipitation time to assimilate C-14 or other radioisotopes in different trophic levels (Odum)

14. Ecosystem Productivity What sets the limits to NPP in terrestrial systems? Highly variable, but some general patterns: NPP is not limited by light in most terrestrial ecosystems NPP limited more by temperature and moisture Nitrogen and phosphorus are often limiting In arid environments, NPP often is limited by water. Remember: CO2 - H2O tradeoff

15. Ecosystem Productivity What sets the limits to NPP in aquatic systems? Generally limited by nutrient availability especially P in freshwater systems Especially N in oceans (influences N:P ratios) In ocean, being near coasts and upwellings (vertical mixing) critical open tropical oceans have very low NPP

16. Ecosystem Productivity Global Patterns in NPP?

17. Ecosystem Productivity Global Patterns in NPP (Whittaker and Likens 1973, Human Ecology) Tropical forests= 5% total habitat, 28% NPP Temperate forests= ~2% tot. habitat, ~9% NPP Desert= ~8% total habitat, <1% NPP Open ocean= 63% total habitat, 25% NPP Nearshore ocean/estuary habitats= 0.4% total habitat, 2.3% NPP Swamps/wetlands= ~1% tot. habitat, ~5% NPP Cultivated land= ~3% total habitat, ~5% NPP

18. Ecosystem Development Revisiting Trophic Cascades Focused on consumer effects on ecosystem processes, not species richness as in keystone predator concept Bottom line: NPP can be affected by consumers Effects of predators on prey that alter abundance, biomass, or productivity of multiple trophic levels Examples?

19. Trophic Cascade Examples Introduced crayfish in SW US Grazing ungulates in prairie systems

20. Odum�s Theory of Ecosystem Development (1969, Science) Based on the principles of ecological succession Assumes progression of ecosystems from developing to mature stages Components: Community bioenergetics Community structure/richness Organism life history Nutrient cycling Selection pressure Community �homeostasis� (stability)

21. Ecosystem Development and Productivity - Human Effects Human appropriation of global net primary productivity (Vitousek et al. 1986; BioScience) Recall our definition of: Carrying Capacity - the maximal population size of a given species that an area can support without reducing its ability to support the same species in the future

22. Human Effects: Vitousek et al. 1986 NPP provides the basis for maintenance, growth, and reproduction of all heterotrophs (consumers and decomposers); it is the total food resource on Earth. Human beings are mobilizing a wide array of minerals at rates that rival or exceed geological rates. Examined impact by calculating the fraction of photosynthesis that humans have appropriated.

23. Human Effects 3 Ways to calculate appropriation of NPP: the amount people use directly all the productivity of lands devoted entirely to human activities also include productive capacity lost as a result of converting open land to cities and forests to pastures, or because of desertification or overuse

24. Human Effects Upshot: On lands, humans consume or co-opt an estimated 40% of Net Primary Production!We can�t use Vitousek et al. to directly calculate carrying capacity, because it depends on both the affluence and technology, as well as the size of the population. But they do make a convincing argument that current patterns of exploitation cannot support twice the current global population.

25. Other ways of measuring impacts If we cannot quantify the exact carrying capacity of Earth for Homo sapiens, how can we assess environmental impact in an intelligent and instructive manner? One approach: I = P A T I is the overall environmental Impact; P is the Population�s size; A is the Affluence (often measured as per capita consumption); and T is the environmental damage inflicted by the technologies used to supply each unit of consumption.

26. Impacts of I = P A T Some Observations: Rich nations have a population problem because A and T are large. Modest development in populous countries will have an enormous impact on the global environment, because the P multiplier is so large. Improvement in technology could allow improvement in quality of life for a constant population. Impacts can be lowered by reducing any of these factors, if the others are held constant; improvement in one area will be for naught if other areas are allowed to increase. T and A are very hard to measure. Often per-capita energy use is substituted as a surrogate for their combined effect.

27. The Holdren Scenario

30. Habitat Fragmentation Some ecological factors associated with fragmentation that do not necessarily pertain to habitat loss:  Isolation of habitat patches Lower with-in patch heterogeneity Greater between-patch variance Increased edge effects Others? What are likely ecological implications?

31. Habitat Fragmentation What are likely ecological implications? Loss of species �diversity� Richness (# of species) Evenness (# of individuals of each species) Spread of invasive species adapted to colonizing edge areas Loss of genetic diversity within patches

32. Human-dominated Landscapes All ecosystems are impacted, most terrestrial systems are profoundly affected by human activities. Environmental scientists must incorporate people into the problem identification, analysis, and the formulation of solutions.

33. Human-dominated Landscapes: A Local Example Swamps/wetlands= ~1% of earth�s total habitats ~5% NPP

34. Human-dominated Landscapes: A Local Example Bike path being built along Hwy 180 by Museum of Northern Arizona ADOT received permit from ACE to develop a portion of the path adjacent to/in a wetland (tiny spring-fed drainage) Residents of Coyote Springs noticed that ADOT had removed the old meandering spring flow and replaced it with a barren v-ditch Impacts? Solutions?

35. Reducing Human Impacts on NPP of Tropical Ecosystems: The Coffee Example How do your caffeine consumption habits affect NPP, carbon sinks, and an endangered species?

36. The Coffee Example: Shade Coffee With help: Manuel Santana-Bendix, Cafe Dona Ella Coffea spp. are normally understory trees or shrubs Berries are harvested when ripe (red) Seeds (beans) are removed from berry pulp, and sun-dried Beans are then roasted

37. The Coffee Example: Shade Coffee Bourbon varieties may live to 20 years High quality (most berries picked fully ripe) Requires intensive human labor through pruning Not high yield-producing Prone to diseases, esp. fungus Should promote maximum NPP over time (as a function of total leaf area) Promotes nutrient cycling, ecosystem stability and function, species richness

38. The Coffee Example: Sun Coffee To increase production and decrease disease, new cultivars were bred to tolerate full sun Competition with native species reduced Lower quality, bitter (unripe berries harvested) live 5-10 years maximum Requires fertilizer and herbicide inputs, does not like pruning Usually harvested by machine Cheaper to rip out and replant entire plantations Increases erosion runoff, habitat fragmentation Decreases NPP (?), ecosystem stability and function, nutrient cycling, and species richness

39. Ecological-Economic Impacts of Sun-grown Coffee Ecological (growers maximize production efficiency): Impacts on international food webs (through effects on overwintering migratory bird species) Water pollution Health impacts on farm workers Economic: Cheap coffee gluts the market, driving prices down (small, shade) Growers are not paid enough to cover costs of labor Small farms tend to fail

40. Odum�s Theory of Ecosystem Development (1969, Science) Assumes progression from developing to mature stages Components: Community bioenergetics Community structure/richness Organism life history Nutrient cycling Selection pressure Community �homeostasis� (stability)

41. Odum�s Theory of Ecosystem Development (1969, Science) Important because?

42. Odum�s Theory of Ecosystem Development (1969, Science) Important because: Tied together bioenergetic and traditional concepts of ecosystem function Included humans in the ecosystem made science-based suggestions for sustainable use of ecosystems At least 5 of these suggestions now accepted as best management practices