Notes on ecosystems and biomes

Our discussion of chapters 19 and 20 in the textbook will focus on some basic principles of ecology, structure and function of ecosystems, and the spatial pattern of major terrestrial biomes in relation to the pattern of global climates. The following outline highlights the major points covered.

Chapter 19

• Ecosystem, community, habitat and niche
• Primary producers and their principle characteristics
• Photosynthesis and respiration (expressed as simple chemical equations)
• Net vs. gross primary productivity and biomass
• Global distribution of net primary productivity
  
• Global comparisons of net primary productivity among terrestrial biomes and aquatic ecosystems
  
• Role of climatic factors (primarily light, temperature and precipitation) in spatial distribution of plant communities
• Latitudinal and vertical zonation; life zones
  
• Biogeochemical cycles for major elements: oxygen, carbon,, nitrogen
• carbon storage in biomass (living tissue and fossil fuels) and carbon cycling by photosynthesis and respiration; release of CO₂ by combustion and by breakdown of organic matter
  
• major forms of nitrogen and transformations from one form to another: nitrogen fixation (N₂ to organic-N), breakdown of organic-N to ammonia, bacterial conversion to nitrate, use of ammonia and/or nitrate as plant nutrients, denitrification converting nitrate back to N₂
  
• Human alteration of the carbon and nitrogen cycles, impact on ecosystems
  
• Limiting factors and environmental tolerance as an influence on the spatial distribution  of species and  communities, e.g. light, water, temperature, salinity, nutrients and trace elements, pH
  
• Structure of trophic webs or food webs:
• primary producers
  
• primary, secondary, tertiary consumers
• omnivores - organisms that feed at multiple trophic levels
• complex networks of feeding relationships
  
• importance of decomposers and recycling of carbon and nutrients
  
• efficiency of energy conversion from one trophic level to the next, limiting the number of steps in the ecological pyramid
• cycling of energy through an ecosystem (e.g. fig. 19.19)
  
• Concepts of ecosystem stability and reslieince
• Importance of biodiversity and its relation to ecosystem reslience, nutrient utilization and community productivity
  
• Adaptation of plant communities to environmental change; possible changes in spatial distribution under global warming scenarios and changes in length of growing season; implications of rapid climate change
  
• Ecological succession in plant communities as a response to disturbance
• pioneers ("opportunists") with early adaptive advantages, gradually replaced by perennials with longer life span, deeper roots, ability to compete under different light levels
  
• concept of patch dynamics and the ecological mosaic, as opposed to the concept of a stable "climax community"
  
• Ecology of disturbance, including fire

• Terrestrial ecosystems and the biome concept
• Major biome types (forest, svanna, grassland, shrubland, desert, tundra)
  
• Major growth forms of vegetation (trees, lianas, shrubs, herbs, bryophytes, epiphytes, thallophytes) [note: lianas are a type of epiphyte!]
  
• Major terrestrial biomes and their correspondence to climate types:
• Equatorial/tropical rainforest - Af climate
• high biodiversity, rapid cycling of nutrients, leached, infertile soils (most nutrients stored in biomass)
  
• canopy structure in tropical rainforest; importance of rapid development and deforestation
  
• Tropical seasonal forest/savanna - Am and Aw climates
  
• Midlatitude broadleaf (deciiduous) and mixed forest - Cfa and Cfb climates
  
• Needleleaf or conifer forest (boreal forest and taiga) and its montane varieties - D (microthermal) climates
  
• Temperate rain forest - marine west-coast climates (esp. Pacific northwest of U.S. and Canada)
  
• Mediterranean shrubland and chaparral - Mediterranean (Csa) climates; sclerrophylllous vegetation, adapted to frequent fire
  
• Midlatitude grassland and steppe - semiarid BSh and BSk climates
  
• Warm and cold deserts; plant community adaptation to arid conditions - BWh and BWk climates
  
• Arctic and alpine tundra - ET and H (highland) climates