Big Picture 03


BIG PICTURE
for Chapters 3—7
BIOSPHERE and ECOSYSTEMS
  • All species that interact with one another in the same location form a community.
  • A community plus its physical surroundings (rocks, soil, water, air) makes an ecosystem.
  • Similar ecosystems on different continents make up a biome.
    • Each biome is characterized by its average annual temperature, precipitation (rainfall or snow), and seasonal variation.
          Weather averages over long periods of time are called climate, which is an abiotic factor.
    • Terrestrial biomes (See also text pages 93-96):
      • Tropical rainforest: High precipitation and warm temperatures year-round;
        Greatest species diversity of all ecosystems; lots of very tall trees whose branches form a continuous canopy for abundant tree-dwelling animals and epiphytic plants.
      • Tropical grassland or savannah: Warm year-round; rainfall seasonal; lots of grass and many large herbivores (Africa has giraffes, elephants, zebras; South America has llamas, vicunas, capybaras; Australia has kangaroos, wallabies, etc.)
      • Tropical dry forest: Warm year-round but dry; fewer trees, birds and primates search for water during dry season.
      • Desert: Very dry, minimal precipitation; hot, especially at midday; plants with deep roots; most animals burrow and hide at midday; animals include small mammals, snakes, scorpions.
      • Temperate grassland (prairie or 'steppe'): Seasonal variation in both temperature and rainfall, fertile soils; lots of grass and herbivores; best agriculture (wheat, corn, vegetables).
      • Temperate woodland/shrubland (Mediterranean, Chaparral): Mild, rainy winters; warm summers; many bushes and small trees; agriculture for olives, wine grapes, apricots, pistachios.
      • Temperate forest: seasonal variation in temperature, soil rich in humus (dead leaves and other decaying organic matter); mostly hardwood trees with deciduous leaves, many rodents-- includes most of Eastern United States
      • Boreal (conifer) forest or 'taiga' (most of Canada, Norway, Sweden, northern Russia): Pine/spruce forests; heavy winter snow; fur-bearing mammals; no amphibians, few reptiles
      • Northwestern coniferous forest (Washington/Oregon): Similar to boreal forest but much less snow (lots of rain instead) and not as cold; plant and animal species quite varied.
      • Tundra: No trees at all, very cold and wind-swept, lots of snow, ice, and frozen barren ground (permafrost) with only low-growing plants; few animal species (mostly deer & furry mammals; polar bears along coasts)
      Map of biomes (differs a bit from textbook)
    • Rain shadows are local/regional influences on ecosystems: if steadily prevailing winds blow across mountains, they deposit lots of rain on the 'windward' (upwind) side and they send dry winds down the 'lee' (downwind) side, often creating deserts.
    • Marine biomes are not well characterized; they vary mostly by temperature (latitudinal) and depth. Only uppermost 'photic' zone has enough sunlight for photosynthesis.
      • Richest marine ecosystems are coral reefs in warm, shallow waters. Corals are colonial; they build up large reefs of calcium carbonate. They require symbiotic algae (so cannot live deep). Many hiding places for fish, etc.
  • WITHIN EACH ECOSYSTEM,  MATERIALS ARE RECYCLED:
    • Water cycle: Water evaporates from ocean and lake surfaces (also from leaves during transpiration); it then forms clouds.
      When a moist air mass cools, the water precipitates and falls as rain (or snow); it then flows downhill back to lakes and oceans.
    • Carbon cycle (simple):
      • 1. Autotrophs (mostly plants; also algae and cyanobacteria) take CO2
          from the atmosphere and "fix" it into sugars and various other carbon compounds.
      • 2. Heterotrophs (animals, bacteria, fungi, etc.) pass carbon compounds up the food chain;
          their respiration returns it to the atmosphere as CO2.
          Waste products (feces, dead leaves, shed antlers) and dead bodies are decomposed by fungi and
          bacteria; material is returned to the soil in a form that plant roots can absorb.
    • Oxygen cycle (also simple):
        1. Respiration by all organisms uses oxygen from the atmosphere and generates water and CO2.
        2. Photosynthesis by plants and other autotrophs splits water molecules and gives back O2 to the atmosphere.
    • Nitrogen cycle (very complex)--
        Main (inner) cycle:   Soil Nitrates are absorbed by Plants and used to make nitrogen compounds, especially proteins.
            Animals and other consumers convert plant proteins into animal proteins.
            Decomposers (bacteria and fungi) break down waste products and dead bodies and return nitrogen to the soil,
                mostly as ammonia and ammonium compounds.
        Outer cycle:   Nitrogen-fixing bacteria in soil or in plant root nodules convert atmospheric N2 into ammonium compounds.
            Nitrite bacteria convert ammonium salts into nitrites.
            Nitrate bacteria convert nitrites into nitrates that plants can use.
            Denitrifying bacteria convert some nitrates into atmospheric N2.
        Excess nitrogen runoff (mostly from agricultural fertilizers) can produce an "algal bloom" that uses up
            too much oxygen in the water, killing most organisms.

  • ENERGY ONLY FLOWS ONE WAY and is not recycled:
    • Plants and other autotrophs ("producers") use sunlight (radiant energy) to make sugars and other high-energy compounds.
    • "Primary consumers" are those that eat plants; "secondary consumers" eat primary consumers, etc.
    • All consumers pass 5-7% of the energy (inefficiently) up the food chain; most of the energy escapes as (useless) heat.
        This results in an "energy pyramid" (see text p.121); also a related 'pyramid of biomass' or 'pyramid of numbers' (p.122).


POPULATIONS and COMMUNITIES:
  • Age structure of populations: Click here for age pyramids . Compare text page 161.
  • Populations grow if they have enough food and other resources.
    In the early stages of growth (or with unlimited resources), populations tend to grow exponentially, doubling within a certain time, then increasing to 4 times the initial population in the next time interval, then 8x, 16x, 32x, etc. (see graph on text page 168).
    Eventually, a population reaches its carrying capacity when its resources restrict its further increase.
    As a population reaches its carrying capacity, it follows an S-shaped curve (logistic growth), as illustrated on text page 164.
  • Two species are said to interact if the population size of one affects the carrying capacity for the population size of the other.
    • Competition: If two species compete for the same food or other resources, then an increase in either one leads to diminished resources for the other.
    • Predation: If one species eats the other, then an increase in the prey provides more food to allow the predator populaton to increase,   but an increase in the predator population lowers the carrying capacity for the prey and results in fewer prey.
    • Parasitism: If one species lives inside the other (or on the body surface) and causes harm to the host, then more hosts will result in a bigger parasite population,  but an increase in parasites will diminish the health and survival of the hosts and lead to fewer hosts.   (Mathematically, the interactions of predator/prey and parasite/host are quite similar.)
    • Mutualism: If two species live together (symbiosis) and each species benefits from the interaction, then an increase in either population results in an increase of the other.
    • Commensalism is a type of symbiosis that benefits one species but has little or no effect on the other. Many trees provide habitat (including nest sites and hiding places) for birds, primates, rodents, and other species of animals, and perches for epiphytic plants. Many of these interactions are commensal, but, if the animal species pollinates the plant or disperses its seeds then it becomes a case of mutualism.
  • All the species that interact in a given location make up a community.
  • A community is much more stable if it includes large numbers of species of each type: many producers, primary consumers, secondary consumers, etc.
  • Within each community, each species lives in a habitat (a place to live) and also occupies a niche (a way of life, comparable to an occupation, or a role in the ecosystem).
  • Ecological succession: Some communities tend to be replaced by new species that invade and establish a new community. This type of succession may go through multiple stages of succession. Eventually, a stable climax community is reached, after which no further change takes place.
    In certain places, earthquakes or landslides or fires or large storms can wipe out a habitat. A few "pioneer" species specialize in establishing themselves quickly in such denuded (empty) habitats; then they are succeeded by more stable communities that replace one another until a new climax community is reached again.


HUMAN IMPACTS: