Transcript Communities and Ecosystems

Chapter 31
 Depend on many interactions
 Between living things
 Between living things and nonliving parts of the
environment
 Organism relationships
 Nutrient/Chemical cycles
 Community: all of the interacting living things in an
environment
 Various sizes
 They overlap and are not predetermined entities
 Ecosystem: all of the communities and the physical
(nonliving) parts of an environment
 Species richness: a total listing of all the species in the
area
 See pg 559—differences between a pine forest and rain
forest
 Can vary from place to place in types of species and
number of species
 Diversity: species richness and distribution
 It’s not just how many species are in an area
 What if there is only one member of a given species?
 What if one type of plant represents 99% of the plants
in that area?
 Change in an ecosystem over time
 Can be due to:
 A disturbance
 Volcano eruption, fire, tornado
 Gradual change over time
 End of an ice age, gradual warming, continental drift, silting
in a body of water
 Two Types
 Primary—have to make soil from scratch
 Secondary—soil and maybe some seeds already present
 First to appear in an area
 Small, quick growing, hardy, opportunistic
 Often lichens and mosses
 Can break down rock into dirt
 Add organic matter  soil
 Pioneer animal species = herbivore insects followed by
small insectivores
 Equilibrium species
 Larger, k-strategy individuals
 Deer, wolves, large trees
 Ecological Niche—the role an organism plays in its
community
 Habitat—the physical place where an organism lives
 Both can range from very general to very specific
 Recall risk factors for extinction
 Competitive Exclusion Principle
 No two species can occupy the same niche at the same
time
 Competition between two species in the same niche will
eventually lead to one of the species being displaced in
that area
 Small or large scale
 This can lead to specialization of niches
 Resource partitioning; pg 563
 Increases specialization and can drive evolution
 Can be very subtle
 I’ll scratch your back if you’ll scratch mine!
 Both members benefit, sometimes to the point of
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codependence
Pollinators and flowers
Lichens
Ants and various plant
Pg 564, middle paragraph
 Keystone species—one species that is
disproportionately important for the stability of an
ecosystem
 Not always the most numerous
 Bats, grizzly bears, otters
 Native = indigenous to an area
 Exotic = nonnative
 Can greatly disrupt an ecosystem
 No natural predators or competitors
 Native species have not had a chance to evolve defenses
 Ex: myrtle trees in Hawaii, fox and rabbit in Australia,
brown tree snakes in Guam, black rats in Galapagos,
zebra mussels in U.S.
 Autotrophs—make their own food
 Photosynthesis—plants, algae, blue-green algae
 Chemosynthesis—caves and hydrothermal vents—all
bacteria
 Heterotrophs—get food from consuming other
organisms
 Herbivores
 Carnivores
 Omnivores
 Decomposers—feed on detritus
 Law of conservation of matter—remember???
 What we have on Earth is all we have, so individual
atoms MUST be recycled
 Many interactions between autotrophs, heterotrophs,
and parts of the physical environment as well
 Water in ground, on ground, in air
 Elements sometimes sequestered in rock layers for long
time periods
 Cycling of atoms can be quick or very slow
 Food chains—follow one flow of energy from
autotroph  herbivore  carnivore (or omnivore) 
decomposer and back to autotroph
 Each step is a trophic level
 Number of organisms at each trophic level gets smaller
and smaller—Rule of 10
 Forms an ecological pyramid
 Food webs—follow total energy in a community with
all of its twists and turns
 Life, physical world recycling atoms
 There’s a cycle for almost everything
 Main:
 Phosphorous
 Nitrogen
 Carbon
 Rate at which producers capture and store energy and
nutrients
 Pg 576—deserts vs. swamps and rain forests