Chapter 13.2 p 404 answers
Biology
1) Describe biotic and abiotic factors in a familiar ecosystem
Name an ecosystem (I choose the Sonoran desert), the biotic factors would include
anything living there including the plants - Saguaro Cactus, mesquite, ocotillo, the animals –
sidewinders, roadrunners, Turkey Vultures, scorpions, plus the bacteria, fungi etc. The abiotic
factors would include the lack of rain, the hot days and cold nights, the rocky and sandy soil low
in nutrients, etc.
2) The removal of a keystone species can raise OR lower biodiversity. If it is something the
ecosystem depends on, like the beavers creating new habitat with their pond, or like the Oak
trees that provide living places and many different foods, then the ecosystem will lose diversity
(there will be less different species). But if it is a species like the sea otter that keeps a
predator’s population low, its removal can decrease biodiversity.
3. Predict how a change in an abiotic ecosystem will affect biodiversity
If the amount of sunlight available decreases (lets say that trees grow tall to shade the forest
floor) then the populations of species that need lots of sunlight will decrease or disappear and
other species will replace them. Biodiversity will decrease at first, until the new species arrive
to fill their niches.
Chapter 13.2 p 404 answers
Biology
4. I think that humans are definitely a keystone species. We change ecosystems in a way that
decreases biodiversity (cutting down forests, changing natural ecosystems into farms, cities,
etc., and hunting large predators to extinction. We can also increase biodiversity by bringing
new species into an ecosystem- with unpredictable results.
The test is, if humans were to disappear from an area, would the ecosystem change in
other ways??
Chapter 13.6 p 419 answers 1-5
1) An energy pyramid shows visually how energy is distributed between, or
passes through, the trophic levels in a community. Energy pyramids show
how much of the energy that is captured by producers is passed up to each
level of consumers that depend on the producers of the community.
2) Instead of estimating energy transfer, a biomass pyramid shows the
amount of living material – the dry weight, at each trophic level of the
community, a pyramid of numbers just says how many organisms are at
each level
3) You would put the source of energy at the bottom of the pyramid and the
feeders on top of it. It would look like this:
20 Fleas
1
d
o
g
4) 10 kcalories are left at the 3rd level
90% lost at
each level
10kcal
kcal
100 kcalories
1000 kcalories
Chapter 13.2 p 404 answers
Biology
5) Because so much of the Sun’s energy captured by producers is lost at each
level, if you eat organisms from low trophic levels, less energy is lost by the
time it gets to you than if you eat organisms from higher trophic levels.
Or
If you eat beef, 90% of the energy of the plants the cow ate is already gone
by the time you kill the cow.