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Tolerance" or the "Law of the Minimum": the abundance of
any species is controlled by the minimum availability of any
necessity of life (or the maximum limit of a negative
force), sort of like a chain being only as strong as its
weakest link.
Land plant abundance and distribution is most often limited by
water. The limiting resources for aquatic plants are most often
light energy and mineral nutrients. All plants must have
water, light, minerals, and carbon dioxide for producing their
photosynthetic "food."
For animals, the minimum resource (or limiting factor) most
often is food energy. Food is always dependent on plants,
either because the animal eats plants or because the animal's food
(its prey or host) is some other animal which eats plants.
Usually, therefore, plant abundance and distribution is the
most important factor in limiting animal abundance and
distribution because the minimum resource for animals most often
is food energy.
- Of course, for the critter which gets eaten the limiting
factor may be not its own food but instead the abundance and
motivation of its predators or parasites. That's
why your textbook focuses on Adaptations and the arms race
= Co-evolution of interacting species =
- foraging and host-seeking behaviors of consumers
evolve,
- consumers with defensive adaptations survive to pass on
their adaptations
- predators and parasites with mutations which confer new
and improved hunting prowess feed their offspring so that
stronger hunting pressure causes
- death of weakly-armed prey, but survival of individuals
with mutations for new and improved defenses makes it
harder for predators and parasites to find them
- so..... we have continuing cycles of .....
"Adaptation and
Counter-Adaptation"
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Law
of the Minimum
Law
of Competitive Exclusion
lecture
key points
sample quiz
web links
back to Bio103
home
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Key textbook points
.
- Overall goal: Define and give examples of producers, consumers
(predators, parasites, herbivores where the prey or hosts are
plants), and mutualists. Be able to describe examples of
adaptation and counter-adaptation.
- pp. 951-4 PARASITISM.
- Case study: Malaria. The ultimate
counter-adaptation has just been achieved: sequenced
genomes for the malaria parasite and its two hosts--
mosquitoes and humans-- may allow one host to replace
natural selection with artificial genetic engineering to
turn this whole situation into history. we
hope
You don't have to memorize all the technical terms,
but you should be able to explain how malaria parasites and
mosquitoes find us and what kinds of defenses we have evolved
so far. This activity is fine:
Activity 49.1 Life Cycle of the Malaria Parasite.
- General characteristic:. Write the script for the
typical parasite-host arms race
- pp. 954-8 PREDATION
- Case study. Wolves and Moose. Do they regulate
each others' population density? Explain.
- Prey counter-adaptations. List a bunch to be
prepared to explain, including "inducible
defenses."
- keystone predators. important concept
- pp. 958-961 HERBIVORY. Serious evo-eco
question: WHY IS THE WORLD GREEN? (In other words,
why haven't herbivores eaten everything and then died of
starvation?)
POSSIBLE ANSWERS:
(Why haven't ecologists agreed on which of these
is right?)
- "Top-down" hypothesis = carnivores.
- "Vegetarians need protein" hypothesis
- "The world is not green; it's prickly and tastes
funny" hypothesis
- pp. 961- 6 Competition for resources:
- Each species (=different kind of living critters) has its own
niche (=set of resource requirements).
- The resources may include specific habitat space for
nesting or hiding, water, food (including prey and hosts),
mineral nutrients--fertilizer for plants, light, services like
pollination and cleaning, etc.
, too.)
- Interactions among different species involve or affect
resources, and thus the presence of one species may affect another species' distribution
in time or space. Niche differentiation or partitioning causes "realized
niches." Adaptation to competition and
partitioning causes character displacement. Is
this "adaptation and counter-adaptation" different
from the co-evolution examples and principles earlier in
this chapter?
- limited resources and the Law of
Competitive Exclusion
LAW OF COMPETITIVE EXCLUSION: When two species compete for a limited
resource one species always eventually wins and the losing species becomes excluded
(locally extinct)
unless
- environmental heterogeneity (a range of resources in the natural habitat) allows one
species to survive just beyond the niche limits of the other competing species so that at least in
part of the habitat they're not competing at precisely the same time and space.
(see Connell's
barnacles)
- the losing species can re-colonize (re-immigrate or "hide") (=recruitment)
(see metapopulations)
- or the winning species is prevented from its monopoly by mild disturbances
(unpredictable weather, etc., predators, parasites).
(see keystone species)
[these exceptions are the interesting and important
parts]
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- pp. 964-6. MUTUALISM: Is "adaptation
and counter-adaptation" always an arms race? Outline
some generalizations about mutualism.
- CHECKLIST: parasitism, parasites, hosts, generalists,
specialists, ectoparasites, endoparasites, coevolutionary
arms race, adaptation, counteradaptation, transmission,
predation, predator, prey, herbivore, inducible defenses,
keystone species, herbivory, top-down hypothesis, poor nutrition
hypothesis, plant defense ("the world is prickly &
tastes bad") hypothesis, competition, niche, niche overlap,
principle (LAW) of competitive exclusion, competitive exclusion,
coexistence, niche differentiation, resource partitioning,
fundamental niche, realized niche, mutualism, reciprocal
parasitism, cost-benefit analysis
SAMPLE QUIZ
QUESTIONS
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http://wps.prenhall.com/esm_freeman_biosci_1/0,6452,501279-,00.html
- summary review #2, 3, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
- figure review #1, 2, 3
- Content Review #1, 2, 3, 4, 5, 6; Conceptual #1, 3, 4, 5;
Applying ideas #1, 2, 3
- If you're a science major or if you hope to make an
A, be sure to study (try to remember) some classic examples which
come up in conversations at biology nerd parties:
---barnacle (Connell's)
--Darwin's finches, of course,
because they exemplify niche partitioning
---Gause's Paramecium experiments, (fine print)
---any type of ant mutualism
---nitrogen-fixing symbiotic bacteria case and lichen case as examples of
mutualism (may have been mentioned on your field trip)
- And try these:
- A raccoon and some field mice are both raiding your peanut cracker
munchies. This is an example of
- a. realized niches
- b. competition
- c. resource partitioning.
- d. mutualism.
- e. parasitism.
- The barnacle example showed that when both species of barnacles were
present
- a. both species became more abundant.
- b. at least one species’ distribution was more limited than when each species grew
alone.
- c. one species eventually wiped out the other species completely.
- The Paramecium example showed that when both species of these protozoa
were present
- a. both species grew better.
- b. at least one species’ distribution was more limited than when each
species grew alone.
- c. one species eventually wiped out the other species completely.
- When a population of frogs has plenty of food, the other resources in the
froggy niche
a. are irrelevant; the world runs on energy.
b. could limit the abundance of frogs because frogs are controlled by the least available
resource.
c. will be consumed by the frogs’ competitors.
bbcb
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