MY REMAINING LECTURES FOR TEST 3
ECOLOGY -- INTERACTIONS UNIT
Chapter 13: Competition -- don’t forget
my images page on my website for chapter 13
Intra-/interspecific; interference, resource
(exploitative) competition
Intra- within individuals of the same species;
inter- between individuals of different species.
Resource (exploitative) – does not have to be direct fighting; this can be
different plants competing for the same
soil nutrients but not DIRECT interference competition, where
individuals do directly interact
Damsel (and other) fish example –
on page 283.
This is interference competition where the fish directly compete for
space in the coral reef. This can
be both within (intra-) and between (inter-) species of fish.
Pine forest root trenching experiment
– also on page 283.
When a trench was cut between some pine trees in the forest, and the
roots of these nearby pine trees cut, there was a sudden burst of growth in the
herbaceous plant growth and seedlings of trees in the trench.
This suggests that these plants, whose seeds were lying dormant in a seed
bank, have been released from the resource competition and “allowed” to grow.
Intraspecific Competition -- the logistic growth
curve can have the assumption with it that intraspecific
competition for limited resources
largely determines K.
Examples:
PLANTS
Sorghastrum nutans (competing for N in soil); Medicago sativa
(Alfalfa)
See second and third images (figs. 13.3 and 13.5 in
your text)--
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2013.html
With Sorghastrum nutans, when grown in low
density, increasing nitrogen content of the soil (to a point) resulted in
increased size of the plants. Not
so at high density of the plants, where there is still not enough nitrogen for
individual plants to grow larger.
With Medicago sativa, the density of plants gets lower and lower as they
mature, suggesting that some have a distinct advantage and crowd out others
(others die) as they get bigger.
This process is called, as you will see below, self-thinning.
Two important results can occur as
plants are grown in increasing density:
1. Low
density -- plants of same species may be larger than when grown under higher
density. WHY?
(S. nutans example above)
2.
Self-thinning -- exhibited by many plants; the idea being that as a patch
of one species
grows, more and more of the biomass is in fewer and fewer large individuals.
WHY?
(M.
sativa example above)
Examples:
ANIMALS
Homopterans
-- aphids, planthoppers, leafhoppers. All share a feeding habit almost
unique
in the insect world -- can tap into flowing "sap" with a very flexible "beak"
At higher densities, these insects experience reduced survivorship, slower
growth and
development, resulting from reduced protein, water content and photosynthetic
capability
of host plants.
(see figure 13.6 in text; fourth and fifth images on my
Chapter 13 webpage)
Isopods
(Grosholz) -- supplementing food APPEARED to have little effect on survivorship
(though Grosholz used what turned out to be rather low densities of isopods
– 50 or 100 in a third of a
square meter plot; densities
can be as high as 2000 per square meter in nature), but higher
density decreased survivorship, apparently because of cannibalism. Is
there a possible
paradox here? Should Grosholz have done further experiments to clarify
food limitation?
With such low densities compared to natural
populations, supplementing food may not have been necessary at ALL in the plots,
so it is possible that at higher densities extra food WOULD have made a
difference.
Niches -- a
niche consists of all the necessary factors to allow a species to subsist in a
particular
place and time. Another way of
looking at the word niche would be that the niche represents the
role the species plays in the
ecosystem -- all its interactions, including what it eats and, in turn,
acting as food for other predators.
One important result of this definition is that the niche does
not exist without the species.
Although you may see the discussion of empty "niches" in various
ecosystems, technically this is
strictly an incorrect usage of the term as there IS no niche without
the species, as indicated, and there
may be no single species that can "fill" the "niche" that is
being considered empty -- instead, IF
species "fill" the niche, it could be many species that divide
up the "empty niche".
Fundamental vs. Realized Niche -- realized
niche breadth necessarily narrower than fundamental
niche
breadth.
We discussed this before; the realized niche is what an organism actually does
in a given
place and time, and the same organism in different places can have
different realized niches.
The Competitive Exclusion Principle --
local extinction; as opposed to resource partitioning re-
sulting from
character displacement (remember MacArthur's warbler study in Chapter 1?)
The idea here is that if you have two species
utilizing the same resources in a given place, that one may be a superior
competitor and ultimately exclude the other species in that place.
(The other alternative is, as we discussed before, not only with the
warblers but with Darwin’s finches (see Fig. 13.8, and the image on my webpage),
that the two species partition the resources, with the two species evolving to
use different parts of the available resources, a phenomenon called character
displacement).
Examples:
ANIMALS
the warbler
example mentioned above
the classic:
Galapagos (Darwin's) Finches -- Beak width and seed size. Different
species
feed on different sized seeds based
on beak width and length. During drought times (remember
from Chapter 11), smaller & softer
seeds eaten first, leaving larger & harder seeds. So drought
may impact the smaller species more
severely, and within species, it may be the larger, stronger
individuals that survive through the
drought. So, food and water availability largely shape the
niche of the finches (of course,
many, many organisms are largely influenced by food/water)
Interspecific Competition -- Mathematical Models. (an extension of
the Lotka/Volterra models)
This involves modifying the logistic growth curve to include competitive
effects.
dN1/dt = rmax1
N1 ((K1 - N1- α12N2)/K1)
This represents growth of species 1 with affects
on numbers from competition with species 2.
dN2/dt = rmax2
N2 ((K2 - N2- α21N1)/K2)
This represents growth of species 2 with affects
on numbers from competition with species 1.
α12 &
α21 are competition coefficients, where the first
represents competitive effects of species
2 on species
1, and the second represents competitive effects of species 1 on species 2.
If α12 > 1, then
competitive effects of species 2 on 1 are greater than intraspecific effects.
If α12 < 1, then
competitive effects of species 2 on 1 are less than intraspecific effects.
Likewise, if α21 > 1, then competitive effects of species 1 on
2 are greater than intraspecific effects.
and, if α21 < 1, then
competitive effects of species 2 on 1 are less than intraspecific effects.
It should also be obvious (hopefully) that α12
and α21 can BOTH be less than one, meaning that individuals
compete for resources more with individuals of their own species and not others.
Indeed, in communities where species have been interacting for a long time, this
is what we would EXPECT, as different species should have somewhat different
needs from each other, whereas individuals of the same species will have the
SAME resource needs, and therefore higher levels of competition.
If either competition coefficient is > 1, then you ultimately might
expect competitive exclusion of the species with the lower competition
coefficient. Understand that BOTH
competition coefficients cannot be >1; if one is >1 then the other WILL BE <1.
Also understand if α12 = 1, then α21 will also = 1
(meaning they equal each other) which means individuals of these two species are
equivalent competitors, and one individual of one species will have the same
competitive effect as an individual of the other.
Zero population growth will occur
for each species when:
N1 =
K1 - α12N2 (for species 1)
and N2 =
K2 - α21N1 (for species 2)
Let me help break this down.
The whole idea here is that the higher number of another species of
competitor there is, and the stronger the competition (indicated by the
coefficient), the lower the possible number of the first species.
So, if either N2 or α12 is low, then there will be
little impact on the carrying capacity for species one.
The higher either of those numbers get, then the greater the impact on
species one. Indeed, you can look
at K1 - α12N2 as representing the current lower
carrying capacity for species one because of species two.
On the test, you will be GIVEN the above equations,
and be expected to indicate what each of the factors represents.
And you would be expected to find out what N1 and N2
would be at the new carrying capacity (zero population growth) given the
competition coefficient, carrying capacity and number of the other species.
Hopefully, it is obvious that with
the added competition from another species, the ACTUAL
value for K
COULD go down for both species. Also, needless to say, if you added other
competitive
species, the equation becomes more complex, but K COULD "decline" for
EACH species
involved. However, depending on competitive capabilities of the species,
one could
exclude the other, or they could partition the resources and coexist (see pg.
290)
Laboratory Examples:
Paramecium
species: aurelia and caudatum
See Figure 13.15
Grown separately, both species quickly reached a K based on intraspecific
competition,
and K was higher for aurelia on both half (HS) and full strength (FS)
growth media.
Grown together, aurelia outcompetes caudatum, w/ complete
exclusion on HS in 16 days.
Tribolium
(flour) beetles: confusum and castaneum
See Figure 13.16
Grown separately, the species both did approximately equally as well.
Grown together, castaneum outcompetes confusum when conditions
were warm and
humid, but confusum outcompetes castaneum when conditions were
cool and drier.
Under intermediate conditions, the species first establishing a pop with greater
numbers
typically wins out -- the priority effect.
There will NOT always be a priority effect, but it
is a real phenomenon in many cases.
Clearly, competition can have a very strong influence on shaping niches
in the lab. What
about in
nature?
Competition and Niches
Natural examples:
PLANTS See
Figure 13.18
Bedstraw (Galium)
species on acidic (saxatile "wins") vs. basic (sylvestre "wins")
soils
Both establish healthy populations on a variety of soils when grown separately
Natural examples:
ANIMALS
See Figure 13.19 and 13.20, and my webpage
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2013.html
Barnacles:
Chthamalus and Balanus (mentioned before in Chap 9, pg. 203)
Competition critically important in middle intertidal, but
desiccation-resistance becomes
more important in upper intertidal, and predation becomes more important lower.
So the dessication-resistant Chthamalus does better in
the upper intertidal, and Balanus is a better competitor in the middle
intertidal (and more predation-resistant in the lower intertidal).
Desert
Rodents: Dipodomys (Kangaroo rats; large granivores);
Perognathus (Pocket
mice; small granivores); and Onychomys (insectivorous rodents)
very ambitious study in SE AZ with large plots and removal strategies; we'll
discuss
this example at some length (make sure to read pages 295 and 296 carefully, and
understand figures on page 297).
See also my webpage.
In enclosures constructed in the natural
environment, when both Dipodomys and Perognathus were together,
Perognathus numbers were always very low, suggesting Dipodomys is a
better competitor than Perognathus. When Dipodomys was removed,
numbers of Perognathus went up quickly.
The Onychomys were unaffected by numbers of Dipodomys or Perognathus
(high or low), because they feed on a different resource (insects).
Character Displacement --
will expand further on our previous discussion of Geospiza
finches and
then other organisms. A definitive example of character displacement must
meet
several
criteria (page 296, 298; figures on page 298).
The criteria are numbered 1-6 on the bottom of page
296 and top of page 298. The
example (Fig. 13.25) shows that two separate species of finches, when they were
the only species on a particular island, showed a similar range of beak depths
(though fuliginosa is a bit smaller than fortis).
However, when both occur together on an island, fuliginosa beak
depth shifted downward a bit and fortis beak depth shifted up.
This suggests that when they occur together, they evolve to use separate
species of seeds, instead of overlapping and competing.
Chapter 14: Exploitative Interactions -- Predation, Herbivory,
Parasitism, Disease
See my webpage:
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2014%20&%2015.htm
Trophic levels in the ecosystem:
Plants (the producers), herbivores (first order
consumers; depending on plant consumed,
may or may not eat entire plant),
predators (second and higher level consumers; DO kill
food), parasites (feed on, but
do not usually kill, host), parasitoids (larva consumes host,
often from inside,
and matures as the host dies; functionally
equivalent to predators), pathogens (induce
disease; for the most part, functionally equivalent to . . . ?
-- that would be parasites most often).
All
consumers are exploitative, i.e., make their living at the expense of
others.
Complex Interactions -- There are far more
interactions than numbers of species. WHY?
Pathogens/Parasites that alter
Host Behavior
Examples:
ANIMALS
Starling (Sturnus vulgaris), Isopod (Armadillidium vulgare), and a
parasite (a spiny-
headed worm [acanthocephalan], Plagiorhynchus cylindraceus). The
parasite
changes the phototactic behavior (- to +) in the isopod. WHY?
(See Fig. 14.2).
Fungal parasites of moth caterpillars. Near maturation of the fungus
inside the host, the
caterpillar crawls to top of a plant, becomes stiff and dies. WHY?
In the first case, the parasite inside the isopod
(pillbug) makes the isopod crawl into the light, which makes the isopod an easy
target to get eaten by the starling.
The worm WANTS the isopod to do this, because to complete its (the
worm’s) development, it must do so inside the starling.
The worm then lays eggs in the starling’s gut, which are pooped out, and
then consumed by the isopods (and the cycle starts again).
In the second case, the larva is “coerced” to crawl up, so that when the
caterpillar dies, the skin will split open and allow the tiny fungus spores to
be carried away by the wind and affect others.
Examples:
PLANTS
Mustard (Arabis sp.) host and a rust fungus (Puccinia monoica).
Puccinia alters life
history of infected individual, causing plant to form a pseudoflower,
with sweet sticky
hyphae that attract "pollinators" to move spermatia from one fungus to another.
Flies
are the most common and effective rust fertilizers, but bees and butterflies
also can.
Infected plants may be killed, though some survive . . . however, those that do
never
produce an actual flower, so fitness of infected
plants is zero.
See Figs 14.4 and 14.5.
Competition/Predation/Parasitism
overlap
Obviously, it will be difficult to untangle the different interactions and their
individual
effects on organisms; some experiments, however, show clear alterations in
numbers
and success due to competitive and exploitative interactions.
Examples:
Tribolium castaneum/confusum See
Fig 14.6.
Besides being affected by humidity/temperature (see the
competition information in Chapter 13 above
for this example), a
parasite (Adelina tribollii) also influences the competitive balance.
Both
species of Tribolium
are a bit cannibalistic on eggs, but T. castaneum strongly prefers T.
confusum
eggs when present
(explains a LOT about the competition experiments). The Adelina
parasite
strongly affects
castaneum but not confusum, largely shifting the competition in favor
of confusum.
Exploitation and Abundance -- Predator and prey
abundance intimately tied together
Already talked about several examples
(like the Canadian Lynx, Snowshoe Hare, Dwarf
Willow
example -- see below); more examples presented here in Chapter 14:
Examples:
1. Bats
and birds and arthropod densities on plants (in Panama).
See Fig 14.10.
Birds are largely daytime predators of insects and bats are nighttime
predators of insects. When birds
are excluded, arthropod density increased 65%, but when bats are excluded,
arthropod density increased 150%.
Bats have a greater influence on overall arthropod density (but we don’t know
for sure if each bat eats a lot more than each bird, or if there are just MORE
bats [or both]).
2.
Cactoblastis cactorum and Opuntia stricta in Australia; the moth was
introduced
from South America as a biocontrol
agent. Larval feeding introduces both fungal and
bacterial pathogens into the
Opuntia. Extremely effective -- reduced pops from 12,000 per
hectare to 27, and from area of
infestation of 24 million hectares to a few thousand. This same
moth, however, has turned out to be a
potential threat to North American Opuntia, as the
moth is now spreading out from
Florida north and westward.
Similarly,
rabbits overran parts of Australia as well early in the last century, but were
largely
brought under control by introduction
of the rabbit papilloma virus.
Both rabbits and Opuntia are now in low abundance in Australia, where
much lower density
allows them to escape the moth/virus
for a while (probably similar to where they naturally occur).
See images on my webpage for both Cactoblastis and the rabbit
papilloma virus
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2014%20&%2015.htm
3.
Foxes, Hares and Mange Mites (Sarcoptes scabiei) in Sweden; as mange
spread across
Sweden, reduction of fox populations
resulted in increased hare populations, as well as other
prey species of the fox (grouse, deer
fawns).
See Figs. 14.11 and 14.12, page 312.
This is a common effect – if you reduce the
populations of a particular predator, it only makes sense that some prey species
will become more abundant.
Dynamics -- Virtually all interactions are
dynamic; as indicated previously, parasites may reduce
host populations which may increase
populations of prey (what would happen to a predator
whose prey was affected by a
parasite/pathogen?). However, very few of these interactions
result in some sort of continuously
stable population levels for all species involved; instead, the
populations are temporally
dynamic.
Example: The classic example of the
Canadian Lynx/Snowshoe Hare/Dwarf Willow (and
other shrubs) shows how abundances of
each species are tied to each other, and may change
through time. See Fig. 14.14.
The up and down fluctuations run at about
10-year cycles, with the lynx
lagging behind the hare, and the hare lagging behind the dwarf willow.
The main reason is that as dwarf
willow numbers go up, then hare numbers follow since they eat the dwarf
willow, and then lynx numbers
go up since they eat the hares. As hare numbers go up, competition
stiffens and dwarf willow numbers go
down. This causes hare
numbers to decline, especially as lynx numbers are increasing. In turn, the lynx
numbers then crash. We have
this data going all the way back into the middle 1800’s because of
trapping data and pelt counts.
An added interactive effect we had not discussed before is that
the shoots of
the Dwarf Willow (and others) that the Snowshoe hares browse on increase
their terpenoids and
phenolic resins in response to high
rates of feeding, making the plants less tolerable to hares,
effects which can persist for up to
two years.
On the
predator side of the story, there are other predators which feed on Snowshoe
Hares,
such as foxes, coyotes, goshawks,
owls, and mink/weasel. It appears as though these predators
experience some population cycling as
well. Coyote diet may be 2/3 Snowshoe hares at peak
hare density, suggesting a predatory
functional and numerical response to hare density. Both
coyote and lynx numbers increase 6 -
7 fold during high hare densities, though the functional
responses were a bit different.
Both killed more than they could eat at the highest hare densities,
with coyotes in particular caching
for later, though coyotes kill the most during hare increases
(and apparently would kill more if
they could as their predatory response showed no sign of
levelling off), while lynx killed the
more when hare pops were declining already (probably
attacking already weakened
individuals). Experimental manipulation of food abundance and
predator abundance led to expected
results (see Fig. 14.15).
Mathematical Modelling of population cycles:
(more Lotka/Volterra "stuff")
The host/prey equation is as follows:
dNh/dt = rhNh
- pNhNp where "h" refers to host & "p" refers to
predators/parasites/pathogens
"p" is the RATE of predation/parasitism, which means that "pNhNp"
is the rate at which exploiters destroy hosts in the whole population.
Similarly for the
predator/parasite/pathogen population numbers:
dNp/dt = cpNhNp
- dpNp where "c" is a conversion factor
representing rate at which exploiters
convert hosts to offspring; "d" represents death rate
As before, with the modified competition equations,
on the tests I’ll provide you with these equations but you must be able to
identify the different variables. Remember that this equation started out as
simply dN/dt = rN. If you ignore
immigration and emigration, you can rewrite this equation as dN/dt = (b-d)N
(birth and death). Realize the host equation can be rewritten dNh/dt
= (rh - pNp)Nh. As such, for the host equation
equation , “r” (the intrinsic rate of increase) in this case is the birth rate .
. . which means that pNp represents the death rate.
This makes sense because death should increase as p (the rate of
predation) and Np (the number of predators) goes up.
Similarly, for the predator/parasite equation, it can be rewritten dNp/dt
= (cpNh - dp)Np, which again makes sense
because birth rate of the predator/parasites, namely cpNh, will
increase as predation rate, conversion efficiency and number of prey/hosts go
up.
SEE
Figs. 14.17 & 14.18. These equations tie numbers of hosts to numbers
of exploiters --
indeed, as Nh increases,
so, too, does exploitation rate (pNhNp), which, in turn,
declines Nh and,
in turn, Np.
So, increasing host and exploiter population numbers in this model lead to
significant
decrease in numbers later -- a cycle
that is repeated. Though this model has some obvious utility,
remember again, however, that NO
system in nature is so simple as to be ONE prey item with
just ONE predator or
parasite/pathogen.
Laboratory
attempts to produce cyclic fluctuations in exploiter/host populations have
proved
extremely difficult, though Utida was
able to show remarkable cyclic fluctuations between prey
bean weevils (Callosobruchus
chinensis) and it's parasitoid wasp (Heterospilus prosopidis) for up
to 112 generations in very small, simple, environmentally controlled, petri dish
habitats.
See Fig. 14.18.
Refuges -- to persist in the face of
exploitation, prey/hosts need refuges
Examples:
1.
Didinium nasutum (predators) and their prey Paramecium aurelia (see
Fig. 14.19)
Gause was able to produce
oscillations, but only if there was a refuge for the Paramecium, and
an immigration source (lab cultures)
for the Didinium.
2.
Huffaker and the ballooning/crawling herbivorous mite (Eotetranychus
sexmaculatus) and its
crawling predatory mite (Typhlodromus
occidentalis). The ballooning capability of the herbivore
allowed it to get to at least
temporary refuges on other fruits ahead of the predator, and resulted in
oscillations of predator-prey
populations (see Fig. 14.20)
For this experiment, the refuges were the tops of
oranges covered in petroleum jelly, making it difficult (but not impossible) for
the predatory mites to discover some (but not all) of the ballooning mites.
Spatial Refuges -- typically what we think
of in terms of refuges; Opuntia has not been driven
extinct in Australia as a
result of the introduction of the moth Cactoblastis cactorum. Why?
It
has spatial refuges
where, at least momentarily, it has escaped the moth.
Spatial refuges include any place that an organism
of any kind can “hide”.
Numerical Refuges -- "safety in numbers".
Hosts/prey can overwhelm exploiters, resulting in
predator
satiation. Schools of fish, flocks of birds, etc.
Examples: 1.
The thirteen and seventeen year periodical Cicadas
See Figure 14.22
These types of Cicadas only emerge on these multiple
year cycles. They emerge in such
massive numbers that no predator can eat even a small fraction of these. Here’s
a link to an image of such a cicada:
https://i.ytimg.com/vi/dSKAi6H9k3A/maxresdefault.jpg
2. Masting by plants (synchronous seed/fruit production), often
after disturbance (eg., fire)
Size as a refuge – Elephants, Redwood
trees, etc.
Though young may fall prey to
predators, many species reach an ultimate adult size that puts them
outside the
range of prey that can be handled by the predator.
This has led to "appear big"
behaviors -- cat defensive posture
Chapter 15: Mutualism -- Interactions where both benefit
Commensalism -- interaction where one benefits, and other is
largely unaffected
OBVIOUS examples of mutualism:
You and your E. coli; pollinators and flowers;
Make sure you spend some time looking at my webpage,
and the different shapes of flowers and the types of organisms that pollinate
them. These images are at the
beginning of the Chapter 15 images.
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2014%20&%2015.htm
fruits and seed dispersers; many plant (cellulose) eaters and their
digestive microorganisms – termites for instance; the
termites themselves cannot digest the wood (cellulose), but their gut has
microbes that can; in turn, the microbes get a safe nutrient-rich environment to
live in.
Facultative vs. Obligate
(A facultative mutualism is when the
mutualism is not required by one or both of the organisms, but they make use of
each other when possible; an obligate mutualism is when the two organisms cannot
live without each other)
Margulis (and others) and the
endosymbiont theory (now "proven" by DNA analysis)
The endosymbiont theory is that mitochondria and
chloroplasts were once separate organisms. It turns out that mitochondrial
DNA/ribosomes are indeed shared with bacteria, and chloroplast DNA/ribosomes are
indeed shared with cyanobacteria. This shows that these organelles did indeed
originate as separate organisms.
Plant Mutualisms -- (some already mentioned above)
Plants and Mycorrhizal Fungi -- a
400 million± year relationship
[a facultative mutualism]
Some plants grow root "chambers" for the fungi, other types form a
network around roots.
These fungi help plants w/ water extraction; nitrogen and
phosphorus/copper/zinc sequestration;
access to more phosphorus allows
plants to grow more roots, which allow them to claim more
water. The fungi, in turn, get
carbohydrates produced by the plant. See
Fig. 15.7
Conflict
of interest? The balance sheet is not always nice and equal.
Different mycorrhizal
species and even different strains
within the same species may not "treat" their hosts the same, and
may parasitize the host plant.
Fungi may be more likely to act parasitically in more fertile soils,
as plants release less soluble carbs
in root exudates in more fertile soils, which apparently has
selected for more aggressively
carbohydrate sequestering mycorrhizae. In Andropogon (bunch-
grass), both shoot growth and
inflorescence production are maximized when grown with associated
mycorrhizae from unfertilized
soils rather than fertilized.
This suggests that as long as the fungi are limited by
resources in the soil, that the interaction is truly mutualistic, as the fungi
truly “need” the plants under these circumstances.
Bullhorn Acacias and ant (Pseudomyrmex)
symbiotes
[an obligate mutualism for the ant]
Hollow thorns
for ant abodes. The ants are fast, aggressive, agile climbers, that
vigorously attack
growing vines/epiphytes or other
animals (caterpillars) that grow/eat the tree, which is already well
protected by nasty spines!
Additionally, the Acacias provide foliar nectaries and Beltian
bodies
to "keep" ants fed and on the host
tree. Acacias without ants both grow slower (leaves, shoots,
thorns, etc.) and show higher
infestation (by other insects) and lower propagation.
See Figs. 15.8 – 15.11
and my webpage
Conflict
of interest? The ants may be at odds with pollinators, both in
competition for nectar and
driving them away. However,
inflorescences offer scant nectar, and have an ant repellant chemical.
Aspen Sunflowers (Helianthella) and
Formica (and other) ants in the temperate zone
See Fig.
15.13/14
Ants are
attracted to this Rocky Mtn. sunflower because of extrafloral nectaries,
with nectar
rich in sucrose and numerous amino
acids, sufficient to keep the ants attention. During times when
the flowers are budding and just
opening, ants rigorously patrol the flowers and help deter potential
bud/seed predators, but once flowers
are open, the rays form a "shield" between the nectaries and
the open face of the flower, so the
ants do not generally interfere with pollinators.
There are
several species of ants involved here, and
NONE have an obligate
relationship with
Helianthella. The reason
probably has to do with, at least in some populations, late frosts which
kill the flowers (including the
nectaries; see Fig. 15.15) -- if ants were obligate, the ants would die
at that point. This event
actually helps the sunflower, as it kills any and all seed predators in that
year. Clearly, the TEMPERATE
climate plays a significant role in the nature of this mutualism.
Coral Mutualisms -- a mutualism between the coral and
algae (zooxanthellae)
Coral reefs
have exceptional diversity, and among the highest productivity of any ecosystem,
even
though surrounded by the nutrient poor ocean. How?
The mutualism: dinoflagellates that
are photoautotropic, and therefore productive. They live within
coral tissues, and receive nutrients
from the coral animal, while the coral receives organics from the
zooxanthellae produce during PS.
Corals induce release of nutrients from zooxanthellae when
needed by coral with chemicals that
change zooxanthellae cell membrane permeability, whereby they
release large amounts of fixed
carbon. The corals also keep growth of the zooxanthellae at 1/10 to
1/100 that of individuals cultured
separately, because of higher levels of carbon fixation. Doesn't
sound like a mutualism so far, but .
. .
The zooxanthellae appear to get access to higher levels of nutrients, especially
nitrogen (in
ammonia waste). Corals with
zooxanthellae partners, don't APPEAR to release ammonia, as it is
metabolized by the zooxanthellae.
Crab/Shrimp mutualism with coral:
The coral gain protection, and the crab/shrimp mutualists get food (extra fat
bodies produced)
and shelter.
Other examples of mutualisms: Orchids and orchid bees (obligate, see
video link), Yucca and Yucca Moths
(obligate), Mullerian mimicry (facultative), the honeyguide
and humans (see the "Applications" section
of chapter 15).
See the end photos on the webpage:
http://www.galeps.org/jadams/Biol%203500/Projectable%20images/Chapter%2014%20&%2015.htm
Orchids are pollinated exclusively by orchid bees
(see this video
Orchids and orchid bees), and the orchids provide
male bees with chemicals that they use to make pheromones to attract female
bees.
Yucca plants are pollinated exclusively by Yucca moths; the Yucca moth females
do not feed as adults, but appear to “purposely” pollinate the flowers (the
anthers are reflective in UV and therefore VERY easy for females to locate);
once pollinated, the female moth will lay one egg in one of three seed chambers,
and she marks it with a pheromone so that no other females will lay an egg in
that seed pod. Apparently,
sacrificing one set of seeds (which benefits the larva of the moth) is offset by
getting pollinated and producing two other sets of seeds.
Again, see the images at the end of my webpage.
Mullerian mimicry, which we have talked about
before, where two+ “bad” organisms look like one another, benefits all of the
members of the mimicry complex.
The Honeyguide example is an interesting one. Originally, the honeyguide,
a bird that likes honey (!) evolved to call when it located beehives, which
attracted honey badgers which would come and open nests, which would allow the
bird access. Turns out, however, that humans started using this strategy,
and honeyguide birds have evolved to call to humans instead of honey badgers to
guide the humans to the hives.
Evolution of Mutualism -- in general, we would
expect mutualism to evolve and persist in a population
when and where mutualistic
individuals have a higher fitness than non-mutualistic individuals. This
will happen when the benefits to the
two organisms exceeds the costs of the relationship.
