Week
1: Introduction to Class and Materials
A.
Course requirements and goals
1.
The course is generally aimed at understanding tropical biodiversity and
the causative mechanisms that may have produced it
B.
Format of facilitation
C.
Format of summaries
D.
Format of individual research project
E.
Format of individual research presentation
F.
Potential need to eliminate several days or shorten class times (only if
less than four students)
G.
Class schedule and modules in the course
H.
Daily meeting schedule
A.
Latitudinal gradient exists for many taxa
1.
This was the first pattern that attracted scientific attention to species
diversity
2.
Diversity for most TERRESTRIAL plants and animals is lowest near the poles
and increases toward the tropics (equatorial regions)
3.
Highest in tropical rainforests
4.
What is the characteristic structure of a rainforest as far as the number
of individuals per species? ANS: very few per species, but many species
per unit area
5.
Actually, if you look at the northern hemisphere (North America, Europe,
Asia) many fewer species are being described as new there, in comparison
to those in the Southern Hemisphere
a.
Nearly all of the insects that are found on England have been described
b.
Almost 90% of the species described in the tropics are undescribed
c.
This is a hindrance to those interested in doing large-scale faunistic
surveys
d.
Example of Steve Ashe’s cloud forest work and best habitat to preserve
6.
Originally described from trees
a.
Nearly a single species monoculture in the northern tiaga (Northern Spruce)
b.
Overwhelming diversity of the rainforest (as we’ve already discussed)
c.
Fig. 2.2 - relatively even progression in diversity as you go from north
to south - although the isoclines are not absolutely east-to-west in direction
(more later)
d.
Fig. 2.1 - a relatively neat regression line could be fit to these data,
but you’ll notice that there is quite a bit of spread at the lower latitudes
-- we’ll come back to this later
7.
Also found in many animals and plants (Tables 2.1-2.2)
a.
Difference between these two tables is that 2.1 shows all species that
were found in a region and how they were distributed north to south
b.
2.2 shows the species present at survey location points (not as thorough
on a small scale, but has a much larger area covered and included in the
study
8.
Why do you think that the organisms don’t show clean isocline lines and
that the spread in the number of plants found in the equatorial regions
is pretty broad? -- Generally, because there are more forces at work than
just latitude and increasing heat in determining climate (what were the
others? ANS: Temperature, humidity, wind, sunlight)
a.
So - what would you expect is the type of habitat that is at this point
(very low equatorial value)? ANS: probably coastal desert (Namib desert
off the west coast of Africa)
b.
Write their suggestions on the board as to why (at this point) the distributions
do not accord absolutely with latitude
A.
Exceptions that increase in diversity as you go north or south towards
the poles
1.
Sea birds - feeding on marine crustaceans and fish
a.
Why may this be important? Where do whales feed? Where are whales killed
and harvested? Where then is the greatest quantity and diversity of the
food on which the whales live? What do whales feed on? Marine crustaceans
and fish
b.
It has been advanced that it is just productivity that accounts for this
disparity
2.
Lichens - highest diversity and abundance occurs at high altitude or northern
climates, particularly where plants cannot grow
a.
Why may this be important? ANS: they are outcompeted by plants wherever
plants grow
b.
How does this jibe with the sea birds example? ANS: similar reason in that
it is available nutrients at the higher latitudes that allows for the Lichen
growth -- higher nutrient availability where plants are not there to outcompete
the lichens and use all the available resources (primarily light and growing
space)
3.
Soil Nematodes (primarily soil predators of small arthropods) - highest
diversity and abundance in the middle latitudes than in the tropics and
in northern latitudes
a.
This was attributed to the “partial ecological release due to the absence
of tropical competitors” by Proctor 1984-- What is “Ecological Release”?
ANS: when the main selective pressures that have been keeping the population
in check are removed and the species is “released” and can explode (in
the short term in numbers and abundance, but in the long term in the numbers
of species)
b.
Other possible explanations for this observation? Where is soil thickest?
Where is the soil condition ideal for soil nematodes (i.e., not frozen)?
c.
Again it could be thought to boil down to productivity and available nutrients
available to the nematodes - more soil in mid latitudes than in either
direction, and thus more arthropods
1.
Productivity!!
2.
This is the explanation that I lean towards for explaining why the tropics
are more diverse than elsewhere
a.
However there have been many examples where we observe an INVERSE relationship
between productivity and diversity
b.
Anyone remember the term for this seemingly paradoxical situation? ANS:
The Paradox of Enrichment
c.
When does it occur?
1.
Increasing quantities of nutrients in an area (say due to fertilizer or
manure effluent)
2.
Leads to algal blooms and eutrophication (what’s that?)
d.
Seems that the trend towards increasing abundance and species diversity
does not continue indefinitely, but rather is highest at intermediate productivity
levels
e.
Doesn’t eviscerate the explanation, only makes it more precise
A.
Age of topics
1.
Increasing age allows for greater number of species to evolve
2.
And for more to disperse to it
3. And for the community to come to a climax community
a.
And thus the more rare species that are only found in these types of communities
b.
What’s that?
C.
ANS: the terminal community that will be found in an area if left undisturbed
indefinitely
d.
OR the community where energy coming into the system (sunlight) = energy
leaving it (dead organic matter)
1.
Why is this important?
2.
More individuals, more opportunity and probability of speciation
3.
Plus you get a greater target effect -- what’s that? ANS: in island biogeography,
the larger the target, the greater the probability that a dispersing organism
will encounter your site
4.
Plus - you get a greater heterogeneity in habitats available to the organisms
1.
Glaciation did in fact disturb the tropics greatly through climatic changes
by expanding savannahs and decreasing the lowland rainforest area
1.
Why would this be important?
2.
ANS: increased pressure and ability to specialize on a diversity of hosts,
prey, etc.
1.
Why would this produce an increase in number of species?
2.
ANS: faster time through life cycle, more generations per time unit, more
opportunities for evolution to rapidly occur