Transcript Species diversity - Marine Discovery at the University of Arizona

Announcements
• Midterm exam (1 hour) next week, here in
ILC. Bring your field trip data and calculator,
too (for after exam) Sign up next week for
date for presentations
• Extra Credit Opportunities (12 points each)
ASDB (5 volunteers) - contact Erin Keller
• Catalina Boy’s School (1 volunteer, next
week, male, 30 min drive with Lee, name and
ssn needed - contact Doug or Lee)
• 2 people for October 28th, Friday, 12-2:30,
Koffler 511
Marine Community Ecology
• How do marine animals get to the reef?
(reproduction and dispersal)
• How and where do they land on the reef?
• What determines who wins in competition for space
on rocks?
• What can rocky intertidal community tell us about
species diversity in general? (intermediate
disturbance hypothesis)
Marine Invertebrates - How do they
reproduce and disperse?
•Eggs and sperm
•Internal or external fertilization
•Planktonic larvae*
•Metamorphosis on the reef into adult
*Definition: larvae = a pre-adult form, often
free-floating in marine invertebrates
Tadpole larvae of adult
tunicate (Botryllus) above
Life cycle
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
R.K. Grosberg
Actinula larvae
of a hydroid
Phylum Cnidaria
Class Hydroidea
Tubularia
http://www.mbl.edu/marine_org/marine_org.
php?func=reveal&myID=BX10002
http://raven.zoology.washington.edu/embryos/
Veliger larvae
of a snail
Phylum Mollusca
Class Gastropoda
Calliostoma
http://raven.zoology.washington.edu/embryos/
http://www.marlin.ac.uk/species/
Calliostomazizyphinum.htm
Setiger
larvae of
a polychaete
worm
(note gut)
Phylum Annelida
Class Polychaeta
Serpula
http://raven.zoology.washington.edu/embryos/
http://www.marlin.ac.uk/baski/image_
viewer.asp?images=Server&topic=Species
http://www.marlin.ac.uk/baski/image_viewer.asp?images=Server&topic=Species
Setiger larvae
of a polychaete
Worm
Phylum Annelida
Class Polychaeta
Sabellaria
http://www.mba.ac.uk/PMF/PMF_Sp_Sabalv.htm
http://raven.zoology.washington.edu/embryos/
Tailbud embryo
of a tunicate
Phylum Chordata
Corella
http://raven.zoology.washington.edu/embryos/
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Pilidium larvae
of a ribbon worm
Phylum Nemertea, Micrura
http://raven.zoology.washington.edu/embryos/
http://www.nwmarinelife.com/htmlswimmers/m_verrilli.html
Veliger larvae
of a scallop
Phylum Mollusca
Class Bivalvia
Chlamys
http://raven.zoology.washington.edu/embryos/
http://www.seaotter.com/marine/research/chlamys
/rubida/html/pacscallop.jpg.html
Pluteus
larvae
of a brittle
star
Phylum
Echinodermata
Class Stelleroidea
Subclass Ophiuroidea
Ophiopholis
http://raven.zoology.washington.edu/embryos/ (above)
http://www.afsc.noaa.gov/kodiak/photo/misophiur.htm (right)
Actinotroch larvae
of a phoronid worm
Phylum Phoronida
Phoronis
“horseshoe worms”
http://raven.zoology.washington.edu/embryos/
http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html
Larvae
Summary of invertebrate reproduction and larvae
Most marine invertebrates have
planktonic larvae
They feed and drift passively in the water until
they settle out on the reef and metamorphose
into the adult form.
Larvae use chemical and physical cues to tell them
where to settle and metamorphose (key decision!)
The adults produce gametes, that develop into
larvae,
that are released into the water.
Some larvae travel 100s of miles, some a few feet.
What happens after the larvae find a good spot?
Sessile marine organisms compete fiercely for space
Definitions:
Sessile = attached permanently or semi permanently
(eg, sponge, tunicate, bryozoan, coral, algae)
Clone = a group of genetically identical individuals living in a
colony
Reef = marine habitat of hard substrate (rock, coral, worm…)
Intertidal = area covered and uncovered by the tides each day
Subtidal = area below the intertidal
Competition for space on rocks in the intertidal
Space is ultimate limiting resource
Soup of larvae and food landing on the reef always
Sessile, clonal species fight for space on rocks
Two general ways to compete:
Be a good fighter (chemical warfare, overgrowth,
fusion - beat ‘em or join ‘em)
Have abundant and frequent settlement of larvae
(swamp out competitors, be the first one there)
Botryllus schlosseri
(tunicate)
Fusion occurs
between close relatives
Instead of fighting with
your relatives, you fuse
with them.
Benefits: larger colonies
compete better, reproduce
earlier.
Costs:Reduces offspring of your
genotype, but genes
passed on in relatives.
R. Grosberg, UC Davis
Tadpole larvae of adult
tunicate (Botryllus) above
Life cycle
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
R.K. Grosberg
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Three colonies of tunicates - overgrowth in direction of arrows.
Two are fused on left, one colony on right. What do you predict
about degree of relatedness between the three colonies?
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Two colonies on the left are probably closely related genetically,
And both more distantly related to the colony on right.
What is it? How many clones?
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Fusion of multiple colonies (clones) of bryozoans.
Those more closely related are more fused.
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Another bryozoan species: Symmetry suggests one clone,
but it is actually two clones! Black dots are original
settlers.
http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html
Algae also compete for space on the reef
Macroalgae (brown, green and red algae)
•Settle out from spores in the water
•Adults require light for photosynthesis
•Incorporate toxins and calcium carbonate
to deter predators (snails, fish, etc)
Division: green algae (Chlorophyta)
Require most light
Example: Sea lettuce (Ulva)
Division: brown algae (Phaeophyta)
Need moderate light
Example: Zoned-fan algae (Padina)
Division: Red algae Rhodophyta)
Can grow with least light
Example: Encrusting coralline algae
What determines species diversity?
LOTS of theories…
•Time (older communities more diverse)
•Competition (agreeable climate and niche
partitioning leads to many species)
•Stability (unchanging habitat allows many species
to exist)
•Intermediate disturbance (most species
where there is intermediate disturbance)*
* We will focus on this one today.
Intermediate Disturbance Hypothesis: Background
Connell 1972 “Diversity in tropical rain forests and coral
reefs”
• Disturbance (eg, tree falls, storms) creates patchiness
and new space to be colonized
•Patchwork is created across the landscape with
- early and late successional species
- inferior and superior competitors
This theory is considered a non-equilibrium view of how
natural communities are structured because landscape is a
patchwork of different stages of succession.
Two studies we will focus on today:
Sousa, Wayne (1979) Disturbance in marine intertidal boulder
fields: the non-equilibrium maintenance of species diversity.
Lubchenco, Jane (1978) Plant species diversity in a marine
intertidal community: importance of herbivore food preference
and algal competitive ability.
Both researchers:
- marine intertidal, temperate communities (California, Maine)
- interested in explaining patterns of species diversity.
- multiyear studies
Ultimate question: Why are there so many species?
Sousa Study (California)
Boulder fields - number of Newtons to move boulders
Number of (algae) species beneath boulders over
time
Lubchenco Study (Maine)
She observed two types of tidepools:
- dominated by one species of algae (seaweed)
- 10 or more species in one pool
She noticed that density of snails (Littorina) varied, too
Species diversity - how to measure?
Species diversity - how to measure?
1) Count number of species (simplest)
2) Use an Index (mathematical formula)
that considers relative abundance of each
species as well as total number of species
Example: Shannon-Weaver Index H’
Break and activity
Contrast the likely life history characteristics
of the most abundant species on boulders
that roll over often versus those that move
seldom.
For many years, ecologists have debated
what is meant by disturbance. What aspects of
disturbance did Sousa look at in his study?
Why might some snails prefer some algae
over others?
Imagine what 300 snails per meter squared
looks like. Is this a reasonable density for
snails in this habitat? Why is this an important
question?