Transcript Competition in Triclads

Competition in
Triclads
Juan M. Jiménez
University of Houston
Biology and Biochemistry
Pop. Bio Seminar
Spring 2007
• Classification and natural hist.
• Definition of Competition
• Development of competition studies on
Triclads
• Current tendencies
Triclads
classification
•
Phylum Platyhelminthes
(flatworms)
– Class Cestoda (tapeworms)
– Class Trematoda (flukes)
– Class Turbellaria (planarians)
• Order Tricladida (triclads)
Life history: Turbellaria
Also called planarians
Simple animals, bilaterally symmetrical and
triploblastic
No body cavity other than the gut and lack an anus
Mostly aquatic (sea and fresh water) but some can
live in humid environments. Free living
Size: less than 1 mm to more than 10 mm
In temeperate zones Univoltine but elsewhere can
be multivoltine
Simple reproductive cycle with small replicas of
adults directly hatching from eggs
Dugesia tigrina
Competition?
• “The antagonistic rivalry in
which living beings are
engaged in a life and death
struggle for a part of the
existing means of survival
which are insufficient for the
minimum needs of all. This
situation is inherent in nature
and among wild animals
incapable of social
cooperation. …”
Interference
Exploitation
Why do we care?
• Distribution and abundance of species
• Community structure
6.6 ºC
6.6 to 16.5 ºC
P. montenegrina
P. Gonocephala
6.6 to 23 ºC
14 ºC
Beauchamp and
Ullyot 1932
Competition in Triclads
A natural experiment.
Temperature: limiting factor
23 ºC
Rheocrene
Limnocrene
P alpina
Pol cornuta
13.5 ºC
Pol cornuta
13.5 ºC
P alpina and
Pol cornuta
17 ºC
17 ºC
Limiting factor: rate flow of Water
This method is inconclusive …
• Patterns do not hold in many rivers.
• Niche overlapping: weak evidence
• Competition can only be demonstrated
by manipulative experiments.
Andrewartha and Birch (1954), Miller(1967) and Reynoldson and Bellamy (1970)
Lock and Reynoldson 1976
• Tried to Perform manipulative experiments on the field
• Used new technology for establishing “shared resources”
• Crenobia alpina Vs. Polycelis felina
Armitage and Young 1991
• First to look at factors other than competition to
explain distr. and abundance of triclads
– Predation, Intraguild P. and Cannibalism
• Lab manipulation of proportions in competition
experiment with two different food resources.
Superior
Superior
Equilibrium
But Strong
tendency to
equilibrium
Phagocata vitta vs. P. felina
Phagocata vitta vs. C. alpina
Critique …
Cons:
• No combination of lab and field experiments,
weakens conclusions. Under natural
conditions you have more than one resouse
available.
• Presence of common predators opens the
possibility for “Apparent competition”
Pros:
• starts looking at other factors than
competition
Seaby et al. 1996
• Lab and field experiments to look at
competition between triclads and
leeches.
• Look at competition under two
“conditions” of a shared prey.
• Discrepancy: niche overlap but they still
coexist
Prey”condition” may affect
competition
• Live intact prey Vs. damaged prey
• Developed suckers Vs.
sophisticated
chemosensory
system
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Interspecific interactions may
change in time…
• This paper shows how interactions can
change from competition to coexistence and
even facilitation with changes on prey
condition over time.
• This highlights the importance of experiments
at longer time scales
• And that interactions are not static
Studies on Ecology of Triclads
are stocked in time
• Changes in methods …
• But, continues focused on population effects
of competition.
• Species are immersed in communities and
interactions with multiple species may
change the outcome of competition.
• Presence of common predators may allow for
“apparent competition”
…
• Today we know that populations and
communities structure are determined
by multiple factors acting at the same
time (top-down, bottom-up and side to
side)
• We know about keystone species that
can control the presence and
abundance of species
Thank you
…
• The latest trend is to consider genotypic
changes in key species populations and
their effects at the community and
ecosystem level
– Whitham et al. 2006
Whitham et al. 2006.
Nature 7, July, 510-523.
• A framework
for community
and ecosystem
genetics