Competition in Triclads

1
Competition in Triclads

• Juan M. Jiménez
• University of Houston
• Biology and Biochemistry
• Pop. Bio Seminar
• Spring 2007

2

• Classification and natural hist.
• Definition of Competition
• Development of competition studies on Triclads
• Current tendencies

3
Triclads classification

• Phylum Platyhelminthes
• (flatworms)
• Class Cestoda (tapeworms)
• Class Trematoda (flukes)
• Class Turbellaria (planarians)
• Order Tricladida (triclads)

4
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
5
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.

6
Why do we care?

• Distribution and abundance of species
• Community structure

7
Beauchamp and Ullyot 1932

• Competition in Triclads
• A natural experiment.
• Temperature limiting factor

8
Beauchamp and Ullyot 1932
Rheocrene
Limnocrene
Limiting factor rate flow of Water
9
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)

10
Lock and Reynoldson 1976

• Tried to Perform manipulative experiments on the
  field
• Used new technology for establishing shared
  resources
• Crenobia alpina Vs. Polycelis felina

11
(No Transcript)
12
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.

13
Superior
Equilibrium
Phagocata vitta vs. P. felina
Phagocata vitta vs. C. alpina
14
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

15
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

16
(No Transcript)
17
Preycondition may affect competition

• Live intact prey Vs. damaged prey

sophisticated chemosensory system

• Developed suckers Vs.

18
(No Transcript)
19
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

20
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

21

• 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

22
Thank you
23

• 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

24
Whitham et al. 2006. Nature 7, July, 510-523.

• A framework for community and ecosystem genetics