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

Beauchamp and Ullyot 1932 Competition in Triclads A natural experiment. Temperature: limiting factor 6.6 ºC 23 ºC 14 ºC P. montenegrina P. Gonocephala 6.6 to 16.5 ºC 6.6 to 23 ºC

Beauchamp and Ullyot 1932 RheocreneLimnocrene Pol cornuta P alpina 13.5 ºC 17 ºC Pol cornuta P alpina and Pol cornuta 13.5 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.

Phagocata vitta vs. P. felinaPhagocata vitta vs. C. alpina Superior Equilibrium Superior But Strong tendency to equilibrium

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 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

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 Nature 7, July, A framework for community and ecosystem genetics