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Bio 299 Projects Available!

Lotka Volterra Lab based competitionCompetitive exclusion principleResource competitionCompetition and NichesCharacter displacement

Thursday, March 4, 2010

Bio 299 Projects

• A number of new projects have been posted since February 16th. !Just a reminder that applications for Biology 299 projects are now being accepted.! The deadline for applications is March 26th. !For more information students can check the course website at www.biology.ualberta.ca/courses/biol299/ !


There are four ways to plot these two species together

Each red arrow is a vector of the combined direction of

both species.

Species 1 increasing while species 2 is

decreasing

Fig13.4 Molles and Cahill


Example d: Isoclines for the two species cross; the K values on each axis are lower than the K/a values

Two species coexist when each species is regulated more by intraspecific competition rather than by competition with the other species,.

From N1 axis:

K2/a21>K1

thus K2>K1α21

Indicating that species 2 is regulated more by intraspecific competition than by interspecific competition

From the N2 axis:

K2<K1/α12

so K2α12<K1

Indicating that species 1 is regulated more by intraspecific competition than by interspecific competition


Biom

ass

(rel

ativ

e vo

lum

e) When both paramecieum species were grown alone carrying capacity was determined by intraspecific competition for food

For both species changes in food density result in changes to carrying capacity

Lab Models of competition

Gause 1934

Fig 13.5 Molles and Cahill

Fig 13.5 Molles and Cahill


What differences do you notice when Paramecium species are grown together compared to when they were grown separately?

How about between low and high resources when grown together?



When the two are grown together P. aurelia survived while P. caudatum declined.

Reduction in food concentration resulted in local extinction of P. caudatum. This suggests that reduced resources increase intensity of competition.



Competitive Exclusion Principle“Complete competitors cannot coexist” (Hardin 1960)

If species that are similar in their ecology come into competition one of them will persist and the other will go locally extinct.

What does this mean?

Similar habitat, food source etc

BUT. . . . . .


Competitive Exclusion PrincipleIf this is true why are there so many examples of species that appear to coexist?

http://images.tsn.ca/images/stories/20081230/bnlonnhlontsn430_62017.jpghttp://www.buxtononline.net/2008e/meadowflowers3.jpg

http://k41.pbase.com/u45/chammett/upload/29290136.vansanimalsatwatering.jpghttp://oceanexplorer.noaa.gov/explorations/03mex/logs/sept30/media/deep_fish_diversity_600.jpg


Maybe competition in those communities isn’t occurring at all! So competitive exclusion can’t

occur.

EnvironmentPredationDisease

May have greater effect on species

Actually we find that in many cases there is both coexistence and competitive exclusion going on and it depend on how you look at

things


How species can coexist?Spatial heterogeneity

Heterogeneity: an object or system consisting of multiple items having a large number of structural variations

Areas of low resources - High interspecific competition

Areas of moderate resources - Moderate interspecific competition

Areas of High resources - No interspecific competition

Can substitute resource with environmental stress, disease, predation and get same result


How species can coexist?Variation in competitive abilities within a species (Lotka Volterra assumes α21 is constant.)

Separately grown

Grown together



How species can coexist?

Alone

Together

Fig13.8 Molles and CahillFig13.7 Molles and CahillThursday, March 4, 2010

Does humidity and temperature vary in natural landscapes?

Would you expect competition between two species then to also vary?


Resource CompetitionSelf thinning - intraspecific competition

Over time population is made up of fewer but larger individuals

http://www.harvestwizard.com/lettuce4.jpg

http://www.norcalblogs.com/sustainable/2007/10/the_lettuce_dilemma.html

http://www.strocel.com/something-is-eating-my-plants/

Lettuce seedlings

Lettuce ready for harvest

Guy born with Lettuce headThursday, March 4, 2010

Resource CompetitionSelf thinning - intraspecific competition

Over time population is made up of fewer but larger individuals

What would this look like if there wasn’t a -3/2 self thinning rule?

(Log

arith

m o

f Tot

al b

iom

ass)




How species can coexist?

Other mechanisms include:i) Competitive equivalenceSpecies on average win and lose about the same number of times across the landscapeii) non equilibrium conditionsCompetitive exclusion is not instantaneous - so before it occurs species are in coexistence (even though this relationship is not stable).

Think about spatial and temporal scale.

Could your conclusions about who wins and who loses change if you look at a relatively small portion of the landscape compared to a larger one?

Could your conclusions about who wins and who loses if you look at a relatively small time frame compared to a larger one?


Intraspecific competition

Planthoppers grown with varying densities of Spartina seedlings

http://www.dpughphoto.com/images/planthopper%20acanalonia%20conica

%20mason%20farm%2072207.JPGhttp://epod.typepad.com/.a/

6a0105371bb32c970b0120a560a675970c-750wi

Resource limited!



Intraspecific Interference competition

Floater: Male song sparrows without established territories within habitat. Challenge territorial males or wait for then to die!

http://ib.berkeley.edu/birdgroup/birdgroup_files/Song_Sparrow.jfif

Owner’s age and health important in likelihood of intrusion Older males less physically fitYounger males less experienced



If you were crazy with hunger for ice cream who would you approach?

http://www.geekologie.com/2008/05/04-week/

http://www.archiesicecream.com/gallery/slideshow.php?set_albumName=

Imagine photo of small boy

with ice cream


French Fries à la mode


Overview of Competition in Natural SystemsHow important is competition in the ecology and evolution of natural species?

So far we have said important but not always.

Reviews of the experiments done in this area of science show this.Tom Schoener (1983), Joe Connell (1983), Jessica Gurevitch ( 1992).Reviews - analyses of many many experiments. From literature.

Competition intensities differ amongst animals compared to plants. Why should this be?

Plants grow in close proximity -intense light competition, root competition.

http://jrscience.wcp.muohio.edu/photos/CorcovadoSecUnderstory00.jpg

Tropical jungle understory

http://images.travelpod.com/users/mlloyd/churchill-2006.1163371560.tundra-w-bear2.jpg

Bear on frozen tundra


For plant ecologists one of the big question has been:

How does competition vary with resource abundance (resource gradient)?

gradient: a graded change in the magnitude of some physical quantity

Exam question - define “gradient” in the biological sense


Overview of Competition in Natural Systems

Phil Grime vs the ROTWGrime: Tolerance to stress is more important than competitive ability in unproductive (stressful) area. Life history of plants found in marginal habitats are suited to deal with enviroment rather than competition. In productive areas life history of plants are geared towards competition. Grime(1973, 1977, etc etc)

Tilman: In both areas of low and high productivity plants that are best at drawing down resources wins. Competitive ability is important in both cases.1987.

Newman (1973): Competition overall stays the same over productivity gradient BUT competition for soil decreases while competition for light increases.

Productivity

Nutrient poor ----- Soil --------Nutrient rich

Light availability high ----- Light -------- Light availability lowROTW = rest of the world



Epic competition study by Richard Reader 1994 (University of Guelph Ontario Canada):

20 teams

Identical studies at 12 sites throughout world along productivity gradientsIdentical species and methodsNo evidence that competition varied with productivity!



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