1. BIOL 4120: Principles of Ecology Lecture 12: Interspecfic competition
Dafeng Hui
Room: Harned Hall 320
Phone:

2. Outline (chapter 13) 13.1 Interspcific competition
13.2 Lotka-Volterra model
13.3 Laboratory experiments support L-V model
13.4 Competitive exclusion principle
13.5 Competition is influenced by nonresource factos
13.6 Temporal variation in environmental factors
13.7 Multiple resources
13.8 Competition change along environmental gradients
13.9 Niches of species
13.10 Resource partitioning
13.11 Competition influence national selection
13.12 Competition involves biotic and abiotic factors
Lecture 12:
Chapter 13:

3. 13.1 Interspecific competition
A relationship in which the populations of two or more species are affected adversely (--)
Seek a common resource in short supply
Food; Living space; etc
An example: squirrels, mice, deer, various birds competing for acorns
Model One. Two forms
Exploitation
Interference
Model Two. Six forms
Consumption
preemption
Overgrowth
Chemical interaction
Territorial
encounter

4. Consumption Preemption Overgrowth Chemical interaction Territorial
Utilization of a shared resource by 2 species
Preemption
Occupation of a site by 1st organism stops occupation by 2nd organism
Usually sessile organisms
Overgrowth
Where organism covers another preventing access to a resource. Trees shade other plants
Chemical interaction
Release of toxin to inhibit or kill competing organisms
Allelopathy in plants
Territorial
Behavioral exclusion of 1st organism by 2nd organism defending territory
Encounter
Non-territorial encounters cause a negative effect on one or both species
Lion and wild dogs over a antelope kill

5. 12.2 Possible outcomes of Interspecific competition
When two species compete, how many outcomes?
Species 1 wins, species 2 loses
Species 1 loses, species 2 wins
Coexistence (stable equilibrium)
Competition can go wither way (unstable equilibrium)
These competition results can be described by Lotka-Volterra model.

6. Lokta-Volterra Model Derived from logistic equation
Add influence of another species (a competition component)
alpha(2,1)=alpha
Alpha(1,2)=beta

7. Lokta-Volterra Model
αN2 and βN1: effect of interspecific competition, namely, where α and β per capita effects of competition
In term of resource use, an individual of species 2 is equal to α individuals of species 1
No interspecific competition, then α and β are 0 and normal growth to carrying capacity
Interspecific competition is density dependent
Need to explain dN/dt=0, then N1=K1-alpha N2
dN2/dt=0, then N2=K2-beta N1
These two are the zero growth isoclines

8. (a) Species 1 alone or no competition
Diagonal line is zero growth isocline

9. (b) Species 2 alone or no competition

10. (c) Species 1 inhibits growth of species 2 and latter goes extinct

11. (d) Species 2 inhibits growth of species 1 and latter goes extinct

12. (e) Unstable situation, both inhibit in a density dependent manner
(e) Unstable situation, both inhibit in a density dependent manner. Depending on initial density, either can make other extinct

13. 4/23/2017
(f) Each species inhibits its own population growth more than competitor. Neither can eliminate competitor

14. 4/23/2017
How to remember which wins?
Easy: large K wins, (c) K1 larer, species 1 wins, (d), K2 large, species 2 win, (e) one side sp1 wins, one side sp2 wins, (f) nobody wins, co-exist

15. 13.3 Laboratory experiments support the Lotka-Volterra Equations
Russian biologist G.F. Gause
Competition between two species
P. aurelia has a high growth rate and can tolerate a higher population density
Two Paramecium (unicellular ciliated protozoan)
One with higher rate of growth: Extinction of slower grower
With different food supplies:
Coexistence

16. Diatom experiment David Tilman, University of Minnesota
Asterinella formosa (Af) and Synedra ulna(Su) compete for silica for the formation of cell walls.
Adequate silica, coexist
Insufficient silica, Su drove Af to extinction

17. 13. 4 Competitive exclusion principle
Complete competitors can not coexist. One species must go extinct
Complete competitions: two species that live in the same place and possess exactly the same ecological requirements.
Assumptions:
Exactly the same resource requirement (no more, no less)
Environmental conditions remain constant
Most of the time species can coexist

18. 13.5 Competition is influenced by non-resource factors
Many non-resource factors would influence the outcomes of the competition. For example, space, light.
Favor species with high photosynthetic rate, allocate C to height growth and leaves production (fast-grow species)

19. Patterns of seed germination along T gradient
Fakhri Bazzaz, Harvard University (Retired)
Five annual species
T influences the germination, thus seedling establishment, resource competition and structure of community.

20. 13.6 Temporal variation in environment influences competition interactions
As environmental conditions vary, the competition advantages change
No one species can reach sufficient density to displace its competitors;
Thus lead to co-exist.
Shift in dominant grass species caused by moisture

21. 13.7 Competition occurs for multiple resources
Systems are not simple one resource situations
Usually competition for more than one resource
Territorial defense against wide range of other species
Plants
Monoculture
Root competition
Skeleton weed reduce by 35%
Shoot competition
Skeleton weed reduced by 53%
Root and shoot competition
Skeleton weed reduced by 69%
Thus clover superior to skeleton weed for all resources

22. 13.8 Relative competition abilities change along environmental gradients
Effect of interspecific competition across an environmental gradient
Note changes in response when in mixture

23. Similar effect for summer annuals and moisture gradient
Also happens in nature with water, anoxia and salt stress in a salt marsh

24. Chipmunks Alpine Lodgepole Yellow Pine Least Cold tolerant
Most aggressive
Needs shade
Yellow Pine
aggressive
Least
Heat tolerant
Least chipmunk can occupy from sagebrush to alpine zone. If yellow pine is removed, least chipchunk will move up.
If least chipchunk is removed, yellow pine chipmunk will not move down.
Lodgpole pine chipmunk is restricted to shade area, is vulnerable to heat. Lodgepole is the most aggressive, may limit the downslope range of alpine chipmunk.

25. 13.9 Niche of a species Concepts of niche
describes how an organism or population responds to the distribution of resources and competitors (e. g., by growing when resources are abundant, and predators, parasites and pathogens are scarce) and how it in turn alters those same factors.
dimensions of a niche: represent different biotic and abiotic variables.
These factors may include descriptions of the organism's life history, habitat, trophic position (place in the food chain), and geographic range.
According to the competitive exclusion principle, no two species can occupy the same niche in the same environment for a long time.

26. Concepts of niche
Fundamental niche: range of conditions and resources a species can use to survive and reproduce under no interference by other species
Realized niche: portion of fundamental niches that a species actually exploits as a result of interactions with other species (e.g., competition).

27. Examples
Distribution of twp species of cattail (Typha latifolia and T. angustifolia)
Fundamental Niche:
Tl: water depth: -20~ 70 cm
Ta: ~110 cm
Realized Niche:
Tl: -20 ~ 70 cm
Ta: 20 ~ 110 cm (Changes)
Niche overlap: cm

28. Fundamental and realized niches

29. Competition release
A species expands its niche in response to the removal of a competitor
Two examples
Response of Stipa neomexicana plants
Commercial whaling in Antarctic Ocean

30. Response of Stipa neomexicana plants
Jessica Gurevitch
University of New York at Stony Brook
Stipa: C3 perennial grass
Semi-arid grassland in Arizona

31. Commercial whaling in Antarctic Ocean
Baleen whales: 1 million a century ago
eat Antarctic krill (4% of body weight)
Now, less than 200,000
Other krill-dependent predators such as seals and penguins have been found greatly increased in abundance
Competition release due to the dramatic decrease in baleen whale population

32. 13.10 Resource partitioning
“Complete competitors can not co-exist”
Why did not the best competitor force others out?
Co-existing species must be different in the use of resources
Niche differentiation: differences in the range of resources used or environmental tolerance
Examples:
Plants grow together
Animals share the same habitat

33. Resource partitioning
Use water and nutrients at different depths
Spatial differentiation.

34. Resource partitioning
Size (diameter) of canine teeth for small cat that co-occur in Israel. Size is correlated with size of prey selected by different species.
Morphological differentiation.

35. Another example Seven Anolis lizards in tropical rainforest
Share common food needs — mainly insects.
They avoid competition by occupying different sections of the rainforest
the leaf litter floor
shady branches
All resources are subject to partitioning, such as space, food, nesting sites.
This minimizes competition between similar species.
(Temporal differentiation.)

36. Niche dimensions
Rarely do two or more species possess exactly the same combination of requirement. Species may overlap on one D of the niche, but not on another.

37. 13.11 Competition can influence natural selection
Competition is at the heart of Darwin’s theory of natural selection. Characteristics that enable an organisms to reduce competition will function to increase fitness.
Character displacement

38. Character displacement
The outcome of the competition was a shift in feeding niches. When the shift involves features of the species’ morphology, behavior, or physiology
The process of evolution toward niche divergence in the face of competition

39. 13.12 Competition involves both biotic and abiotic factors
Removal experiment is an effective method to study competition
Hidden treatment effects: removal changes space, light, soil temperature, and moisture, evaporation.
Competition is a complex interaction involving a variety of environmental factors that directly influence survival, growth, and reproduction.
Outcome of competition may differ markedly under different set of environmental conditions.
Finally, we need to understand that

40. End

41. FACILITIES MANAGEMENT DEPARTMENT DEPARTMENTAL NOTIFICATION
LOCATION
CAMPUS-WIDE
PROJECT
IN RESPONSE TO THE DROUGHT AND HEAT THIS SUMMER, ALL TREES THAT HAVE EXCEEDED THEIR PERMANENT WILTING POINTS WILL BE REMOVED
DURATION  
TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)

42. Science 12 October 2007: Vol. 318. no. 5848, pp. 268 – 271
Reports
Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
Theory suggests it should be difficult for asexual organisms to adapt to a changing environment because genetic diversity can only arise from mutations accumulating within direct antecedents and not through sexual exchange.

43. Science Reports (cont.)
Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
In an asexual microinvertebrate, the bdelloid rotifer, we have observed a mechanism by which such organisms could acquire the diversity needed for adaptation. Gene copies most likely representing former alleles have diverged in function so that the proteins they encode play complementary roles in survival of dry conditions.

44. Science Reports (cont.)
Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
One protein prevents desiccation-sensitive enzymes from aggregating during drying, whereas its counterpart does not have this activity, but is able to associate with phospholipid bilayers and is potentially involved in maintenance of membrane integrity. The functional divergence of former alleles observed here suggests that adoption of asexual reproduction could itself be an evolutionary mechanism for the generation of diversity.

45. Al Gore, UN panel share Nobel for Peace
U.N.'s IPCC (Intergovernmental Panel on Climate Change)
For Global warming