BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 12: Interspecfic Lecture 12: Interspecfic competitioncompetition

Dafeng HuiDafeng Hui

Room: Harned Hall 320Room: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

OutlineOutline (chapter 13)(chapter 13)13.1 Interspcific competition13.1 Interspcific competition13.2 Lotka-Volterra model13.2 Lotka-Volterra model13.3 Laboratory experiments support L-V model13.3 Laboratory experiments support L-V model13.4 Competitive exclusion principle13.4 Competitive exclusion principle13.5 Competition is influenced by nonresource factos13.5 Competition is influenced by nonresource factos13.6 Temporal variation in environmental factors13.6 Temporal variation in environmental factors13.7 Multiple resources13.7 Multiple resources13.8 Competition change along environmental 13.8 Competition change along environmental

gradientsgradients13.9 Niches of species13.9 Niches of species13.10 Resource partitioning13.10 Resource partitioning13.11 Competition influence national selection13.11 Competition influence national selection13.12 Competition involves biotic and abiotic factors13.12 Competition involves biotic and abiotic factors

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

Consumption• 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

12.2 Possible outcomes of 12.2 Possible outcomes of Interspecific competitionInterspecific competition

When two species compete, how many outcomes?When two species compete, how many outcomes?1.1. Species 1 wins, species 2 losesSpecies 1 wins, species 2 loses2.2. Species 1 loses, species 2 winsSpecies 1 loses, species 2 wins3.3. Coexistence (stable equilibrium)Coexistence (stable equilibrium)4.4. Competition can go wither way (unstable Competition can go wither way (unstable

equilibrium) equilibrium)

These competition results can be described by Lotka-These competition results can be described by Lotka-Volterra model.Volterra model.

Lokta-Volterra ModelLokta-Volterra Model

Derived from logistic equationDerived from logistic equation

Add influence of another species (a competition Add influence of another species (a competition component)component)

alpha(2,1)=alpha

Alpha(1,2)=beta

Lokta-Volterra ModelLokta-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

(a) Species 1 alone or no competition

Diagonal line is zero growth isocline

(b) Species 2 alone or no competition

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

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

(e) Unstable situation, both inhibit in a density dependent manner. Depending on initial density,

either can make other extinct

(f) Each species inhibits its own population growth more than competitor. Neither can

eliminate competitor

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 growerWith different food supplies:

Coexistence

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

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

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)

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.

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

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

Effect of interspecific competition across an environmental gradient

Note changes in response when in mixture

13.8 Relative competition abilities change along environmental gradients

Similar effect for summer annuals and moisture gradient

Also happens in nature with water, anoxia and salt stress in a salt marsh

ChipmunksAlpine

Cold tolerantLodgepole

Most aggressiveNeeds shade

Yellow Pineaggressive

LeastHeat tolerant

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.

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).

ExamplesDistribution of twp species of cattail (Typha latifolia and T. angustifolia)

Fundamental Niche:

Tl: water depth: -20~ 70 cm

Ta: -20~110 cm

Realized Niche:

Tl: -20 ~ 70 cm

Ta: 20 ~ 110 cm (Changes)

Niche overlap: 20-70 cm

Fundamental and realized niches

Competition release

A species expands its niche in response to the removal of a competitor

Two examplesResponse of Stipa neomexicana plantsCommercial whaling in Antarctic Ocean

Response of Stipa neomexicana plants

Jessica Gurevitch

University of New York at Stony Brook

Stipa: C3 perennial grass

Semi-arid grassland in Arizona

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

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

Resource partitioning

Use water and nutrients at different depths

Spatial differentiation.

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.

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.)

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.

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

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

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.

EndEnd

FACILITIES MANAGEMENT FACILITIES MANAGEMENT DEPARTMENTDEPARTMENT

DEPARTMENTAL NOTIFICATIONDEPARTMENTAL NOTIFICATION

LOCATION LOCATION CAMPUS-WIDECAMPUS-WIDE    PROJECTPROJECT IN RESPONSE TO THE DROUGHT AND HEAT THIS SUMMER, IN RESPONSE TO THE DROUGHT AND HEAT THIS SUMMER,

ALL TREES THAT ALL TREES THAT HAVE EXCEEDED THEIR PERMANENT HAVE EXCEEDED THEIR PERMANENT WILTING POINTS WILL WILTING POINTS WILL BE REMOVEDBE REMOVED

   DURATION   DURATION   TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)

ScienceScience 12 October 2007:12 October 2007:Vol. 318. no. 5848, pp. 268 – 271Vol. 318. no. 5848, pp. 268 – 271

ReportsReports

Functional Divergence of Former Alleles in Functional Divergence of Former Alleles in an Ancient Asexual Invertebratean Ancient Asexual Invertebrate

Natalia N. Pouchkina-Stantcheva, et al. Natalia N. Pouchkina-Stantcheva, et al. Theory suggests it should be difficult for asexual Theory suggests it should be difficult for asexual

organismsorganisms to adapt to a changing environment to adapt to a changing environment because genetic diversitybecause genetic diversity can only arise from can only arise from mutations accumulating within direct mutations accumulating within direct antecedentsantecedents and not through sexual exchange.and not through sexual exchange.

ScienceScience Reports (cont.)Reports (cont.) Functional Divergence of Former Alleles in Functional Divergence of Former Alleles in

an Ancient Asexual Invertebratean Ancient Asexual Invertebrate Natalia N. Pouchkina-Stantcheva, et al. Natalia N. Pouchkina-Stantcheva, et al. In an asexual microinvertebrate,In an asexual microinvertebrate, the bdelloid the bdelloid

rotifer, we have observed a mechanism by whichrotifer, we have observed a mechanism by which

such organisms could acquire the diversity such organisms could acquire the diversity needed for adaptation.needed for adaptation. Gene copies most likely Gene copies most likely representing former alleles have divergedrepresenting former alleles have diverged in in function so that the proteins they encode play function so that the proteins they encode play complementarycomplementary roles in survival of dry conditions. roles in survival of dry conditions.

ScienceScience Reports (cont.)Reports (cont.) Functional Divergence of Former Alleles in Functional Divergence of Former Alleles in

an Ancient Asexual Invertebratean Ancient Asexual Invertebrate Natalia N. Pouchkina-Stantcheva, et al. Natalia N. Pouchkina-Stantcheva, et al. One protein prevents desiccation-sensitiveOne protein prevents desiccation-sensitive

enzymes from aggregating during drying, enzymes from aggregating during drying, whereas its counterpartwhereas its counterpart does not have this does not have this activity, but is able to associate with activity, but is able to associate with phospholipidphospholipid bilayers and is potentially involved bilayers and is potentially involved in maintenance of membranein maintenance of membrane integrity. The integrity. The functional divergence of former alleles observedfunctional divergence of former alleles observed

here suggests that adoption of asexual here suggests that adoption of asexual reproduction could itselfreproduction could itself be an evolutionary be an evolutionary mechanism for the generation of diversity.mechanism for the generation of diversity.

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