COMPETITION(Chapter 13)

COMPETITION: INTRASPECIFIC versus INTERSPECIFIC

13Leafhopper

Demonstrating Intraspecific Competition in Animals

Fig. 13.6 in Molles 2008

Number of Leafhoppers (per cage)

Number of Leafhoppers (per cage)

Demonstrating Intraspecific Competition in Animals

10Alfalfa

11

12

Demonstrating IntraspecificCompetition in Plants

Fig. 13-5 in Molles 2008

-3/2 Thinning Rule (Sometimes)

Demonstrating Intraspecific Competition in Plants

COMPETITION: INTERFERENCE vs. RESOURCE

Interference Competition

Resource Competition

Trenched (Treatment) Untrenched (Control)

7

8

Demonstrating Resource Competition

Trenched Untrenched

Demonstrating Resource Competition(Results)

Demonstrating Interference Competition.36m2 Plots, Stocked with Sliced Carrots and Potatos

Density: 50 Isopods Density: 100 Isopods

Demonstrating Interference Competition

Fig. 13.7 in Molles 2008

INTERSPECIFIC COMPETITION

Giant Kelp (Macrocystis)

Bull Kelp (Nereocystis)

Galium saxatile Galium pumilum

67

Demonstrating Interspecific Competition in Plants

Tansley (1917)

Demonstrating Interspecific Competition in Plants

Understanding Interspecific Competitionin Context of Niche

Giant Kelp (Macrocystis)

Bull Kelp (Nereocystis)

Graphical Depiction of Giant Kelp Niche(Three Axes)

Nutrients

Light

Car

bon

Dio

xid

e

15

Giant Kelp Niche:Other Abiotic

Factors?

•

•

•

•

N – Dimensional Hypervolume: Hypothetical Space that Represents ALL N Physical Factors that Influence Growth, Survival and Reproduction

Range of physical conditions in which a given species can live in the absence of negative interactions with other species

FUNDAMENTAL NICHE

Nutrients

Light

Car

bon

Dio

xid

e

1615

Negative Interactions with Other Species

NICHE OVERLAP

Fundamental Niches of Giant Kelp, Bull Kelp in One Dimension

Giant Kelp Bull Kelp

Light Intensity

Photosynthesis Rate

Photosynthesis Rate

ADJUSTMENT OF FUNDAMENTAL NICHE IN PRESENCE OF COMPETITOR

Giant Kelp Bull Kelp

Giant Kelp Bull Kelp

Light Intensity

Light Intensity

Range of physical conditions in which a given species can live in the presence of negative interactions with other species

REALIZED NICHEP

hot

osyn

thes

is R

ate

Giant Kelp Bull Kelp

Light Intensity

Fig. 13.20 in Molles 2008

Consequences of Interspecific Competition

Fundamental and Realized Niche of Chthalamus

Two Species with Same or Very Similar Niche:

Is Coexistence Possible?R

esou

rce

Uti

liza

tion

Competitive Exclusion Principle:(G.F. Gause)

Two Species with Identical Niches

CAN NOT Coexist Indefinitely

Mathematical Modeling of Interspecific Competition I(Begin with Logistic Rate Equations for N1, N2)

Note: These equations incorporate effects of intraspecific competition

Mathematical Modeling of Interspecific Competition II(Incorporate Interspecific Competition)

Mathematical Modeling of Interspecific Competition III(Assume Equilibrium Conditions)

Mathematical Modeling of Interspecific Competition IV(Determine Equations for Zero-Change Isoclines)

Fig. 14.13 in Molles 2008

Mathematical Modeling of Interspecific Competition V(Species 1 Strong Competitor, Species 2 Weak Competitor)

Mathematical Modeling of Interspecific Competition VI(Species 1 Weak Competitor, Species 2 Strong Competitor)

Mathematical Modeling of Interspecific Competition VII(Both Species are Strong Competitors)

N2

Mathematical Modeling of Interspecific Competition VII(Both Species are Weak Competitors)

Competitive Exclusion Principle:(G.F. Gause)

Two Species with Identical Niches

CAN NOT Coexist Indefinitely

(i.e., Two Strong Competitors for the Same Resource CAN NOT Co-Exist Indefinitely)

Paramecium aurelia

1

Paramecium caudatum

2

3

Testing Competitive Exclusion Principle

Fig. 13.15 in Molles 2008

Paramecium Species: Grown Separately

(Gause 1934)

Testing Competitive Exclusion Principle

Fig. 21-1 in Ricklefs and Miller 2000

Paramecium Species: Grown Together(Gause 1934)

Testing Competitive Exclusion Principle

Tribolium confusumTribolium castaneum

4 5

Testing Competitive Exclusion Principle

Fig. 13.16 in Molles 2008

Flour Beetle Species: Grown Separately

(Park 1954)

Testing Competitive Exclusion Principle

Fig. 13-16 in Molles 2008

Flour Beetle SpeciesGrown Together

(Gause 1934)

Interspecific Competition in Animals:Consequences

Wide-Leaf Cattail(Typha latifolia)

Narrow-Leaf Cattail(Typha angustifolia)

CATTAIL COMPETITION

Wide-Leaf Cattail(Typha latifolia)

Narrow-Leaf Cattail(Typha angustifolia)

Cattail Species Grown Together

Wide-Leaf Cattail(Typha latifolia)

Narrow-Leaf Cattail Removed

Narrow-Leaf Cattail (Typha angustifolia)

Wide-Leaf Cattail Removed

Balanus

9

Chthamalus10

Zonation in Barnacle Communities

Fig. 13.19 in Molles 2006

Balanus Removal:Middle Intertidal Zone

Chthamalus Survivorship

9

Dipodomys (Kangaroo Rat)

10

Perognathus (Pocket Mouse)

Large Granivores

Small Granivores

Insectivores

Onychomys

DESERT RODENTS

24 Study Plots: Chihuahuan Desert near Portal AZ

Fig. 13.23 in Molles 2006

Experiment: Removal of Large Granivores (Heske et al. 1994)

Geospiza fortis(Medium Ground-Finch)

Darwin’s Finches

Geospiza fuliginosa(Small Ground-Finch)

13

EVOLUTIONARY CONSEQUENCES OF COMPETITION

Fig. 13.25 in Molles 2006

Allopatric versus Sympatric Populations

G. fortis

G. fuliginosa

G. fortis, G. fuliginosa

G. fortis

G. fuliginosa

G. fortis, G. fuliginosa

CHARACTER DISPLACEMENT: BEAK DEPTH