Competition Species Interactions Competition Competition 3 Key Points of Definitions Types of Competition Passive Competition Ac

Species Interactions

Species A Species Harmed No-effect Benefitted B - 0 + Competition Competition Competition PredationHarmed Parasitism No-effectHerbivory Commensalism Benefitted(facilitation) Mutualism (facilitation)

Competition occurs when animals Interspecific competition occurs utilize common resources that are when two or more species in short supply; or if resources are experience depressed growth rate not in short supply, competition or equilibrium population level occurs when the animals seeking attributed to their mutual presence those resources nevertheless in an area. - Emlen 1973 harm one another in the process. - Birch 1957

3 key points of Types of Competition definitions 1. Reciprocal reduction in fitness Passive (utilize resource w/o 2. Resource is limited intefering) 3. Density dependent Active Scramble Contest Interference Exploitation

Passive Competition Active Competition

The 2 species (or individuals of Results from passive competition same species) utilize the limited If r or K is depressed due to resource without interfering with passive competition, it may be one another in any way. advantageous to exclude the other species or individual from the resource; It may not though if it is too costly. Territoriality Scramble Competition

Intraspecific A scramble for the resources and Possessing and defending a territory insures no single individual necessarily breeding site, food supply, etc. obtains a sufficient amount. Interspecific Redwing and yellow-headed blackbirds Hummingbirds

Contest Competition Interference

Each individual possesses its own Behavior patterns of one species supply of the resources so that harms the other species. some always have sufficient and Example: Mus and Microtus otherss may not. Territoies Social hierarchies

Exploitation Examples

Passive Competition Gause’s Yeast and Paramecium Scramble Parks’s Flour beetles Brown and Munger’s desert rodents

Theory of Competition Phase Plane

K 1926 - Italian Mathematician K1 2 N N Volterra 1 2 1932 - American Mathematician

Lotka Time Time Started with logistic pattern of N K growth 1 1 Extended it to include 2 species

N2 Elk at National Bison Range Elk at National Bison Range

1000 1000

K1/α21

No. of No. of Bison Bison

600 600 K1 K1 No. of Elk No. of Elk

Bison at National Bison Range Elk and Bison at NBR

1000 1000

K1/α21

K2 K2 No. of No. of Bison Bison

K /α 600 600 2 12 K /α K1 No. of Elk No. of Elk 2 12

Competitive Exclusion Competitive Exclusion

Gause (1934) in his book The Miller (1967) study of gophers Struggle for Existence stated: “Complete competitors cannot coexist.” “Gause’s competitive exclusion principle.”

Evaluation Similarity of 2 bird species

How do we evaluate the potential Are they together geographically? for competition? Elevations Compare resource use-distributions in presence and Habitats (plant communities, seral absence of the other species. stages) Evaluate the similarity of the Where do they feed? species. What do they eat? Best would be to compare growth rates and equilibria in presence What size of insects? and absence of other species. Where do they nest? Niche Niche

Grinnell (1914) used the term Hutchinson (1957) suggested niche or ecological niche to defining niche in terms of an express the species position in the abstract space in which the axes community in terms of habitat. represent habitat or resource Elton (1927) : role that species factors.Example: Blue-gray gnatcatcher plays in a community Fundamental niche = The range of conditions in which the species G. E. Hutchinson (1957) expanded could potentially survive. the concept to include both Realized niche = The actual range aspects of conditions occupied.

Niche of Blue-gray Gnatcatcher - Root 1967 Niche

Height Height Realized Niche Fundamental Niche

Size of Insect Size of Insect

Niche Galapagos Finches

Example: Planaria Anolis lizards Character displacement Galapagos Finches Darwin, Lack and most recently Peter Grant (1986, Ecology and Evolution of Darwin’s Finches. Princeton Univ. Press) have inferred the adaptive radiation of finches on Galapagos Islands driven by competition.

Structuring Chipmunks (Eutamias now Tamias) Classic communities study by Heller (1971) Does competition structure Sierra Nevadas Physiological communities? Tolerance T. alpinus Simberloff, Strong and others Alpine Zone argue that the evidence is very weak. Lodgepole Pine T. speciosus

Same patterns without competition Pinyon Pine T. amoenus Sagebrush Species kept well below K Sagebrush T. minimus Alternate hypotheses Ayala’s fruit flies (1970) Ayala’s fruit flies (1970)

D. pseudoobscura D. pseudoobscura

Kp Kp

K K w D. willistoni w D. willistoni

Resource Competition Diversity and Productivity Tilman (1982) Resource Is diversity higher in richer (more Competition and Community productive) places? Structure Desert to grassland to forest to tropical Experimental studies of rainforest? relationship between species What happens if we fertilize an richness (diversity) and resource area? Does the species diversity richness (productivity) increase?

Let’s look at what Tilman found.

Tilman - Resource Competition Monod equation

“Monod equation” relating Population resource availability to per capita growth rate Abundance

Resource per capita growth rate

0 Time Resource X

Tilman’s theory 2-Species Exclusion

Species A & B Region 2 Survive

Species survives and reproduces Resource Y Resource Y ZNGI A Species B Survives ZNGI ZNGI B Region 1 Species does not survive and Region 1 reproduce

Resource X Resource X 2 Species - Coexistence

3 4

2 Resource Y

ZNGI A 6 1 ZNGI B

Resource X