Types of Interactions Between Organisms I The Niche

Types of Interactions Between Organisms

I. The Niche • Each niche is occupied by only one species. • Joseph Grinnell (1917) – The niche is a subdivision of habitat. • Physical location in the environment. • Charles Elton (1927) – The "role" of the species in the community. • The functional role of the species. • G. Evelyn Hutchinson (1957) – The range of resources and factors tolerated by an organism • What does a species need to survive, grow, and reproduce

G. E. Hutchinson (1957) Uses range of tolerance for each resource

Hutchinsonian Niche • We can continue to include resources until we have all possible resources • The niche is described as an

Niche • Fundamental Niche • Realized Niche

Niche Breadth The concept of niche breadth can then be employed to exam niche overlap

• Fundamental vs Realized Niche

NICHE SPACE – No overlap HUMIDITY No competition SPECIES A SPECIES B LIGHT

NICHE SPACE – Overlap; Species B wins HUMIDITY Region of Overlap SPECIES A SPECIES B LIGHT

NICHE SPACE – Overlap; Species A wins HUMIDITY Region of Overlap SPECIES A SPECIES B LIGHT

NICHE SPACE – Complete overlap HUMIDITY Species A wins SPECIES A SPECIES B LIGHT

• Exploitation Competition – Use up resources available to other species by intaking the resources

Types of Competition • Interference Competition (contest) – Prevent other organisms from getting resources by interfering with consumption • Allelopathy • Antibiotics

Types of Competition • Diffuse Competition – Competition can occur for a variety of resources from multiple other species

Competition • Intraspecific – Between individuals of the same species • Interspecific – Between individuals of different species

Competitive Exclusion Gause’s Competitive Exclusion Principle Experiments with Paramecium No two species with the same niches can coexist.

III. How does one obtain evidence of competition? • Experimental studies – J. H. Connell 1961 - barnacles

Connell Results: Middle Intertidal Fundamental vs. Realized Niche Interspecific Competition

IV. Effects of Competition Niche Shifting Niche variable

Observational studies Manipulation is not always possible J. M. Diamond 1975 Inferred competition resulted in the distributional patterns he observed for dove species

Niche partitioning Robert Mac. Arthur - warbler study

IV. Effects of Competition Character Displacement We are assuming that competition for a resource is the only thing which effects this character

Character Displacement

Character Displacement

King, C. M. 1989. in Carnivore behavior, ecology, and evolution

Lotka-Volterra Model of Competition Population size in the presence of intraspecific competiton How do we incorporate interspecific competiton?

Lotka-Volterra Model of Competition Population size in the presence of intraspecific competiton How do in incorporate interspecific competiton? We need to convert one species into the equivalent of another – add

Lotka-Volterra Model of Competition Population size in the presence of intraspecific competiton Intraspecific competition How do in incorporate interspecific competiton? We need to convert one species into the equivalent of another Interspecific competition

Competition • Lotka-Voltera Interspecific competiton – Convert individuals of species 1 into species 2 equivalents.

Competition – Isocline Analysis • Rearrange equations when = 0 • Predict population growth for the two species will stop – Graph of these = straight lines = isoclines = d. N/dt = 0 – Zero Growth Isoclines – Above: Population decreasing – Below: Population increasing

Competition K 2 • Isoclines don’t cross? K 1/α 12 N 1 K 2/α 21 N 1 K 1/α 12 • Isoclines cross? K 2 N 2 K 2/α 21 *Pp 257 -260

Competition • * = all sp 1, no sp 2 • ** = all sp 2, no sp 1 K 1/α 12** d. N 1/dt =0 N 2 N 1 * K 1

Competition K 2 N 2 d. N 2/dt =0 N 1 K 2/α 21

Competition K 1/α 12 K 2 K 1/α 12 N 2 N 1 K 2/α 21 K 1 N 1 K 2/α 21

Isocline Analysis Species 1 wins Species 2 wins K 2 K 1/α 12 K 2 N 2 N 1 K 2/α 21 K 1 N 1 K 2/α 21 • Sp. 1 isocline above • Sp. 2 most vulnerable to interspecific competition • Sp. 1 most vulnerable to interspecific competition

Isocline Analysis Unstable Coexistence K 2 N 2 K 1/α 12 N 2 K 2/α 21 N 1 K 2/α 21 K 1

Isocline Analysis Stable Coexistence K 1/α 12 K 2 N 2 N 1 K 1 K 2/α 21

What would be the outcome of competition based on the Model? • Species 1 wins – Species 2 goes extinct • Species 2 wins – Species 1 goes extinct • Both species win – A stable equilibrium is reached • Neither species goes extinct • Because the species have a greater competitive effect on themselves than on each other. – Intraspecific competition > interspecific competition • We don’t know who is going to win, but one species goes extinct – An unstable equilibrium exists • Either species 1 reaches K 1 and species 2 becomes extinct or vice versa. • Because both species compete more strongly with individuals of the other species than they do among themselves. – Interspecific competition > intraspecific competition