Class Notes (1,100,000)
CA (630,000)
UTSC (30,000)
BIOB50H3 (300)
Lecture 9

BIOB50H3 Lecture Notes - Lecture 9: Isocline, Interspecific Competition, Flea Beetle


Department
Biological Sciences
Course Code
BIOB50H3
Professor
Marc Cadotte
Lecture
9

This preview shows pages 1-3. to view the full 17 pages of the document.
Lecture 9 and 10
Chapter 11
Competition
A.G. Tansley did one of the firt experiments on competition in 1917
He wanted to explain the distribution of two species of bedstraw: GALIUM HERCYNICUM, which was restricted to
acidic soils, and G. PUMILUM, restricted to calcareous soils.
Tansley found that if grown alone, each species could survive on both acidic and calcaereous soils
But when grown together, soil type determined which would survive
Tansley inferred that competition restricted the two species to particular soil types in nature
Organisms compete for resources such as food, water, light, and space
COMPETITION CAN LIMIT THE DISTRIBUTIONS AND ABUNDANCES OF COMPETING SPECIES
As far back as Darwin, competition between species has been seen as an influence on evolution and species
distributions
INTERSPECIFIC COMPETITION is an interaction between two species in which each is harmed when they both use
the same limiting resource
INTRASPECIFIC competition can occur between individuals of a single species
Competition for Resources
COMPETITION occurs between organisms that share the use of a resource that limits the growth, survival, or
reproduction of each species.
Examples of resources that be consumed to depletion include FOOD, WATER IN TERRESTRIAL HABITATS, LIGHT
FOR PLANTS, SPACE (ESPECIALLY FOR SESSILE ORGANISMS), AND SPACE FOR REFUGE AND NESTING (MOBILE
ANIMALS)
An example of competition for space is corals and sea plants on rocks in the ocean
Competing organisms reduce the availability of resources
Experiments using two species of diatoms (single celled algae that make cell walls of silica, SiO2) were done by
tilman et al. (1981)
When each species was grown alone, they reached a carrying capacity and silica concentrations were reduced
When grown together, the two species competed for silica, and one species drove the other to extinction

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

When grown alone, synedra and asterionella (purple and red linesrespectively) each reached a stable
population size and reduced silica concentrations at low levels. Synedra reduced silica concentration levels to
lower levels than did asterionella, and may explain why synedra outcompeted asterionella when the two
species were grown together (graph below). When the two were grown together in competition, synedra drove
asterionella to extinction

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

The population that is able to persist at lower resources concentrations will out compete other species. THIS IS
REFFERED TO AS R* or R-STAR
How important is competition in ecological communities?
Schoner (1983) found that 390 species studied, 76% showed effects of competition under some conditions;
57% showed effects under all conditions tested.
Connell (1983) found that competition was important for 50% of 215 species in 72 studies
Gurevitch et al. (1992) analyzed the magnitude of competitive effects found for 93 species in 46 studies. They
showed that competition had significant effects on a wide range of organisms
General Features of Competition
EXPLOITATION COMPETITION: species compete INDIRECTLY through their mutual effects on the availability of a
shared resource
Competition occurs simply because individuals reduce the availability of a resource as they use it and R-STAR
becomes very important then
INTERFERENCE COMPETITION: species compete DIRECTLY for access to a resource
Individuals may perform antagonistic actions for example try to kill eachother over resources
Interference competition can also occur in sessile species (animals or plants that are permanently attached to
something). An example is the acorn barnacle
ALLELOPATHY: a form of interference competition in which individuals of one species release toxins that harm
other species
Example: cattle do not eat the introduced spotted knapweed, giving it an edge over native plants that cattle do
eat. It also releases a toxin called CATECHIN into surrounding soils, which has been shown to reduce
germination and growth of native grasses
You're Reading a Preview

Unlock to view full version