Class Notes (838,343)
Canada (510,861)
Biology (6,824)
Hugh Henry (242)
Lecture 11

Lecture 11 - Competition

5 Pages
112 Views
Unlock Document

Department
Biology
Course
Biology 2483A
Professor
Hugh Henry
Semester
Fall

Description
LECTURE 11: COMPETITION  Competition – an interaction between individuals in which each is harmed by their shared use of a limiting resource  Competition occurs between species that share the use of a resource that limits the growth, survival or reproduction of each species  Interspecific competition: Interaction between two species in which each is harmed when they both use the same limiting resource.  Intraspecific competition: Between individuals of a single species. Competition for Resources  Resources – features of the environment required for growth, survival, or reproduction, and which can be consumed to the point of depletion  Examples of resources: o Food o Light for plants o Water in terrestrial habitats o Space, especially for sessile organisms o For mobile animals, space for refuge, nesting, etc.  Species are also influenced by physical factors (abiotic) that are not consumed, such as temperature, pH, salinity. o These factors are not considered to be resources  Competition reduces availability of resources. o Experiments with two diatom species by Tilman et al. (1981) showed that when each species was grown alone, a stable population size was reached. o When grown together, they competed for silica, and one species drove the other to extinction. o Minimum concentration of silica that both species can live at (shown by first two graphs) o Evidently, being able to tolerate the lowest drawdown of resources can be a big advantage for some species  Competition can intensify when resources are scarce  Competition among plants should increase in nutrient-poor soils  Wilson and Tilman (1993) studied grass plants that were transplanted into fertilized and unfertilized plots  Each plot had three treatments: 1. Neighbors left intact (belowground and aboveground competition) 2. Neighbor roots left intact but neighbor shoots tied back (belowground competition) 3. Neighbor roots and shoots both removed (no competition)  Belowground competition (treatment 2) was most intense in nitrogen-limited plots  Aboveground competition for light increased when light levels were low  How important is competition? o Connell (1983) found that competition was important for 50% of 215 species in 72 studies. o Gurevitch et al. (1992) analyzed the magnitude of competition in 93 species in 46 studies: Competition had significant effects on a wide range of organisms.  Potential biases: Researchers may not publish studies that show no significant effects, and a tendency for investigators to study species they suspect will show competition.  Still, they document that competition is common, though not ubiquitous.  Exploitation competition—Species compete indirectly: Individuals reduce the availability of a resource as they use it.  Interference competition: Species compete directly for access to a resource. o Individuals may perform antagonistic actions (e.g., when two predators fight over a prey item, or voles aggressively exclude other voles from preferred habitat) o Interference competition in sessile species (those that aren’t able to move around):  The acorn barnacle crushes or smothers nearby individuals of another barnacle species as it grows, and directly excludes the other species from portions of a rocky intertidal zone o Interference competition in plants:  Individuals of one species grow on or shade other species, reducing their access to light  Allelopathy – plant of one species release toxins that harm other species  “Chemical warfare” between plants  For a resource in short supply, competition will reduce the amount available to each species.  The effects of competition are often unequal, or asymmetrical, and one species is harmed more than the other.  Example: When one species drives another to extinction.  Competition can occur between distantly related species.  In experiments with rodents and ants that eat the same seeds, Brown and Davidson (1977) set up plots with four treatments, as follows: 1. Rodents excluded: ant colonies increased by 71% 2. Ants excluded: rodents increased in number and biomass 3. Both rodents and ants excluded: seed density increased 450% - implies that seeds are a much-needed resource 4. Undisturbed control plots  Competition can influence species distributions: o Connell (1961) examined factors that influence the distribution, survival, and reproduction of two barnacle species on the coast of Scotland.  Distribution of larvae of the two species overlapped.  Adult distributions did not overlap: o Chthamalus were found only near the top of the intertidal zone o Semibalanus were found throughout the rest of the intertidal zone  Using removal experiments, Connell found that Semibalanus excluded Chthamalus from all but the top of the zone.  Semibalanus smothered, removed, or crushed the other species.  However, Semibalanus dried out and survived poorly at the top of the intertidal zone  A “natural experiment” is a situation in nature that is similar in effect to a controlled removal experiment.  Patterson (1980, 1981) studied chipmunk species in mountain forests and found that when a species lived alone on a mountain, it occupied a wider range of habitats than when it lived with a competitor species. Competitive Exclusion  Competing species are more likely to coexist when
More Less

Related notes for Biology 2483A

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit