BIOB50H3 Chapter Notes - Chapter L#10: Niche Differentiation, Cyanobacteria, Desiccation
CHAPTER 14: COMPETITION (317-325 / 329-332)
- Carnivorous plants use animal prey as an alternative nutrient source when competition
is intense
Pitcher plant only benefited from animal prey when neighbours were removed
INTRODUCTION
- Tansley work on 2 species of bedstraw plants one was restricted to acidic soils, the
other to calcareous even in places where the 2 species grew w/I inches of eachother,
each remained confined to its soil type found that if grew each alone, they could
survive on the soil type, but if grew together on a specific one, one or the other would
drive the other into extinction
Work is one of the first on competition: a non-trophic interaction between
individuals of 2> species, in which all species are negatively affected by their shared
use of a resource that limits their ability to grow, reproduce, or survive
oInterspecific competition: between indiv. Of different species
oIntraspecific competition: between indiv. Of a single species
oBoth are density dependent factors
-Resources: the components of the env. Such as
food/water/light/space that are required by
species
- Full set of resource, along with other biotic and
abiotic requirements, is known as the
fundamental/ecological niche
Realized niche: a more restricted set of
conditions a species is limited to, largely
because of species interactions
GENERAL FEATURES OF COMPETITION (14.1)
- Each species requires and obtains resources in diff. ways these mechanisms are used
to compete, and the intensity and ultimate outcome of competition can vary widely
among species
Species may compete directly or indirectly
-Exploitation competition: species often compete indirectly through their mutual effects
on the availability of a shared resource occurs b/c indiv. Reduce the supply of a shared
resource, as they use it
-Interference competition: case in which one species directly interferes w/ the ability of
its competitors to use a limiting resource (eg. Carnivores fighting eachother over an
animal prey // eg. Acorn barnacle crushes other barnacle species as it grows)
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- Interference comp. also occurs in plants w/ regards to light interference comp. can
take the form of allelopathy: individuals of one species realise toxins that harm the
other species
Competition can vary in intensity depending on resource availability and type
-Plants can compete aboveground for light, and below ground for soil and nutrients
relative importance changes depending on which is more scarce
(pg 320) Eg. Below ground might increase if competing in nutrient poor soils
Wilson and Tilman experiment used a perennial grass selected series of 5x5m
plots of natural vegetation growing in sandy, nitrogen poor soils for 3 years,
treated ½ plots w/ nitrogen-rich fertilizer (this period allowed those plants to adjust
to the change in soil nitrogen levels) at end of 3 year period, planted the grass
(Schizachyrium) into all the plots (high-nitrogen plots and low-nitrogen plots), they
were grown under 3 treatments
o1. w/ neighbours present (competition)
o2. Neighbour present, but w/ neighbour stems tied back (which prevented
above ground competition)
o3. W/ neighbour roots and stems removed (no competition)
Results: found that while total comp. did not differ between low nitrogen and high
nitrogen plots (total underground +
aboveground comp.), belowground
comp. was most intense in the low-
nitrogen plots
oAlso found that
aboveground comp.
increased when light levels
were low
Conclusion: intensity of comp.
depends on what resource is more
scarce
Competition is often
asymmetrical
-Competing w/ other
species = both have less
resource = both species
become less abundant
however: in most cases,
effects of competition
are unequal or
asymmetrical; one
species harms another
more than it is harmed
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- Thus: even though one species is superior, the inferior one still takes up some resources,
but the effect of the superior is stronger than the inferior
-Amensalism (-/0): interaction in which individuals of one species are harmed, while
individuals of the other species are not affected at all
Eg. Corals grow over one another and deprive them of light
Eg. Tilman between w/ freshwater diatoms competiton for silica grew 2 diatom
species along and in competition w/ eachother when grown alone, each species
reduced silica to a lower concentration reached stable pop. Size
oWhen grew in comp. Synedra diatom drove the Asterionella diatom into
extinction b/c it reduced silica to low levels that asterionella couldn’t survive
under
Competition can occur between closely or distantly related species
-Brown and Davidson experiment 3 year experiment in desert of Tucson, Arizona b/c
suspected rodents and ants may compete b/c both eat seeds used 4 treatments
1. Plots in which 1/4inch wire mesh excluded seed-eating rodents and
from which rodents w/I the fence were removed by trapping
2. Plots in which seed-eating ants were excluded by applying insecticides
3. Plots in which both rodents and ants were excluded by fencing,
trapping, and insecticides
4. Plots in which both rodents and ants were left undisturbed
Results: relative to control, number of ant colonies increased by 71% in plots w/o
rodents, and rodents 18% in plots ants were excluded // plots w/o ants/rodents saw
plant seed density increase by 450%
oFound that when one group was excluded, the one that remained ate as
much as the rodents + ants combined would eat that much if didn’t have to
compete for resources
COMPETITIVE COEXISTENCE (14.2)
-Competitive exclusion: if a dominant species prevents another species from using
essential resources, the inferior species may become locally extinct
In reality, most species show a competitive coexistence: ability to coexist w/ one
another despite sharing limiting resources
Competitors that use limiting resources in the same way cannot coexist
-Gause study of 3 species of Paramecium P.auerlia in comp. w/ P.Caudatum drove
P.Caudatum to extinction
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Document Summary
Carnivorous plants use animal prey as an alternative nutrient source when competition is intense. Pitcher plant only benefited from animal prey when neighbours were removed. Of different species: intraspecific competition: between indiv. Of a single species: both are density dependent factors. Such as food/water/light/space that are required by species. Full set of resource, along with other biotic and abiotic requirements, is known as the fundamental/ecological niche. Realized niche: a more restricted set of conditions a species is limited to, largely because of species interactions. Each species requires and obtains resources in diff. ways these mechanisms are used to compete, and the intensity and ultimate outcome of competition can vary widely among species. Exploitation competition: species often compete indirectly through their mutual effects on the availability of a shared resource occurs b/c indiv. Reduce the supply of a shared resource, as they use it.
