Chapter 11: Competition
COMPETITION IN PLANTS THAT EAT ANIMALS: A CASE STUDY
Charles Darwin (1875) provided clear experimental evidence of carnivory by plants
- Plants use a variety of mechanisms to eat animals
o Venus flytrap has modified leaves that look like fanged jaws, yet attract insects with a sweet smelling nectar
o Other plants lack moving parts, yet still can eat animals. Pitcher plants, use nectar or visual cues to lure insects into a pitcher-
- Why do some plants eat animals?
o Carnivory in plants may be an adaptation for life in nutrient-poor environments—perhaps providing a way to avoid competing
with other plants for soil nutrients.
- Typically, the root systems of carnivorous plants are less extensive than those of non carnivorous plants that live in the same area
Tansley conducted an experiment with two species of bedstraw plants
- The two species competed with each other, and that when grown on its native soil type, each species drove the other to extinction
- He restriction in nature of G. hercynicum and G. pumilum to a particular soil type resulted from competition between these specie
Tansley’s work on bedstraws is one of the first experiments ever performed on competition
Competition – an interaction between individuals of two species in which each is harmed by their shared use of a resource that
limits their ability to grow, survive, or reproduce
- Competition can also occur between individuals of a single species, in which case it is referred to as intraspecific competition
- As a result of intraspecific competition, the resources available to members of a high-density population can be reduced to such an
extent that growth, survival, or reproduction decreases or emigration increases
- Intraspecific competition can cause density-dependent reductions in population size
Concept 1.1 Competition Occurs Between Individuals of Two Species that Share the Use of a Resource that Limits their Growth, Survival, or
COMPETITION FOR RESOURCES
Organisms compete for resources, which are features of the environment that are required for growth, survival. Or reproduction and which can be
consumed or otherwise used to the point of depletion
ORGANISMS COMPETE FOR RESOURCES SUCH AS FOOD, WATER, LIGHT AND SPACE
When food is scarce, population growth rates plummet
Food and water are intuitive examples of resources because organisms literally consume them
But an organism does not need to absorb, eat, or drink a substance for it to be a resource
- Plants “consume: light
Space can also be viewed as a resource
- Although space is not consumed in the sense of being eaten. Organisms can fill all the available space—thus depleting it—and when
they do, population growth rates decrease
Physical Factors (abiotic factors) – features of the environment that affect population growth rates but are not consumed or
The same substance can be a physical factor for some organisms and a resource for others
- Ex. Terrestrial animals, and aquatic animals oxygen
COMPETING ORGANISMS REDUCE THE AVAILABILITY OF RESOURCES
Organisms can consume resources to such an extent that resource availability drops and population growth rates fall
When the two species competed with each other, Synedra drove Asterionella to extinction, apparently because it reduced silica to such low levels
that Asterionella could not survive
COMPETITION CAN INCREASE IN INTENSITY WHEN RESOURCES ARE SCARCE
Researchers have suggested that the relative importance of aboveground and belowground competition in plants might change depending on
whether aboveground or belowground resources are scarcer
S. scoparium individuals were grown under three treatments:
1. With neighbors left intact
2. with neighbor roots left intact but neighbor shoots tied back
3. with neighbor roots and shoots both removed.
In treatment 1 there was both belowground and aboveground competition, while in treatment 3 there was no competition.
In treatment 2, the tied-back neighbor shoots did not shade S. scoparium, but the act of tying did not appear to affect neighbor roots, so that
treatment was interpreted as belowground competition.
Aboveground competition was estimated as the amount of competition in treatment 1 minus the amount in treatment 2.
Wilson and Tilman found that while the total competition (the sum of belowground and aboveground competition) did not differ between the low-
and high-nitrogen low-nitrogen plots
They also found that aboveground competition for light increased when light levels were low
Thus, their work demonstrates that the intensity of competition can increase when the resource being competed for is scarce.
COMPETITION FOR RESOURCES IS COMMON IN NATURAL COMMUNITIES
Schoener, Connell and Guravitch showed that competition had significant (though variable) effects on a wide range of organisms, including
carnivores, herbivores, and producers such as plants
Concept 11.2 Competition, Whether Direct or Indirect, Can Limit the Distributions and Abundances of Competing Species
GENERAL FEATURES OF COMPETITION
Since the beginning of ecology as a field of science, ecologists have thought that competition between species was important in natural
SPECIES MAY COMPETE DIRECTLY OF INDIRECTLY
Exploitation Competition – Species often compete indirectly through their mutual effects on the availability of a shared resource
Interference Competition – occurs when species compete directly for access to a resource that both require, such as food or space
In interference competition, individuals perform antagonistic actions that directly interfere with the ability of their competitors to use a limiting
Interference competition also occurs in plants
Competition in plants that eat animals: a case study. Charles darwin (1875) provided clear experimental evidence of carnivory by plants (cid:173) plants use a variety of mechanisms to eat animals. Venus flytrap has modified leaves that look like fanged jaws, yet attract insects with a sweet smelling nectar: other plants lack moving parts, yet still can eat animals. Tansley"s work on bedstraws is one of the first experiments ever performed on competition. Intraspecific competition can cause density-dependent reductions in population size (cid:173) Concept 1. 1 competition occurs between individuals of two species that share the use of a resource that limits their growth, survival, or. Organisms compete for resources, which are features of the environment that are required for growth, survival. Or reproduction and which can be consumed or otherwise used to the point of depletion. Organisms compete for resources such as food, water, light and space. When food is scarce, population growth rates plummet.