14.6.2 Interspecific Competition: Ecological Niches

Question 1

Interspecific Competition: Ecological Niches

Answer 1

• Interactions between species can be described in terms of the impact they have on each other.
• Predation can be described as a +/- interaction because one individual benefits and the other is harmed.
• By performing a series of experiments on Paramecium sp., G. F. Gause demonstrated that competitive exclusion could occur.
• Competitive exclusion is considered a -/- interaction because the species are negatively affected.
• Evidence of competitive exclusion in nature includes character displacement in finches that coexist with closely related species.

Question 2

predation

Answer 2

• In predation, an organism obtains most of its food by eating other animals. This term is also applied to herbivores, which “prey” on plants.
• Predation can be described as a +/- interaction because the predator benefits and the prey does not.

Question 3

competitive exclusion

Answer 3

• In 1934, G. F. Gause tested the hypothesis that two species vying for the same resources could not coexist.
• When each of the two species Paramecium aurelia and Paramecium caudatum are grown separately, each population reaches its respective carrying capacity. When they are grown together, P. caudatum is driven to extinction and P. aurelia approaches but does not reach carrying capacity.
• The term competitive exclusiondescribes the elimination of one species by another. Competitive exclusion is difficult to determine in nature because of the variables that must be accounted for.
• One alternative is controlled experiments involving
  competitive species, but these experiments are sometimes logistically difficult. J.H. Connell coined the phrase, “ghost of competition past”, which describes the difficulty of providing scientific explanations for events that have already occurred.

Question 4

character displacement

Answer 4

• Character displacement is the occurrence of characteristics that are more divergent in co-occurring populations than in geographically separated populations.
• Character displacement provides evidence that competitive exclusion has occurred.
• For example, two species of finches have greater similarity in beak length and depth when living in geographically separated areas than when they occur together. When the species coexist, their beaks are more morphologically distinct, most likely because of natural selection favoring less
  competition between the species.

Question 5

An ecological niche

Answer 5

• is an organisms role in the environment

- is the total of an organism’s use of biotic and abiotic factors.

Question 6

True or false?

Competitive exclusion is defined as two species with similar needs and limited resources being unable to coexist.

Answer 6

• true

Question 7

Why might competitive exclusion be difficult to study in the field?

Answer 7

• We have no way of knowing which species have already been excluded by natural selection.

Question 8

Which of the following is not evidence for character displacement?

Answer 8

• If two species of protozoan are innoculated into the same culture vessel, only one will survive.

Question 9

Which of the following graphs illustrates competitive exclusion between two similar species of bacteria grown in the same culture?

Answer 9

• graph B

Question 10

Laboratory experiments have demonstrated that competitors cannot coexist in homogenous, simple environments. Yet in nature, many species with similar resource requirements are able to coexist together within an ecological community. The reason is that

Answer 10

• natural environments are variable in space and time.
• natural environments have a heterogeneous food supply.
• under natural conditions, diseases, bad weather, and predators keep populations well below their carrying capacity.