Chapter 06 INTERSPECIFIC COMPETITION.docx

1、Chapter 06 INTERSPECIFIC COMPETITIONChapter 06 INTERSPECIFIC COMPETITION (种间竞争)Individuals of one species interact with individuals of another species. The effects of those interactions on population growth can be neutral, positive or negative.1. Neutral interactions have no effect on the growth of

2、the population. This is called neutralism.2. Positive interactions benefit both organisms. They are called mutualism.3. Commensalism occurs when on species benefits and the other is not affected in any way. 4. Amensalism is the coaction in which one species is adversely affected by other species, wh

3、ich remains unaffected.5. Predation is the killing and consumption of a prey.6. Parasitism is in an interaction in which one organism, usually small, lives in or on another from which it obtains food. There is adverse effect on the two species or individuals that compete for a resource that is in li

4、mited supply. This interaction between species is interspecific competition. Interspecific competition may be exploitative or interference.Exploitation means that the individual takes as much of the resource as it can but does not interact with other members of the population, e.g. each pig at a tro

5、ugh has a place and eats as much as it could. The focus of competition is the food.Interference is the type of intraspecific competition that involves interaction between individuals, e. g. lions eating a zebra in which the non-dominant lions cannot get a place to feed and have to wait until the mor

6、e dominant animals have finished.Place becomes the focus of competition rather than the food.CLASSIC COMPETITION THEORYTHE LOTKA-VOLTERRA MODEL.The Lotka-Volterra predatory model assumes that the number of predators depend on the prey population.Lotka and Volterra arrived independently to mathematic

7、al expressions that describe the interaction between two species using the same resource.Both began with the logistic equation for population growth: for species 1 and species 2 dN1 = r1N1 (K1 N1) dt K1 dN = instantaneous rate of change dtN = number of individuals; r = biotic potential t = timeK= ca

8、rrying capacity(K - N) it is a measure of the environmental resistance or the effect of K crowding. This represents the opportunity for further population growth.dN2 = r2 N2 (K2 N2) dt K2 they then added to the logistic equation for each species a coefficient to account for the competitive effect of

9、 one species on the population growth of another. For species 1, N2 is the coefficient that gives the competitive effect of species 2. N2 is the number of species 2 individuals and is the competitive impact per individual of species 2 on species 1.This constant converts the number of members of one

10、species population, 2, into an equivalent number of members of the other , 1.For species 2, the coefficient is N1.The paired equations, which now consider both intraspecific and interspecific competition aredN1 = r1N1 (K1 N1 N2) dt K1 dN2 = r2 N2 (K2 N2 N1) dt K2 In the logistic equation, as the num

11、ber of individuals in each population (N) increases toward its carrying capacity (K), the growth of the population (dN/dt) approaches zero.The addition of each new individual has an inhibitory effect on its further population growth: intraspecific competition. This inhibitory effect of species 1 on

12、itself is 1/K1, an of specie 2 on itself is 1/K2.The inhibitory of effect of each new individual of species 2 on species 1 is /K1, and each new individual of species 1 on species 2 is /K2.Any one species will stop growing when its carrying capacity has been reached by the combination of its own numb

13、ers plus the individuals of the other species multiplied by the appropriate competition coefficientSpecies 1 will stop growing when N1 + N2 = K1Species 2 will stop growing when N2 + N1 = K2When N2 is 0, then N1 = K1; when N1 is 0, then N2 = K1/. When N1 is 0, then N2 = K2; when N2 is 0, then N1 = K2

14、/The presence of species 1 decreases the carrying capacity of species 2, and vice versa.The two species will reach equilibrium when dN1 = dN2 = 0 dt dtSEE GRAPHS ON PAGE 245. MAKE SURE YOU UNDERSTAND THESE GRAPHS AND CAN INTERPRET THEM.The Lotka-Volterra model produces a cyclic population curve show

15、ing the population fluctuation of prey and predator.It is too simple to fit any real interacting populations of prey and predator.COMPETITIVE EXCLUSIONGauses rule or the competitive exclusion principleTwo species with identical ecological requirements cannot occupy the same environment. Two species

16、cannot occupy the same ecological niche. Complete competitors cannot coexist.Conditions for necessary for competitive exclusion to take place:1. Resources are short supply for competition to take place.2. Competitors must remain genetically unchanged for a sufficiently long period to time for one species t