Chap. 21 Competition theoryChap.22 Competition in nature

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Competition

• Intraspecific or interspecific competition

• Interference competition occurs when one individual actively interferes with another individual's access to a resource.

• Exploitative competition is usually an interspecific interaction. While the use of the resource by the individuals of one species reduces the availability of the resource to the other.

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Competition

• 21.1 The emergence of competition as a central theory in ecology was slow and tentative.

• 21.2 The experiments of Tansley, Gause, and Park provided early experimental demonstrations of competition.

• 21.3 The competitive exclusion principles states that two species cannot coexist on a single limiting resource.

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• Fig. 21-1 (a) Increase in population of two species of Paramecium when grown in separate cultures.

• (b) when grown together.

• (Gause 1934)

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• 21.4 Populations may be regulated by intraspecific and interspecific competition.

• 21.5 The logistic equation can be modified to incorporate interspecific competition.

• 21.6 Equilibrium competition models reveal conditions for coexistence of tw competing populations.

• 21.7 A graphic representation illustrates the basic features of logistic cometition.

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The logistic equation

• dNi/dt = riNi (1-Ni/Ki)

• dNi/dt = riNi (1-Ni/Ki - aijNj/Ki) (21-3)

• dNj/dt = rjNj (1-Nj/Kj - ajiNi/Kj) (21-4)

at equilibrium

• (Ki - Ni - aijNj) / Ki = 0

• (Kj - Nj - ajiNi) / Kj = 0

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Fig. 21-4

(b) Ki - Ni - aijNj = 0

(c) Kj - Nj - ajiNi = 0

二元一次方程式Ni 和 Nj

.

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Fig. 21-5 Graphic representation f the equilibrium conditions for two species of which species i is the

better competitor.

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Fig. 21-6 The course of competition between two populations.

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Fig. 21-7 (a) conditions for the stable coexistence of two competing species.

(b) outcome of competition between two species that are both more strongly limited by interspecific competition than by intraspecific competition. The populations tend to diverge

from the equilibrium point.

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•請應用 Lotka-Volterra model 預測兩種相互競爭的族群 , 其間競爭的最後結果。假設甲族群對乙族群的競爭系數是 β; 乙族群對甲族群的競爭系數是 α; 甲族群的族群數量是Ｎ 1; 而其承載量是Ｋ 1; 乙族群的族群數量是Ｎ 2; 而其承載量是Ｋ 2。起初時 , 甲族群數量是50, 乙族群有 90。請按下列 (4與 5題 )的數值 , 寫出甲乙族群最後的數量 (Ｎ 1, Ｎ 2)。

※同時必要寫出其相關的計算過程，才可得分。公式如下 (參考用 )：※ dN1/dt = r1N1 (k1 - N1 - αN2)/K1 ，※ dN2/dt = r2N2 (k2 - N2 - βN1)/K2 。

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計算出其結果• (1) 若 α=1.2 β=0.8 Ｋ 1 =200 Ｋ 2 =200,

• (2) 若 α=0.8 β=1.2 Ｋ 1 =160 Ｋ 2 =250,

• (3) 若 α=1.4 β=1.4 Ｋ 1 =260 Ｋ 2 =260,

期末考題範例

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Chap.22 competition in nature• How does competition occur?

• 1. Consumptive competition ( 可再生資源 )

• 2. Preemptive competition (open space 的佔有 )

• 3. Overgrowth competition ( 個體成長 )

• 4. Chemical competition ( 產出 toxin)– allelopathy

• 5. Territorial competition (defense of space)

• 6. Encounter competition

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Chemical competition

• Several species of sage of the genus Salvia apparently use chemicals to inhibit the growth of other vegetation.

• Clumps of Salvia usually are surrounded by a halo of bare soil separating the sage from neighboring grassy areas (Fig. 22-1).

• Bartholomew (1970) suggested that the halo zone around Salvia could be caused by grazing or by seed eating birds and mammals.

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Fig. 22-1 (a) bare patch at edge of a clump of sage includes a 2-meter-wide with no plants (A-B) and a wider area of

inhibited grassland (B-C).(b) aerial view shows sage and California sagebrush invading

annual grassland in the Santa Inez Valley of California.

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Chemical competition

• In order to test his hypothesis, he placed cages in the halo zone to keep out small birds and mammals.

• After 1 year, the exclosure cages contained about 20 times as much plant biomass as the controls, and about the same amount as found in the grassy area beyond the halo.

• Harper interpreted these results as suggesting that "the toxin hypothesis is unnecessary to account for the observed pattern of vegetation.

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• Fig. 22-25 The phenomenon of character displacement.

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• Fig. 22-26 Proportions of individuals with breaks of different sizes in populations of ground finches on several of the Galapagos islands.

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