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Chap. 21 Competition theory
Chap.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)
• dNj/dt = rjNj (1-Nj/Kj - ajiNi/Kj)
at equilibrium
• (Ki - Ni - aijNj) / Ki = 0
• (Kj - Nj - ajiNi) / Kj = 0
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(21-4)
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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Ｎ1;
而其承載量是Ｋ1; 乙族群的族群數量是Ｎ2;
而其承載量是Ｋ2。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(Ｎ1, Ｎ2)。
※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 Ｋ1 =200 Ｋ2 =200,
• (2) 若 α=0.8 β=1.2 Ｋ1 =160 Ｋ2 =250,
• (3) 若 α=1.4 β=1.4 Ｋ1 =260 Ｋ2 =260,
期末考題範例
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Chap.22 competition in nature
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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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問題與討論
 請提出問題！
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