プリンキピア

第45章個体群と群集の生態学

Section Summaryこの節のまとめ

Populations with unlimited resources grow exponentially, with an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve. The population of a species will level off at the carrying capacity of its environment.
資源が無制限の個体群は、増加速度を加速させながら指数関数的に増える。資源が制限要因になると、ロジスティック増加曲線に従う。個体群は、その環境の収容力で横ばいになる。

Visual Connection Questions図を使った問題

Exercises 13練習問題 13
Exercise 13問題 13
Figure 45.10b If the major food source of the seals declines due to pollution or overfishing, which of the following would likely occur?
図45.10b 汚染や乱獲でアザラシの主な餌が減少した場合、次のどれが起こりやすいか。
  1. The carrying capacity of seals would decrease, as would the seal population.
    アザラシの環境収容力が低下し、個体群も減少する。
  2. The carrying capacity of seals would decrease, but the seal population would remain the same.
    アザラシの環境収容力は低下するが、個体群サイズは変わらない。
  3. The number of seal deaths would increase but the number of births would also increase, so the population size would remain the same.
    死亡数が増えるが出生数も増えるため、個体群サイズは変わらない。
  4. The carrying capacity of seals would remain the same, but the population of seals would decrease.
    アザラシの環境収容力は変わらないが、個体群は減少する。
Solution解き方

Review Questions確認問題

Exercises 14–16練習問題 14–16
Exercise 14問題 14
Species with limited resources usually exhibit a(n) ________ growth curve.
資源に限りのある種は、通常、________増殖曲線を示す。
  1. logistic
    ロジスティック
  2. logical
    論理的
  3. experimental
    実験的
  4. exponential
    指数
Solution解き方
A
A
Exercise 15問題 15
The maximum rate of increased characteristic of a species is called its ________.
ある種に固有の最大増加率を、その種の________と呼ぶ。
  1. limit
    限界
  2. carrying capacity
    環境収容力
  3. biotic potential
    繁殖ポテンシャル
  4. exponential growth pattern
    指数増加パターン
Solution解き方
C
C
Exercise 16問題 16
The population size of a species capable of being supported by the environment is called its ________.
環境が支えられる、ある種の個体群サイズを________と呼ぶ。
  1. limit
    限界
  2. carrying capacity
    環境収容力
  3. biotic potential
    繁殖ポテンシャル
  4. logistic growth pattern
    ロジスティック増加パターン
Solution解き方
B
B

Critical Thinking Questions考察問題

Exercises 17–18練習問題 17–18
Exercise 17問題 17
Describe the rate of population growth that would be expected at various parts of the S-shaped curve of logistic growth.
ロジスティック増加のS字型曲線の各部分で、予想される個体群の増加速度を説明しなさい。
Solution解き方
In the first part of the curve, when few individuals of the species are present and resources are plentiful, growth is exponential, similar to a J-shaped curve. Later, growth slows due to the species using up resources. Finally, the population levels off at the carrying capacity of the environment, and it is relatively stable over time.
曲線の最初の部分では個体が少なく資源が豊富なので、J字型に似た指数増加を示す。その後、資源を使い尽くすにつれて増加は鈍る。最後に、環境収容力で横ばいとなり、時間がたっても比較的安定する。
Exercise 18問題 18
Describe how the population of a species that survives a mass extinction event would change in size and growth pattern over time beginning immediately after the extinction event.
大量絶滅を生き延びた種の個体群について、絶滅の直後から時間がたつにつれて、サイズと増加パターンがどう変わるか説明しなさい。
Solution解き方
Following a mass extinction event, the few surviving species can be considered to have access to unlimited natural resources since there would be minimal competition (due to low organism density). This means that the species would initially experience rapid exponential population growth, and the number of species members in the environment would rapidly increase over time. However, the further time progresses past the mass extinction event, the more the environment becomes populated by the species and its competitors. As resource availability declines the population growth rate will slow and enter logistic growth. Eventually, the population will meet the carrying capacity of the environment and stop increasing.
大量絶滅の後、生き残った少数の種は、個体密度が低く競争もほとんどないため、自然資源を無制限に利用できると考えられる。そのため、最初は急速な指数増加が起こり、環境内の個体数が速やかに増える。しかし時間がたつにつれ、その種と競争相手が環境を占めるようになる。資源の利用可能量が減ると増加速度が下がり、ロジスティック増加に移る。やがて環境収容力に達し、増加は止まる。
biotic potential (rmax)
繁殖ポテンシャル（rmax）
maximal potential growth rate of a species
ある種が潜在的にもつ最大の増加率。
birth rate (B)
出生率（B）
number of births within a population at a specific point in time
特定の時点における、個体群内の出生数。
carrying capacity (K)
環境収容力（K）
number of individuals of a species that can be supported by the limited resources of a habitat
生息地の限られた資源によって支えられる、ある種の個体数。
death rate (D)
死亡率（D）
number of deaths within a population at a specific point in time
特定の時点における、個体群内の死亡数。
exponential growth
指数増加
accelerating growth pattern seen in species under conditions where resources are not limiting
資源が制限されない条件で見られる、加速する増加パターン。
intraspecific competition
種内競争
competition between members of the same species
同じ種の個体間の競争。
J-shaped growth curve
J字型増殖曲線
shape of an exponential growth curve
指数増加曲線の形。
logistic growth
ロジスティック増加
leveling off of exponential growth due to limiting resources
資源の制限によって、指数増加が横ばいになること。
population growth rate
個体群増加速度
number of organisms added in each reproductive generation
繁殖世代ごとに加わる個体数。
S-shaped growth curve
S字型増殖曲線
shape of a logistic growth curve
ロジスティック増加曲線の形。
zero population growth
個体群のゼロ成長
steady population size where birth rates and death rates are equal
出生率と死亡率が等しく、個体群サイズが一定となる状態。