Ecology — Practice Problems with Detailed Solutions

1.Question 1. A population has carrying capacity K equal to one thousand and intrinsic growth rate r equal to zero point five. When population size N equals two hundred, what is the population growth rate dN dt? The logistic growth formula is dN dt equals r N times K minus N over K.

題目一。某族群的環境容納量 K 等於 1000，內在增長率 r 等於 0.5。當族群大小 N 等於 200 時，族群增長速率 dN dt 為多少？邏輯斯成長公式為 dN dt 等於 r N 乘以 K 減 N 除以 K。

2.Answer: eighty individuals per unit time. Substitute: dN dt equals zero point five times two hundred times eight hundred over one thousand, equals one hundred times zero point eight, equals eighty.

答案：每單位時間 80 個個體。代入：dN dt 等於 0.5 乘 200 乘 800 除以 1000，等於 100 乘 0.8，等於 80。

3.Follow up: when is growth rate maximized? At N equals K over two, that is five hundred. At that point dN dt equals zero point five times five hundred times zero point five, equals one hundred twenty-five.

追問：增長速率何時最大？當 N 等於 K 除以 2，即 500。此時 dN dt 等於 0.5 乘 500 乘 0.5，等於 125。

4.Question 2. Which of the following statements about biomagnification is INCORRECT? Options: A, lipophilic toxins are more likely to undergo biomagnification than water-soluble ones; B, top predators have the highest toxin concentration; C, DDT causing eggshell thinning in bald eagles is a biomagnification example; D, biomagnification causes the highest toxin concentration in primary producers.

題目二。下列關於生物放大作用的敘述，何者錯誤？選項：A 脂溶性毒素比水溶性毒素更容易發生生物放大；B 頂級掠食者體內毒素濃度最高；C DDT 造成白頭海鵰蛋殼變薄是生物放大的例子；D 生物放大會使初級生產者體內毒素濃度最高。

5.Answer: D is incorrect. The defining feature of biomagnification is that higher trophic levels have higher concentrations — primary producers have the LOWEST. A B C are all correct: lipophilic substances accumulate in fat, top predators accumulate the most, and DDT in bald eagles is the classic case.

答案：D 錯誤。生物放大的特徵恰恰是越高營養級濃度越高——初級生產者最低。A B C 都正確：脂溶性物質累積在脂肪、頂級掠食者累積最多、DDT 在白頭海鵰是經典案例。

6.Question 3. A large tree canopy blocks sunlight, killing the seedlings below. The tree itself is unaffected. What type of interaction is this? Options: A, competition; B, commensalism; C, parasitism; D, amensalism.

題目三。大樹樹冠遮蔽陽光，使樹下的幼苗死亡。大樹本身不受影響。此交互作用屬於？選項：A 競爭；B 片利共生；C 寄生；D 片害共生。

7.Answer: D, amensalism. The tree is unaffected zero, the seedlings are harmed minus, so the relationship is zero minus — exactly amensalism. Competition would be minus minus on both sides, and the problem says the tree is unaffected, ruling that out.

答案：D 片害共生。大樹不受影響為 0，幼苗受害為負，關係為 0 負——正是片害共生。競爭應該是雙方互負，但題目說大樹不受影響，排除競爭。

8.Question 4. On a new volcanic island formed after eruption, which organisms are most likely to colonize first? Options: A, herbaceous plants; B, lichens and mosses; C, shrubs; D, coniferous trees.

題目四。火山爆發後形成的新火山島上，首先定殖的生物最可能是？選項：A 草本植物；B 地衣和苔蘚；C 灌木；D 針葉樹。

9.Answer: B, lichens and mosses. A volcanic island is brand new substrate with no soil — this is primary succession. Pioneer species must grow on bare rock without soil. Lichens secrete acids that break rock down, gradually forming thin soil; mosses then colonize and accumulate organic matter. Herbaceous plants need some soil depth and represent the second or third stage.

答案：B 地衣和苔蘚。火山島是全新基質，沒有土壤——這是初級演替。先驅物種必須能在裸岩上生長，不需要土壤。地衣分泌酸液分解岩石，逐漸形成薄土壤；苔蘚隨後定殖累積有機物。草本植物需要一定土壤深度，是第二或第三階段。

10.Question 5. Regarding thermocline and El Nino, which statement is correct? Options: A, thermocline is a deep layer where temperature changes slowly; B, thermocline promotes mixing between surface and deep water; C, during El Nino years, eastern Pacific upwelling strengthens and fish catches increase; D, during El Nino years, equatorial trade winds weaken and eastern Pacific sea temperature rises.

題目五。關於溫躍層和聖嬰現象，下列何者正確？選項：A 溫躍層是溫度緩慢變化的深水層；B 溫躍層促進表層與深層水混合；C 聖嬰年東太平洋上升流增強，漁獲增加；D 聖嬰年赤道信風減弱，東太平洋海溫升高。

11.Answer: D. A is wrong because thermocline is the middle layer where temperature changes RAPIDLY. B is wrong because thermocline acts as a barrier that PREVENTS mixing. C is wrong because during El Nino, upwelling WEAKENS — nutrients drop and fish catches DECLINE. D correctly describes: weakened trade winds let warm water flow back east, raising eastern Pacific temperature and weakening upwelling.

答案：D。A 錯誤，溫躍層是溫度急速變化的中間層。B 錯誤，溫躍層是阻擋上下混合的物理屏障。C 錯誤，聖嬰年上升流減弱、營養鹽減少、漁獲下降。D 正確：信風減弱使溫暖海水回流東太平洋，海溫升高、上升流減弱。