本篇文章共分 5 段，從一般的生物共同演化、矮松與藍頭松鴉看似奇特的搭配、矮松特別的種子產量模式、到藍頭松鴉所發展出來的特殊適應能力，說明這兩種生物是如何相互利用以達到共存共榮的繁衍模式。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

Pinyon Pines and Pinyon Jays 矮松與藍頭松鴉

1. 生物的共同演化關係

   Organisms of different species frequently evolve adaptations that make them utterly and specifically dependent on each other for resources. For example, many trees must have mycorrhizal fungi living in their root systems, fungi that are indispensable to the tree because they facilitate mineral uptake from the soil. In turn, the fungi rely on the trees to photosynthesize: they use some of the tree's chemical food as their only energy source. Such intimate relationships are examples of coevolution through which two species become so interdependent that they can thrive only in each other’s presence.

   不同物種的生物經常演化出一些適應性，使它們在資源方面完全和特別地依賴對方。例如，許多樹木的根系中必須有菌根真菌，這些真菌對樹木來說是不可或缺的，因為它們有助於從土壤中吸收礦物質。反過來，真菌依靠樹木進行光合作用：它們使用樹木的一些化學食物作為其唯一的能量來源。這種親密的關係是共同演化的例子，通過這種關係，兩個物種變得如此相互依存，以至於它們只能在對方的存在下才能茁壯成長。

2. 矮松與藍頭松鴉

   At first glance, the relationship between pinyon pine trees and the pinyon jay does not appear to be one of coevolution. Pinyon pines produce cones and seeds that attract seed predators, especially the pinyon jay. A seed, of course, contains an embryonic plant for the next generation. Why sacrifice it to an animal? Some plants have poisonous seeds, an obvious adaptation to reduce loss to animals. Pinyons, however, have an array of characteristics that combine to encourage jays to visit the pines and help themselves to the seeds. Cones are positioned upward and outward on the tree, so the seeds inside are in plain sight of the jays, essentially inviting them to partake. Pinyon seeds are unusually large, and each seed is high in energy. The seed coat is thin, meaning that birds such as pinyon jays can not only ingest the seeds but also digest them. In many plants, an indigestible seed coat permits the seed to pass unharmed through the bird’s alimentary system. Pinyon seed coats differ in color between edible and nonviable seeds, signaling the jays as to which they should select.

   乍一看，矮松與藍頭松鴉之間的關係似乎不是一種共同演化的關係。矮松產生的松果和種子會吸引種子捕食者，特別是藍頭松鴉。當然，一顆種子包含了下一代的植物胚胎。為什麼要把它獻給動物？有些植物的種子是有毒的，這顯然是為了減少因動物而造成的損失。然而，矮松有一系列的特點，這些特點結合在一起，鼓勵藍頭松鴉造訪並幫助其取得種子。松果在樹上的位置是向上和向外的，所以裡面的種子在藍頭松鴉的視線範圍內，基本上是在邀請它們來吃矮松的種子，矮松的種子異常大，每顆種子的能量都很高。種皮很薄，這意味著像藍頭松鴉這樣的鳥類不僅可以攝取種子，還可以將其消化。在許多植物中，不可消化的種皮可以讓種子毫髮無損地通過鳥類的消化系統。矮松的種皮在可食用和不可食用的種子之間有顏色上的差異，這顯示鳥類應該選擇哪種種子。

3. 矮松種子產量與藍頭松鴉習性

   Attracting seed predators would not seem to be a successful survival strategy for pinyon pines. However, pinyon jays are behaviorally adapted to bury any seeds in excess of their immediate survival needs. This is a useful behavior for the jays, providing they can retrieve some of the buried seeds during winter, and good for the trees, as the unretrieved seeds are ready to germinate. Still, for the jays to bury any seeds, there must be an abundance of seeds far beyond the jays’ immediate needs. One tree could never produce so many seeds, but if all the pinyons in a region produced heavy seed crops at once, they would indeed “flood the market” with vastly more pinyon seeds than the local population of jays could consume. In fact, that is exactly what the pinyon pines do.

   吸引種子捕食者似乎不是矮松的成功生存策略。然而，藍頭松鴉在行為上適應於掩埋任何超過其直接生存需要的種子。這對藍頭松鴉來說是一種有益的行為，因為它們可以在冬季取回一些被埋的種子，對樹木來說也是好事，因為未取回的種子已經可以發芽了。不過，要讓藍頭松鴉埋下任何種子，必須有大量的種子，遠遠超過藍頭松鴉的直接需求。一棵樹不可能產生這麼多的種子，但如果一個地區的所有矮松同時產生大量的種子產量，它們確實會「淹沒市場」，因為大量的矮松種子超出了當地藍頭松鴉的消費能力。事實上，這正是矮松所做的事。

4. 矮松的間歇性爆量種子生產

   It requires a great deal of energy to make so many seeds, so much energy that it is unlikely that a pinyon population could produce such a bumper seed crop every year. More important, however, it would be to the severe disadvantage of the trees to produce large seed crops annually, even if they could. Doing so would make the resource not only abundant but also predictable. Seed predators could, over the years, steadily build their populations, eventually increasing so much that they could, indeed, consume virtually all of the seeds. It is much more adaptive for the plants to produce seed cornucopias intermittently. Doing so has several major advantages. First, energy can be stored for some years and then devoted to cone and seed production, ensuring adequate energy to produce a large seed crop. Second, seed-predator populations will decline in years of low seed production, either through starvation, reduced reproduction, or emigration. Pinyons in most areas have a roughly six-year interval between heavy seed crops.

   製造這麼多的種子需要大量的能量，這麼多的能量使得矮松種群不可能每年都產生如此豐碩的種子產量。然而，更重要的是，每年生產大量的種子產量對樹木來說是非常不利的，即使它們有能力如此做。這樣做將使資源不僅豐富，而且可以預測。多年下來，種子掠奪者可以穩定地增加它們的數量，而的確最終會增加到可以吃掉幾乎所有的種子。對於植物來說，適應性要高的話，應該要能夠間歇性地生產大量種子。這樣做有幾個主要優點。首先，能量可以儲存若干年，然後用於松果和種子生產，確保有足夠的能量來生產大量的種子產量。第二，在種子產量低的年份，種子捕食者的數量會減少，要麼是餓死，要麼是減少繁殖，要麼是遷徙。大多數地區的矮松在大量種子產量之間大約有六年的間隔。

5. 藍頭松鴉的相應適應

   Pinyon jays have so completely adapted to the cycle of the pinyons that their reproduction is tied to it. Most species of birds mature sexually in response to changes in day length. In pinyon jays, however, day length is only one stimulus for reproduction. The other cue is availability of pinyon seeds. When seeds are abundant, jays can breed very early in spring continue breeding through summer, and reenter breeding condition as early as the winter solstice. So the jay population temporarily enlarges in response to one of the intermittent large crops of pinyon seeds. But the increase in the population of jays is less than the increase in the size of the seed crop. Thus many of the seeds of a bumper crop are buried and subsequently germinate, many more than would germinate without planting by the jays.

   藍頭松鴉已經完全適應了矮松的週期，它們的繁殖與矮松的週期息息相關。大多數鳥類的性成熟是對日長變化的反應。然而，在藍頭松鴉中，日長只是繁殖的一個刺激因素。另一個線索是矮松種子的可用性。當種子豐富時，藍頭松鴉可以在春天很早的時候繁殖，繼續繁殖到夏天，並且最早在冬至時重新進入繁殖狀態。因此，藍頭松鴉的數量會暫時增加，以應對間歇性的大量矮松種子的收成。但是藍頭松鴉數量的增加要比種子產量的增加少。因此，許多豐收的種子被埋藏起來，隨後發芽，數量比沒有藍頭松鴉參與播種時發芽的種子要多得多。