英語教育・英語学習に関する独り言29　ー　模擬TOEFL問題作成について⑤

前回記事の続き。自分はインフルから回復したが、今度は妻が罹患。外出するわけにもいかず、家でコツコツと問題作成。

TOEFL iBT リスニングのスクリプトを生成系AIに書かせるが、何回やっても思うクオリティにならない。色々とプロンプトを試してはみるものの、TOEFL特有の、あのインフォーマルかつアカデミックな雰囲気というのは、結局人間が書くことでしか出せないような気もする（現時点では）。

ということで、ChatGPT や Gemini の手を借りつつ、作り上げたのが以下のやりとり。

Professor:
All right, class, settle down. Up until last week, we had been discussing many examples of keystone species. Today, we will be getting into a new chapter. But before we do that, can someone reiterate the definition of a keystone species?

Female Student:
Um, a keystone species is like, a species that has a huge impact on everything around it, even though there might not be many of them. This species helps maintain the structure of the whole ecological community. Without these keystone species, the whole ecosystem would change, or even disappear.

Professor:
Right. You did well, Susan. So, give us one example of a keystone species and briefly summarize its impact on the environment. Caleb?

Male Student:
Ah, one good example of a keystone species is elephants. They are not a majority on the savanna, but they are responsible for keeping trees from growing. Without them, the savanna could soon turn into a forest.    

Professor:
Very well. They feed on grass and shrubs. When they come across a tree, they eat branches and bark, and eventually knock it down and even uproot it. Also, they often trample vegetation as they move through the savanna, which can inhibit seed germination and plant growth. Their size and weight cause soil compaction, making it difficult for tree roots to penetrate and access nutrients and water. In this sense, elephants, although few in number, play a central role in maintaining the environment, and are indeed a keystone species. All right. Today, we will turn our attention to something a little similar but greatly different. That is, ecosystem engineers. Susan, can you define what ecosystem engineers are?

Female Student:
Well, ecosystem engineers are species that directly or indirectly modify their environment. They alter the physical features of their habitat in a way that benefits other organisms. 

Professor:
Correct. And therein lies the difference. Keystone species maintain the ecological structure of the environment, while ecosystem engineers modify it. So, Caleb, what is the most prominent ecosystem engineer?

Male Student:
Umm, beavers? They build dams and change the whole landscape.

Professor:
Excellent! Beavers are ecosystem engineers found across North America and in parts of Eurasia. But today, we will shift our focus from beavers to a specific bird species, a bird species that is very unique and is found worldwide. We’ll be discussing woodpeckers to examine how they are masters at forest engineering. First, let me begin by asking you this question. What springs to mind first when you think of woodpeckers?

Male Student:
Well, obviously, their pecking. They peck on trees. And they do so because, umm, they want to find something to eat, like insects, larvae, and tree sap. 

Professor:
For sure. They do keep down the number of harmful insects by eating them. Because of this behavior, they are sometimes referred to as Tree Doctors or Doctors of the forest. Technically, however, this is foraging, not engineering. So Susan, what came to your mind?

Female Student:
What came to my mind first and foremost is their drilling. They drill holes in the tree bark to create nesting sites. You just said they are called tree doctors, but they are also skilled carpenters. 

Professor:
There you go. That’s a good metaphor to describe what they do. Indeed, they modify the environment by excavating cavities in trees. These tree holes serve as their homes. To be more precise, they use these holes mostly for breeding purposes. Many woodpecker species do not reside in the nesting holes permanently, but that’s another discussion. Back on track. They create nesting sites every breeding season, which means that there are new tree cavities every year. What happens to the old ones? Well, these abandoned nesting cavities become invaluable secondhand real estate for other forest neighbors like owls, tits, wood ducks, squirrels, flying squirrels, you name it. Now, let’s remember. Just a minute ago, Susan successfully recapped what ecosystem engineers are. And I quote. They alter the physical features of their habitat in a way that benefits other organisms. In this regard, woodpeckers perfectly fit the mold here. 

Male Student:
Professor, I have a question. Yeah, OK, woodpeckers offer housing to other animals in the forest. That’s good. But doesn’t their drilling behavior cause much damage to the tree?  

Professor:
You just raised an important point, Caleb. It’s true that woodpeckers inflict damage on the trees. Nevertheless, they are still excellent ecosystem engineers. How? Well, many woodpecker species tend to peck on old trees. Decaying trees, really, because one: these trees tend to provide them with more food sources. There are more larvae beneath the bark of a decaying tree than beneath the bark of a young, healthy tree. And two. It is easier to excavate holes in the bark of a decaying tree. What happens as a result is, they damage the tree to the point where the nutrient circulation between leaves and roots is significantly disrupted. Then, the tree eventually falls and dies. However, we have to see the big picture here. The fallen tree will soon turn into a haven for other organisms like beetles, termites, and fungi. They are the decomposers of the forest environment, and they play a crucial role in breaking down dead trees and returning essential nutrients to the soil. Nutrient-rich soil is literally the foundation of any and all forests. So, in a way, it can be said that woodpeckers help accelerate the rebirth cycle of the forest. I hope this answers your question.

Male Student:
Yes, of course. I think I’m starting to see what forest engineering is all about. 

Professor:
That’s good to hear. Now, I will project several slides of different kinds of woodpeckers to show you that, while varied in size and color, they all share the distinctive features of hammer-like heads and chisel-like bills.

セリフ部分だけだと943語？一応、話者のスピードを200WPMぐらいに設定するとすると、4分半～5分弱ぐらい。まあ、TOEFL iBTとしては普通か、ちょっと長いぐらいか。使われている語彙のレベルは極めて標準的。トピックも、ちゃんと勉強していれば、別に中学生ぐらいでも理解できるはず。全体的な難易度は、TOEFL iBT と TOEFL Junior の中間、やや iBT 寄りだろうか。

あとはこれに関連して設問を５つほど考える。その際にサインポストをつけ加えることもある。サインポストについてはこちらの記事を参照のこと。TOEFL大好きな人なら知っているはず。

設問と選択肢を考えたら、次に音声作成が必要となる。以前は複数グーグルアカウントで ElevenLabs を使っていたが、有料アカウントがちょっと高額に感じられるのと、試しに再生した音声でも free characters が消費されるのが気になった。さらに先日、悪魔のささやきで $67 ＝一万円ちょっとを払って、revoicer の一番ベーシックなプランを購入してしまった。なので、今回の音声作成は自分自身が revoicer に慣れるためにも、そちらを使ってみようと思う。