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27.5:

יעילות תזונה

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Biology
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JoVE Core Biology
Trophic Efficiency

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במהלך זרימת אנרגיה דרך רמות ההזנה במערכת אקולוגית, כמויות גדולות נאבדות בצורת חום כשהאנרגיה משתנה מצורה אחת לשנייה, לפי החוק השני של התרמודינמיקה. במערכת אקולוגית של יער ממוזג, האנרגיה הזמינה לצרכנים ראשוניים מיצרנים ראשוניים היא כ-6000 קילוקלוריות למטר מרובע לשנה. אולם, הצרכנים הראשוניים יכולים להטמיע רק כ-10%מהכמות הזמינה המקורית הזאת ברמת ההזנה הבאה.מדידה זו של מעבר אנרגיה נקראת יעילות מעבר רמת ההזנה, והיא בדרך כלל הגורם העיקרי TLTE או שמגביל אורך שרשראות המזון במערכת אקולוגית, מכיוון שאין מספיק אנרגיה לתמיכה ברמות העליונות.

27.5:

יעילות תזונה

Trophic level transfer efficiency (TLTE) is a measure of the total energy transfer from one trophic level to the next. Due to extensive energy loss as metabolic heat, an average of only 10% of the original energy obtained is passed on to the next level. This pattern of energy loss severely limits the possible number of trophic levels in a food chain.

Trophic Level Transfer Efficiency

Following the second law of thermodynamics, large amounts of energy are lost from the ecosystem and from one trophic level to the next as it is transferred and transformed. In biological systems, this energy is lost as metabolic heat during respiration as one organism consumes the next. The measurement of energy transfer from one trophic level to the next is known as trophic level transfer efficiency (TLTE) and is a function of energy production of the present trophic level and that at the previous level. This measurement has broad implications concerning the total length of food chains.

The “10s Rule”

In general, only about 10% of energy is transferred from one trophic level to the next, and this number can vary from 5-20% depending on the ecosystem. This means that 90% of obtained energy is lost at each trophic level, greatly affecting the maximum number of possible levels in the ecosystem. For example, if an ecosystem received 600,000 Kcal of solar energy from the sun, primary producers would pass on only 60,000 Kcal to herbivores, which would pass only 6,000 Kcal to secondary consumers, 600 Kcal to tertiary consumers and 60 Kcal to quaternary consumers at the top of the food chain. An apex predator like a wolf—needing an average of 2000 Kcal per day—would need to consume a very high quantity of secondary or tertiary consumers to meet its calorie quota per day.

Suggested Reading

Tucker, Marlee A., and Tracey L. Rogers. “Examining Predator–Prey Body Size, Trophic Level and Body Mass across Marine and Terrestrial Mammals.” Proceedings of the Royal Society B: Biological Sciences 281, no. 1797 (December 22, 2014). [Source]

Sanders, Dirk, Andrea Moser, Jason Newton, and F. J. Frank van Veen. “Trophic Assimilation Efficiency Markedly Increases at Higher Trophic Levels in Four-Level Host–Parasitoid Food Chain.” Proceedings of the Royal Society B: Biological Sciences 283, no. 1826 (March 16, 2016). [Source]