Ecology: the biology of interaction. 5.20. Concept of effective temperatures
The development of many poikilothermic organisms is fairly well described using the concept of effective temperatures, which treats heat as a resource necessary for development.
Ukrainian Language (latest version) / Russian Language (update stopped)
5.19. Thermobiological Types of Organisms
D. Shabanov, M. Kravchenko. Ecology: Interaction Biology Chapter 5. Autecology and Fundamentals of Environmental Studies
5.21. Climatic variability and some ecological rules
{ "title": "5.19. Thermobiological Types of Organisms", "summary": "The section discusses the influence of temperature on poikilothermic organisms, introducing the concepts of physiological zero and effective temperature, methods for calculating heat units (degree‑days), and examples of thermal requirements for various species.", "body": "Ukrainian language (latest version) / Russian language (update discontinued)\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules\n\n5.20. Concept of Effective Temperatures\nWe have repeatedly noted that temperature is one of the most important ecological factors. One reason is that the rate of chemical reactions depends strongly on temperature. For a rough estimate of this influence the Van’t Hoff rule can be used: the rate of chemical reactions roughly doubles or triples with a 10 °C increase in temperature. This effect of ambient temperature is especially pronounced for poikilothermic organisms. The change in the rate of some biological processes also follows the Van’t Hoff rule. For example, this regularity is well illustrated by the variation in soil carbon dioxide emission (dependent on soil bacterial activity), the locomotion speed of centipedes, intestinal peristalsis in caterpillars, etc.\nIn some cases the temperature regime exerts a regulatory influence on development. Thus, the phenomenon of vernalization in wheat and other plants is known. To explain it, one must point out that wheat (as well as rye, cabbage, etc.) has winter and spring forms. Under warm and moist conditions winter varieties begin to germinate but then halt their development, awaiting winter cold. After exposure to cold for 1–3 months, winter forms resume development and eventually proceed to flowering and fruiting. Spring varieties lack this phase and can complete their whole development at positive temperatures. Vernalization consists in the fact that exposure to low positive temperatures (e.g., holding at +1 °C to +10 °C for several days) triggers the transition of winter forms to normal development, which ends with flowering and fruiting. For many organisms, exposure to low temperatures (cold diapause) is a necessary condition for the initiation of seed development (in plants), egg development (in insects or crustaceans), or other dormant stages.\nHowever, even once development has started, its rate depends heavily on temperature. The development of many poikilothermic organisms is well described by the concept of effective temperatures, which treats accumulated heat as the resource required for development.\nThe study of heat accumulation on development was begun by the well‑known physicist René Réaumur in 1735. Assigned to determine why fruit crops develop differently in various regions of France, he found that the heat required for plant development could be calculated simply by summing the mean daily temperatures over the warm part of the year. If the sum reaches the species‑specific requirement, the crop matures; if not, it does not.\nInitially, researchers summed only positive (above 0 °C) temperatures, but later it became clear that for some species a different temperature threshold is needed. Ultimately the notion of a physiological zero was introduced.\nPhysiological zero (T₀) – the temperature above which development of a poikilothermic organism begins.\nAlthough physiological zero values for many organisms are close to 0 °C, animals living in snow grow and develop at sub‑zero temperatures, while some other organisms cease growth even at positive temperatures. A more precise physiological zero can be determined by examining the relationship between development rate and temperature, as shown in Fig. 5.20.1.\n[IMG_1]\nFigure 5.20.1. Relationship between development rate and development time versus temperature for poikilothermic organisms. A selected segment of the rate‑temperature curve (in this example, from 7 °C to 15 °C) can be treated as linear; development time over this segment follows a hyperbolic relationship. Within this segment, development rate can be calculated using the concept of effective temperatures. The physiological zero (in the example, 4 °C) is the intersection of this line with the zero‑rate axis.\nThe dependence of development time of a poikilothermic organism on temperature is hyperbolic. In contrast, development rate (the inverse of time) varies linearly with temperature over a fairly wide range of this factor. Note that at very low temperatures close to T₀ the linear relationship may break down. This means that the definition of physiological zero given above is not entirely accurate. On the graph, the temperature corresponding to the zero‑rate line is 5 °C, whereas T₀ = 4 °C. T₀ should be calculated by extending the linear portion of the rate‑temperature curve to the zero‑rate level. Moreover, physiological zero may differ for different developmental stages (the figure does not reflect this).\nHaving clarified physiological zero, the concept of effective temperature can be defined. Effective temperature (Tₑ) is the difference between the actual temperature (T) and the physiological zero (T₀): Tₑ = T − T₀.\nThe essence of the effective‑temperature concept is that each developmental stage of a poikilothermic organism requires a specific sum of mean daily effective temperatures, called the thermal constant (TConst). Examples of physiological zero values and thermal constants for several organisms are given in Table 5.20.1.\nTable 5.20.1. Examples of thermal parameters for the development of selected organisms\n\nOrganism | Physiological Zero (T₀) | Developmental Stage | Thermal Constant (TConst)\n--- | --- | --- | ---\nColorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days\nAgrotis segetum (turnip moth) | +10 °C | Full cycle | 955 degree‑days\nCod (roe) | –3.6 °C | Roe development | 150 degree‑days\nIce‑worm | –3 °C | — | —\nWheat | 0 °C | — | —\nPine | +7 °C | — | —\nPea | –2 °C | — | —\nChicken egg | +20.5 °C | — | —\n\nIn fact, the sum of effective temperatures is a measure of physiological time for a poikilothermic organism.\nThus, if development occurs under variable temperature, we must calculate the mean daily effective temperature for each day. The condition for completing a developmental stage is that the accumulated effective temperatures reach the thermal constant. Under constant temperature the calculations simplify: TConst = t × Tₑ, or TConst = t × (T − T₀), where t is the development period (in days).\nThe unit for the sum of effective temperatures and the thermal constant is degree‑days, the product of degrees Celsius and days.\nNaturally, when computing the heat accumulated by the organism, it makes sense to calculate effective temperatures only for those days when T ≥ T₀, because development stops when temperature falls below the physiological zero. If, however, within such a day the temperature exceeds the critical threshold for part of the time, it is sensible to measure time in units other than days (e.g., hours). Hours rather than days should also be used for processes that proceed rapidly.\n\"To assess the growth rate of microorganisms, ‘degree‑hours’ can be used, a fact known to any baker working with yeast. At higher temperatures they develop more intensively, so dough or kvass will be ready faster than at lower temperatures. Temperature also influences the proliferation of lactic‑acid bacteria: milk that stays fresh for a long time in a refrigerator will sour in a warm room within a few hours\" (B.M. Mirkin, L.G. Naumova, 2005).\nFrom the above it follows that, knowing the development period of an organism at two different temperatures (corresponding to the linear segment in Fig. 5.20.1), we can estimate its development period at other temperatures. Suppose at temperature T₁ the organism develops in t₁ days, and at temperature T₂ in t₂ days. Because t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) = TConst, we have t₁T₁ − t₁T₀ = t₂T₂ − t₂T₀, thus t₂T₀ − t₁T₀ = t₂T₂ − t₁T₁. Determining T₀ allows easy calculation of TConst. The development period at temperature T₃ can be computed as t₃ = TConst / (T₃ − T₀).\nFor example, we know that grasshopper eggs develop in 17.5 days at 20 °C and in 5 days at 30 °C. Substituting these values into the equation t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) gives 17.5 × (20 − T₀) = 5 × (30 − T₀), from which T₀ = 16 °C and TConst = 70 degree‑days. Consequently, development would take about 10 days at 23 °C.\nSome data on physiological zero values and thermal constants for particular developmental stages are presented in Table 5.20.1.\nAre calculations based on the effective‑temperature concept always accurate? No. The described logic applies only to narrow temperature ranges, not to all organisms or all processes within them. The most significant drawback of this concept is the discrepancy between development times under constant versus variable temperatures. For instance, a chicken egg develops in 21 days at 40–41 °C; increasing temperature yields no gain. The Colorado potato beetle develops in 23 days at 20 °C, 15 days at 25 °C, and 19 days under fluctuating temperatures, regardless of whether the mean temperature is 20 °C or 25 °C. Variable temperatures are more natural!\nNevertheless, even simple mathematical models provide an advantage in managing biosystems. Imagine you need to plan an agrotechnical measure to protect crops from a pest, and this measure is most effective at a specific developmental stage of the pest (e.g., before pupation). Knowing the timing of mass egg laying and the weather forecast, you can estimate the optimal window for intervention. Is a certain inaccuracy in your calculations really a problem?\nAdditional material:\nEducational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules" }
Species
Physiological zero (T0)
Species
Colorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days
Thermal constant (TConst)
Cod (roe) | –3.6 °C | Roe development | 150 degree‑days
+13,5 °C
Cod (roe) | –3.6 °C | Roe development | 150 degree‑days
Full cycle
{ "title": "5.19. Thermobiological Types of Organisms", "summary": "The section discusses the influence of temperature on poikilothermic organisms, introducing the concepts of physiological zero and effective temperature, methods for calculating heat units (degree‑days), and examples of thermal requirements for various species.", "body": "Ukrainian language (latest version) / Russian language (update discontinued)\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules\n\n5.20. Concept of Effective Temperatures\nWe have repeatedly noted that temperature is one of the most important ecological factors. One reason is that the rate of chemical reactions depends strongly on temperature. For a rough estimate of this influence the Van’t Hoff rule can be used: the rate of chemical reactions roughly doubles or triples with a 10 °C increase in temperature. This effect of ambient temperature is especially pronounced for poikilothermic organisms. The change in the rate of some biological processes also follows the Van’t Hoff rule. For example, this regularity is well illustrated by the variation in soil carbon dioxide emission (dependent on soil bacterial activity), the locomotion speed of centipedes, intestinal peristalsis in caterpillars, etc.\nIn some cases the temperature regime exerts a regulatory influence on development. Thus, the phenomenon of vernalization in wheat and other plants is known. To explain it, one must point out that wheat (as well as rye, cabbage, etc.) has winter and spring forms. Under warm and moist conditions winter varieties begin to germinate but then halt their development, awaiting winter cold. After exposure to cold for 1–3 months, winter forms resume development and eventually proceed to flowering and fruiting. Spring varieties lack this phase and can complete their whole development at positive temperatures. Vernalization consists in the fact that exposure to low positive temperatures (e.g., holding at +1 °C to +10 °C for several days) triggers the transition of winter forms to normal development, which ends with flowering and fruiting. For many organisms, exposure to low temperatures (cold diapause) is a necessary condition for the initiation of seed development (in plants), egg development (in insects or crustaceans), or other dormant stages.\nHowever, even once development has started, its rate depends heavily on temperature. The development of many poikilothermic organisms is well described by the concept of effective temperatures, which treats accumulated heat as the resource required for development.\nThe study of heat accumulation on development was begun by the well‑known physicist René Réaumur in 1735. Assigned to determine why fruit crops develop differently in various regions of France, he found that the heat required for plant development could be calculated simply by summing the mean daily temperatures over the warm part of the year. If the sum reaches the species‑specific requirement, the crop matures; if not, it does not.\nInitially, researchers summed only positive (above 0 °C) temperatures, but later it became clear that for some species a different temperature threshold is needed. Ultimately the notion of a physiological zero was introduced.\nPhysiological zero (T₀) – the temperature above which development of a poikilothermic organism begins.\nAlthough physiological zero values for many organisms are close to 0 °C, animals living in snow grow and develop at sub‑zero temperatures, while some other organisms cease growth even at positive temperatures. A more precise physiological zero can be determined by examining the relationship between development rate and temperature, as shown in Fig. 5.20.1.\n[IMG_1]\nFigure 5.20.1. Relationship between development rate and development time versus temperature for poikilothermic organisms. A selected segment of the rate‑temperature curve (in this example, from 7 °C to 15 °C) can be treated as linear; development time over this segment follows a hyperbolic relationship. Within this segment, development rate can be calculated using the concept of effective temperatures. The physiological zero (in the example, 4 °C) is the intersection of this line with the zero‑rate axis.\nThe dependence of development time of a poikilothermic organism on temperature is hyperbolic. In contrast, development rate (the inverse of time) varies linearly with temperature over a fairly wide range of this factor. Note that at very low temperatures close to T₀ the linear relationship may break down. This means that the definition of physiological zero given above is not entirely accurate. On the graph, the temperature corresponding to the zero‑rate line is 5 °C, whereas T₀ = 4 °C. T₀ should be calculated by extending the linear portion of the rate‑temperature curve to the zero‑rate level. Moreover, physiological zero may differ for different developmental stages (the figure does not reflect this).\nHaving clarified physiological zero, the concept of effective temperature can be defined. Effective temperature (Tₑ) is the difference between the actual temperature (T) and the physiological zero (T₀): Tₑ = T − T₀.\nThe essence of the effective‑temperature concept is that each developmental stage of a poikilothermic organism requires a specific sum of mean daily effective temperatures, called the thermal constant (TConst). Examples of physiological zero values and thermal constants for several organisms are given in Table 5.20.1.\nTable 5.20.1. Examples of thermal parameters for the development of selected organisms\n\nOrganism | Physiological Zero (T₀) | Developmental Stage | Thermal Constant (TConst)\n--- | --- | --- | ---\nColorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days\nAgrotis segetum (turnip moth) | +10 °C | Full cycle | 955 degree‑days\nCod (roe) | –3.6 °C | Roe development | 150 degree‑days\nIce‑worm | –3 °C | — | —\nWheat | 0 °C | — | —\nPine | +7 °C | — | —\nPea | –2 °C | — | —\nChicken egg | +20.5 °C | — | —\n\nIn fact, the sum of effective temperatures is a measure of physiological time for a poikilothermic organism.\nThus, if development occurs under variable temperature, we must calculate the mean daily effective temperature for each day. The condition for completing a developmental stage is that the accumulated effective temperatures reach the thermal constant. Under constant temperature the calculations simplify: TConst = t × Tₑ, or TConst = t × (T − T₀), where t is the development period (in days).\nThe unit for the sum of effective temperatures and the thermal constant is degree‑days, the product of degrees Celsius and days.\nNaturally, when computing the heat accumulated by the organism, it makes sense to calculate effective temperatures only for those days when T ≥ T₀, because development stops when temperature falls below the physiological zero. If, however, within such a day the temperature exceeds the critical threshold for part of the time, it is sensible to measure time in units other than days (e.g., hours). Hours rather than days should also be used for processes that proceed rapidly.\n\"To assess the growth rate of microorganisms, ‘degree‑hours’ can be used, a fact known to any baker working with yeast. At higher temperatures they develop more intensively, so dough or kvass will be ready faster than at lower temperatures. Temperature also influences the proliferation of lactic‑acid bacteria: milk that stays fresh for a long time in a refrigerator will sour in a warm room within a few hours\" (B.M. Mirkin, L.G. Naumova, 2005).\nFrom the above it follows that, knowing the development period of an organism at two different temperatures (corresponding to the linear segment in Fig. 5.20.1), we can estimate its development period at other temperatures. Suppose at temperature T₁ the organism develops in t₁ days, and at temperature T₂ in t₂ days. Because t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) = TConst, we have t₁T₁ − t₁T₀ = t₂T₂ − t₂T₀, thus t₂T₀ − t₁T₀ = t₂T₂ − t₁T₁. Determining T₀ allows easy calculation of TConst. The development period at temperature T₃ can be computed as t₃ = TConst / (T₃ − T₀).\nFor example, we know that grasshopper eggs develop in 17.5 days at 20 °C and in 5 days at 30 °C. Substituting these values into the equation t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) gives 17.5 × (20 − T₀) = 5 × (30 − T₀), from which T₀ = 16 °C and TConst = 70 degree‑days. Consequently, development would take about 10 days at 23 °C.\nSome data on physiological zero values and thermal constants for particular developmental stages are presented in Table 5.20.1.\nAre calculations based on the effective‑temperature concept always accurate? No. The described logic applies only to narrow temperature ranges, not to all organisms or all processes within them. The most significant drawback of this concept is the discrepancy between development times under constant versus variable temperatures. For instance, a chicken egg develops in 21 days at 40–41 °C; increasing temperature yields no gain. The Colorado potato beetle develops in 23 days at 20 °C, 15 days at 25 °C, and 19 days under fluctuating temperatures, regardless of whether the mean temperature is 20 °C or 25 °C. Variable temperatures are more natural!\nNevertheless, even simple mathematical models provide an advantage in managing biosystems. Imagine you need to plan an agrotechnical measure to protect crops from a pest, and this measure is most effective at a specific developmental stage of the pest (e.g., before pupation). Knowing the timing of mass egg laying and the weather forecast, you can estimate the optimal window for intervention. Is a certain inaccuracy in your calculations really a problem?\nAdditional material:\nEducational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules" }
Turnip Moth Agrotis segetum
+10 °C
Cod (roe)
−3,6 °C
Turnip Moth Agrotis segetum
Full cycle
{ "title": "5.19. Thermobiological Types of Organisms", "summary": "The section discusses the influence of temperature on poikilothermic organisms, introducing the concepts of physiological zero and effective temperature, methods for calculating heat units (degree‑days), and examples of thermal requirements for various species.", "body": "Ukrainian language (latest version) / Russian language (update discontinued)\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules\n\n5.20. Concept of Effective Temperatures\nWe have repeatedly noted that temperature is one of the most important ecological factors. One reason is that the rate of chemical reactions depends strongly on temperature. For a rough estimate of this influence the Van’t Hoff rule can be used: the rate of chemical reactions roughly doubles or triples with a 10 °C increase in temperature. This effect of ambient temperature is especially pronounced for poikilothermic organisms. The change in the rate of some biological processes also follows the Van’t Hoff rule. For example, this regularity is well illustrated by the variation in soil carbon dioxide emission (dependent on soil bacterial activity), the locomotion speed of centipedes, intestinal peristalsis in caterpillars, etc.\nIn some cases the temperature regime exerts a regulatory influence on development. Thus, the phenomenon of vernalization in wheat and other plants is known. To explain it, one must point out that wheat (as well as rye, cabbage, etc.) has winter and spring forms. Under warm and moist conditions winter varieties begin to germinate but then halt their development, awaiting winter cold. After exposure to cold for 1–3 months, winter forms resume development and eventually proceed to flowering and fruiting. Spring varieties lack this phase and can complete their whole development at positive temperatures. Vernalization consists in the fact that exposure to low positive temperatures (e.g., holding at +1 °C to +10 °C for several days) triggers the transition of winter forms to normal development, which ends with flowering and fruiting. For many organisms, exposure to low temperatures (cold diapause) is a necessary condition for the initiation of seed development (in plants), egg development (in insects or crustaceans), or other dormant stages.\nHowever, even once development has started, its rate depends heavily on temperature. The development of many poikilothermic organisms is well described by the concept of effective temperatures, which treats accumulated heat as the resource required for development.\nThe study of heat accumulation on development was begun by the well‑known physicist René Réaumur in 1735. Assigned to determine why fruit crops develop differently in various regions of France, he found that the heat required for plant development could be calculated simply by summing the mean daily temperatures over the warm part of the year. If the sum reaches the species‑specific requirement, the crop matures; if not, it does not.\nInitially, researchers summed only positive (above 0 °C) temperatures, but later it became clear that for some species a different temperature threshold is needed. Ultimately the notion of a physiological zero was introduced.\nPhysiological zero (T₀) – the temperature above which development of a poikilothermic organism begins.\nAlthough physiological zero values for many organisms are close to 0 °C, animals living in snow grow and develop at sub‑zero temperatures, while some other organisms cease growth even at positive temperatures. A more precise physiological zero can be determined by examining the relationship between development rate and temperature, as shown in Fig. 5.20.1.\n[IMG_1]\nFigure 5.20.1. Relationship between development rate and development time versus temperature for poikilothermic organisms. A selected segment of the rate‑temperature curve (in this example, from 7 °C to 15 °C) can be treated as linear; development time over this segment follows a hyperbolic relationship. Within this segment, development rate can be calculated using the concept of effective temperatures. The physiological zero (in the example, 4 °C) is the intersection of this line with the zero‑rate axis.\nThe dependence of development time of a poikilothermic organism on temperature is hyperbolic. In contrast, development rate (the inverse of time) varies linearly with temperature over a fairly wide range of this factor. Note that at very low temperatures close to T₀ the linear relationship may break down. This means that the definition of physiological zero given above is not entirely accurate. On the graph, the temperature corresponding to the zero‑rate line is 5 °C, whereas T₀ = 4 °C. T₀ should be calculated by extending the linear portion of the rate‑temperature curve to the zero‑rate level. Moreover, physiological zero may differ for different developmental stages (the figure does not reflect this).\nHaving clarified physiological zero, the concept of effective temperature can be defined. Effective temperature (Tₑ) is the difference between the actual temperature (T) and the physiological zero (T₀): Tₑ = T − T₀.\nThe essence of the effective‑temperature concept is that each developmental stage of a poikilothermic organism requires a specific sum of mean daily effective temperatures, called the thermal constant (TConst). Examples of physiological zero values and thermal constants for several organisms are given in Table 5.20.1.\nTable 5.20.1. Examples of thermal parameters for the development of selected organisms\n\nOrganism | Physiological Zero (T₀) | Developmental Stage | Thermal Constant (TConst)\n--- | --- | --- | ---\nColorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days\nAgrotis segetum (turnip moth) | +10 °C | Full cycle | 955 degree‑days\nCod (roe) | –3.6 °C | Roe development | 150 degree‑days\nIce‑worm | –3 °C | — | —\nWheat | 0 °C | — | —\nPine | +7 °C | — | —\nPea | –2 °C | — | —\nChicken egg | +20.5 °C | — | —\n\nIn fact, the sum of effective temperatures is a measure of physiological time for a poikilothermic organism.\nThus, if development occurs under variable temperature, we must calculate the mean daily effective temperature for each day. The condition for completing a developmental stage is that the accumulated effective temperatures reach the thermal constant. Under constant temperature the calculations simplify: TConst = t × Tₑ, or TConst = t × (T − T₀), where t is the development period (in days).\nThe unit for the sum of effective temperatures and the thermal constant is degree‑days, the product of degrees Celsius and days.\nNaturally, when computing the heat accumulated by the organism, it makes sense to calculate effective temperatures only for those days when T ≥ T₀, because development stops when temperature falls below the physiological zero. If, however, within such a day the temperature exceeds the critical threshold for part of the time, it is sensible to measure time in units other than days (e.g., hours). Hours rather than days should also be used for processes that proceed rapidly.\n\"To assess the growth rate of microorganisms, ‘degree‑hours’ can be used, a fact known to any baker working with yeast. At higher temperatures they develop more intensively, so dough or kvass will be ready faster than at lower temperatures. Temperature also influences the proliferation of lactic‑acid bacteria: milk that stays fresh for a long time in a refrigerator will sour in a warm room within a few hours\" (B.M. Mirkin, L.G. Naumova, 2005).\nFrom the above it follows that, knowing the development period of an organism at two different temperatures (corresponding to the linear segment in Fig. 5.20.1), we can estimate its development period at other temperatures. Suppose at temperature T₁ the organism develops in t₁ days, and at temperature T₂ in t₂ days. Because t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) = TConst, we have t₁T₁ − t₁T₀ = t₂T₂ − t₂T₀, thus t₂T₀ − t₁T₀ = t₂T₂ − t₁T₁. Determining T₀ allows easy calculation of TConst. The development period at temperature T₃ can be computed as t₃ = TConst / (T₃ − T₀).\nFor example, we know that grasshopper eggs develop in 17.5 days at 20 °C and in 5 days at 30 °C. Substituting these values into the equation t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) gives 17.5 × (20 − T₀) = 5 × (30 − T₀), from which T₀ = 16 °C and TConst = 70 degree‑days. Consequently, development would take about 10 days at 23 °C.\nSome data on physiological zero values and thermal constants for particular developmental stages are presented in Table 5.20.1.\nAre calculations based on the effective‑temperature concept always accurate? No. The described logic applies only to narrow temperature ranges, not to all organisms or all processes within them. The most significant drawback of this concept is the discrepancy between development times under constant versus variable temperatures. For instance, a chicken egg develops in 21 days at 40–41 °C; increasing temperature yields no gain. The Colorado potato beetle develops in 23 days at 20 °C, 15 days at 25 °C, and 19 days under fluctuating temperatures, regardless of whether the mean temperature is 20 °C or 25 °C. Variable temperatures are more natural!\nNevertheless, even simple mathematical models provide an advantage in managing biosystems. Imagine you need to plan an agrotechnical measure to protect crops from a pest, and this measure is most effective at a specific developmental stage of the pest (e.g., before pupation). Knowing the timing of mass egg laying and the weather forecast, you can estimate the optimal window for intervention. Is a certain inaccuracy in your calculations really a problem?\nAdditional material:\nEducational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules" }
Glacier
−3 °C
Wheat
0 °C
Cod
Educational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms
{ "title": "5.19. Thermobiological Types of Organisms", "summary": "The section discusses the influence of temperature on poikilothermic organisms, introducing the concepts of physiological zero and effective temperature, methods for calculating heat units (degree‑days), and examples of thermal requirements for various species.", "body": "Ukrainian language (latest version) / Russian language (update discontinued)\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules\n\n5.20. Concept of Effective Temperatures\nWe have repeatedly noted that temperature is one of the most important ecological factors. One reason is that the rate of chemical reactions depends strongly on temperature. For a rough estimate of this influence the Van’t Hoff rule can be used: the rate of chemical reactions roughly doubles or triples with a 10 °C increase in temperature. This effect of ambient temperature is especially pronounced for poikilothermic organisms. The change in the rate of some biological processes also follows the Van’t Hoff rule. For example, this regularity is well illustrated by the variation in soil carbon dioxide emission (dependent on soil bacterial activity), the locomotion speed of centipedes, intestinal peristalsis in caterpillars, etc.\nIn some cases the temperature regime exerts a regulatory influence on development. Thus, the phenomenon of vernalization in wheat and other plants is known. To explain it, one must point out that wheat (as well as rye, cabbage, etc.) has winter and spring forms. Under warm and moist conditions winter varieties begin to germinate but then halt their development, awaiting winter cold. After exposure to cold for 1–3 months, winter forms resume development and eventually proceed to flowering and fruiting. Spring varieties lack this phase and can complete their whole development at positive temperatures. Vernalization consists in the fact that exposure to low positive temperatures (e.g., holding at +1 °C to +10 °C for several days) triggers the transition of winter forms to normal development, which ends with flowering and fruiting. For many organisms, exposure to low temperatures (cold diapause) is a necessary condition for the initiation of seed development (in plants), egg development (in insects or crustaceans), or other dormant stages.\nHowever, even once development has started, its rate depends heavily on temperature. The development of many poikilothermic organisms is well described by the concept of effective temperatures, which treats accumulated heat as the resource required for development.\nThe study of heat accumulation on development was begun by the well‑known physicist René Réaumur in 1735. Assigned to determine why fruit crops develop differently in various regions of France, he found that the heat required for plant development could be calculated simply by summing the mean daily temperatures over the warm part of the year. If the sum reaches the species‑specific requirement, the crop matures; if not, it does not.\nInitially, researchers summed only positive (above 0 °C) temperatures, but later it became clear that for some species a different temperature threshold is needed. Ultimately the notion of a physiological zero was introduced.\nPhysiological zero (T₀) – the temperature above which development of a poikilothermic organism begins.\nAlthough physiological zero values for many organisms are close to 0 °C, animals living in snow grow and develop at sub‑zero temperatures, while some other organisms cease growth even at positive temperatures. A more precise physiological zero can be determined by examining the relationship between development rate and temperature, as shown in Fig. 5.20.1.\n[IMG_1]\nFigure 5.20.1. Relationship between development rate and development time versus temperature for poikilothermic organisms. A selected segment of the rate‑temperature curve (in this example, from 7 °C to 15 °C) can be treated as linear; development time over this segment follows a hyperbolic relationship. Within this segment, development rate can be calculated using the concept of effective temperatures. The physiological zero (in the example, 4 °C) is the intersection of this line with the zero‑rate axis.\nThe dependence of development time of a poikilothermic organism on temperature is hyperbolic. In contrast, development rate (the inverse of time) varies linearly with temperature over a fairly wide range of this factor. Note that at very low temperatures close to T₀ the linear relationship may break down. This means that the definition of physiological zero given above is not entirely accurate. On the graph, the temperature corresponding to the zero‑rate line is 5 °C, whereas T₀ = 4 °C. T₀ should be calculated by extending the linear portion of the rate‑temperature curve to the zero‑rate level. Moreover, physiological zero may differ for different developmental stages (the figure does not reflect this).\nHaving clarified physiological zero, the concept of effective temperature can be defined. Effective temperature (Tₑ) is the difference between the actual temperature (T) and the physiological zero (T₀): Tₑ = T − T₀.\nThe essence of the effective‑temperature concept is that each developmental stage of a poikilothermic organism requires a specific sum of mean daily effective temperatures, called the thermal constant (TConst). Examples of physiological zero values and thermal constants for several organisms are given in Table 5.20.1.\nTable 5.20.1. Examples of thermal parameters for the development of selected organisms\n\nOrganism | Physiological Zero (T₀) | Developmental Stage | Thermal Constant (TConst)\n--- | --- | --- | ---\nColorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days\nAgrotis segetum (turnip moth) | +10 °C | Full cycle | 955 degree‑days\nCod (roe) | –3.6 °C | Roe development | 150 degree‑days\nIce‑worm | –3 °C | — | —\nWheat | 0 °C | — | —\nPine | +7 °C | — | —\nPea | –2 °C | — | —\nChicken egg | +20.5 °C | — | —\n\nIn fact, the sum of effective temperatures is a measure of physiological time for a poikilothermic organism.\nThus, if development occurs under variable temperature, we must calculate the mean daily effective temperature for each day. The condition for completing a developmental stage is that the accumulated effective temperatures reach the thermal constant. Under constant temperature the calculations simplify: TConst = t × Tₑ, or TConst = t × (T − T₀), where t is the development period (in days).\nThe unit for the sum of effective temperatures and the thermal constant is degree‑days, the product of degrees Celsius and days.\nNaturally, when computing the heat accumulated by the organism, it makes sense to calculate effective temperatures only for those days when T ≥ T₀, because development stops when temperature falls below the physiological zero. If, however, within such a day the temperature exceeds the critical threshold for part of the time, it is sensible to measure time in units other than days (e.g., hours). Hours rather than days should also be used for processes that proceed rapidly.\n\"To assess the growth rate of microorganisms, ‘degree‑hours’ can be used, a fact known to any baker working with yeast. At higher temperatures they develop more intensively, so dough or kvass will be ready faster than at lower temperatures. Temperature also influences the proliferation of lactic‑acid bacteria: milk that stays fresh for a long time in a refrigerator will sour in a warm room within a few hours\" (B.M. Mirkin, L.G. Naumova, 2005).\nFrom the above it follows that, knowing the development period of an organism at two different temperatures (corresponding to the linear segment in Fig. 5.20.1), we can estimate its development period at other temperatures. Suppose at temperature T₁ the organism develops in t₁ days, and at temperature T₂ in t₂ days. Because t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) = TConst, we have t₁T₁ − t₁T₀ = t₂T₂ − t₂T₀, thus t₂T₀ − t₁T₀ = t₂T₂ − t₁T₁. Determining T₀ allows easy calculation of TConst. The development period at temperature T₃ can be computed as t₃ = TConst / (T₃ − T₀).\nFor example, we know that grasshopper eggs develop in 17.5 days at 20 °C and in 5 days at 30 °C. Substituting these values into the equation t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) gives 17.5 × (20 − T₀) = 5 × (30 − T₀), from which T₀ = 16 °C and TConst = 70 degree‑days. Consequently, development would take about 10 days at 23 °C.\nSome data on physiological zero values and thermal constants for particular developmental stages are presented in Table 5.20.1.\nAre calculations based on the effective‑temperature concept always accurate? No. The described logic applies only to narrow temperature ranges, not to all organisms or all processes within them. The most significant drawback of this concept is the discrepancy between development times under constant versus variable temperatures. For instance, a chicken egg develops in 21 days at 40–41 °C; increasing temperature yields no gain. The Colorado potato beetle develops in 23 days at 20 °C, 15 days at 25 °C, and 19 days under fluctuating temperatures, regardless of whether the mean temperature is 20 °C or 25 °C. Variable temperatures are more natural!\nNevertheless, even simple mathematical models provide an advantage in managing biosystems. Imagine you need to plan an agrotechnical measure to protect crops from a pest, and this measure is most effective at a specific developmental stage of the pest (e.g., before pupation). Knowing the timing of mass egg laying and the weather forecast, you can estimate the optimal window for intervention. Is a certain inaccuracy in your calculations really a problem?\nAdditional material:\nEducational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules" }
Pine
+7 °C
Pea
−2 °C
Chicken egg
+20,5 °C
{ "title": "5.19. Thermobiological Types of Organisms", "summary": "The section discusses the influence of temperature on poikilothermic organisms, introducing the concepts of physiological zero and effective temperature, methods for calculating heat units (degree‑days), and examples of thermal requirements for various species.", "body": "Ukrainian language (latest version) / Russian language (update discontinued)\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules\n\n5.20. Concept of Effective Temperatures\nWe have repeatedly noted that temperature is one of the most important ecological factors. One reason is that the rate of chemical reactions depends strongly on temperature. For a rough estimate of this influence the Van’t Hoff rule can be used: the rate of chemical reactions roughly doubles or triples with a 10 °C increase in temperature. This effect of ambient temperature is especially pronounced for poikilothermic organisms. The change in the rate of some biological processes also follows the Van’t Hoff rule. For example, this regularity is well illustrated by the variation in soil carbon dioxide emission (dependent on soil bacterial activity), the locomotion speed of centipedes, intestinal peristalsis in caterpillars, etc.\nIn some cases the temperature regime exerts a regulatory influence on development. Thus, the phenomenon of vernalization in wheat and other plants is known. To explain it, one must point out that wheat (as well as rye, cabbage, etc.) has winter and spring forms. Under warm and moist conditions winter varieties begin to germinate but then halt their development, awaiting winter cold. After exposure to cold for 1–3 months, winter forms resume development and eventually proceed to flowering and fruiting. Spring varieties lack this phase and can complete their whole development at positive temperatures. Vernalization consists in the fact that exposure to low positive temperatures (e.g., holding at +1 °C to +10 °C for several days) triggers the transition of winter forms to normal development, which ends with flowering and fruiting. For many organisms, exposure to low temperatures (cold diapause) is a necessary condition for the initiation of seed development (in plants), egg development (in insects or crustaceans), or other dormant stages.\nHowever, even once development has started, its rate depends heavily on temperature. The development of many poikilothermic organisms is well described by the concept of effective temperatures, which treats accumulated heat as the resource required for development.\nThe study of heat accumulation on development was begun by the well‑known physicist René Réaumur in 1735. Assigned to determine why fruit crops develop differently in various regions of France, he found that the heat required for plant development could be calculated simply by summing the mean daily temperatures over the warm part of the year. If the sum reaches the species‑specific requirement, the crop matures; if not, it does not.\nInitially, researchers summed only positive (above 0 °C) temperatures, but later it became clear that for some species a different temperature threshold is needed. Ultimately the notion of a physiological zero was introduced.\nPhysiological zero (T₀) – the temperature above which development of a poikilothermic organism begins.\nAlthough physiological zero values for many organisms are close to 0 °C, animals living in snow grow and develop at sub‑zero temperatures, while some other organisms cease growth even at positive temperatures. A more precise physiological zero can be determined by examining the relationship between development rate and temperature, as shown in Fig. 5.20.1.\n[IMG_1]\nFigure 5.20.1. Relationship between development rate and development time versus temperature for poikilothermic organisms. A selected segment of the rate‑temperature curve (in this example, from 7 °C to 15 °C) can be treated as linear; development time over this segment follows a hyperbolic relationship. Within this segment, development rate can be calculated using the concept of effective temperatures. The physiological zero (in the example, 4 °C) is the intersection of this line with the zero‑rate axis.\nThe dependence of development time of a poikilothermic organism on temperature is hyperbolic. In contrast, development rate (the inverse of time) varies linearly with temperature over a fairly wide range of this factor. Note that at very low temperatures close to T₀ the linear relationship may break down. This means that the definition of physiological zero given above is not entirely accurate. On the graph, the temperature corresponding to the zero‑rate line is 5 °C, whereas T₀ = 4 °C. T₀ should be calculated by extending the linear portion of the rate‑temperature curve to the zero‑rate level. Moreover, physiological zero may differ for different developmental stages (the figure does not reflect this).\nHaving clarified physiological zero, the concept of effective temperature can be defined. Effective temperature (Tₑ) is the difference between the actual temperature (T) and the physiological zero (T₀): Tₑ = T − T₀.\nThe essence of the effective‑temperature concept is that each developmental stage of a poikilothermic organism requires a specific sum of mean daily effective temperatures, called the thermal constant (TConst). Examples of physiological zero values and thermal constants for several organisms are given in Table 5.20.1.\nTable 5.20.1. Examples of thermal parameters for the development of selected organisms\n\nOrganism | Physiological Zero (T₀) | Developmental Stage | Thermal Constant (TConst)\n--- | --- | --- | ---\nColorado potato beetle | +13.5 °C | Full cycle | 285 degree‑days\nAgrotis segetum (turnip moth) | +10 °C | Full cycle | 955 degree‑days\nCod (roe) | –3.6 °C | Roe development | 150 degree‑days\nIce‑worm | –3 °C | — | —\nWheat | 0 °C | — | —\nPine | +7 °C | — | —\nPea | –2 °C | — | —\nChicken egg | +20.5 °C | — | —\n\nIn fact, the sum of effective temperatures is a measure of physiological time for a poikilothermic organism.\nThus, if development occurs under variable temperature, we must calculate the mean daily effective temperature for each day. The condition for completing a developmental stage is that the accumulated effective temperatures reach the thermal constant. Under constant temperature the calculations simplify: TConst = t × Tₑ, or TConst = t × (T − T₀), where t is the development period (in days).\nThe unit for the sum of effective temperatures and the thermal constant is degree‑days, the product of degrees Celsius and days.\nNaturally, when computing the heat accumulated by the organism, it makes sense to calculate effective temperatures only for those days when T ≥ T₀, because development stops when temperature falls below the physiological zero. If, however, within such a day the temperature exceeds the critical threshold for part of the time, it is sensible to measure time in units other than days (e.g., hours). Hours rather than days should also be used for processes that proceed rapidly.\n\"To assess the growth rate of microorganisms, ‘degree‑hours’ can be used, a fact known to any baker working with yeast. At higher temperatures they develop more intensively, so dough or kvass will be ready faster than at lower temperatures. Temperature also influences the proliferation of lactic‑acid bacteria: milk that stays fresh for a long time in a refrigerator will sour in a warm room within a few hours\" (B.M. Mirkin, L.G. Naumova, 2005).\nFrom the above it follows that, knowing the development period of an organism at two different temperatures (corresponding to the linear segment in Fig. 5.20.1), we can estimate its development period at other temperatures. Suppose at temperature T₁ the organism develops in t₁ days, and at temperature T₂ in t₂ days. Because t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) = TConst, we have t₁T₁ − t₁T₀ = t₂T₂ − t₂T₀, thus t₂T₀ − t₁T₀ = t₂T₂ − t₁T₁. Determining T₀ allows easy calculation of TConst. The development period at temperature T₃ can be computed as t₃ = TConst / (T₃ − T₀).\nFor example, we know that grasshopper eggs develop in 17.5 days at 20 °C and in 5 days at 30 °C. Substituting these values into the equation t₁ × (T₁ − T₀) = t₂ × (T₂ − T₀) gives 17.5 × (20 − T₀) = 5 × (30 − T₀), from which T₀ = 16 °C and TConst = 70 degree‑days. Consequently, development would take about 10 days at 23 °C.\nSome data on physiological zero values and thermal constants for particular developmental stages are presented in Table 5.20.1.\nAre calculations based on the effective‑temperature concept always accurate? No. The described logic applies only to narrow temperature ranges, not to all organisms or all processes within them. The most significant drawback of this concept is the discrepancy between development times under constant versus variable temperatures. For instance, a chicken egg develops in 21 days at 40–41 °C; increasing temperature yields no gain. The Colorado potato beetle develops in 23 days at 20 °C, 15 days at 25 °C, and 19 days under fluctuating temperatures, regardless of whether the mean temperature is 20 °C or 25 °C. Variable temperatures are more natural!\nNevertheless, even simple mathematical models provide an advantage in managing biosystems. Imagine you need to plan an agrotechnical measure to protect crops from a pest, and this measure is most effective at a specific developmental stage of the pest (e.g., before pupation). Knowing the timing of mass egg laying and the weather forecast, you can estimate the optimal window for intervention. Is a certain inaccuracy in your calculations really a problem?\nAdditional material:\nEducational model: Influence of Heat Accumulation on Development of Poikilothermic Organisms\n\n5.19. Thermobiological Types of Organisms\n\nD. Shabanov, M. Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.21. Clinal Variability and Some Ecological Rules" }
5.19. Thermobiological Types of Organisms
D. Shabanov, M. Kravchenko. Ecology: Interaction Biology Chapter 5. Autecology and Fundamentals of Environmental Studies
5.21. Climatic variability and some ecological rules