Bio week 9
The number of trophic levels can control the flow of energy through food webs
, all things being equal, a three-level food web, in which the secondary consumer affects the primary consumer's abundance, should have higher NPP than a two- or four-level food web in which primary consumers have less secondary consumer control (Figure 56.10B). Omnivory, or feeding on more than one trophic level, can also change the way energy is transferred in food webs by essentially "collapsing" trophic levels on one another. For example, a three-level food web with a secondary consumer feeding on both the primary consumer and primary producer should have lower NPP than a three-level food web without omnivory (Figure 56.10C). That's because even though the secondary consumer indirectly benefits the primary producer by feeding at the primary consumer level, it partially negates this effect by directly feeding on the primary producer as well.
While the number of trophic levels in foods webs can vary, most food webs have three or four trophic levels, with the rare exception of five or more in some systems. What factors might be important in limiting the number of trophic levels in food webs? Several factors have been hypothesized to be important:
-The amount of NPP entering the system: This hypothesis suggests that bottom-up factors can influence trophic structure. Given that a large amount of energy is lost from one trophic level to the next (see Figure 56.9), the number of trophic levels will be limited by the amount of energy that can sustain populations at higher trophic levels. -The amount of disturbance: This hypothesis suggests that longer food webs are less likely to recover from disturbances than shorter food webs, which can presumably reassemble more quickly given the fewer trophic levels, and species, involved. -The evolutionary constraints on top predators: This hypothesis focuses on the idea that no organisms on Earth today, with the exception of humans, have evolved to capture apex predators such as birds of prey, sharks, orcas (Orcinus orca), and polar bears (Ursus maritimus). With evolutionary constraints maintaining top predators at the pinnacle of food webs, the number of higher trophic levels is limited.
Assimilation efficiencies across animals
-metabolic rate has a inverse relationship with assimilation efficiency
Thermoregulatory
Animals that maintain a constant body temperature are called homeotherms, and animals that experience a fluctuating body temperature are called poikilotherms. Another classification is based on the source of heat that predominantly determines body temperature. Endotherms such as birds and mammals have the ability to vary their metabolic heat production to compensate for the loss of heat to the environment. Ectotherms such as invertebrates, fishes, amphibians, and non-avian reptiles are largely dependent on environmental sources of heat. We use the terminology of ectotherm and endotherm in this book, but no classification scheme is perfect. Many ectotherms can generate considerable internal heat to raise their body temperature, and endotherms that hibernate can periodically appear to give up the ability to generate internal heat. To accommodate these departures from a strict dichotomy, we add the term heterotherms—organisms that act like ectotherms some of the time and like endotherms at other times. -Thermoregulatory adaptations enable animals to modulate the various paths of heat exchange between themselves and their environment. -humans and most other mammals are endoterhsm and homeotherms
If a bear is not able to hibernate, what are the implications for how much food it will need? Explain your reasoning by linking body temperature, cellular respiration and eating.
Bears that do not hibernate need to consume more food than bears that do hibernate. As metabolic rate decreases in hibernation, there is less flux through cellular respiration due to decreased diffusion rates and enzymatic activity. This means that less ATP is required by all cells in the body so fewer nutrients are required to drive metabolism.
Assimilaiton, exploration, and ecological efficiency
Exploitation efficiency: How efficient is an organism at capturing energy from food in their environment Assimilation efficiency: How efficient is an organism at converting energy intake into growth/reproduction -prodoucing your heat has a high cost - requires you to eat more food
Environmental Temperature and Mammalian Metabolic Rates
For an endotherm, a metabolic rate versus environmental temperature curve represents the integrated response of all the animal's thermoregulatory adaptations (Figure 38.14). The thermoneutral zone is bounded by a lower critical temperature and an upper critical temperature. When the environmental temperature is within the thermoneutral zone, an endotherm's thermoregulatory responses do not require much energy and could be considered passive; such responses include changing posture, fluffing fur or feathers, and altering blood flow to the skin. When an endotherm is outside its thermoneutral zone, however, its thermoregulatory responses are active and require metabolic energy.
Both ectotherms and endotherms control blood flow to the skin
Heat is mostly moved around the internal environment by blood flow. Heat produced in muscles during exercise is transported out of the muscle and to the heart in the blood. That heat is then distributed around the body by the blood, raising body temperature. Blood flow to the skin enables internal heat to be lost to the environment through radiation, convection, conduction, and evaporation, thus bringing the body temperature back toward normal. When body temperature is too low or the environment is too cold, the blood vessels supplying the skin constrict, reducing heat loss to the environmen Fur acts as insulation to keep body heat in, making it possible for mammals to function in cold environments. When they are active, however, mammals must get rid of excess heat, and it does little good to transport that heat to the skin under the fur. Thus as mentioned at the opening of this chapter, mammals have specialized blood vessels for transporting heat to their hairless skin surfaces. Heat loss from these areas is tightly controlled by the opening and closing of these blood vessels. When you are cold, the blood flow to your hands and feet decreases and they feel cold, but when you exercise, the blood vessels serving these skin areas dilate, increasing the blood flow and therefore the heat dissipation.
Homeostasis
Homeostasis - maintaining internal conditions within "ideal" parameters
Estimating carrying capacities
If you know the body mass of an organism and whether it is an ectotherm or endotherm, you can estimate its basal metabolic rate -actual metabolism (field metabolic rate) is 10x higher Trophic level of an organism lets you estimate how much NPP is required to meet that metabolic demand (10% rule) -Since we know the NPP, we can estimate how many animals of each species can be supported
The amount of energy transferred within food webs depends on trophic efficiency
In addition to understanding how energy flows between individual consumers, we can also consider how it flows between trophic levels. Trophic efficiency is a measure of the amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it. Trophic efficiency varies among ecosystems as well as trophic levels. Pyramid diagrams such as those in Figure 56.9 illustrate the proportions of energy transferred from each trophic level to the next, making it possible to compare energy flow in different ecosystems. Pyramid diagrams can also be used to illustrate the amount of biomass found at each trophic level. As seen in Figure 56.9A,B, terrestrial ecosystems progressively lose energy from one trophic level to the next through trophic inefficiencies, especially between the primary producer and primary consumer levels. Note also that terrestrial ecosystems support less biomass at higher trophic levels than at lower trophic levels. Forest ecosystems have lower trophic efficiency than grasslands because much of the biomass in forests is in the form of wood, most of which is unavailable to primary consumers.
The Uromastyx lizard is also an ectotherm. How does it manage to raise its body temperature so rapidly between 9 and 11 am? Humans are endotherms. If the environmental temperature exceeds our body temperature (37℃), what strategies do we use to ensure our body temperature doesn't rise too high?
Most likely moves into the sun in the morning Sweating - evaporative cooling (internal process), dilate blood vessels to increase contact of blood to surface of the skin (internal mechanism), Take off layers of clothes, move into shade, become less active/rest, take a cold shower (external mechanisms)
brown fat
Most nonshivering heat production occurs in specialized adipose tissue called brown fat. This tissue looks brown because of its abundant mitochondria and rich blood supply (see Figure 38.2). In brown fat cells, a protein called thermogenin uncouples proton movement from ATP production, allowing protons to leak across the inner mitochondrial membrane rather than having to pass through the ATP synthase and generate ATP (review the discussion of brown fat and the chemiosmotic mechanism in Key Concept 9.3). In nonshivering thermogenesis, metabolic fuels are consumed without producing ATP, but heat is still released. In addition to their ability to produce heat, endotherms that live in cold climates have evolved adaptations to reduce their heat loss. Heat is lost from the body surface, and cold-climate species have anatomical adaptations that give them smaller surface area-to-volume ratios than their warm-climate relatives (Figure 38.15). These adaptations include rounder body shapes and shorter appendages. Non-shivering thermogenesis Way of making heat without shivering Done in brown adipose tissue (white fat=energy storage, brown fat=mitochondria where cellular respiration is performed). Brown fat has an uncoupling protein, which allows ions to flow through down their concentration gradient and this energy is used for heat production
Basal heat production rates of endotherms correlate with body size
Physiologists can determine an animal's metabolic rate and therefore its rate of heat production by measuring its consumption of O2 or production of CO2. thermoneutral zone (see Figure 38.8B), the metabolic rates of endotherms (birds and mammals) are at low levels and independent of environmental temperature. The metabolic rate of a resting endotherm at a temperature within its thermoneutral zone is its basal metabolic rate (BMR). BMR is usually measured in animals that are quiet but awake and not using energy for digestion, reproduction, or growth. Thus BMR is the rate at which a resting animal is consuming just enough energy to carry out its minimal body functions. Why should this disproportionate difference exist? There are several possible reasons. As animals get bigger, they have a smaller surface area-to-volume ratio (see Figure 5.2). Since heat production is related to the volume (i.e., mass) of the animal, but its capacity to dissipate heat is related to its surface area, it has been reasoned that larger animals evolved lower metabolic rates to avoid overheating. However, this explanation alone is insufficient because the relationship between body mass and metabolic rate holds for even very small organisms and for ectotherms, in which overheating is not a problem. Other hypotheses have also been proposed. For example, a larger animal has a greater proportion of support tissues (e.g., skin and bone), which are not as metabolically active as other tissue types. The real explanation is probably a mixture of different factors, but the relationship holds over a very broad range of species. -it is harder to maintain body heat the smaller the animal -the one on the right is to consider for assimilation efficeicy
Hibernation Patterns in a Ground Squirrel
Regulated hypothermia that lasts for days or even weeks, during which the body temperature falls close to environmental temperature, is called hibernation (Figure 38.18). Many species of mammals, including bats, bears, marmots, and ground squirrels, hibernate, but only one species of bird (the Common Poorwill, Phalaenoptilus nuttallii) has been shown to hibernate. The metabolic rate needed to sustain a hibernating animal may be only one-fiftieth its basal metabolic rate, and many hibernating animals maintain body temperatures close to freezing. Arousal from hibernation occurs when the hypothalamic set point returns to the normal level. The ability of animals to enter daily torpor or deep hibernation to reduce their thermoregulatory set point so dramatically probably evolved as an extension of the set point decrease that accompanies sleep in all mammals and birds. -. Even within a safe zone, body temperature is a critical factor in limiting physical performance. A working body has to dissipate heat to the environment, and that requires a difference in temperature between the body surface and the environment Three criteria for hibernation: reduced metabolism slower heart rate lowered body temperature
Based on the graph on the left, what is the primary activity that leads to increases in metabolic rate? Note that EMG activity is a measure of shivering . As a consequence of internal thermoregulation such as shivering and non-shivering thermogenesis, an animal's body mass will _________ What form of matter in the body is most likely to change? What will that matter be converted into during the process of thermogenesis? How will those molecules leave the body?
Shivering and Movements correlate well with spikes in metabolic rate (O2 consumption) and body temperature. Also, note the den temp is higher than outside temp, which shows an external strategy the bear uses to stay warm by living in the den in winter. decrease The glycogen in muscle and liver cells and fat in adipocytes. CO2 leaves via breath H2O becomes part of the metabolic water in the body some might leave as urine (not sweating/panting in hibernation)
Apply the 10% rule to determine how many calories of sunlight are needed per day to support your diet. Assume that you are eating 2000 kcal per day and that your diet is 75% plant material and 25% herbivorous animals. Sunlight to provide 1500 kcal of plant Sunlight to provide 500 kcal of herbivorous animal Total sunlight required
Sunlight to provide 1500 kcal of plant _1500x10=15000x100=1.5 x 10^6 kcal__ Sunlight to provide 500 kcal of herbivorous animal _500 x 10 x10 x 100 = 5 x 10^6 kcal Total sunlight required 6.5 x 10^6 kcal
Part 2: Thermoregulation (Hibernation Case Study) Based on the data above, what is the thermoregulatory mechanism of this bear in its den? Explain your reasoning based on the data. As body temperature decreases, what do you predict will happen to the metabolic rate of the bear?
The bear is heterothermic as between December and March, this bear is poikilothermic as its body temperature fluctuates between 36℃ and 30℃. Not shown on this graph, but during the spring and summer months the bear would display homeothermic thermoregulation with its body temperature maintaining around 38℃. The strong correlation between movements and increasing body temperature, indicates that the bear uses endothermic strategies to heat. Although the fact that the bear is in a den also indicates some level of ectothermy. During the winter months, drops in core body temperature appear to be tolerated as they do not quickly spike back to normal summer body temperature. When cells are colder, diffusion takes place more slowly making it harder for metabolic processes to take place. So I would predict that the metabolic rate would drop along with the body temperature. During the summer months, drops in core body temperature result in quick increase in heat generation through endothermic mechanisms such as shivering or activation of brown adipose tissue, which would increase metabolic rate. This is why body temperature is not observed to drop significantly during the summer months.
Endotherms - mutations
We can speculate that a mutation resulting in seemingly faulty or leaky ion channels might underlie the evolution of endothermy. Such a mutation in a small ectotherm would have increased its energy expenditure and therefore its heat production. Increased heat production would have enabled the animal to be active earlier in the morning or for a longer time after sunset. Being active in twilight, and eventually at night, would open up a new world of ecological opportunities—a world in which there was less competition from similar-sized ectotherms and less danger of predation.
Cells response to temperature
When cells heat up: -Diffusion speeds up -Membranes become more fluid (simple diffusion is easier) -Enzyme reactions occur faster Unless its too hot, then: -Membrane integrity is compromised -Proteins unravel and cannot function When cells cool down: -Diffusion slows down -Membranes become more rigid -Enzyme reactions occur slower
Endotherms respond to cold by producing heat and adapt to cold by reducing heat loss
When environmental temperatures fall below the lower critical temperature, endotherms increase metabolic heat production to compensate for heat loss. Mammals can accomplish this by shivering and/or nonshivering heat production. Birds use only shivering heat production. Shivering uses the contractions of skeletal muscles to convert ATP to ADP, with the energy from this process released as heat. Shivering muscles pull against each other so that little movement other than a tremor results. "Shivering heat production" is perhaps too narrow a term, however; increased muscle tone and increased body movements also contribute to increased heat production in cold environments. Shivering - Muscle contractions produce heat -All transformations of energy are inefficient - Energy not converted into work is lost as heat. Contracting muscles need ATP -More cellular respiration necessary to produce ATP (from fatty acid metabolism) -Energy transformations during cell respiration pathways not 100% efficient (some energy transferred to ATP and some energy lost in the form of heat) -Contracting muscles also experience friction as muscle fibers slide past each other which leads to heat production.
Endotherms produce substantial amounts of metabolic heat
Why do endotherms produce more heat than ectotherms? The surprising answer is that the cells of endotherms are less efficient at using energy than are the cells of ectotherms. The cells of endotherms are more "leaky" to ions than are the cells of ectotherms. Therefore Na+ ions are constantly diffusing into the cells, and K+ ions are constantly diffusing out. Even an endotherm at rest must spend considerable amounts of energy to transport Na+ out of the cells and transport K+ back in. Because of their constant need to actively transport ions, endotherms expend more energy than do ectotherms just to maintain the ion concentration gradients across their cell membranes. This situation is analogous to a leaky boat: the faster water comes in (i.e., the faster ions diffuse down their concentration gradients), the more metabolic energy has to be expended to bail the water out (i.e., pump ions back up their concentration gradients). Since endotherms expend more energy than ectotherms do to maintain ion concentration gradients, they produce more internal heat. -Two major differences between endotherms and ectotherms are (1) their resting metabolic rates—the sum total of all energy expenditures in their bodies when at rest—and (2) their responses to changes in environmental temperature.
Energy Flow and Net Secondary Production in an Herbivore
during energy transfer, some energy is lost as "unusable" to the system (second law of thermodynamics) and thus is unavailable to do work. For food webs, the consequence of this loss is that only part of the primary production consumed by heterotrophs is converted into heterotroph biomass. What factors are important to this movement and loss of energy from primary to secondary production? Net secondary production, or the amount of biomass obtained from the consumption of other organisms, depends on how much plant tissue is consumed (consumption efficiency), how much of the consumed food can actually be digested versus released as feces and urine (assimilation efficiency), and how much of the digested food is used in metabolic activities and released as CO2 through respiration versus stored as biomass (production efficiency) (Figure 56.8). We can think of production efficiency as the percentage of energy stored in assimilated food that is used to produce new biomass. -Consumers can vary dramatically in production efficiency. For example, endotherms have much lower production efficiencies than ectotherms (Table 56.1). Because endotherms have to maintain high body temperatures, they have higher metabolic rates than ectotherms, and thus have less energy left over to devote to growth and reproduction. Moreover, endotherms vary in production efficiency depending on body size and metabolism. Larger mammals have lower metabolic rates and higher production efficiencies compared with smaller mammals and birds, whose greater surface area-to-biomass ratios result in more heat loss and higher metabolic rates
Net primary productivity
the sum of all photosynthesis in the square feet (gross primary productivity) - respiration of plants. So what ever is left after meet plant growth and metabolic demands
Humans are endothermic homeotherms
there are mechanisms that bring the body temperature down to the set point
