Physical Ecology of Animals Elements of Ecology: Animal Adaptations: Chapter 7 Size Imposes Fundamental Constraints on the Evolution of Organisms • Size impacts structure/function relationships in animals • Most morphological and physiological features change as a function of body size in a predictable way Size Imposes Evolutionary Constraints • How are surface area and volume related? • Think of the dimensions of a square and a cube 1 2 3 1 2 3 S.A. = 6 24 54 S.A. = 6 24 54 Volume = 1x1x1= 1 2x2x2 = 8 3x3x3=27 S.A. = 6 24 54 Volume = 1x1x1= 1 2x2x2 = 8 3x3x3=27 S.A./Vol. = 6/1 =6 24/8=3 54/27 = 2 Size Imposes Evolutionary Constraints • Size of organisms affects every aspect of their lives • Larger animals have relatively less surface area (to volume) than smaller animals • Smaller organisms have a larger surface area (relative to volume) than do larger organisms of the same shape Size Imposes Evolutionary Constraints • Why does this relationship between surface area and volume impose constraints on the evolution of animals? • Many basic physiological and biochemical processes require the transfer of materials and energy between the exterior (environment) and interior of the organism. • Examples of these processes? Size Imposes Evolutionary Constraints • Surface area is important for: – Gas exchange (O2, CO2) – Heat absorption – Heat loss – Water loss – Digestion efficiency Size Imposes Evolutionary Constraints • Some adaptations to size constraints: – Convoluted/folded surfaces increase surface area (lungs, brains, digestive systems, etc.) – Active transport of oxygen into the interior of the body – Digestive tract variation: the greater the surface area, the greater the ability to absorb nutrients Animal Adaptations to the Environment • Animals feed on many different types of organisms → diverse adaptations • Key processes that all animals share include: – Acquiring and digesting food – Absorbing oxygen – Maintaining body temperature and water balance – Adapting to daily and seasonal environmental changes Animals Have Various Ways of Acquiring Energy and Nutrients • What types of foods do animals eat? • What type of physiological, morphological, and behavioral adaptations allow animals to eat and digest these foods? • What are the four major categories of animal diets? • Herbivores – feed only on plants • Challenges faced by animals that eat only plant tissues? • Plant tissues have a different chemical composition than animal tissues: – Low in proteins – High in carbohydrates • Structural carbohydrates (lignin, cellulose) are difficult to digest – High levels of nitrogen • Herbivores: categorized by plants they eat – Grazers: mainly eat grasses (folivores eat leaves) – Browsers: eat woody material – Granivores: eat seeds – Frugivores: eat fruit – Specialist herbivores: • Nectivores: hummingbirds, butterflies, bees • Sap: birds, insects (aphids) • Which have a diet high in cellulose? Acquiring Energy and Nutrients • Grazers and browsers: diets very high in cellulose; rich in carbon; low in protein • Most animals lack enzymes to digest cellulose • Symbiont bacteria in gut digest cellulose and proteins, and synthesize fatty acids, amino acids, proteins, and vitamins Acquiring Energy and Nutrients • Highest-quality plant food for herbivores contains high nitrogen (as protein) • As nitrogen increases, food assimilation improves (→ increased growth, reproductive success, survival) • Nitrogen is concentrated in new leaves and buds (nitrogen declines as plant ages) Acquiring Energy and Nutrients • Carnivores eat other animals • No problems digesting and assimilating nutrients from prey because the composition of animal tissues is similar • Quantity is important—predators must be able to find enough food https://animal-kingdom-4.weebly.com/uploads/3/0/2/8/30281789/1623995.jpg?280 Acquiring Energy and Nutrients • Omnivores eat plants and animals • Diet can vary with season, life stage, size, and growth rate – red foxes: berries, grasses, insects, small rodents – black bears: vegetation (buds, nuts, tree bark); supplement with insects, fish, mammals – Frogs: algae as tadpoles, insects as adults http://www.loomcom.com/raccoons/gallery/jpegs/fish-coon1.jpg Animals and their Resources • Autotrophs = organisms that make their own food = plants (photosynthesis) and chemosynthetic bacteria https://images.fineartamerica.com/images-medium-large-5/mystical-angel-oak-tree-louis-dallara.jpg Animals and their Resources • Heterotrophs = organisms that must consume other organisms for food = animals • Heterotroph classifications – Predators (carnivores) – Herbivores (grazers) – Omnivores (a little of everything) – Parasites – Decomposers http://www.zutrition.com/wp-content/uploads/2013/09/iStock_000011806506XSmall.jpg Specialists focus on one or few food types http://www3.nationalgeographic.com/animals/images/800/black-footed-ferret.jpg http://www.excellnaturephotography.com/assets/images/mammals/D-M00860-0422.jpg http://www.blackfootedferret.org/gif/factshunting.gif Generalists eat a wide variety of food types http://www.loomcom.com/raccoons/gallery/jpegs/fish-coon1.jpg Responding to Change in the External Environment • Environmental variation occurs across a wide range of time scales: some changes are regular, others are less predictable • An animal can respond to environmental changes in two different ways: conform or regulate Responding to Change in the External Environment • Conformers—changes in the external environment cause parallel changes in the body – unable to maintain internal conditions different than the external environment (solutes, O2) • Ability to survive environmental changes depends on range of tolerance to internal changes Responding to Change in the External Environment • Regulators—changes in external environment do not cause internal changes • Able to maintain internal conditions over a broad range of external environmental conditions • Regulation may be biochemical, physiological, morphological, behavioral Conformers vs. Regulators Figure 7.6 Responding to Change in the External Environment • Regulatory mechanisms may be energetically expensive • Conformers vs. Regulators: the strategies have different costs and benefits • What are some of the costs and benefits for each? Responding to Change in the External Environment • Conformity – Benefits: low energetic expenditure; don’t require mechanisms to maintain a consistent internal environment – Costs: if environmental conditions are not optimal, conformity can lead to reduced activity, growth, reproduction Responding to Change in the External Environment • Regulation – Benefits: greatly extended range of environmental conditions for activity, growth, reproduction and increased level of performance – Costs: energetically expensive Responding to Change in the External Environment • Different strategies under different environmental conditions – may regulate with respect to one feature but conform to another – active girdled lizards regulate body temperature, inactive lizards don’t Figure 7.7 Regulating Internal Conditions Involves Homeostasis and Feedback • Homeostasis: maintenance of relatively constant internal environment (in a varying external environment) • Whenever conditions deviate from the normal state (set point), negative feedback mechanisms engage to restore the system to that state (e.g. thermostat) Animals Require Oxygen to Release Energy Contained in Food • Animals (and plants) use aerobic respiration to covert energy in organic compounds into energy that cells can use • Most organisms are oxygen regulators: able to maintain normal O2 consumption levels even when external oxygen levels drop Animals Require O2 to Release Energy Contained in Food • O2 easily available in terrestrial environments • Tiny organisms acquire O2 via diffusion • Larger organisms cannot use direct diffusion – Insects: spiracles (openings) → tracheal tubes that carry O2 into the body – Terrestrial vertebrates: lungs allow O2 → bloodstream → cells – Some amphibians transfer O2 across moist vascular skin • In aquatic environments, oxygen: – may be limiting – may be hard to acquire – maybe taken from the water or from the atmosphere • Some aquatic animals are oxygen conformers – mainly sedentary marine invertebrates such as cnidarians and echinoderms • Tiny animals (zooplankton), take up O2 by diffusion • Most larger aquatic animals have gills – Gills exchange gases and are in direct contact with the water – Some gills are simple and distributed over the body – Some gills are complex and restricted to a specific region • Some aquatic animals must surface for oxygen – Aquatic insects have a tracheal system and surface to fill it with air – Aquatic turtles and mammals have lungs Animals Maintain a Balance between Water Uptake and Water Loss • Water balance = the balance between water uptake and loss to the surrounding environment • How do aquatic animals gain and lose water? Animals Maintain a Balance of Water Uptake/Loss • Aquatic animals are constantly exchanging water with the external environment through osmosis • Recall passive water transport: – osmotic pressure moves water across membranes – moves from the side of greater concentration to the side of lower concentration https://media.buzzle.com/media/images/buzzle/300-385564-examples-of-osmosis.jpg Animals Maintain a Balance of Water Uptake/Loss • Freshwater animals are hyper-osmotic relative to their environment (they have a higher salt concentration inside their bodies than the surrounding water). • Which way does the water flow between freshwater organisms and the environment? . Animals Maintain a Balance of Water Uptake/Loss • Freshwater animals are hyper-osmotic • They have a higher salt concentration in their bodies than the surrounding water. • Water flows into their bodies from the environment. Water Balance in Fishes http://images.google.com/imgres?imgu rl=http://dobrinishte.org/fishes/index_f iles/image555.gif&imgrefurl=http://do brinishte.org/fishes/index_files/Page43 1.htm&usg=__4CLAu2StppicCDIDoe WE2a8TkYQ=&h=290&w=560&sz= 29&hl=en&start=32&tbnid=eXk4nYf kDHjLeM:&tbnh=69&tbnw=133&pre v=/images%3Fq%3Dhyperosmotic%2 6gbv%3D2%26ndsp%3D20%26hl%3 Den%26sa%3DN%26start%3D20 • Freshwater fishes (hyperosmotic): – Low salt concentration in surrounding water – Water enters fish via osmosis – Salt is lost by diffusion across gills – Water removal: large amounts of dilute urine – Active uptake of salts through gills (requires energy) Animals Maintain a Balance of Water Uptake/Loss • Why aren’t freshwater animals osmoconformers? • The difference between the osmotic concentrations of freshwater and body tissues is too great. Animals Maintain a Balance of Water Uptake/Loss • Freshwater bony fish are osmoregulators. • They drink very little water; produce large amounts of dilute urine. • They take up sodium and chloride ions by pumping them across their gills; active transport is energetically expensive. Figure 7.12a Hyperosmotic Actively takes up ions through gills Absorbs water through skin Drinks little water Excretes dilute urine Movement of water Movement of ions (a) Osmoregulation in a freshwater environment Osmoregulation in Freshwater Fishes http://en.wikipedia.org/wiki/File:Osmoseragulation_Carangoides_bartholomaei_bw_en2.png Animals Maintain a Balance of Water Uptake/Loss • Marine animals are hypo-osmotic—they have a lower salt concentration in their bodies than the surrounding water. • Water flows out of their bodies into the environment. • How do saltwater organisms prevent water loss and salt accumulation? Animals Maintain a Balance of Water Uptake/Loss • Marine animals have different approaches to water balance • Some marine animals are isosmotic (osmoconformers)—body fluids have same osmotic pressure as seawater – tunicates, jellyfish, many molluscs, sea anemones Animals Maintain a Balance of Water Uptake/Loss • Many marine organisms are osmoregulators: e.g. marine bony fish – drink water and absorb it into their gut – produce small amounts of concentrated urine – excrete sodium and chloride ions by pumping them across their gills; active transport is energetically expensive Water Balance in Fishes http://images.google.com/imgres?imgu rl=http://dobrinishte.org/fishes/index_f iles/image555.gif&imgrefurl=http://do brinishte.org/fishes/index_files/Page43 1.htm&usg=__4CLAu2StppicCDIDoe WE2a8TkYQ=&h=290&w=560&sz= 29&hl=en&start=32&tbnid=eXk4nYf kDHjLeM:&tbnh=69&tbnw=133&pre v=/images%3Fq%3Dhyperosmotic%2 6gbv%3D2%26ndsp%3D20%26hl%3 Den%26sa%3DN%26start%3D20 • Saltwater fishes (hypoosmotic): – High salt concentration in surrounding water – Tendency toward dehydration (water lost via osmosis) – Actively drink saltwater to re-hydrate; tendency to gain salt – Concentrated urine expels salt, retains water – Active removal of salt through gills (uses energy) Figure 7.12b Movement of water Movement of ions Hypoosmotic Loses water through skin Drinks ample water Excretes ions through gills Direction of ion movement (Na+, K+, Cl-) Direction of water movement Excretes concentrated urine (b) Osmoregulation in a saltwater environment Osmoregulation in Saltwater Fishes http://en.wikipedia.org/wiki/File:Osmoseragulation_Carangoides_bartholomaei_bw_en2.png Animals Maintain a Balance of Water Uptake/Loss • Many marine organisms are osmoregulators – Cartilaginous fish (sharks and rays) retain urea in their body tissues so they are at a slightly higher concentration than the seawater – Birds and sea turtles drink seawater and excrete the salt through salt glands – Marine mammals eliminate salt through their kidneys Animals Maintain a Balance of Water Uptake/Loss • Water balance is the balance between the uptake and loss of water with the surrounding environment • How do terrestrial animals gain and lose water? Terrestrial Life Needs to Control Water Loss • Gas exchange requires contact between air and moist membranes • Potential water loss • How to keep from drying out? http://www.redorbit.com/modules/reflib/article_images/45_ee4c8f9f191953b9998ddb1 9ffef6c91.jpg How to Control Water Loss 1. Reduce rate of water loss -or2. Maintain more water in body -or3. Tolerate water loss from body How to Control Water Loss 1. Reduce rate of water loss – Evolve a better skin – Feathers, scales, fur prevent water loss, unlike amphibian skin How to Control Water Loss – Evolve adaptive behavior • Become inactive during hot, dry periods • Be active at night • Seek moist conditions • Hang out in burrows How to Control Water Loss 2. Maintain more water in body – Excrete highly concentrated urine (lose less H2O) – Produce dry feces How to Control Water Loss 2. Water retention cont’d. – Use metabolism to produce water from food – Drink lots and store it – Condense breath to maintain moisture How to Control Water Loss 3. Tolerate water loss from body – Evolve dehydration tolerance – Get big: warm up more slowly; radiate heat at night Animals Maintain a Balance of Water Uptake/Loss • Some animals migrate, leaving areas during the dry season Figure 7.10 Animals Maintain a Balance of Water Uptake/Loss • Estivation: avoid effects of drought through a period of dormancy (physiological inactivity) Figure 7.11 • Diapause (many insects): enter a stage of arrested development; emerge when conditions improve Physical Ecology of Animals—Part 2 Elements of Ecology: Animal Adaptations: Chapter 7 Physical Ecology of Organisms • The physical environment can affect abundance and distribution of species • Organisms adapt to their environment http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/co mmons/7/71/Banksia_menziesii_cone.jpg&imgrefurl=http://en.wikipedia.org/wiki/F ile:Banksia_menziesii_cone.jpg&usg=__rrnB6vQX0GgCZT2rzocUjgAfheg=&h=2 725&w=1706&sz=2186&hl=en&start=43&um=1&tbnid=boQZVE00rkGVpM:&tb nh=150&tbnw=94&prev=/images%3Fq%3DBanksia%2Bmenziesii%26ndsp%3D2 0%26hl%3Den%26sa%3DN%26start%3D40%26um%3D1 Physical Limitations to Life • Temperature – Heat – Cold • Water • Gas exchange • Light • Body size • Energy use • Digestion efficiency http://www.nps.gov/yose/historyculture/images/history-tree-web.jpg Physical Limitations to Life • Food and nutrient acquisition • Metabolism – Energy acquisition – Energy use • Waste elimination http://farm2.static.flickr.com/1385/1464058565_726f5ccf20.jpg Temperature • Enzymes work best in a narrow temperature range • Freezing destroys cells • Heating de-natures proteins http://www.maryedwardsphotography.com/m_edwards/3Pictures/Flora/hoar_frost_crab_apples500.jpg https://qph.fs.quoracdn.net/main-qimg-2b822565382284cb01c3583cef88bb93 Temperature • Temperature affects water balance • Water balance affects temperature http://www.colorado.edu/geography/class_homepages/geog_3251_sum08/02_cloud_forest.jpg • Light levels affect temperature • Temperature affects metabolism Temperature • Organisms regulate their body temperatures • Most animals are mobile, can seek or escape heat and cold • Many animals can produce significant quantities of heat through metabolism https://www.industrytap.com/wp-content/uploads/2016/12/batt9.jpg https://s3images.coroflot.com/user_files/individual_files/158547_n5P3goKJ6EGvCNdk0Q5uTIAkv.jpg Animals Exchange Energy with Their Surroundings • To maintain its core temperature, an animal balances heat gain/loss to environment 1. Changes in metabolic rate 2. Heat exchange: • Body core exchanges heat with surface through conduction (influenced by insulation thickness and blood flow) • Body surface exchanges heat through conduction, convection, radiation, evaporation • Terrestrial animals experience a much larger thermal environmental range than aquatic animals • Air temps change rapidly • Aquatic animals generally experience milder temp changes; have a lower tolerance for temperature changes https://www.chicagotribune.com/weather/ct-viz-chicago-hot-weather-summer-2020-20200709-mvpxoqdexbcajeb5fk3xjgxr7e-htmlstory.html Organisms gain and lose heat many ways • Conduction: – Two objects in direct contact – E.g. a lizard basking on a hot rock Organisms gain and lose heat many ways • Radiation: – Energy gained as light —> heat Poikilotherms may use multiple strategies for thermoregulation Fig. 7.17 Poikilotherms = animals that have variable body temperatures Organisms gain and lose heat many ways • Radiation: – Energy lost as heat http://www.thermalimagingcanada.com/images/rabbit.jpg Organisms gain and lose heat many ways • Convection: – Heat transfer between two bodies through a liquid or gas layer https://www.chicagotribune.com/columns/mary-schmich/ct-met-winter-coats-mary-schmich-20181019-story.html Organisms gain and lose heat many ways • Evaporation: – Water requires much energy to become gas – Water can remove excess heat from the body – But water loss can lead to dehydration —> over-heating Animal Body Temperature Reflects Different Modes of Thermoregulation • Thermoregulation implies maintaining the average body temperature or variations in body temperature within a certain range • What are the two categories of thermal regulation in animals? • Poikilotherms = animals that have variable body temperatures • Homeotherms = animals that maintain nearly constant body temperatures *These terms are not synonymous with conformers and regulators; only true thermoconformers are animals that live in environments with almost no temperature variation (e.g. deep ocean) • Cold-blooded/warm-blooded: animals are cool/warm to the touch: out-dated term • Poikilotherms = animals that have variable body temperatures • Homeotherms = animals that maintain nearly constant body temperatures *These terms are not synonymous with conformers and regulators; only true thermoconformers are animals that live in environments with almost no temperature variation (e.g. deep ocean) • Endotherms: generate heat internally via metabolism • Ectotherms: require an external heat source to warm up https://lh3.googleusercontent.com/proxy/73TAUA0WBBDmx6fxcCkrtKOYbiaUa84B3hnWTJNYgGTzevG8-2IXs2Z54u38KIhwUGBZassYjug2A-PYi2oiONREAswpuaiJ Endotherm Endotherm (brood patch) Endotherm Ectotherms Ectotherms Poikilothermic Endotherms Functional endotherm Functional endotherm Functional endotherms https://fishionary.fisheries.org/wp-content/uploads/2015/04/endotherm_fish_temp_balance.png https://img.sfist.com/2020/08/bluefin-tuna-getty.jpg Poikilotherms Regulate Body Temperature Primarily through Behavioral Mechanisms • Performance measures that vary as a function of body temperature in poikilotherms include: – locomotion – growth – development – fecundity – survivorship • Each species has Tmin and Tmax at which performance approaches zero and temperature(s) at which performance is optimal (Topt) • Optimal temperature varies by species • Characteristics of a species’ habitat are correlated to environmental temperature • In 20 crab species, Tmax was positively correlated with H20 temperature and the max temperature in which the species was found Figure 7.15 Homeotherms Regulate Body Temperature through Metabolic Processes • Birds and mammals produce heat through aerobic cellular respiration; process is not 100% efficient (energy lost as heat) • Basal metabolic rate is measured by the rate of O2 consumption; respiration rate is proportional to body mass https://www.sciencesource.com/archive/-SS2236127.html Oxygen consumption (cm3/hr) 106 Elephant 105 Human 104 Cat 103 102 10 Squirrel Mouse 0.01 Figure 7.19 Dog 0.1 1 10 Body mass (kg) 100 1000 Homeotherms Regulate Body Temp through Metabolic Processes • Thermoneutral zone: an endotherm’s temperature tolerance range; outside of this zone, past the critical high and low temperatures, metabolic rate increases Homeotherms Regulate Body Temp through Metabolic Processes • Homeotherms save heat by using insulation: – Insulating fat layer – Fur (thickness) – Feathers (fluffed up) https://media.wired.com/photos/5b1888cf8d2bb71017128a7e/master/w_660,h_436,c_limit/picture1.jpg https://sites.ehe.osu.edu/beyondpenguins/files/2011/07/web_Wiki_polarbear.jpg Homeotherms Regulate Body Temp through Metabolic Processes • Homeotherms generate heat by: – Shivering: involuntary muscle action increases heat production – Brown fat: has many more mitochondria than regular fat; generates more heat Homeotherms Regulate Body Temp through Metabolic Processes • Homeotherms reduce body temperature through evaporative cooling: – Moisture evaporates from the skin, heat is lost – When body temperatures is above the upper critical temperature, panting and sweating accelerate evaporative cooling – Water, mud baths Endothermy and Ectothermy Involve Trade-offs • Benefits of Ectothermy: – lower metabolic rate requires fewer calories per gram of body weight (less food) – can allocate more energy to producing biomass than to metabolism – can reduce metabolic activity when resources are limited, or environmental conditions are extreme – can live in environments where food and water are limited Endothermy and Ectothermy Involve Trade-offs • Costs of Ectothermy – temperature of the environment determines activity – maximum body size is constrained because heat is absorbed across the body surface • surface/volume ratio becomes to low for heat to warm the entire body mass • larger ectotherms can live in only in warmer environments Endothermy and Ectothermy Involve Trade-offs • Benefits of Endothermy: – Homeotherms can remain active even if environmental temperature varies – Maximum body size is not constrained because heat is generated internally – Large endotherms can live in cool environments Endothermy and Ectothermy Involve Trade-offs • Costs of Endothermy: – Higher metabolic rate = more calories per gram of body weight = more food needed – Small endotherms must eat almost constantly; usually allocate more energy to metabolism than to producing biomass – Producing insulation Endothermy and Ectothermy Involve Trade-offs • One cost of endothermy is that endotherms usually allocate more energy to metabolism than to producing biomass • How does this affect the growth of young endotherms? Endothermy and Ectothermy Involve Trade-offs • Young endotherms are often altricial (blind, naked, helpless, ectotherms) • Depend on parents to maintain body temperature • Allows them to allocate more energy to growth early in life Heterotherms Take on Characteristics of Ectotherms and Endotherms • Hibernation: body temperature drops to near-ambient temperature for a long period of time (winter) • A state of controlled hypothermia: heart rate, respiration, total metabolism drop; body temperature goes below 10C; animal goes into acidosis; CO2 levels in the blood increase, blood pH decreases, drops shivering threshold • Bears don’t hibernate, they enter winter sleep – body temperature drops only a few degrees – do not eat, drink, urinate/defecate – are easily roused • Undergo a metabolic change—instead of excreting urea, it’s broken down into amino acids recycled to make proteins. Energy: Food Storage • Fat is good! Energy: Food Storage • Fat is good • More fat = better chance of surviving hard times • Organisms exposed to regular starvation events evolve the ability to survive starvation better Energy: Metabolism • Organisms need a certain baseline amount of energy just to live • They need additional (net) energy to: – Grow – Reproduce – Support additional activity Energy is the Basis for Evolutionary Tradeoffs • Energy intake is limited • All organisms lose energy: heat, excreted waste products • Adaptations that require energy will have to get it from the organism’s energy budget • Energy use in one area may preclude it in another Energy is the Basis for Evolutionary Tradeoffs • Temperate birds consistently lay more eggs than tropical birds. Why? https://www.audubon.org/news/why-do-tropical-birds-have-fewer-chicks Energy is the Basis for Evolutionary Tradeoffs • Why do temperate (northern) birds lay more eggs than tropical birds? – Food is more abundant in north – More biodiversity in tropics = more competition in the tropics – More energy needed to compete, find food, avoid predators – Less energy available to produce eggs Some Animals Use Unique Physiological Means for Thermal Balance • Animals in hot dry climates face a challenge— losing heat without losing too much water through evaporative cooling • Camels and oryx store body heat during the day; heat dissipates at night • Reduces the need for evaporative cooling → reduces water loss • Ectotherms in cold climates endure long periods of temperatures below freezing—how do they withstand this without freezing solid? • Supercooling of body fluids—the body temperature falls below the freezing point of water but does not freeze – Solutes in the blood lower the freezing point – Animals from many groups increase glycerol in body fluids; protects against freezing damage Some Animals Use Unique Physiological Means for Thermal Balance • A countercurrent heat exchange system requires blood vessels that flow in opposite directions in close proximity • This can conserve heat or cool depending on the configuration Counter-Current Heat Exchange: Staying Warm • Animals in cold climates could radiate significant heat through limbs (a) • Run warm arterial blood next to colder venous blood to warm it up (b) Figure 7.23a, b • Cetaceans’ blubber layer conserves body heat, but uninsulated flippers can lose heat • Heat is exchanged between arteries (warm blood from the body) and veins (returning cool blood from limb) • As arterial blood moves further into the flipper, it encounters cooler blood, so the transfer of heat continues the length of the vessels within the flipper • The same arrangement of blood vessels is seen in the legs of many birds Some Animals Use Unique Physiological Means for Thermal Balance • Rete = a vascular bundle/net of arteries and veins • Countercurrent exchange occurs when blood flows in opposite directions through these parallel vessels • Can be used to cool or heat – the desert oryx cools its brain with a rete – some fast-swimming fish use a rete to warm swimming muscles Functional endotherms https://fishionary.fisheries.org/wp-content/uploads/2015/04/endotherm_fish_temp_balance.png https://img.sfist.com/2020/08/bluefin-tuna-getty.jpg Counter-Current Heat Exchange: Staying Cool • Evaporation through nose/mouth rete cools venous blood before it returns to heart • Run warm arterial blood past cooled venous blood • Rete cools blood before it reaches the rest of the body Figure 7.24 Learning Objectives • Discuss the significance • Discuss the differences and of the surface area to challenges of specialists vs. volume ratio generalists • List some adaptations to • Costs/benefits of size constraints homeothermy vs. poikilothermy/heterothermy • List different categories of herbivores • Discuss different countercurrent exchanges and how • Discuss the feeding they work challenges herbivores face • List the different categories of heterotrophs Vocabulary to Know • Constraint • Herbivore • Carnivore • Omnivore • Autotroph • Heterotroph • Specialist • Generalist • Endotherm • Ectotherm • Homeotherm • Poikilotherm • Hibernation • Torpor • Evolutionary tradeoff • Supercooling • Counter-current exchange • Rete 
Purchase answer to see full attachment