Ecology Notes Week 2
Ecology Notes Week 2 Bio 369
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This 8 page Class Notes was uploaded by Joseph Notetaker on Friday September 2, 2016. The Class Notes belongs to Bio 369 at Missouri State University taught by Brain Greene in Fall 2016. Since its upload, it has received 27 views. For similar materials see General Ecology in Biology at Missouri State University.
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Date Created: 09/02/16
Ecology Notes Week Two The Importance Of Water In The Physical Environment: Water has important properties essential to life: o Thermal inertia and high specific heat Remains as a liquid over a broad range of temperatures Resists temperature changes o High density and viscosity Facilitates buoyancy for aquatic organisms o Ability to dissolve inorganic nutrients Allows minerals to exist in solution and be absorbed by organisms The availability of water to terrestrial plants depends on the soil’s water holding capacity: o The amount of water held by soil against gravity is its field capacity o The attractive forces creating field capacity are due to soil particle attraction (matric potential) o Getting water into the plant requires roots to have an osmotic potential stronger than matric potential Roots extract water from soil by adjusting osmotic potential The transport of water in plant stems is accomplished through cohesion-tension mechanisms Maintenance of water balance can include regulation of salt o Osmoregulation challenges depend on how much (or little) water is available o Salt concentration can exceed tolerable levels in dry environments or saline aquatic habitats o Salt-tolerant (halophytic) plants remove salt by active transport in roots or excretion by specialized glands Solutions to hypersaline environments: o Bony Fish make physiological adjustments to control the intake and excretion of water and ions in different environment Kidneys and gill filaments adjust function to remove or conserve water Fresh water: excrete ammonia (dilute, toxic) and retain ions in kidney gills Sat water: excrete salt from kidneys and gills Some fish can adjust and survive a wide range of conditions (euryhaline) Others cannot and have narrow salinity tolerances (stenohaline) o Salinity also creates osmoregulatory problems for animals Marine vertebrates have independently evolved glands to secrete excess salt Some animals preferentially drink fresh water in marine systems o Metals are toxic to most organisms at high concentrations Plants evolve locally adapted ecotypes with tolerance for metal-contaminated soils o Plant responses to water related stress depend on adaptations and plasticity potential Drought results in wilting and premature leaf drop Chronic water shortage: Develop higher water use efficiency, grow smaller leaves, and increase relative root mass Flooding saturates air spaces in soil, suffocating and dehydrating the plant Adaptations to chronically flooded habitats include: o Aerenchyma: spongy tissue that allows for gas exchange o Pneumatophores: Arial roots that specialize in gase exchange Water affects gas exchange in aquatic organisms: o The low solubility of O2in water limits its availability to aquatic organisms o Many aquatic species have adaptations to maximize gas exchange Large respiratory surface area Countercurrent exchange o Organisms living in oxygen poor environments have adaptations to compensate Low rates of activity High hemoglobin levels Air breathing Extra respiratory surfaces Mechanisms to supplement oxygen supply A lack of water can also cause environmental challenges: o Anhomeostatsis: Physiological tolerance of high ion concentrations o Adjustment of kidney function Concentrated urine Uric Acid o Nasal passages that conserve water o Estivation: Opposite of hibernation in which creatures’ burrow and sleep for long period of time to conserve water o Adjusting body posture Light and Heat: Photosynthesis in aquatic environments has adapted to the filtering effects of water: Photosynthetic algae have adapted their photosystems to water depth Red wavelengths absorbed quickly Green penetrates to greater depth Use of light by ecosystems: o 70% absorbed by plants Location of absorption varies with plant community Deciduous forest crown absorption (95-99%) o Pines (10-15% reaches ground Grassland: most light penetrates to near ground level Aquatic systems vary with water qualities o The rest is transmitted or reflected (mostly in green and far red wavelengths) Photosynthesis is constrained by dry conditions: Access to CO 2through stomata) requires gas exchange that creates an avenue for water loss. This is a major problem for plants in dry areas Adaptations to minimize water loss are both structural and biochemical Can be reduced by minimization of surface area and reducing air movement over leaf surfaces Hairs on leaves trap air and reduce evaporation Photosynthesis has been modified to accommodate environmental conditions: o C 3athway-used by most plants Uses least energy but is inefficient at harvesting CO 2 Stomata must remain open to provide high concentrations of CO 2 o C 4ycle-higher energy cost but more effective at harvesting CO 2 than C 3ycle Functions well at low cellular CO 2oncentrations allowing stomata to remain closed most of the time Thought to have evolved multiple times during historically low CO2periods Currently prominent in tropical grasses and dicot herbs from hot arid regions o CAM (Crassulaceae Acid Metabolism)-desert-adapted plants (cactus, euphorbs, and Crassulaceae) Inefficient but allows plants to open stomata at night to minimize loss of water Seasonal effects on photosynthesis: o Early Spring is the best time for forest plants to grow because light can reach the ground but it’s still warm enough for plants to grow. Photoperiodicity is responsible for many seasonal processes o Plants and animals both respond to light as an environmental cue for reproductive cycles o Critical day length (the factor that determines when plants flower) varies by species: Short-day Long-day Day-neutral Biological activity is strongly influenced by temperature: o Biological processes are mainly limited to a range of temperatures over which water remains a liquid (0-100) Most organisms can survive only within much narrower temperature ranges o Proteins denature at high temperatures Thermophiles have proteins with very stable bonds between amino acids o Fluidity of cell membranes is compromised at low temperatures Heat exchange is regulated by physical processes: o Radiation: radiant heat absorbed: Intensity Surface area exposure Reflectance (Light colors reflect light waves; dark colors absorb them) o Convection: exchange due to passage of air over body o Conduction: exchange directly with another object o Evaporation: heat lost during respiration or drying of wet surface o Heat exchange in plants is mainly through leaves Heat lost through: Air movement Evaporation of surface moisture Transpiration Enhanced by increased surface area Small lobed leaves most efficient-abundant in hot regions Some plants fold leaves or orient them parallel to sun in hot conditions Photosynthesis is thermally-sensitive: o The rate of photosynthesis increases with temperature to an optimum value and then declines at higher temperatures. If temperatures get too high plants can switch to cellular respiration to produce energy o Optimum values vary among species and locations with C 4 species tolerating higher temperatures than C p3ants. Thermal exchange in animals: o Endothermy: maintenance of a constant body temperature through production of metabolic heat Constant body temperature solves thermal performance problems but at a high energy cost o Ectothermy: thermoregulate by exploiting environmental heat sources Most ectotherms are poikilothermic (they use a range of body temperatures that vary with environmental temperature) Conserves energy but limits activity and performance Ectotherms thermoregulate when they have the opportunity Move from hot to cold areas depending on body temperature The maintenance of a constant body temperature is an example of homeostasis Heat energy directly influences the rate of life processes: o Q10measurements provide a way to evaluate the thermal sensitivity of physiological processes Metabolism increases with temperature o Many applications: muscle contraction, nerve function, metabolism, etc. o Physiological functions have ecological consequences Why is temperature so important? o Body temperature affects physiological and ecological performance which have high fitness consequences Muscle movement Rate and accuracy of embryonic development o Body forms of animals reflect thermoregulation method Mammals are larger and have less surface area so they lose heat more slowly. Hair acts as insulation Reptiles have thin body types with a lot of surface area so they can lose heat easily. They can be much smaller than mammals and birds because they are not worried about heat loss. Ectotherms can actively maintain a high body temperature This helpful during pregnancy o Thermogenesis in Pythons Pythons brood eggs and regulate gestation temperatures by shivering Heat generated by muscular contractions Can increase brood temperature 6-7 degrees above average o Circulatory adaptations Counter current flood flow conserves body heat Paired arteries and veins allow extremity blood temperature to increase before reentering the body Since the veins and arteries are in close proximity, the veins can absorb heat as they transfer blood to the body, preventing a net heat loss. The boundaries between ectothermy and endothermy are not always distinct o Torpor: state of reduced body temperature and metabolism in endotherms, this allows them to conserve energy Short term (daily) Long term (seasonal) o Used to survive cold evenings or seasonal food scarcity (hibernation) o Red bats remain active all winter using torpor Forage only on warm nights Roost in the leaf litter and remain torpid during cold periods o Gigantothermy allows large ectotherms to maintain constant body temperatures in cold environments (Great White Shark, Leatherback Sea Turtle, Dinosaurs??) Thermal stability through minimaliztion of heat loss These creatures perform very well despite cold temperatures Combination of many qualities Low surface/volume ratio Countercurrent exchange High metabolism Insulation Aerobic muscle tissue May have also allowed dinosaurs to live in cold regions o Sensitivity to cold High concentrations of cryogenic chemicals in both plants aod animals can lower their freezing point of fluids up to 3 C Abscisic acid (plants) Glucose and glycerol (a few species of frogs) Protection also provided by super cooling ability Water drops below freezing point without formation of ice crystals Physiological Acclimation allows organisms to function optimally over a range of conditions Species can only survive within ranges of environmental conditions that are tolerable o Original concept stems from Leibigs (Law of the Minimum) Population growth constrained by the most limiting nutrient Extended to recognize that high and low quantities of a factor can be limiting (Law of limiting Factors) o Species vary in their tolerance of environmental factors Eury=Broad Steno=narrow o Can be used to understand geographic distribution As the optimal conditions fade so do the population densities Climate and Weather: Climate: The long term conditions of a particular area Weather: The short term conditions of a particular area The importance of Solar Radiation: o Causes most heating of the atmosphere o Some is deflected by the atmosphere (25%) o Some is absorbed by the atmosphere (25%) o Some reaches the surface (45%) Some that reaches the surface is immediately reflected back into the atmosphere (5%) Air Temperature: o Sensible heat produced by collisions between molecules o Density of gasses decreases with elevation resulting in lower temperatures o The cooling of air due to pressure differences