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Article Summaries for BIO120

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James Thomson

1 – introduction to the basic drivers of climate  Climate is the long term prevailing weather determined by temperature and precipitation - Largest determinant of life in a region  Long term changes in climate are due to changes in intensity and distribution of solar radiation Sunlight and Atmospheric Ciruclations  Sunlight intensity is key in climate – energy from the sun is not evenly distributed throughout earth - Higher latitudes receive less solar energy  The different orientation of the earth as it orbits the sun creates seasons - Tropics have minor temperature changes – their seasons are characterized by the presence or absence of rain - Both hemispheres have equal solar input during spring and fall equinox  The sun is most intense at the equator – this warms up the air, making it less dense, and causes it to rise - The warm arm rising in the tropics is wet, as it rises and cools, the water condenses and falls as rain - Sunlight also creates winds that push the now dry tropical air away from the equator  Descends at 30 degrees north or south and absorbs moisture from the ground, creating dry areas - At 60 degrees, the air rises again and precipitates - Some of the cold, dry, rising air flows to the poles, absorbs moisture, and create cold polar climates Oceanic Currents  Wind is also generated through earth’s rotation (east and westward winds) - Warm tropical water carry heat on the east side of continents to the poles, and cold water is forced down the west side from the poles  Brings temperate climates to areas away from tropics - Melted ice caps flow deep underwater towards the equator  Oceanic currents depend on earth’s rotation, and temperature differences between the poles and the equation - Current flow varies with depth  Wind and ocean currents redistribute heat - 60% by atmospheric circulation, 40% by ocean currents  High heat capacity of water leads to the moderating effect – along with heat redistribution of heat by currents, creates mild climates  Coastal regions are wet, continental regions are dry (They lack bodies of water to recharge moisture) - E.g. mountain ranges force air to rise, cool, and precipitate on the windward side  Consequently, the dry air descends on the leeward side and absorbs ground moisture  Creates a dry and arid rain shadow  Microclimates are the variation in physical structure of an area - Due to different ground colour, vegetation, etc.  El Nino: usually winds blow strong from east to west, carrying with it the warm surface water. This warm water piles around the west pacific, and the cold water rises in the east to replace it. As the winds decrease, the warm water starts pooling around the east as well, which then decreases the winds even more (positive feedback) - Consequences: precipitation in the eastern pacific  Flooding in north and south America, drought in Australia, Indonesia, and Africa - Typical arid regions become wet and experience a population boom in Americas  Causes an increase in diseases and viruses - Marine life: cold water rising brings nutrients as well, with El Nino, the nutrient supply is cut. Phytoplankton declines and marine populations decline 2 – Terrestrial Biomes  Biomes differ most in vegetation, and are defined by temperature and rainfall  Warm and wet climates  cool and dry climates - Decrease in height, density, and species diversity of plants  Raunkiaer classified life form based on the perannating organ location on the plant  Climate regions are classified into biomes Tropical - centered around equator - little seasonal variation - high rainfall, biodiversity, and productivity - poor, phanerotype dominated soils - high decomposition rates due to heat and moisture (and mycorrhizae) - contains ½ of terrestrial species on Earth Savanna - lower rainfall, longer dry seasons - dominated by grasses and small trees - transition from tropical forests to deserts - repetitive fires – releases nutrients in dead plant - decomposition is fast – dung beetles break down animal droppings - large herbivore diversity Deserts - between 15 and 30 degrees latitudes - low precipitation and productivity - different types: hot, cold, high elevation, rainshadow deserts - perennial shrubs dominate - annuals survive dry periods as seeds Grassland - occur in the interior of continents - temperature varies largely over seasons – hot summers and cold winters - summer-peak precipitation - transition into deciduous on wet side, and deserts on dry side - fire, droughts, and grazing are the selective forces on plants - world’s largest terrestrial animals can be found Temperate - high precipitation, high litter production, high biodiversity Deciduous - cool winters, warm summers - trees that drop their leaves Mediterranean - divided into 5 separate regions - hot dry summers, cool moist winters - productivity decreases after 10-20 years due to collection of litter and biomass - fire recycles nutrients - lots of therophytes (plants that survive unfavourable conditions as seeds) Northern Coniferous - needle leaved, drought tolerant, evergreen trees - long cold winters, short cool summers, precipitates mostly in summer - low biodiversity and productivity - permafrost, trees have shallow root systems dependent on mycorrhizae - slow decomposition - mid-hight latitudes Tundra - below freezing temperatures - marshy - lots of mosses and lichens (60% hemicryptophytes – budding near surface) - animals have extended hibernation or migrate 3 – Physiological Ecology  Temperature and water availability significantly affects physiological ecology (how organisms are physiologically adapted to their environments) 4 – Physiological Optima and Critical Limits  Distribution limits are dependent on biotic and abiotic factors  Organisms have an optimal environmental range where fitness is optimized and critical limits where they can only survive for short periods of time Thermal Performance Curves  Illustrate how well an organisms perform across a range of environmental conditions (such as temperature)  Eurythermal: wide thermal range – ectotherms - Behaviourally thermoregulate – move into different environment - No TNZ, but still has an optimal temperature - Pejus temperatures are when performance begins to decline  Stenothermal: narrow thermal range (must thermoregulate) – endotherms - Have a thermal neutral zone where metabolism is constant and minimized - Going lower or higher than the TNZ leads to elevation of metabolic rate to maintain body temp  E.g. shivering or seating Mechanistic Bases of Thermal Curves Lower critical thermal limits  Organisms can survive temperatures below their freezing point by preventing the formation of intracellular ice  Ectotherms and marine invertebrates prevent intracellular ice formation by: - Using solutes such as glycerol to lower the freezing point of the cystosolic/intracellular fluid - Encourage extracellular fluid to freeze - Concentrate solute in extracellular fluid creates an osmotic pressure gradient that draws water from inside the cells  E.g. wood frog – ice formation stimulates transportation of glucose from organs to extracellular spaces – draws water out - Using antifreeze proteins to limit size of ice crystals by coating them  Endotherms (mammals) undergo hibernation – periods of reduced temperature and metabolism Marginal Stability  Enzymes function with conformational shifts and depend on weak bonds  Highly temperature sensitive  Temperature change  higher rate of biological reactions and reduced stability of enzymes Reduction in Metabolic Efficiency  Rising temperatures  weak bonds break in membrane  proton barriers are weakened  proton gradient is less efficient  less ATP is produced Cellular Stress Response  At high temperatures, proteins lose their structure and unfold  Triggers the heat shock response – heat shock proteins refold proteins that are damaged Membrane Integrity  High temperatures  phospholipid bilayer breaks  barred between cell and environment is gone  Homeoviscous adaptation – reordering membrane composition in ectotherms to maintain membrane fluidity - A type of homeophasic adaptation – any mechanism to ensure shape of membrane Upper Thermal Limit  Neuromuscular coordination is lost Distributional Limits  In the rocky coast, different levels contain different organisms growing in horizontal bands  Upper distribution limit is set by abiotic tolerance  Lower distribution limit is set by biotic interactions (competition for space, predation)  The performance curve or each organism on different vertical zones vary 5 – Homeostatic Processes for Thermoregulation  Two major types: - Poikilothermy – cold blooded ectotherms that can’t produce body heat and instead conform to the outside environment  Can behaviourally thermoregulate by moving into different environments  E.g. wood turtles move into forest clearings in the day and into streams at night  E.g. rattlesnakes form ball groups during high temperatures - Homeothermy – warm blooded endotherms that have physiological adaptations to regulate body temperature  Do not depend solely on environment for heat  In the cold: isometric contractions (shivering), blood vessel dilation  Or non-shivering thermogenesis – brown adipose tissue is catabolised for heat  In the heat: seating, vasodilation of blood vessels to promote heat loss  Thermoneutral zone: needs are met through basal metabolism – temperatures above or below will increase metabolism  Heterotherymy: variations in body temperature spatially and temporally - Spatially: warmer in the core and lower in extremities  E.g. jackrabbits have very warm ears to dissipate heat - Temporally: body temperature varies over time  E.g. fever to fight off pathogens  Torpor in black tailed prairie dogs – state of reduced metabolism and hypothermia in harsh conditions (otherwise the energy would be used to thermoregulate) Control of Thermoregulation  By nervous system: hypothalamus that acts as a thermostat which triggers physiological responses  By endocrine system: melatonin in ectotherms, and thyroid hormone in endotherms  E.g reindeers have thick fur for insulation and regional heterothermy to conserve heat in body core  E.g. camels have thick fur to prevent excess heat in the atmosphere from entering the body Conclusion  Homeotherms have a higher metabolic rate, and active over wider temperature ranges - A large portion of energy is devoted to thermoregulation  Poikilotherms can feed less and live in resource poor environments  As organisms adapt to climate change, there are ecological traps – where a behaviour that is adaptive has negative consequences - E.g. sockeye salmon must move to habitats where the water is cooler, but the new habitat is also much more open to predation 6 – Population Ecology  Study of factors that affect population and how a population changes over time 8 – Population Limiting Factors  Geometric populations grow through pulsed reproduction – e.g. the reproduction of deer, which have a constrained mating season  Exponential populations grow continuously, with reproduction occurring at any time – e.g. humans  Logistic growth – as resources are depleted, population growth rate slows and eventually stops - Population size stops growing at the carrying capacity (K)  Recall the predator prey cycle - As predators increase  prey decrease, and thus  predators decrease, and consequently  prey increase, and the cycle continues Density Dependent Limitation (Biotic)  Density dependent factors include disease, predation, and competition - Positive relationship: factor increases with population size (thus stopping population growth) - negative relationship: factor limits at low populations, and is less limited as it grows  Red squirrels: at high densities, some females were pushed to low quality territory  reproductive success was reduced  per capita birth rate decreased  Density dependent factors can affect males and females differently Density Independent Limitation (Abiotic)  Density independent factors include food limitation, pollutants, catastrophes and climate extremes  Quality of nutrients affect organisms – the lower the quality, the higher the environmental stress - E.g. in the great lakes, phosphorus mass was the limiting factor in harmful algal growth. A decrease in the phosphorus load led to a reduction of algal biomass  Amphibians are susceptible to pollutants such as pesticides, heavy metal contaminations, etc. - In salamanders: increase deformities, delay development, lengthen vulnerability to predators by remaining small sized for longer periods  Environmental catastrophes (fires, earthquakes, volcanoes, floods) affect population growth rates directly through direct mortality and habitat destruction 9 – Allee Effects  Allee effect: population growth is reduced at low densities  Allee noticed undercrowding in species, and that it limited population growth - Contradictory to the Malthusian principle (that intraspecific competition does not decrease with population size) and his logistic model  Allee effects have two manifestations: - Component Allee effects – positive association between a fitness component and population size - Demographic Allee effects – component Allee effects produce a positive association between per capita population growth and population size - E.g. if mate limitation is a component Allee effect, it only becomes a demographic Allee effect at low populations. At high population, the demographic effect is erase, but the component effect remains  And Allee effect is a positive association between absolute average individual fitness and population size over finite time (i.e. as population size increase, individual fitness increases) - Might give rise to critical population sizes below which the population cannot exist  Strong Allee effects cause critical population sizes, weak Allee effects don’t Mechanisms that Cause Allee Effects  Mate limitation: - Plants: if gametes are released into the environment - Animals: if males and females have difficulty locating each other  Cooperative breeding, feeding, or defenses  Presence of other individuals with no cooperation – risk of predation is smaller in large prey populations  Inbreeding depressing in small populations reduces average fitness  All in all: small populations suffer from reduced average fitness Evidence  Component Allee effects: most common is mate limitation in both animals and plants - Others include predator satiation (which really affects all prey populations that the predator feeds on)  Demographic Allee effects: harder to demonstrate because: - Small populations give high variance and obscure analysis - Allee effects at low density may be offset by other factors that increase fitness at low densities (e.g. resource competition)  x is the population size, k is the carrying capacity, and a is the critical point  Strong and weak Allee effects can be distinguished by whether or not the y intercept of the per capita growth rate is below zero  In panel c, the dotted line represents a starting population of 21, and the solid line represents a start of 19 - Small changes in population size don’t have effects of normal populations or populations with weak Allee effects, but is drastic for populations with strong Allee effects  In populations with Allee effects, the growth is also at first, limited by the small population - Creating an inflection point Evolution  Rare species usually have adaptations to
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