Bio 1070 – Unit 8An Artic Ecosystem

• carbon dioxide (CO2) in the air influences the overall mean temperature of the planet• from burning fossil fuels and other anthropogenic activity therefore contributes to a

warming of the Earth• Arctic is a special concern in this regard as it is warming at a much higher rate than most

parts of the world• its ecosystems are based on the properties of cold habitats

Why does the Arctic warm faster than lower latitudes?1. As snow and ice melt, darker land and ocean surfaces absorb more solar energy2. More of the extra trapped energy goes directly into warming rather than into evaporation3. Atmospheric layer that has to warm in order to warm the surface is shallower in Arctic4. As sea ice retreats, solar heat absorbed by oceans is more easily transferred to atmosphere5. Alterations in atmospheric and oceanic circulation can increase warming

• North Pole may raise up to 8°C warmer unless we slow down greenhouse gas emissions• The sub-Arctic regions of Canada (e.g., Churchill, Manitoba) contain a wide variety of

both aquatic and terrestrial ecosystemso In the high Arctic, near the communities of Resolute and Devon Island, much of

the terrestrial environment is dominated by tundrao However, even at very high latitudes, there are both freshwater (rivers, ponds,

lakes) and marine (Arctic ocean) habitats

Arctic Organisms• A distinguishing feature of Arctic aquatic ecosystems is ice (sea ice, pack ice, ice caps,

glaciers, icebergs)• Many animals and plants are adapted to life in such icy conditions

Aquatic animals:NarwhalBow head WhalePolar BearAtlantic PuffinArctic Char (type of fish)Greenland Cod

• For marine mammals (e.g., narwhal, bowhead whale, polar bear) that must maintain a constant body temperature of around 37°C, exposure to near freezing water temperatures presents obvious challenges

o They have a thick layer of insulating blubber just under the skin• Animals that generate their own internal heat through metabolism are

called endotherms (meaning “inside heat”)o this is restricted to the “warm-blooded” vertebrates — that is, mammals and birds

• Fishes do not regulate their body temperatures internally, so they usually have the same internal temperature as the surrounding water

• Animals such as fishes (and amphibians, reptiles, and invertebrates) that rely on environmental sources of heat are called ectotherms (meaning “outside heat”)

Terrestrial Animals:Musk OxCaribouArctic FoxArctic Ground SquirrelWoolly CaterpillarRock Ptarmigan

• The high north has been called “the land of the midnight sun” because the sun does not set at summer solstice, and at winter solstice the sun does not climb above the horizon

• Some terrestrial mammals and birds stay active in winter (e.g., Musk Ox, Caribou, Arctic Fox, Rock Ptarmigan), find scarce food, and maintain a body temperature at about 37ºC

• Alternatively, some animals hibernate in protected burrows and drop their body temperatures to just above freezing (e.g., Arctic Ground Squirrel)

• Some ectothermic animals, by contrast, can’t avoid freezing and survive numerous freeze-thaw cycles over many years (e.g., Woolly Caterpillar).

Arctic Plants:MossesLichensFlowering plantsShrubsTreesSedges

• Plants face both a short growing season and challenges related to extreme cold• Vascular plants in the Arctic tend to be small and freeze tolerant• Lichens are even more well suited to these harsh conditions because they lack roots, do

not require soil, and are tolerant of desiccation (dehydration) and very low temperatures (page 239 field guide)

Impacts at Different Levels of Organization• Populations: Within a group of individuals of the same species living together climate

change may affect survival, growth and reproductiono For example, an Arctic plant may thrive as temperatures increase, but they may

now dominate an area where a competing species is negatively impacted by increased temperature

• Communities: When one considers populations of different species living in the same area, climate change may cause changes in species distribution or frequency within that community

• Ecosystems: Within the broader context of an entire ecosystem (e.g. arctic ecosystem), climate change may have many complex effects that influence nutrient cycling between the abiotic and biotic factors

• Temp impacts the motion of molecules: higher temp increases motion, lower temp decreases motion

• Most macromolecules (e.g. lipids, proteins, nucleic acids) are sensitive to temp change.

o Ex. Enzymes (proteins) act as catalysts to speed up reactions within cells. Typically function best within the normal range of temps that the cell experiences.

o Decrease in temp slows down enzyme function and reaction will be slower

o Increase in temp will speed up an enzyme reaction in the short term

• Temp changes may cause cells to undergo a stress responseo Usually involves an increase in the amount of heat-shock

proteins (HSPs) (attach to other proteins and stabilize them). When temp decrease back to normal, HSPs release their bound proteins which then can return to their normal “job” in the cell

o Ex. most plant/animal cells can tolerate a brief increase in temp, but if longer the cell may die mostly because enzymes are not functioning properly

• At higher levels of organization, temp changes have more complex effects

o Ex. Arctic Char (Salvelinus alpinus) are found in cold arctic lakes, rivers and oceans. As ectotherms, their body temp is matched to the temp of the surrounding water. An increase in water temp will increase the amount of blood the heart pumps per minute. This increased output from the heart, plus other temp effects on the properties of the blood and blood vessels, will induce multiple changes within the cardiovascular system

• Endotherms regulate body temperature (thermoregulation) by sensing changes in internal temp and altering physiological processes and behavior to bring internal temperatures back to normal

• Physiological processes: functions and activities of living organisms that support life in organisms from their origin through the progression of their life

o Ex. if a caribou is too warm after running away from a predator it will pant to dissipate some of the extra body heat. After panting for a few minutes some of the excess internal heat is lost to the environment, bringing the body temperature back to ~37ºC and then a signal turns off the panting response. In this way, body temperature is regulated

∗ Just to make sure you understand the difference between endotherms and ectotherms, have a look at the x-axis (ambient temperature) and y-axis (body temperature) on this graph

∗ Make sure you could plot a similar graph if you were asked to show the relationship between external and internal body temp in different animals from the arctic

• Homeostasis is the maintenance of a constant internal environment maintained by the organism’s responses to changes in the external or internal environment

o Endotherms maintain body temp within narrow limitso Ectotherms don’t maintain a constant body temp, but other factors (e.g. ions,

oxygen) are under homeostatic control

Bio 1070 – Unit 9

Challenges of Living in the Arctic• Basic processes by which Arctic animals exchange materials with the external

environment1. Gases – most animals require O2 for metabolism and release CO2 as the

respiratory waste product2. Nutrients – animals utilize many different types of food, obtaining carbohydrates,

fats, and proteins in their diets3. Wastes – fluid and solid wastes from digestion and metabolism are released.

Animals must also balance the ion composition of their internal fluids. Ions are obtained from food or directly from the environment (especially in aquatic animals)

• The amount of substances that must be exchanged, across membranes, depends on the volume of the animal

o In small animals this occurs directly from the external medium to the internal cello However, for most larger multicellular animals the circulatory system delivers and

carries away substances from the interstitial fluid bathing the cells• Every cell must be in contact with an aqueous environment where dissolved substances

can be exchanged• Fluid surrounding cells is called the interstitial fluid• Complex animals must also have a circulatory fluid that carries gases, wastes, and

nutrients to the interstitial fluid• Respiratory systems and digestive systems have direct contact with the external

environment

Homeostasis and Feedback Mechanisms• Homeostasis occurs more so in endotherms (mammals and birds)

o regulate body temp and other variables within a narrow range around a set point• Ectotherms (e.g., amphibians, fishes) do not regulate temperature, but do regulate many

other internal variables, such as blood [Na+]• Neural/hormonal processes are involved in keeping internal variables relatively constant• Negative feedback is a regulatory mechanism that counteracts a change in a variable

away from a set point or normal state• Organisms have built-in regulatory systems that are usually based on negative feedback

o Ex. Thermoregulation in mammals controlled by the hypothalamus• Positive feedback is not as common because it pushes the system farther away from the

initial state, but is necessary in cases where a maximal response is beneficialo Ex. During the birthing process of mammals the hormone oxytocin is released

which stimulates uterine contractions. As the uterine muscles contract, signals are sent that reinforce/strengthen these contractions

• Different time scales: acute (short-term), chronic (long-term within an organism’s lifetime), and generational (across multiple generations)

• Adjustment by individual organisms to chronic stresses is known as acclimatization• The evolution of populations across generations under natural selection is adaptation• As seasons change, temperature, photoperiod, food availability and a host of other

external factors may also change; in turn modifying the physiology

Cell Membrane Acclimatization• Ectotherms change the composition of their cell membranes with changing temperatures

to maintain membrane fluidity• Cell membranes are composed of lipids with embedded membrane proteins

o different lipids have different influences on membrane fluidity• The fluidity of the membrane affects how the cell functions

o Ex. If an Arctic char is exposed to lower water temperatures, body temperatures will decrease and initially cell membranes will become more rigid and less fluid

• Cell membranes have a bilayer of phospholipids (a head group and two fatty acids)• The maintenance of relatively constant membrane fluidity regardless of tissue

temperature is called homeoviscous adaptation• Ectotherms exposed to seasonal changes in temperature in the Arctic undergo cell

membrane acclimatization between seasons• The range of tolerance defines the range of environmental parameters (e.g. temperature,

salinity) that an animal can easily tolerate without losing functional capacity

Circadian Rhythms• Most living things are exposed to a rhythm of light and dark and if the pattern observed

follows a rhythm over 24 hours, this is called a circadian rhythmControlled by an endogenous or internal mechanism that acts like a clockMay be altered by external factorsThe internal biological clock is set by external light conditions (e.g. travel to a new time zone, eventually your sleep pattern will adjust), but is not dependent on light (e.g. if you live in a cave with complete darkness, you will still sleep for ~8 hours out of every 24 hour period)

• Circannual rhythms: longer time cycle that proceeds over the course of a year

Bio 1070 – Unit 10

Surviving the Arctic WinterBody Size and Surface Area:

• Exchange with the environment and the amount of material that must be exchanged are both strongly influenced by body size and surface area

o Ex. the larger the animal, the greater its absolute requirements are for gases and nutrients. An elephant needs more food and oxygen each day than a mouse does (Thus, absolute requirements go up with body size)

• Relative (per gram or kilogram) metabolic requirements go down with body size

o Ex. one elephant would use much less oxygen than a group of mice weighing the same total amount as the elephant.

• The key points are:1. Bigger body size means lower surface area to volume ratio, which means less

efficient exchange with the environment.2. When more surface area is needed, organs may have specialized structures that

increase total area such as extensive folding.o Ex. membranes in the digestive, respiratory, and circulatory systems o Ex. small intestine(digestive system) and lungs (respiratory system) have a

higher surface area by increased folding/pouches of the epithelial surface.

Metabolic Rate and Temperature• Metabolic rate: overall indication of how much energy is being consumed per unit time• This is usually done in a controlled lab setting in a metabolic chamber or respirometer• In ectotherms (such as the woolly caterpillar) a decrease in environmental temp decreases

body temp and in turn, the overall metabolic rate. Therefore, less O2 will be consumed per unit time by the caterpillar at lower temperatures.

• This is most often done by calculating the temperature quotient or “Q10” which describes the change in rate with an increase in temperature of 10 degrees

Q10 = Rate (T) / Rate (T-10)

• For most physiological processes, Q10 values are between 2 and 3. Although metabolic rate is often used to calculate Q10, researchers can use other rate processes such as swimming rate, enzyme activity rate, or breathing rate to calculate Q10.

Why Hibernate?• For endotherms, when temps start to fall, there is a larger gap between internal and

external temperature and therefore greater heat loss• To maintain a set point (~37°C), active mammals in the Arctic need to have active stores

food and fat• These animals can hibernate so that their metabolic rates will decrease, meaning needs

for a lot of fat and energy will decrease

• Hibernation usually lasts for several weeks or even months, whereas a shorter period of dormancy are called torpor (hummingbirds may enter torpor nightly) last a day

• Metabolic rate per kilogram of tissue is higher in a small animal, therefore small mammals need to supply more energy for each cell than larger mammals

• Smaller mammals lose heat faster than larger animals (higher surface area : volume ratio)

Brown Fat and Non-Shivering Thermogenesis• Need to build up their stores of white fat prior to entering the hibernaculum (the “den”)

because over long winter months they will burn fat even if metabolic rate is set very low• Most hibernating mammals leave the den at a lower body mass than when they entered as

a result of diminished fat stores• Some hibernators store food in their dens and arouse to eat periodically• However, whether they arouse periodically or just once at the end of the winter, arousal

from hibernation consumes a great deal of energyo By way of analogy, we can consider a car idling (hibernation) that rapidly

accelerates to 100km/h (arousal from hibernation), a process that obviously consumes fuel

• Brown fat is used to re-activate the bodies regular body metabolism and increase it back to 37˚C

• They are cells that consist of a high concentration of mitochondria• The mitochondria in these cells release a protein called thermogenin which is used to

increase the heat production by 10 fold• Non-Shivering thermogenesis: this is the process that involves brown fat cells being

used to generate body heat

Active Overwintering Small Mammals• Voles and lemmings are found throughout the Arctic

• Voles may look like mice, but their bodies are plumper with blunt noses, small eyes and short ears (weight~22g)

• Lemmings have larger heads, chubby bodies, furry feet and stubby tails (weight~70g). • Neither voles nor lemmings hibernate in the winter, instead they construct long tunnels

under the snow and build nests on the ground• In winter, voles rely on twigs and other parts of arctic shrubs for food, whereas lemmings

eat old grasses blanketed by snowcover• Recent research in Norway compared the reproductive habits of lemmings and voles in

the winter months. Researchers found that the population of lemmings living under the snow increased as the winter months passed, but the vole populations decreased

• Ecologists have known for some time that lemming populations in arctic regions go through 'boom and bust' cycles.

• This new research showed that large increases in lemming populations are driven by their winter behaviour, and not by common factors such as food and predators. However, the authors also cautioned that rising temperatures in the Arctic could drastically affect lemming populations because snow cover will not remain as long in the spring, reducing their reproductive window

Key Points for Hibernation:• Hibernation is more advantageous for smaller animals that have a higher surface area to

volume ratio• Brown Fat cells are specifically used for arousal from hibernation because it is able to

produce much more energy that the white fat cells• White fat cells are used to sufficiently sustain a low level of fuel and metabolic activity

Bio 1070 – Unit 11

Arctic Biodiversity: History1) Past, including how the regions now known as the Arctic have changed over time and some particularly interesting organisms that evolved in former environments2) Present, including how some modern-day organisms survive freezing winter conditions and how we can assess current biodiversity in the Arctic 3) Future, including a critical evaluation of some predictions of what will happen as global temperatures rise

The Arctic of the Past• Arctic has not always been a harsh, icy place• For various reasons, this major change in climate over millions of years makes the Arctic

a particularly interesting place to search for fossils• Areas such as Churchill, Manitoba and Resolute, Nunavut are home to enormous

numbers of fossil brachiopods — a group that is now relatively rare but which once dominated marine environments in the way that bivalve molluscs now do

• Not only marine invertebrate fossils that can be found in the Arctic. Some very important transitional fossils of vertebrate groups have been discovered in the Canadian Arctic

o One such example is Puijila darwini, an extinct mammal that is thought to be a transitional form in the evolution of modern seals

Surviving in an Icy Arctic• Osmosis is the passive movement of water across a membrane from a solution of low

[solute] to a solution of high [solute] (from lower osmotic pressure to one with higher) • Hypertonic: water leaves cell at higher [ ] than coming in, cause cells to shrink• Hypotonic: water enters cell at higher [ ] than going out, causes cells to swell • Isotonic: cell remains the same

• When tissues are exposed to temps below freezing, ice crystals form (of pure water; solutes are excluded) in the extracellular fluid reduce the amount of free water outside the cell, although [solute] increases creates an increase in osmotic pressure

• In addition, the formation of ice crystals inside cells can cause significant physical damage to cell membranes and other cellular structures.

• Uncontrolled freezing in which ice crystals form in the body is therefore a significant problem for ectotherms living in subzero conditions

To Freeze or Not to Freeze?The two possible strategies for overwintering insects are presented in the figure below:

• Freeze tolerant insects/animals start producing ice nucleating agents which initiate freezing outside of the cells in the extracellular fluids.

Produce glycerol and/or sugars to decrease the freezing point of the cytosol to protect their cellsIt is all about “controlled” ice formation (the site and rate of ice crystal formation)May also synthesize antifreeze proteins which slow down or inhibit ice crystal formation in specific tissues or cells

o The woolly caterpillar, Gynaephora groenlandica lives in the high Arctic. Often it will be exposed to extreme low temperatures (-70°C) on the tundra where the snow has blown away. In the brief few weeks of summer the caterpillar thaws out, feeds and grows a bit. But for most of the year this species remains frozen and they may survive 13 to 14 years in this freeze-thaw cycle before they metamorphose into an adult moth

• Freeze avoiding insects/animals void their digestive tracts to remove any microbes or small particles which act as ice forming agents

Produce glycerol and other sugars to decrease freezing point of the cytosol to protect their cells and allow body fluids to remain unfrozen at temperatures well below 0°C. This is called supercoolingSynthesize antifreeze proteins to further prevent ice crystal formation and stabilize the supercooled state, but they also decrease the freezing point of body fluids. Antifreeze proteins are thought to work by binding to ice crystals and inhibiting further growth

Many insect species overwinter in a supercooled state, but only at consistently moderate low temperaturesSupercooling can be dangerous because some insects/animals super-cool too quickly which could cause total freezing, causing death

o Some fish species inhabiting cold northern seas synthesize antifreeze proteins in winter months. If they swim into waters containing ice crystals, they have antifreeze proteins in their skin, as well as other tissues, that prevent ice formation. These fish do not supercool, but remain unfrozen in waters that would freeze unprotected animals. Just think about it - if a fish froze solid it would float and be easily spotted by predators.

o In at least one vertebrate, the North American wood frog winter survival involves freezing solid. (Of course, frogs are not found in the Arctic)Wood frogs find refuge under leaf litter or soil before they freeze so that predators can't easily find them

• Another strategy used by some animals is to produce resting eggs: various crustaceans that inhabit temporary ponds in the Arctic produce resting eggs that remain dormant during the harsh winter and are very resistant to both cold and desiccation.

o Can be found in water fleas, fairy shrimp, and tadpole shrimp in the Arctic o The adults do not survive, but their resting eggs do and then hatch when

conditions become favourable once again

Assessing Current Arctic Diversity• One approach is to undertake a massive international biodiversity survey, such as the

recently-completed Census of Marine Life• It has been extremely successful in improving our knowledge of ocean biodiversity, with

more than 2,600 scientific publications, 6000 potential new species discovered, and 28 million distribution records achieved to date.

• However, this comes at a significant cost. The project lasted 10 years, involved 2,700 scientists from 80 nations, required 540 expeditions, and had a price tag of $650 million. Research of this magnitude is difficult to accomplish, meaning that much of the exploration of Arctic biodiversity will require a more accessible approach

• It so happens that a promising method for biodiversity surveys using DNA technology has been developed here at the University of Guelph and is being applied to a major study of the fauna and flora of Churchill, Manitoba

• One of the challenges for a biodiversity assessment such as this is the fact that many of the species encountered are not yet described and do not have scientific names

• We use “species accumulation curves” to evaluate the effectiveness of our sampling efforts. When the curve begins to level off, we know that we have found most of the diversity in an area.

• The same approach can be used when species do not have scientific names, using “molecular operational taxonomic units” (MOTUs) or “DNA barcode clusters” in place of species names and plotting the same type of graph