Ecology Notes PDF

lOMoARcPSD|38714865 Ecology-notes Ecology (The University of Western Ontario) Scan to open on Studocu Studocu is not sponsored or endorsed by any college or university Downloaded by Ella ([email protected]) ...

lOMoARcPSD|38714865 Ecology-notes Ecology (The University of Western Ontario) Scan to open on Studocu Studocu is not sponsored or endorsed by any college or university Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 1: ECOLOGY INTRODUCTION Ecology 1. The scientific study of interactions between organisms and their environment 2. The scientific study of interactions that determine the distribution (geographic location) and abundance of organisms  Other meanings in public usage  Differs from environmental activism and environmental science (solutions to environmental problems) General Misconceptions  Balance of nature – return to original preferred state after disturbance  Each species has a distinct role to play in maintaining that balance Ecological Maxims (Guiding Principles) 1. Organisms interact and are interconnected 2. Everything goes somewhere 3. No population can increase in size forever 4. Finite energy and resources result in tradeoffs  Tradeoffs can be thought of as an investment of energy by species 5. Organisms evolve 6. Communities and ecosystems change over time  Change can happen either very rapidly or very slowly, depending on the species; biased/limited by our own perception because of our own lifespan so we overlook changes 7. Spatial scale matters Ecological Hierarchy  ORGANISM  POPULATION  COMMUNITY  ECOSYSTEM  BIOSPHERE  Population: group of individuals of a species that are living and interacting in a particular area  Community: association of populations of different species in the same area  Ecological studies often include both the biotic (living components), and abiotic (physical components) of natural systems  Ecosystem: community of organisms plus the physical environment o An ecosystem is not simply a collection of communities, but nutrients, water, and abiotic components are considered o Landscapes are collections of ecosystems  Landscapes: areas with substantial differences, typically including multiple ecosystems  All the world’s ecosystems comprise the biosphere—all living organisms on Earth plus the environments in which they live Key Terms for Studying Connections in Nature  Adaptation: a characteristic that improves survival or reproduction  Natural selection: individuals with certain adaptations tend to survive and reproduce at a higher rate than other individuals  If the adaptation is heritable, the frequency of the characteristic may increase in a population over time Ecological Experiments can be done at Different Scales  Lab work – microbial activity in response to a certain environmental stressor can be tested in the lab; a disadvantage, however, is that realistic information is lost  Studies in natural environment – less control in comparison to lab work  Artificial unit is placed in a natural environment Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 Ecosystem Processes  Producers capture energy from an external source (e.g. the sun) and use it to produce food  Net primary productivity (NPP): Energy captured by producers, minus the amount lost as heat in cellular respiration – currency with which we describe ecosystems  Consumers get energy by eating other organisms or their remains Ecological Experiments: Design and Analysis 1. Assignments of treatments and control 2. Replication 3. Random assignment of treatments 4. Statistical analyses (statistical vs. biological significance) Scientific Method  Scientists use a series of steps called the scientific method: 1. Make observations and ask questions 2. Use previous knowledge or intuition to develop hypotheses 3. Evaluate hypotheses by experimentation, observational studies, or quantitative models 4. Use the results to modify the hypotheses, pose new questions, or draw conclusions about the natural world  The process is iterative and self-correcting  Sometimes experiments cannot be done due to scope or scales, so instead, modeling approaches are used (e.g. computerized stimulations) Case Study: Deformity and Decline in Amphibian Populations  High incidence of deformities in amphibians  Declining populations of amphibians worldwide  Amphibians are “biological indicators” of environmental problems – because of their vulnerable physiological characteristics o Skin is permeable; pollutant molecules can pass through easily o Eggs have no protective shell o They spend part of life on land and part in water—exposed to pollutants and UV in both environments.  Observation of Pacific tree frogs suggested that a parasite could cause deformities  Small glass beads implanted in tadpoles to mimic the effect of cysts of Ribeiroia ondatrae, a trematode flatworm, also produced deformities  Further studies: deformities of Pacific tree frogs occurred only in ponds, which also had an aquatic snail, Planorbella tenuis, the intermediate host of the parasite The Life Cycle of Ribeiroia  More complex life cycle for parasite in comparison to other species  Contingent on other species that need to be present in the environment for them to cleave their lifecycle properly  A controlled experiment: o Tree frog eggs were exposed to Ribeiroia parasites in the lab o Four treatments: 0 (the control group), 16, 32, or 48 Ribeiroia parasites  A field experiment: o Six ponds, three with pesticide contamination Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Six cages in each pond, three with mesh size that allowed parasite to enter  Hypothesis: pesticides decrease the ability of frogs to resist infection by parasites  Another lab experiment: Tadpoles reared in presence of pesticides had fewer white blood cells (indicating a suppressed immune system) and a higher rate of Ribeiroia cyst formation  Studies have suggested that a range of factors may be responsible for amphibian declines  The relative importance of factors such as habitat loss, parasites, pollution, UV exposure, and others are still being investigated  Synthetic pesticide use began in 1930s; use has increased dramatically.  Amphibian exposure to pesticides has also increased  Any action (increased use of pesticides) can have unanticipated side effects (more frequent deformities in amphibians)  Interaction – non-additive effect – difference between ponds with and without pesticides  Not a fully controlled experiment, so link between pesticide and deformation is not strong  Fertilizer use may also be a factor: o Fertilizer in runoff to ponds increases algal growth o Snails that harbor Ribeiroia parasites eat algae o Greater numbers of snails result in greater numbers of Ribeiroia parasites  Skerrat et al. (2007) argued that some declines may be due to pathogens such as a chytrid fungus that causes a lethal skin disease, and has spread rapidly in recent years  But climate change and altered conditions may be favoring growth and transmission of disease organisms  Hatch and Blaustein (2003) studied the effects of UV light and nitrate on Pacific tree frog tadpoles o At high elevation sites, neither factor alone had any affect. But together, the two factors reduced tadpole survival o At low elevation sites, this effect was not seen  Stuart et al. (2004) analyzed studies on 435 species: o Habitat loss was the primary cause for 183 species; overexploitation for 50 species o The cause for the remaining 207 species was poorly understood LECTURE 2: THE PHYSICAL ENVIRONMENT Case Study: Salmon Decline  Potential causes of salmon declines in the North Pacific Ocean: o Dam construction o Sediment from logging operations o Water pollution o Overharvesting  But the conditions of oceans, where salmon spend most time as adults, have also been implicated. Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Hare and Francis (1994) studied fish harvest records and showed alternating periods of high and low production associated with climatic variation in the North Pacific.  Mantua et al. (1997): Periods of high salmon production in Alaska corresponded with periods of low production in Oregon and Washington.  They also found a correlation between salmon production shifts and sea surface temperatures.  The physical environment ultimately determines where organisms can live, and the resources that are available  Thus, understanding the physical environment is key to understanding all ecological phenomena Climate  Weather: Current conditions—temperature, precipitation, humidity, cloud cover  Climate: Long-term description of weather, based on averages and variation measured over decades  Climatic variation includes daily and seasonal cycles, as well as yearly and decadal cycles  Long-term climate change results from changes in the intensity and distribution of solar radiation  Current climate change is due to increased CO2 and other gases in the atmosphere due to human activities  Climate determines the geographic distribution of organisms  Climate is characterized by average conditions; but extreme conditions are also important to organisms because they can contribute to mortality  The sun is the ultimate source of energy that drives the global climate system  Energy gains from solar radiation must be offset by energy losses if Earth’s temperature is to remain the same  The atmosphere contains greenhouse gases that absorb and reradiate the infrared radiation emitted by Earth  These gases include: o Water vapor (H2O) o Carbon dioxide (CO2) o Methane (CH4) o Nitrous oxide (N2O)  Without greenhouse gases, Earth’s climate would be about 33°C cooler Latitudinal Differences in Solar Radiation at Earth’s Surface  Amount of energy per square meter coming in at the equator is much higher than that of the amount of energy coming in at the poles  Solar radiation heats Earth’s surface, which emits infrared radiation to the atmosphere, warming the air above it  Warm air is less dense than cool air, and it rises—this is called uplift  Air pressure decreases with altitude, so the rising air expands and cools Differential Solar Heating of Earth’s Surface  Pockets of warm air rises up, causing it to expand and cool  Moisture can no longer be retained, thus producing rain  Tropical regions receive the most solar radiation and the most precipitation  Uplift of air in the tropics results in a low atmospheric pressure zone  When air masses reach the troposphere–stratosphere boundary, air flows towards the poles Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 Global Atmospheric Circulation Cells and Climatic Zones  Polar cells, Ferrell cells, and Hadley cells result in the three major climatic zones in each hemisphere – tropical, temperate, and polar zones  Areas of high and low pressure created by the circulation cells result in air movements called prevailing winds  The winds appear to be deflected due to the rotations of the Earth – the Coriolis effect  Water has a higher heat capacity than land – it can absorb and store more energy without changing temperature  Summer: air over oceans is cooler and denser, so air subsides and high pressures develop over the oceans  Winter: air over continents is cooler and denser; high pressure develops over continents  These are known as semi-permanent high and low pressure cells  Prevailing wind patterns in July: o Over land – low pressure systems o Over water – high pressure systems  Prevailing wind patterns in January: o Over water – low pressure systems o Over land – high pressure systems  Major ocean surface currents are driven by surface winds, so patterns are similar  Speed of ocean currents is about 2 – 3% of the wind speed  Ocean currents affect climate, the warm Gulf Stream warms the climate of Great Britain and Scandinavia  At the same latitude, Labrador is much cooler because of the cold Labrador Current  Where warm tropical surface currents reach polar areas, the water cools, ice forms, the water becomes more saline and more dense and sinks (downwelling)  Upwelling is where deep ocean water rises to the surface o Upwelling occurs where prevailing winds blow parallel to a coastline. Surface water flows away from the coast and deeper, colder ocean water rises up to replace it o Upwellings influence coastal climates o Upwellings bring nutrients from the deep sediments to the photic zone – where light penetrates and phytoplankton grow o This provides food for zooplankton and their consumers. These areas are the most productive in the open oceans  Coastal areas have a maritime climate: Little daily and seasonal variation in temperature, and high humidity  Areas in the center of large continents have continental climates: Much greater variation in daily and seasonal temperatures  Air temperatures over land show greater seasonal variation than those over the oceans  On mountain slopes, vegetation shifts reflect climate changes as temperature decreases, and precipitation and wind speed increase with elevation  When air masses meet mountain ranges, they are forced upwards, cooling and releasing precipitation  North–south trending mountain ranges create a rain shadow: The slope facing prevailing winds (windward) has high precipitation, while the leeward slope gets little precipitation  Vegetation can also influence climate  Albedo – capacity of a land surface to reflect solar radiation – is influenced by vegetation type, soils and topography  For example, a coniferous forest has a darker color and lower albedo than bare soil or a dormant grassland  Loss or change in vegetation can affect climate Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Deforestation increases albedo of the land surface: less absorption of solar radiation and less heating  Lower heat gain is offset by less cooling by evapotranspiration, due to loss of leaf area  Decreased evapotranspiration results in less moisture in the atmosphere and less precipitation  Deforestation in the tropics can lead to a warmer, dryer regional climate The Effects of Deforestation – Influence of Vegetation on Climate  Over time, deforestation occurs and energy balance of this system changes  More albedo is reflected back in deforested areas, and sensible heat loss is also higher in deforested areas  But in vegetated areas, evapotranspiration is higher in comparison to deforested areas – this is what causes more rainfall in vegetated areas Climatic Variation Over Time  Earth is tilted at an angle of 23.5° relative to the sun’s direct rays  The angle and intensity of the sun’s rays striking any point on Earth vary as Earth orbits the sun, resulting in seasonal variation in climate  In temperate-zone lakes, stratification changes with the seasons  In summer, the warm epilimnion lies over the colder hypolimnion. The thermocline is the zone of transition  Complete mixing (turnover) occurs in spring and fall when water temperature and density become uniform with depth  El Niño events, or the El Niño Southern Oscillation (ENSO), are longer-scale climate variations that occur every 3 to 8 years and last about 18 months o The positions of high- and low-pressure systems over equatorial Pacific switch, and the trade winds weaken o Upwelling of deep ocean water off the coast of South America ceases, resulting in much lower fish harvests  Earth is currently in a cool phase characterized by formation of glaciers (glacial maxima), followed by warm periods with glacial melting (interglacial periods)  These glacial–interglacial cycles occur at frequencies of about 100,000 years  We are currently in an interglacial period; these have lasted about 23,000 years in the past  The last glacial maximum was about 18,000 years ago  The glacial–interglacial cycles have been explained by regular changes in the shape of Earth’s orbit and the tilt of its axis— Milankovitch cycles  The intensity of solar radiation reaching Earth changes, resulting in climatic change  The shape of Earth’s orbit changes in 100,000-year cycles  The angle of axis tilt changes in cycles of about 41,000 years  Earth’s orientation relative to other celestial objects changes in cycles of about 22,000 years Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 3: THE BIOSPHERE  An overview of what the world is made of biologically  The biosphere is the zone of life on Earth  Biomes are large-scale biological communities shaped by the physical environment, particularly climate.  Biomes are categorized by dominant plant forms, not taxonomic relationships  Plants occupy sites for a long time and are good indicators of the physical environment, reflecting climatic conditions and disturbances o From an ecological standpoint, this means that plants need to be able to tolerate their surroundings no matter what as they cannot move  Terrestrial biomes are characterized by growth forms of the dominant plants, such as leaf deciduousness or succulence Plant Growth Forms  Plants have taken many forms in response to selection pressures such as aridity, extreme temperatures, intense solar radiation, grazing, and crowding  Similar growth forms can be found on different continents, even though the plants are not genetically related  Convergence: evolution of similar growth forms among distantly related species in response to similar selection pressures  Temperature has direct physiological effects on plant growth form  Precipitation and temperature act together to influence water availability and water loss by plants  Water availability and soil temperature determine the supply of nutrients in the soil Global Biome Distribution  Human activities influence the distribution of biomes  Land use change: conversion of land to agriculture, logging, resource extraction, urban development  The potential and actual distributions of biomes are markedly different  There are nine major terrestrial biomes  Climate diagrams show the characteristic seasonal patterns of temperature and precipitation at a representative location Tropical Rainforests  High biomass, high diversity – about 50% of Earth’s species  Light is a key factor – plants must grow very tall above their neighbors or adjust to low light levels  Emergents rise above the canopy Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Lianas (woody vines) and epiphytes use the trees for support  Understory trees grow in the shade of the canopy, and shrubs and forbs occupy the forest floor  Tropical rainforests are disappearing due to logging and conversion to pasture and croplands  About half of the tropical rainforest biome has been altered  Recovery of rainforests is uncertain: soils are nutrient-poor, and recovery of nutrient supplies may take a very long time Tropical Seasonal Forests and Savannas  Wet and dry seasons associated with movement of the ITCZ o Period of drought occurs  Shorter trees, deciduous in dry seasons, more grasses and shrubs  Fires promote establishment of savannas; some are set by humans  In Africa, large herbivores – wildebeests, zebras, elephants, and antelopes – also influence the balance of grass and trees o Can convert areas of forest to areas of savannas  On the Orinoco River floodplain, seasonal flooding promotes savannas  Less than half of seasonal tropical forests and savannas remain  Human population growth in this biome has had a major influence  Large tracts have been converted to cropland and pasture Hot Deserts  High temperatures, low moisture  Often in areas of subsidence, high pressure systems  Sparse vegetation and animal populations  Low water availability constrains plant abundance and influences form o Plants are always in a state of moisture stress  Many plants have succulent stems that store water  Convergence of this form is shown by cacti (Western Hemisphere) and euphorbs (Eastern Hemisphere)  Humans use deserts for agriculture and livestock grazing  Agriculture depends on irrigation, and results in soil salinization  Long-term droughts and unsustainable grazing can result in desertification – loss of plant cover and soil erosion Temperate Grasslands  Warm, moist summers and cold, dry winters  Grasses dominate; maintained by frequent fires and large herbivores such as bison  Grasses grow more roots than stems and leaves, to cope with dry conditions o Have deep root systems o This results in accumulation of organic matter and high soil fertility  Most fertile grasslands of central North America and Eurasia have been converted to agriculture because of the rich organic component to the soil  In arid grasslands, grazing by domesticated animals can exceed capacity for regrowth, leading to grassland degradation and desertification  Irrigation in some areas cause salinization Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 Temperate Shrublands and Woodlands  Reversal of growing season – summers are very dry, plant growing season starts in the fall, despite the cool weather, when precipitation increases  Evergreen leaves allow plants to be active during cooler, wetter periods  They also lower nutrient requirements—the plants don’t have to develop new leaves every year  Sclerophyllous leaves—tough and leathery—deter herbivores and prevent wilting.  After fires, shrubs sprout from underground storage organs, or produce seeds that sprout and grow quickly.  Without regular fires at 30–40-year intervals, shrublands may be replaced by forests Temperate Deciduous Forests  Deciduous leaves in response to extended periods of freezing  Need fertile soils and enough water to support tree growth  Fertile soils and climate make this biome good for agriculture. Very little old- growth temperate forest remains  As agriculture has shifted to the tropics, temperate forests have regrown  Shifts in species composition are due to nutrient depletion by agriculture and invasive species, causing damage such as chestnut blight Temperate Evergreen Forests  Includes temperate rainforests, but spans a wide range of environmental conditions  Commonly found on nutrient-poor soils  Evergreen trees are used for wood and paper pulp, and this biome has been logged extensively  Very little old-growth temperate evergreen forest remains  In some areas, trees have been replaced with non-native species in uniformly aged stands  Suppression of fires in western North America has increased the density of forest stands, which results in more intense fires when they do occur.  It also increases the spread of insect pests and pathogens.  Air pollution has damaged some temperate evergreen forests. Boreal Forests  Systems are often water saturated due to permafrost  Permafrost (soil that remains frozen year-round) prevents drainage and results in saturated soils  Long, severe winters  Trees are conifers – pines, spruces, larches  Cold, wet conditions in boreal soils limit decomposition, so soils have high organic matter.  In summer droughts, forest fires can be set by lightning, and can burn both trees and soil. In low-lying areas, extensive peat bogs form.  Boreal forests have not been as affected by human activities.  Logging, and oil and gas development, occur in some regions. Impacts will increase as energy demands increase. Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Climate warming may increase soil decomposition rates, releasing stored carbon and creating a positive feedback to warming. Tundra  Where growing season length and temperatures decrease, trees cease to be the dominant vegetation (the tree line marks the boreal to tundra transition)  Characterized by sedges, grasses, forbs and low growing shrubs  Human influence is increasing as exploration and development of energy resources increases  Arctic has experienced significant climate change, with warming almost double the global average  On mountains, temperature and precipitation change with elevation, resulting in zones similar to biomes  Smaller scale variations are associated with slope aspect, proximity to streams and prevailing winds Streams and Rivers  Plants are not as dominants in aquatic systems as they are on land  Most plants in aquatic systems such as algae are mobile, unlike land plants  Streams and rivers are lotic (flowing water) systems  Benthic organisms are bottom dwellers, and include many kinds of invertebrates  Some feed on detritus (dead organic matter), others are predators  Some live in the hyporheic zone—the substratum below and adjacent to the stream  Lakes and still waters (lentic) occur where depressions in the landscape fill with water  The littoral zone is near shore, where the photic zone reaches the bottom o Macrophytes occur in this zone  Pelagic zone: Open water; dominated by plankton (small and microscopic organisms suspended in the water)  Phytoplankton are photosynthetic, restricted to the upper layers through which light penetrates (photic zone)  Zooplankton are non-photosynthetic protists and tiny animals  Estuaries – where rivers flow into oceans  Salt marshes – shallow coastal wetlands dominated by grasses and rushes  Mangrove forests – mudflats dominated by salt-tolerant trees  Sandy shores, kelp forests, coral reefs, and rocky intertidal are among other near shore areas o Very diverse o Disproportionate amount of salt water work is done here by ecologists because they are accessible and they are homes to many species that are not mobile thus making it easier to study Marine Biological Zones  Pelagic zone – open ocean beyond the continental shelves  The photic zone, which supports the highest densities of organisms, extends to about 200 m depth  Below the photic zone, energy is supplied by falling detritus  Below the photic zone, temperatures drop and pressure increases  Crustaceans such as copepods graze on the rain of falling detritus from the photic zone  Crustaceans, cephalopods, and fishes are the predators of the deep sea Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 4: COPING WITH ENVIRONMENTAL VARIATION – TEMPERATURE AND WATER  The physical environment influences an organism’s ecological success in two ways: o Availability of energy and resources—impacts growth and reproduction. o Extreme conditions can exceed tolerance limits and impact survival.  Energy supply can influence an organism’s ability to tolerate environmental extremes.  The actual geographic distribution of a species is also related to other factors, such as disturbance and competition. Abundance across Environmental Gradients  Based on physiological tolerance of an organism, potential distribution tends to be highest at a moderate level  The actual distribution, however, is more constrained because of factors such as competition, environmental disturbances, or other biological factors Aspen Distribution  Because plants don’t move, they are good indicators of the physical environment  Aspen distribution can be predicted based on climate. Low temperatures and drought affect reproduction and survival  Predicted distribution based on known physiological knowledge  Actual distribution corresponds well with predicted distribution in the Northern range limit, but other factors play a role in the Southern range limit and these factors may explain the difference between predicted and actual distributions  A species’ climate envelope is the range of conditions over which it occurs Physiological Ecology  Physiological ecology is the study of interactions between organisms and the physical environments that influence their survival and persistence  Physiological processes have optimal conditions for functioning  Deviations from optimum reduce rate of the process  Stress—environmental change results in decreased rates of physiological processes, lowering the potential for survival, growth,  Acclimatization: Adjusting to stress through behavior or physiology  It is usually a short-term, reversible process  Acclimatization to high elevations involves higher breathing rates, greater production of red blood cells, and higher pulmonary blood pressure  Over time, natural selection can result in adaptation of a population to environmental stress  Individuals with traits that enable them to cope with stress are favored. Over time, these genetic traits become more frequent in the population or reproduction  Acclimatization and adaptation require investments of energy and resources, representing possible trade-offs with other functions that can also affect survival and reproduction  Ecotypes – populations with adaptations to unique environments Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Ecotypes can eventually become separate species as populations diverge and become reproductively isolated Temperature  Environmental temperatures vary greatly throughout the biosphere.  Survival and functioning of organisms is strongly tied to their internal temperature.  Some archaea and bacteria in hot springs can function at 90°C  Lower limits are determined by temperature at which water freezes in cells (–2 to –5°C)  40 – 50°C – optimum range for most organisms  Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal function. High temperature destroys enzymes function (denatured)  Bacteria in hot springs - enzymes stable to 100°C; Antarctic fish and crustaceans – enzymes function at – 2°C; soil microbes - active at temperatures as low as – 5°C.  Some species produce different forms of enzymes – isozymes – with different temperature optima that allow acclimatization to changing conditions  Temperature also affects the properties of cell membranes, which are composed of two layers of lipid molecules.  At low temperatures, these lipids can solidify, embedded proteins can’t function, and the cells leak metabolites.  Plants that thrive at low temperatures have higher proportions of unsaturated lipids (with double bonds) in their cell membranes o Double bonds create kinks which results in a very fluid-like membrane  Ectotherms – regulate body temperature through energy exchange with the external environment  Endotherms – rely primarily on internal heat generation – mostly birds and mammals o Can maintain internal temperatures near optimum for metabolic functions, can extend geographic range  Some other organisms that generate heat internally include bees, some fish, such as tuna, and even some plants o Skunk cabbage warms its flowers using metabolically generated heat in early spring  Ectotherm surface area-to-volume ratio of the body is an important factor in exchanging energy with the environment  Larger surface area allows greater heat exchange, but makes it harder to maintain internal temperature  Small aquatic ectotherms remain the same temperature as the water  Some large ectotherms can maintain higher body temperature: o Skipjack tuna use muscle activity and heat exchange between blood vessels to maintain a body temperature 14°C warmer than the surrounding seawater  Many terrestrial ectotherms can move around to adjust temperature  Many insects and reptiles bask in the sun to warm up after a cold night, but this increases predation risk, increasing benefits of camouflage  Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behavior includes seasonal migration to lower latitudes or to microsites that are above freezing (e.g., burrows in soil)  Tolerance to freezing involves minimizing damage associated with ice formation in cells. Some insects have high concentrations of glycerol, a chemical that lowers the freezing point of body fluids  Vertebrates generally do not tolerate freezing temperatures  Cryogenics is the preservation of bodies by freezing, in hope that they can be brought back to life in the future. Farfetched?  Two frog species live in the Arctic tundra and can survive winter in a semi-frozen state o Shallow burrows, with no heartbeat, no blood circulation, and no breathing  In most organisms, freezing results in tissue damage as ice crystals perforate cell membranes and organelles. In animals that withstand freezing, the freezing water is limited to the space outside the cells  Ice-nucleating proteins outside cells serve as sites of slow, controlled ice formation, in the right area where damage will not be caused. Additional solutes, such as glucose and glycerol are made inside the cells to lower the freezing point Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Endotherms can remain active at subfreezing temperatures  The cost of being endothermic is a high demand for energy (food) to support metabolic heat production  Metabolic rates are a function of the external temperature and rate of heat loss  Rate of heat loss is related to body size and surface area-to- volume ratio  Small endotherms with large surface area-to-volume ratio have higher metabolic rates, and require more energy and higher feeding rates than large endotherms  Thermoneutral zone – the range of environmental temperatures over which a constant basal metabolic rate can be maintained  Lower critical temperature – when heat loss is greater than metabolic production; body temperature drops and metabolic heat generation increases o More energy must be expended  Mammals in the Arctic have lower critical temperatures than mammals in tropical regions  The rate of metabolic activity increases more rapidly below the lower critical temperature in tropical mammals as compared to Arctic mammals  Evolution of endothermy required insulation – feathers, fur, and fat  Insulation limits conductive and convective heat loss  Fur and feathers provide a layer of still air adjacent to the skin. Some animals grow thicker fur for winter  Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little or no metabolic activity occurs  Small mammals have thin fur and not much for energy storage, but high demand for metabolic energy below the lower critical temperature  They survive in cold climates by entering a dormant state called torpor. Body temperature and basal metabolic rates are low, which conserves energy  Energy reserves are needed to come out of torpor. Small endotherms may undergo daily torpor to survive cold nights  Longer periods of torpor, or hibernation, are possible for animals that can store enough energy Heat Stress in Animals  Some organisms use behavioral changes to control exchange of energy with the environment  Examples: o Elephants swim and spray water onto their backs with their trunks to cool their bodies o Moving into the shade reduces the amount of solar radiation received  Evaporative heat loss in animals includes sweating in humans, panting in dogs and other animals, and licking of the body by some marsupials  Ectotherms in hot environments can gain too much heat from the environment and body temperature can reach lethal levels Water Stress  Arid conditions are a widespread challenge for organisms  Some tolerate dry conditions by going into suspended animation. Many microorganisms do this, as do some multicellular organisms Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Desiccation-tolerant organisms can lose 80 – 90% of their water – extreme physiological change  Reptiles are very successful in dry environments. They have thick skin with layers of dead cells, fatty coatings, and plates or scales  Mammals and birds have thick skin plus fur or feathers to minimize water loss  Sweat glands in mammals are a trade-off between water loss resistance and evaporative cooling  Organisms must be able to not only tolerate water loss, but effectively minimize water loss too Energy Exchange in Terrestrial Plants  Conduction – transfer of energy from warmer to cooler molecules  Convection – heat energy is carried by moving water or air  Plants can adjust energy inputs and outputs  Transpiration rates can be controlled by specialized guard cells surrounding leaf openings called stomates  If soil water is limited, transpirational cooling is not a good mechanism o Dry environments and evaporative water loss presents problems – other adaptations/acclimations are necessary  Some plants shed their leaves during dry seasons  Other mechanisms include pubescence – hairs on leaf surfaces that reflect solar energy. But hairs also reduce conductive heat loss  Pubescence was studied in three Encelia species (plants in the daisy family) o Desert species with high pubescence were compared with non-pubescent species from wetter, cooler habitats o Plants of all three species were grown in both locations (common gardens) o In the cool, moist location, the three species showed few differences in leaf temperature and stomatal opening o In the desert, species with no hairs maintained leaf temperature by transpiration; the pubescent species leaves reflected about twice as much solar radiation o The desert species (E. farinosa) also has smaller, more pubescent leaves in summer than in winter, representing acclimatization to hot summer temperatures  If air temperature is lower than leaf temperature, heat can be lost by convection  Convective heat loss is related to speed of air moving across a leaf surface  Boundary layer – a zone of turbulent flow due to friction, next to the leaf surface o Thick boundary layer = low convective heat  The boundary layer lowers convective heat loss  Boundary layer thickness is related to leaf size and surface roughness  Small, smooth leaves have thin boundary layers and lose more heat than large or rough leaves  In cold, windy environments, convection is the main heat loss mechanism  Most alpine plants hug the ground surface to avoid high wind velocities  Some have a layer of insulating hair to lower convective heat loss Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 5: COPING WITH ENVIRONMENTAL VARIATION: ENERGY  Autotrophs – assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis) o The energy is converted into chemical energy stored in the bonds of organic molecules  Heterotrophs – obtain their energy by consuming organic compounds from other organisms o This energy originated with organic compounds synthetized by autotrophs  Some heterotrophs consume non-living organic matter  Parasites and herbivores consume live hosts, but do not necessarily kill them  Predators capture and consume live prey animals  Some plants are holoparasites – they have no photosynthetic pigments and get energy from other plants (heterotrophs) o Dodder is a holoparasite that is an agricultural pest and can significantly reduce biomass in the host plant o Very extreme draw down in terms of energy from the host  Mistletoe is a hemiparasite – it is photosynthetic, but obtains nutrients, water, and some of its energy from the host plant  Sea slugs have functional chloroplasts that are taken up from the algae that the slug eats o Assimilates the chloroplast of algae into its own tissues allowing it to photosynthesize  Photosynthesis - (most autotrophs): sunlight provides the energy to take up CO 2 and synthesize organic compounds  Chemosynthesis (chemolithotrophy): energy from inorganic compounds is used to produce carbohydrates. o Chemosynthesis is important in nutrient cycling bacteria, and in some ecosystems such as hydrothermal vent communities  Most of the biologically available energy on Earth is derived from photosynthesis  Photosynthetic organisms include some archaea, bacteria, and protists, and most algae and plants Photosynthesis  Photosynthesis has two major steps: 1. Light reaction—light is harvested and used to split water and provide electrons to make ATP and NADPH 2. Dark reaction—CO2 is fixed in the Calvin cycle, and carbohydrates are synthesized  Photosynthetic rate determines the supply of energy, which in turn influences growth and reproduction  Environmental controls on photosynthetic rate are an important topic in physiological ecology  Light response curves show the influence of light levels on photosynthetic rate.  Light compensation point – where CO2 uptake is balanced by CO2 loss by respiration o Amount of light where respiratory cost of the plant is balanced out by photosynthesis – no net photosynthesis  Saturation point – when photosynthesis no longer increases as light increases  Plants can acclimatize to changing light intensities with shifts in light response curves  Shifts in light saturation point involve morphological and physiological changes  Leaves at high light intensity may have thicker leaves and more chloroplasts  Water availability influences CO2 supply in terrestrial plants  Low water availability causes stomates to close, restricting CO2 uptake  This is a trade-off: Water conservation versus energy gain  Closing stomates increases chance of light damage: If the Calvin cycle isn’t operating, energy accumulates in the light- harvesting arrays and can damage membranes.  Plants have various mechanisms to dissipate this energy, including carotenoids  Plants from different climate zones have enzyme forms with different optimal temperatures that allow them to operate in that climate  Plants can acclimatize by synthesizing different enzyme forms  Nutrients can also affect photosynthesis: Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Most nitrogen in plants is associated with rubisco and other photosynthetic enzymes o Thus, higher nitrogen levels in a leaf are correlated with higher photosynthetic rates  But nitrogen supply is low, relative to demand for growth and metabolism  Increasing nitrogen content of leaves increases the risk that herbivores will eat them, as plant-eating animals are also nitrogen-starved  Some metabolic processes decrease photosynthetic efficiency  Rubisco can catalyze two competing reactions: o Carboxylase reaction: photosynthesis o Oxygenase reaction: O2 is taken up, carbon compounds are broken down, and CO2 is released (photorespiration)  Uses energy, and causes loss of carbon compounds – not good from a plant’s perspective  Does photorespiration have any benefits? o Experiments with Arabidopsis thaliana plants with a mutation that knocks out photorespiration:  These plants die under normal light and CO2 conditions. o Hypothesis: Photorespiration may protect plants from damage at high light levels. o Altered tobacco plants with high rates of photorespiration showed less light damage than plants with normal or lowered photorespiration rates (Kozaki and Takeba 1996)  But photorespiration is not advantageous if CO 2 is low and temperatures high.  Such conditions existed 7 million years ago, when C4 photosynthesis first appeared.  The C4 photosynthetic pathway reduces photorespiration, and evolved independently several times  Many grass species use this pathway, including corn, sugarcane, and sorghum. It involves biochemical and morphological specialization.  CO2 uptake and the Calvin cycle occur in different parts of the leaf.  CO2 is taken up in the mesophyll by PEPcase, which has greater affinity for CO 2, and does not take up O2  CO2 concentration is increased in bundle sheath cells where rubisco is operating in the Calvin cycle, which reduces O 2 uptake by rubisco  More ATP is required for the C4 pathway, but higher photosynthetic efficiency gives these plants an advantage at high temperatures  Transpiration losses are minimized because PEPcase can take up CO2 even when stomates are not fully open  If photosynthetic rates determine ecological success, climatic patterns should predict regions where C4 plants will dominate  There is a close correlation between temperature and the proportion of C4 species in the community  Crassulacean acid metabolism (CAM) minimizes water loss  CO2 uptake and the Calvin cycle are separated temporally  CAM plants open their stomates at night when it’s cooler and humidity is higher, and close them during the day  Heterotrophs consume energy-rich organic compounds (food) and convert them into usable chemical energy (ATP).  The energy gain depends on the chemistry of the food, and how much effort is need to find and ingest the food  Soil microorganisms that feed on detritus invest little energy to find food, but the food has low energy content.  A cheetah hunting a gazelle invests a lot of energy to find, chase, and kill its prey, but it gets an energy-rich meal Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Feeding methods are accordingly very diverse among heterotrophs.  Multicellular animals have evolved specialized tissues and organs for absorption, digestion, transport, and excretion.  They have tremendous diversity in morphological and physiological feeding adaptations  Humans view tool-making as something that differentiates us from other animals  But tool-making in chimpanzees has been known since the 1920s  Jane Goodall observed chimps in the wild using plant stems to retrieve termites from a mound  Some birds also make tools o Crows on South Pacific islands use tools to snag insects from decomposing trees (Hunt 1996). o The crows make two different kinds of tools from plant materials.  Food availability can vary greatly over time and space  If energy is in short supply, animals should invest in obtaining the highest-quality food that is the shortest distance away  Optimal foraging theory – animals will maximize the amount of energy gained per unit time, energy, and risk involved in finding food  It assumes that evolution acts on the behavior of animals to maximize their energy gain.  Profitability of a food item (P) depends on how much energy (E) the animals gets from the food relative to the amount of time (t) it spends finding and obtaining the food: P = E / t  An animal’s success in acquiring food increases with the effort it invests; but at some point, more effort results in no more benefit, and the net energy obtained begins to decrease.  Test of the model: In a study of Parus major, proportions of prey types and encounter rates were varied. o The time it took birds to subdue and consume the prey (handling time) was measured. o The model correctly predicted consumption rates of large mealworms as profitability of prey items varied  A field study of Eurasian oystercatchers (Meire and Ervynck 1986) showed that the birds select prey items in a specific size range o Small bivalves don’t have enough energy to offset the energy needed to find and open them o Largest bivalves are too difficult to open  Northwestern crows (Corvus caurinus) pick up shellfish, then fly up and drop them on rocks to crack them open  Richardson and Verbeek (1986) estimated the size of clams that provide the most benefit, based on energy content, abundance of size classes, and handling time needed  Optimal foraging theory considers habitat to be heterogeneous—patches have different amounts of food  To optimize energy gain, an animal should remain in a patch with the highest food density, until it becomes equal to nearby patches  Marginal value theorem (Charnov 1976): an animal should stay in a patch until the rate of energy gain has declined to match the average rate for the whole habitat (giving up time). o Giving up time is also influenced by distance between patches  The longer the travel time between food patches, the longer an animal should spend in a patch  Cowie (1977) tested this in lab experiments with Parus major  A “forest” of wooden dowels contained food “patches” of plastic cups containing mealworms.  “Travel time” was manipulated by covering food cups, and adjusting ease of mealworm removal  Results matched predictions made by the theorem very well.  Munger (1984) tested the theorem in a natural setting, using horned lizards o The lizards eat ants that occur in patches of varying densities o The rate of ant consumption at the giving up time was compared with overall consumption rate o Again, results matched the predictions  Optimal foraging theory does not apply as well to animals that feed on mobile prey.  The assumption that energy is in short supply, and this dictates foraging behavior, may not always hold  Resources other than energy can be important, such as nitrogen or sodium content of the food Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 6: EVOLUTION AND ECOLOGY Trophy Hunting and Inadvertent Evolution: A Case Study  Bighorn sheep populations have been reduced by 90% by hunting, habitat loss, and introduction of cattle. Hunting is now restricted; permits for a large “trophy ram” cost over $100,000  Trophy hunting removes the largest and strongest males—the ones that would sire many healthy offspring.  In one population, 10% of males were removed by hunting each year, the average size of males and their horns decreased over 30 years of study.  This is also being observed in other species: o African elephants are poached for ivory; the proportion of the population that have tusks is decreasing. o Rock shrimp are all born male, and become females when they are large enough to carry eggs. Commercial harvesting takes the largest individuals, which are all females.  Genes for switching sex at a smaller size became more common, resulting in more females, but smaller females lay fewer eggs. What is Evolution?  Evolution can be viewed as genetic change over time or as a process of descent with modification  Biological evolution is change in organisms over time  Evolution can be defined more broadly as descent with modification.  As a population accumulates differences over time and a new species forms, it is different from its ancestors.  But the new species has many of the same characteristics as its ancestors, and resembles them  Populations change over time through natural selection: o Individuals with certain heritable traits survive and reproduce more successfully than other individuals. Mechanisms of Evolution  Natural selection, genetic drift, and gene flow can cause allele frequencies in a population to change over time  Phenotype: Observable characteristics that are determined by the genotype.  Individuals differ from one another in part because they have different alleles for genes  Different alleles arise by mutation: change in DNA  Mutations can result from copying errors during cell division, mechanical damage, exposure to chemicals (mutagens) or high-energy radiation  Formation of new alleles is critical to evolution o If mutation did not produce new alleles, all members of a population would have identical genotypes and evolution could not occur  Mutations are actually very rare o In a generation, one mutation would occur in every 10,000 to 1,000,000 copies of a gene o In one generation, mutation acting alone causes virtually no change in allele frequencies of a population o Mutations are not a strong source of genetic variation – more like a seed that introduces it, and other factors such as natural selection or gene flow, act upon it and increase genetic variation Types of Natural Selection  Directional selection: Individuals at one phenotypic extreme (e.g., large size) are favored o Example: Drought favored large beak size in medium ground finches  Stabilizing selection: Individuals with an intermediate phenotype are favored. o Example: Parasitic wasps select for small gall size of Eurosta flies; while birds select for large gall size  Disruptive selection: Individuals at both phenotypic extremes are favored. o Example: African seedcrackers (birds) have two food sources—hard seeds that large beaks are needed to crack, and smaller, softer seeds that smaller beaks are more suited to crack Genetic Drift  Genetic drift occurs when chance events determine which alleles are passed to the next generation o Only significant for small populations  Genetic drift has four effects on small populations: 1. It acts by chance alone, thus causing allele frequencies to fluctuate at random. Some may disappear, other may reach 100% frequency (fixation) 2. Because some alleles are lost, genetic variation of the population is reduced 3. Frequency of harmful alleles can increase, if the alleles have only mildly deleterious effects 4. Differences between populations can increase  Number 2 and 3 can have dire consequences o Loss of genetic variation reduces the ability of the population to respond to changing environmental conditions Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Increase of harmful alleles can reduce survival and reproduction o These effects are important for species that are near extinction  Greater prairie chicken populations in Illinois have been reduced by loss of habitat to farmland. o In 1993, population was less than 50. DNA from this population compared with museum specimens from the 1930s showed a decrease in genetic variation. o 50% of eggs failed to hatch, suggesting fixation of harmful alleles Gene Flow  Gene flow: Alleles move between populations via movement of individuals or gametes.  Gene flow has two effects: 1. Populations become more similar – alleles are shared, becomes more uniform 2. New alleles can be introduced into a population  In the 1960s, new alleles that provide resistance to insecticides arose by mutation in mosquitoes in Africa or Asia o Mosquitos with the new alleles were blown by winds or transported by humans to new locations o The allele frequency increases rapidly in populations exposed to insecticides o Resistance to insecticide – became a very high selection pressure Natural selection is the only evolutionary mechanism that consistently causes adaptive evolution  Adaptations are features of organisms that improve their ability to survive and reproduce  Natural selection is not a random process  By consistently favoring individuals with certain alleles, natural selection causes adaptive evolution – traits that confer advantages tend to increase in frequency over time  Example: Soapberry bugs feed on fruits by piercing them with a needle-like beak. o Feeding is most efficient if beak size matches fruit size o In populations with different food sources, Carroll and Boyd (1992) predicted that beak size would evolve to adapt to fruits of introduced tree species o Beak length is a heritable trait, so the observed changes must have been due to changes in allele frequencies. o The goldenrain tree was introduced to Florida about 35 years ago, so natural selection caused adaptive evolution in a relatively short time  There are many examples of rapid adaptive evolution: o Antibiotic resistance in bacteria. o Insecticide resistance in insects. o Drab coloration in guppies, which makes them harder for predators to see. o Increased beak size in Geospiza finches  Depending on the organisms involved, evolution can either occur over a long period or short period of time – depends on the relative life span of the organisms  Rapid adaptive evolution can happen on a continental scale  Clines – patterns of change in a characteristic over a geographic region  In Drosophila, the Adh allele of the alcohol dehydrogenase gene decreases in frequency as latitude increases S S o Adh is less effective in colder temperatures, so natural selection resulted in this cline with latitude S o In the past 20 years in Australia, the Adh cline has shifted about 4° latitude south, as mean temperature has increased 0.5°C o This shift indicates an adaptive change in allele frequency in response to climate change  Gene flow can limit adaptation to local conditions.  Adaptive evolution can occur in a population if the natural selection forces are strong enough to overcome gene flow o Example: Bentgrass populations o Bentgrass can grow in soils that are contaminated with heavy metals o At former mine sites, the tolerant genotypes were dominant, but also occurred in populations growing in normal soils o Bentgrass is wind-pollinated, so alleles are easily carried to other populations Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Plants at the mine site also received pollen (alleles) from the population on normal soils, but allele frequencies didn’t change—at the mine site there was very strong selection against plants without tolerance to heavy metals o Natural selection was strong enough to overcome the effects of ongoing gene flow  Natural selection does not result in a perfect match between organisms and their environments; environments are constantly changing, and there are constraints on evolution: o Lack of genetic variation  If there is no beneficial allele, adaptive evolution at that gene can not occur  Example: Initially, mosquito populations lacked alleles for pesticide resistance so the pesticides were effective  Advantageous alleles arise by chance, not “on demand.” o Evolutionary history  Natural selection works on traits that already exist  Organisms have certain characteristics and lack others because of their ancestry  Example: Dolphins evolved from terrestrial mammals; they have lungs and cannot “breathe” underwater o Ecological tradeoffs  The ability to perform one function may reduce the ability to perform another function  Adaptations represent compromises in the abilities of organisms to perform different and sometimes conflicting functions  Species: Groups of organisms whose members have similar characteristics and can interbreed.  Speciation: The process by which one species splits into two or more species. o Speciation most commonly occurs when a barrier prevents gene flow between two or more populations of a species. o Barriers can be geographic or ecological. The populations then diverge genetically over time.  The key step in speciation occurs when a population accumulates so many genetic differences that they cannot produce viable, fertile offspring if they mate with the parental species.  Reproductive barriers can arise as a by-product of natural selection.  Example: Experiments with two populations of fruit flies selected to grow on different food sources. o After 40 generations, most matings occurred between flies feeding on the same food source.  In some cases, a trait favored by selection is the same trait that drives speciation.  Example: Mosquitofish in pools with fish predators have evolved a body shape for high-speed escape swimming. o Female mosquitofish prefer to mate with males that have same body shape as they do o Natural selection favors different body shapes in mosquitofish, depending on the presence or absence of predators. o The different body shapes drive the early stages of speciation through their effects on mate choice  Genetic drift can also lead to evolution of reproductive barriers  But gene flow slows down or prevents speciation  Populations that exchange alleles tend to remain genetically similar, making evolution of reproductive barriers less likely  The rise of new species in one group can lead to increased diversity of other groups  Example: When apples were introduced into North America, some apple maggot fly populations switched to eating apples. These populations are probably forming a new species o Populations of parasitic wasps that feed on apple maggot flies have also diverged and become reproductively isolated from the parent species  Evolution can alter ecological interactions. If a predator evolves a new way to capture prey, prey species may go extinct, decline, migrate to other areas, or evolve new ways to cope with the more efficient predator.  About 200 million years ago, 70% of marine species were lost in the western Atlantic. o This event affected the behavior of predatory snails because their predators and competitors were reduced  In experiments on modern snails, edge drilling increased when densities of competitor species were increased Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Human actions can alter the course of evolution – habitat fragmentation leaves isolated patches which can affect evolutionary processes  Fragmentation leaves populations small and at a vulnerable state as they cannot adapt to environmental change easily LECTURE 7: LIFE HISTORY Introduction  An organism’s life history is a record of events relating to its growth, development, reproduction, and survival  Life history characteristics include: o Age and size at sexual maturity o Amount and timing of reproduction o Survival and mortality rates Nemo Grows Up: A Case Study  In real life, two to six clownfish spend their entire adult lives within one sea anemone, but are not usually related.  The largest fish is a female; the next largest is the breeding male. The remaining fish are immature non-breeders.  There is a strict pecking order in the group, based on body size.  If the female dies, the breeding male becomes a female, and the next largest fish becomes the breeding male.  Hatchlings move out of the anemone, and juveniles must find a new anemone to inhabit.  Why do clownfish maintain the hierarchy? o They are completely dependent on protection by the sea anemone. They are easy prey outside the anemone. o Conflicts result in expulsion and death, probably without having reproduced.  So there is a strong selection pressure to avoid conflict. Sea anemones are a scarce resource for clownfish.  Growth regulation mechanisms have evolved because individuals that avoid growing to a size that necessitates conflict are more likely to survive and reproduce Life History Diversity  Individuals within a species show variation in life history traits due to genetic variation or environmental conditions  The life history strategy of a species is the overall pattern in average timing and nature of life history events  “Decisions” made in a life history are dictated by natural selection  Some life history traits are determined genetically  Natural selection favors individuals whose life history traits result in their having a better chance of surviving and reproducing  Ideal or optimal life histories maximize fitness (genetic contribution to future generations)  But none are perfect; all organisms face constraints and ecological trade-offs  Phenotypic plasticity: One genotype may produce different phenotypes under different environmental conditions Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  For example, growth and development may be faster in higher temperatures  Changes in life history traits can cause change in adult morphology  Phenotypic plasticity may result in a continuous range of sizes; or discrete types called morphs  Polyphenism—a single genotype produces several distinct morphs  Spadefoot toad tadpoles have small omnivore morphs and larger carnivore morphs  Carnivore tadpoles grow faster and metamorphose earlier. They are favored in ephemeral ponds that dry up quickly – advantageous to get out of the pond as quick as possible  Omnivores grow more slowly and are favored in ponds that last longer; they metamorphose in more favorable conditions and have more chance of survival – tradeoff here is that although they grow slower, once they are mature, their chances of survival are higher in the end  Different body morphology results from different growth rates of body parts in both the Ponderosa pines and spadefoot toads  Allometry – different body parts grow at different rates, resulting in differences in shape or proportion – eventually determines body form/size Modes of Reproduction  Asexual reproduction – simple cell division (binary fission) – all prokaryotes and many protists  Some multicellular organisms reproduce both sexually and asexually (e.g., corals)  Benefits of sexual reproduction: recombination promotes genetic variation and increased ability to respond to environmental challenges  Disadvantages of sexual reproduction: an individual transmits only half of its genome to the next generation; population growth rate is slower  Isogamy – gametes are equal in size o e.g. the green alga Chlamydomonas reinhardii  Anisogamy – gametes of different sizes. Usually the egg is much larger and contains nutritional material. Most multicellular organisms produce anisogametes  Some species have direct development – the fertilized egg develops into a juvenile without passing through a larval stage  Most vertebrates have simple life cycles without abrupt transitions. But complex life cycles are common in insects, marine invertebrates, amphibians, and in some plants, algae, protists and fish  Complex life cycles have at least two stages, with different body forms and that live in different habitats  Metamorphosis – abrupt transition in form between the larval and juvenile stages Classification of Life History Strategies  Number of reproductive events per lifetime: o Semelparous species reproduce only once o Iteroparous species can reproduce multiple times  Semelparous species include: o Annual plants o Agave—vegetative growth can last up to 25 years (but also produces clones asexually)  Iteroparous species include: o Trees such as pines and spruces o Most large mammals  r-selection and K-selection describe two ends of a reproductive strategy continuum.  r is the intrinsic rate of increase of a population  r-selection: For high population growth rates; an advantage in newly disturbed habitats and uncrowded condition  r-selected (“live fast, die young”): o Short life spans, rapid development, early maturation, low parental investment, high reproduction rates o Most insects, small vertebrates such as mice, weedy plant species  K is the carrying capacity for a population  K-selection: For slower growth rates in populations that are at or near K; this is an advantage in crowded conditions; efficient reproduction is favored Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  K-selected (“slow and steady”): o Long-lived, develop slowly, late maturation, invest heavily in each offspring, low reproduction rates o Large mammals, reptiles such as tortoises and crocodiles, and long-lived plants such as oak and maple trees  One classification scheme for plant life histories is based on stress and disturbance (Grime 1977)  Stress – any abiotic factor that limits growth  Disturbance – any process that destroys plant biomass  Four habitat types possible: o Low stress, low disturbance o High stress, low disturbance o Low stress, high disturbance o High stress, high disturbance—not suitable for plant growth  Low stress/low disturbance: o Competitive plants with superior ability to acquire light, minerals, water, and space—have a selective advantage.  High stress/low disturbance: o Stress-tolerant plants with phenotypic plasticity, slow rates of water and nutrient use—not palatable to herbivores.  Low stress/high disturbance: o Ruderal plants with short life span, rapid growth rates, heavy investment in seed production. o Can exploit habitats after disturbance has removed competitors. o Seeds can survive a long time until conditions are right for rapid germination and growth  Grime’s Triangle – realistically, most species fall in the center of the triangle  Trade-offs – organisms allocate limited energy or resources to one function at the expense of another o Trade-offs between size and number of offspring:  The larger the investment in each individual offspring, the fewer offspring can be produced  Investments – energy, resources, and loss of time for other activities such as foraging  “Lack clutch size” – maximum number of offspring a parent can successfully raise to maturity o Named for David Lack (1947) who noticed that bird’s clutch size increases with latitude; longer daylight hours may allow parents more time to forage and feed more offspring o Experimental manipulation of clutch size in lesser black-backed gulls showed that in larger clutches, offspring have less chance of survival.  In species without parental care, resources are invested in propagules (eggs or seeds). Size of the propagule is a trade- off with the number produced.  The size-number trade-off can also occur within species o Experiments by Sinervo (1990) on lizard eggs showed that smaller eggs developed faster and produced smaller hatchlings, but small hatchlings were not able to sprint as fast to escape predators o Selection may favor early hatching in northern populations, because of shorter growing seasons. Faster sprinting speed may be favored in southern populations where there are more predators  Trade-offs between current and future reproduction: o For an iteroparous organism, the earlier it reproduces, the more times it can reproduce over its lifetime o But the number of offspring produced often increases with size and age of the organism  Atlantic cod females produce more eggs, as they grow larger. Commercial fishing removes older, larger fish, favoring fish that reproduce earlier at smaller sizes (evolutionary change).  It may be advantageous to delay reproduction and invest more energy in growth and survival in order to increase lifetime reproductive output o Example: a fish with a 5-year lifespan can increase its total reproductive output by delaying maturation by one year o Either of these strategies can work, depending on the environments surrounding the organism  If adult survival rates are low, future reproduction may never occur, so early reproduction rather than growth would be favored.  If adult survival rates are high with long life spans, or fecundity increases with body size, it makes sense to allocate energy to growth rather than reproduction. Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Senescence – decline in physiological function with age  Onset can set an upper age limit for reproduction  Semelparous species undergo very rapid senescence and death following reproduction  In some large social mammals, such as humans and elephants, senescence is long  But, post-reproductive individuals contribute to the group’s welfare by parental and grandparental care and other ways  Senescence may occur earlier in populations with high mortality rates or predation.  In guppy populations with high mortality rates, they may be investing less energy in immune system development, resulting in higher rates of senescence due to disease.  As selection pressures change, different morphologies and behaviors are adaptive at different life cycle stages  Small early life stages can be vulnerable to predation and competition for food  But small size can allow early stages to do things that adult stages can’t  Organisms have various mechanisms to protect the small life stages  Parental investment: o Provisioning eggs or embryos – yolk and protective coverings for eggs, nutrient-rich endosperm in plant seeds o Parental care – invest time and energy to feed and protect offspring Dispersal and Dormancy  Small offspring are well-suited for dispersal  Dispersal can reduce competition among close relatives, allow colonization of new areas, and allow escape from areas with diseases or high predation  Sessile organisms such as plants, fungi, and marine invertebrates disperse as pollen, seeds, spores, gametes or larvae  Dormancy – state of suspended growth and development in which an organism can survive unfavorable conditions  Small seeds, spores, eggs and embryos are best suited to dormancy – less metabolic energy is needed to stay alive. But some larger animals also enter dormancy.  Complex life cycles may result from stage-specific selection pressures, and minimize drawbacks of small, vulnerable stages.  Even in species with gradual morphological change, individuals may have different ecological roles depending on size and age – niche shift  The ecological niche is the physical and biological conditions that an organism needs to grow, survive and reproduce  In the Nassau grouper, small juvenile fish hide in algae clumps; larger ones stay in rocky habitats. o Dahlgren and Eggleston (2000) found that smaller juveniles are very vulnerable to predators in the rocky habitats, but larger ones were not. o Niche shift was timed to maximize growth and survival.  If the larval habitat is very favorable, metamorphosis may be delayed or eliminated.  Some salamanders mature sexually while retaining larval morphology and habitat – this is known as being paedomorphic  Mole salamander have both aquatic paedomorphic adults and terrestrial metamorphic adults in the same population  Sequential hermaphroditism – change in sex during the course of the life cycle  Timing should take advantage of high reproductive potential of different sexes at different sizes LECTURE 8: POPULATION DISTRIBUTION AND ABUNDANCE  Population – group of interacting individuals of the same species living in a particular area  Interactions within populations include sexual reproduction and competition o Influence each other  Populations are dynamic – distribution and abundance can change over time and space. Understanding the factors that influence these dynamics help us manage populations for harvest or conservation  Distribution – geographic area where individuals of a species occur  Abundance – number of individuals in a given area o Abundance can be reported as a population size (# of individuals), or density (# of individuals per unit area) o Example: On a 20-hectare island there are 2,500 lizards.  Population density = 125/hectare  Sometimes the total area occupied by a population is not known.  It is often difficult to know how far organisms or their gametes can travel.  When the area is not fully known, an area is delimited based on best available knowledge of the species.  Species vary in their ability to disperse o In plants, dispersal occurs by seed movement. The distance moved can be very small o Other species, such as whales, can move thousands of kilometers in a year Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Some populations exist in isolated patches that are linked by dispersal  This can result from physical features of the environment, or human activities that subdivide populations o Example: Heathlands in England have been fragmented by human development  For some species, it’s hard to determine what an individual is o We see this a lot in plants, but it can be seen in animals  Individuals can be defined as products of a single fertilization: The aspen grove would be a single genetic individual, or genet  If members of a genet are independent physiologically, each member is called a ramet o A ramet is a “subset” of a genet Distribution and Abundance  The distributions and abundances of organisms are limited by habitat suitability, historical factors, and dispersal  Habitat suitability o Abiotic features: moisture, temperature, pH, sunlight, nutrients, etc.  Availability limits the distribution of some species o Some species can tolerate broad ranges of physical conditions, others have narrow ranges o Creosote bush is very tolerant of dry conditions and occurs widely in North American deserts. o Saguaro cactus can tolerate dry conditions, but not cold temperatures and has a more limited distribution o Biotic features: organisms are affected by herbivores, predators, competitors, parasites, and pathogens o In Australia, an introduced cactus became a pest species, spreading over vast areas. o A moth that feeds on cactus was then released, and distribution and abundance of the cactus has been greatly reduced  Abiotic and biotic features can interact to determine distribution and abundance  The range of the barnacle Semibalanus balanoides is restricted by temperature. But competition from other species precludes it from some areas with suitable temperatures.  Some species distributions depend on disturbance—events that kill or damage some individuals, creating opportunities for other individuals to grow and reproduce. o Example: Some species persist only where there are periodic fires  Seeds that are designed to respond to fires, fire-dependent in order to avoid competition with other species  Historical factors o Evolutionary history and geologic events affect modern distribution of species o Example: Polar bears evolved from brown bears in the Arctic. They are not found in Antarctica because of an inability to disperse through tropical regions. o Continental drift explains the distributions of some species. o Wallace (1860) observed very different animal species on the Philippines and New Guinea, even though they are close together  Were not historically close together, separated by expansive body of water  Dispersal o Dispersal limitation can prevent species from reaching areas of suitable habitat. o Example: The Hawaiian Islands have only one native mammal, the hoary bat, which was able to fly there o Dispersal limitation has also been shown in plant species o Dispersal can also affect population density, and vice versa o Many species of aphids produce winged forms (capable of dispersing) in response to crowding  As crowding increases, the number of winged form aphids increases as well o Desert pupfish live in pools that are sometimes connected after heavy rains o Dispersal may result in better chances for survival and reproduction than staying in crowded pools with limited food Geographic Range  Geographic range—the entire geographic region over which a species is found  Many species have a patchy distribution of populations across their geographic range  There is also great variation in species ranges: Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 o Many tropical plants have small ranges. In 1978, 90 new species were discovered, restricted to a single mountain ridge in Ecuador. o Other species, such as they coyote, have very large geographic ranges o Some species are found on several continents o Few species are found on all continents except humans, Norway rats, and the bacterium E. coli  Geographic range includes areas occupied during all life stages  Some species, such as monarch butterflies, migrate long distances between summer and winter habitats  For some species, it is difficult to find all the life stages and the ranges they inhabit  Not all habitats within a range are suitable, resulting in patchy distributions  This can operate at different spatial scales  At large scales, climate may dictate locations of populations. At small scales, soils, topography, other species, etc., can determine patchiness  Patchiness at different scales is illustrated by the shrub Clematis fremontii o It is restricted to areas of dry, rocky soil with few trees, called barrens or glades o The glades occur on outcrops of limestone on south- or west-facing slopes  Abundance can vary throughout a species’ range o Density of red kangaroos varies throughout their range in Australia, including areas of high density, and areas where they are absent  For some species population density is greatest in the center of the range and it decreases as you move to the peripheries of the range o This occurs in many North American species, including indigo buntings and other animals and plants Dispersion  Dispersion – spatial arrangement of individuals within a population  The dispersion of individuals within a population depends on the location of essential resources, competition, dispersal and behavioral interactions  Regular – individuals are evenly spaced  Random – individuals scattered randomly  Clumped – the most common pattern  Dispersion patterns often result from the distribution of resources.  Random or clumped dispersion can also result from short dispersal distances.  Competition appears to result in the regular dispersion of some species.  Interactions can also influence dispersion: individuals may repel or attract others  Seychelles warblers are territorial, which results in regular dispersion  But some territories provide better resources than others  In high quality territories, cooperative breeding occurs—young birds postpone breeding and instead help their parents raise more offspring  The high quality sites attract more birds and can result in clumped dispersions o If there are no more territories available, genetic information is being passed on to the generation through cooperative breeding, increasing breeding success  Cooperative breeding is advantageous when high-quality territories are scarce  A young bird will survive and produce more offspring over its lifetime if it stays to help the parents, and delays breeding.  If high-quality territories are abundant, cooperative breeding is not favored. Estimating Abundances and Distributions  Population abundances and distributions can be estimated with area-based counts, distance methods, mark-recapture studies, and niche modeling  Complete counts of individual organisms in a population are often difficult or impossible  Several methods are used to estimate the actual abundance or absolute population size  Relative population size: Number of individuals in one time period or place relative to the number in another  Estimates are based on data presumed to be related to absolute population size o Example: Number of cougar tracks in a given area, or number of fish caught per unit of effort Downloaded by Ella ([email protected])  lOMoARcPSD|38714865  Interpretation of relative population size can be tricky o Example: Number of cougar tracks is related to population density, but also activity levels of individuals  Area-based counts – used most often to estimate abundance of immobile organisms  2 Quadrats – sampling areas of specific size, such as 1 m. o Individuals are counted in several quadrats; the counts are averaged to estimate population size  Distance methods – distances of individuals from a line or point are converted into estimates of abundance  Line transects – observer travels along line and counts individuals and their distance from the line  Mark-recapture studies – used for mobile organisms o A subset of individuals is captured and marked or tagged, then released o At a later date, individuals are captured again, and the ratio of marked to unmarked individuals is used to estimate population size  Long-term data sets can help solve applied problems: o Outbreak of a new disease in 1993 in New Mexico was caused by a new strain of hantavirus, carried by the deer mouse. o Deer mouse specimens indicated the virus had been present for 10 years. Why was there an outbreak? o Deer mouse populations had been studied at Sevilleta National Wildlife Refuge since 1989 o Densities of several species had increased between 1992 and 1993. High rainfall had led to more plant growth, providing more food for rodents. o High mouse densities increase the chances of contact with humans, thus resulting in an outbreak that year  The geographic ranges of many species are not well known  Ecologists often wish to predict the future distribution of a species o Pests or disease carriers o Changing distributions as a result of global warming  Niche modeling – o Ecological niche – physical and biological conditions that a species needs to grow, survive, and reproduce o A niche model predicts a species’ distribution based on conditions at locations the species is known to occupy o Niche model for chameleons in Madagascar: 2  Environmental data were recorded for 1x1 km “grid cells.”  “Habitat rules” for each species described environmental conditions where it was most likely to be found o A computer program (GARP) compared grid cell data with habitat rules for each species  Prediction of species occurrences were correct 75-85% of the time o In areas where predictions were not correct, researchers found seven previously unknown chameleon species Downloaded by Ella ([email protected])  lOMoARcPSD|38714865 LECTURE 9: POPULATION GROWTH AND REGULATION Human Population Growth: A Case Study  Humans have a large impact on the global environment: our population has grown explosively