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Lecture 21 INTRODUCTION TO ECOLOGY Overview: Discovering Ecology • Ecology is the scientific study of the interactions between organisms and the environment – what environmental factors limit the geographic distribution of an organism? – what factors can affect the size of its population? • interactions of an organism with its environment (e.g. other organisms, food supply, pathogens) determine the distribution of organisms and their abundance Global ecology Landscape ecology Ecosystem ecology The Scope of Ecological Research • ecologists work at levels ranging from individual organisms to the planet Community ecology Population ecology Organismal ecology Global Ecology • The biosphere is the global ecosystem – the sum of all the planet’s ecosystems and landscapes • Global ecology examines the influence of how the regional exchange of energy and materials influences the function and distribution of organisms across the biosphere Global ecology Landscape Ecology • A landscape or seascape is a mosaic of connected ecosystems • Landscape ecology focuses on the factors controlling the exchanges of energy, materials, and organisms across multiple ecosystems Landscape ecology Ecosystem Ecology • An ecosystem is the community of organisms in an area and the physical factors with which they interact • Ecosystem ecology emphasizes energy flow and chemical cycling between organisms and the environment Ecosystem ecology Community Ecology • A community is a group of populations of different species in an area • Community ecology examines how interactions between species affect community structure and organization – e.g. predation, competition Community ecology Population Ecology • A population is a group of individuals of the same species living in an area • Population ecology analyzes factors that affect population size and how and why it changes with time Population ecology Organismal Ecology • Organismal ecology studies how an organism’s structure, physiology, and behavior meet environmental challenges • Organismal ecology includes physiological, evolutionary, and behavioral ecology Organismal ecology Earth’s climate varies by latitude and season and is changing rapidly • the most significant influence on the distribution of organisms on land and in the water is climate • climate = the long-term prevailing weather conditions in an area • four major physical components of climate are temperature, precipitation, sunlight, and wind • climate can be described on two scales – Macroclimate consists of patterns on the global, regional, and landscape level – Microclimate consists of very fine patterns, • such as those encountered by the community of organisms underneath a fallen log Global Climate Patterns • determined largely by solar energy and the planet’s movement in space • The warming effect of the sun causes temperature variations – variations in temperature drive evaporation and the circulation of air and water – causes latitudinal variations in climate Latitudinal Variation in Sunlight Intensity • Earth’s curved shape causes latitudinal variation in the intensity of sunlight – due to the angle • the angle at which sunlight hits Earth affects its intensity – intensity determines the amount of heat and light per unit of surface area • The intensity of sunlight is strongest in the tropics (between 23.5 north latitude and 23.5 south latitude) Atmosphere Low angle of incoming sunlight 90°N (North Pole) 60°N 30°N 23.5°N (Tropic of Cancer Sun overhead at equinoxes 0° (Equator) 23.5°S (Tropic of Capricorn) 30°S Low angle of incoming sunlight 60°S 90°S (South Pole) Latitudinal variation in sunlight intensity Global Air Circulation and Precipitation Patterns • • • • • • • solar radiation near the equator sets up a global pattern of air circulation and precipitation high temperature in the tropics: water evaporates and warm, wet air masses flow toward the poles rising air masses release water and causes high precipitation, especially in the tropics release of water dries the air – air begins to descend dry, descending air masses create arid climates - near 30 degrees north and south flows back toward the poles – picking up moisture as the air reaches 60 degrees in latitude – air mass rises again and the cycle repeats 66.5°N (Arctic Circle) 60°N 30°N Westerlies 30°N Northeast trades 0° Southeast trades 30°S Westerlies 60°S 66.5°S (Antarctic Circle) Global air circulation and precipitation patterns 0° Descending dry air absorbs moisture. Ascending moist air releases moisture. Global Air Circulation and Precipitation Patterns • • • • • air flowing close to Earth’s surface creates predictable global wind patterns as the Earth rotates – land near the equator moves faster than at the poles this deflects the wind from their vertical pattern – creates westerly and easterly flowing wind patterns cooling trade winds blow from east to west in the tropics prevailing westerlies blow from west to east in the temperate zones 66.5°N (Arctic Circle) 60°N 30°N 30°N Westerlies Northeast trades Ascending moist air releases moisture. 0° Southeast trades 30°S Westerlies 60°S 66.5°S (Antarctic Circle) circulation and precipitation patterns © 2011Global Pearson air Education, Inc. Descending dry air absorbs moisture. 0° Regional and Local Effects on Climate • Climate is affected by: seasonality, large bodies of water, and mountains © 2011 Pearson Education, Inc. Seasonality • Seasonal variations of light and temperature increase steadily toward the poles – Seasonality seen from the middle to high latitudes – is caused by the tilt of Earth’s axis of rotation and its annual passage around the sun – as a result, belts of wet and dry air straddling the equator shift throughout the year with the changing angle of the sun – also changing wind patterns affect ocean currents March equinox December solstice 60°N 30°N 0° (equator) 30°S Constant tilt of 23.5° June solstice September equinox Bodies of Water • Oceans currents, and large lakes moderate the climate of nearby terrestrial environments – by heating and cooling overlying air masses that pass across the land • coastal areas are generally wetter than inland areas at the same latitude – the cool climate produced by the California current flowing southward supports the coniferous and redwood forest of the Pacific coast Labrador Current California Current 30°N North Pacific Subtropical Gyre Gulf Stream North Atlantic Subtropical Gyre Equator Indian Ocean Subtropical Gyre Antarctic Circumpolar Current 30°S South Pacific Subtropical Gyre South Atlantic Subtropical Gyre • oceans and large lakes tend to moderate the climate of nearby land • during a hot day, air over the land heats up and rises draws a cool breeze from the water across the land • as the land cools at night, air over the warmer water rises and draws cooler air from land back over the water, which is replaced by warm air from offshore Leeward side of mountains Air flow Mountain range Ocean Mountains • when moist air approaches a mountain – air rises and cools and releases its moisture on the windward side of a peak • this creates a “rain shadow” as it absorbs moisture on the leeward side • the leeward rain shadow determines where many deserts are found • mountains can also affect the amount of sunlight and temperature in an area • in the Northern Hemisphere, south-facing slopes receive more sunlight than north-facing slopes • every 1,000 m increase in elevation produces a temperature drop of approximately 6C Leeward side of mountains Air flow Mountain range Ocean © 2011 Pearson Education, Inc. Microclimate • in addition to regional and local effects on climate – have microclimates • a microclimate is determined by fine-scale differences in the environment that affect light and wind patterns • every environment is characterized by smallscale differences in: – Abiotic (non-living) factors - temperature, light, water, and nutrients – Biotic (living) factors - organisms that are part of an individual’s environment Global Climate Change • changes in Earth’s climate can profoundly affect the biosphere – by changing the distribution of plants and animals • one way to predict the possible effects of future global climate change is to study previous changes – since the last ice age • as glaciers retreated 16,000 years ago and the climate warmed tree distribution patterns expanded northward – seen as a fossilized pollen record • the current climatic limits of current distributions of organisms can be used to predict how these distributions might change in the future – e.g. models predict the American beech may move 700-900 km further north with warming and will shift even further south Current range Predicted range Overlap (a) 4.5°C warming over next century (b) 6.5°C warming over next century Biome structure and distribution are controlled by climate and disturbance • Biomes = major life zones characterized by vegetation type (terrestrial biomes) or physical environment (aquatic biomes) • Climate is very important in determining why terrestrial biomes are found in certain areas © 2011 Pearson Education, Inc. Climate and Terrestrial Biomes • terrestrial biomes show strong latitudinal patterns • one way to highlight the important of climate on a terrestrial biome – to create a climograph 30°N Tropic of Cancer Equator Tropic of Capricorn 30°S Tropical forest Savanna Desert Chaparral Temperate grassland Temperate broadleaf forest Northern coniferous forest Tundra High mountains Polar ice • climograph – a plot of the annual average temperature and precipitation in a region • biomes are affected not just by average temperature and precipitation, but also by the pattern of temperature and precipitation through the year – e.g. wet and dry seasons in addition to rainfall amounts Annual mean temperature (°C) Desert Temperate grassland Tropical forest 30 Temperate broadleaf forest 15 Northern coniferous forest 0 Arctic and alpine tundra 15 0 100 200 300 Annual mean precipitation (cm) 400 General Features of Terrestrial Biomes • most terrestrial biomes are named for major physical or climatic factors and for their predominant vegetation – e.g. temperate grasslands in the middle latitudes – moderate climates, dominated by various grass specific • each biome is also characterized by specific microorganisms, fungi and animals that have adapted to its environment • terrestrial biomes usually grade into each other, without sharp boundaries • where biomes overlap – area of intergradation or an ecotone – may be wide or narrow • Vertical layering is an important feature of terrestrial biomes • in a forest, it might consist of an upper canopy, lowtree layer, shrub understory, ground layer of herbaceous plants, the forest floor, and root layer • non-forest biomes also have layers – not as pronounced – grasslands – grass layer, a litter layer and a root layer • layering of vegetation in the biomes provides diverse habitats for animals Disturbance and Terrestrial Biomes • biomes are dynamic and usually exhibit extensive patchiness due to disturbances • disturbance is an event such as a storm, fire, or human activity that changes a community • even the dominant plants in a biome need disturbances from time to time – frequent fires can kill woody plants and keep a savanna from becoming a woodland that the environment would support – fires and outbreaks of pests create gaps in forests that allow different species to grow – fire are rare across the Great Plains due to the change into agricultural fields Terrestrial Biomes • Terrestrial biomes can be characterized by: – – – – distribution precipitation temperature plants & animals © 2011 Pearson Education, Inc. Tropical Forest • distribution: equatorial and subequatorial regions • precipitation: tropical rain forests, rainfall is relatively constant, while in tropical dry forests precipitation is highly seasonal • temperature: high year-round with little seasonal variation • plants: vertically layered, and competition for light is intense • animals: home to millions of animal species, including an estimated 5–30 million still undescribed species of insects, spiders, and other arthropods A tropical rain forest in Borneo Desert • distribution: occur in bands near 30 north and south of the equator, and in the interior of continents • precipitation: is low and highly variable, generally less than 30 cm per year • temperature: hot or cold • plants: adapted for heat and desiccation tolerance, water storage, and reduced leaf surface area • animals: include many kinds of snakes and lizards, scorpions, ants, beetles, migratory and resident birds, and seed-eating rodents; many are nocturnal A desert in the southwestern United States Savanna • distribution: equatorial and subequatorial regions • precipitation: seasonal rainfall with a long dry season • temperature: warm year round – averages (24–29C) - more seasonally variable than in the tropics • plants: grasses and forbs (broad-leaf plants) make up most of the ground cover – The dominant plant species are fire-adapted and tolerant of seasonal drought • animals: include insects and mammals such as wildebeests, zebras, lions, and hyenas • Fires set by humans may help maintain this biome A savanna in Kenya Chaparral • Distribution: mid-latitude coastal regions on several continents • Precipitation: is highly seasonal with rainy winters and dry summers • Temperature: summer is hot (30C+); fall, winter, and spring are cool (10–12C) • Plants: dominated by shrubs, small trees, grasses, and herbs – many plants are adapted to fire and drought • Animals: include amphibians, birds and other reptiles, insects, small mammals, and browsing mammals • Humans have reduced chaparral areas through agriculture and urbanization An area of chaparral in California Temperate Grassland • Distribution: on many continents – e.g. plains and prairies of North America • Precipitation: highly seasonal • temperature: seasonal - winters are cold and dry; summers are hot and wet • plants: grasses and forbs – are adapted to droughts and fire • animals: include large grazers such as bison and wild horses and small burrowers such as prairie dogs • Most grasslands have been converted to farmland Grasslands National Park, Northern Coniferous Forest • distribution: northern North America and Eurasia and is the largest terrestrial biome on Earth • Precipitation: varies – some have periodic droughts and others, especially near coasts, are wet • temperature: winters are cold; summers may be hot (e.g., Siberia ranges from –50C to 20C) • plants: conifers such as pine, spruce, fir, and hemlock dominate – the conical shape of conifers prevents too much snow from accumulating and breaking their branches • animals: include migratory and resident birds and large mammals such as moose, brown bears, and Siberian tigers • Some forests are being logged at an alarming rate A forest in Norway Temperate Broadleaf Forest • distribution: mid-latitudes in the Northern Hemisphere – smaller areas in Chile, South Africa, Australia, and New Zealand • precipitation: significant amounts of fall during all seasons as rain or snow • Temperature: winters average 0C; summers are hot and humid • plants: vertical layers – dominated by deciduous trees in the Northern Hemisphere and evergreen eucalyptus in Australia • animals: Mammals, birds, and insects make use of all vertical layers in the forest – in the Northern Hemisphere, many mammals hibernate in the winter • These forests have been heavily settled on all continents but are recovering in places Great Smoky Mountains National Park in North Carolina, in autumn Tundra • distribution: expansive areas of the Arctic – alpine tundra also exists on high mountaintops at all latitudes • Precipitation: is low in arctic tundra and higher in alpine tundra • Permafrost, a permanently frozen layer of soil, prevents water infiltration • Temperature: winters are cold (below –30C); summers are relatively cool (less than 10C) • plants: herbaceous (mosses, grasses, forbs, dwarf shrubs and trees, and lichen) and supports birds, grazers, and their predators • animals: musk oxen, caribou, reindeer, bears, wolves, and foxes; many migratory bird species nest in the summer • Settlement is sparse, but tundra has become the focus of oil and mineral extraction Denali National Park, Alaska, in autumn Aquatic biomes • Aquatic biomes account for the largest part of the biosphere in terms of area • show less latitudinal variation than terrestrial biomes • marine biomes have salt concentrations of about 3% – the largest marine biome is made of oceans, which cover about 75% of Earth’s surface and have an enormous impact on the biosphere • freshwater biomes have salt concentrations of less than 0.1% – freshwater biomes are closely linked to soils and the biotic components of the surrounding terrestrial biome Zonation in Aquatic Biomes • Many aquatic biomes are stratified into zones or layers - defined by light penetration, temperature, and depth • upper photic zone has sufficient light for photosynthesis (b) Marine zonation Intertidal zone Neritic zone Oceanic zone • lower aphotic zone receives little light – Deep in the aphotic zone lies the abyssal zone with a depth of 2,000 to 6,000 m • The photic and aphotic zones make up the pelagic zone • • 0 200 m Continental shelf Pelagic zone The organic and inorganic sediment at the bottom of all aquatic zones is called the benthic zone Detritus, dead organic matter, falls from the productive surface water and is an important source of food to animals in the lower zones Photic zone Benthic zone Aphotic zone 2,000 6,000 m Abyssal zone (b) Marine zonation Intertidal zone Neritic zone 0 200 m (a) Zonation in a lake Littoral zone Limnetic zone Continental shelf Oceanic zone Photic zone Pelagic zone Photic zone Benthic zone Benthic zone Pelagic zone Aphotic zone Aphotic zone 2,000 6,000 m Abyssal zone -lake environment is classified on the basis of three criteria: light penetration (i.e. photic and aphotic), distance from shore (littoral and limnetic) and open water (pelagic) or the bottom (benthic). -the marine environment is classified the same way but distance from shore is intertidal, neretic/coastal and oceanic -also there is an abyssal zone in addition to the benthic zone • In oceans and most lakes, a temperature boundary called the thermocline separates the warm upper layer from the cold deeper water • Many lakes undergo a semiannual mixing of their waters called turnover • Turnover mixes oxygenated water from the surface with nutrient-rich water from the bottom Winter Spring Summer 0° 2° 4°C 4° 4° 22° 18° 8° 4°C 4°C Thermocline © 2011 Pearson Education, Inc. Autumn 4°C • Communities in aquatic biomes vary with depth, light penetration, distance from shore, and position in the pelagic or benthic zone • Most organisms occur in the relatively shallow photic zone • The aphotic zone in oceans is extensive but harbors little life 30°N Tropic of Cancer Equator Tropic of Capricorn 30°S Oceanic pelagic and benthic zones Intertidal zones Estuaries Coral reefs Rivers Lakes Aquatic Biomes • Major aquatic biomes can be characterized by their: – physical environment – chemical environment – geological features – photosynthetic organisms – heterotrophs © 2011 Pearson Education, Inc. Lakes • size can vary from small ponds to very large lakes • temperate lakes may have a seasonal thermocline • tropical lowland lakes have a year-round thermocline • littoral zone had rooted and floating aquatic plants – littoral zone is shallow and well-lighted and close to shore – good for rooted plants • limnetic zone has small drifting animals called zooplankton – water is too deep in the limnetic zone to support rooted aquatic plants – zooplankton are drifting heterotrophs that graze on the phytoplankton in the limnetic zone • invertebrates live in the benthic zone • fishes live in all zones with sufficient oxygen Lakes • two kinds: – Oligotrophic – Eutrophic • Oligotrophic lakes: nutrient-poor and generally oxygen-rich An oligotrophic lake in Grand Teton National Park, Wyoming Lakes • Eutrophic lakes: nutrientrich • are often depleted of oxygen if ice covered in winter • have more surface area relative to depth than oligotrophic lakes A eutrophic lake in the Okavango Delta, Botswana Wetlands • among the most productive biomes on Earth • wetland = a habitat inundated by water at least some of the time – supports plants adapted to water-saturated soil • high organic production and decomposition and have low dissolved oxygen • can develop in shallow basins, along flooded river banks, or on the coasts of large lakes and seas •Plants: water lilies, cattails, sedges, tamarack, and black spruce •animals: diverse invertebrates and birds, otters, frogs, and alligators •Humans have destroyed up to 90% of wetlands; wetlands purify water and reduce flooding A basin wetland in the United Kingdom Streams and Rivers • most prominent physical characteristic of streams and rivers is a current • headwaters: generally cold, clear, turbulent, swift, and oxygenrich – often narrow and rocky • downstream waters: form rivers and are generally warmer, more turbid, and more oxygenated A headwater stream in the Great Smoky Mountains – often wide and meandering and have silty bottoms – may contain phytoplankton or rooted aquatic plants • diversity of fishes and invertebrates inhabit unpolluted rivers and streams The Loire river (in France) far from its headwaters Estuaries • estuary = transition area between river and sea • include a complex network of tidal channels, islands, natural levees, and mudflats • nutrient-rich and highly productive – algae are the base of the “food-chain” • abundant supply of food attracts marine invertebrates, fish, waterfowl, and marine mammals – e.g. oysters, crabs and fish • salinity can vary with the rise and fall of the tides An estuary in the southeastern United States Intertidal Zones • intertidal zone = periodically submerged and exposed by the tides • animals include: sponges, sea anemones, echinoderms, and small fishes • organisms are challenged by variations in temperature and salinity and by the mechanical forces of wave action • Oxygen and nutrient levels are high • sandy intertidal zones support sea grass and algae – worms, clams, and crustaceans bury themselves in sand • rocky intertidal zones support attached marine algae – many animals have structural adaptations for attaching to the hard substrate • Oil pollution has disrupted many intertidal areas Rocky intertidal zone on the Oregon coast Oceanic Pelagic Zone • • • • covers approximately 70% of Earth’s surface constantly mixed by wind-driven oceanic currents high oxygen levels temperate oceans have a lot of turnover – renews nutrients in the photic zones • tropical oceans exhibit year-round stratification – leads to lower nutrient concentrations • dominant organisms: phytoplankton and zooplankton – zooplankton includes protists, worms, copepods, krill, jellies, and invertebrate larvae Open ocean off the island of Hawaii Coral Reefs • formed from the calcium carbonate skeletons of cnidarians (i.e. corals) • shallow reef-building corals: live in the photic zone in warm, clear water • deepsea corals: live at depths of 200–1,500 m • require high oxygen concentrations and a solid substrate for attachment • progresses from a fringing reef to a barrier reef to a coral atoll A coral reef in the Red Sea Marine Benthic Zone • known as the seafloor • found below the surface waters of the coastal/ neritic zone and the offshore pelagic zone • deep benthic zone – known as the abyssal zone – organisms here are adapted to continuous cold and extremely high water pressure • substrate is mainly soft sediments • some areas can be rocky Interactions between organisms and the environment limit the distribution of species • • • • Species distribution is the result of ecological and evolutionary interactions through time Ecological time: minute-to-minute time frame of interactions between organisms and the environment – events in ecological time can lead to evolution – adaptations from one generation to another increases their fitness Evolutionary time: spans many generations and captures adaptation through natural selection both biotic and abiotic factors influence species distribution – e.g. climate, predation • Ecologists ask questions about where species occur and why species occur where they do Why is species X absent from an area? Yes Does dispersal limit its distribution? No Area inaccessible or insufficient time Does behavior limit its distribution? Yes Habitat selection Yes No Do biotic factors (other species) limit its distribution? Predation, parasitism, competition, disease No Do abiotic factors limit its distribution? Physical factors Temperature Light Soil structure Fire Moisture, etc. Chemical factors Water Oxygen Salinity pH Soil nutrients, etc. Dispersal and Distribution • Dispersal: movement of individuals away from centers of high population density or from their area of origin • contributes to the global distribution of organisms • natural range expansions show the influence of dispersal on distribution Current 1970 1966 1965 1960 1961 1958 1943 1951 1937 1956 1970 cattle egret range expansion Dispersal and Distribution • biotic & abiotic factors affect the distribution of organisms • Biotic factors may include: – Predation – Herbivory • e.g. sea urchins can limit the distribution of seaweeds – Competition • abiotic factors include: – – – – – Temperature Water Sunlight Wind Rocks and soil Factors affecting species distribution • Behavior and Habitat Selection: some organisms do not occupy all of their potential range • Environmental temperature: has an effect on biological processes • Water and O2 availability: water affects oxygen availability as oxygen diffuses slowly in water – Oxygen concentrations can be low in deep oceans and deep lakes • Salinity: salt concentration affects the water balance of organisms through osmosis • Sunlight: light intensity and wavelength affect photosynthesis – water absorbs light - aquatic environments most photosynthesis occurs near the surface – deserts, high light levels increase temperature and can stress plants and animals • Rocks and Soil: characteristics of soil limit the distribution of plants and thus the animals that feed on them – Physical structure – pH – Mineral composition Why is species X absent from an area? Does dispersal limit its distribution? Yes Area inaccessible or insufficient time No Does behavior limit its distribution? Yes Habitat selection No Do biotic factors (other species) limit its distribution? No Yes Chemical factors Do abiotic factors limit its distribution? Physical factors Predation, parasitism, competition, disease Water, oxygen, salinity, pH, soil nutrients, etc. Temperature, light, soil structure, fire, moisture, etc. Species Transplants • include organisms that are intentionally or accidentally relocated from their original distribution • can disrupt the communities or ecosystems to which they have been introduced