INTRODUCTION TO ECOLOGY

Lecture 21

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

Community ecology

Population ecology

Organismal ecology

The Scope of Ecological Research

• ecologists work at levels ranging from individual organisms to the planet

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

• 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

Earth’s climate varies by latitude and season and is changing rapidly

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)

Latitudinal variation in sunlight intensity

90°N (North Pole)60°N

30°N23.5°N (Tropic of Cancer

60°S90°S (South Pole)

0° (Equator)

23.5°S (Tropic of Capricorn)30°S

Low angle of incoming sunlight

Atmosphere

Sun overhead at equinoxes

Low angle of incoming sunlight

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

Global air circulation and precipitation patterns

Westerlies

Northeast trades

Southeast trades

Westerlies

30°N

0°

AR

ID ZO

NE

66.5°N (Arctic Circle)

30°N

0°

30°S

60°N

60°S66.5°S (Antarctic Circle)

Descendingdry airabsorbsmoisture.Ascendingmoist airreleasesmoisture.

Global Air Circulation and Precipitation Patterns

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• 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

Global air circulation and precipitation patterns

Westerlies

Northeast trades

Southeast trades

Westerlies

30°N

0°

AR

ID ZO

NE

66.5°N (Arctic Circle)

30°N

0°

30°S

60°N

60°S

66.5°S (Antarctic Circle)

Descendingdry airabsorbsmoisture.

Ascendingmoist airreleasesmoisture.

Regional and Local Effects on Climate

• Climate is affected by: seasonality, large bodies of water, and mountains

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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

Decembersolstice

September equinox

60°N

30°S

30°N

0° (equator)

Constant tiltof 23.5°June solstice

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

IndianOcean

SubtropicalGyre

California Current30°N North Pacific

Subtropical Gyre

30°S

Equator

South PacificSubtropical Gyre

Labrador Current

Gulf StreamNorth AtlanticSubtropical

Gyre

SouthAtlantic

SubtropicalGyre

Antarctic Circumpolar Current

• 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

Air flow

Ocean

Mountainrange

Leeward sideof mountains

Mountains

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Air flow

Ocean

Mountainrange

Leeward sideof 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

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 small-scale 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

CurrentrangePredictedrangeOverlap

(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

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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

Tropic of Cancer

30°N

30°S

Tropic of Capricorn

Equator

Tropical forestSavannaDesertChaparralTemperate grassland

Temperate broadleaf forestNorthern coniferous forestTundraHigh mountainsPolar 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

Temperatebroadleafforest

Arctic andalpinetundra

Northernconiferousforest

An

nu

al

me

an

te

mp

era

ture

(°C

)

Temperate grassland Tropical forest

30

15

0

15

Desert

Annual mean precipitation (cm)0 400100 200 300

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, low-tree 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

• 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

Disturbance and Terrestrial Biomes

Terrestrial Biomes• Terrestrial biomes can be characterized by:

– distribution– precipitation– temperature– plants & animals

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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 southwesternUnited States

A savanna in Kenya

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

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 chaparralin 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,Saskatchewan

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

Great Smoky MountainsNational Park inNorth Carolina, in autumn

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

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

• 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

• 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

(b) Marine zonation

0

200 m

Continentalshelf

2,0006,000 m

Abyssalzone

Benthiczone

Photic zone

Intertidal zoneNeriticzone Oceanic zone

Aphoticzone

Pelagiczone

(a) Zonation in a lake

(b) Marine zonation

Littoralzone Limnetic

zone

Photiczone

Benthiczone

Aphoticzone

Pelagiczone

0200 m

Continentalshelf

2,0006,000 m

Abyssalzone

Benthiczone

Photic zone

Intertidal zoneNeriticzone Oceanic zone

Aphoticzone

Pelagiczone

-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 isintertidal, 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

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Winter Spring

Thermocline

Autumn

0°2°

4°C 4°C

4°

4°C

4°

4°C

22°18°

8°

Summer

• 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

Tropic ofCancer

Tropic ofCapricorn

30°N

30°S

Equator

Oceanic pelagic and benthic zonesIntertidal zonesEstuariesCoral reefsRiversLakes

Aquatic Biomes• Major aquatic biomes can be characterized

by their:– physical environment– chemical environment– geological features– photosynthetic organisms– heterotrophs

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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 GrandTeton National Park, Wyoming

Lakes• Eutrophic lakes: nutrient-

rich • 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 OkavangoDelta, 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

A basin wetland in the United Kingdom

• 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

Streams and Rivers• most prominent physical

characteristic of streams and rivers is a current

• headwaters: generally cold, clear, turbulent, swift, and oxygen-rich– often narrow and rocky

• downstream waters: form rivers and are generally warmer, more turbid, and more oxygenated– 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

A headwater stream in the GreatSmoky Mountains

The Loire river (in France) farfrom 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 speciesX absent

from an area?

Does dispersallimit its

distribution? No

Yes

Yes

Yes

No

No

Does behaviorlimit its

distribution?Do biotic factors(other species)

limit itsdistribution?

Do abioticfactors limit itsdistribution?

Habitat selection

Area inaccessibleor insufficient time Predation,

parasitism,competition,disease

WaterOxygenSalinitypHSoil nutrients,etc.

Physicalfactors

Chemicalfactors

TemperatureLightSoil structureFireMoisture, 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

1970

19661965 1960

19611958

1943

1951 1937

1956

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?

Does behavior limit its distribution?

Do biotic factors (other species)limit its distribution?

Do abiotic factors limitits distribution?

No

No

No

Yes

Yes

Yes

Physicalfactors

Chemicalfactors

Area inaccessible orinsufficient time

Habitat selection

Predation, parasitism,competition, disease

Temperature, light, soilstructure, fire, moisture,etc.

Water, oxygen, salinity,pH, soil nutrients, 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