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Ecology: The Study of Ecosystems
Ecology (from the Greek oikos meaning "house" or "dwelling", and logos meaning "discourse" or "study") - the study of interactions of organisms with each other and
Ecology is a natural science, not a sociopolitical discipline (such as environmentalism, conservation, etc.). Ecologists employ hypothetico-deductive methods to address ecological questions.
Ecology can be considered at many levels.
- species - (biological definition) similar organisms able to interbreed under natural conditions to produce fertile, viable offspring
- population - all members of a single species living in a defined location
- community - all populations living in a defined location
- ecosystem - the community and the abiotic components of its world
- biosphere - all the earth's ecosystems, considered collectively
An ecosystem consists of
Evolution by natural selection is driven by ecological interactions.
- biotic components - the living organisms
- abiotic components - non-living factors, such as light,
temperature, water, nutrients, topography, etc.
Levels of Ecological Study
Ecology and evolution are inextricably related.
One of the first to apply ecological principles to modern awareness of our role in the biosphere was Rachel Carson, author of Silent Spring (1962).
Components of the Biosphere
combination of temperature, water, light, and wind over time--of a region determines its flora. Climate and flora directly
affect composition of the fauna.
- contributes to soil erosion and creation
- major component of organism habitats
- Natural selection has been driven by
- lack of water in terrestrial environments
- lack of solutes in fresh water
- animals that have secondarily returned to marine environments face
different osmotic challenges: ocean is saltier than when their ancestors left it.
- Green plants can be categorized on the basis of their adaptations for dealing with water availability in their habitat.
- hydrophyte - adaptations for a very wet environment; for example:
- thin cuticle
- stomates on upper leaf surfaces, if leaves are floating
- adaptations for obtaining nitrogen via the leaves instead of the soil (where acid conditons sequester nitrogen)
- spongy, air-filled parenchyma to aid floating
- may have specialized roots (pneumatophores) that protrude above water level to obtain oxygen
- mesophyte - adaptations for a moderately wet environment
- xerophyte - adaptations for a very dry environment; for example:
- very thick cuticle
- reduced leaves
- stomates protected in grooves
- pubescent (fuzzy) epidermis (protects against evaporation/desiccation)
- water-filled tissues and/or organs
...depending on the biological activity.
- Life is strongly affected by sunlight
- daily duration
- angle of incidence of the sun (seasonal changes)
- competition for light can be an important force driving natural selection
- aquatic environment: community composition determined by depth, as photosynthetic pigments needed for deeper water are different from those on land and in shallow water.
- photoperiodicity: The rhythm of certain biological phenomena (e.g., hibernation, reproductive cycles) are determined by the regularly recurring changes in light and dark caused by earth's rotation and its annual passage around the sun.
- photoperiodicity can cycle
Circadian rhythm: regular recurrence of a biological activity in cycles of approximately 24 hours.
For example, sleep cycles occur at a regular intervals, regardless of constant darkness or other conditions of illumination.
- contributes to erosion
- affects perceived temperature via
- facilitates evaporation & evaporative cooling
- affects temperature via convection
- affects desiccation rate
- affects growth form of plants
Major Environmental Disturbances
- topography creates habitat
- pH, and mineral content of rock affects flora composition
- substrate composition affects the quality of water in contact with that
substrate (dissolved minerals, pH, etc.)
- eluvium - geological deposits and soils derived by in situ weathering and/or gravitational movement and wind accumulation (adjective = eluvial)
- alluvium - soil or sediments deposited by a river or other running water (adjective = alluvial)
- finely resolved look at soil horizons
- severe storms (hurricanes, tornadoes, etc.)
- volcanic activity
- insert your favorite environmental disaster here
Review: Global Climate
The ultimate source of climate is the sun, which provides not only the
majority of energy on earth, but also creates climatic events when its
randomizing energy interacts with the earth.
Less than half of the solar radiation striking the earth's atmosphere
successfully penetrates the atmosphere to reach earth.
irradiance (i.e., solar radiation incident on the earth's surface) ranges
from approximately 250nm (ultraviolet) to 1500nm (near infrared). Shorter
and longer wavelengths are absorbed or reflected by atmospheric ozone,
When the sun is directly overhead in a cloudless sky, solar irradiance (i.e., the sunlight that actually strikes the earth's surface) is
most intense and peaks near 540nm ("green").
Environmental conditions and angle of incidence
affect both intensity and spectral distribution of incident sunlight.
- the tropics lie between the Tropic of Cancer (23.5o N) and the Tropic of Capricorn (23.5o S). These receive the highest annual input of solar energy, and are
the only place on earth that the sun ever shines directly overhead (on
the equinoxes, March 21 and September 21).
- the subtropics lie between the Tropic of Cancer and
30oN in the northern hemisphere, and between the
Tropic of Capricorn and
30oS in the southern hemisphere. (Miami is in the
- the temperate regions lie between 30oN and
60oN in the Northern Hemisphere and between 30oS and
60oS in the Southern Hemisphere.
- the polar regions lie above 60oN and S
Flora and fauna are profoundly affected by environmental and seasonal changes in solar
intensity and spectral distribution. Note also that because the earth is
tilted 23.5o on its axis (defining those tropical latitudes),
there are seasonal changes in solar irradiation in both hemispheres:
Solar warming of earth creates
global air and water vapor movement
- Warm, high levels of precipitation: tropics
- Relatively warm, arid: subtropics and temperate regions
- Cool, high levels of precipitation: just below polar area;
coniferous forests dominate
- Cold, arid: polar regions (arctic and antarctic)
Climate can be affected locally by
proximity to ocean, lakes, rivers
This creates smaller, localized ecosystems within biomes.
A biome is a major ecosystem spread over a wide geographic area, and
characterized by certain types of flora and fauna.
Major Aquatic Biomes
Earth is sometimes called "the Water Planet." Aquatic biomes occupy most of the biosphere
Life originated in the oceans, and stayed there for nearly 3 billion
years. The oceans are the most influential of all terrestrial features
affecting climate and biomes.
Aquatic biomes may be
- marine (average salinity 3%)
- freshwater (average salinity 1% or less)
- brackish (salinity between 1-3%)
The major types of aquatic biomes are...
Aquatic Biome Strata
- Freshwater or brackish
- intertidal regions
- coral reefs
- oceanic pelagic zones
- benthic/abyssal zones
Light is absorbed by water and by living aquatic organisms. photic zone - light sufficient for photosynthesis
aphotic zone - light insufficient for photosynthesis
Temperatures vary with depth, and aquatic habitats of any depth generally
have a thermocline--a narrow band of water where temperature suddenly
Freshwater Biome Zones
- littoral zone - inshore, shallow, high light levels
- limnetic zone - offshore, high light levels, upper regions of water
- profundal zone - aphotic
- benthic zone - bottom substrate; often rich in detritus
Marine Biome Zones
- intertidal - region that is covered at high tide, but exposed at
- neritic zone - inshore, shallow, high light levels
- oceanic zone - offshore, high light levels, upper regions of water
- pelagic zone - water column; contains both photic and aphotic regions
- benthic zone - bottom substrate; often rich in detritus
Productivity in Freshwater Biomes
Productivity is a measure of how much biomass
(dry organic matter) a particular ecosystem gains over a specified period
of time. Freshwater ecosystems/biomes can be characterized by their level of productivity.
oligotrophic - deep, nutrient poor, water very clear; LOW productivity
eutrophic - shallower, nutrient rich, murky with phytoplankton; HIGH productivity
(note on cultural eutrophication)
mesotrophic - in between the above two classifications; MODERATE productivity
Polar Ice Sheet
- Located above 60o north (arctic) and south (antarctic) latitudes
- Also found at extremely high mountain elevations (e.g., Everest, Denali)
- bitterly cold
- day length varies tremendously over the course of a year, with 24 hour daylight or night at the respective solstices.
- low biodiversity
- low productivity
- Most photosynthetic organisms are marine, and most solar energy is
captured in the water.
- Phytoplankton and zooplankton form the bottom of the food web
- Some typical vertebrates you might find here: penguins (antarctic only), seals, walruses, whales of various species,
polar bear (arctic only).
- Ice sheet images and more images
- Located just south of the polar regions in the northern hemisphere.
- Arid (as are the polar regions)
- Characterized by permafrost: a permanently frozen layer of soil,
which may lie deeper under the surface in summer than in winter, but still prevents the
growth of large trees with deep root systems.
- most plants are scrubby and small
- lichens (fungus/algae symbiosis) are a major photosynthetic food
- High winds and cold temperatures prevail
- Very short days in winter, very long days in summer
- Typical vertebrates: reindeer/caribou, Snowy Owls, Grizzly Bear, Brown
Bear, Wolf, Arctic Fox, Ptarmigan (a partridge-like bird), migratory
birds, lemmings (small rodents), voles (another rodent).
- Tundra images and more images.
- also known as coniferous or boreal (northern) forest
- Found south of the arctic and tundra regions, primarily in
the northern hemisphere
- High levels of precipitation in summer (rain) and winter (snow)
conical shape of pines may help them shed snow and avoid damage to their
branches from the weight of snow.
- Highly endangered, these ecosystems are being rapidly logged out,
especially in North America.
- Also found along the the Andes of South America
- short duration of sunlight in winter favors conifers, which can photosynthesize all year round (they do not shed their leaves/needles)
- Major plant form: evergreen, coniferous trees such as pines, firs,
spruce, etc. Under the trees grow shrubs, mosses, ferns, and other shade tolerant plants.
- Typical vertebrates: deer, wolf, bear, foxes, many migratory birds,
squirrels, rabbits, etc. Higher species diversity than tundra.
- See more images of the taiga/boreal forest.
Temperate Deciduous Forest
- Found in latitudes south of the coniferous forest where there is relatively high rainfall and relatively high elevation
- longer average day length than in taiga regions
- Major plant form: deciduous (i.e., trees that seasonally drop their
leaves) flowering trees and shrubs.
- Typical temperate deciduous forest areas are the northeastern
U.S. and most of Europe.
- Typical vertebrates: deer, wolf, bear, foxes, many migratory birds,
squirrels, rabbits, etc. Somewhat higher species diversity than coniferous
forest. Some species hibernate through the winter, when food is scarce in
the snowy landscape.
- Deciduous forest photos
- Also known as temperate
grassland or steppe
- Characterized by distinct seasonal changes, moderate rainfall,
extremely rich, organic soil.
- Major plant forms: annual grasses and flowering plants; some areas
with more standing water become marshes characterized by small trees such
as willows, cottonwoods, etc.
- Very fertile land, but with harsh seasonal variations: hot summers,
- The "veldt" of South Africa, the "puszta" of Hungary, the "pampas"
of Argentina, the steppes of Central Asia and Russia, and the plains of
the central U.S. are all examples of this highly productive biome.
- Most of these grasslands have been converted to farmland for human
use, but some native grasslands have been preserved.
- Typical vertebrates: American Bison (sometimes erroneously called
"buffalo"), prairie dog, jackrabbit, fox, coyote,
deer, many migratory birds (especially predatory birds such as hawks and
falcons), etc. Many animals undergo winter hibernation.
- Prairie photos.
- Also known as tropical/subtropical grassland)
- Characterized by extreme seasonal climate changes
- Very fertile land, but with harsh seasonal variations: very wet
season followed by extremely harsh dry season
- Lush grass and shrubbery growth in the rainy season provides ample
food for large animals, but they must migrate to greener pastures during dry season.
- Major plant forms: annual grasses and flowering plants; Trees are
generally xerophytes with high canopies due to herbivory
by large animals such as elephants and giraffes.
- Fire is a major abiotic component of this biome, and most plant
species are evolved to withstand periodic fires
- Typical vertebrates: grazing hoofed mammals (gazelles, antelopes,
etc.), lions, leopards, cheetahs, elephants, giraffes, true buffalo
(Water Buffalo, Cape Buffalo), rhino, hippopotamus, etc.
- Also known as Mediterranean Scrub Forest
- Found in arid regions with Mediterranean climate (e.g., southern
California, Spain, European and African areas bordering the Mediterranean
Sea; southern tip of Africa, southwestern tip of Australia)
- Winters are rainy and mild; summer days are long, hot, and very dry
- Characterized by periodic, seasonal fires
- Major plant forms: Dense, spiny, evergreen shrubs
- Some chapparal plants produce seeds that will germinate and grow only after they've been through a fire.
- Typical vertebrates: coyote, mule deer, various rodents, many lizards,
snakes, migratory birds.
- Chaparral photos.
- Historically distributed around the equator between the Tropic of Cancer and the Tropic of Capricorn
- Extremely high levels of rainfall
- Poor nutrient content in soils due to high levels of rainfall
- Highest biodiversity of any terrestrial ecosystem
- Most ancient of all biomes; species have coevolved for millions of years
- Tremendous plant diversity; large trees have shallow root systems
evolved to be able to quickly absorb nutrients as soon as they become
available (due to decay of dead things), before the rains wash them away.
- Very dense plant growth and very high level of productivity
- In mature rainforest, the forest floor is relatively clear of plants,
since the upper canopy of trees blocks most sunlight. Only when there's
a large treefall does a new growth of shrubby "pioneer species" germinate
from the soil and provide cover for the forest to re-grow.
- Typical vertebrates: More than 50% of all the earth's
terrestrial animal species are found in the tropical rainforest.
Examples: monkeys, toucans, parrots, lizards, snakes, amphibians,
and representatives of just about every major terrestrial animal phylum.
- Extremely arid.
- Very hot in the daytime; in many regions, extremely cold at night
- High nutrient levels in the soil due to very little rainfall
- Sparse plant life due to very low humidity and available water
- Plants are xerophytes (from the Greek xer, meaning "dry"
and phyt meaning "plant"): many adaptations for water conservation
- typical plants: cactus, Yucca, xerophytic shrubs of various species
- Spring rains often trigger a spectacular explosion of flowering annuals
- typical vertebrates: drought-tolerant mammals such as desert foxes,
burros, jackrabbits, high diversity of snakes and lizards, tortoises,
Roadrunner and other desert-adapted birds such as ravens and raptors (hawks, eagles)
- Famous North American examples include
Note the link between soil nutrient content and precipitation. Consider...
Which of these biomes has the highest productivity?
Which has the lowest soil nutrient content?
Which has the highest soil nutrient content?
Which biomes are most most suitable for agriculture?
Which do you like the best? (That's the hardest question!)