An Introduction to Ecology and the Biosphere
Ecology is the scientific study of the interactions between organisms and their
environments
Humans have always had an interest in other organisms and their environments
Valuable insight can be gained from a discovery-based approach of watching nature
and recording its structure and processes
Hypothesis-driven science performed in natural environments is fundamental to
ecology
But ecologists also test hypotheses using laboratory experiments, where conditions
can be simplified and controlled
Some ecologists take a theoretical approach, devising mathematical and computer
models
Ecology and Environmentalism
Technological innovations have enabled people to colonize just about every
environment on Earth
Earth’s resources affect our survival and have been profoundly altered by our
activities
Environmental problems
can be understood by the science of ecology and
require decisions based on values and ethics
On a personal level, each of us makes daily choices that affect our ecological
impact
Interconnections Within Systems
A Hierarchy of Interactions
Many different factors can potentially affect an organism’s interaction with the
environment
Biotic factors are the living component of the environment consisting of all of the
organisms in the area
Abiotic factors are the environment’s nonliving component and include chemical
and physical factors (temperature, light, water, minerals, air, etc.)
An organism’s habitat is the specific environment it lives in and includes the biotic
and abiotic factors of its surroundings
Ecology can be divided into four increasingly comprehensive levels:
1. organismal ecology
2. population ecology
3. community ecology
4. ecosystem ecology
Organismal ecology is concerned with evolutionary adaptations that enable
organisms
to meet the challenges posed by their abiotic environments
The distribution of organisms is limited by the abiotic conditions they can tolerate
For example, amphibians such as salamanders cannot live in cold climates because
they gain most of their body warmth by absorbing heat from their surroundings
Population ecology concentrates mainly on factors that affect population density and
growth
Biologists studying endangered species are especially interested in this level of
ecology
Community ecology focuses on how interactions between species affect a community’s
structure and organization
Ecosystem ecology
is concerned with ecosystems, all the abiotic factors in addition to the community of
species in a certain area
focuses on energy flow and the cycling of chemicals among the various abiotic and
biotic factors
The biosphere is the global ecosystem, so it is all of life and where it lives
The biosphere includes
the atmosphere to an altitude of several kilometers
the land down to water-bearing rocks about 1,500 m (almost a mile) deep
lakes and streams
caves
the oceans to a depth of several kilometers
Living in Earth’s Diverse Environments
The distribution of life varies on both a global and a local scale
Patterns in the distribution of life mainly reflect differences in the abiotic factors of
the environment
Abiotic Factors
The distribution of life varies on both a global and a local scale
Energy, temperature, water, inorganic nutrients
Energy
All organisms require a usable source of energy
to live
Solar energy from sunlight powers most ecosystems
Lack of sunlight is seldom the most important factor limiting plant growth for
terrestrial ecosystems
In many aquatic environments, light cannot penetrate beyond certain depths
and most photosynthesis occurs near the surface
Surprisingly, life also thrives in environments that are completely dark
Hydrothermal vents are ecosystems powered by chemoautotrophic bacteria
that derive energy from the oxidation of inorganic chemicals such as hydrogen
sulfide
Bacteria with similar metabolic abilities support communities of cave-dwelling
organisms
Temperature
Temperature affects metabolism
Most organisms function best within a specific range of environmental temperatures
Water
Aquatic organisms
are surrounded by water and
face problems of water balance if their own solute concentration does not
match that of their surroundings
For terrestrial organisms, the primary threat is drying out in the air
Many land animals have watertight coverings that reduce water loss, such as
reptilian scales
Most plants have waxy coatings on their leaves and other aerial parts
Inorganic Nutrients
The distribution and abundance of photosynthetic organisms depend on soil
structure, pH, and the availability of inorganic nutrients, especially compounds of
nitrogen and phosphorus
Terrestrial ecosystems are also limited by wind, storms, and/or fire
In many aquatic ecosystems, the growth of algae and photosynthetic bacteria is also
often limited by levels of nitrogen and phosphorus
Aquatic ecosystems are also limited by the levels of oxygen dissolved in water,
salinity, currents, and tides
Evolutionary Adaptations of Organisms
The ability of organisms to live in Earth’s diverse environments demonstrates the
close relationship between the fields of ecology and evolutionary biology
Evolutionary adaptation via natural selection results from the interactions between
organisms and their environments
Environmental Variability
The abiotic factors in a habitat may vary from year to year, from season to season, or
even from hour to hour
Adjusting to Environmental Variability
Birds may adjust to cold by
migrating to warmer regions (behavioral response)
growing heavier feathers (anatomical response)
fluffing up their feathers to trap more heat
(physiological response)
These responses, which occur during the lifetime of an individual, do not qualify as
evolution, which is change in a population over time
Physiological Responses
Acclimation is a gradual, reversible, physiological adjustment that occurs in
response to an environmental change
The ability to acclimate is generally related to the range of environmental conditions
a species naturally experiences
Among vertebrates,
birds and mammals can generally tolerate the greatest temperature
extremes because they are endotherms
ectothermic reptiles can tolerate only a more limited range of
temperatures
Many organisms respond to environmental challenges with some type of change in
body shape and structure
When the change is reversible, the response is an example of acclimation
Some mammals grow a heavier coat of fur before the winter cold sets in
and shed it when summer comes
In some animals, fur or feather color also changes seasonally
Environmental variation can affect growth and development so much that there may
be remarkable differences in body shape within a population
Rooted and unable to move to a better location, plants must rely entirely on their
anatomical and physiological responses to survive environmental fluctuations
Most animals can respond to unfavorable changes in the environment by moving to a
new location
Ectotherms, including reptiles, maintain a reasonably constant body temperature by
shuttling between sun and shade
Migratory birds travel great distances in response to changing seasons
Humans have an especially wide range of
behavioral responses
Earth’s Biomes
Biomes are large terrestrial regions or aquatic life zone of the Earth that have similar
vegetative formations in terrestrial biomes or similar physical environments in
aquatic biomes
Aquatic Biomes
Aquatic biomes occupy roughly 75% of Earth’s surface and are determined by their
salinity and other physical factors
Freshwater biomes have a salt concentration of less than 1% and include lakes,
streams, rivers, and wetlands
Marine biomes typically have a salt concentration around 3% and include oceans,
intertidal zones, and coral reefs
Freshwater Biomes
Freshwater biomes
cover less than 1% of Earth
contain only ~0.01% of its water
harbor about 6% of all described species
are used for drinking water, crop irrigation, sanitation, and industry
Freshwater biomes fall into two broad groups:
1. standing water such as lakes and ponds
2. flowing water such as rivers and streams
Lakes and Ponds
Standing bodies of water range from small ponds to large lakes, such as North
America’s Great Lakes
Freshwater lakes are most productive near their shores and near their surface
Phytoplankton is the collective name for microscopic algae and cyanobacteria that
drift
near the surfaces of aquatic biomes
The amount of phytoplankton growth in a lake or pond is typically regulated by the
amounts of nitrogen and phosphorus
Rivers and Streams
Rivers and streams generally support quite different communities of organisms than
do lakes and ponds
The water in rivers and streams changes dramatically between its source (perhaps a
spring or snowmelt in the mountains) and the point at which it empties into a lake or
the ocean
Near the source of a stream, the water is usually cold, low in nutrients, and
clear
Downstream, the water is usually warmer, murkier, wider, and slower flowing
Many streams and rivers have been affected by pollution from human activities and
the construction of dams to control flooding, provide reservoirs for drinking water,
and/or generate hydroelectric power
Wetlands
A wetland is a transitional biome between an aquatic ecosystem and a terrestrial
one
Wetlands support the growth of aquatic plants and are rich in species diversity
Marine Biomes
Marine biomes are diverse, ranging from vivid coral reefs to perpetually dark realms
in the deepest regions
The seafloor is known as the benthic realm
The pelagic realm includes all of the open water of the oceans
The coral reef biome occurs in the photic zone of warm tropical waters in scattered
locations around the globe
The intertidal zone is where the ocean meets land, the shore is pounded by waves
during high tide (submerged), and the bottom is exposed to the sun and drying winds
during low tide (emerged)
Estuaries are a transition area between a river and the ocean, have a saltiness
ranging from nearly that of fresh water to that of the ocean, and are among the most
productive areas on Earth, where oysters, crabs, and many fishes live or reproduce
and waterfowl nest and feed
Climate and Terrestrial Biomes
Terrestrial biomes are primarily determined by climate, especially temperature and
rainfall
Earth’s global climate patterns are largely the result of the input of solar energy,
which warms the atmosphere, land, and water, and the planet’s movement in space
The equator receives the greatest intensity of
solar radiation
Warm, moist air at the equator rises, then cools, forming clouds, and rain falls
The tropics are located at and near the equator
Temperate zones generally have milder climates than the tropics or the polar
regions
They occur in latitudes between the tropics and the Arctic Circle in the north and the
tropics and the Antarctic Circle in the south
Climate is also affected by the
proximity to large bodies of water and
presence of landforms such as mountain ranges
Mountains affect climate in two major ways
1. Air temperature drops as elevation increases
2. Mountains can block the flow of cool, moist air from a coast and cause
radically
different climates on opposite sides of a
mountain range
Terrestrial Biomes
Terrestrial ecosystems are grouped into biomes primarily on the basis of their
vegetation type
Vegetation type is greatly influenced by precipitation and temperature
Tropical Forests
Tropical forests occur in equatorial areas, where the temperature is warm and days
are 11–12 hours long year-round
The type of vegetation is determined primarily by rainfall
Savannas
Savannas
are dominated by grasses and scattered trees,
are warm year-round, and
experience rainfall of 30–50 cm (roughly 12–20 inches per year) with dramatic
seasonal variation
Fire is an important abiotic factor in the savanna
Many of the world’s large grazing mammals and their predators inhabit savannas,
including zebras, many species of antelope, lions, and cheetahs
But the dominant plant-eaters in savannas are insects, especially ants and termites
Deserts
Deserts
are the driest of all biomes,
are characterized by low and unpredictable rainfall of less than 30 cm (about
12 inches) a year, and
may be very hot or relatively cold
Desert vegetation typically includes water-storing plants, such as cacti, and deeply
rooted shrubs
Common inhabitants include snakes, lizards, seed-eating rodents, and arthropods
such as scorpions and insects
Chaparral
Chaparral vegetation results mainly cool ocean currents circulating offshore
producing mild, rainy winters and hot, dry summers
This biome is limited to small coastal areas, some in California; the largest region of
chaparral surrounds the Mediterranean Sea
Chaparral vegetation is adapted to periodic fires caused by lightning
Many plants contain flammable chemicals and burn fiercely, especially where
dead brush has accumulated
After a fire, shrubs use food reserves stored in the surviving roots to support
rapid shoot regeneration
Some chaparral plants produce seeds that will germinate only after a hot fire
Temperate Grasslands
Temperate grasslands
are mostly treeless,
experience 25–75 cm (10–30 inches) of rain per year,
experience frequent droughts and periodic fires, and
are characterized by grazers including bison and pronghorn in North
America,wild horses and sheep of the Asian steppes, and kangaroos in Australia
Temperate Broadleaf Forests
Temperate broadleaf forest
occurs throughout mid-latitudes where there is sufficient moisture to support
the growth of large trees and
experiences annual precipitation that is relatively high at 75–150 cm (30–60
inches) and typically distributed evenly throughout the year
Temperature varies seasonally over a wide range, with hot summers and cold
winters
In the Northern Hemisphere, dense stands of deciduous trees are trademarks of
temperate forests
Deciduous trees drop their leaves before winter, when temperatures are too
low for effective photosynthesis and water lost by evaporation is not easily
replaced from frozen soil
Numerous invertebrates live in the soil and the thick layer of leaf litter that
accumulates on the forest floor
Many mammals that inhabit these forests hibernate during the winter, and some bird
species migrate to warmer climates
Coniferous Forests
Coniferous forests in the Northern Hemisphere are dominated by cone-bearing
evergreen trees and include the northern coniferous forest, or taiga, the largest
terrestrial biome on Earth
Coniferous Forests
Temperate rain forests are found along coastal North America from Alaska to
Oregon
Tundra
Tundra covers expansive areas of the Arctic between the taiga and polar ice and is
characterized by permafrost (permanently frozen subsoil), bitterly cold
temperatures, high winds, and very little annual precipitation
Tundra vegetation includes small shrubs, grasses, mosses, and lichens
On very high mountaintops at all latitudes, high winds and cold temperatures create
plant communities called alpine tundra
Although these communities are similar to arctic tundra, there is no permafrost
beneath alpine tundra
Polar Ice
Polar ice covers the land at high latitudes north of the arctic tundra in the Northern
Hemisphere and in Antarctica in the Southern Hemisphere
Only a small portion of these landmasses is free of ice or snow, even during the
summer
Interconnections Between Systems: The Water Cycle
All parts of the biosphere are linked by the global water cycle and nutrient cycles
Events in one biome may reverberate throughout the biosphere
Water and air move in global patterns driven by solar energy
Precipitation and evaporation continuously move water between the land,
oceans, and the atmosphere
Water also evaporates from plants, in a process called transpiration
Over the oceans, evaporation exceeds precipitation, resulting in a net
movement of water vapor to clouds that are carried by winds from the oceans
across the land
On land, precipitation exceeds evaporation and transpiration
The excess precipitation may stay on the surface, or it may trickle through
the soil to become groundwater
Human activities that affect the global water cycle include destruction of forests,
pumping large amounts of groundwater to the surface for irrigation, and global
warming, which affects the water cycle in complex ways that have far-reaching
effects on precipitation patterns
Fresh, sanitary water is a scarce commodity even for human beings, despite the fact
that civilization now uses more than half the world’s accessible water
The scarcity of water can be traced in significant part to the inefficient ways in
which humans use it
Human diversion of water from natural environments is having harmful
impacts on species such as fish
Human Impact on Biomes
Sustainability is the goal of developing, managing, and conserving Earth’s resources
in ways that meet the needs of people today without compromising the ability of
future generations to meet their needs
Human Impact on Forests
Tropical forests are being cleared to grow palm oil for products such as cosmetics
and a long list of packaged foods, including cookies, crackers, potato chips, chocolate
products, and soups
Global Climate Change
Global climate patterns are changing because of rising concentration in the
atmosphere of carbon dioxide (CO2) and other greenhouse gases
This was the overarching conclusion of the assessment report released by the
Intergovernmental Panel on Climate Change (IPCC) in 2014
Thus, there is no debate among scientists about whether climate change is
occurring
It all has to do with the enhanced greenhouse effect
The signature effect of rapidly increasing greenhouse gases is the steady increase in
the average global temperature, which has risen 0.8°C (1.4°F) over the last 100 years,
with 75% of that increase occurring over the last three decades
Further increases of 2–4.5°C are likely by the end of this century, according
to the 2014 IPPC report
Major sources of emissions include agriculture, landfills, and the burning of wood
and fossil fuels (oil, coal, and natural gas)
Although there is some uncertainty as to the long term consequences of global
warming because of the uncertain amounts of greenhouse gases that will be emitted
in the coming years, some consequences are certain
Rise in sea levels
Change in rainfall patterns
Alteration in the mix of species in different geographical regions
What can be done to stem the tide of global warming?
Deforestation of the tropical rainforests accounts for ~20% of the excess
CO2 released into the atmosphere
The other ~80% comes from the burning of fossil fuels