Climates, Biomes, and Ecological Restoration

Alexandra Duan
July 2023

Table of Contents
1 Introduction 2

2 Climate 2
2.1 Global Climate Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.2 Regional and Local Climate Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3 Global Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Biomes 4
3.1 Terrestrial Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Aquatic Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1 Zonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 Factors Influencing Species Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Ecosystems 7
4.1 Energy Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2 Chemical Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5 Restoration Ecology 9
5.1 Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2 Biological Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6 Conclusion 11

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1 Introduction
Ecology is the scientific study of the interactions between organisms and the environment. These
interactions may be organized into a hierarchy:
• Organismal ecology: studies how an organism’s structure, physiology, and behavior meet
the challenges of its environment

• Population ecology: a population is a group of individuals of the same species living in an

area; studies the factors that affect changes in population size

• Community ecology: a community is a group of populations in an area; studies how

interspecific interactions affect community structure

• Landscape ecology: a landscape is a group of connected ecosystems; studies the factors

controlling exchanges of energy, materials, and organisms across multiple ecosystems

• Global ecology: a biosphere is the sum of the planet’s ecosystems and landscapes; studies
how the regional exchange of materials influences the global distribution of organisms

2 Climate
Climate, the long-term prevailing weather conditions in a given area, is the most significant influ-
ence on the distribution of terrestrial organisms. Climate is composed primarily of four physical
factors: temperature, precipitation, sunlight, and wind.

2.1 Global Climate Patterns

1. Latitudinal variation in sunlight intensity: The intensity of sunlight varies depending
on Earth’s latitude. Sunlight strikes the tropics, or lower latitudes, more directly, delivering
more heat and light.

Figure 1: Sunlight strikes the tropics most directly and the higher latitudes at more
oblique angles. (Source: Campbell Biology)

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2. Air circulation and precipitation patterns: In the tropics, high temperatures cause
warm, wet air masses to evaporate, releasing water as they expand and cool. The cool, dry
air masses descend at higher latitudes, absorbing moisture and creating an arid climate. This
process repeats as descending air flows further toward the poles.

Figure 2: The circulation of air masses. (Source: Campbell Biology)

2.2 Regional and Local Climate Patterns

At the regional level, climate may vary based on seasonal changes and the presence of large bodies
of water and mountain ranges. Microclimates are very fine, localized patterns in climatic condi-
tions—for example, the area under a forest tree—which are affected by environmental features.

Seasonality: Seasonal cycles in day length, solar radiation, and temperature strengthen in
middle to high latitudes. As the angle of the sun changes, belts of wet and dry air move slightly
northward and southward, producing wet and dry seasons around 20◦ north and 20◦ south and
causing the development of tropical deciduous forests. Seasonal changes in wind patterns alter
ocean currents, sometimes causing upwelling zones of cold, nutrient-rich water from deep ocean
layers.

Bodies of water: Due to water’s high specific heat, large bodies of water moderate the climate
of nearby land. Ocean currents flowing toward the equator carry cold water from the poles, while
currents flowing away from the equator carry warm water to the poles.

Mountains: Mountains influence air flow over land. Warm, moist air on the windward side
of a mountain rises and cools as it ascends, releasing moisture; cool, dry air on the leeward side
absorbs moisture as it descends, producing a “rain shadow” where little precipitation occurs. Many
deserts, such as the Mojave and Gobi Deserts, are located in such leeward rain shadows.
Mountains also influence sunlight patterns: south-facing slopes in the Northern Hemisphere are
warmer and drier, allowing shrubby, drought-resistant plants to grow, while plants such as conifers
grow on the cooler north-facing slopes.

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Vegetation: Forests are darker in color than deserts and grasslands and therefore absorb
more solar energy, increasing transpiration, the evaporative loss of water from a plant that cools
the plant’s surface. Because transpiration is much greater in forests than in other ecosystems,
forests reduce Earth’s surface temperature and increase precipitation rates.

2.3 Global Climate Change

Climate change is a long-term (lasting three or more decades) directional change to the global cli-
mate. The burning of fossil fuels and deforestation are increasing the concentrations of greenhouses
gases in the atmosphere, warming Earth’s temperatures, shifting wind and precipitation patterns,
and increasing the frequency of extreme weather events (e.g., major storms and droughts).

Rapid warming forces species distributions to expand northward into more suitable habitats.
While some species move northward rapidly, slower species experience a “lagging” effect in which
their range expansion lags several thousand years behind the shift in suitable habitat. Decreased
rain and snow at higher elevations has also caused plant species to move to lower elevations. Species
forced to move into new geographic areas may harm other organisms living there.

Figure 3: Current and predicted ranges for the American beech under two climate-change
scenarios. (Source: Campbell Biology)

3 Biomes
3.1 Terrestrial Biomes
Life on earth is distributed across biomes, or major life zones. Terrestrial biomes are characterized
by vegetation type, which is in turn influenced strongly by climate. Biomes can be plotted on a
climograph, a graph of the annual mean temperature and precipitation in a particular region.

Most terrestrial biomes are named for their major climactic features and predominant vegeta-
tion (i.e., temperate grasslands are located in moderate climates and dominated by grass species).
Rather than having distinct boundaries, terrestrial biomes usually grade into neighboring biomes;
this area of intergradation is called an ecotone.

Vegetation in terrestrial biomes is vertically layered : many forests consist of, from top to bot-
tom, the (1) upper canopy, (2) low-tree layer, (3) shrub understory, (4) ground layer of herbaceous
plants, (5) forest floor (litter layer), and (6) root layer. This layering provides many different
habitats for organisms, which sometimes exist in well-defined feeding groups.

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Figure 4: The distribution of major terrestrial biomes. (Source: Campbell Biology)

3.2 Aquatic Biomes

Aquatic biomes are characterized by their physical (light penetration; temperature; depth) and
chemical (salinity; oxygen concentration; nutrient density) environment and show less latitudinal
variation than terrestrial biomes. The oceans make up the largest marine biome, covering about
75% of Earth’s surface.

3.2.1 Zonation
Many aquatic biomes are stratified both vertically and horizontally. Light is absorbed by water
and photosynthetic organisms, so its intensity decreases rapidly with depth.

Figure 5: The marine environment is classified

based on light penetration (photic and aphotic),
distance from shore and water depth (itnertidal,
neritic, and oceanic), and whether the environ-
ment is open water (pelagic) or on the bottom
(benthic and abyssal).
(Source: Campbell Biology)

• Pelagic zone: contains the photic zone, where there is sufficient light for photosynthesis,
and the aphotic zone, where where little light penetrates
• Abyssal zone
• Benthic zone: made up of sand and sediment; inhabited by communities of organisms
collectively called the benthos, many of which feed on dead organic matter called detritus
which drifts down from the photic zone

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The ocean and most lakes contain a thermocline, a narrow layer of abrupt temperature change
which separates the warm upper layer from cold deeper layers. Many temperate lakes undergo a
turnover, or semiannual mixing of their waters, in autumn (as surface water cools and sinks) and
spring (as surface water warms and mixes with the below layers). This turnover mixes oxygenated
water from the surface and nutrient-rich water from the bottom.

• Lakes: Large standing bodies of water. Lakes range widely in salinity, oxygen concentration,
and nutrient content.

– Oligotrophic lakes are nutrient-poor and oxygen-rich, with low amonts of decomposable
organic matter, while eutrophic lakes are nutrient-rich and oxygen-poor, with high rates
of decomposition.
– T he shallow, well-lit littoral zone contains aquatic plants, while the farther, deeper
limnetic zone contains a variety of phytophankton.
– Runoff from fertilized land leads to nutrient enrichment in lakes, which can produce
large numbers of algae (called an algal bloom) and deplete oxygen. This is known as
cultural eutrophication.

• Wetlands: Habitats inundated by water at least some of the time which support plants
adapted to water-saturated soil. Wetlands are productive and low in dissolved oxygen, with
high rates of organic production and decomposition, and have a high capacity for filtration
of dissolved nutrients and chemicals.

• Streams and rivers: Bodies of continuously-flowing water, stratified into vertical zones.
Headwaters are generally cold, clear, and rich in oxygen, while downstream waters are gen-
erally warmer and more turbid.

• Estuaries: Transition areas between rivers and seas. Salinity varies spatially and with the
rise and fall of the tides. Nutrients from the river make estuaries highly productive, acting
as crucial feeding areas for waterfowl and some marine mammals.

• Intertidal zones: Highly diverse zones which are periodically submerged and exposed by
the tides (twice daily on most marine shores).

• Ocean pelagic zone: A vast zone of open water, constantly mixed by ocean currents.
Covers approximately 70% of Earth’s surface. Photosynthetic plankton in the ocean pelagic
zone account for about half of Earth’s photosynthetic activity.

• Coral reefs: Areas formed largely from the calcium carbonate skeletons of corals. Coral
reefs typically begin as fringing reefs on young, high islands, then form an offshore barrier
reef and eventually become a coral atoll as the island submerges.

• Marine benthic zone: The seafloor below the surface waters of the coastal (neritic) zone
and the offshore pelagic zone. Contains no sunlight; temperature declines and pressure
increases with depth. Most consumers depend entirely on organic matter from the photic
zone. Unique organisms live near deep-sea hydrothermal vents.

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Example 3.1 (USABO Semifinal Exam 2016) Seasonal turnover of lakes occurs during

(A) Summer only.

(B) Spring and autumn.
(C) Summer and winter.
(D) Spring, summer, and autumn.
(E) All four seasons.

Solution: Turnover, or the mixing of surface water and lower layers, occurs semiannually: once
when the icy surface water warms and mixes with the below layers, and once when temperatures
lower, causing surface water to cool and sink. The answer is therefore (B) Spring and autumn.

3.3 Factors Influencing Species Distribution

• Dispersal is the movement of individuals of gametes away from their area of origin or from
centers of high population density, often resulting in range expansion. Successful transplan-
tation of a species to a new area indicates that the potential range of the species is larger
than its actual range.

• Biotic factors, or other species, limit a species’ ability to survive and reproduce through
predation or herbivory.

• Abiotic factors are physical conditions such as temperature, salinity, and sunlight. Unsuit-
able conditions limit a species’ distribution.

4 Ecosystems
An ecosystem consists of all of the organisms in a community and the abiotic factors with which
they interact. Ecosystems can be as large as the entire biosphere or as small as the area under
a fallen log, and ecosystem dynamics are governed by two processes: energy flow and chemical
cycling. These processes are determined by trophic relationships.

• Primary producers: Autotrophs; mostly photosynthetic plants, algae, or prokaryotes that

use light energy to synthesize organic compounds.

• Primary consumers: Herbivores that eat primary producers.

• Secondary consumers: Carnivores that eat herbivores.

• Tertiary consumers: Carnivores that eat other carnivores.

• Detritivores: Get energy from detritus, nonliving organic material such as the remains of
dead organisms, feces, and wood (i.e., prokaryotes and fungi).

– Detritivores recycle chemical elements back to primary producers by converting organic

materials to inorganic compounds usable by primary producers.

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4.1 Energy Flow

Energy enters most ecosystems in the form of sunlight, which is converted to chemical energy by
autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat.

According to the first law of thermodynamics, energy cannot be created or destroyed. In

ecosystems, solar energy is converted to chemical energy by plants and photosynthetic organisms,
so the total amount of energy stored in organic molecules plus the amounts reflected and dissipated
as heat must equal the total solar energy intercepted by the plant.

According to the second law of thermodynamics, every exchange of energy increases the entropy
of the universe. In an ecosystem, some energy is lost as heat in any conversion process.

The amount of light energy converted by chemical energy by an ecosystem’s autotrophs in

a given period is an ecosystem’s primary production. The total primary production in an
ecosystem is gross primary production (GPP), the amount of light energy that is converted
to chemical energy by photosynthesis per unit time. Net primary production (NPP) is equal
to gross primary production minus the energy used by primary producers for respiration (R):
N P P = GP P − R
In many ecosystems, NPP is about half of GPP. NPP represents the stored chemical energy that
is available to consumers in the ecosystem.
• Net primary production can be expressed as energy per unit area per unit time (J/m2·yr),
or as biomass of vegetation added to the ecosystem per unit area per unit time (g/m2·yr).
• The standing crop is the total biomass of photosynthetic autotrophs present in a given
time, while NPP is the amount of new biomass added in a given period of time.
• Forests have a large standing crop biomass, but their primary production may actually be less
than that of some grasslands, which do not accumulate vegetation because animals consume
the plants rapidly and because grasses and herbs decompose more quickly than trees do.
– Tropical rainforests have high NPP per unit area and contribute a large portion of
Earth’s overall NPP.
– Estuaries and coral reefs have very high NPP per unit area, but they cover only about
one-tenth the area covered by tropical rain forests, so they contribute less to global
NPP.
– The open ocean has a relatively low NPP per unit area but contributes as much global
net primary production as terrestrial systems because of its vast size.
In aquatic ecosystems, light and nutrients limit primary production, because solar radiation can
penetrate to only a certain depth (the photic zone). A limiting nutrient is an element that must
be added for production to increase in a particular area. In marine zones, the limiting nutrient is
most often nitrogen or phosphorus, which are very low in the photic zone.
• Nutrient limitation is common in freshwater lakes. In eutrophication, sewage and fertilizer
pollution add large amounts of nutrients to lakes, causing cyanobacteria and algae popula-
tions to grow rapidly, ultimately reducing oxygen concentrations and visibility in the water.

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In terrestrial ecosystems, temperature and moisture are the key factors limiting primary pro-
duction. Contrasts in climate can be represented by actual evapotranspiration, the annual amount
of water transpired by plants and evaporated from a landscape.

4.2 Chemical Cycling

Chemical elements are cycled among abiotic and biotic components of an ecosystem.

• Photosynthetic organisms assimilate chemical elements in organic form from the air, soil,
and water, and incorporate them into their biomass.

• Some of these chemical elements are consumed by animals.

• The elements are returned in organic form to the environment by the metabolism of plants
and animals and by decomposers such as bacteria and fungi, which break down organic
wastes and dead organisms.

Example 4.1 (USABO Semifinal Exam 2018) The main distinction between nutrient and
energy dynamics in rangeland ecosystems is:

(A) Nutrients flow through ecosystem components while energy is cycled.

(B) Nutrients cycle through ecosystem components while energy flows.
(C) Nutrients are confined to living portions of the ecosystem while energy is
not.
(D) The main source of all nutrients is the soil while the sun supplies energy.

Solution: As covered in this section, the answer is (B) Nutrients cycle through ecosystem
components while energy flows.

5 Restoration Ecology
Conservation biology integrates ecology, evolutionary biology, physiology, molecular biology,
genetics, and behavioral ecology to conserve biological diversity at all levels. Restoration ecology
applies ecological principles in an effort to return degraded ecosystems to conditions as similar as
possible to their natural, predegraded state.

5.1 Biodiversity
The accelerated rate of extinction caused by human activity threatens Earth’s biodiversity. Bio-
diversity has three levels:

• Genetic diversity refers to the genetic variation within a species. It comprises the individ-
ual genetic variation within a population and the genetic variation between populations.

• Species diversity is the variety of species in an ecosystem or the biosphere, and is greatly
affected by the biodiversity crisis.

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– Endangered species are in danger of extinction throughout a significant portion of their

range, and threatened species are likely to become endangered in the foreseeable future.
Species extinction may be local (lost in one area) or global (lost in all locales).
• Ecosystem diversity is the variety of the biosphere’s ecosystems. Ecosystems such as
wetlands in the U.S. and native riparian communities in California, Arizona, and New Mexico
are being altered at a rapid pace.
The three major threats to biodiversity are habitat loss, introduced species, and overexploita-
tion.
• Habitat loss is the single greatest threat to biodiversity, caused mainly by human activities
such as urban development, deforestation, and mining. Habitat fragmentation, the breaking
up of natural landscapes, leads to species loss in almost all cases.
• Introduced species are moved by humans from native locations to new geographic regions.
Introduced species often disrupt their adopted community by outcompeting native species for
resources—for example, zebra mussels native to Europe have extensively disrupted freshwater
ecosystems and clogged water-intake systems in North America.
• Overexploitation is the human harvesting of wild plants and animals at rates that exceed
the ability of those populations to rebound. Species with restricted habitats (i.e., small
islands) and large organisms with low reproductive rates are particularly vulnerable to over-
exploitation.

Example 5.1 (USABO Semifinal Exam 2018) What are the three principal levels of biodi-
versity?

(A) genetic, species and ecosystem

(B) individual, population and community
(C) population, community and ecosystem
(D) community, ecosystem and landscape

Solution: As covered in this section, the main levels of biodiversity are (A) genetic, species
and ecosystem diversity.

5.2 Biological Strategies

• Bioremediation is the use of living organisms, usually prokaryotes, fungi, or plants, to
detoxify (remove toxins from) polluted ecosystems.
– Example: Plants adapted to soils containing heavy metals can remove high concentra-
tions of potentially toxic metals from polluted environments.
• Biological augmentation uses organisms to add essential materials to a degraded ecosys-
tem.
– Example: Nitrogen-fixing herbs can be planted in ecosystems disturbed by mining to
increase nitrogen concentrations in soil.

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6 Conclusion
This handout covered the basics of ecology at the global and landscape levels, focusing largely on
the interactions between organisms and abiotic factors found across Earth’s biomes. Information
not covered in this handout includes details on the major terrestrial biomes and nutrient cycles,
which you may want to review after reading. To learn about the interactions between organisms
at the community and population levels, read on to the Population Ecology, Community Ecology,
and Ethology handout.

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