Biology 2483A: Ecology Notes
Lecture/Chapter One: Introduction
Ecology is the study of interactions between organisms and environment and deals with the distribution and
abundance of species within specific environments. (Not environmental science).
There is not a balance in nature. Species don’t each have a specific role to play. When a species is removed they
can always be replaced; although major influences can affect the environment greatly.
The Ecological Maxims:
1. Organisms interact and are interconnected
2. Everything goes somewhere
Ecology likes to monitor where: pollution, nutrients, energy, etc.
3. No population can increase in size forever
Every species has a carrying capacity
4. Finite energy and resources result in tradeoffs
A species will select where to ration their energy which they think will be most beneficial to
survival: hunting, defense, camouflage, etc.
5. Organisms evolve: Evolution
Adaptation: A characteristic that improves survival or reproduction.
Natural selection: Individuals with certain adaptations tend to survive and reproduce at a higher
rate than other individuals.
If the adaptation is heritable, the frequency of the characteristic may increase in a population
6. Communities and ecosystems change over time
7. Spatial scale matters
2. Population: Group of individuals of a species that are living and interacting in a particular area
3. Community: Association of populations of different species in the same area
4. Ecosystem: Community of organisms plus the physical environment: biotic +abiotic
5. Landscapes: Areas with substantial differences, typically including multiple ecosystems
6. Biosphere: Entire planet plus all its organisms
Producers: capture energy from an external source (e.g. the sun) and use it to produce food.
Net primary productivity (NPP): Energy captured by producers, minus the amount lost as heat in cellular
Consumers: get energy by eating other organisms or their remains.
Ecosystem Flow of Energy and Nutrients:
Energy: moves in a single direction only—it cannot be recycled and is lost as heat (convection, metabolism,
conduction, latent heat exchange: respiration/sweating, radiation)
Nutrients: are continuously recycled from the physical environment to organisms and back again
1. Make observations and ask questions.
2. Use previous knowledge or intuition to develop hypotheses.
3. Evaluate hypotheses by experimentation, observational studies, or quantitative models.
4. Use the results to modify the hypotheses, pose new questions, or draw conclusions about the natural world. Amphibian Deformities and Mortalities:
“Biological indicators” for environmental problems: due to permeable skin, eggs with no protective shells,
double environment (land and water) means exposure in both areas
Many became extinct and deformed.
Parasite Ribeiroia causes deformities and mortality—cysts formed on amphibians
Life Cycle of Ribeiroia:
Eggs are in the water, and develop in snails (1 intermediate host), form free-swimming cercariae which then
inhabit amphibian tadpoles (2 intermediate host), they form cysts here causing deformities, and when they are
eaten by birds (definitive host), they mature to adulthood in the bird and release their eggs back into the water
through bird feces.
Factors Influencing Deformities:
1. Pollutants. Impair immune system making amphibians more susceptible to parasite
2. Fertilizer runoff. Increases algae growth and therefore snail population and then parasite population
since it is the first intermediate host.
3. Habitat loss
4. UV exposure and Nitrate levels. High levels of both reduced mortality.
5. Pathogens. Chytrid fungus—causes a lethal skin disease.
6. Climate change
Lecture/Chapter Two: The Physical Environment
The physical environment determines where organisms can live, and the resources that are available. Thus,
understanding the physical environment is key to understanding all ecological phenomena.
Weather: Current conditions—temperature, precipitation, humidity, cloud cover.
Climate: Long-term description of weather, based on averages and variation measured over decades.
• Climatic variation includes daily and seasonal cycles, as well as yearly and decadal cycles.
• Long-term climate change results from changes in the intensity and distribution of solar radiation.
• Current climate change is due to increased CO2 and other gases in the atmosphere due to human
• Climate determines the geographic distribution of organisms.
• Climate is characterized by average conditions; but extreme conditions are also important to organisms
because they can contribute to mortality. Atmosphere contains greenhouse gases that absorb and reradiate infrared radiation emitted by Earth.
These gases include:
• Water vapor (H2O).
• Carbon dioxide (CO2).
• Methane (CH4).
• Nitrous oxide (N2O).
Without greenhouse gases, Earth’s climate would
be about 33°C cooler.
Solar radiation heats Earth’s surface, which emits
infrared radiation to the atmosphere, warming the
air above it.
Warm air is less dense than cool air, and it rises
—this is called uplift.
Air pressure decreases with altitude, so the rising
air expands and cools.
Tropical regions receive the most solar radiation and the most precipitation.
Uplift of air in the tropics results in a low atmospheric pressure zone—wet
Downdraft of air around 30° creates a high atmospheric pressure zone—dry
When air masses reach the troposphere–
stratosphere boundary, air flows towards the
These three cells result in the three major
climatic zones in each hemisphere—tropical,
temperate, and polar zones.
Areas of high and low pressure created by the
circulation cells result in air movements called
The winds appear to be deflected due to the
rotation of the Earth—the Coriolis effect.
Water has a higher heat capacity than land—
it can absorb and store more energy without
Summer: Air over oceans is cooler and denser,
so air subsides and high pressures develop over
Winter: Air over continents is cooler and denser;
high pressure develops over continents.
These are known as semipermanent high and
low pressure cells.
Major ocean surface currents are driven by
surface winds, so patterns are similar.
Speed of ocean currents is about 2%–3% of the
Ocean currents affect climate.
Example: the warm Gulf Stream warms the
climate of Great Britain and Scandinavia. Example: Labrador is much cooler because of the cold Labrador Current.
Where warm tropical surface currents reach polar areas, the water cools, ice forms, water becomes more saline
and denser and sinks (downwelling).
Upwelling is where deep ocean water rises to the surface.
Upwelling occurs where prevailing winds blow parallel to a
coastline. Surface water flows away from the coast and
deeper, colder ocean water rises up to replace it.
Upwellings influence coastal climates.
Upwellings bring nutrients from the deep sediments to the
photic zone—where light penetrates and phytoplankton grow.
This provides food for zooplankton and their consumers.
These areas are the most productive in the open oceans.
Coasts have a maritime climate: Little daily and seasonal variation in temperature and high humidity.
Areas in the center of large continents have continental climates: Much greater variation in daily and seasonal
On mountain slopes, vegetation
shifts reflect climate changes as
temperature decreases, and
precipitation and wind speed
increase with elevation.
When air masses meet mountain
ranges, they are forced upwards,
cooling and releasing precipitation.
North–south trending mountain
ranges create a rain shadow: The
slope facing prevailing winds
(windward) has high precipitation,
while the leeward slope gets little
Vegetation can also influence climate.
Albedo—capacity of a land surface to reflect solar radiation—is influenced
by vegetation type, soils, and topography.
For example, a coniferous forest has a darker color and lower albedo than
bare soil or dormant grassland.
Loss or change in vegetation can affect climate.
Deforestation increases albedo of the land surface: Less absorption of solar
radiation and less heating.
Lower heat gain is offset by less cooling by evapotranspiration, due to loss
of leaf area.
Decreased evapotranspiration results in less moisture in the atmosphere
and less precipitation.
Deforestation in the tropics can lead to a warmer, dryer regional climate.
Climatic variation over time:
Earth is tilted at an angle of 23.5° relative to the sun’s direct rays. The angle and intensity of the sun’s rays striking any point on Earth vary as Earth orbits the sun, resulting in
seasonal variation in climate.
In temperate-zone lakes, stratification changes with
Complete mixing (turnover) occurs in spring and fall
when water temperature and density become uniform
This pattern is due to the fact that Water has a higher
heat capacity than land. Therefore at greater depths the
water will retain the previous season’s temperature—in
winter it gets warmer as you go down and in summer it
El Niño events, or the El Niño Southern Oscillation
(ENSO), are longer-scale climate variations that occur
every 3 to 8 years and last about 18 months.
The positions of high- and low-pressure systems over
equatorial Pacific switch, and the trade winds weaken.
Upwelling of deep ocean water off the coast of South
America ceases, resulting in much lower fish harvests.
Greenhouse Gases Again:
Over the past 500 million years, Earth’s climate has
alternated between warm and cool cycles.
Warmer periods are associated with higher
concentrations of greenhouse gases.
Earth has cycles of cool phases with formation of glaciers (glacial maxima), followed by warm periods with
glacial melting (interglacial periods).
These glacial–interglacial cycles occur at frequencies of about 100,000 years.
We are currently in an interglacial period; these have lasted about 23,000 years in the past.
The last glacial maximum was about 18,000 years ago.
The glacial–interglacial cycles have been explained by regular changes in the shape of Earth’s orbit and the tilt
of its axis—Milankovitch cycles.
The intensity of solar radiation reaching Earth changes, resulting in climatic change.
The shape of Earth’s orbit changes in 100,000-year cycles. (glacial-interglacial frequency)
The angle of axis tilt changes in cycles of about 41,000 years.
Earth’s orientation relative to other celestial objects changes in cycles of about 22,000 years. Lecture/Chapter Three: The Biosphere
The biosphere is the zone of life on Earth.
Biomes are large-scale biological communities shaped by the
physical environment, particularly climate.
Biomes are categorized by dominant plant forms, not taxonomic
Plants occupy sites for a long time and are good indicators of
the physical environment, reflecting climatic conditions and
Terrestrial biomes are characterized by growth forms of the
dominant plants, such as leaf deciduousness or succulence. Plants have taken many forms in response to selection pressures such as aridity, extreme temperatures, intense
solar radiation, grazing, and crowding.
Similar growth forms can be found on different continents, even though the plants are not genetically related.
Convergence: Evolution of similar growth forms among distantly related species in response to similar selection
Temperature has direct physiological effects on plant growth form.
Precipitation and temperature act together to influence water availability and water loss by plants.
Water availability and soil temperature determine the supply of nutrients in the soil.
Biomes Vary with Mean Annual Temperature and Precipitation:
This does not account for seasonal
Human activities influence the
distribution of biomes.Land use
change: Conversion of land to
agriculture, logging, resource
extraction, urban development. The
potential and actual distributions of
biomes are markedly different.
There are nine major terrestrial biomes:
1. Tropical Rainforests
High biomass, high diversity—about 50% of Earth’s species.
Light is a key factor—plants must grow very tall above their
neighbors or adjust to low light levels. Emergents rise above
the canopy. Lianas (woody vines) and epiphytes use the trees
for support. Understory trees grow in the shade of the canopy,
and shrubs and forbs occupy the forest floor. Biome is
disappearing due to logging and conversion to pasture and
croplands. About half has been altered. Soils are nutrient-
poor, and recovery of nutrient supplies may take a very long
time. 2. Tropical Seasonal Forests and Savannas
Yellow is drought period. Wet and dry seasons associated
with movement of the ITCZ. Shorter trees, deciduous in dry
seasons, more grasses and shrubs. Fires promote
establishment of savannas; some are set by humans. In Africa,
large herbivores—wildebeests, zebras, elephants, and
antelopes—also influence the balance of grass and trees. On
the Orinoco River floodplain, seasonal flooding promotes
savannas. Less than half of seasonal tropical forests and
savannas remain. Human population growth in this biome has
had a major influence. Large tracts have been converted to
cropland and pasture.
3. Hot Deserts
High temperatures, low moisture. Sparse vegetation and
animal populations. Low water availability constrains plant
abundance and influences form. Many plants have succulent
stems that store water. Convergence of this form is shown by
cacti (Western Hemisphere) and euphorbs (Eastern
Hemisphere). Both plants developed succulent stems
separately in evolution. Humans use deserts for agriculture
and livestock grazing.
Agriculture depends on irrigation, and results in soil
salinization. Long-term droughts and unsustainable grazing
can result in desertification—loss of plant cover and soil erosion.
4. Temperate Grasslands
Warm, moist summers and cold, dry winters. Grasses dominate;
maintained by frequent fires and large herbivores such as bison.
Grasses grow more roots than stems and leaves, to cope with dry
conditions. This results in accumulation of organic matter and
high soil fertility. Most fertile grasslands of central North
America and Eurasia have been converted to agriculture. In arid
grasslands, grazing by domesticated animals can exceed capacity
for regrowth, leading to grassland degradation and
desertification. Irrigation in some areas causes salinization.
5. Temperate Shrublands and Woodlands
Evergreen leaves allow plants to be active during cooler,
wetter periods. They also lower nutrient requirements—the
plants don’t have to develop new leaves every year.
Sclerophyllous leaves—tough and leathery—deter herbivores
and prevent wilting. After fires, shrubs sprout from
underground storage organs, or produce seeds that sprout and
grow quickly. Without regular fires at 30–40-year intervals,
shrublands may be replaced by forests.
6. Temperate Deciduous Forests
Deciduous leaves in response to extended periods of freezing.
Need fertile soils and enough water to support tree growth.
Fertile soils and climate make this biome good for agriculture.
Very little old-growth temperate forest remains. As agriculture
has shifted to the tropics, temperate forests have regrown.
Shifts in species composition are due to nutrient depletion by
agriculture and invasive species, causing damage such as
chestnut blight. 7. Temperate Evergreen Forests
Includes temperate rainforests, but spans a wide range of
environmental conditions. Commonly found on nutrient-poor
soils. Evergreen trees are used for wood and paper pulp, and
this biome has been logged extensively. Very little old-growth
temperate evergreen forest remains. In some areas, trees have
been replaced with non-native species in uniformly aged stands.
Suppression of fires in western North America has increased
the density of forest stands, which results in more intense fires
when they do occur. It also increases the spread of insect pests
and pathogens. Air pollution has damaged some temperate evergreen forests.
8. Boreal Forests
Boreal Forests (Taiga): Long, severe winters. Permafrost (soil
that remains frozen year-round) prevents drainage and results in
saturated soils. Trees are conifers—pines, spruces, larches.
Cold, wet conditions in boreal soils limit decomposition, so
soils have high organic matter. In summer droughts, forest fires
can be set by lightning, and can burn both trees and soil. In
low-lying areas, extensive peat bogs form. Boreal forests have
not been as affected by human activities. Logging, oil and gas
development, occur in some regions. Impacts will increase as
energy demands increase. Climate warming may increase soil
decomposition rates, releasing stored carbon and creating a positive feedback to warming. This creates many
Where growing season length and temperatures decrease, trees
cease to be the dominant vegetation (the tree line marks the
boreal to tundra transition). Characterized by sedges, grasses,
forbs, and low growing shrubs. Human influence is increasing
as exploration and development of energy resources increases.
The Arctic has experienced significant climate change, with
warming almost double the global average.
Mountain Biological Zones:
On mountains, temperature and precipitation change with elevation, resulting in zones
similar to biomes. Smaller scale variations are associated with slope aspect, proximity
to streams, and prevailing winds. Streams and rivers:
Streams and rivers are lotic (flowing water) systems.
Benthic organisms are bottom dwellers, and include
many kinds of invertebrates. Some feed on detritus
(dead organic matter), others are predators. Some live
in the hyporheic zone—the substratum below and
adjacent to the stream.
Lakes and still waters (lentic) occur where
depressions in the landscape fill with water.
Littoral zone (near shore): Where the photic
zone reaches the bottom. Macrophytes occur in
Photic zone: Supports the highest densities of
organisms, extends to about 200 m depth.
Below the photic zone, energy is supplied by
Pelagic zone: Open water beyond the
continental shelves; dominated by plankton
(small and microscopic organisms suspended in
Phytoplankton are photosynthetic, restricted to
the upper layers through which light penetrates
Zooplankton are non-photosynthetic protists and tiny animals (don’t need photic zone).
The Deep Pelagic Zone: Below the photic zone, temperatures drop and pressure increases. Crustaceans such as
copepods graze on the rain of falling detritus from the photic zone. Crustaceans, cephalopods, and fishes are the
predators of the deep sea.
Estuaries: Where rivers flow into oceans.
Salt marshes: Shallow coastal wetlands dominated by grasses and rushes.
Mangrove forests: Mudflats dominated by salt-tolerant trees.
Sandy shores, Kelp forests, Coral reefs, Rocky intertidal are others.
Lecture/Chapter Four: Coping with Environmental Variation: Temperature and Water
The physical environment influences an organism’s ecological success in two ways:
1. Availability of energy and resources—impacts growth and reproduction.
2. Extreme conditions can exceed tolerance limits and impact survival.
Energy supply can influence an organism’s ability to tolerate environmental extremes.
The actual geographic distribution of a species is also related to other factors, such as disturbance and
• Because plants don’t move, they are good indicators of the physical environment.
• A species’ climate envelope is the range of conditions over which it occurs.
Physiological ecology is the study of interactions between organisms and the physical environments that
influence their survival and persistence.
• Physiological processes have optimal conditions for functioning.
• Deviations from the optimum reduce the rate of the process.
• Stress—environmental change results in decreased rates of physiological processes, lowering the potential
for survival, growth, or reproduction. Acclimatization: Adjusting to stress through behavior or physiology.
• It is usually a short-term, reversible process.
• Acclimatization to high elevations involves higher breathing rates, greater production of red blood cells, and
higher pulmonary blood pressure.
Adaptation: Adjusting to envrionmental stress over many generations through natural selection
• Individuals with traits that enable them to cope with stress are favored. Over time, these genetic traits
become more frequent in the population.
Acclimatization and adaptation require investments of energy and resources, representing possible trade-offs
with other functions that can also affect survival and reproduction.
Ecotypes: Populations with adaptations to unique environments.
• Ecotypes can eventually become separate species as populations diverge and become reproductively
• Environmental temperatures vary greatly throughout the biosphere.
• Survival and functioning of organisms is strongly tied to their internal temperature.
• Some archaea and bacteria in hot springs can function at 90°C.
• Lower limits are determined by temperature at which water freezes in cells (–2 to –5°C).
• Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal function.
High temperature destroys enzymes function (denatured).
• Bacteria in hot springs - enzymes stable to 100°C; Antarctic fish and crustaceans -enzymes function at –
2°C; soil microbes - active at temperatures as low as –5°C.
• Some species produce different forms of enzymes (isozymes) with different temperature optima that allow
acclimatization to changing conditions.
• Temperature also affects the properties of cell membranes, which are composed of two layers of lipid
• At low temperatures, these lipids can solidify, embedded proteins can’t function, and the cells leak
• Plants that thrive at low temperatures have higher proportions of unsaturated lipids (with double bonds) in
their cell membranes
Ectotherms: Regulate body temperature through energy exchange with the external environment.
• Ectotherm surface area-to-volume ratio of the body is an important factor in exchanging energy with the
• A larger surface area allows greater heat exchange, but makes it harder to maintain internal temperature.
• Small aquatic ectotherms remain the same temperature as the water.
• Some large ectotherms can maintain higher body temperature:
• Skipjack tuna use muscle activity and heat exchange between blood vessels to maintain a body temperature
14°C warmer than the surrounding seawater.
• Many terrestrial ectotherms can move around to adjust temperature.
• Many insects and reptiles bask in the sun to warm up after a cold night, but this increases predation risk,
increasing benefits of camouflage
• Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behavior includes
seasonal migration to lower latitudes or to microsites that are above freezing (e.g., burrows in soil).
• Tolerance to freezing involves minimizing damage associated with ice formation in cells. Some insects have
high concentrations of glycerol, a chemical that lowers the freezing point of body fluids.
• Vertebrates generally do not tolerate freezing temperatures. • Heat Stress: In hot environments can gain too much heat from the environment and body temperature can
reach lethal levels.
Endotherms: Rely primarily on internal heat generation—mostly birds and mammals.
• Can maintain internal temperatures near optimum for metabolic functions. Can extend geographic range
• Some other organisms that generate heat internally include bees, some fish, such as tuna, and even some
• Skunk cabbage warms its flowers using metabolically generated heat in early spring.
• Endotherms can remain active at subfreezing temperatures.
• The cost of being endothermic is a high demand for energy (food) to support metabolic heat production.
• Metabolic rates are a function of the external temperature and rate of heat loss.
• Rate of heat loss is related to body size and surface area-to-volume ratio.
• Small endotherms with large surface area-to-volume ratio have higher metabolic rates, and require more
energy and higher feeding rates than large endotherms.
• Thermoneutral zone: The range of environmental temperatures over which a constant basal metabolic rate
can be maintained.
• Lower critical temperature: When heat loss is greater than metabolic production; body temperature drops
and metabolic heat generation increases.
• Metabolic Rates in Endotherms Vary with
• Mammals in the Arctic have lower critical
temperatures than mammals in tropical
• The rate of metabolic activity increases more
rapidly below the lower critical temperature
in tropical mammals as compared to Arctic
Figure only graphing
the lower critical
thermal neutral zone • Evolution of endothermy required insulation—feathers, fur, and fat. Insulation limits conductive and
convective heat loss.
• Fur and feathers provide a layer of still air adjacent to the skin. Some animals grow thicker fur for winter.
• Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little
or no metabolic activity occurs.
• Small mammals have thin fur and not much fat for energy storage, but high demand for metabolic energy
below the lower critical temperature.
• They survive in cold climates by entering a dormant state called torpor. Body temperature and basal
metabolic rates are low, which conserves energy.
• Energy reserves are needed to come out of torpor. Small endotherms may undergo daily torpor to survive
• Longer periods of torpor, or hibernation, are possible for animals that can store enough energy.
• Heat stress in animals:
• Some organisms use behavioral changes to control exchange of energy with the environment.
• Examples: Elephants swim and spray water onto their backs with their trunks to cool their bodies.
• Moving into the shade reduces the amount of solar radiation received
• Evaporative heat loss in animals includes sweating in humans, panting in dogs and other animals, and
licking of the body by some marsupials.
• Water stress in animals:
• Arid conditions are a widespread challenge for organisms.
• Some tolerate dry conditions by going into suspended animation. Many microorganisms do this, as do some
• Desiccation-tolerant organisms can lose 80%–90% of their water.
• Reptiles are very successful in dry environments. They have thick skin with layers of dead cells, fatty
coatings, and plates or scales.
• Mammals and birds have thick skin plus fur or feathers to minimize water loss.
• Sweat glands in mammals are a trade-off between water loss resistance and evaporative cooling.
Cryonics is the preservation of bodies by freezing, in hope that they can be brought back to life in the future.
Two frog species live in the Arctic tundra and can survive winter in a semi-frozen state.
They overwinter in shallow burrows, with no heartbeat, no blood circulation, and no breathing.
• In most organisms, freezing results in tissue damage as ice crystals perforate cell membranes and organelles.
• In animals that withstand freezing, the freezing water is limited to the space outside the cells.
• Ice-nucleating proteins outside cells serve as sites of slow, controlled ice formation.
• Additional solutes, such as glucose and glycerol are made inside the cells to lower the freezing point.
Energy Exchange in Terrestrial Plants Conduction—transfer of energy
from warmer to cooler molecules.
Convection—heat energy is carried
by moving water or air.
Plants can adjust energy inputs and
Transpiration rates can be
controlled by specialized guard
cells surrounding leaf openings
Variation in degree of opening and
number of stomates control the rate
of transpiration and thus leaf
Transpiration - Stomatal Control of Leaf Temperature
• If soil water is limited, transpirational cooling is not a good mechanism.
• Some plants shed their leaves during dry seasons.
• Other mechanisms include pubescence—hairs on leaf surfaces that reflect solar energy. But hairs also
reduce conductive heat loss.
• Pubescence was studied in three Encelia species (plants in the daisy family).
• Desert species with high pubescence were compared with non-pubescent species from wetter, cooler
• Plants of all three species were grown in both locations (common gardens).
• In the cool, moist location, the three species showed few differences in leaf temperature and stomatal
• In the desert, species with no hairs maintained leaf temperature by transpiration; the pubescent species
leaves reflected about twice as much solar radiation.
• The desert species (E. farinosa) also has smaller, more pubescent leaves in summer than in winter,
representing acclimatization to hot summer temperatures.
• If air temperature is lower than leaf temperature, heat can be lost by convection.
• Convective heat loss is related to speed of air moving across a leaf surface.
• Boundary layer: A zone of turbulent flow due to friction, next to the leaf surface. • The boundary layer lowers convective heat loss.
• Boundary layer thickness is related to leaf size and surface roughness.
• Small, smooth leaves have thin boundary layers and lose more heat than large or rough leaves.
• In cold, windy environments, convection is the main heat loss mechanism.
• Most alpine plants hug the ground surface to avoid high wind velocities.
• Some have a layer of insulating hair to lower convective heat loss.
Lecture/Chapter Five: Coping with Environmental Variation: Energy
Autotrophs: Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds
• The energy is converted into chemical energy stored in the bonds of organic molecules.
• Sea slugs have functional chloroplasts that are taken up from the algae that the slug eats.
• Photosynthesis - (most autotrophes): sunlight provides the energy to take up CO2and synthesize organic
• Chemosynthesis (chemolithotrophy): Energy from inorganic compounds is used to produce carbohydrates.
Chemosynthesis is important in nutrient cycling bacteria, and in some ecosystems such as hydrothermal
• Most of the biologically available energy on Earth is derived from photosynthesis. Photosynthetic organisms
include some archaea, bacteria, and protists, and most algae and plants.
Photosynthesis has two major steps:
1. Light reaction—light is harvested and used to split water and provide electrons to make ATP and
2. Dark reaction—CO is 2ixed in the Calvin cycle, and carbohydrates are synthesized. • Photosynthetic rate determines the supply of energy, which in turn influences growth and reproduction.
• Environmental controls on photosynthetic rate are an important topic in physiological ecology.
Light response curves show the influence of light levels on photosynthetic rate.
Light compensation point: Where CO2 uptake is
balanced by CO2 loss by respiration.
Saturation point: When photosynthesis no longer
increases as light increases.
Plants can acclimatize to changing light intensities with
shifts in light response
Shifts in light saturation
• Leaves at high light intensity may have thicker leaves and more chloroplasts.
• Water availability influences CO 2upply in terrestrial plants.
• Low water availability causes stomates to close, restricting CO2uptake.
• This is a trade-off: Water conservation versus energy gain.
• Closing stomates increases chance of light damage: If the Calvin cycle isn’t operating, energy accumulates
in the light-harvesting arrays and can damage membranes.
• Plants have various mechanisms to dissipate this energy, including carotenoids.
• Plants from different climate zones have enzyme forms with different optimal temperatures that allow them
to operate in that climate.
• Nutrients can also affect photosynthesis: Most nitrogen in plants is associated with rubisco and other
• Thus, higher nitrogen levels in a leaf are correlated with higher photosynthetic rates.
• But nitrogen supply is low, relative to demand for growth and metabolism.
• Increasing nitrogen content of leaves increases the risk that herbivores will eat them, as plant-eating animals
are also nitrogen-starved.
Some metabolic processes decrease photosynthetic efficiency.
Rubisco can catalyze two competing reactions:
1. Carboxylase reaction: Photosynthesis.
2. Oxygenase reaction: O is2taken up, carbon compounds are broken down, and CO is rele2sed
• Does photorespiration have any benefits?
o Experiments with Arabidopsis thaliana plants with a mutation that knocks out photorespiration:
o These plants die under normal light and CO co2ditions.
o Hypothesis: Photorespiration may protect plants from damage at high light levels.
• Used more in high O and high temperature
• However it is less efficient than photosynthesis so plants are at risk at high oxygen and temp
• When atmosphere was like this (7 million years ago) they created a solution: C4 photosynthesis The C4 photosynthetic pathway reduces photorespiration,
and evolved independently several times.
• Many grass species use this pathway, including corn,
sugarcane, and sorghum. It involves biochemical and
• CO 2ptake and the Calvin cycle occur in different parts
of the leaf.
• CO 2s taken up in the mesophyll by PEPcase, which has
greater affinity for CO2, and does not take up O2.
• CO concentration is increased in bundle sheath cells
where rubisco is operating in the Calvin cycle, which
reduces O 2ptake by rubisco.
• More ATP is required for the C p4thway, but higher
photosynthetic efficiency gives these plants an
advantage at high temperatures.
• Transpiration losses are minimized because PEPcase
can take up CO e2en when stomates are not fully open.
• There is a close correlation between temperature and the proportion of C s4ecies in the community.
o High temperatures = more C4 plants
Crassulacean acid metabolism (CAM) minimizes water loss.
• CO2 uptake and the Calvin cycle are separated temporally.
• CAM plants open their stomates at night when it’s cooler and humidity is higher, and close them during the
• CAM plants are often succulent, with thick, fleshy leaves or stems.
• They are common in hot dry areas and some humid tropics with less access to water
Heterotrophs: Obtain their energy by consuming energy-rich organic compounds from other organisms.
• Some heterotrophs consume non-living organic matter.
• Parasites and herbivores consume live hosts, but do not necessarily kill them.
• Predators capture and consume live prey animals.
• Some plants are holoparasites: They have no photosynthetic pigments and get energy from other plants
(heterotrophs). Dodder is a holoparasite that is an agricultural pest and can significantly reduce biomass in
the host plant.
• Mistletoe is a hemiparasite—it is photosynthetic, but obtains nutrients, water, and some of its energy from
the host plant.
• The energy gain depends on the chemistry of the food, and how much effort is need to find and ingest the
o Soil microorganisms that feed on detritus invest little energy to find food, but the food has low
o A cheetah hunting a gazelle invests a lot of energy to find, chase, and kill its prey, but it gets an
• Multicellular animals have evolved specialized tissues and organs for absorption, digestion, transport, and
• They have tremendous diversity in morphological and physiological feeding adaptations.
• Humans view toolmaking as something that differentiates us from other animals
o Chimps, crows, and dolphins do it too
• Optimal foraging theory: Animals will maximize the amount of energy gained per unit time, energy, and
risk involved in finding food. • Food availability can vary greatly over time and space.
o If energy is in short supply, animals should invest in obtaining the highest-quality food that is the
shortest distance away.
• Profitability of a food item (P) depends on how much energy (E) the animal gets from the food relative to
the amount of time (t) it spends finding and obtaining the food:
P = t
• An animal’s success in acquiring food increases with the effort it invests; but at some point, more effort
results in no more benefit, and the net energy obtained begins to decrease.
• Marginal value theorem (Charnov 1976):
o An animal should stay in a patch until the rate of energy gain has declined to match the average rate
for the whole habitat (giving up time).
o Giving up time is also influenced by distance between patches: The longer the travel time between
food patches, the longer an animal should spend in a patch.
o NOTE: this doesn’t just apply to distance but the giving up time between how long an organism
should go after a certain energy source (ie. How long it should try to open a shell, etc.)
o Optimal foraging theory does not apply as well to animals that feed on mobile prey.
o The assumption that energy is in short supply, and this dictates foraging behavior, may not always
Lecture/Chapter Six: Evolution and Ecology
Case Study: Bighorn sheep hunting
Trophy hunting removes the largest and strongest males—the ones that would sire many healthy offspring.
In one population, 10% of males were removed by hunting each year, the average size of males and their horns
decreased over 30 years of study.
This is also being observed in other species:
• African elephants are poached for ivory; the proportion of the population that have tusks is decreasing.
• Rock shrimp are all born male, and become females when they are large enough to carry eggs. Commercial
harvesting takes the largest individuals, which are all females.
• Genes for switching sex at a smaller size became more common, resulting in more females, but smaller
females lay fewer eggs. What Is Evolution?
• Evolution can be viewed as genetic change over time or as a process of descent with modification.
• Biological evolution is change in organisms over time.
• Evolution can be defined more broadly as descent with modification.
• As a population accumulates differences over time and a new species forms, it is different from its
• But the new species has many of the same characteristics as its ancestors, and resembles them