Ecology
Chapter 44-46 Lecture
AP Biology
2013
44
Ecological and Evolutionary
Consequences of Species
Interactions
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Interspecific interactions (between individuals
of different species) affect population densities,
species distributions, and ultimately lead to
evolutionary changes.
The interactions can be beneficial or detrimental
to either of the species.
Figure 44.1 Types of Interspecific Interactions (Part 1)
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Interspecific competition refers to
–/– interactions
Members of two or more species use the same
resource.
At any one time there is often one limiting
resource in the shortest supply relative to
demand.
Figure 44.1 Types of
Interspecific
Interactions (Part 2)
Green plants
compete for light.
The leaves of tall
trees have
reduced light
available to the
plants growing on
the forest floor.
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Consumer–resource interactions—organisms
get their nutrition by eating other living
organisms.
+/– interactions—the consumer benefits while
the consumed organism loses
Includes predation, herbivory, and parasitism.
Kills and
consumes
individuals of
another species
Animal
consumes
part of or all
of a plant
A parasitic organism
consumes part of a
host individual but
usually does not kill
it
Figure 44.1 Types of Interspecific Interactions (Part 3)
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Mutualism benefits both species: +/+ interaction
Examples:
• Leaf-cutter ants and the fungi they cultivate
• Plants and pollinating or seed-dispersing
animals
• Humans and bifidobacteria in our guts
• Plants and mycorrhizal fungi
• Lichens
• Corals and dinoflagellates
Figure 44.1 Types of Interspecific Interactions (Part 4)
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Commensalism—one species benefits while the
other is unaffected (+/0 interaction).
• Brown-headed cowbird follows grazing cattle
and bison, foraging on insects flushed from the
vegetation.
• Cattle convert plants into dung, which dung
beetles can use.
Dung beetles disperse other dung-living
organisms such as mites and nematodes,
which attach themselves to the bodies of the
beetles.
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Amensalism—one species is harmed while the
other is unaffected (–/0 interactions).
Tend to be more accidental than other
relationships.
Example: a herd of elephants that crush plants
and insects while moving through a forest.
Concept 44.1 Interactions between Species May Be
Positive, Negative, or Neutral
Relationships between species
do not always fit perfectly into
these categories.
Fish that live with sea
anemones escape predation
by hiding in the anemone
tentacles.
Effects of this on the anemones
is unclear. Do the fish steal
some of their prey? Do they
get nutrients from fish feces?
It may depend on the
availability of nutrients.
Concept 44.2 Interspecific Interactions Affect Population
Dynamics and Species Distributions
Density-dependent population growth reflects
intraspecific (within-species) interactions
among individuals in a population.
They are usually detrimental because per capita
resource availability decreases as population
density increases.
Concept 44.2 Interspecific Interactions Affect Population
Dynamics and Species Distributions
Resource partitioning—different ways of using
a resource.
Example: Paramecium caudatum can coexist
with P. bursaria.
P. bursaria can feed on bacteria in the lowoxygen sediment layer at the bottom of culture
flasks.
P. bursaria has symbiotic algae that provides it
with oxygen from photosynthesis.
Figure 44.5 Resource Partitioning Can Result in Intraspecific Competition Being Greater than
Interspecific Competition
Leaf Cutting Ants and Fungi
Watch. Can you explain their mutualistic
existence?
Answer to Opening Question
In the mutualism between leaf-cutter ants and
the fungus they cultivate, both species gain
nutrition from the interaction.
Ants also disperse the fungus and protect it from
pathogens.
It may have started when ants began eating the
fungi growing on refuse in their nests. Ants that
provided better growing conditions had more
fungus to eat and thus higher fitness.
Answer to Opening Question
Fungi that provided ants with more nutrients
were more likely to be propagated by ants.
The ants expanded their food base by feeding
leaves to the fungi (ants can’t digest the
leaves).
The fungi then had access to food they would
not be able to use if ants did not chop it up for
them.
Figure 44.11 A Fungal Garden
Answer to Opening Question
Leaf-cutter ants and their fungi have been very
successful:
They are major herbivores in the Neotropics,
and have expanded into dry environments that
are normally hostile to fungi.
45
Ecological Communities
Concept 45.1 Communities Contain Species That Colonize and
Persist
Community—a group of species that coexist
and interact with one another within a defined
area
Biologists may designate community boundaries
based on natural boundaries (e.g., the edge of
a pond) or arbitrarily.
They may restrict study to certain groups (e.g.,
the bird community).
Concept 45.1 Communities Contain Species That Colonize and
Persist
Communities are characterized by species
composition; that is, which species they
contain and the relative abundances of those
species.
A species can occur in a location only if it is able
to colonize and persist there.
A community contains those species that have
colonized minus those that have gone extinct
locally.
Concept 45.1 Communities Contain Species That Colonize and
Persist
Local extinctions can occur for many reasons:
• Species unable to tolerate local conditions
• A resource may be lacking
• Exclusion by competitors, predators, or
pathogens
• Population size too small; no reproduction
Concept 45.1 Communities Contain Species That Colonize and
Persist
In 1883 the volcano on Krakatau erupted, killing
everything on the island.
Scientists studied the return of living organisms.
Within 3 years, seeds of 24 plant species had
reached the island.
Later, as trees grew up, some pioneering plant
species that require high light levels
disappeared from the island’s now-shady
interior.
Species composition continues to change as
new species colonize and others go extinct.
Figure 45.1 Vegetation Recolonized Krakatau (Part 1)
Concept 45.2 Communities Change over Space and Time
Species often replace one another in a
predictable sequence called succession.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Each species in a community has a unique
niche.
This concept refers to the environmental
tolerances of a species, which define where it
can live.
Also refers to the ways a species obtains energy
and materials and to patterns of interaction with
other species in the community.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Consumer–resource, or trophic interactions
cause energy and materials to flow through a
community.
Trophic levels—feeding positions
Primary producers, or autotrophs, convert
solar energy into a form that can be used by
the rest of the community.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Heterotrophs get energy by breaking apart
organic compounds that were assembled by
other organisms.
Primary consumers (herbivores) eat primary
producers.
Secondary consumers (carnivores) eat
herbivores.
Tertiary consumers eat secondary
consumers.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Omnivores feed from multiple trophic levels.
Decomposers, or detritivores, feed on waste
products or dead bodies of organisms.
Decomposers are responsible for recycling of
materials; they break down organic matter into
inorganic components that primary producers
can absorb.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Trophic interactions are shown in diagrams
called food webs.
Arrows indicate the flow of energy and materials
—who eats whom.
Figure 45.6 A Food Web in the Yellowstone Grasslands
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Gross primary productivity (GPP)—total
amount of energy that primary producers
convert to chemical energy.
Net primary productivity (NPP)—energy
contained in tissues of primary producers and
is available for consumption.
Change in biomass of primary producers (dry
mass) per unit of time is an approximation for
NPP.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Ecological efficiency is about 10%:
Only about 10% of the energy in biomass at one
trophic level is incorporated into the biomass of
the next trophic level.
This loss of available energy at successive levels
limits the number trophic levels in a community.
Concept 45.3 Trophic Interactions Determine How
Energy and Materials Move through Communities
Ecological efficiency is low because:
• Not all the biomass at one trophic level is
ingested by the next one.
• Some ingested matter is indigestible and is
excreted as waste.
• Organisms use much of the energy they
assimilate to fuel their own metabolism.
Concept 45.4 Species Diversity Affects Community Function
Species diversity has two components:
Species richness—the number of species in the
community.
Species evenness—the distribution of species’
abundances
Figure 45.9 Species Richness and Species Evenness Contribute
to Diversity
Less diverse than B
because it contains 3
equally abundant
species rather than 4
Most Diverse!
Less diverse than
B because it has
an uneven
distribution of the
4 species
46
The Global Ecosystem
Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Ecosystem—an ecological community plus the
abiotic environment with which it exchanges
energy and materials.
Ecosystems are linked by processes and
material movements.
Concept 46.2 Biological, Geological, and Chemical Processes
Move Materials through Ecosystems
All the materials in the bodies of living organisms
are ultimately derived from abiotic sources.
Primary producers take up elements from
inorganic pools and accumulate them as
biomass.
Trophic interactions pass the elements on to
heterotrophs.
Decomposers break down the dead and waste
matter pool into elements that are available
again for uptake by primary producers.
4 Biogeochemical Cycles
Water Cycle
Nitrogen Cycle
Carbon Cycle
Phosphorus Cycle
WATER CYCLE
The global water (hydrological) cycle:
Water is essential for life; makes up 70% of living
biomass.
Flowing water is an erosion agent and transports
sediment—moves material around the planet.
Because of high heat capacity, water
redistributes heat as it circulates through the
oceans and atmosphere.
Figure 46.6 The Global Water Cycle
Concept 46.3 Certain Biogeochemical Cycles
Are Especially Critical for Ecosystems
Solar-powered evaporation moves water from
ocean and land surfaces into the atmosphere.
The energy is released again as heat when
water vapor condenses.
WATER CYCLE
Humans affect the water cycle by changing land
use:
• Reduced vegetation (deforestation, cultivation,
etc.) reduces precipitation retained in soil and
increases amount that runs off.
• Groundwater pumping depletes aquifers, brings
water to surface where it evaporates.
• Climate warming will melt ice caps and glaciers
and cause sea level rise and increased
evaporation. Water vapor is a greenhouse gas.
NITROGEN CYCLE
The global nitrogen cycle:
Involves chemical transformations.
N2 gas is 78% of the atmosphere, but most
organisms cannot use this form.
Nitrogen fixation: some microbes can break the
strong triple bond and reduce N2 to ammonium
(NH4+).
Figure 46.7 The Global Nitrogen Cycle
NITROGEN
Other microbial species convert ammonium into
nitrate (NO3−) and other oxides of nitrogen.
N-fixing reactions are reversed by yet another
group of microbes in denitrification, which
returns N2 gas to the atmosphere.
NITROGEN
Human activities affect the nitrogen cycle:
• Burning fossil fuels, rice cultivation, and raising
livestock releases oxides of nitrogen to the
atmosphere.
• These oxides contribute to smog and acid rain.
• Humans fix nitrogen by an industrial process to
manufacture fertilizer and explosives.
NITROGEN
• Topsoil and dissolved nitrates are lost from
farm fields and deforested areas by wind and
water runoff.
• The nitrates are deposited in aquatic
ecosystems and result in eutrophication—
increased primary productivity and rapid
phytoplankton growth.
Decomposition of the phytoplankton can
deplete oxygen; other organisms can not
survive, and dead zones form offshore in
summer.
Figure 46.9 High Nutrient Input Creates Dead Zones
NITROGEN
• Excess nitrogen in terrestrial ecosystems can
change plant species composition.
Species adapted to low nutrient levels grow
slowly, even when fertilized, and can be easily
displaced by faster-growing species that take
advantage of additional nutrients.
In the Netherlands, this has caused 13% of the
recent loss of plant species diversity.
CARBON
The global carbon cycle:
Movement of carbon is linked to energy flow
through ecosystems; biomass is an important
pool.
The largest pools occur in fossil fuels and
carbonate rocks.
Photosynthesis moves inorganic carbon from the
atmosphere and water into the organic
compartment; respiration reverses this flux.
Figure 46.10 The Global Carbon Cycle
CARBON
Dissolved CO2 in the oceans: some is converted
by primary producers, and enters the trophic
system.
Organic detritus and carbonates continually drift
down to the ocean floor.
Some organic detritus in ocean sediments is
converted to fossil fuels. Carbonates can be
transformed into limestone.
CARBON
Human activities affect the global carbon cycle:
• Any activity that impacts primary productivity
can alter fluxes.
• Runoff brings carbon to aquatic ecosystems.
• Deforestation and fossil fuel burning increase
atmospheric CO2.
• Atmospheric CH4 is increased through livestock
production, rice cultivation, and water storage
in reservoirs (microbes in water-logged soils
produce CH4).
CYCLES ARE CONNECTED!
Biogeochemical cycles are interconnected.
If carbon uptake by primary producers increases,
uptake of P, N, and other elements also
increases.
If decomposition rates increase, flux of elements
back to inorganic compartments increases.
Any nutrient can limit biological functions; the
limiting one is the one that is in lowest supply
relative to demand.
CYCLES ARE CONNECTED!
Biogeochemical cycles can interact in hard-topredict ways.
Increased atmospheric CO2 can increase wateruse efficiency by terrestrial plants;
In a high CO2 environment, the plants have
stomata open less, which reduces loss of water
vapor.
Concept 46.4 Biogeochemical Cycles Affect Global Climate
All objects that are warmer than absolute zero
emit electromagnetic radiation.
Most of the incoming solar radiation is in the
visible range of wavelengths.
Some is absorbed in the atmosphere, some is
reflected back to space, and some is absorbed
by the Earth’s surface.
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Greenhouse effect:
Earth’s surface re-emits energy in longer, less
energetic infrared wavelengths.
Some of this infrared radiation is absorbed by
gas molecules in the atmosphere (greenhouse
gases).
The molecules are warmed and radiate photons
back to Earth’s surface, keeping the energy
within the Earth system as heat.
Figure 46.11 Earth’s Radiation Balance
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Greenhouse gases include H2O, CO2, CH4, N2O.
Without the atmosphere, Earth’s average surface
temperature would be about 34°C colder than
at present.
Keeling’s measurements from atop Mauna Loa
in Hawaii show a steady increase in CO2 since
1960.
Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are
Increasing (Part 1)
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Analyses of air trapped in glacial ice
demonstrate that CO2 and other greenhouse
gases began increasing after about 1880.
Average annual global temperature has also
increased.
Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are
Increasing (Part 2)
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Higher global temperatures are affecting climate:
• Hotter air temperatures
• A more intense water cycle, with greater overall
evaporation and precipitation.
• Precipitation will increase near the equator and
at high latitudes and decrease at mid-latitudes.
Concept 46.4 Biogeochemical Cycles Affect Global Climate
• Warming is spatially uneven, so precipitation
changes will be season- and region-specific.
• In general, wet regions are expected to get
wetter and dry regions drier.
Precipitation trends in the twentieth century
support these expectations.
Figure 46.14 Global Precipitation Patterns Have Changed
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Warming may also increase storm intensity.
Strong hurricanes (category 4 and 5) have
become more frequent since the 1970s.
Concept 46.4 Biogeochemical Cycles Affect Global Climate
Human activities affect Earth’s radiation balance:
• Adding greenhouse gases to the atmosphere
• Deposition of dust and dark-colored soot
particles (“black carbon”) from fossil fuel
burning increases amount of solar energy
absorbed by snow and ice—increases melting.
Concept 46.4 Biogeochemical Cycles Affect Global Climate
• Adding aerosols to the atmosphere increases
reflectance of solar energy, less reaches
Earth’s surface.
When all human effects are added to climate
models, climate scientists conclude human
activities have contributed significantly to
recent climate warming.
Concept 46.5 Rapid Climate Change Affects Species and
Communities
Recent warming and other climate changes are
far more rapid than anything organisms have
experienced in their evolutionary histories.
Life cycles have evolved so that critical events
occur at favorable times of year.
Climate change is altering the timing of
environmental cues.
Rates of evolution may be too slow to keep up
with an environment that changes too rapidly.