Ecology
I. Introduction
A. Definition
The study of the interactions between organisms &
organisms with their environment.
B. Parameters
1. Abiotic – non-living. Like?
2. Biotic – living. Like?
C. Levels of Organization
1. Chemistry
Subatomic Particles
Atoms
Molecules
Macro - Molecules
2. Biology
Organelles
Cells
Tissues
Organs
Organisms
3. Ecology
Population
Community
Ecosystem
D. Distribution of Life
Biome
Biosphere
1. Dispersal Limitations
a. Not all areas are accessible – geographic isolation
b. Each species has an actual and a potential range
Potential range = area over which a species could
survive if transplanted
2. Behavior and Habitat Selection
a. Animals mainly
3. Biotic Factors
a. Disease
b. Herbivory
c. Absence of symbionts
d. Lack of pollinators
e. Competition
4. Competition
a. Factors
i. Whenever the quantity of useful matter or
energy falls below the level needed for the
maximal growth of two or more organisms which
must draw on the same supply, a contest begins.
ii. The more similar the needs the greater the
intensity of competition.
iii. Competition from introduced species can
shrink an organism’s actual range
b. Reasons?
i. water
ii. nutrients (minerals)
iii. light
iv. heat
v. carbon dioxide, oxygen
vi. space
vii. pollinators
Strategies????
5. Abiotic Factors
a. Limits
i. Climate
Varies from place to place, season to season.
Each organism has an optimum environment needed for
maximum growth.
Temperature & annual precipitation (climate vs.
weather) are the most important factors
determining the distribution of organisms on a
global scale (biomes).
……Thus scientists predict that climate change may
radically alter the distribution of organisms/ecosystems
on earth.
Fig 52.9
Effects of climate on biogeography
Climate varies with latitude because of
differences in the angle of sunlight (seasons)
Solar radiation creates wind currents, ocean
currents, and precipitation (from evaporation)
Fig 52.4
Coriolis Effect
Fig 52.3 & 5
ii. Weather = Local climate
Proximity to water, mountains
E or W side of land mass
S slope drier than N slope (thus different plant
communities)
iii. Precipitation = Microclimate
Forest floor vs. canopy
Under a log
Within the litter layer
Your ecosystem type: coastal temperate rainforest
Fig 52.6
Fig. 52.13
II. Biomes
A. General Characteristics
1. Limits Locations of the earth’s biomes due to:
a. Latitude – affects temperature, precipitation
b. Positions of the continents
2. Structure One biome type may occur in different
areas of the world but different plant species but same:
a. Physiognomic structure – size; shape; types of
organisms & their relation to each other & the physical
Environment
b. Due to convergent evolution – similar
phenotypes due to similar selection pressures over time.
Similar climate, soils, disturbance patterns,…
B. Types
Fig. 52.8
1. Terrestrial (figure 52.12)
a. Name
Tropical rainforest
b. Location
Equatorial region
c. Characteristics
High average annual temp and precipitation,
Lush, dense vegetation, Very diverse! Large vertical
stratification due to competition for light (Canopy)
a. Name
Savanna
b. Location
rimming Equatorial region
c. Characteristics
Grasslands with scattered trees, Large
herbivores & predators, Rainy & dry season! Fire
adapted
a. Name
Desert
b. Location
Along Tropic of Cancer and Capricorn (23.5o)
c. Characteristics
< 30 cm of rain per year, High temperatures,
CAM plants! Unique plants with adaptations to harsh
environment
a. Name
Chapparal
b. Location
Along rugged hilly salt water coasts
c. Characteristics
Evergreen shrubs, Hot dry summers, mild
wet winters, Fire-dependent! – seeds germinated
after fire, roots fire-resistant
a. Name
Temperate Grassland
b. Location
Along 30o N and S parallel, inland
c. Characteristics
No trees, Typically 4 seasons, Occasional
fire, Fertile soils
a. Name
Temperate deciduous forest
b. Location
Along 30o N and S parallel coastal
c. Characteristics
Deciduous trees, 4 seasons (cold winter –
dormant), Open forests
a. Name
Coniferous Forest
b. Location
N hemisphere above 30o or elevation
c. Characteristics
Evergreen trees (gymnosperms), Largest
Biome on earth, 4 seasons, large amounts of snowfall
a. Name
Tundra
b. Location
N hemisphere or high altitude
c. Characteristics
Permafrost – permanently frozen subsoil,
Very cold, high winds, No trees or tall plants, 20%
of land area on earth, Low annual precipitation
2. Aquatic (Figure 52.12)
a. Name
Fresh water, relatively still - Lakes
b. Location
???
c. Characteristics
Thermocline, vertical zones, turbidity
varies, oligotrophic versus eutrophic
a. Name
Fresh moving water - Rivers and Streams
b. Location
???
c. Characteristics
Current, temperature and turbidity varies,
vertical zones
a. Name
Wetlands
b. Location
???
c. Characteristics
Temporary to semi-permanent, temperature
and turbidity varies
a. Name
Estuaries
b. Location
???
c. Characteristics
Salt fluctuations, temperature, depth, and
turbidity varies
a. Name
Oceanic
b. Location
Duh?
c. Characteristics
Salt fluctuations, temperature, depth, and
turbidity varies, vertical zones
Fig 52.12
Plant Population Ecology
I. Introduction
A. Characteristics
1. Dispersion
a. Patterns of Dispersion:
i. Clumped – individuals in patches (ex. due to
soil types, seed dispersal by animals)
ii. Uniform – evenly spaced due to: Competition for
resources or Allelopathy – plants secrete chemicals to
inhibit nearby growth
iii. Random – unpredictable; position of one individual
cannot be predicted from position of another.
Allelopathic plant
Rows of black walnut
interplanted with corn in an
alley cropping system
Rows of Leucaena
interplanted with crops in an
alley cropping system
Lantana, a perennial woody
weed pest in Florida citrus
Sour orange, a widely used
citrus rootstock in the past,
now avoided because of
susceptibility to citrus tristeza
virus
Red maple, swamp chestnut
oak, sweet bay, and red cedar
Eucalyptus and neem trees
Chaste tree or box elder
Mango
Tree of heaven
Rye, fescue, and wheat
Broccoli
Jungle rice
Forage radish
Jerusalem artichoke
Sunflower and buckwheat
Impact
Reduced corn yield attributed to production of juglone, an allelopathic compound from black walnut,
found 4.25 m (~14 ft) from trees
Reduced the yield of wheat and turmeric but increased the yield of maize and rice
Lantana roots and shoots incorporated into soil reduced germination and growth of milkweed vine,
another weed
Leaf extracts and volatile compounds inhibited seed germination and root growth of pigweed,
bermudagrass, and lambsquarters
Wood extracts inhibited lettuce seed as much as or more than black walnut extracts
A spatial allelopathic relationship if wheat was grown within 5 m (~16.5 ft)
Leachates retarded the growth of pangolagrass, a pasture grass, but stimulated the growth of bluestem,
another grass species
Dried mango leaf powder completely inhibited sprouting of purple nutsedge tubers.
Ailanthone, isolated from the tree of heaven, has been reported to possess non-selective postemergence
herbicidal activity similar to glyphosate and paraquat
Allelopathic suppression of weeds when used as cover crops or when crop residues are retained as
mulch
Broccoli residue interferes with growth of other cruciferous crops that follow
Inhibition of rice crop
Cover crop residue suppression of weeds in the season following the cover crop
Residual effects on weed species
Cover crop residues reduced weed pressure in fava bean crop
Clumped lupine
Uniform dispersal of sagebrush
Random trees
2. Population Size
a. Demography = study of factors that affect the
growth & decline of populations
i. Increase by reproduction, immigration
ii. Decrease by death, emigration
Change in Population size = (B + I) – (D + E)
If B – D = 0, then zero population growth
Fig. 53.15
b. Life History = events from birth, through
Reproduction, to death
i. Dormancy, germination, growth, reproduction,
dispersal, death
ii. Trade-offs between investments in reproduction
& survival when there are limited resources
Controls at every stage of life history
death
New resources
reproduction
available, perfect
growing conditions,
mature plant
freedom from
disease, competition,
growth
drought
Herbivory, disease,
competition,
drought, flood,
freeze
seedling
Seeds rain
from mature
plants
Dormancy (seed bank)
Seeds washed
away, eaten,
decomposed
3. Growth
a. Patterns
i. Exponential
Occurs when resources are abundant or when an important
constraint has be removed.
Ex. Recolonization after fire
Represents a doubling of the population in a specified time.
The j-shaped curve
Number of
Individuals
Time
ii. Logistical
Steady increase followed by a plateau due to ????.
Initial population
density
Logistic growth
Number of
New population
density
Individuals
Time
b. Limits Biotic Potential (r)
i. Intrinsic Factors
Plenty of food, living space, and other resources.
No competition
Habitat is free of predators and pathogens.
Density & competition for resources will
cause reproduction rates to decline or stabilize.
Any essential resource that is in short supply is
a limiting factor on population growth.
•
•
•
•
•
Food (Why?)
Micro-nutrients
Refuge from predators
Living space
Pollution-free environment
ii. Environmental resistance affects the number of
individuals of a given species that can be sustained
indefinitely in a particular area.
Naturalization
K
Number of
Colonization
Individuals
Introduction
Time
iii. Carrying Capacity (K)
The maximum population size a particular area or habitat
can support at a particular time.
Is not fixed - K may decrease when a large population
damages or depletes its own resource supply.
4. Control
a. Factors
i. Density Independent Control
ii. Density Dependent Control
5. Adaptations
a. At low density, a population is limited only by
intrinsic rate of growth (r)
b. At high density, population is limited by
carrying capacity (K)
c. r versus K strategy
d. Competitive, Ruderals, or Stress Tolerant
i. r - selection
Disturbance creates low-density conditions, frees
resources (fire, flood, volcano)
Biotic potential (r) limits population size
Adaptations that are successful for these conditions:
– Produce large # of seeds fast
– Wind dispersal of seed
– Plants grow & flower quickly (annuals)
– Few chemical/mechanical defenses
ii. K-selection
High density, population size close to K
Not much “new” space – competition for resources
Adaptations that are successful for these conditions:
– Perennial
– Fewer, larger seeds
– Defenses against herbivores, pathogens
– Adaptations to shading, poor soils
K & r selected species exist together because smallscale disturbances create space (exposed soil) for r
species (colonizers)
– Ex. Downed tree, badger holes, grazing
disturbance
Plant Community Ecology
I. Background
A. Definition
1. Groups of organisms of different species (populations)
living and interacting with each other and the habitat
B. Hypothesis of Structure
1. Question?
Are plant communities a real entity in nature? Why
are certain species found together?
2. Hypotheses:
a. Individualistic hypothesis - Gleason
i. Species are found together in nature because they have
similar abiotic requirements
ii. No distinct boundaries between communities
iii. Each species distributed along its tolerance range
iv. Thus communities change continuously along a
gradient
b. Integrated Hypothesis - Clements
i. Plant communities function as a real, integrated unit.
ii. Plant species found together because of interactions
with each other & the rest of the ecosystem.
iii. Thus species are clustered into discrete communities
with definite distribution boundaries.
Which is correct?
c. So? Individualistic/Continuum “more correct”, but
evidence of both – some sharp boundaries due to dramatic
environmental changes.
II. Characteristics of communities
A. Diversity – composed of:
1. Richness – the total number of species in the
community
2. Evenness – the relative abundance of
species in the community (some dominant, some rare)
a. Relative abundance = # individuals of
species X divided by total # of individuals in the
community
Fig 54.11
Which community is more diverse??
Fig. 54.11
B. Factors
1. Abiotic
a. Each species has a tolerance range – range
of conditions under which it can survive & reproduce
b. Climate – temp, moisture
c. Soil – types, pH
d. Latitude & Altitude
e. Disturbance
i. Decrease or total elimination of the biotic
components of the habitat
ii. Results: decrease in biomass, diversity
iii. Natural events – fire, flood, volcano, avalanche
iv. Human-caused – herbicides, roads, development,
logging, grazing, farming, mining
v. Opens resources, creating opportunities for new
species, different composition
vi. All communities have evolved with some type of
disturbance, varying in type, frequency, & severity
vii. Small-scale, frequent disturbance
Creates patches within the ecosystem
Thus increase in diversity
Ex. Trees downed in wind storm
Can prevent large-scale disturbance – fire!
Ex. Yellowstone fire of 1988
Fire suppression in fire-dependent ecosystem
caused massive, stand-replacing fire
viii. Human Caused
Example Cheatgrass – wildfire cycle
Overgrazing in ecosystem that did not evolve with
large herbivores
Cheatgrass introduction
Decrease in fire frequency (100 yr to 5 year cycle)
Conversion of ecosystem with tremendous loss of
Diversity
These types of problems creating mass extinction
worldwide.
2. Biotic
a. The plant itself
i. Can modify the environment
ii. Modifications can be +, -, or neutral to the plant
iii. Benefit ex: beech/oak forest creates shade
needed for other young beech & oak to grow
iv. Detriment ex: pine forest creates shade but
pines need lots of light to grow (succession)
b. Other plant species
i. Theory of competitive exclusion: When two
species compete for the same limiting resource
(occupy the same niche), the species that is less
adapted will be excluded from the community by the
superior competitor.
If this theory is true, then actually very little competition in
nature, because each plant occupies a niche.
Species B
Species A
A
low
B
C
Light intensity 
D
high
Resource partitioning creates niches
Species A
A
Species B
B
C
D
ii. Niche
A set of conditions exploited best by only one species
Includes all aspects of a species’ use of biotic & abiotic
resources (microclimate, rooting zone, pollinators, etc.)
A species’ role in the ecosystem.
c. Other (non-plant species)
i. Mutualism – both organisms benefit
Examples:
Mycorrhizal fungi, N-fixing bacteria in root nodules
Pollinator gets nectar and plant gets pollen transfer
Animals eat fruit (nutrition) and seeds are dispersed
Acacia trees get defense from herbivores & ants get
home, food
ii. Commensalism – one species benefits & other is
not affected
Bird nests in trees, seeds stuck on animal fur
iii. Competition – both harmed
iv. Predation – one harmed, other benefits
Herbivory
Pathogens
Predation or the need to keep your wits about you?
C. Controls on community structure
a. Dominant species = species with the highest
abundance or biomass in the community
i. Best species among all species in the
community at exploiting the limiting resource
ii. Controls occurrence & distribution of other
species
iii. If eliminated, other species take over
Example: Douglas fir
b. Keystone species
i. Control community structure by their ecological role
ii. If eliminated, drastic change in community structure
or composition Example Sea otter – reduction in
populations caused boom in sea urchin population,
destroying kelp forests (drastic decline in diversity)
Succession
III. Succession
A. Definition
1. Changes in community structure &
composition over time following a disturbance
2. Species thriving on a site are gradually
replaced by other species.
3. Species replacement continues until the
composition of species becomes relatively steady
under prevailing climatic conditions & disturbance
regimes (dynamic equilibrium, not climax).
B. Types
1. Primary Succession
a. Characteristics
i. New area of mineral rock – no soil yet (volcano, glacier
retreat)
b. Sequence:
i. Lichens & mosses colonize bare rock
ii. As these decay, acids weather the rock & primitive soil
forms
iii. Pioneer plants establish (r-selected or Stress tolerant)
iv. Pioneers replaced by K-selected (Ruderal and
Competitive)
c. The Nature of Pioneer Species
i. Adapted to growing in habitats that cannot support
most species: intense sunlight, wide swings in
temperature, moisture deficits.
ii. Typically small plants, short life cycles, producing
an abundance of small seeds which are quickly
dispersed (wind & water)
iii. Can grow in N-poor soil because of their
mutualistic interactions with nitrogen-fixing bacteria.
Example of primary succession: glacial retreat
Alders & cottonwoods dominate
Spruce enter forest and replace alders/cottonwoods
Hemlock slowly replace Spruce. Hemlock is “climax”
iv. Facilitation
Improve the living conditions for other species, setting the
stage for their own replacement.
Accumulation of their wastes and remains adds volume to
the soil and enriches it with nutrients that allow other
species to take hold.
2. Secondary Succession
a. Characteristics
i. Plant community is destroyed but soil remains
while new soil exposed
ii. Examples?
abandoned farm fields, clear cuts, wind storms, fire.
iii. Typical progression: small herbs & grasses
shrubs trees
b. Pioneer species
i. r-selected (stress tolerant) (species move in first when
competition is low (low density).
ii. Sometimes these opportunistic species (especially
invasive weeds!) inhibit the growth of the native climax
species changing the structure and type of climax
community forever. Ex. cheatgrass
It has been a journey worth taking.