Community Ecology, Population
Ecology and Sustainability
Chapter 4
General Types of Species
• Native – naturally live and coexist –
evolved through natural selection
• Non-native (exotic or alien) – accidentally
or purposefully introduced
• Indicator – species that can alert to
harmful changes
Species native to
Washington State
Species not native to
Washington State
Frogs are good indicator species because the life histories
are vulnerable to environmental disruption
No protective shells to block U/V
Plant, insect
prey expose
tadpoles to
insecticides
Decline in Frog Populations
• Tells us:
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Loss of habitat and fragmentation
Climate change (droughts)
Pollution
Increase in ultraviolet radiation
Should we care about
extinction? (especially to an
indicator species?)
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Telling us that environment is degrading
Important ecological roles
Benefits to humans
What are some local
Indicator species?
Organism Interactions
General Types of Species
• Keystone species
• Species that play roles affecting many other
organisms in an ecosystem.
• Removal of that species greatly changes the
entire ecosystem
Keystone predator (Pisaster) on Washington’s
rocky coast
Mussels will grow out of reach of Pisaster
Competition
• As resources get scarce,
COMPETITION becomes a factor.
– COMPETITION is the interaction that
results when one organism uses the
resource at the expense of another.
Interspecific competition
• Two organisms of different species compete to
obtain the same limited resource.
• In general, the more similar the competing
species, the more intense the competition.
Resource Partitioning and Niche
Specialization
Resource Partitioning and
Niche Specialization
Competitive Exclusion
• Interspecific competition – competition
between species for the same resource
• When one species eliminates another
by out competing, it is called
competitive exclusion.
Intraspecific Competition – between
members of the same species
Organism Interactions
• Predation - One animal kills/eats another.
– Predator benefits from food.
– Prey species may benefit by eliminating
non-adaptive genes from the gene pool.
Predator:prey Relationships
Living together – symbiotic
relationships
• Symbiotic relationship - Special, close,
physical relationship between two different
species. At least one species benefits from
the interaction.
• Commensal relationships – one species
benefits from another without harm
• Parasitism – one species benefits from
another with harm
• Mutualism – both species benefit
Commensalism – one
Benefits from the other
without harm
Parasitism – one benefits
from the other with harm
Mutualism – both benefit
Parasitism - One organism (parasite)
living in or on another organism
(host), from which it derives
nourishment.
• Mistletoe is a
parasitic plant
Commensalism - One organism
benefits - other is not affected.
– epiphytic plants like ferns, mosses
and orchids find a home on trees
– the epiphyte benefits
– the tree neither benefits
nor is harmed
Mutualism - Both species benefit - in many
cases neither can exist without the other.
Coral and the
dinoflagellate
zooxanthellae
Mutualism
Commensalism
Mutualism
Mutualism
Ecological Succession:
Communities in Transition
• Disturbance – an event that alters an
ecosystem, either significantly changing it,
or wiping it out entirely.
• Examples include fire, flood, volcano, serious
insect or disease outbreak, drought, glacier…
• Primary Succession
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Begins with bare mineral surfaces or water.
Nothing remains of the previous ecosystem.
Follows severe disturbance.
Hundreds or thousands of years
Succession
• Succession is often dictated by what time of
year the space opened up, and what
organism settled there first.
• Predators can ultimately determine the
ultimate species composition
• Outside disturbance increases diversity by
interfering with competitive exclusion
• Succession will eventually end up “climaxed”,
which is a community with a stable number
species and populations.
Succession
• Highest diversity occurs when there is
enough disturbance to prevent the
dominant competitors from taking over,
but not so much that the community is
unable to develop.
Predation is disturbance that allows other organisms and increases
biodiversity.
Primary Succession
Secondary Succession
• Occurs when an existing community is disturbed
or destroyed, but some parts are left behind:
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soil and organic matter
seed bank
rootstock or bulbs for re-sprouting
maybe some living plants
snags, logs
mycorrhizae (fungus and plant roots)
• Tends to be more rapid than primary succession.
Secondary Succession
Mt. St. Helens
May 18, 1980
Mt. St. Helens
Millions of trees were pulled
up by their roots and blown
over from the initial blast.
Mt. St. Helens
A new river carves a new channel
down the mountain side.
Mt. St. Helens
The first new plants to grow within the
zone were those started from seeds blown
in on the wind
Mt. St. Helens
New grasses and wildflowers were the first
plants to grow, and now 25 years later are
now thriving.
Mt. St. Helens
Some trees are starting to grow
back naturally.
Ecological Stability and Sustainability
• How predictable is succession?
• Depends on biotic, abiotic factors
• Pioneer Community – early colonizers
• Climax Community (like old growth
forests)
• Balance of nature – ongoing struggle by
different species for their essential life
requirements
Populations
• Population - Group of individuals of the
same species (humans or any other
species) inhabiting the same area
simultaneously.
• 4 variables govern size:
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Birth
Death
Immigration
Emigration
Populations
• Natality and Mortality
• Natality - Number of individuals added
through reproduction
• Birth Rate
• Mortality - Number of individuals removed
via death
• Death Rate
Population Density and
Spatial Distribution
• Population Density - Number of individuals
per unit area.
• Spatial Distribution - Describes where the
population is found, such as even or
clumped.
• Dispersal - Movement of individuals into
new areas.
• Emigration - Out movement
• Immigration - In Movement
Population Density and
Spatial Distribution
• Population Change =
(Births + Immigration) –
(Deaths + Emigration)
(Income) – (Expenditures)
Population Dynamics
• Biotic Potential - “r”
• intrinsic rate of increase
• Rate at which a population would grow if it had
unlimited resources
• Reproductive capacity, or ability of a
population to produce offspring.
• Usually higher than replacement level.
• Leads to exponential growth curve.
Carrying Capacity
• Carrying Capacity - Number of individuals
of a species than can be indefinitely
sustained in a given area.
• “K” stands for carrying capacity
Exponential and Logistic Growth
Food
limit
Pop’n exceeds carrying capacity of environment; moves or
switches to new resources
Population Density Effects
• Environmental Resistance - Any factor in the
environment limiting carrying capacity. Four
main types:
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Raw material availability – food, air, water
Energy availability
Waste accumulation and disposal
Organism interaction
• Density-dependent factors - gets more limiting
as population density increases (food, air, water,
space)
• Density-independent factors – does not vary by
density (climate)
Reproductive Patterns and Survival
• Not all species reach a stable carrying capacity
• Species can be broadly lumped into two
categories:
• K- selected species (competitors) logistic growth
• Small number of offspring, high parental care
• Late successional species
• r- selected species (opportunists) exponential
(boom or bust)
• Large number of offspring, low parental care
• Early successional species
Reproductive Patterns and Survival
The Role of Predation in Controlling
Population Size
 Predator-prey cycles
Human Impacts on Ecosystems
 Habitat degradation and fragmentation
 Ecosystem simplification
 Genetic resistance
 Predator elimination
 Introduction of non-native species
 Over-harvesting renewable resources
 Interference with ecological systems
Human carrying capacity may be interpreted as the maximum rate of
resource consumption and waste discharge that can be sustained
indefinitely without progressively impairing the functional integrity and
productivity of relevant ecosystems.
In other words…..
Resource consumption
Waste discharge
Functional integrity and
productivity of relevant
ecosystems.
Habitat Loss and
Fragmentation
Ecosystem Simplification
Genetic Resistance
Over-harvesting of Renewable
Resources
100,000 calories
1 million calories
10 mill calories
On average, 10% of energy in one trophic level is passed on to the
next higher level.
10,000 calories ?
1 million calories
10 mill calories
On average, 10% of energy in one trophic level is passed on to the
next higher level.
Introduction of nonnative species
Interference
with ecological
processes
Zooplankton
Nutrients
(nitrogen, phosphorus, carbon)
Hood Canal communities have seen tremendous
growth in recent years.
Nutrients
Zooplankton
Nutrients
(nitrogen, phosphorus, carbon)
The primary sources of nitrogen associated with human activities collectively put
between 100 to 300 tons of nitrogen into the canal every year, broken down as follows:
60% human sewage
14% agriculture manure
13% chum salmon carcasses
11% storm water runoff
Learning from Nature
• Principles of sustainability
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Solar energy
Population control
Biodiversity
Nutrient recycling