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Species, Populations,
Interactions in Water Ecosystems
We are being hired to:
• Research
for writers of
a science fiction book and screenplay.
• The writers want to create a doomsday
scenario in a scientific, research-based context
Our job:
Provide comprehensive input about:
• Physical, chemical, and biological properties of
water environments
• Species interactions
• Population dynamics
• Human impacts
water ecosystems
Marine (Ocean) / Reefs
Mangroves / swamps
Estuaries / Wetlands / Lagoons
River / Riparian
Ice / Glaciers
Physical, Chemical
Geographic location or location type
Presence of oxygen, nutrients, salt
Geological factors – rock, soil
Chemical factors – inorganic reactions
Species and Niche
Community Properties
Environmental Pressures
Population Dynamics
Properties of Water
Makes up 70% of Earth’s surface
97% is salt, 2% is frozen, 1% is fresh
Greatest density at 4° C.
Due molecular polarity, it has high adhesion
High Specific heat - can absorb energy without
rapid temperature increase
Ice (solid) is less dense than liquid form
The most common solvent – ionic compounds
dissolve readily
Acid, base, neutral pH depending on solutes
Conducts electricity if salts are dissolved
Geographic Location or type
Mangroves occur along coastlines in tropical climates
Geographic Location or type
Wetlands occur at different latitudes
Zones - ocean
• Different depths
have different
• Ocean depths
range to 5 miles
• Energy sources
range from solar
to volcanic
Zones - Lake
Different depths
have different
Light, oxygen
levels, and
temperature all
determine plant,
While water depth determines how much light
gets through, turbidity is also a huge factor.
Turbidity of a water body can be impacted by
natural and human activity, and turbidity impacts
water ecosystems.
Temperatures change seasonally,
changing water density
Ocean temperatures:
latitude and currents
Arrows show the direction of water flow. The white current is
the Gulf Stream, which flows along the East Coast of NA,
across the Atlantic Ocean, and warms Western Europe.
Presence of oxygen, nutrients, salt
Geological factors – rock, soil
Sea sediment Jasper
Rare Earth metal deposits
Human Impact
• Chemicals –
Fossil fuel combustion biproducts
Manufacturing effluent
N2 and PO4 Fertilizers eutrophism, algal blooms
Herbicides, pesticides, pH
• Sediment
– Land management
– Forest management (or mismanagement)
• Fecal matter – human and animal waste
• Garbage
• Temperature
– Manufacturing effluent
– Global warming
• Tolerance for environmental conditions
• Limiting factors – temperature, nutrients, space, oxygen
Community properties
Primary productivity
Biodiversity – species richness
Abundance – # of organisms of a species
Complexity – # of species at each trophic level
– The more complex the food web,
the more resistant it is to disturbance
Communities in Transition
Primary Succession – life has never been there
and it starts
Secondary Succession – life was destroyed and
Climax Community – life has developed
complexity, abundance, and can develop no
Species and Niche
NICHE – an organism’s role in the community
Generalists – can survive in a wide range of habitats
Specialists – survive in only a narrow range of habitats
Indicator species reflect living
Keystone species – Exotic species –
play a significant
compete with
role; other species natives
depend on them
No two species can occupy the same niche and
compete for the same resources.
This will lead to either:
– Extinction of one species
– Behavior change
• Temporal isolation
• Geographic isolation
• Symbiotic cooperation
– Genetic change: Adaptation
Adaptation - Natural Selection
• Genetic traits that survive in harsh conditions
are passed onto offspring
• When members of a population are isolated
by (ecologic or geographic) barriers, they can
change enough to become a separate species
Population Change
J-curve - exponential growth without limit
S-curve - growth that responds to limits
Doubling time – 70 / rate of growth
Oscillation – cycles of growth and decline
Species Type
– r-adapted: high reproduction, high mortality
– K-adapted: few offspring, larger, live longer
Factors that impact populations
Life expectancy
Abiotic factors
– human impact on Earth Systems
– natural disasters
• Stress and crowding
• Conservation / Restoration efforts