Download Ecosystems, Energy And Production

Ecosystems, Energy
And Production
Kenneth Williams
Fisheries Extension Specialist
Langston University
Aquaculture Extension
Program
Ecological Communities
Loose term
Assemblages of plants, animals and
microbes that have colonized particular
locations.
Biotic community + physicochemical
environmental factors.
Aquatic Communities
Energy
Energy flows through the ecosystem and
is used only once.
Minerals and nutrients are recycled or
used over and over again in ecosystem.
Ecosystem Characteristics
Biotic and abiotic components of the
ecosystem are intimately connected.
One cannot be understood without
including the other.
Diversity
2 main components
Species richness – number of species in
a community or habitat.
Species equitability – evenness of
distribution numerically among species.
Maximum equitability would be if all
species in a sample were represented
equally.
Diversity
Shannon / Weaver Index - a measure of
species equitability.
It use to be thought that diversity =
stability.
Not necessarily so.
Community Succession
Community species composition may alter
over time.
One group of species may replace
another.
Succession may result in a climax
community or it may be a cyclical
succession.
Aquatic
Succession
Community Disruption
Community structure and succession can
be disrupted by introduction of exotic
species.
Ex. Largemouth bass in Lake Atitlan.
Food Webs
Primary producers – plants
Community primary consumers,
(herbivores) and omnivores use primary
producers for food.
These organisms are fed on by secondary,
tertiary, etc. consumers, (carnivores).
Decomposers – microbes that gain energy
from decaying consumers and producers.
Ecologically Equivalent Species,
AKA, Ecospecies
Different species that perform the same
ecological function in separate
communities
Ex. Bluegill sunfish in N. Am. – convict
cichlid in S. Am.
Biogeochemistry and cycles
Interaction among the biosphere,
atmosphere, lithosphere and hydrosphere.
Water cycle – nitrogen cycle etc.
Biosphere in equilibrium with physical
environment
Energy flow in ecosystems
Only minerals and nutrients are recycled.
Energy passes through the system. It is
not recycled and must be continually
replenished.
Second law of thermodynamics
Disorder tends to increase with time. So it
takes energy to maintain any system over
time. Energy flows from a region of
concentration to one of lesser
concentration and is degraded as it is
transformed.
Measuring community
metabolism
Gross total photosynthesis (P) during
daylight hours is compared with total
respiration (R) over 24 hours.
P/R Ratio can be established this way
without dealing with each individual
organism.
Measuring community
metabolism
P/R Ratio varies daily and seasonally
Oligotrophic lakes have P/R ratios around
1.
Eutrophic lakes the P/R ratio is often much
greater than 1. Excess production is
stored in sediments and does not break
down until oxygen becomes available.
During cloudy weather or ice cover,
P/R ratio less than 1. More oxygen used
than is produced.
Pollution sequence in streams
and rivers
Immediately below pollution source – P/R
less than 1, no photosynthesis, low
oxygen. – farther downstream in the early
recovery zone, photosynthesis increases.
Heavy algal production present. –
Even further downstream – primary
production and respiration lessen, P/R
ratio approaches 1.
Primary Production
The energy approach to studying
ecosystems. The goal is balancing the
energy budget.
Biomass produced from sun is accounted
for throughout ecosystem.
Primary Production
primary production = total oxygen
produced, (subtracting for oxygen used in
respiration).
Primary producers (autotrophs) 2
kinds
Chemoautotrophs – bacteria. Energy
source – inorganic chemical bonds in
compounds of sulfur nitrogen Or ferrous
iron. Ex. Sea floor hydrogen sulfide vents
support tremendous communities of sulfuroxidizing bacteria
Primary Producers
Photoautotrophs – photosynthetic
organisms, mostly plants. Energy source
– solar radiation.
Primary Producers
Both kinds of producers require an energy
source and usable inorganic carbon.
Photosynthesis produces most new
organic compounds. Phytoplankton most
important producers.
Biomass
Eltonian pyramid used to show
relationships among ecosystem trophic
levels.
Pyramids can be constructed in terms of
numbers, mass or energy.
Tiny organisms generally have low
standing crops but high productivity.
Assimilation Number
The mass of chlorophyll a is very closely related
to primary production.
A fairly constant relationship exists between
chlorophyll and photosynthesis at any given light
intensity.
Assimilation number – The milligrams of C fixed
per m3 during an average hour of daylight is
divided by the mg of chlorophyll a in the same
volume.
Mg C per hour
___________
mg chlorophyll a = assimilation number
Assimilation Number
This is important because chlorophyll a is
easy to measure so it can be used to
determine the amount of carbon fixed
(Primary Production).
Primary Production
3 other methods to measure primary
production
Oxygen released over a period of time.
Radiocarbon uptake rate.
pH change caused by removal of carbon
dioxide from water by photosynthesis.
Primary Production
Primary production efficiency
Efficiency low. 1-2% (only 1-2 % of
available sunlight is used.)
Secondary Production
Derive food from primary production – The
animal members of the community.
Includes: Herbivores, Omnivores and
Carnivores (predators).
Secondary Production
Assignment to distinct trophic levels is
difficult. They often occupy more than 1
level.
Categories: primary, secondary, tertiary
and quaternary consumers.
Secondary Production
Measuring secondary production is
difficult. Complications arise from
mortality, reproduction and predation.
Estimating Secondary
Production
Goal is to balance energy inputs and flow
through each trophic level.
Can estimate:
Calories of energy used in growth.
Metabolic loss through excretion and
respiration.
Energy eliminated with feces
Estimating Secondary
Production
Net production through life span can be
determined by measuring:
Body growth
Reproductive organ gamete production
(eggs)
Energy in molted products (exoskeletons,
feathers ,etc.).
Energy Budget
Energy budget equation
C=P+R+F+U
C = consumption, P = energy content
of the biomass from food digested, R =
respiration (energy converted to heat and
lost) F = egesta, undigested food
passed through body. U = excreta
Useful Generality
Approximately 99% of solar radiation
energy lost through primary production.
There is about a 90% loss of energy
through each following trophic level.
This means that the biomass of the first
carnivore level should be about 1% of
primary production. Or 0.01% of solar
radiation
Cascading Effects
Happenings in one trophic level can effect
some or all others.
Example. Lake Tanganyika. Snails
develop hard shells. Fish and crabs
develop strong jaws and claws to eat
these snails. Body changes in prey
species can be brought about the
presence of predators. This is called
cyclomorphosis.
The End