Lecture 32 - Ecology (part 3) Flashcards
What do community interactions rely on?
the species composition
Species diversity
number of species present
Relative abundance
the evenness or proportion of each species
Trophic structure
feeding relationships
Species richness
number of species
What do we usually equate biodiversity with?
species richness (number of species) • Need to also consider the relative abundance of each species….somethings are rarer in some communities than others
Why do ecologists use indexes?
to quantify the species composition
Shannon’s diversity index (H)
- ρA = relative abundance of species A, etc
- ln is the natural logarithm
- Higher H means higher diversity
𝐻 = −(ρ𝐴 ln ρ𝐴 + ρ𝐵ln(ρ𝐵) + ρ𝐶ln(ρ𝐶)…etc)
Higher H (in Shannon’s diversity index) means…
higher diversity
The transfer of food energy up ______ ______ from its source to its apex is called the ______ ______, which are linked together into complex _____ _____
trophic level
food chain
food webs
Food webs are _____ ______, but food chains are _____ ______ (4 linkages)
quite complex
generally short
Energetic hypothesis
suggests the length of a food chain is limited by the inefficiency of energy transfer along the chain
Trophic efficiency
is the ratio of production of energy at one trophic level to the next lower level
• Ie. The percentage of energy that consumers in trophic level gain and convert into biomass from the total stored energy of the lower level
Why is there energy loss?
Lost via heat from metabolism
What are the species with large impacts?
- Dominant species
- Keystone species
- Ecosystem engineers
Dominant species
are species in a community that has the HIGHEST abundance or collectively the HIGHEST biomass
What do dominant species exert?
Exert great control over the community
• Could be a result of competitive exclusion or the adaptations to avoid predation/herbivory and disease
Example of dominant species:
Ex. Sugar maples in eastern North America are dominant, resulting in shading
which affects the abiotic conditions of the underlying soil, which in turn affects
what other species are present
• Could be a result of competitive exclusion or the adaptations to avoid predation/herbivory and disease
Keystone species
are not abundant in the community (and quite often rare) yet EXERTS A STRONG CONTROL on community structure
Example of keystone species:
ex. Sea otters are keystone species in kelp forests
• They feed on sea urchins, which can eliminate kelp forests
• Removal of the otters resulted in overgrazing of the urchins on the kelps, wiping out kelp populations and altering the community structure
Ecosystem engineers
dramatically alter their community by CHANGING the PHYSICAL environments within the community
Examples of ecosystem engineers:
• Ex beavers building dams and flooding streams and meadows
• Ex foxes in the arctic
- Den sites are rich in nitrates from fecal matter and decaying prey items
- Add nutrient loads to an otherwise nutrient poor arctic tundra
- Provides nutrients for lush vegetation and grasses in otherwise barren landscape
What controls the biomass of a species?
- Top-down control (Trophic cascade model)
* Bottom-up control
Top-down control (Trophic cascade model)
reducing number of predators increases prey
• ie. Predation limits herbivores, which limits plants, which limits nutrient uptake
Bottom-up control
increase in food, increases higher trophic levels
• ie nutrient levels control plants, which controls herbivores, which controls predators
Disturbances and succession can also affect…
species composition
Intermediate disturbance hypothesis
states that MODERATE amounts of disturbance harbours the HIGHEST species diversity
• High levels of disturbance stress species out and low levels of disturbance allows for dominant species to out-compete others
Ecological succession
disturbed areas may be colonised by different species, which in turn get replaced by other species
Primary succession
building a community from initially nothing (such as a new volcanic eruption or on debris left behind glacial retreat) -> can take 100s to 1000s of years
• Lichens are usually the first to colonise newly disturbed areas and start weather rock into soils. Mosses follow shortly after
• Then they are overgrown by grasses and fast growing shrubs and trees and become the community’s dominant vegetation
Secondary succession
occurs when the existing community has been cleared by a disturbance that leaves the soil intact (ie forest fires, floods, insect swarms)
• Earliest plants to take the area over again are faster growing herbaceous plants that had seeds carried by animals or wind
• Woody shrubs and trees come in later
Where does energy flow & chemical cycling occur?
in every ecosystem regardless of its size
Describe energy flow & chemical cycling:
- Energy enters ecosystems via light
- Converted to chemical energy by autotrophs (photosynthesis in primary producers)
- Passed to heterotrophs from eating plants and other animals
- Lost through heat
What do ecologists study?
interactions of organisms with the physical environment so they utilise a lot of chemistry and physics concepts
What are the conservation of energy (Laws of Thermodynamics)
- Energy cannot be created nor destroyed, but only transferred or transformed
- The amount of energy stored in organic molecules equals the amount of solar energy intercepted
- A lot of energy is lost as heat, which increases the entropy of the environment
What are the conservation of mass?
- Matter cannot be created nor destroyed (Law of Conservation of Mass)
- Chemical elements as organisms decay are recycled into the environment
Order of trophic levels (bottom to top)
- primary producers
- primary consumers
- secondary consumers
- tertiary consumers
- detritivores
Primary producers
The largest trophic level (photosynthetic autotrophs)
What is the largest trophic level?
primary producers (photosynthetic autotrophs)
Primary consumers
heterotrophs, usually herbivores
Secondary consumers
usually predators (carnivores)
Tertiary consumers
carnivores eating carnivores
Detritivores
There are also detritivores (decomposers) that eat decaying organic matter (dead animals, fecal matter, fallen leaves and wood)
What are detritivores considered?
a primary consumer
What are detritivores eaten by?
Eaten by secondary and tertiary consumers
Primary production (definition)
The amount of light energy converted to chemical energy by photoautotrophs
• Since primary consumers get their energy second hand (by eating primary producers), primary production sets the energy budget
Gross primary production (GPP)
the amount of energy from light (or chemicals from chemoautotrophs) converted
to chemical energy of organic molecules per unit time
Net Primary Production (NPP)
GPP – energy used by primary producers for their own metabolism (respiration)
• ~1/2 of GPP • Usually expressed as energy J/(m2 x year) or biomass g/(m2x year)
• Reflected of the amount of new biomass added in a given time
Net Ecosystem Production (NEP)
total biomass accumulation per unit time (GPP - total respiration of all organisms)
In aquatic ecosystems, what are important in controlling primary production?
light and nutrients
Light limitation
- Depth of light penetration affects the primary production in the photic zones in water bodies
- Half of all solar radiation is absorbed in the first 15 m of water
Nutrient limitation
- Limiting nutrients must be added for primary production to increase (usually N or P, but others can be limiting too)
- Concentrations are LOWER in the PHOTIC ZONE because they are readily absorbed by primary producers
- Eutrophication occurs when TOO MUCH limiting nutrient is added (ex. Lake Winnipeg)
Limiting nutrients…
must be added for primary production to increase (usually N or P, but others can be limiting too)
Why are concentration low in the photic zone?
because they are readily absorbed by primary producers
Eutrophication
occurs when too much limiting nutrient is added (ex. Lake Winnipeg)
In terrestrial ecosystems, soil nutrients…
limit primary production
What are often the limiting nutrient?
Nitrogen and phosphorous
Nitrogen
limits plant growth most
Phosphorous
limitations common in older soils where P has leached away over time or precipitates due to basic soils
How does plant symbioses help primary producers?
overcome a lot of these limitations
• Mycorrhizae
• Nitrogen-fixing bacteria
Climate change increases in…
temperatures and changes in precipitation
What can affect NPP?
climate change
Overall NPP has…
increased 6% between 1982 – 1999 in terrestrial ecosystems, especially in tropical rainforests
NEP >0
ecosystem is storing more carbon (ie carbon sinks)
NEP <0
ecosystem is losing more carbon than it stores (ie carbon source)
Secondary production
The amount of energy that is converted from the consumer’s food to the consumer’s biomass in the ecosystem
• Cannot completely digest all that they consume, so is eaten by detritivores
Production efficiency
is the percentage of energy stored in assimilated food that is not used in metabolic processes in an individual
Production Efficiency =
𝑁𝑒𝑡 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑥 100% /
𝐴𝑠𝑠𝑖𝑚𝑖𝑙𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜�
Trophic efficiency
is the percentage of production transferred from one trophic level to the next
Why is trophic efficiency always less than production efficiences?
because they take into account the energy loss via feces and metabolism AND energy stored in organic matter at lower trophic levels that has not been consumed
What is trophic efficiency usually?
- Usually about 10%, but can range from 5%-20%
* In other words, 90% of available energy at one trophic level is not transferred to the next
What gets recycled within the ecosystems?
Chemical
What does carbon form?
the framework for all of life’s organic molecules
What is CO2 used by?
by plants in photosynthesis and converted to sugars that are used by consumers
How is CO2 returned to the ecosystem?
via respiration
What is much of the carbon stored as?
fossil fuels, soils, sediments in aquatic ecosystems, dissolved in oceans as calcium carbonate, atmospheric CO2 and plant/animal biomass
What does burning of fossil fuels & wood add?
adds more CO2 to the atmosphere, as well as volcanic eruptions
What does increased forest fires & peat bog fires also contribute to?
also contribute to everincreasing CO2 levels in the atmosphere
