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Week 5: Ecology and Ecosystem Services

Terms in this set (44)

What is ecology?
The study of interactions between organisms and their environment (biotic and abiotic).

How are communities structured? How does energy cycle around ecosystems?
What are the 2 types of producers? How are they different and similar? Which dominate energy fixation in wetlands?
Photoautotrophs and chemoautotrophs.

Both fix organic C from CO2. Photoautotrophs use energy from the sun, while chemoautotrophs use energy from chemicals (ie, oxidizing Fe2+).

Photoautotrophs do >90% of energy fixation in wetlands.
What is the maximum trophic level of terrestrial ecosystems, and why?
4-5 trophic levels (quaternary/tertiary consumers), since the energy yield becomes too inefficient past that.
What is a trophic pyramid?
The idea that at each higher trophic level, energy/biomass/numbers decrease by 80-90%. This is because of energy being used up by respiration. Therefore, a community with more biomass at the base of the pyramid will have more potential to support more trophic levels and more biodiversity.
What is a food web?
A visual way of showing the energy and biomass flow through key species/species of interest in an ecosystem. Arrows show the direction of energy flow.
What is net primary productivity?
NPP = total producer fixation - producer respiration

Unit: g C m^-2 y^-1

The net rate of carbon fixed as biomass by producers.
What is the relationship between NPP and biodiversity? What might cause you to NOT see this relationship?
Globally, there is a positive relationship between them. But at small scales, ie comparing a few individual ecosystems, this is not always seen. This might be because of competition, where a highly competitive, high biomass species dominates over other species and reduces diversity.
How does NPP compare between wetlands vs uplands?
Uplands: NPP can be predicted by climate

Wetlands: NPP is more variable, due to factors like soil type and hydropattern

Overall, wetlands have less stored biomass than forests, but have a similar NPP.
How does NPP compare between tropical and temperate regions?
Tropical regions have higher NPP, due to receiving more sunlight and precipitation.
Assuming a temperate climate, how does NPP vary between wetland classes?
Bogs: lowest
Fens: almost as low as bogs
Marshes and swamps: highest
Coastal wetlands: high because of ocean water bringing in nutrients
How do different soil types affect NPP?
Carbonate soils (nutrient rich and circumneutral) tend to have higher NPP than nutrient poor silicic soils
How does hydropattern affect NPP?
Hydropatterns with alternating dry and wet periods promote the highest NPP (subsidy stress model), since the dry periods allow nutrient mineralization to occur.

The figure shows how periods where the water table is below ground (to the left of the dotted line) have the highest NPP.
What is species diversity? what are 2 ways to measure it?
The number or variety of species in the world/a region.

Can be measured by:
1. richness: the # of species
2. evenness/relative abundance/equitability (all the same thing): skewness or evenness of the #s of different species
What are 3 controls on biodiversity?
1. habitat diversity (ie, lots of microhabitats)
2. competition
3. hydropattern
What are microhabitats? How do they compare between bogs and fens?
Small unique habitats that can support more specialized species, like hummocks/hollows. Microhabitats occur more in fens than in bogs.
What are some situations in which competition may cause NPP to stay high, but biodiversity to decrease?
A highly competitive, high biomass species dominates over other species and reduces diversity. This could occur because of:
- high nutrients --> fast growing plants dominate
- invasive species
- removal of herbivores/keystone species
- low landscape diversity with no microhabitats
How does hydropattern affect biodiversity?
It affects the kinds of species that can live there. For example, most annual plants require damp, not flooded, soil during the growing season in order for their seeds to propagate. On the other hand, perennials often have persistent roots/tubers.

The Johnson et al study in the figure found that when the growing season was flooded, perennials dominated. When the growing season was moist, annuals were more likely to take over, especially when there was no later season flooding.
What are stable isotopes?
Non radioactive isotopes of an element: they have same number of protons but different number of neutrons
What can C and N isotope ratios tell you about the food chain?
They can tell you about an heterotroph's diet/an autotrophs CO2 and inorganic N sources
What types of isotopes tend to be enriched in smaller vs larger molecules?
Larger molecules release more energy when forming bonds, and are therefore preferentially taken up in larger molecules with more bonds - ie, biomass.

Smaller molecules are lighter and tend to be "removed" more easily, so tend to be enriched in smaller molecules such as the product of evaporation (gas).
How can you tell how common an isotope is based on it's weigth?
Heavier isotopes tend to be rarer, ie C-13 is rarer than C-12
What is the delta notation used to describe stable isotope ratios?
R = Rare/abundant

ie, C-13/C-12
N-15/N-14
What are the standards used for O, N and C stable isotope ratios?
O - Vienna Standard Mean Ocean Water, pure water collected from the ocean with all other molecules removed (ie salts)
N - atmospheric N2
C - Vienna Pee Dee Belemnite, a cretaceous carbonate fossil representing oceanic DIC
What causes variation of delta C-13 and dleta N-15 values in different plant food sources?
C:
- different CO2 sources, like atmospheric vs dissolved in water
- photosynthesis enzymes used

N:
- biological transformations (fixation, (de)nitrification) all affect the ratios
What is isotope fractionation? what are the 2 different types of isotope fractionation?
Isotope fractionation: changing of isotope ratio between reactants and products. α is the isotope fractionation factor and represents R_prod/R_react, where R is the rare/abundant isotope ratio.

Equilibrium isotope fractionation: occurs due to the extent of reaction in reversible equilibrium reactions, like water condensation, CO2 dissolution. Where the equilibrium is (ie, how far the reaction goes) affects the α value, which is a consistent point but temperature dependent.

Kinetic isotope fractionation: occurs due to the rate of a non-reversible reaction, like biological (often enzyme dependent) reactions (photosynthesis, digestion). Since the α value depends on the rate which has many factors affecting it, the resulting α value is less consistent.
What is the delta C-13 value for atmospheric CO2 vs oceanic DIC?
Atmospheric: -8, Oceanic: ~0

Both have a very small range, because the difference between the two is a result of equilibrium fractionation (via CO2 dissolution) which produces a very predictable/constant α value.
Why is the delta C-13 range of plants so large?
there are 3 groups of plants (C3, C4 and CAM) using different photosynthesis pathways, resulting in different degrees of C fractionation
What types of plants have C3 vs C4 photosynthetic pathways? How do the delta C-13 values compare for these plants?
C3: 95% of plants
- lower (more negative) delta C-13 value

C4: plants that are adapted to drier, warmer conditions like tropical grasses
- ie, spartina (cord)grasses
- retain C3 enzymes (wetland grasses often switch between C3 and C4 pathways)
- higher (less negative) delta C-13 value
Why and how do the delta C-13 values of submerged C3 plants look different from terrestrial C3 plants?
They uptake dissolved CO2 from water rather than atmospheric CO2. Therefore, the delta C-13 value of their CO2 source is 0, rather than -8. So their tissues will also have a higher delta C-13 value compared to terrestrial C3 plants.

This makes their delta C-13 signature appear similar to that of terrestrial C4 plants.
How does delta C-13 and delta N-15 change with trophic level? How is this used to determine food webs?
delta C-13 increases by ~1 permil for each trophic level.

delta N-15 increases by ~3.4 permil for each trophic level.

Based on this standard/framework plot of where different trophic levels fall on the delta C-13 and delta N-15 values, the delta values of species from the same ecosystem can be plotted against each other and relative trophic level relationships deduced in this method. (The delta values of the autotrophs will determine where on the plots the higher trophic levels fall.)
Given the R ratios of C and N isotopes for a plant, how would you calculate the delta C-13 and delta N-15 values for a consumer that only eats that plant?
1. Convert the R ratios of the plant into delta C-13 and delta N-15 notation
2. Add 1 and 3.4 to those values, respectively, in order to predict what the values would be for a consumer one trophic level higher.
1. What was the research question for the California salt marsh stable isotope case study? 2. What was the methodology used?
1. Which producers do fish in the salt marshes eat? Micro or macro algae? Low or high marsh graminoids?

2. Used C, N, S stable isotopes to assess the foodwebs of two salt marshes. One salt marsh had Spartina, a C4 grass, + sewage input. One salt marsh had neither. Producers, invertebrates, fish, and birds were collected.
In the California salt marsh stable isotope case study, what was the result of estimating the trophic levels of all the species based on delta N-15 values? What do "fractional" trophic levels indicate?
Invertebrates (squares) were low on the trophic level chain, fish (circles) were higher. The two bird species (crosses) fed at very different trophic levels.

The fractional trophic level values indicate organisms that eat at multiple trophic levels.
In the California salt marsh stable isotope case study, what was the fish food source at the site with no Spartina grass and no sewage?

What does the position of the species on the graph tell us?

What is the relationship between salicornia grass and the fish?
The arrow represents a change of 1 trophic level. Therefore, the macro and microalgae seem to be the species the fish is feeding on, since the arrow from these species points to the fish.

The algae species that are further to the right are more submerged species, with a higher delta C-13 value due to their utilization of dissolved CO2. The salicornia species at the left is a C3 plant.

The fish are not feeding on the salicornia, since this is an upper marsh plant that would not be submerged.
In the California salt marsh stable isotope case study, what was the fish food source at the site with Spartina grass and with sewage?

What the does the position of the spartina tell us? How does the position of the spartina compare to that of the submerged algae?
The arrow represents a change of 1 trophic level. Therefore, the macro/micro algae and spartina seem to be the species the fish is feeding on, since the arrow from these species points to the fish.

The spartina is position at the far right, since it is a C4 emergent plant. It is higher on the delta N-15 axis than the submerged algae, which also are on the far right.
In the California salt marsh stable isotope case study, where do these categories of plants and animals plot on the delta C-13 vs delta N-15 graph?
a) C3 emergent plants
b) submerged species
c) C4 emergent plants
d) macroalgae that the fish feed on
e) fish
a) to the mid left
b) to the bottom right, since they have a higher delta C-13 uptake from dissolved CO2 in the water
c) to the mid right, similar to the submerged species but with a higher delta N-15
d) in the middle
e) in the top right, approximately 1 permil delta C-13 and 3.4 permil delta N-15 away from the algae
What were the conclusions (3) and implications (2) of the california salt marsh stable isotope study?
Conclusions
1. Spartina is an important part of the fish's diet, as well as algae
2. Where spartina isn't present, algae are more important
3. Sewage organic matter and C3 plants don't seem important in affecting the fish's diet

Implications
1. No evidence that the sewage organic matter feeds the ecosystem (although it may be a source of N to the algae, due to similar delta N-15 values)
2. Fish depend on the marsh for food, especially spartina and macroalgae in the lower marsh
3. Upper marsh C3 plants don't affect the fish food chain
What are the 3 types of ecosystem services?
1. provisioning services: products from ecosystems (wood, food, water, furs etc)
2. regulating services: regulating air quality, climate, water quality, pollination
3. cultural services: spirituality, recreation, education, cultural heritage
What are 5 examples of ecosystem provisioning services from wetlands?
food and fur animals

edible wild plants

timber

rushes/cattails for baskets and mats

peat
What are 5 examples of ecosystem regulating services by wetlands?
1. flood mitigation - wetlands collect water and release it slowly, especially riparian wetlands controlling release to rivers

2. coastal protection - mangrove swamps and tidal marshes reduce erosion, reduce wind speed/wave surges/sediment suspension from storms

3. aquifer recharge - mostly at the edges of wetlands (due to clay at the bottom), so smaller wetlands are more important for this service

4. water quality improvement

5. carbon storage - low rate of C storage but it's stored over long time periods. However, can also produce C gasses, so not necessarily a C-sink.
What are 4 ways that wetlands improve water quality?
1. sedimentation due to slowed flows
2. plant uptake and burial of minerals
3. biochemical reactions
4. high sed-water contact --> adsorption
Why is ecological valuation used?
In order to quantify the value of ecosystem services, and decide what development projects should be chosen that limit the loss of ecosystem value
What are 3 types of economic valuation?
1. Willingness to pay: amount we are willing to pay minus what we actually pay
- ie, willing to pay $100/year to prevent backyard flooding, park taxes to maintain wetland are $80/year --> wetland benefit is $20/year

2. replacement value: cheapest replacement for a service using anthropogenic equivalents

3. net marginal benefits: replacement value of intact wetland minus value of system after development/conversion
What are 5 challenges to quantifying wetland value?
1. we are biased towards human uses and culture
2. valuable functions often have public value but not specific to the landowner
3. compare short term economic gain with long term ecological value
4. ecosystem value depends on context in landscape, not overall scarcity
5. valuation may help public understanding but may also cause tie between conservation and economy
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