Ecology Quiz 9

Question 1

Ecological levels of Organization:

Answer 1

Biosphere - global processes

Ecosystem - Energy flux and cycling of nutrients

Community - Interactions among populations

Population - Population dynamics the unit of evolution

Organism - survival and reproduction the unit of natural selection

Question 2

Ecosystem concept:

Ecosystem ecology:

Biogeochemical Cycles:

Major Biogeochemical Cycles:

Answer 2

Ecosystem concept:
“Though the organisms may claim our prime interest, when we are trying to think fundamentally, we cannot separate them from their special environments, with which they form one physical system.” Arthur G. Tansley, 1935
Can take organism out of their environment but they won’t function the same way

Ecosystem ecology:
The study of processes involving the ‘transformation’ and ‘flux of energy and chemical cycling in habitats.
These processes link the living components to non-living components.
Biotic + Abiotic interactions

Biogeochemical Cycles:
Elements and water cycle better abiotic and biotic components of ecosystems

Major Biogeochemical Cycles: water, carbon, nitrogen, and phosphorus

Question 3

Trophic-Dynamic View of Ecosystems

Answer 3

Lindeman, R.L. (1942) The trophic-dynamic aspect of ecology. Ecology [1st rejected, then eventually published postmortem]
Linderman’s diagram described the movement of energy among groups of organisms at Cedar Bog Lake - trophic interactions of organism at cedar creek and the center is called the OOZE which is the primary producing and feeding the origins in the food web - the food web is carbon flow through bacteria

Question 4

Pool =

Flux =

Answer 4

Pool = how much mass of an element is held in a biotic or abiotic component of an ecosystem

Flux = how much of an element moves out of a pool into another at a given time (rate)

Question 5

Primary Production

The currency used for the measurement of primary production?

Answer 5

Energy in ecosystems originates with primary production by autotrophs(makes its own energy or carbon through acquisition of C02).

Primary production is the chemical energy generated by autotrophs, derived from fixation of CO2 in photosynthesis and chemosynthesis.

Primary production is the ultimate source of energy for all organisms, from bacteria to humans.

Energy assimilated by autotrophs is stored as carbon compounds in plant tissues - plant are primary producers in most ecosystem - energy from sun is harvest into chemical synthesis

Carbon is the currency used for the measurement of primary production.
Units: C mass/area/time (e.g. g/m-2/yr-1)

Question 6

Gross Primary Production

Leaf Area Index (LAI) =

Answer 6

Gross primary production (GPP)—total amount of carbon fixed by autotrophs by photosynthesis in an ecosystem.

GPP depends on climate(temp and perception), which influences photosynthetic rate and the leaf area index (LAI).

Differences in allocation of resources within plants leads to differences in primary production - One key allocation decision is how many layers of leaves are produced:
Leaf Area Index (LAI) = leaf area / canopy area
LAI > 1 → more leaf area than canopy area, so there must be leaf overlap
LAI low is 0.25 and high is 1.5

Tremendous LAI variation among biomes:
Arctic tundra- LAI = 0.1 (<10% of ground area has leaf cover)
Moist tropical forests (Gabon, Africa) LAI ≈ 12 (= on average 12 leaves above every point on the forest floor)

Question 7

Net Primary Production: NPP

Why is it Important?

Answer 7

Plants use about half of the carbon fixed in photosynthesis for respiration. All living plant tissues respire, but not all tissues photosynthesize (e.g., woody stems, roots).

Net primary production (NPP): NPP = GPP – respiration
NPP represents the biomass gained by the plant

Why is it Important?
NPP is the ultimate source of energy for all organisms in an ecosystem.
Variation in NPP is an indication of ecosystem health—changes in primary productivity can be symptomatic of stress or disturbance.
NPP is associated with the global carbon cycle (central to climate change).

Question 8

Secondary Production

Answer 8

Energy derived from consumption of organic compounds produced by other organisms

Net secondary production depends on the “quality” of food (digestibility and nutrient content), and heterotroph physiology

Question 9

Measuring NPP: Biomass harvest

Measuring NPP: Biomass dynamics

Answer 9

Measuring NPP: Biomass harvest:
- For many herbaceous plant communities, aboveground NPP estimates simply involve harvesting and weighing all the plant material in a sample area that is produced within a year…
- All the roots found in a 10 x 10 x 15 cm soil sample underneath one small annual wildflower
- Root production: more challenging to measure accurately. Difficult to distinguish between species and individuals grown together. Fine roots have fast dynamics (constantly growing and dying back); total root biomass at the season end can underestimate NPP allocated to roots

Measuring NPP: Biomass dynamics:
- Litterfall traps
- Dendrometer - diameter growth increment
- Rhizotron: Belowground NPP Dynamics

Question 10

Measuring NPP: Gas Exchange

Answer 10

Enclose ecosystem within tent or structure: net change in [CO2] inside tent is a balance of GPP uptake and total respiration—net ecosystem production or net ecosystem exchange (NEE).

NEE = GPP – (AResp + HResp) or

Heterotrophic respiration (bacteria, detritivores, etc) must be subtracted to obtain NPP.

Negative value means losing carbon a net loss and no longer a carbon sink which means gain

Question 11

Measuring NPP: Remote Sensing - Spectral signature

Answer 11

Biomass techniques are impractical for large or biologically diverse ecosystems

Chlorophyll concentrations can provide a proxy for GPP and NPP. They can be estimated using remote sensing methods that rely on reflection of solar radiation.

NDVI (Normalized Difference Vegetation Index): NDVI = (NIR – VIS) (NIR + VIS) This is then used to estimate C fixation

NDVI in Winter - Tan= low NDVI

NDVI in Summer - Dark Green= high NDVI

Question 12

Environmental Controls on NPP

Water availability:

Temperature:

Nutrient Limitation of NPP:

Answer 12

Determination of the factors which control primary production is critical to understanding ecosystem function. NPP varies substantially over space and time through different ecosystems.

Water availability affects photosynthesis (on land) - primary driver of NPP:
Low water causes water stress and stomatal closure
At very high precipitation, NPP may decrease
Greater cloud cover
Lower sunlight
Leaching of nutrients
Soil saturation, which results in anoxic conditions

Temperature affects photosynthesis - with higher temp is higher photosynthesis
Enzyme activity and membrane fluidity

Nutrient Limitation of NPP:
Nutrients, particularly nitrogen & phosphorus, often control NPP
e.g., fertilization experiment in dry and wet alpine meadows
In the absence of a water limitation, soil nutrient availability is often implicated as the principal factor determining variation in primary production

Question 13

Global Patterns of NPP: Land

Global Patterns of NPP: Oceans

Answer 13

Global Patterns of NPP: Land
NPP decreases in arid regions at about 25° N and S. Low water availability limits LAI and photosynthesis - desserts have no perception with low productivity
High latitudes have short growing seasons
Low temperatures constrain nutrient supply by lowering decomposition rates (limit nutrient cycling)
Low temperatures reduce photosynthesis
Freezing limits water availability

Global Patterns of NPP: Oceans
Ocean NPP peaks at mid-latitudes, where zones of upwelling are found

Question 14

Trophic levels describe the

Feeding Relationships -
Many organisms do not fit neatly into one trophic level:

Answer 14

Trophic levels describe the feeding positions of groups of organisms in ecosystems

Omnivores feed at multiple trophic levels (e.g., coyote eat vegetation, herbivorous rodents, & other carnivores)

Intraguild predators do not merely feed on trophic levels below, but feed on other predators (each other)

Question 15

Food Web Models

Some Limitations of Food Web Models

Answer 15

Diagrams showing connections between organisms and the food they consume
- Important tools to model ecological interactions
- Show energy flows among ecosystem components
- More organisms or species = more complexity
- A balance between clarity, simplicity and generality

Some Limitations of Food Web Models:
- Trophic interactions are dynamic - black bear consume diff organisms throughout the year
- Variable trophic interaction strength - some strong some weak
- Mutualists! Parasites! Microorganisms! - don’t consider these

Question 16

Trophic Pyramids:

Aquatic pyramids may be:

Answer 16

Trophic Pyramids: Attenuation of energy, biomass, or abundance with trophic transfers from bottom to top.
The second law of thermodynamics states that during transfer of energy, some is lost to increasing disorder (entropy). All lot of energy and biomass found in the trophic level - decreasing amount of energy and biomass as you move out - energy gets released with heat as you move out and it gets lost to heat - it gets to lost to heat because the energy is being used to maintain metabolic processes

Aquatic pyramids may be inverted, or less steep
NOTE: Trophic pyramids based on energy are never inverted Pyramids based on biomass or numbers can be inverted
- Biomass can be flipped not energy but is rare - seen in nutrient limiting areas like aquatic

Question 17

What determines food chain length in an ecosystem? (chain is subcomponent of food web)

Answer 17

The amount of resource entering an ecosystem through primary production

Dispersal ability may constrain the ability of top predators to enter an ecosystem

The frequency of disturbances can determine viability of top predator populations

Larger areas may support larger populations and more species to exploit

Question 18

Trophic Efficiency:

Trophic Efficiency Components:

Answer 18

Trophic Efficiency: Amount of energy at one trophic level divided by amount of energy at the next lowest trophic level

Trophic Efficiency Components:

1. Consumption efficiency:
   Proportion of available energy ingested. Higher in aquatic ecosystems than in terrestrial ecosystems, and higher in carnivores.
2. Assimilation efficiency: Assimilation efficiency is proportion of ingested food that is assimilated; depends on food quality(how nutritious) and consumer physiology. - can’t acquire energy from fiber
   What influences assimilation efficiency?
   - Quality of plants and detritus is low due to complex compounds such as cellulose, lignins, and humic acids, which are not easily digested, and low concentrations of N and P.
   - Animals have carbon-to-nutrient ratios similar to the animals consuming them, so are assimilated more readily.
   - Assimilation efficiencies of -herbivores and detritivores are 20%– 50%; carnivores are about 80%.
   - Endotherms(warm blooded animal) digest food more completely than ectotherms and thus have higher assimilation efficiency
3. Production efficiency: Proportion of assimilated food that goes into new consumer biomass; related to thermal physiology and size of consumer
   What influences production efficiency? Production efficiency is related to thermal physiology and size.
   - Endotherms allocate more energy to heat production(regulate own heat) and have less for growth and reproduction than ectotherms.
   - Body size affects heat loss in endotherms. As body size increases, the surface area-to-volume ratio decreases. Elephant lower surface area to ratio and maintains more heat
   - A small endotherm (e.g., a shrew), loses a greater proportion of its heat across its body surface than a large endotherm, such as a grizzly bear, and will have lower production efficiency.
   - Endotherms allocate more energy to heat production = lower production efficiencies
   As body size increases, surface area-to volume ratio decreases
   Small endotherms lose a greater proportion of its heat than a large endotherms = lower production efficiency

Question 19

Why is the World Green?

Trophic Cascades:

Answer 19

The “bottom-up” view: resources that limit NPP determine energy flow and trophic structure throughout an ecosystem.

The “top-down” view: energy flow is governed by predators at the highest trophic level, which influence trophic levels below them.

Trophic Cascades:
Consumption at one trophic level results in a change in biomass or composition at lower trophic levels. An indirect effect e.g., sea otters-sea urchins-kelp forest

Question 20

Food web interactions

Trophic interaction strength:

Interaction strength =

Are more complex food webs more stable?

Answer 20

Trophic interaction strength: not all trophic connections are equally important

Interaction strength = quantitative measure of the impact that one species in the food web has on the abundance of a 2nd species
Interaction strengths are not normally distributed; tend to heavy skew towards weak interactions. “weak interactions may be the glue that binds natural communities together”
Interaction strengths can be determined through removal experiments. Impractical to do this for all links in a food web.

Less direct methods:
observation of feeding preferences of predators
change in the population size of predators and prey over time.

Bob Paine: energy flow and community structure might be controlled by a few key species (or keystones?)

Are more complex food webs more stable?
Stability: how much populations change over time.
Large oscillations in population size increase susceptibility of species to local extinction. Thus, a less stable food web means a greater potential for extinction of its component species