Study Guide 10 Ecosystems

Question 1

Explain why positive interactions are more likely or common under “stressful” conditions

Answer 1

Positive relationships are more common under stress because partners benefit more. In non-stressful conditions, species can meet needs alone, but stress makes cooperation advantageous.

Question 2

draw a graph depicting how the strength of positive interactions changes along some environmental stress gradient (predation pressure, physical stress, etc)

Answer 2

Example graph from lecture: plants and mycorrhizae across different soil nutrient levels

Question 3

using a specific example of an interspecific interaction, describe how the same two species can interact to produce a range of outcomes, form positive (facilitative, mutualistic, etc) to negative (competitive, parasitic, etc). what components of the physical or biotic environment determine whether the interaction is positive or negative?

Answer 3

The plant/mycorrhizae relationship thrives under low soil nutrients: plants gain nutrients via fungal hyphae, and fungi receive sugars. In high nutrients, fungi still benefit, but plants may face a cost since they can rely on their roots. At moderate nutrients, the relationship may become commensal, benefiting fungi without affecting plants much.

Question 4

describe the differences between primary and secondary succession

Answer 4

-Primary succession starts on bare ground with no soil (e.g., glacier retreat, dunes, lava flows).
-Secondary succession occurs where soil exists, even if above-ground life is destroyed.

Question 5

give an example of the type of disturbance that would lead to each pattern of succession

Answer 5

Examples from lecture include: fire, land use change (like abandoned agricultural land

Question 6

what are the characteristics of typical early successional species

Answer 6

Early succession: Pioneer species are mostly r-selected.

Question 7

what are the characteristics of typical late successional species

Answer 7

Late succession: Climax species are primarily K-selected.

Question 8

left graph: show growth of species 1 in habitats A and B when species 2 is present and absent

right graph: show growth of species 2 in habitats A and B when species 1 is present and absent.

complete the bar graphs with data that represent a conditional interaction

Answer 8

Conditional relationships vary by habitat. In low nutrients (A), plants and mycorrhizae benefit each other, while in high nutrients (B), plants may face costs, but fungi still benefit.

Question 9

ecosystem A has primary production of 1000 g C /m2/yr and ecological efficiency of 10%

ecosystem B has a primary production of 300 g C /m2/yr and an ecological efficiency of 25%

a)which ecosystem will have more production at the secondary consumer (carnivore) trophic level?

Answer 9

Ecosystem B

Question 10

ecosystem A has primary production of 1000 g C /m2/yr and ecological efficiency of 10%

ecosystem B has a primary production of 300 g C /m2/yr and an ecological efficiency of 25%

b)which ecosystem is more likely to support an exothermic primary consumer (herbivore)?

Answer 10

Ecosystem A, because it has more energy available at the primary consumer level and endotherms generally require more energy than ectotherms

Question 11

ecosystem A has primary production of 1000 g C /m2/yr and ecological efficiency of 10%

ecosystem B has a primary production of 300 g C /m2/yr and an ecological efficiency of 25%

c)if a trophy level requires at least 1 g C /m2/yr in order to exist, how many trophic levels can each of these ecosystems support?

Answer 11

4 trophic levels for Ecosystem A, 5 for Ecosystem B

Question 12

ecosystem A has primary production of 1000 g C /m2/yr and ecological efficiency of 10%

ecosystem B has a primary production of 100 g C /m2/yr and an ecological efficiency of 25%

d) given your answer to part C, which do you think has a larger impact on the energy available at upper trophic levels: primary productivity or efficiency of energy movement across trophic levels?

Answer 12

Ecosystem A has higher primary productivity, but Ecosystem B’s 2.5x greater efficiency allows more energy at upper trophic levels, supporting an extra trophic level. Efficiency impacts energy availability more than productivity.

Question 13

describe how the following terms relate to one another: consumption efficiency, assimilation efficiency, production efficiency, and ecological efficiency

Answer 13

-Consumption efficiency is the biomass consumed from the lower trophic level.

-Assimilation efficiency is the portion digested, not excreted.

-Production efficiency is the digested biomass converted to new biomass, not used for metabolism.

-Together, they determine ecological efficiency: biomass transfer between trophic levels.

Question 14

the diagram describes how every moves through a trophic level. real that definition of the different types of efficiencies to answer the question below

a)would you expect the assimilation efficiency to be higher for a carnivore or an herbivore?

Answer 14

Carnivores have higher assimilation efficiency than herbivores, as digesting plant cellulose is difficult. Herbivores need adaptations like multiple stomachs, fermentation chambers, or coprophagy to aid digestion.

Question 15

the diagram describes how every moves through a trophic level. real that definition of the different types of efficiencies to answer the question below

b)would you expect the production efficiency to be higher for an ectotherm or an endotherm?

Answer 15

Ectotherms have higher production efficiency than endotherms because they lose less energy to respiration, as they don’t maintain constant body temperatures.

Question 16

the diagram describes how every moves through a trophic level. real that definition of the different types of efficiencies to answer the question below

c) would you expect the consumption efficiency of primary consumers to be higher in a forest or a grassland?

Answer 16

Grassland herbivores have higher consumption efficiency than forest herbivores because grasses are more consumable than wood.

Question 17

the diagram describes how every moves through a trophic level. real that definition of the different types of efficiencies to answer the question below

d) which would you expect to have higher production efficiency: a C3 plant or a C4 plant?

Answer 17

C3 plants have higher production efficiency due to greater energy efficiency, while C4 plants are more water-efficient but spend more energy on sugar production.

Question 18

why is terrestrial net primary productivity higher in the tropics, but marine net primary productivity is higher in coastal areas?

Answer 18

Terrestrial net primary productivity is driven by temperature, with high productivity in the tropics due to heat and moisture. Marine productivity is driven by nutrient availability, with coastal areas having the highest productivity from land runoff and upwelling of deep ocean nutrients.

Question 19

you may have heard it argued that being vegetarian is more energy efficient than eating meat. use your knowledge of energy transfer across trophic levels to describe whether you accept or reject this argument.

Answer 19

Eating at a lower trophic level is more energy efficient because you bypass inefficiencies in consumption, assimilation, and production. For example, feeding a cow corn results in less meat than the corn’s original mass, while eating the corn directly provides more energy. Lower trophic levels also contain more energy in energy pyramids.

Question 20

what are dead zones and why do they commonly form at the mouth of large rivers?

Answer 20

Dead zones form when nutrient runoff causes algal blooms that deplete oxygen during decay, suffocating organisms. They are common at river mouths, like the Mississippi River, due to large watersheds and agricultural runoff.

Question 21

in the diagram of the hydrologic cycle states that groundwater plats a small role in the global water cycle because it is ‘locked in’ to rock and soil layer.

how is groundwater important for humans?

Answer 21

Groundwater is crucial for human activities, especially for agricultural irrigation, drinking water, and industrial uses. In areas like the Midwest U.S., it supports 20% of the country’s corn, wheat, cotton, and beef production.

Question 22

in the diagram of the hydrologic cycle states that groundwater plats a small role in the global water cycle because it is ‘locked in’ to rock and soil layer.

how does this disconnect of ground water from the global water cycle impact our future?

Answer 22

Since groundwater is “locked in” rock and soil layers and recharges slowly, it is disconnected from the faster-moving surface water cycle. This slow recharge means it’s being depleted faster than it can be replenished, leading to future water shortages and increasing costs, especially by 2150.

Question 23

in class, laci stated that diagrams of energy across trophic levels must always have a pyramid shape (most energy in the producers, decreasing at each level up to the top predators), but that diagrams of biomass or numbers of individuals in each trophic level can be a variety of shapes.

describe why energy diagrams must be a pyramid

Answer 23

Energy diagrams are pyramid-shaped because energy enters the system only at producers via photosynthesis, and energy is lost at each higher level due to inefficiencies like respiration.

Question 24

in class, laci stated that diagrams of energy across trophic levels must always have a pyramid shape (most energy in the producers, decreasing at each level up to the top predators), but that diagrams of biomass or numbers of individuals in each trophic level can be a variety of shapes.

describe examples of ecosystems that may have biomass or number of individuals that are not pyramid-shaped.

Answer 24

In the open ocean, plankton producers have low biomass but high turnover, allowing more consumers. In tropical rainforests, herbivores may outnumber producers due to fast plant growth and reproduction.

Question 25

you are an environmental consultant hired by a town adjacent to a small lake in the sierras. the figure below describes what you know about the food web of the late. the town is economically depressed, and residents have proposed two ideas for stimulating the local economy

1) introduce northern pike (a finish act only eats other fish) into the system to attract sport fishers (and their money) to the area

the town wants you to predict for them the consequences of the proposals for the health of their like, long renowned for its clear water

Answer 25

Introducing Northern Pike could cause a top-down trophic cascade by increasing predation on planktivorous fish, which reduces their population. This decreases the predation pressure on zooplankton, increasing their population and herbivory on algae. This could help maintain or even improve water clarity.

Question 26

you are an environmental consultant hired by a town adjacent to a small lake in the sierras. the figure below describes what you know about the food web of the late. the town is economically depressed, and residents have proposed two ideas for stimulating the local economy

2) harvest filter-feeding bivalves from the lake for food (they are quite a delicacy and fetch a hefty price).

the town wants you to predict for them the consequences of the proposal for the health of their like, long renowned for its clear water

Answer 26

Removing filter feeders would reduce herbivory on algae, likely increasing algae growth and reducing water clarity. While this could benefit local fishers, it would negatively impact the lake’s health, as water clarity decreases.

Question 27

what is a top-down trophic cascade? given an example

Answer 27

A top-down trophic cascade starts at the top of the trophic levels, with changes affecting lower levels. An example is orca > sea otter > urchin > kelp, where the orca’s impact on sea otters cascades down to affect kelp.

Question 28

what is a bottom-up trophic cascade? given an example

Answer 28

A bottom-up trophic cascade starts at the bottom of the trophic levels, with changes affecting higher levels. An example is nutrient changes in aquatic plants leading to algal blooms, which then cause fish deaths.

Question 29

in class, laci referred to the Ogallala Aquifer as ‘fossil water.’ how are aquifers similar to other ‘fossil’ resources like oil and coal?

Answer 29

Aquifers are like fossil fuels because they’re slow to replenish and non-renewable, but they don’t form from fossilized organisms like coal and oil.

Question 30

using the diagram below of the global nitrogen cycle to answer the following questions. note: for the nutrient cycle diagrams, I do NOT want you to memorize pools and fluxes, I DO want you to be able to read and interpret a cycle diagram

a)what is the largest flux? what is the largest pool?

Answer 30

The largest pool is the atmosphere. The largest flux connects marine biomass and dissolved nitrogen in the ocean, though it’s unlabeled due to multiple processes with unclear contributions.

Question 31

using the diagram below of the global nitrogen cycle to answer the following questions. note: for the nutrient cycle diagrams, I do NOT want you to memorize pools and fluxes, I DO want you to be able to read and interpret a cycle diagram

b)which of the fluxes are anthropogenic (caused by humans)? how do these fluxes compare in magnitude to the natural fluxes?

Answer 31

Human activities like livestock/agriculture, biomass burning, fossil fuel burning, and industrial N fixation contribute 81 units to the atmospheric pool (vs. 268 from natural denitrification) and 130 units to the plant biomass pool, surpassing natural N fixation, which contributes 128.

Question 32

using the diagram below of the global nitrogen cycle to answer the following questions. note: for the nutrient cycle diagrams, I do NOT want you to memorize pools and fluxes, I DO want you to be able to read and interpret a cycle diagram

c) describe a pathway by which a molecule of nitrogen in the atmosphere could move through both terrestrial and aquatic pools and then return to the atmosphere.

Answer 32

One pathway: Nitrogen moves from the atmosphere through atmospheric deposition onto the landscape, then through runoff into dissolved nitrogen in the ocean, and finally returns to the atmosphere via denitrification.