Ecology - Community Energetics Final 1

Question 1

what consists of the bodies of living organisms within a given area, which consists of a certain amount of biomass

Answer 1

standing crop

Question 2

what refers to the actual mass of organisms per unit area which is usually expressed in units of energy

Answer 2

biomass

Question 3

what is the rate at which biomass is produced per unit area by plants

Answer 3

primary productivity of a community

Question 4

what refers to the total fixation of energy by photosynthesis, a portion of which is lost as respiratory heat (R) Community Energetics

Answer 4

gross primary productivity

Question 5

what is the difference between GPP and R representing the actual rate of production of new biomass that is available for consumption by heterotrophic organisms

Answer 5

new primary productivity

Question 6

what refers to the rate of biomass produced by such heterotrophs

Answer 6

secondary productivity

Question 7

What are some of the most productive ecosystems on Earth?

Answer 7

The most productive systems are found among swamps, marshes and estuaries

Question 8

Why do P:B ratios decrease during succession?

Answer 8

Early pioneers are rapidly growing herbaceous species with relatively little support tissue and later woody vegetation

Question 9

What is potential evapotranspiration and how is it important in predicting patterns of primary productivity

Answer 9

Potential evapotranspiration refers the theoretical maximum rate at which water might evaporate into the atmosphere under the prevailing conditions

Question 10

Give two factors that determine how much light is intercepted by a forest canopy

Answer 10

seasonality in leaf production and shedding or because of defoliation by grazing animals, pests and diseases

Question 11

what is the period during which there is active photosynthesis also affecting productivity, accounting partly for observed latitudinal gradients in productivity

Answer 11

length of growing season

Question 12

what is autochthonous

Answer 12

In aquatic communities, organic matter (and fixed energy) generated within the community

Question 13

how does autochthonous work / run

Answer 13

Most of this input is through photosynthesis by large plants and attached algae in shallow waters and by microscopic plankton in the open water

Question 14

what type of material is often labeled because of how it arrives in rivers or is blown in by wind

Answer 14

allochthonous

Question 15

How does the river continuum concept relate to the importance of autochthonous and allochthonous energy inputs

Answer 15

the importance of autochthonous energy inputs increases from the headwaters toward the lower reaches of a river

Question 16

What are the sources of nutrient inputs into lakes and marine ecosystems?

Answer 16

in a large lake (or the ocean) the organic inputs may be due almost entirely to photosynthesis by phytoplankton

Question 17

what refers to the depth within which net photosynthesis is positive

Answer 17

euphotic zone

Question 18

what is the depth at which gross primary productivity is just balanced by respiration

Answer 18

compensation point

Question 19

what is described as one way to measure the clarity of the water is to lower a black and white disk on a calibrated line and note the exact depth at which it disappears

Answer 19

secchi depth

Question 20

what is secchi depth mainly used to determine

Answer 20

water clarity

Question 21

What key factor influences the depth of the euphotic zone in aquatic ecosystems?

Answer 21

clarity of the water and anything that reduces visibility reduces primary productivity

Question 22

Compare and contrast a food chain with a food web

Answer 22

Although a food chain represent a linear series of trophic exchanges, it is obvious that most organisms have diets that include more than one type of food, giving rise to more complex food webs

Question 23

what refers to situations in which the structure (i.e. abundance, number of species, productivity, etc.) of the lower trophic levels depends on the effect of consumers (predators) from higher trophic levels

Answer 23

top-down control

Question 24

what is an example of top-down control

Answer 24

marine ecosystems dominated by kelp forests

Question 25

what refers to ecosystems in which the nutrient supply, productivity and type of primary producers (plants and phytoplankton) control the structure of the ecosystem

Answer 25

bottom-up control

Question 26

what does bottom-up control depend on

Answer 26

nutrient concentration and prey availability that influence a trophic level from below

Question 27

what is an example of a bottom-up community

Answer 27

plankton populations are controlled by the availability of nutrients

Question 28

Under what conditions do trophic cascades occur

Answer 28

predators in a food web suppress the abundance of their prey, thereby releasing the next lower trophic level from predation or herbivory if the intermediate trophic level is an herbivore

Question 29

what is the potential result of trophic cascades

Answer 29

changes in biomass and species composition

Question 30

Why are trophic cascades thought to be more common in aquatic ecosystems than terrestrial ones?

Answer 30

a decrease in one species would be compensated for by increases in similar species that were not being consumed as heavily

Question 31

Give a couple of examples aquatic trophic cascades

Answer 31

-abundance of large fish- eating fish is increased in a lake, the abundance the smaller fish prey decreases
-fish (steelhead and roach) consume fish larvae and predatory insects
-In areas where sea otters have been hunted to extinction, sea urchins increase in abundance and kelp populations are reduced

Question 32

What happened when brown trout were introduced to New Zealand in the 1860s?

Answer 32

Brown trout reduced total invertebrate density more than the galaxias did * Algal abundance also increased more with brown trout present

Question 33

true or false:
brown trout had a greater effect on primary production than native fish did in New Zealand when they were introduced

Answer 33

true

Question 34

Describe the trophic cascade that may have been caused by the reintroduction of gray wolves (Canis lupus) into Yellowstone National Park in 1995 and 1996.

Answer 34

three-tiered trophic cascade has been reestablished involving wolves, elk (Cervus elaphus) and woody browse species such as aspen (Populus tremuloides), cottonwoods (Populus spp.) and willows

Question 35

What are riparian communities

Answer 35

those that border rivers and streams

Question 36

how might riparian communities have been affected by the reintroduction of the wolves in Yellowstone National Park?

Answer 36

effect is particularly noted among the range’s riparian plant communities (i.e. those that border rivers and streams) with upland communities only recently beginning to show similar signs of recovery

Question 37

what limits carnivores, herbivores and plants?

Answer 37

limited by strong competition for resources such as light, water and nutrients

Question 38

How does the HSS hypothesis explain “why the world is green”?

Answer 38

The relatively little exploited plant populations are therefore limited by strong competition for resources such as light, water and nutrients

Question 39

Provide some examples of habitats that may not “be green”

Answer 39

steppe and tundra habitats whose greenness is maintained for only a few weeks

Question 40

give the reasons why areas may not be green

Answer 40

a severe shortage of forage during the unfavorable season, when herbivores may have a heavy impact on vegetation

Question 41

Give three other criticisms of the HSS hypothesis

Answer 41

1. Plants possess numerous defenses against herbivory
2. Herbivore populations may be limited by factors other than food or predation, such as nesting sites or available territory
3. For trophic cascades to be ubiquitous, communities must generally act as food chains, with discrete trophic levels

Question 42

What is meant by the description of wood webs as “static descriptions of energy flow and trophic interactions”?

Answer 42

As more organisms are added to a food web, complexity increases to reflect the complexity of real ecosystems

Question 43

In what ways may food webs be more dynamic?

Answer 43

changing feeding patterns

Question 44

What do interaction strengths in food webs measure?

Answer 44

the effect of one species on the population size of another species

Question 45

Why did Paine (1966) call the sea star Pisaster a keystone species?

Answer 45

having a greater influence than its abundance or biomass would predict!

Question 46

How might a keystone species lead to greater species diversity in a community?

Answer 46

implies that protecting a keystone species may be critical for protecting the many other species that depend on it!

Question 47

The potential for indirect effects to offset or reinforce the direct effect of a predator should be greatest when the direct effect is weak. How was this idea tested by Berlow (1999) using predatory whelks, mussels, and acorn barnacles?

Answer 47

A predator has a direct effect on its prey and indirectly affects other species that compete
with, facilitate or modify the environment of the prey species

Question 48

The potential for _______ effects to offset or reinforce the direct effect of a predator should be __________ when the direct effect is _______

Answer 48

1. indirect
2. greatest
3. weak

Question 49

what is measured by how much the populations change over time

Answer 49

stability of food webs

Question 50

What are the factors that allow naturally complex food webs to be stable?

Answer 50

an ecosystem responds to species loss or gain is strongly related to the stability of food webs

Question 51

What is the relationship between plant production and more diverse communities

Answer 51

Plant production is often higher in more diverse communities, and more diverse plant communities are better able to recover from disturbances