Lecture Eight

Question 1

What are Ecosystem Engineers?

Answer 1

A type of organism that creates, modifies, and maintains habitats.

Question 2

What are some examples of Ecosystem Engineers?

Answer 2

Corals, elephants, trees.

Question 3

Define Biological Diversity.

Answer 3

The variety or number of organisms that make up the community. Composed of Species Richness and Species Diversity.

Question 4

What is Species Richness?

Answer 4

The total number of species in the community.

Question 5

What is Species Diversity?

Answer 5

The number of species in the community relative to the number of individuals.

Question 6

How does the Species Richness of Birds vary?

Answer 6

It increases from polar to temperate to a maximum in tropical areas (closer to to equator).

Question 7

How does Species Richness typically vary?

Answer 7

Increases by topographical variation and decreases by peninsular effects.

Question 8

What is the Time Hypothesis for the Polar-Equatorial Gradient of Species Richness?

Answer 8

It’s a fact that communities diversity (gain species) with time, so possible temperate regions have less diversity because they are younger and have only recently recovered from glaciation. Species have not had the time to evolve and fully exploit niches in temperate and polar regions, and equatorial species have not fully migrated back to temperate regions.

Question 9

What evidence exists for the polar-equatorial gradient?

Answer 9

A comparison of Lake Baikal with Great Slave Lake (Lake Baikal is an ancient unglaciated lake while Great Slave Lake is a glaciated lake).
Baikal has 580 species of benthic invertebrates while Great Slave only has 4.

Question 10

What problem exists with the Time Hypothesis?

Answer 10

It explains terrestrial species richness, but it does not apply to marine organisms. Marine organisms would be expected to recolonize the temperate and polar regions rapidly after glaciation; however, richness of marine organisms follows the same polar-equatorial species gradient.

Question 11

What is the Area-Hypothesis for the Polar-Equatorial Gradient of Species Richness?

Answer 11

The Species Area Effect - larger areas have more species because they can support larger populations and have greater range or habitats. There is considerable evidence for this theory, as the equatorial region is the largest climatically similar region of the globe and therefore, because this region covers a large area, one might expect greater biodiversity.

Question 12

What problems exist with the Area-Hypothesis?

Answer 12

The Tundra biome is the second largest terrestrial region, but has low species richness. The open ocean has the largest area of any marine habitat, but has fewer species that tropical surface waters (which have smaller volume).

Question 13

What is the Productivity Hypothesis for the Polar-Equatorial Gradient of Species Richness?

Answer 13

Greater production of plants results in greater overall species richness. An increase in plant biomass will support more herbivores and hence more predators, parasites, and scavenger species.

Question 14

What evidence is there for the Productivity Hypothesis?

Answer 14

Bird and mammmal species richness increases with productivity (evapotranspiration rate) in NA.

Question 15

What is the Metabolic Theory for the Polar-Equatorial Gradient of Species Richness?

Answer 15

Accumulating theoretical and empirical studies suggest that the single most important factor is kinetics - specifically, ecological and evolutionary rates are temperature dependent. The relatively high temperatures in the tropics generate and maintain high diversity.

Question 16

What is Succession?

Answer 16

Succession is the temporal change in community structure at a given location.

Question 17

How does abandoned cropland undergo succession?

Answer 17

First, grasses and weedy herbaceous plants colonize, followed by shrubs. Over time, shrubs are replaced by pine trees, eventually forming a canopy forest. Hardwood trees begin to occupy the understory. Eventually, deciduous hardwoods dominate the landscape.

Question 18

What is a Seral Stage?

Answer 18

A change in succession; a point on the continuum of vegetation through time. These stages often can be recognized as distinct communities, with characteristic structure and species composition. Stages may last years or decades, and some stages may be missed or abbreviated/altered.

Question 19

What does succession begin with?

Answer 19

A disturbance.

Question 20

What is a disturbance?

Answer 20

A force that alters a biological community and removes or destroys organisms. Disturbances may be storms, fires, floods, droughts or human caused. Disturbances exhibit different frequencies and intensities.

Question 21

Example the Succession that occurred in the rocky intertidal algal community in Southern California.

Answer 21

There is natural disturbance - wave action overturns rocks, creating cleared surfaces that algae colonize.

Question 22

What are pioneer species?

Answer 22

Early successional species that are the initial colonists.

Question 23

What doe pioneer species often have?

Answer 23

High growth rates, smaller size, high degree of dispersal and colonization, and high rates of per capita population growth.

Question 24

What are climax species?

Answer 24

Late successional species.

Question 25

What doe climax species often have?

Answer 25

Longer lifespans, larger size, lower rates of dispersal and colonization, lower rates of per capita population growth. The patterns of species replacement through time are not random.

Question 26

What is primary succession?

Answer 26

Occurs at a location that was not previously occupied by a community; a newly exposed surface. This type of succession occurs in a baron, lifeless environment.

Question 27

What is secondary succession?

Answer 27

Occurs at a location that was previously occupied by a community and then underwent a disturbance that removed all or part of the existing community. This type of succession can build on the remainder of a pervious community.

Question 28

What type of succession can a sand dune undergo?

Answer 28

Primary succession. Sand is a product of weathered rock, deposited by wind and water. Unlike soil it has minimal nutrients and ability to retain water. Pioneering species such as grasses stabilize the dune with extensive rhizomes, then mat-forming shrubs colonize. Subsequently, trees invade: first pine (conifers), then oak (hardwoods). Trees that need more moisture rarely succeed the pines and oaks except in depressions or other areas where moisture accumulates. During succession, colonizing species can change the environment, making it more hospitable for other species.

Question 29

What kind of succession occurs at an abandoned crop field?

Answer 29

Secondary succession.

Question 30

How does crabgrass begin the succession of a crop field?

Answer 30

First summer is dominated by crabgrass. Dormant seeds in the soil receive light and moisture and germinate, Horseweed seeds are blown in by the wind, germinate, and begin to grow in early winter. In the spring, it outcompetes the crabgrass and in the second summer other plants begin to invade.
Third summer – broomsedge, a perennial bunchgrass, colonizes the field, which now has abundant organic material. Pine seedlings begin to grow in open areas. In five to ten years, pines trees shade the broomsedge and eventually, hardwood trees (ash and oak) grow up through the pines, replacing them as they die.

Question 31

What is a key and natural disturbance of secondary succession in many ecosystems?

Answer 31

Fire. Some coniferous trees require fire for reproduction. For example, jack and lodge pole pines are well adapted to fire; their cones require the heat of the fire to open and release seeds.
Fire is also key to maintaining native prairie grasslands. In many areas trees will eventually replace the grasslands, if not for fire.

Question 32

How can major fires be prevents?

Answer 32

By having frequent small fires. Fire suppression in forests permits the build up of dead wood. A buildup of wood is very susceptible to burning, especially during lightening strikes during dry summers.