BIOL 1011 Lecture Notes - Lecture 8: Urchin Barren, Kelp Forest, Keystone Species

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3 May 2018

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Community Dynamics

February 24, 2015

Species Interactions:

• Competition

• Mutualism

• Commensalism

• Parasitism

Trophic Interactions:

• Predation

• Herbivory

Food webs represent trophic interactions. The arrows represent the direction of

energy flow. Smaller chains are present within a food web.

There are central species evident within food webs that are well connected.

For example, the collard lemming eats many plants and is a main prey for predators.

Therefore, some species are equal but some are more significant in the community

and impact the ecosystem is their presence is lost.

Species With a Large Impact:

1. Dominant Species – large impact due to high biomass (ex. Lemming)

2. Keystone Species – large impact despite low biomass and abundance;

usually predators (ex. Wolf)

Are top predators really important?

• Sea Otter Example:

o On the pacific coast of British Columbia there were no sea otters and

many sea urchin barrens that eat the kelp

o Once the sea otters were introduced, they started eating the sea

urchins which then caused the growth of kelp forests

Therefore, keystone species affects primary producer’s productivity.

o The number of sea stars declined (food for otters) as the number of

mussels increased

Therefore, keystone species affects abundance and growth of other species.

o The kelp forests provide habitat for fish

Therefore, keystone species affects species richness.

o More bald eagles and gulls ate more fish

Therefore, keystone species affects species interactions.

o In 1990s in Alaska it was noted that presence of urchin barrens was

increasing

o It was noted that the killer whales were feeding on the sea otters

o This was causing a major change to the ecosystem

Trophic Cascade – top predator influences the abundance of lower trophic levels

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Scientists believe it was other disruptions in the ecosystem that caused the killer

whales to start feeding on sea lions.

On the Atlantic coast there are no sea otters but kelp beds are present. Wolf fish and

other predatory fish were historically eating sea urchins so kelp beds could flourish.

In the 1980s the urchin barrels in the Atlantic died off in shallow waters due to a

protozoa disease, which then caused an increase on kelp beds. Once the urchin

population recovered, the kelp beds were turned into urchin barrens once again.

A scientist discovered that the offshore area can exist in the two states (alternate

states) of an urchin barren and kelp bed with factors that cause the transition (all

influenced by the urchins). He found a correlation between the presence of

hurricanes and the presence of the urchin disease.

Top-Down Control – higher trophic levels control lower levels (predator or

disease)

Bottom-up Control – lower trophic levels control higher level abundance/biomass

Cod are top predators in Atlantic coastal ecosystems.

Around 1980 there was a major Atlantic cod decline which cause the crab and

shrimp biomass to increase.

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Document Summary

The arrows represent the direction of energy flow. Smaller chains are present within a food web. There are central species evident within food webs that are well connected. For example, the collard lemming eats many plants and is a main prey for predators. Therefore, some species are equal but some are more significant in the community and impact the ecosystem is their presence is lost. Species with a large impact: dominant species large impact due to high biomass (ex. Lemming: keystone species large impact despite low biomass and abundance; usually predators (ex. Therefore, keystone species affects primary producer"s productivity: the number of sea stars declined (food for otters) as the number of mussels increased. Therefore, keystone species affects abundance and growth of other species: the kelp forests provide habitat for fish. Therefore, keystone species affects species richness: more bald eagles and gulls ate more fish. Trophic cascade top predator influences the abundance of lower trophic levels.

Related Questions

7) According to the Red Queen hypothesis,

A) the population density of a predator depends on thepopulation density of its prey.

B) natural selection should favor the most efficientforagers.

C) prey must continually evolve means of avoiding capture toavoid extinction.

D) most predators consume a varied diet in order to meet theirnutritional requirements.

8) Which of the following is an example of crypticcoloration?

A) a brown bird that nests on the ground

B) a deer with a large, white tail

C) skunks with black and white stripes

D) snakes with black, yellow, and red bands

9) Which of the following is not a class of plant secondarycompounds?

A) terpenoids

B) phenolics

C) nitrogen-based compounds

D) alkanes

15) When an ecologist compares the diversity of differentcommunities by counting the number of species within eachcommunity, the measure of diversity being used is called

A) species evenness.

B) species diversity.

C) species richness.

D) relative abundance.

16) In a rank-abundance curve comparing two communities, thecommunity with the greater species richness is characterized bya

A) lesser length of the curve and a more gradual slope.

B) lesser length of the curve and a steeper slope.

C) greater length of the curve and a more gradual slope.

D) greater length of the curve and a steeper slope

19) The layer of a forest in which decomposition takes place andmineral nutrients are released for reuse by plants is calledthe

A) canopy.

B) understory.

C) herb layer.

D) forest floor.

20) Zonation within a community is typically the result ofdifferences in the

A) patterns of predation among species within a community.

B) rates of reproduction among species within a community.

C) patterns of competition among species within a community.

D) physical characteristics of the environment across a spatialgradient.

21) Food webs are typically arranged into trophic levelswith

A) primary producers at the bottom, herbivores in the middle,and carnivores at the top.

B) herbivores at the bottom, carnivores in the middle, andprimary producers at the top.

C) carnivores at the bottom, herbivores in the middle, andprimary producers at the top.

D) primary producers at the bottom, carnivores in the middle,and herbivores at the top.

22) When top-down control occurs within an intertidal zone alongthe rocky coastline of the Pacific Ocean, which of the followingspecies controls the abundance of other species?

A) kelp

B) mussels

C) barnacles

D) starfish

23) In coastal aquatic environments, the three majorenvironmental gradients of water that directly influence thedistribution and dynamics of communities include

A) temperature, depth, and top down regulation.

B) depth, aposematic coloring, and salinity.

C) pressure, temperature, and depth.

D) tidal action, salinity, and oxygen content.

28) The number of species within a community is usually greatestwhen

A) no disturbance occurs.

B) a low frequency of disturbance occurs.

C) an intermediate frequency of disturbance occurs.

D) a high rate of disturbance occurs

29) Succession in a community involves

A) only autotrophic species.

B) only heterotrophic species.

C) both autotrophic and heterotrophic species.

D) only detritivorous species.

32) The highest diversity of plant and animal life occurs in

A) tropical savannas.

B) tropical rain forests.

C) temperate deciduous forests.

D) boreal forests.

33) Plants that root and grow on other plants in the tropicalrain forest are called

A) phreatophytes.

B) succulents.

C) epiphytes.

D) halophytes.

34) Tropical Savannas typically occur in

A) cold areas with little rainfall in polar regions.

B) cold areas with little rainfall at high altitudes in thetropics.

C) very dry areas in the rain shadow of mountains of bothtemperate and tropical latitudes.

D) warm areas with seasonal rainfall in the tropics.

37) The vegetation of tundra is dominated by

A) broadleaf deciduous trees.

B) short ground covering plants such as sedges and heaths.

C) needle-leaf evergreen trees.

D) sclerophyllous broadleaf evergreen shrubs.

38) The part of a rocky shore in which barnacles, oysters,mussels, limpets, and brown algae are most common is called the

A) littoral or intertidal zone.

B) infralittoral or subtidal zone.

C) supralittoral or supratidal zone.

D) superlittoral or supertidal zone.

39) In comparison to rocky coasts, intertidal organisms livingon sandy or muddy beaches

A) experience greater variability in salinity.

B) experience greater variability in temperature.

C) are more likely to be attached to the substrate.

D) are more likely live burrowed and emerge with the incomingtide.

40) In salt marshes, predatory fish move in when

A) the tide is high.

B) migratory fishes are spawning.

C) the sun goes down.

D) salinity is low.

41) Intertidal mud flats in tropical regions are typicallycomposed of

A) salt marshes.

B) peatlands.

C) mangrove forests or mangals.

D) oysterbeds.

42) Mangrove swamps

A) are formed by a single species of tree adapted to variablesalinities.

B) have relatively anoxic soils.

C) occur mostly in temperate latitudes.

D) typically occur along rocky coastlines subjected to heavywave action.

43) Freshwater wetlands dominated by woody vegetation arereferred to as

A) swamps.

B) marshes.

C) mangrove forests or mangals.

D) prairie potholes.

44) The number of species of living organisms on the planet isprobably closest to

A) 100,000.

B) 1,000,000.

C) 10,000,000.

D) 100,000,000.

45) The end of the Permian period was characterized by a massextinction of

A) shallow-water marine invertebrates.

B) dinosaurs and other large reptiles.

C) small mammals.

D) large mammals.

46) The dinosaurs and many other animals became extinct at theend of the

A) Cambrian period.

B) Permian period.

C) Cretaceous period.

D) Pleistocene epoch.

47) Species richness of terrestrial plants and animals increaseswith

A) latitude.

B) the structural diversity of plant communities.

C) elevation.

D) flatter terrain.

48) In marine environments,

A) both species richness and productivity increase withlatitude.

B) species richness increases and productivity decreases withlatitude.

C) species richness decreases and productivity increases withlatitude.

D) both species richness and productivity decrease withlatitude.

49) As temperatures decreases with latitude in marineenvironments,

A) both species richness and species dominance increase.

B) species richness increases and species dominancedecreases.

C) species richness decreases but productivity increases.

D) both species richness and species dominance decrease.

50) All species eventually become extinct

A) True

B) False

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