BIOL 1004 Lecture Notes - Lecture 20: Keystone Species, Interspecific Competition, Species Richness

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11 Sep 2016

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Community is an association of interacting species inhabiting a defined area

In application communities are often defined by groups restricted taxonomically (e.g. song birds, aquatic

insects, small mammals) or functionally (e.g. trees, pollinators, predators, microbes). 

A central theme in community ecology is to understand how abiotic factors and species interactions

influence the characteristics of a community. 

The key characteristics of a community (community structure)

• Species richness: number of species

• Relative abundance:

percentage of the total number of individuals of all the species represented by one species

• Species diversity: the combination of species richness and their relative abundance

• Ecosystem stability is argued to increase with species diversity

Species Interactions: Interspecific

competition

Occurs when two species overlap in at least one type of resource 

For two competing species: a reduction in the abundance of a species should lead to an

increase in the abundance of the other species 

Evidence for competition in nature: Niche partitioning

• Niche: the total requirements (physical and resources) for a species to grow and reproduce

• Niche partitioning: ecologically similar species exploiting different resources

• Niche partitioning between closely related species suggests that interspecific competition may

have played a role in the evolution of diversity

Predators can influence prey abundance and vice-versa

Predator-prey interactions are an important selective agent

• Many animals produce or can segregate toxins from other organisms

• Aposematism is the advertisement of toxicity to predators

Predator-prey interactions are an important selective agent

Mullerian mimicry: A group of toxic species sharing similar coloration advertising toxicity.

Predator-prey interactions are an important selective agent

Batesian mimicry: A non-venomous species sharing the same coloration as a venomous one

Species Interactions: parasitism

Symbiotic relationship between organisms of different species in which the parasites gets some

benefits at the expense of the host (usually food and habitat) 

The most common life-style on earth 

Parasites are increasingly recognized as important in ecological processes (population,

community, ecosystem level) 

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Document Summary

Community is an association of interacting species inhabiting a defined area. In application communities are often defined by groups restricted taxonomically (e. g. song birds, aquatic insects, small mammals) or functionally (e. g. trees, pollinators, predators, microbes). A central theme in community ecology is to understand how abiotic factors and species interactions influence the characteristics of a community. Occurs when two species overlap in at least one type of resource. For two competing species: a reduction in the abundance of a species should lead to an increase in the abundance of the other species. Predator-prey interactions are an important selective agent: many animals produce or can segregate toxins from other organisms, aposematism is the advertisement of toxicity to predators. Mullerian mimicry: a group of toxic species sharing similar coloration advertising toxicity. Batesian mimicry: a non-venomous species sharing the same coloration as a venomous one.

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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