Ecology Chapter 16

Which description is true for most communities?

A few species are common and the remainder are rare.

Draw a diagram of a simple food web with three trophic levels, and describe the difference between a food chain and a food web.

A food chain outlines who eats whom. A food web is all of the food chains in an ecosystem. Each organism in an ecosystem occupies a specific trophic level or position in the food chain or web.

A(n) ________ is a type of community with relatively consistent species composition; a uniform, general appearance; and a distribution that is characteristic of a particular habitat.

association

A key limitation of the coefficient of community is that it lacks the ability to

compare relative abundances of each species.

The greater the number of links in a food chain, the higher the

connectance.

During the summer, the bottom, cold layer of dense water in a well-stratified lake is called the ________.

hypolimnion

The view developed by H. A. Gleason that communities result from similarities in species' requirements and tolerances for environmental factors is referred to as the ________ concept of communities.

individualistic or continuum

An ecologist samples the abundance of various species along an environmental gradient and fails to find clusters of species. Instead, peaks of abundance of dominant species are merely randomly spaced segments along a continuum. This distribution of species supports the

individualistic or continuum concept of a community.

Which of the following is considered a guild?

insect-feeding birds

The garter snake in this diagram is an example of a(n)

intermediate species.

Within a food web, herbivores are considered to be

intermediate species.

A species that has a disproportionate impact on a community, relative to its abundance, is called a(n) ________ species.

keystone

The total number of observed links in the food web divided by the total number of species is the

linkage density.

What might be a result of hunting sea otters to extinction for their fur?

loss of kelp beds

In a well-stratified lake in summer, the subsurface layer of water, which is characterized by a steep and rapid decline in temperature with depth, is called the

metalimnion.

The species at the top of a food web

species and are not subject to predation.

Which of the following groups of species represents a guild?

species of birds that feed on nectar

When an ecologist compares the diversity of different communities by counting the number of species within each community, the measure of diversity being used is called

species richness.

In which of the following zones would you most likely expect to find flounders (a type of fish)?

subtidal

Communities with low evenness will have rank-abundance curves

that are very steep.

In a sandy beach community, ghost crabs and beach flies occur within

the supratidal zone.

If you get a Simpson's index of 1, this means

there is only one species in the community.

In a food web diagram, groups of species that derive food energy from a similar source are called ________ levels.

trophic

In a forest community, the layer containing tall shrubs, small trees, and young trees is called the ________.

understory

Changes in the physical and biological structures of communities as one moves across the landscape are referred to as ________.

zonation

The relative abundance of a tree with 100 individuals in a community of 1000 would be

0.1.

Which of the following values of evenness represents a completely even distribution?

1

Which elevational gradient has the most species?

1370-1680 m

Which of the following has the highest species richness? A community with

36 species with very low evenness.

Which score suggests a high degree of community similarity?

90

Define a keystone species. Give an example of the changes that may occur within a community when a keystone species is removed.

A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept. Keystone species have low functional redundancy. This means that if the species were to disappear from the ecosystem, no other species would be able to fill its ecological niche. The ecosystem would be forced to radically change, allowing new and possibly invasive species to populate the habitat. A trophic cascade occurs when a keystone species is removed from an ecosystem. A trophic cascade involves reciprocal changes in the relative populations of predator and prey through a food chain, which often results in dramatic changes in ecosystem structure and nutrient cycling.

Which is the most dominant species?

A) largest in number B) highest in relative abundance C) most relative biomass D) All of the above can indicate dominance.

An organismic concept of communities was developed by

Clements.

(T/F) If a forest canopy is dense and closed, the understory and shrub layers tend to be well developed.

FALSE

(T/F) Most communities have many common species and a few rare species.

FALSE

(T/F) Species composition does not usually differ much within a local area, such as between a hilltop and a stream bottomland.

FALSE

(T/F) The aphotic zone of a lake is inhabited primarily by phytoplankton.

FALSE

(T/F) The boundaries between communities are usually sharply defined and easily discerned.

FALSE

(T/F) The characteristics of a community are generally not dependent on the spatial scale at which the community is examined because communities are tightly integrated groups of species.

FALSE

(T/F) The removal of a keystone species from a community typically results in an increase of diversity.

FALSE

(T/F) The species within a guild are unlikely to interact with one another.

FALSE

Discuss the physical structure of either a forest or a lake, and explain how the physical structure affects the biological structure.

Forest structure is the three-dimensional arrangement of trees and other plants, in combination with nonliving spatial elements such as soils, slopes, and hydrology. In short, structure is the physical geography of the forest, considered at a range of spatial scales. Forest structure is the three-dimensional arrangement of trees and other plants, in combination with nonliving spatial elements such as soils, slopes, and hydrology. In short, structure is the physical geography of the forest, considered at a range of spatial scales.

Explain the difference between a guild and a functional type, and discuss why it may be useful for ecologists to classify species in these ways.

Guilds are concerned with identifying species that share a common resource and determining how this resource is shared among them, the "similar way" of the Root's definition, whereas functional groups are concerned with how the resource is processed by different species in such a way that it provides an ecosystem Functional diversity is of high ecological importance because it is capable of influencing several aspects of ecosystem functioning like ecosystem dynamics, stability, nutrient availability, etc. Functional diversity of a community can be measured by functional richness and evenness.

Describe the zonation of a terrestrial or aquatic community, and discuss the factors that cause zonation to occur.

Lentic waters are generally divided into three zones or sub-habitats: littoral, limnetic, and pro-fundal. A small pond may consist entirely of littoral zone. This zonation is determined by tidal changes, elevation of the land, and salinity of the soil and water. Red mangroves are found along the water's edge, with full exposure to tidal variation and winds. They are well adapted to these conditions with prop roots extending from the trunk and branches.

________ index (D) represents the probability that two individuals randomly selected from a sample will belong to the same species.

Simpson's

The percentage of individuals in a community that belong to one species is called the relative ________ of that species.

abundance

Explain how ecologists define species diversity. What data must be collected to determine the diversity of a community?

Strictly speaking, species diversity is the number of different species in a particular area (species richness) weighted by some measure of abundance such as number of individuals or biomass. Species diversity is defined as the number of species and abundance of each species that live in a particular location. The number of species that live in a certain location is called species richness. ... Abundance is the number of individuals of each species. Species diversity is measured by determining the number of species present in a given area or community and calculating how evenly distributed a species is within that community. ... Surveys done by scientists, camera traps, environmental DNA, and light traps are all examples of methods used to measure species diversity.

(T/F) A food web is more complicated than a food chain.

TRUE

(T/F) Among the array of species that make up a community, not all are equally abundant.

TRUE

(T/F) Dominance is the converse or opposite of diversity.

TRUE

(T/F) Ecologists use a variety of useful sampling and statistical techniques for delineating and classifying communities.

TRUE

(T/F) Every community has an associated vertical structure.

TRUE

(T/F) In a well-stratified lake, the thermocline refers to a steep and rapid decline in temperature relative to the waters above and below.

TRUE

(T/F) Some aquatic communities are defined by physical features of the abiotic environment rather than by the dominant organisms.

TRUE

(T/F) The form and structure of terrestrial communities are defined more by the plants than the animals present.

TRUE

(T/F) The organismic concept views communities as clusters of species associating together as an interacting, integrated component.

TRUE

(T/F) The species within a community interact with one another either directly or indirectly.

TRUE

Choose either of the two most common indices of community similarity (Sorenson's coefficient of similarity and percent similarity), and explain how it is calculated. For what purpose might such an index be used?

The Sørensen index equals twice the number of elements common to both sets divided by the sum of the number of elements in each set. It is different from the Jaccard index which only counts true positives once in both the numerator and denominator. DSC is the quotient of similarity and ranges between 0 and 1. CC = 2c / (a + b + 2c). As you can see, this index differs from Jaccard's in that the number of species shared between the two sites is divided by the average number of species instead of the total number of species for both sites. For both indices, the higher the value the more ecologically similar two sites are.

Explain the difference between the organismic concept of communities and the individualistic continuum concept. Which of these concepts best describes the majority of communities? Explain your answer.

The organismal concept suggests that the organisms live together in a community because they are all dependent on each other. The individualistic concept suggests that the organisms live in a community together randomly and not because they are interdependent.

Who was Aldo Leopold?

a conservationist

Which statement best describes a keystone species?

a rare or uncommon species that has a strong effect on its community

In aquatic habitats, the bottom zone where decomposition is most active is referred to as the ________ zone.

benthic

In a forest community, the upper layer is called the ________.

canopy

In a forest community, the layer in which most photosynthesis occurs is the

canopy.

A straight-line diagram illustrating the flow of food energy from prey to predator is referred to as a food ________.

chain

A species that has massive effects on an ecosystem but in proportion to its abundance is a

dominant species.

When a single or a few species are most prevalent in a community, the species are called ________.

dominants

The layer of a forest in which decomposition takes place and mineral nutrients are released for reuse by plants is called the

forest floor.

In a rank-abundance curve comparing two communities, the community with the greater species richness is characterized by a

greater length of the curve and a more gradual slope.

Within a community, a group of species that carries out similar functions or exploits the same resource is called a(n) ________.

guild

Dominant species tend to be more abundant than other species because they

outcompete other species.

In aquatic habitats, the upper zone of water where the availability of light supports photosynthesis by phytoplankton is called the ________ zone.

photic

Which of the following physical structures would a lake possess?

photic layer

Zonation within a community is typically the result of differences in the

physical characteristics of the environment across a spatial gradient.

A ________ diagram plots each species in a community, beginning with the most abundant and ending with the least abundant, along the x-axis, with the corresponding value of relative abundance on the y-axis.

rank-abundance

The goal of restoration ecology is to

return the community to its pre-disturbance condition.

The simplest measure of community structure is a count of the number of species present and is referred to as species ________.

richness

In the following community, which serves as the keystone species?

sea otters