Chapter 47 Summary

1042

Core Concepts Summary

47.1 The niche encompasses the physical habitat and ecological role of a species.

The niche reflects the biological and nonbiological factors that determine where an organism lives and how it functions. page 1022

The fundamental niche is the full range of physical conditions and food resources that permit an organism to live. page 1023

The realized niche is the actual range of habitats where an organism lives, and it is often smaller than the fundamental niche because of competition, predation, and other interactions between species. page 1023

Many closely related species have broadly similar niches as a result of their shared evolutionary history. page 1023

47.2 Competition, predation, parasitism, and herbivory are interactions in which at least one species is harmed.

Competition is a form of interaction that occurs when two individuals of the same or different species use the same limited resource. page 1023

Intraspecific competition is competition between individuals of a single species; interspecific competition is competition between individuals of different species. page 1024

Competitive exclusion prevents two species from occupying the same niche at the same time. page 1024

Over time, competitive exclusion can lead to resource partitioning, in which two species evolve in such a way that they occupy different niches. page 1025

Individuals can compete for food, space, mates, or other resources. page 1025

Predation, parasitism, and herbivory are interactions in which one species benefits and one is harmed. page 1025

Two species that attack a third can help each other in a process called facilitation. page 1027

47.3 Mutualisms are interactions in which both species benefit.

In mutualisms, the benefits to both species outweigh the costs of participation. page 1028

Mutualisms can be obligate, meaning that they are required for survival or reproduction, or facultative, meaning that they are not required. page 1030

Interactions in which one species benefits and the other is unaffected are called commensalisms. page 1030

Species interactions can change over time. For example, partners can become parasites. page 1031

47.4 Communities are composed of local populations of multiple species that may interact with each other.

An ecological community consists of all the organisms living in one place at a given time. page 1031

Biodiversity, or biological diversity, includes the diversity of genetic sequences, cell types, metabolisms, species, life histories, phylogenetic groups, communities, and ecosystems. page 1032

Biodiversity is often measured by the number of species present in a given area. page 1032

Extreme environments can provide useful settings for the study of species interactions because of the relatively few number of species present. page 1032

Species that have a large influence on the composition of a community disproportionate to their numbers are known as keystone species. page 1033

Physical disturbances, such as a storm or drought, can reshape communities. page 1034

Succession is the predictable order of species colonization and replacement in a new or newly disturbed patch of habitat. page 1035

47.5 The cycling of materials and the flow of energy through ecosystems reflect ways that species interact in communities.

An ecosystem is the community and physical habitat in which the organisms live. page 1036

A food web describes how carbon cycles through ecosystems, and a trophic pyramid describes how energy flows through ecosystems. page 1036

Carbon cycles through ecosystems, but energy is used and dissipated. page 1037

Because of energy lost to heat, work, and the inefficiencies of consumers, each trophic level in an ecosystem generally has about 10% of the biomass found at the next-lower level. page 1037

In most terrestrial ecosystems, water and nutrients limit rates of primary production. page 1038

In the sea, primary production is commonly limited by nutrients. page 1038

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Self-Assessment

  1. Choose an organism, such as an oak tree, and define its niche.

    Self-Assessment 1 Answer

    The niche of an oak tree depends on several pieces of information, including: what type of climate/environment/resources can support an oak tree; what other types of vegetation are found alongside oak trees (and how these different plant species interact); and what organisms either feed on oak tree products, or require oak trees for shelter. An oak tree is found in a deciduous forest, which contains nutrient-rich soil and experiences a moderate climate and defined seasons. These trees provide shade, which creates an appropriate environment for underlying vegetation (that is, ferns, shrubs). Oak trees also provide nesting spots for a variety of birds and mammals, and provide food for a variety of insects (which feed on oak leaves) and vertebrates (that is, squirrels eat acorns).

  2. Give an example of mutualism and predation, and in each case describe the benefits and costs to the participants.

    Self-Assessment 2 Answer

    A mutualistic relationship is one in which both species involved benefit in some way. The relationship between aphids and the bacteria that colonize them is an example of mutualism. Here, the bacteria benefit because they are provided with a safe environment within the aphids, and aphids benefit because their nutrient-poor diet is supplemented with products from the bacteria. Conversely, predation is an interaction in which one species benefits and another is harmed. For example, consider the relationship between killer whales and seals. Here, a killer whale benefits by gaining energy from the seals it eats. A seal that is consumed is certainly negatively affected. Once killed, the seal no longer has the opportunity to mate and reproduce, and cannot continue to spread its genetic information to the next generation.

  3. Name three factors that help determine the species composition of a community.

    Self-Assessment 3 Answer

    A community encompasses all of the species within a given habitat. The composition of a given community can be shaped by (1) inter- and intraspecific competition; (2) the frequency of disturbances (like fires) occurring within an environment; and (3) seasonal changes that result in different weather patterns, as well as species’ migration.

  4. Describe how a physical disturbance, such as a drought, can affect community composition.

    Self-Assessment 4 Answer

    When a disturbance occurs in a given environment, it can drastically alter the composition of that area’s community. A drought can seriously reduce the population size of species not equipped to deal with the scarcity of water. This may have an effect similar to what occurs when a wildfire clears a portion of a forest. Such a change allows for new species (adapted for dry conditions) to enter and colonize an area, leading to the process of ecological succession. If droughts are common in a specific region, these disturbances can select for organisms that can tolerate a lack of water and dry conditions. This, in turn, can limit the species diversity in a given community.

  5. Explain what is meant by “ecological succession” and give an example.

    Self-Assessment 5 Answer

    Ecological succession describes the temporal colonization of a new habitat by different species. Each species changes that habitat, making conditions favorable for a new species to move in. A prime example of ecological succession is what occurs after a new island is formed by volcanic activity. Initial colonization by lichen (and associated invertebrates) leads to soil formation and subsequent colonization by grasses and shrubs, which eventually make way for larger trees.

  6. Describe how herbivores can affect the abundances of organisms at higher and lower trophic levels.

    Self-Assessment 6 Answer

    Herbivores occupy the trophic level between primary producers (i.e., plants) and predators. If there is an ample supply of vegetation, herbivores consume this plant material and reproduce. This increase in herbivore numbers provides food for predators at higher trophic levels, and results in an increase in the predator population. If herbivores exhaust the resources provided by primary producers, their numbers decrease, resulting in less food for predators and a smaller predator population. In this manner, changes in an herbivore population can influence predator and primary producer populations at different trophic levels.