CK-12 Life Science
Page 65
Community interactions include competition, predation, and symbiosis.
Competition can be either direct or indirect.
Intra- and inter-specific competition occur when individuals share a limiting resource in the same area.
The competitive exclusion principle plays an important role in natural selection.
Functional types of predation include true predation, grazing, and parasitism.
Predators can also be classified by degree of specialization.
Prey use different adaptations to avoid detection, attack and capture by predators.
Symbiosis includes mutualism, commensalism, and parasitism.
Review Questions
Define competition.
If the geographic distributions of two similar species do not overlap, would you expect the two species to have character displacement? Why or why not?
Observations of natural populations and manipulative experiments show that two recently evolved species of threespine stickleback fish (Gasterosteus spp.) show two distinct morphologies and feeding strategies in order to co-exist in the post-glacial lakes in which they live in western Canada. Morphologically they differ in the size, shape and the number and length of gill rakers, structures used in their feeding. Name two ways in which these fish species could use different feeding strategies in order to co-exist.
How might a predator lower a prey’s fitness?
In most types of grazing, does the predator lower a prey’s fitness? Why or why not?
A drone fly looks a lot like a bee, yet it is completely harmless as it cannot sting at all. What anti-predator mechanism is the drone fly using? Would you expect predators to always avoid drone flies?
In the mutualistic relationship between the Ocellaris clownfish and the Ritteri sea anemones, what benefit does the fish get?
Hosts may evolve defenses against their parasites. In turn, parasites evolve in response to these defense mechanisms, including evolving adaptations that are specific to a particular host taxon, even specializing to the point at which they infect only a single species. How might such narrow host specificity be costly over evolutionary time? What would help to reduce this cost?
Further Reading / Supplemental Links
en.wikipedia.org/wiki/Symbiosis
http://www.sciencenewsforkids.org/pages/search.asp
http://www.blm.gov/education/LearningLandscapes/students.html
http://www.nclark.net/CommunitiesBiomes
http://www.ecokidsonline.com/pub/index.cfm
Vocabulary
camouflage
When species have an appearance which helps them blend into the background.
character displacement
Two or more species within the same area develop different specializations in order to coexist.
commensalism
A type of symbiosis in which one species benefits while the other is not affected.
community
An assemblage within the same area, of populations of different species interacting with one another.
competition
Organisms of the same or different species compete for a limited supply of at least one resource, thereby lowering the fitness of one organism by the presence of the other.
competitive exclusion principle
Species less suited to compete for resources will either adapt, be excluded from the area, or die out.
grazing
A type of predation where the predator eats part of the prey, but rarely kills it.
keystone species
A predator species that plays an important role in the community by controlling the prey population and, thus, the populations of other species in the community as well.
mutualism
A type of symbiosis in which both species benefit.
parasitism
A type of symbiosis in which the parasite species benefits, while the host species is harmed.
predation
An interaction where a predator organism feeds on another living organism or organisms, known as prey.
symbiosis
Close and often long-term interactions between different species, in which at least one species benefits.
true predation
A type of predation where the predator kills and eats the prey.
Points to Consider
How do you think predation helps a species to survive?
Lesson 23.4:: Ecosystems
Lesson Objectives
Explain what an ecosystem is.
Discuss how biotic and abiotic factors play a role in the ecosystem.
Explain what a niche is and its importance in an ecosystem.
Describe what a habitat is and how an organism is adapted to live in the habitat.
Check Your Understanding
What is a community?
What are the different types of community interactions?
Introduction
Now that you have studied what a community is, you have seen some of the interactions that occur between species. The next level, the ecosystem, includes not only the biological components, but also the abiotic components, all functioning together. You will examine in more depth biotic and abiotic factors, and how the concepts of the niche and habitat play important roles in the ecosystem.
What is an Ecosystem?
An ecosystem is a natural unit consisting of all the biotic factors (plants, animals and micro-organisms) functioning together in an area along with all of the abiotic factors (the non-living physical factors of the environment). The concept of an ecosystem can apply to a large body of freshwater, for example, as well as a small piece of dead wood. Other examples of ecosystems include the coral reef, the Greater Yellowstone ecosystem, the rainforest, the savanna, the tundra, the desert and the urban ecosystem (Figure below).
Figure 23.16
An example of a desert ecosystem, a desert in Baja California, showing Saguaro cactus.
Ecosystems, like most natural systems, depend on continuous input of energy from outside the system, mostly in the form of sunlight. In addition to energy's being transferred within the ecosystem, matter is recycled. Thus, elements such as carbon and nitrogen, and water, all needed by living organisms, are used over and over again. These topics will be discussed in more detail in the Ecosystem Dynamics chapter.
Ecosystems can be discussed with respect to humans as well. A system as small as a household, neighborhood, or college, or as large as a nation, may then be suitably discussed as a human ecosystem. While they may be bounded and individually discussed, human ecosystems do not exist independently, but interact in a web of complex human and ecological relationships connecting all human ecosystems.
Since humans touch virtually all surfaces of the earth today, all ecosystems can be more accurately considered as human ecosystems. In 2005, the largest assessment ever conducted of the earth’s ecosystems was done by a research team of over 1,000 scientists. The study concluded that in the past 50 years, humans have altered the earth’s ecosystems more than any other time in our history.
Biotic and Abiotic Factors
Biotic factors of an ecosystem include all living components, from bacteria and fungi, to unicellular and multicellular plants, to unicellular and multicellular animals. Abiotic factors are non-living chemical and physical factors in the environment. The six major abiotic factors are water, sunlight, oxygen, temperature, soil and climate (such as humidity, atmosphere, and wind). Other factors which might also come into play are other atmospheric gases, such as carbon dioxide, and factors such as physical geography and geology.
Abiotic and biotic factors not only interrelate within an ecosystem but also between ecosystems. For example, water may circulate between ecosystems, by the means of a river or ocean current, and some species, such as salmon or freshwater eels, move between marine and freshwater systems. This concept will be explained more fully in the Biomes and the Biosphere lesson.
Niche
One of the
most important ideas associated with ecosystems is the niche concept. A niche refers to the role a species or population plays in the ecosystem, with respect to all the interactions with its abiotic and biotic components. A shorthand definition is that a niche is how an organism “makes a living”. Some of the important aspects of a species’ niche are the food it eats, how it obtains the food, nutrient requirements, space, etc.
The different dimensions of a niche represent different biotic and abiotic variables. These factors may include descriptions of the organism’s life history, habitat, trophic position (place in the food chain), and geographic range.
Different species can hold similar niches in different locations, and the same species may occupy different niches in different locations. Species of the Australian grasslands, although different from those of the Great Plains grasslands, occupy the same niche.
Once a niche is left vacant, other organisms can fill in that position. When the tarpan (a small, wild horse, chiefly of southern Russia) became extinct in the early 1900s, the niche it left vacant as filled by other animals, in particular a small horse breed, the konik (Figure below).
Figure 23.17
The konik horse, which filled the niche left vacant by the tarpan, a horse that became extinct in the early 1900s in southern Russia.
When plants and animals are introduced, either intentionally or by accident, into a new environment, they can occupy the new niches or niches of native organisms, and sometimes outcompete the native species, and become a serious pest. For example, kudzu, a Japanese vine, was introduced intentionally to the southeastern United States in the 1870s to help control soil erosion. Kudzu had no natural enemies there and was able to outcompete native species of vines and take over their niches (Figure below).
Figure 23.18
Kudzu, a Japanese vine, introduced intentionally to the southeastern United States, has outcompeted the native vegetation.
As already discussed in the Communities lesson, the competitive exclusion principle states, that if niche overlap occurs, either one species will be excluded, character displacement will occur (as in Darwin’s Finches), or extinction occurs.
Habitat
The habitat is the ecological or environmental area in which a particular species lives; the physical environment to which it has become adapted and in which it can survive (Figure below). A habitat is generally described in terms of abiotic factors, such as the average amount of sunlight received each day, the range of annual temperatures, and average yearly rainfall. These and other factors determine the kind of traits an organism must have in order to survive there (Figures below and below).
Figure 23.19
Santa Cruz, the largest of the northern Channel Islands, has the most diverse of habitats in the sanctuary, including a coastline with steep cliffs, coves, gigantic caves, and sandy beaches.
Figure 23.20
Another example of a type of habitat, showing a meadow and representative vegetation.
Figure 23.21
Winter flock of Bearded Reedlings in their natural habitat of dense wetland reeds, in Helsinki, Finland
Habitat destruction is a major factor in causing a species population to decrease, eventually leading to its being endangered or even going extinct. Large scale land clearing usually results in the removal of native vegetation and habitat destruction. Poor fire management, pest and weed invasion, and storm damage can also destroy habitat. National parks, nature reserves, and other protected areas all provide adequate refuge for organisms by preserving habitats. The Environmental Problems chapter will discuss habitat destruction in further detail.
Habitats can also be examined from a human point of view. Thus, it is the environment in which humans live, work, recreate, and move about. Human habitat is the sum total of all factors which constitute the total environment where humans live, work, and perform their essential and day-to-day obligations.
Lesson Summary
An ecosystem is a natural unit consisting of all the biotic and abiotic factors functioning together in an area.
Biotic factors include all living components of an ecosystem and abiotic factors are the non-living chemical and physical factors in the environment.
There are six major abiotic factors.
The niche concept is one of the most important ideas associated with ecosystems.
If niche overlap occurs, then the competitive exclusion principle comes into play.
The habitat is the area where a particular species, species population, or community lives.
Habitat destruction is a major cause of population decrease, leading to possible extinction.
Both the ecosystem and habitat can be looked at from a human point of view.
Review Questions
Give three examples of ecosystems.
List three abiotic components of importance to trees living in a forest.
Give an example of an organism filling a vacant niche.
Why might an introduced species become a pest?
How could separation of breeding periods in frogs result in niche differentiation in the tadpoles?
Name three abiotic factors that a habitat is generally described in terms of.
Species which travel distances between important areas for their survival, such as breeding and feeding areas may be particularly vulnerable to habitat destruction. How might the creation of multiple national parks or nature reserves help such species?
Further Reading / Supplemental Links
Unabridged Dictionary, Second Edition. Random House, New York, 1998.
http://www.kidsgeo.com/geography-for-kids/0164-ecosystems.php
http://www.bellmuseum.org/distancelearning/prairie/index.html
http://www.epals.com/projects/ducks_unlimited
http://www.fws.gov/endangered/kids/index.html
http://www.blm.gov/education/LearningLandscapes/students.html
http://en.wikipedia.org/wiki
Vocabulary
abiotic factors
All the non-living chemical and physical factors in the environment.
biotic factors
All the living components of an ecosystem.
ecosystem
A natural unit consisting of all the biotic factors functioning together in an area along with all of the abiotic factors.
habitat
Ecological or environmental area where a particular species live.
niche
A specific role that an organism occupies within an ecosystem.
Points to Consider
Now that you understand what makes up an ecosystem, what additional factors do you think might be added to get to the next level, the biome?
How do you think what you have learned about abiotic and biotic factors might be applied to the classification of different biomes?
The biosphere is considered to be a global ecological system. Given all you now know about ecology, what do you think the biosphere consists of?
Lesson 23.5: Biomes and the Biosphere
Lesson Objectives
Explain what biomes are.
Describe terrestrial biomes.
Describe aquatic biomes.
Describe the features of the biosphere and list specific systems.
Check Your Understanding
What is an Ecosystem?
How can Ecosystems be discussed with respect to Humans?
Introduction
The concept of biomes and the largest biome of all, the biosphere, is the highest level of organization in ecology, building on everything you have already studied at the population, community, and ecosystem levels. There is a wide variety of biomes, classified into two major groups, terrestrial and aquatic biomes. Because the biosphere integrates all living beings, and can be considered itself a kind of living organism, human activities on one part of Earth can have a major effect on another. In order to better understand all the interactions on Earth, scientists have created various small-scale models.
What a
re Biomes?
A biome is a climatically and geographically defined area of ecologically similar communities of plants and animals, often referred to as ecosystems. Biomes are often identified with particular patterns of ecological succession and climax vegetation (See the Ecosystem Dynamics chapter).
Biome type may also be based on differences of the physical environment (for example, mountain ranges or oceans). Their variation is generally related to the distribution of species according to their ability to tolerate temperature and/or dryness. For example, one may find photosynthetic algae only in the part of the ocean where light penetrates, while conifers are mostly found in mountains.
The biodiversity characteristic of each biome, especially the diversity of fauna and subdominant plant forms, is a function of abiotic factors and the biomass productivity of the dominant vegetation. Species diversity tends to be higher in terrestrial biomes with higher net primary productivity, moisture availability, and temperature. Biodiversity also generally increases most rapidly near the equator and less rapidly toward the poles, and increases with humidity.
The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity. One scheme, developed by the World Wildlife Fund (WWF), identified fourteen biomes, called major habitat types, and further divided the world’s land area into 825 terrestrial ecoregions. This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation. Some of these habitat types are similar to others already discussed, while others include mangroves, flooded grasslands, and savannas.