Download Chapter 4 – Biological Communities and Species Interactions

- 34 Chapter 4 – Evolution, Biological Communities, and Species Interactions
Key Terms
abundance
climax community
coevolution
commensalism
competition
complexity
convergent evolution
divergent evolution
diversity
ecological niche
ecological succession
ecotone
edge effect
environmental indicators
evolution
exotic species
fire climaxed communities
fundamental niche
generalist
habitat
interspecific competition
intraspecific competition
keystone species
natural selection
mutualism
parasitism
pathogen
pioneer species
predation
primary productivity
primary succession
principle of tolerance
realized niche
resilience
resource partitioning
secondary succession
specialist
stability
symbiosis
territorality
tolerance limits
Skills
1. Relate tolerance limits to the survival of an organism.
2. Examine the concept of natural selection and understand how adaptation plays a role in
evolution.
3. Distinguish between niche and habitat. Compare and contrast the ecological, fundamental,
and realized niches an organism may occupy. Explain the following species interactions and
give examples of each: predation, parasitism, mutualism, commensalism, and coevolution.
4. Define keystone species and give examples.
5. Differentiate between Batesian and Müllerian mimicry.
6. Relate competition to the survival of individual organisms and to species survival.
Characterize resource partitioning as a way to avoid competition.
7. Relate the primary productivity of an ecosystem to its diversity.
8. Characterize an ecotone. Relate their significance in species diversity.
9. Summarize ecological succession. Differentiate between primary and secondary succession.
10. Assess the potential damage to an ecosystem and indigenous species when an invasive exotic
species is introduced.
Take Note: It is of paramount importance that you understand the basic ecological precepts
presented in this chapter. You can expect to have to explain the role of certain species in the
environment. Species that are keystone or exotic dramatically influence their environments. You
must be able to explain species interactions, discuss human impacts on species, and give specific
examples of these species. Understand ecological succession and how climax communities are
determined by the climate and soil in different biomes.
- 35 Law of Tolerance
The law of tolerance states that the factor in lowest supply in an environment will be the factor
that determines the survival of an organism. Tolerance limits are the maximum and minimum values
that encompass an organism’s ability to survive. Occasionally a single factor determines the
tolerance limit for a species; more often, several factors function together to determine survival.
A tolerance curve illustrates the range for survival of a species. The optimal range is the set of
conditions that result in abundant numbers of the species. In the zone of physiological stress, the
old, sick, and young are culled from the population. The zone of intolerance is the range of
conditions that will result in death of even the most hearty of the species.
Environmental Indicators
Figure 4.1 Range of tolerance
Environmental indicators are species whose presence indicates a certain environmental parameter is
present in a community. Environmental indicators are a direct, visible key to determine the condition
of the environment. The presence of cattails in Florida’s Everglades is a sign of high levels of
phosphates in the water. Cattails are therefore indicative of phosphate pollutants and serve as an
environmental indicator of the pollution. In studies of stream benthic macroinvertebrates, mayfly,
dobsonfly, and caddisfly larvae are indicative of excellent water quality, whereas the presence of
blood worms, leeches, and pouch snails are indicative of very poor water quality.
Take Note: You must be able to define environmental indicator and explain their significance
to ecosystems. You should also be able to give specific examples of indicator species, and
explain what their presence or absence implies.
Natural Selection and Evolution
Charles Darwin did not devise the theory of evolution; he proposed a mechanism by which natural
selection occurs. Organisms more suited to their environment survive to reproduce. Those
organisms not as suited do not survive, therefore, they do not reproduce. To a biologist, the term
fitness refers to an organism’s ability to reproduce successfully. Therefore, survival of the fittest
means survival and reproduction of those most suited to the environment. In this fashion,
favorable adaptations are passed to subsequent generations and unfavorable adaptations are phased
out of the population of organisms. An individual organism cannot evolve; only populations can
evolve. Natural selection can be attributed to the alteration of the gene pool in these populations.
- 36 The ultimate source of variation in genes is mutation. If a mutation is favorable, the organism
becomes more suited to the environment. If the mutation is unfavorable, the trait will be unlikely
to enhance the survivability of the species. The environmental conditions that result in natural
selection cause selective pressure to be placed upon organisms. The pressure selects for those
most suited to survive in the environment. Some selective pressures include physiological stress,
predation, competition, and chance. For example, the Galapagos finches underwent adaptive
radiation. When an ancestral finch landed on the islands from the mainland of South America,
there were numerous niches to fill. Over time, the finches developed adaptations to allow them to
fill the available niches. The adaptations allowed the finches to radiate.
Divergent evolution is when organisms become less alike over time but share a common ancestry. An
example is the arm of a human and the forelimb of a dog. The bone structure is similar but each
limb is adapted for its particular function. In convergent evolution, selective pressures cause two
organisms lacking a recent common ancestor to become more similar. An example is the wing of a
bird and the wing of a butterfly. Because both fly, they require wings; however, the structure of
the two types of wings is dissimilar.
Take Note: Organisms cannot evolve because they want to evolve in a certain pattern, nor can
organisms pass on acquired characteristics. Organisms may possess a mutation that makes them
more suited, and because they possess that mutation they can survive to reproduce, thus making
their offspring more “fit.” Ensure that you are familiar with the concept of natural selection
and be able to give examples of selective pressures.
Niches
A habitat is the place where an organism lives out its life. The ecological niche is the role it fulfills in
an ecosystem. The niche is controlled by the abiotic and biotic conditions of the ecosystem. An
organism can occupy its fundamental niche if it is not experiencing competition, a situation highly
unlikely in nature. The fundamental niche is the full range of resources or habitat it could use in the
absence of competition. The realized niche is the range of resources and habitat an organism
occupies due to the constraints of competition. For example, the arrival of the exotic lizard species,
the Cuban brown anole, has displaced the native green Carolina anole in parts of Florida. The Cuban
anole resides close to the ground, and the green anole lives in the upper layers of vegetation instead
of the entire vegetated area that they would occupy in the absence of the Cuban anoles.
Species that can eat a wide variety of foods and live in a great variety of habitats are called
generalists. Examples of generalists include rabbits and raccoons. A species that occupies a very
narrow niche is called a specialist. Koalas are specialists because they eat only eucalyptus.
The Law of Competitive Exclusion states that two organisms cannot occupy the same niche for an
indefinite period without one eventually migrating, dying, or undergoing resource partitioning. The
classic example is growing two species of paramecium together in culture. One species was able to
use the resources more efficiently and rapidly multiply and the other species died out, as shown in
figure 4.2. Occasionally some species appear to occupy the same niche with both surviving, but
resource partitioning is usually occurring. Resource partitioning is the use of the resource in a
- 37 slightly different way or at a different time to allow both species to use the same resource. For
example, warblers use different layers of the forest, and yet all use the same forest resources.
Population density
P. aurelia alone
P. caudatum alone
Population
density
Both species grown
Time (days)
together
Figure 4.2 Competitive exclusion
Species Interactions
Predators are organisms that feed on other living organisms. The predator feeds upon a prey
species. For example an osprey is a predator that preys upon small fish. Predators rely on a strong
sense of smell, speed, or stealth to catch their prey. Prey have evolved a variety of mechanisms to
avoid predation, including camouflage, noxious taste, spines or thorns, and speed. Some species
have evolved camouflage by mimicking vegetation, larger animals, or even eyes. Batesian mimicry is
observed when a species evolves to mimic a harmful or noxious species for protection. The Viceroy
butterfly is tasty to birds, whereas the Monarch butterfly is noxious. That the mimic resembles
the toxic model is protective for the Viceroy butterfly. Müllerian mimicry is based upon the fact
that two species may resemble one another when both are toxic. Both species are protected
because predators will avoid interacting with them. An example of Müllerian mimicry is that most
wasps have yellow and black stripes to demonstrate to predators that they are dangerous.
A special type of predation is parasitism. A parasite is an organism that benefits from a
relationship, and the host is the organism harmed by the relationship. Parasites can live on or in the
host species. Examples of parasites include ticks, mosquitoes, tapeworms, and flukes. Pathogens,
disease causing microbes such as bacteria or fungi, may also be considered parasitic.
Symbiosis is the relationship between two organisms. Parasitism is an example of a symbiotic
relationship. Two other types of symbiosis are mutualism and commensalism. Mutualism is an
interaction where both species benefit. An example would be lichens or mycorrhizae. Lichens are
an interaction between a fungus and an algae or cyanobacteria. The fungus provides shelter and
moisture to the algae, and the algae provides sugars to the fungus. Mycorrhizae are interactions
between a plant’s roots and a fungus. The plant gains surface area for absorption, and the fungus
receives sugars in return. Commensalism is when one species is benefited and the other is neither
harmed nor benefited. An example is barnacles on a whale. The whale is not damaged or helped by
- 38 the presence of the barnacle, but the barnacle is given more feeding opportunities by traveling on
the body of the whale instead of remaining attached to a stationary surface.
Coevolution is evolution occurring because species are exerting selective pressures on each other.
An example of coevolution is that moths pollinate flowers that are strong smelling, light in color,
and open at night because most moths are nocturnal species. The animal gains a food resource in
the nectar and the plant benefits from having its pollen spread to other plants. This is also an
example of mutualism.
Take Note: You must be able to explain advantages and disadvantages of the species
interactions. Also, be able to recognize the type of interaction when presented with a
scenario, and be able to give examples when presented with questions regarding species
interactions.
Keystone Species
A keystone species is a species whose relative abundance may not reflect its importance to an
ecosystem. Many keystones are top predators. Gopher tortoises dig burrows in soft sand.
Numerous other species use the burrows, including rattlesnakes, foxes, burrowing owls, armadillos,
frogs, and insects. Gopher tortoises are therefore extremely important in the biological
community, and their removal can interfere with the survival of the other species that depend upon
their burrows for protection.
Take Note: You must understand the importance of keystone species to the environment that
they inhabit, and be able to give examples and explain their role in community interactions.
Competition
Organisms compete for food, water, shelter, space, mates, and any other component they require
for life. Competition between organisms of the same species is known as intraspecfic competition,
and competition between different species is known as interspecific competition. Territoriality is a
form of intraspecific competition where organisms maintain their own area for mating, food
sources, and even nesting sites. Territoriality has the additional benefit of decreasing
environmental degradation because species are usually spread out.
Exotic Species
Exotic species are organisms that are not native to an area but are introduced. They may out
compete endemic (native) species, lack predators, or damage ecosystems. If they are not held in
check in the new environment, they are known as invasive exotic species. These species can cause
tremendous amounts of environmental damage, as well as be expensive to eradicate once they
establish successful populations. Characteristics of areas that make them more susceptible to
invasion by exotics include tropical/semi-tropical climate and high levels of tourism. Examples of
exotic species include water hyacinth, zebra mussels, and fire ants.
- 39 Community Properties
Primary productivity is the rate at which biomass is accumulated in an ecosystem. The energy left
over after cellular respiration is the net primary productivity (NPP). Areas that have high NPP
include marshes, coral reefs, and tropical rain forests. Areas with low NPP include deserts, the
tundra, and open ocean.
The more complex an ecosystem is, the more likely it is able to withstand damage. Ecosystem
diversity is the number of different species occupying different trophic levels. An ecosystem that
has great diversity is more stable and therefore more resilient in the event of a disruption.
Boundaries between adjacent ecosystems have tremendous diversity because the two ecosytems
transition into each other in an area known as an ecotone. Therefore, species from each ecosystem
may survive in the ecotone, resulting in tremendous diversity known as the edge effect. A good
example of an ecotone is an estuary. Organisms from both fresh- and saltwater systems can
survive in the estuary, thus making it a diverse ecosystem with high NPP.
Succession
Succession is the orderly change of species in an ecosystem over time. Primary succession occurs
when an area is newly exposed and has previously not had a biological community. The area lacks
soil, and soil must be formed prior to invasion by plant species. Examples of primary succession
would be a boulder falling on a mountainside or volcanic flow hardening into bare rock. Pioneer
species are the first to grow in an area. Lichens can grow on bare rock and even facilitate the
formation of soil by releasing carbonic acid, which breaks down rock into soil. They are the pioneer
species in primary succession.
The process by which an early species makes subsequent species more likely to be successful is
facilitation. Lichens that contribute to the formation of soil facilitate future plant growth. The
lichens and mosses that are pioneer species give way to grasses and shrubs. The next community is
the appearance of conifers. Finally, a community of broadleaf hardwoods appears in the site.
Secondary succession takes place after an original biological community is damaged and the area
undergoes regeneration.
Secondary is much more rapid than primary succession due to the presence of soil. An example of
secondary succession would be recovery of an area after a fire or forest regeneration in an
abandoned field. Grasses and weeds are the pioneers in secondary succession. Communities
continue to change during succession until the final community the ecosystem can support is
established. The final community that resists change is known as a climax community. If fire
maintains the ecosystem then they are called fire climax communities. These communities
regenerate quickly and are able to maintain their stability due to moderate, fairly frequent
disturbances.
Take Note: It is important that you understand the process of succession. The final climax
community of an ecosystem will be evident in each biome. Also, know the role of fire in
maintaining ecosystems.
- 40 Chapter 4 Questions
Use the following choices for questions 1–4.
a. commensalism
b. mutualism
c. competition
d. predation
e. parasitism
1.
aphids make a secretion called honeydew that ants feed upon, and the ants protect the
aphids from predators
2. an epiphytic orchid living on an oak tree
3. dolphins chasing mullet in a bay
4. schistosoma worms in a human’s blood vessels
5. Primary productivity is highest in which of the following ecosystems?
a. desert
b. grassland
c. open ocean
d. boreal forest
e. estuary
6. A glacier has retreated from a valley in Glacier National Park, leaving a pile of rocks known
as moraine. The type of succession expected in this ecosystem would be
a. primary.
b. secondary.
c. transitional.
d. equilibrium.
e. introduced.
7.
a.
b.
c.
d.
e.
Which of the following is an example of Müllerian mimicry?
distasteful Monarch and harmless Viceroy butterflies look alike
a moth that resembles a wasp
all species of poison arrow frogs have vivid coloration with black markings
a fly that is fuzzy and brown like a honey bee
a kingsnake has coloration similar to the dangerous coral snake
8. Yellow-headed and red-winged blackbirds live in marshes. Both species can nest in the
emergent vegetation in the marsh. If both speices are present, the red-winged blackbirds
are pushed into the shallower, drier areas on the outer limits of the marsh. What niche are
the red-winged blackbirds using when the yellow-headed blackbirds are in the marsh?
a. classical
b. fundamental
c. competitive
d. realized
e. ecological
9.
a.
b.
c.
d.
e.
All of the following are adaptive responses to decrease intraspecific competition except
tadpoles are aquatic herbivores and frogs are semiterrestrial carnivores.
maple seeds use their flat wings to move away from the parent plant.
butterflies consume nectar whereas caterpillars ingest leaves.
floating crab larvae and benthic adult crab.
tigers marking their territory.
- 41 10.
Nocturnal owls minimize competition with diurnal hawks even though they share the same food
resource by using
a. parasitism.
b. resource partitioning. c. coevolution.
d. intraspecific competition.
e. commensalism.
11.
The peppered moths of England underwent directional selection from a light version to a much
darker version after the industrial revolution caused tree bark to darken because of the air
pollution. Which of the following statements explains the shift?
a. The presence of the pollutants induced a mutation in the moths, shifting them to a darker
coloration.
b. The organisms were able to mutate to adapt to the new environment.
c. The new environment caused the darker moths to predominate because the lighter ones were
consumed by birds before they could reproduce.
d. Natural selection caused the dark moths to outcompete the light moths for resources.
e. The competition between the moths for mates caused the lighter moths to become more rare.
12. Which of the following is true of vegetation during succession?
a. Grasses predominate in the midsuccessional stages.
b. Plant biodiversity is greatest in the early successional stages.
c. The pine forest community facilitates the growth of the hardwoods because they acidify the
soil.
d. Hardwoods will tolerate a few scattered cedars in a late successional forest.
e. Lichens hinder the growth of grasses as they prevent soil formation when they thickly cover
rocks.
13.
The flying phalanger, an Australian marsupial, and the North American flying squirrel, a
placental mammal, both possess flaps between their front and rear legs to glide for short
distances between trees. These animals illustrate the concept of
a. coevolution.
b. homologous structures. c. convergent evolution.
d. adaptive radiation.
e. analogous structures.
Questions 14–17 refer to the food web of the chapparal shown below.
Coyote
Haw
k
Snake
Roadrunner
Cicada
Vole
Lizard
Grasshopper
Grasses and shrubs
14.
a.
Which animal occupies the highest trophic level?
hawk
b. snake
c. roadrunner
d. coyote e. lizard
- 42 -
15.
a.
The available energy will be the highest in
grasses and shrubs
b. voles c. grasshopper
16.
a.
b.
c.
d.
e.
If the population of lizards were to increase, which of the following would occur?
The snake and hawk populations will decline.
All voles may experience a population increase.
The cicada population would increase.
There will be a increase in the grasshopper population.
The roadrunner population will decrease.
17.
a.
The organisms shown form a(n)
ecosystem.
b. biome.
c. tolerance range.
18.
The African elephant is known to push over trees in the African savanna. The trees would
outcompete the native grasses that many species rely upon without the elephant’s intervention.
The African elephant’s role in the ecosystem is as a(n)
keystone species. b. exotic species. c. predator. d. top competitor. e. parasite.
a.
d. roadrunner
e. hawk
d. community.
e. population.
19.
a.
Which of the following would you expect to be the pioneer species on an abandoned farm?
hardwood trees
b. pine trees c. lichens d. grasses and weeds
e. shrubs
20.
a.
b.
c.
d.
e.
Exotic species damage in ecosystems because they
are specialists that die out fairly easily.
compete with native species for the same resources.
have numerous predators that cause an increase in the number of predators.
carry diseases that infect native species.
engage in mutualistic relationships with native species.
Explanations
1. b. Both species benefit, so the relationship is mutualistic.
2. a. Epiphytes live on trees, making it a commensal relationship; they do not parasitize them.
3. d. Dolphins are predatory mammals that are carnivores.
4. e. Schistosoma worms are parasites in humans.
5. e. Estuaries have high primary productivity because they are ecotones. The presence of
shallow, brackish allows a great variety of flora, and thus more animals. Deserts, grasslands,
and boreal forests lack the precipitation necessary for high productivity. Open ocean is too
vast and deep to be very productive.
6. a. Transitional, equilibrium, and introduced succession are not terms used in ecology. The
example is primary succession, because there is only rock with no soil. Soil must be formed to
establish a community.
7. c. All examples are Batesian mimicry except the frogs. Batesian mimicry is when a non toxic
mimic is patterned after a toxic model. Müllerian mimicry is when both species are unpalatable
and have evolved to be similar. Therefore, that all poison arrow frogs are vividly colored with
black markings makes them have Müllerian mimicry.
- 43 8. d. The red-winged blackbirds are filling their realized niche, as they are driven from their
fundamental niche by the yellow-headed blackbird. The terms classical and competitive niche
are not used. The ecological niche is the role played in the community.
9. e. Territorality is an intense form of intraspecific competition. The other choices are
mechanisms by which offspring can avoid direct competition with the parent organism.
10. b. Although hawks and owls both feed primarily on rodents, they do so at different times of
the day. Therefore, they use resource partitioning allowing for use of the same resource.
11. c. Survival of the fittest explains that the most suited (the darker moths) would predominate
as the other moths die out because they are eaten before they can reproduce. Mutations are
random and are not induced by the presence of a chemical, nor because the organisms decide to
mutate. There is no evidence in the question that the dark moths are able to outcompete the
lighter moth for resources or mates.
12. d. The hardwoods will tolerate some conifers in a late successional forest. Grasses would
predominate in the early successional stages, and biodiversity is greatest later in succession. A
pine forest community inhibits the growth of the hardwoods because they acidify the soil, and
lichens facilitate grass growth because they help to make soil from bare rock.
13. c. The flying phalanger and the flying squirrel evolved a similar characteristic due to similar
selective pressures.
14. d. The coyote is a quarternary consumer when it eats the roadrunner, a tertiary consumer. The
hawk, snake, and lizard are secondary consumers.
15. a. Grasses and shrubs. In all ecosystems the autotrophs would have the greatest energy.
16. d. The grasshopper population will increase. The snakes and hawks would likely increase
slightly, since the voles might increase due to a lack of competition with the cicada.
17. d. Community. The organisms form a community because it is a group of interacting populations
of animals.
18. a. The African elephant benefits the other species as well as itself by preserving the
grassland, so it is a keystone species.
19. d. Secondary succession would take place on an abandoned farm, so soil would be present.
Therefore, the pioneer species would be the grasses and weeds.
20. b. Exotic species frequently are generalists that easily compete with native species for
resources. They rarely have predators in their new environment. Causing disease is not their
primary impact. If they engaged in mutualistic relationships with native species they would not
be harmful to the native species.