Download Microsoft Word - Chapter 06

Chapter 6
Testing Your Comprehension
1
Both interspecific and intraspecific competition can restrict the ecological role played by an
individual, leaving it to fill just a portion of its full potential role, the so-called fundamental niche. This
more limited role is the so-called realized niche. Species adapt to competition by evolving to use
different resources, or to use shared resources in different ways.
2
Predation is the relationship in which one organism, a predator, consumes another, its prey.
Parasitism is a relationship in which one organism, the parasite, depends on another, the host, for
nourishment or some other benefit while simultaneously harming the host (but generally not killing it).
Herbivory is the consumption of a plant or a portion of a plant by an animal, the herbivore.
3
Fungi and plant roots that form associations called mycorrhizae are symbiotic mutualisms. Bees
pollinating plants while ingesting nectar exemplify a non-symbiotic mutualism. Many agriculturally
important plant species require insect pollination. Moreover, each one of us depends on symbiotic
bacteria in our digestive tracts to continue living.
4
A trophic level is a rank in the feeding hierarchy of a community, with plants and/or
chemoautotrophic producers occupying the first trophic level, and various consumers occupying the
second trophic level. If this list of who eats whom is extended, you have a food chain. In reality, it is
common for one species to consume and be consumed by multiple species, resulting in a network of
feeding relationships called a food web.
5
A species might be considered a keystone species if its removal from the ecosystem causes
pervasive ripple effects throughout the food web. Removal of predators at high trophic levels can result
in increased prey abundance, which may cause decreased abundance of their food as they overgraze.
Other species that have major effects because they physically modify the environment shared by
community members (as beavers and their dams do) are more often considered “ecosystem engineers.”
6
Primary succession involves the establishment of an ecological community in an area that has
never before been colonized by life (e.g., on fresh lava flows or land that has been uncovered by melting
glaciers). Secondary succession begins with the recolonization of an area following a significant
disturbance, such as the regrowth of natural vegetation on an abandoned farm field. In each case, the
community alters the physical environment over time and responds to that changing environment.
7
Clements viewed communities as cohesive entities, much like superorganisms. Gleason viewed
them as temporary associations of species.
8
Changes to the Great Lakes include increased numbers of zebra mussels, decreased smaller
zooplankton and plankton-eating fish, decreased numbers of native molluscs that compete with zebra
mussels, increased cyanobacterial populations, increased numbers of benthic organisms that make use of
zebra mussel waste nutrients, and increased food for organisms that eat zebra mussels (e.g., ducks,
crayfish, muskrats, etc.). See Fig 6.16a.
9
Terrestrial biomes’ distributions are most strongly influenced by climate, which can be
summarized in a climatograph of average monthly temperature and precipitation. Water temperature,
depth, salinity, dissolved nutrients, wave action, currents, and type of substrate shape aquatic
ecosystems’ distributions.
10
See Figure 6.23b and Figure 6.26b. These diagrams indicate the range and timing of temperature
and moisture stresses likely to be faced by organisms in those biomes.
Interpreting Graphs and Data
1
The 2007 population estimate is about 230–240% greater than that of 1983.
2
The recent increase in the sea otter population should be helping to keep sea urchin numbers
down, which should allow lush underwater forests of kelp to grow and provide habitat for many other
species.
3
Each graph should have years along the x axis and numbers of individuals along the y axis. The
sea urchin graph (a) should show decreasing numbers of sea urchins—that is, a trend line going in the
opposite direction as that of sea otters. The kelp graph (b) should show increasing amounts of kelp. The
fish graph (c) should show increasing amounts of fish, because they benefit from increasing amounts of
kelp as habitat.
Calculating Ecological Footprints
Table 1. Introduced Species
Taxon
Percentage of total
introduced
50
Number of species
introduced
25,000
Mammals
0.04
2,000
Birds
0.19
9,500
Molluscs
0.18
9,000
Arthropods
9
45,000
Microbes
40
20,000
Percentage of total
costs
60
Economic cost
Plants
Table 2. Aquatic Invaders
Invader
Fish species
$5.4 billion
Zebra/quagga mussels
11
$0.99 billion
Asiatic clam
11
$0.99 billion
West Nile virus
11
$0.99 billion
Aquatic plant species
5
$0.45 billion
Shipworm
2
$0.18 billion
Green crab
1
$0.09 billion
1
Plant species that happen to do well in soils and conditions where they have been introduced, or
those that have been freed from their herbivores and parasites, may spread quickly, often with seeds that
disperse long distances. Invasive plant species can overrun vast regions, competing with and displacing
native vegetation.
2
Answers will vary. Judging by the aquatic data, animals and microbes seem to have greater
impacts than plants in aquatic environments. However, half of all terrestrial introduced species are
plants, so perhaps they would have large impacts overall.
3
In gardening, you might plant exotic species that could proliferate. You might accidentally
spread aquatic invasives through boating activity. You might release exotic fish from an aquarium into
the wild. You might spread seeds of invasive weeds from place to place when they get stuck on your
shoes. To address such risks, you could carefully research the source and potential impacts of anything
you plant in the ground. You could check boat propellers for aquatic plants and dispose of bilge water in
upland waters before entering sensitive waters. You could refrain from disposing of home aquarium
water into any area that could enter or run off into a public waterway. You could check your socks and
shoes for weed seeds, especially after a hike. You could help monitor your environment for invasive
species, and assist with invasive species removal projects in your community.