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CHAPTER 50
AN INTRODUCTION TO ECOLOGY
AND THE BIOSPHERE
Explain why the field of ecology is a multidisciplinary science.
Ecology is the scientific study of the interaction between organisms and their
environments. It is a multidisciplinary science because it involves the use of
mathematical models, as well as the knowledge of science to develop itself.
Describe the relationship between ecology and evolution.
Since Ecology is the scientific study of the interaction between organisms and their
environments, it is also the study of how those organisms change over time. This change
over time is caused by evolution. In turn, some of the topics studied in Ecology cause
evolution.
Explain the importance of temperature, water, light, soil, and wind to living organisms.
Temperature, water, light, soil, and wind are some of the important abiotic factors that
affect the distribution of species. Environmental temperature affects biological processes
and body temperature. Water is essential for life and adaptations for water balance and
conservation help determine a species’ habitat range. Sunlight provides the energy that
drives nearly all ecosystems although only photosynthetic organisms use it directly as an
energy source. Wind amplifies the effects of temperature by increasing heat loss by
evaporation and convection. The physical structure, pH, and mineral composition of soil
limit distribution of plants and hence animals that feed on those plants.
Describe how environmental changes may produce behavioral, physiological,
morphological, or adaptive responses in organisms.
Catastrophic disturbances such as fires, hurricanes, typhoons, and volcanic
eruptions can devastate biological communities. After the disturbance, the area is
recolonized by organisms or repopulated by survivors, but the structure of the community
undergoes a succession of changes. Disturbances that are infrequent do not elicit
adaptations. Adaptations do evolve to periodically recurring disturbances such as fires.
Describe the characteristics of the major biomes: tropical forest, savanna, desert,
chaparral, temperate grassland, temperate forest, taiga, tundra.
The tropical forest gets lots of rain and has a lot of variety in the species. It is usually
found along the equator. A savanna is a rolling grassland, dotted with trees, which can be
found between a tropical rainforest and desert biome. Not enough rain falls on a savanna
to support a rainforest or for it to be called a prairie. Deserts cover about one fifth of the
Earth’s surface and occur where rainfall is less than 50 cm/year. The chaparral biome has
many different types of terrain. Some examples are flat plains, rocky hills and mountain
slopes. Chaparral is characterized as being very hot and dry. Grasslands are
characterized as lands dominated by grasses rather than large shrubs or trees. Temperate
forests are often called deciduous forests. In a temperate forest, most of the trees lose
their leaves in the winter. During the fall, when the weather gets cooler, the trees begin to
shut down. A biome is the type of habitat in certain places, like mountaintops, deserts,
and tropical forests, and is determined by the climate of the place. The taiga is the biome
of the needle leaf forest. Living in the taiga is cold and lonely. Tundra is the coldest of
all the biomes. Tundra comes from the Finnish word tunturia, meaning treeless plain. It is
noted for its frost-molded landscapes, extremely low temperatures, little precipitation,
poor nutrients, and short growing seasons. Dead organic material functions as a nutrient
pool.
Using a diagram, identify the various zones found in the marine environment.
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CHAPTER 52
POPULATION ECOLOGY
Define the scope of population ecology.
Population ecology is concerned with measuring changes in population size and
composition and identifying the factors that cause these changes.
Distinguish between density and dispersion.
Population density is the number of individuals per unit area or volume. Population
dispersion is the pattern of spacing among individuals within the geographical boundaries
of the population.
Explain how ecologists measure density of a species.
It is usually impractical or impossible to count all individuals in a population, so
ecologists use a variety of sampling techniques to estimate the densities and total
population size. These include counting all the individuals in a sample of representative
plots; estimates become more accurate as sample plots increase in size or number. Also,
estimating by indirect indicators such as the number of nests of burrows or droppings or
tracks.
Explain how age structure, generation time, and sex structure of populations can affect
population growth.
Many populations have overlapping generations where individuals of more than one
generation coexist. Age structure is the relative numbers of individuals of each age in a
population. Sex ratio is the proportion of individuals of each sex found in a population.
In general, a population with more older, nonreproductive individuals will grow more
slowly than a population with a larger percentage of young, reproductive aged
individuals. A shorter generation time usually results in faster population growth,
assuming birth rate is greater than death rate and all other factors being equal. In strictly
monogamous species, the number of males is more significant in the affecting the birth
rate than in nonmonogamous species.
Describe the characteristics of populations, which exhibit Type I, Type II, and Type III
survivorship curves.
Type I: curves are flat during early and middle life and drops suddenly as death
rates increase among older individuals. Associated with species such as humans and
other large mammals that produce few offspring that are well cared for.
Type II: curves are intermediate with mortality being more constant over the life
span. Seen in Hydra, gray squirrels, and some lizards.
Type III: Curves show very high death rates for the young followed by lower
death rates after individuals have survived to a certain critical age. Associated with
organisms such as oysters, that produce very large numbers of offspring but provide little
or no care.
Explain how density-dependent factors affect population growth.
Density dependent factors intensify as the population size increases, affecting each
individual more strongly. They also affect a greater percentage of individuals in a
population as the number of individuals increases.
Describe how weather and climate can function as density-independent factors in
controlling population growth.
Density independent factors are unrelated to population size and affect the same
percentage of individuals regardless the size of the population. Weather, climate and
natural disasters such as freezes, seasonal changes and fires are examples. The severity
and time of occurrence is the determining factor on what proportion of the population is
affected. In some natural population, these effects routinely control population size
before density dependent factors become important.
Explain how density-dependent and density-independent factors may work together to
control a population's growth.
Density dependent and density independent factors sometimes work together to regulate a
population, although the relative importance of each may vary seasonally. A severe
winter may greatly reduce a population due to cold temperature (density independent)
and intraspecific competition for limited food (density dependent). This reduction in
population size may benefit the surviving adults by reducing competition for food in the
following spring.
Explain how predation can affect life history through natural selection.
Predation is when the predator eats its prey. Though repeated encounters with predators
over evolutionary time, various defensive adaptations have evolved in prey species.
Distinguish between R-selected populations and K-selected population.
R-Selected population (Opportunistic population)- are likely to be found invariable
environments in which population densities fluctuate, or in open habitats where
individuals are likely to face little competitions.
K-Selected population (Equal liberal population)- are those that are likely to be living at a
density near the limit imposed by their resources.
CHAPTER 53
COMMUNITY ECOLOGY
Explain the relationship between species richness, relative abundance, and diversity.
Specific richness- the number of species they contain
Relative abundance- of species within community has an enormous impact on its general
character
Diversity- Specific richness, relative abundance
List four properties competition may affect community structure.
Competition- The competitive principle, formulated by G. F Gause, states that no two
species can sustain coexistence if they occupy the same niche.
Resource Partitioning- By pursuing slightly different resource or securing their resource
in slightly different ways, individuals minimize competition and maximize success.
Character Displacement- Selection of these characteristics reduces competition with
individuals in other partitions and leads to a divergence of features, or character
displacement.
Niche- when competitors are present, however, one or both species may be baker to
coexist by occupying their realized niches, that part of their existence where niche
overlap is absent, that is, where they do not compete for the same resources.
Explain how inter-specific competition may affect community structure.
These interactions may have positive, negative, or neutral effects on one ore more of the
population involved.
Describe the competitive exclusion principle, and explain how competitive exclusion
affects community structure.
When two specific complete for exactly the same resources, one is likely to be more
successful. As a result, one species out competes the other, and eventually, the second
species is eliminated.
Distinguish between and organism’s fundamental niche and realized niche.
Fundamental Niche- The niche organism occupies the absence of competing species
Realized Niche- when competitors are present, however, one or both species may be
baker to coexist
Distinguish between Batesian mimicry and Mullerian mimicry.
Batesian mimicry- Occurs when an animal without any specific defense mechanism
mimics the coloration of an animal that does posses a defense.
Mullerian mimicry- Occurs when several animals, all with some social defense
mechanism, share the same coloration.
Distinguish among parasitism, mutualism, and commensalism.
Parasitism- A symbiotic relationship in which the symbiont (parasite) benefits at the
expense of the host by living either within the host (endoparasite) or outside the host
(ectoparasite).
Mutualism- A symbiotic relationship in which both the host and the symbiont benefit.
Commensalism- A symbiotic relationship in which the symbiont benefits but the host is
neither helped nor harmed.
Distinguish between primary succession and secondary succession.
Primary succession- A type of ecological succession that occurs in an area where there
were originally no organisms.
Secondary succession- A type of succession that occurs where an existing community has
been severely cleared by some disturbance.
CHAPTER 54
ECOSYSTEMS
List and describe the importance of the four consumer levels found in an ecosystem.
Herbivores, which eat plants or algae, are the primary consumers. The next tropic level
consists of secondary consumers, carnivores the eat herbivores. Other carnivores that are
tertiary consumers may in turn eat these carnivores, and some ecosystems have
carnivores of an even higher level. Some consumers, the decomposers (also called
detritivores), derive their energy from detritus, which is organic waste such as feces or
fallen leaves and the remains of dead organisms from the other tropic levels.
Explain how the plants in an ecosystem allocate gross primary productivity.
The amount of light energy converted to chemical energy (organic compounds) by the
autotrophs of an ecosystem during a given time is called primary productivity. Total
primary productivity is known as gross primary productivity (GPP). Not this entire
product is stored as organic material in the growing plants, because the plants use some
of the molecules as fuel in their own cellular respiration.
Explain why productivity declines at each trophic level.
As energy flows through an ecosystem, much of it is dissipated before organisms at the
next level can consume it. If all of the plants in a prairie were piled into a huge mound,
another mound of all the herbivores would be dwarfed beside the plants. However, the
herbivore mound would be much larger than a mound of secondary consumers. The
amount of energy available to each tropic level is determined by the net primary
productivity and the efficiencies with which food energy is converted to biomass in each
link of the food chain. These efficiencies are never 100%.
Distinguish between energy pyramids and biomass pyramids.
Energy pyramid is a multiplicative loss of energy from a food chain in which the tropic
levels are stacked in blocks, with primary producers forming the foundation of the
pyramid. The size of each block is proportional to the productivity of each tropic level
(per unit time).
Biomass pyramid is an important ecological consequence of decreasing energy transfers
through a food web. They generally narrow sharply from producers at the base to toplevel carnivores at the apex because energy transfers between tropic levels are so
inefficient.
Describe the carbon cycle, and explain why it is said to result from the reciprocal
processes of photosynthesis and cellular respiration.
The reciprocal process of photosynthesis and cellular respiration are responsible for the
major transformations and movements of carbon. A seasonal pulse in atmospheric CO2 is
caused by decrease photosynthetic activity during the Northern Hemisphere’s winter. On
global scale, the return of CO2 to the atmosphere by respiration closely balances its
removal by photosynthesis. However, the burning of wood and fossil fuels adds more
CO2 to the atmosphere; as a result, the amount of atmospheric CO2 is steadily increasing.
Atmospheric CO2 also moves into or out of aquatic systems, where it is involved in a
dynamic equilibrium with other inorganic forms, including bicarbonates.
Describe the nitrogen cycle, and explain the importance of nitrogen fixation to all living
organisms.
Plants in the form of nitrate take up most of the nitrogen cycling through food webs.
Most of this, in turn, comes from the nitrification of ammonium that results from the
decomposition of organic material. The addition of nitrogen from the atmosphere and its
return via denitrification involve relatively small amount compared to the local recycling
that occurs in the soil or water. Nitrogen is found an all amino acids, which make up the
proteins of organisms.
Explain how phosphorus is recycled locally in most ecosystems.
Phosphorus cycling does not include movement through the atmosphere because there are
no significant phosphorus–containing gases. It occurs in only one important inorganic
form, phosphate (PO4^3+), which plants absorb and use for organic synthesis.
Describe how increased atmospheric concentrations of carbon dioxide could affect the
Earth.
Increased productivity by vegetation is one predictable consequence of increasing CO2
levels. One factor that complicates predictions about the long-term effects of rising
atmospheric CO2 concentration is its possible influence on Earth’s heat budget, which
would increase the temperature level causing ice at the poles to melt and raise the sea
level an estimated of 100m, gradually flooding coastal areas 150 or more km inland from
the current coastline.
Describe how human interference might alter the biosphere.
Human activity often intrudes in nutrient cycles by removing nutrients from one part of
the biosphere and adding them to another. This may result in the depletion of key
nutrients in one area, excesses in another place, and the disruption of the natural
equilibrium in both locations.