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Unit V
CHAPTER 50
AN INTRODUCTION TO ECOLOGY
AND THE BIOSPHERE
Explain why the field of ecology is a multidisciplinary science.
The field of ecology is a multidisciplinary science because its challenging. Ecological questions
form a continuum with these from other areas of bioogy, including genetics, evolution, physiology,
and behavior, as well as, those from other sciences, such as chemistry, physics, geology, and
meterology.
Describe the relationship between ecology and evolution.
The relationship between ecology and evolution is that it was the geographical distribution of
organisms and their exquisite adaptions to specific environments that provided Charles Darwin
with evidence for evolution. An important cause of evolutionary change is the response of
organisms to both biotic and abiotic features of their enviroment. Thus, events that occur in the
frame of what is sometimes called ecological time translate into effects over the longer sclae of
evolutionary time.
Explain the importance of temperature, water, light, soil, and wind to living organisms.
Temperature, water, light, soil, and wind are all important abiotic factors. Environmental
temperature is an important factor in the distribution of organisms because of its effect on
biological processes and the inability of most organisms to regulate body temperatures precisely.
Water is essential to life, but its availability varies dramatically among habitats. The unique
properties of water have effects on organisms and their environments. Sunlight provides the
energy that drives nearly all ecosystems, although only plants and other photosynthetic
organisms use their energy source directly. The physical structure, pH, and mineral composition
of rocks and soil, limit the distribution of plants and the animaols that feed upon them, thus
contributing to the patchiness we see in terrestrial biomes. Wind amplifies the effect of
environmental temperature on organisms by increasing heat loss due to evaporation and
convection.
Describe how environmental changes may produce behavioral, physiological, morphological, or
adaptive responses in organisms.
Environmental cahnges may produce behavioral responses in organisms by how animal interact
with their environments. For example, the quickest response to many animals to an unfavorable
change in the environment is to move to a new location. Physiological responses include
regulation and homeostasis. All organisms functon most efficiently under certain environmental
conditions. Physiological responses to environmental variation can also include acclimation.
Morphological responses in organisms may occur when organisms react to some change in the
environment with responses that alter the form of internal anatomy of the body. The various
behavioral, physiological, and morphological mechanisms are responses of individual organisms
operating on an ecological tie scale. These responses occur within a frame work of adaptions
fashioned by natural selection acting over evolutionary time.
Describe the characteristics of the major biomes: tropical forest, savanna, desert, chaparral,
temperate grassland, temperate forest, taiga, tundra.
Tropical forests are found within a 23.5 degree latitude of the equator, where the average
temperature and length of daylight vary little throughout the year. Rainfall is quite variable in
tropics, and amount of precipitation is the prime determinant of the vegetation growing in an area.
There 3 types of tropical forests; tropical dry, tropical deciduous forests, and tropical rain forests.
A savanna is grassland with scattered individuals trees. There are 3 distinct seasons: cool and
dry, hot and dry, and warm and wet, in that sequence. Most savanna soils bare low in nutrients,
which results in the rapid drainage of water. Deserts are the driest of all terrestrial biomes,
characterized by low and unpredictable precipitation. Chaparral are stands of dense, spiny shrub
with tough evergreen leaves. A combination of environmental stresses in chaparral-aridity, short
growing season, low-nutrient soil, and frequent fires-has prevented trees from growing and
resulted in the shrubby vegetation. Temperate grassland share some of the characteristics of
tropical savanna, but they are found in regions of relatively cold winter temperatures. The key to
the persistence of all grasslands is seasonal drought, occasional fires, and grazing by large
mammals, all of which prevent woody shrubs and trees from invading and becoming established.
Grasslands soils tend to be deep and among the most fertile in the world. Temperate forests
occur throughout mid latitude regions where there is sufficient moisture to support the growth of
large trees. These temperate forests are characterized by broad leaf, deciduous trees. The taiga,
also known as the coniferous or boreal forests, is the largest terrestrial biome on Earth, and at
cool high elevations in more temperate latitudes. The taiga is characterized by long, cold winters
and short, wet summers that are occasionally warm. Taiga soil is usually thin, nutrient-poor, and
acidic. Plant forms are limited to low shrubby or mat-like vegetation in arctic tundra. Permafrost,
bitterly cold temperatures, and high winds are responsible for the absence of trees and other tail
plants in arctic tundra.
Using a diagram, identify the various zones found in the marine environment.
Figure 46.26
CHAPTER 52
POPULATION ECOLOGY
Define the scope of population ecology.
The scope of population ecology are density and its dispersion.
Distinguish between density and dispersion.
Density is the number of individuals per unit area or volume, while dispersion is the distribution of
individuals within geographical population boundaries.
Explain how ecologists measure density of a species.
Ecologists often use a variety of sampling techniques to estimate densities and total populations
sizes. For example, they might estimate the number of alligators in the Florida Everglades by
counting individuals in a few representative plots in an appropriate size. Such estimates are more
accurate when there are more numerous or larger sample plots and when the habitat is
homogenous. In some cases, population sizes are estimated not by counts of organisms but by
indirect indicaters. Another sampling technique commonly used to estimate wildlife population is
the mark-recapture method.
Explain how age structure, generation time, and sex structure of populations can affect population
growth.
Many organisms exhibit overlapping generations, or the coexistence of individuals from more
than one generation. Only organisms such as annual plants and animals, such as many insects,
in which adults all reproduce at about the same time and then die, do not have overlapping
generations. The coexistence of generations gives most populations an age structure, which is
the relative number of individuals of each age. Demographers often use age pyramid to show the
age structure of a population. A population’s structure is very important in determining the rate at
which it is growing. Small organisms generally have short generation times, achieving
reproductive maturity quickly. Generation time increases with body size because larger
organisms generally take longer to reach the size at which they can produce
Describe the characteristics of populations which exhibit Type I, Type II, and Type III survivorship
curves.
A Type I curve is relatively flat at the start, reflecting low death rates during early and middle life,
dropping steeply as death rates increases among older age groups. Humans and many other
large mammals that produce relatively few offspring but provide them with good care often exhibit
this kind of curve. Type II curves are intermediate, with mortality more constant over the life span.
This kind of survivorship has been observed in some annual plants, various invertebrates, such
as the gray squirrel. Type III curves drops sharply at the left of the graph, reflecting very high
death rates decline for those few individuals that have survived to a certain critical age. This type
of curve is usually associated with organisms that produce very large numbers of offspring but
provide little or no care, such as many fishes and marine invertebrates.
Explain how density-dependent factors affect population growth.
Density-dependent affects population growth by as population size increases, the competition
becomes more intense, and growth rate declines in proportion to the intense of competiotion.
Density-dependent factors reduce the population growth rate by decreasing reproduction or by
increasing mortality in a crowded population.
Describe how weather and climate can function as density-independent factors in controlling
population growth.
The occurrence and severity of density-independent factors are unrelated to population size; they
affect the same percentage of individuals regardless of population size. The most common and
important density-dependent factors are related to weather and climate. For example, a freeze in
the fall may kill a certain percentage of the insects in a population. Some natural populations
grow exponentially, not reaching the carrying capacity of their environment, until their numbers
are reduced by weather, predators or another density-independent component of the
environment.
Explain how density-dependent and density-independent factors may work together to control a
population's growth.
Density-dependent and density-independent factors may work together to control a population’s
growth by density-dependent factors reduce the population growth rate by decreasing
reproduction or by increasing mortality in a crowded population. Density-independent, before a
population reaches its carrying capacity, numbers are drastically reduced due to weather and
climate. Both work together to control a population’s growth.
List the three major characteristics of a life history and explain how each affects the:
a. Number of offspring produced by an individual
b. Population's growth
Explain how predation can affect life history through natural selection.
Predation can affect life history through natural selection by it causes season variation in life
history. For example, the freshwater crustacean Daphnia retrocurva shows maked seasonal
variation in morphology and clutch size. In spring, the phyto-plankton eaten by Daphnia are
abundant and predators that eat Daphnia are scarce. Under these conditions, individuals develop
into a lounder from with a large broos chamber containing six eggs. However, in the summer,
other plankton that feed on Daphnia are abundant. Daphnia developing at this time of year have
large "hemelts" and long tail spines, presumably making them more difficult for predators to
comsume. These morphological changes use their energy reserves and compress the brood
chamber so that only half as many eggs can be carried. Natural selection has apparently
sacrificed the larger clutch size in favor of a better chance of producing at least some eggs and
surviving to reproduce again.
Distinguish between r-selected populations and K-selected populations.
R-selected populations are the populations that have high reproductive rate as the chief
determinant of life history. K-selected populations is the population where life history is centered
around producing relatively few offspring that have a good chance of survival.
CHAPTER 53
COMMUNITY ECOLOGY
Explain the relationship between species richness, relative abundance, and diversity.
Communities differ dramatically in their species richness, the number of species they contain.
Yet, some communities consists of a few common species and many rare ones, whereas others
contain an equivalent number of species that are all about equally common. The relative
abundance of species within a community has an enormous impact on its general character. A
different community that had the same species richness, but in which the numbers were more
evenly divided among the ten numbers were, would seem more diverse. The term species
diversity considers both components of diversity species richness and relative abundance.
List four properties of a community, and explain the importance of each.
Explain how interspecific competition may affect community structure.
Interspecific competition may affect community structure by as population densities increase,
every individual has access to a smaller share of some limiting resource; as a result, mortality
rates increase, birth rates decrease, and population growth is curtailed. The population growth of
a species may be limited by the density of competing species as well as by the density of its own
population.
Describe the competitive exclusion principle, and explain how competitive exclusion may affect
community structure.
The concept of the competitive exclusion principle is basically, when the populations of two
species compete for the same limited resources, one population will use the resources more
efficiently and have a reproductive advantage that will eventually lead to the elimination of the
other population. Competitive exclusion may affect community structure by competitive exclusion
would lead to the extinction of one of the species and that one of the species will evolve enough
to use a different set of resources. Thus, there would no longer be competition.
Distinguish between an organism's fundamental niche and realized niche.
Fundamental niche refers to the set of resources a population is theoretically capable of using
under ideal circumstances. The resources a population actually uses are collectively called its
realized niche.
Distinguish between Batesian mimicry and Mullerian mimicry.
Batesian mimicry is when a palatable or harmless species mimics an unpalatable or harmless
model. Mullerian mimicry is when two or more unpalatable, apostematically colored species
resemble each other
Explain the role of predators in community structure.
The role of predator is to moderate the competition among its prey species.
Distinguish among parasitism, mutualism, and commensalism.
Parasitism is when one organism, the parasite, harms the host. Mutualism is when both partners
benefit from the relationship. Commensalism is when one partner benefits without significantly
affecting the other.
Distinguish between primary succession and secondary succession.
Primary succession is when there is an essentially lifeless area where soil has not yet formed,
whereas secondary succession is when there is an existing community that has been cleared by
some disturbances that leaves the soil intact.
CHAPTER 54
ECOSYSTEMS
Explain the importance of autotrophic organisms with respect to energy flow and nutrient cycling
in ecosystems.
Each ecosystem has a trophic structure of feeding relationships that determines the pathways of
energy flow and chemical cycling. The trophic level that ultimately supports all others consists of
autotrophs, or the primary producers of the ecosystem Most producers are photosynthetic
organisms that use light energy to synthesize sugars and other organic compounds, which they
then use as fuel for cellular respiration and as building material for growth.
List and describe the importance of the four consumer levels found in an ecosystem.
Primary consumers- consists of herbivores, which eat plants or algae.
Secondary consumers- consists of carnivores, which eat herbivores.
Tertiary consumers- consists of carnivores, which eat other carnivores.
Decomposers- also called detritivores, derive energy from detritus, which is organic waste such
as feces or fallen leaves and remains of dead organisms from the other trophic levels.
Explain how gross primary productivity is allocated by the plants in an ecosystem.
Gross primary productivity is allocated by plants in an ecostem by the plants use some of the
molecules as fuel in their own cellular respiration.
Explain why productivity declines at each trophic level.
Productivity declines at each trophic level because as energy flows through an ecosystem, much
is lost at each trophic level. As energy flows through an ecosystem, much of it is dissipated
before it can be consumed by organisms at the next level. The amount of energy available to
each trophic level is determined by net primary productivity and the efficiencies with which food
energy is converted to the biomass in each link of the food chain.
Distinguish between energy pyramids and biomass pyramids.
A Biomass pyramid is when decreasing energy transfers through a food web, in which each tier
represents the standing crop biomass in a trophic level.
Describe the carbon cycle, and explain why it is said to result from the reciprocal processes of
photosynthesis and cellular respiration.
The reciprocal processes of photosynthesis and cellular respiration are responsible for the major
transformations and movements of carbon. A seasonal pulse in atmospheric CO2 is caused by
decreased photosynthetic activity during the Northern Hemisphere’s winter. On a 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 atmospheric; 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 dynamic equilibrium with other inorganic forms,
including bicarbonates.
Describe the nitrogen cycle, and explain the importance of nitrogen fixation to all living organisms.
Most of the nitrogen cycling through food webs is taken by plants in the form of nitrate. 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 amounts compared to the local recycling that occurs in the soil or water. Also, in some
ecosystmes, atmospheric depositon of NH4+ and NO3- that is dissolved in rain adds nitrogenous
minerals to the soil.
Explain how phosphorus is recycled locally in most ecosystems.
Phosphorus, which does not have an atmospheric component, tends to cycle locally. Exact rates
vary in different systems. Generally, small losses from terrestrial systems caused by leaching are
balanced by gains from the weathering of rocks. In aquatic systems, as in terrestrial systems,
phosphorus is cycled through food webs. Some phosphorus is lost from the ecosystem because
of chemical precipitation or through settling may lock away some of the nutrient before biological
processes can reclaim it. On a much longer time scale, this phosphorus may become available to
ecosystems again through geological processes such as uplifting.
Describe how increased atmospheric concentrations of carbon dioxide could affect the Earth.
Increases atmospheric concentrations of carbon dioxide could affect the Earth by it would affect
global temperatures. Warming can result to the melting of polar ice that might raise sea levels by
an estimated 100m, gradually flooding coastal areas 150 or more km inland from the current
coastline. A warming trend would also alter the geographical distribution of precipitation, making
major agricultural areas of the central United States much drier.
Describe how human interference might alter the biosphere.
Human interference might alter the biosphere by human activities are altering species distribution
and reducing biodiversity. Human population have intruded in one way or another into the
functioning of many ecosystems. Humans have disrupted the trophic structure, energy flow, and
chemical cyling of ecosystems in most areas of the world.