CHAPTER 50
AN INTRODUCTION TO ECOLOGY
AND THE BIOSPHERE
1. 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.
3. 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.
4. 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.
6. 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.
8. 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.
10. Using a diagram, identify the various zones found in the marine environment.
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CHAPTER 52
POPULATION ECOLOGY
1. 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.
2. 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.
3. 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.
4. 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.
6. 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.
8. 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.
9. 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.
10. 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.
12. 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.
13. 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
2. 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
3. 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.
4. 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.
6. 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.
6. 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
10. 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.
13. 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.
15. 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
2. 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.
3. 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.
5. 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%.
6. 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 top-level carnivores at the apex because energy transfers between tropic levels are so inefficient.
8. 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.
9. 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.
10. 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.