Lecture 25 Potential Exam Questions

Chapter 26

1. Can the global human population continue to grow at the current rate? Explain why or why not.
-There is some minor academic disagreement that the earth can support its current 2% growth, but Ricklefs says no. Already human impact, at its current population, is having a deleterious effect on the animal and plant species of all environs (air, land and sea). The earth might support more people than it does currently, but the quality of life would begin to be reduced in the short term and the prospect for long-term sustainability is unrealistic at best.

2. Why should we be concerned not only with preserving species diversity but also with preserving genetic diversity and phylogenetic diversity?
-Genetic diversity is the measure of genetic variation in a population, species or community. Biodiversity results from genetic change or evolution which underlies the formation of new species. All species are related by evolutionary descent from common ancestors, some recent and some in the distant past. Phylogenetic diversity is a measure of biodiversity that takes into account the degree of relationship among organisms, giving greater weight to more distantly related forms.

3. What factors are used to identify biodiversity "hotspots," and why? Areas known to be rich in species of large plants, birds, mammals and reptiles are also likely to be rich in species belonging to less conspicuous groups.
-Hotspots account for a mere 1.4% of total land area on earth but consist of more than 44% of all plant species and 35% of all species of terrestrial vertebrates. Therefore, endemism should be a key criterion in the identifying and ranking of the conservation value of an area. Also, areas with a high degree of endemism which are located to growing human populations should be targeted for conservation.

4. In what ways can preserving biodiversity provide economic benefits?
- ecotourism, game species, sources of natural products, drugs, organic chemicals, food, etc …

5. How does the diversity of an ecosystem affect its ability to withstand environmental variation? Higher diversity ecosystems are more likely to have some species that can withstand particular types of stresses.
-As the environment changes, different species can take over the roles as predominant producers in and ecosystem.

6. Compare and contrast mass extinction and anthropogenic extinction.
-Mass extinction refers to the dying off of large numbers of species because of natural catastrophe. Anthropogenic extinction is caused by humans and is similar to mass extinction in the number of taxa affected and in its global dimensions and catastrophic nature. Anthropogenic differs from mass extinction, however, in that is its causes theoretically are under our control.

7. By what mechanisms can habitat fragmentations lead to the extinction of a species?
-Habitat reduction causes extinction by wiping out suitable places for species to live. Fragmentation of habitat into smaller remnant patches is a direct extension of the island biogeography theory. Smaller populations are at greater risk of extinction due to stochastic processes. In the same way, as the habitat for a species on the main-land is reduced in area, that species' population becomes smaller, and its risk of extinction increases.

8. Why are introduced species often a threat to native biodiversity?
-Because they are introduced as new pathogens, predators or competitors so quickly that the native species have not had an opportunity to develop a defense against them.

9. Why are emerging diseases a concern to species that are not directly affected by them?
-The secondary effects of emerging diseases can be just as damaging at the primary effects in that they can remove an organism and dramatically alter an ecosystem. Ricklefs gave the example of rinderpest in the mid 1900s which decimated the wildebeest population in the Serengeti, which resulted in taller grass and a higher propensity for fire. When these fires came, they killed the few trees on the parks and savannas and completely altered the ecosystem.

Chapter 27

1. What does your knowledge of ecology suggest will happen to human populations as they exceed their carrying capacity.
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2. Under what conditions would species introductions not affect ecosystem functions.
- When they fill the ecosystem role of the native species they replaced. However, the effects of introduced species are difficult to predict. In aquatic systems in particular, introductions of consumers at higher trophic levels have seriously altered ecosystem function and have caused basic changes in community structure.

3. What are some of the major costs of using irrigation water?
-The primary costs are the negative environmental effects of developing the dams, wells, canals, and dike work required to support irrigation: depletion of aquifers; lower water tables where wells are the source of irrigation water; accumulation of salts in soils as irrigation water evaporates in arid zones; reduction of groundwater quality through the concentration of naturally occurring toxic elements and the introduction of pesticides and fertilizers; and transmission of diseases by aquatic organisms.

4. Since many toxins naturally occur in ecosystems, why are we so concerned about the current effects of toxins on ecosystems?
-Although they occur naturally, human activities have increased their accumulation. Also, these toxins often accumulate and remain in the ecosystem for a long time and require extensive financial investment for remediation and removal.

5. How can bioremediation be helpful in preserving ecosystem functions?
-Bioremediation is the use of biological agents to clean up the environment and help restore habitats. One concept in practice is the use of some microorganisms (some genetically engineered to have special biochemical properties) to metabolize pesticides and other toxic compounds to innocuous by-products. This process can potentially be used to help clean up pesticides that have been released into the environment.

6. What is thought to be the underlying cause of the thinning ozone layer in the upper atmosphere?
-The release of CFCs (chlorofluorocarbons) for years as propellants in spray cans and as coolants in air conditioning and refrigeration systems. Decreases in stratospheric ozone concentrations of 50% or more — so-called ozone holes — have been observed at high latitudes in both hemispheres.

7. What are some of the expected costs and benefits of global warming?
- On the positive side, warmer temperatures will lengthen the growing season and speed metabolism and will thereby tend to enhance production in moist environments. Plant productivity is likely to be increased due to increased CO2 levels. ON the negative side is the likelihood of increased drought stress in arid environments, which may reduce agricultural production and accelerate the conversion of overused grazing lands and croplands to deserts. Other potential problems include the inundation of coastal human settlements by rising sea levels fed by melting polar ice caps.

8. How does the concept of ecological footprint highlight the impact of humans on the environment?

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