ENVS 112 Exam 1 – Examples of a well-crafted answers

Question A

The over-usage of fertilizer has no immediate effect on the local ecosystems such as the Kokosing River. Why not just throw a little extra fertilizer on your corps? The surplus won’t cost too much more and it will ensure that you have maximized the potential growth of the given crops. Although there is no visible effect on the local environment, when using a systems approach on the matter one must expand much further than the influences of a particular position on a local ecosystem. The systems approach measures the possible and likely outcomes of the actions on every ecosystem and that is what the farmers in Ohio need to consider. When it rains or due to other weather conditions, the excess fertilizer will run-off the plants and find its way into the river. The fertilizer has little to no effect on the local ecosystems either because of the types of plants found in the Kokosing, or because the fertilizer is too trace of an amount to have significant effect. However, the Kokosing flows into the Mississippi eventually and travels a great distance. Over this vast distance the plants and animals begin to change as the ecosystems change. The amount of fertilizer is also likely increasing as more and more rivers connect to the Mississippi where likely more farmers over-used the fertilizer. Regardless of the reasoning on why, the negative impact of the over-use of nitrogen fertilizer is realized at the mouth of the Mississippi with the Gulf. It is here that a dead-zone has been created and the eco-systems is way out of whack. The plants here have used the fertilizer and now too overgrown or too plentiful and it is having a negative impact on the various species that live there. Through the systems approach it is easier to see the various extenuating circumstances and effects our particular actions could have on other areas and other species and it is imperative that this is considered. [The scale of your system is important. Since fertilizer is a nutrient and is recycled within the system, it is important to recognize that the system of interest is not limited to the Kokosing River.]

Question B

Both riding a bike and driving a car increase the amount of carbon dioxide in the air and impact the global carbon cycle. However, the amount of carbon dioxide released is vastly different. When riding a bike, a human is rerspiring more quickly and breathing out more carbon dioxide. This energy demands are higher and so he eats more, taking carbon out of plant/animal matter and putting it into the air. However, this impact is extremely small when compared to driving – this directly burns fossil fuels to propel a multi-ton object at much greater speeds. The engine's efficiency is very low, and the car is converting a massive amount of stored carbon into gaseous carbon dioxide. Also the carbon emissions involved with producing and transporting gasoline are huge, so the overall cost on carbon dioxide emission of driving is staggering when compared with the simple, much more efficient system of riding a bike. [Finally, Carbon stored in petroleum is a long-term process – millions of years, whereas Carbon stored in food is a very short term storage stock.]

This huge difference in the amount of carbon dioxide emissions produced for these two types of transport would lend to a very real (if long-term) impact on global mean temperature. If biking replaced half of all driving, carbon dioxide emissions based on transport would be effectively cut in half. Less carbon dioxide emission by drivers would lend to lower carbon dioxide concentrations in the atmosphere, and the imbalance between carbon capture and release would be minimized. Less carbon dioxide in the atmosphere would mean a smaller greenhouse effect, as there would be fewercarbon dioxide molecules to absorb and trap heat in the atmosphere. Over time, this effect would be huge and the current process of global warming would likely be slowed, perhaps dramatically so, as personal driving is a large proportion of man-made carbon dioxide emissions.

(Note: This argument assumes that anthropogenic carbon dioxide emissions [and transportation-based emissions, in particular] are at least partly responsible for global mean temperature increases, a highly supported but not yet proven hypothesis).

Question C

Tolerance limit is a useful concept to describe the extremes of an environmental gradient across which an organism can live (such as heat, O2 concentration, etc…). In the middle of the survivable range is an ideal, at which a great number of organisms are supported, with a great deal of variability. However, moving towards one end of the gradient, fewer and fewer organisms can survive, and only those with a genetic makeup conducive to survival at an extreme can continue to reproduce. Eventually, the gradient is too far towards an extreme, and no organisms survive: this is the tolerance limit.

Natural selection is the result of variable, heritable, fitness. Any species has a great deal of variety in its gene pool, and some resulting phenotypes in the population are slightly different from others. Because of this variability, some individuals are better [suited] to their environment than others. Due to limited resources, there is always competition, even within a species, and better-[suited] individuals are more likely to compete effectively, survive, and reproduce. Because their adaptive traits are encoded in their genes, their offspring share those traits, and are also well-[suited]. Over time this variable level of reproductive success lends to a higher prevalence of the advantageous trait in the overall population. This is natural selection.

In the case of the red squirrels, these two concepts led to the observed changes. As global mean temperature increases, an environmental gradient (temp.) moves more towards an extreme, approaching the tolerance limit of the population. Here, the environment supports fewer squirrels, and there is heightened competition, favoring squirrels that are well adapted to warm temperatures (those that breed earlier in this example). This increased pressure means that more early breeders survive and reproduce effectively, which selects for the early breeding trait through the process of natural selection, leading to more early breeders and a much earlier mean breeding time.

Question D

Bringing large predators from Africa to the United States would be irresponsible. These large predators would be considered non-native, and therefore, [potentially] invasive species. [An invasive species is one that is non-native and has negative impact on the ecosystem.] We have no idea what kind of effects they could have on our ecosystem. Scientists might know some immediate effects, but problems down the road can be unexpected and take generations to develop. For example, what if these predators did not have enough prey of what they usually would eat, being that they are tertiary consumers and require a lot of prey and energy to survive, where would they turn? They might eat an unsuspecting creature, wipe them out and then whatever that creature ate would be without its natural predator. The effects could be endless and ones that were never factored into the equation. Invasive species are not species that are inherently bad, they just behave badly in their situation. Although these species were once native in the US, they went extinct for a reason and reintroducing them is not worth it. Economically, it is also just not an option. Not only would we need to do much research beforehand, if something unexpected happens we would need to fund ways to solve the problem and restore our ecosystem. It is a shame that large predators have gone extinct, but introducing them back is not practical. Maybe more conservation efforts should be made in the areas where they already live, but introducing [potentially] invasive species into an area is an extremely big decision and if it’s not necessary (or even if it seems that it is), it should be avoided at all costs.

Question E

Biodiversity is a result of a greater number of species in a given area. The more species an area can support simultaneously, the more bio diverse it will be. One major factor in the number of species present is the number of available niches. No two species can inhabitat the same niche, as competition will drive one out or make it die out. In the rain forest, there are a great deal more niches than in the Sahara, for a variety of reasons. The largest is based on conditions. Rainforests have more water, a requirement for life, have much greater access to nutrients, and exist at temperatures much more favorable for life. These much more favorable conditions provide more ways for organisms to survive by effectively using those nutrients. Another reason, directly linked, is diversity of environments. Because of the great conditions, a vast number of plant species can grow, from large trees to small shrubs. These provide three-dimensionality to the environment that provides more separate niches (ground-level, shrub-level, trunk-level, canopy-level, etc…) for other organisms to inhabit. These plant species also produce a great deal of food matter in a great variety, providing even more niche opportunities for nutrition. There is also a great deal more sub state variety, with dry soils, rocks, wet soils, lakes, ponds, and rivers, things that don’t exist in places like the Sahara.

All of these various niches provide opportunities for resource partitioning, because there are so many resources, and so much variety among them. Organisms must effectively partition resources if they are to survive as separate species, for one species would dominate all other if resources were not divided into exploitable niches. Because of the great number of separate isolated modes of existence within the lush rainforest, many species can coexist simultaneously. First, the rainforest exists at a favorable spot along many gradients for life to flourish, including water, temperature, etc…, meaning that a great deal of life can be supported, and few species face their tolerance limits within that ecosystem. Second, the idea of niches and resource partitioning tie in to tolerance limits, as species competition does represent a factor that puts pressure on the number of individuals. Species can only abound within their own [fundamental] niche, and cannot push their tolerance limits by involving other niches, allowing each [realized] niche to be filled by a different species and increasing bio diversity.

Question F

Ice cores, such as the Vostok Ice Core, can be used to evaluate what global temperatures were in the past. While they do show that global temperature changed “naturally” in the past, before the humans use of fossil fuels, they also show that the rate at which global temperature is currently changing is greater than any time in the past, meaning that global temperature is increasing faster now than it did “naturally” before. Greenhouse gasses, such as carbon dioxide, (in the atmosphere) trap and contain heat in our atmosphere. This is because thermal energy that is not reflected off the atmosphere and makes it to the planet surface is absorbed and reflected back onto the planet by greenhouse gases in the atmosphere. Burning fossil fuels releases carbon dioxide into the atmosphere. If there was no correlation between the burning of fossil fuels, the amount of carbon in the atmosphere, and the global temperature, then one could potentially argue that temperature is not increasing due to human activities. However, there is a strong correlation between the three with all three exhibiting increasing trends. The use of fossil fuels by humans in the last 100 to 200 years is correlated with an increase in atmospheric carbon. This increase in atmospheric carbon did not exist to this extent before the use of fossil fuels. The amount of CO₂in the atmosphere is also correlated with an increase in global temperature, both of which are increasing.

Question G

The systems approach to the environment is that everything is interconnected in the ecosystem. Nothing is [considered] separately and organisms in a system occupy a specific time, space and/or function. This approach is extremely important to understanding the environment because it is crucial to realize that everything is interconnected and that the whole is greater than the sum of its parts (holism). In a forest, the flow of energy is linear, meaning energy is not recycled [it flows through the system] and that in every step of the cycle, energy is lost; this is due to the second law of thermodynamics. [In contrast], the flow of nutrients is circular; they are recycled through the system through consumption, death, decomposers and then reused.

Diagram with explanations not included