TopicsB

Chapter 26

The ecological principles we have studied so far can be used both to predict where environmental problems will occur, and to suggest possible solutions. Most of the problems of environmental degradation arise from the growth of human populations; "natural" density-dependent mechanisms which would control population would include wars, famine, and diseases. Still, to control human population is to go against evolution, which dictates that fitness is achieved through reproduction. Thus, our "natural" instincts are to reproduce. We can reduce some environmental problems by applying simple ecological principles, such as eating plants rather than meat (and thus shortening the food chain and avoiding the loss of energy to respiration that would occur in the herbivore link of the food chain).

There are various ways of defining and measuring diversity. There are about 1.5 million described species (and millions of undescribed species) . You should be familiar with Figure 26.1 in Ricklefs and know the approximate proportions of the major groups. The data below might be of some help as well.

Inner ring shows species described in 1992; the outer ring shows the estimated number of total species.

Why should we preserve species? Some think there is a moral imperative to do so, but how can we convince everyone to follow this moral imperative when we routinely kill each other, fight wars, etc.? If we cannot agree on a moral reason to protect species, then we need to make the argument on economic grounds. Organisms can be used for food, fuel, and shelter and pharmaceuticals, and values can be placed on these products. Of course, some of these organisms will be cultivated, but it is either impossible or not feasible to cultivate others, and we must rely on healthy, natural ecosystems to support them. Intact ecosystems may also attract tourists and the dollars they bring to a region, although not every natural system is an attractive destination location and some of those that are may be to fragile to support tourists. Ricklefs makes a none-to-subtle point that in many cases, the real ecological problems arise when a greedy few put profits over the greater good.

There are 3 types of extinction. Background extinction occurs at a low rate as ecosystems change, species evolve, and small natural disasters claim their victims. In background extinction, the extinct species are usually replaced relatively quickly. Mass extinction occurs when large-scale natural disasters (meteor strikes, hurricanes, volcanic eruptions, etc.) wipe out a larger number of species simultaneously. Anthropogenic (literally "born of humans") extinction is caused by human activities, and it is the form of extinction we are most concerned with now.

Whatever the type of extinction, there seem to be 4 mechanisms that drive extinction: climate change, habitat reduction, habitat decline, and overexploitation.

Species faced with climate change have three choices - adapt, migrate, or die. If the climate changes faster than organisms can adapt or move, then it is likely that they will become extinct. Barriers such as mountain ranges, oceans or deserts may prevent migration, and climate may change faster than certain organisms - such as plants - can move. Global warming caused by humans burning fossil fuels is contributing to anthropogenic extinction by climate change.

In general, the larger the area the larger the populations that can be maintained. Small populations are more likely to go extinct just due to random chance, a phenomenon known as stochastic extinction. Small populations are also unable to maintain high genetic diversity, even if they later recover to large numbers there might not be much genetic diversity left. This is known as the bottleneck effect and it is illustrated by the examples of the elephant seals and the cheetahs. Reduction (or fragmentation) of habitat thus leads to smaller populations which are not as viable in the long run.

Predators and competitors can ruin an organism’s whole day. Their introduction into a habitat thus lowers its quality, as does any impact that makes it easier for the predators and competitors. Pollution also may degrade a habitat, either through direct toxicity, or perhaps by encouraging predators or competitors. For example, large parts of the everglades are being overrun by cattails, which thrive on the phosphorus leaching from fertilized cane sugar fields. For any species that depends on the native sawgrass, the cattail invasion represents a decrease in habitat quality.

Humans, through technology, have gone from being intelligent but generally harmless predators, to one of the most efficient, and as a result, we have hunted many species to extinction. Face it, a human, barehanded, may be able to kill a bear or two, but you wouldn’t be able to make a career of it. A rifle changes the picture dramatically. It’s not just modern technology either; our ancestors probably killed off the mammoths with spears. Overexploitation, however, does not have to be anthropogenic; species go extinct due to overexploitation by natural predators. It just doesn’t happen s often as it does with humans.

Vulnerability to extinction is increased by attractiveness as a resource to human hunters, isolation from predation or disease for long periods of time (followed by a sudden influx of predators or diseases), small geographic range, narrow habitat tolerances, and small population sizes. All of these leave a species more open to one of the 4 mechanisms of extinction.

The basic requirement is to sustain a species in large enough numbers that they won’t be wiped out by a chance event. Beyond this, it is necessary to preserve enough habitat to support the species. This can be very complicated when a species requires a lot of room per individual (grizzly bears) or when a species migrates long distances (bison, many songbirds). To be practical, many conservation plans are focused on maintaining key or critical habitat. Such key habitat often supports a variety of species. Ideally, areas with high numbers of endemic species are protected. Often, it is advantageous to set aside numerous smaller preserves rather than one large one of equal area; this approach does not work, however, to protect all kinds of species.

Those who design nature preserves take notice of the species/area curve (see the Biodiversity section in Part 4) and the edge effect in designing the preserves. The edge effect refers to the tendency of areas around the edge of a habitat to have conditions unlike those in the center of the habitat. This often leads to higher diversity, but it does have the disadvantage of making the edges of the habitat less suitable for organisms who would normally live at the center. Since these are the species one is trying to protect in creating the preserve, it makes sense to limit edges by keeping the habitat in one large piece and avoiding disruptions such as roads, pipelines, powerlines, etc. If the habitat is uniform it is better to create one large area rather than several smaller areas of the same size. It is also useful to connect areas with corridors allowing the wildlife to move between the areas. Circular areas are best because they minimize edge effects. On the other hand, if the habitats are different, it makes sense to create more smaller habitats than one large one which does not incorporate all the differing habitat types.

It is possible, if you spend enough money, to keep a species from going extinct - provided you can breed it in captivity. Unfortunately, it also costs a lot of money to do this. In general, we are probably better off preventing such cases of near-extinction by conserving species and their habitat before we reach that point.

Chapter 27

Since we know human populations will continue to increase - for a while, at least - it is important that we take care not to totally destroy the ecosystems on which we all depend. To some extent, this means changing many of our current practices.

It is crucial that ecosystems retain the basic ability to balance the chemical transformations needed for life. Detritivores must break down detritus, photosynthesis must balance respiration, etc.

Several examples are given here of human activities which damage ecological processes, either directly or indirectly.

Normally, when a prey population drops to low numbers, the predator has to spend so much time looking for the prey that it turns its attention to other, more numerous prey. This gives the original prey a chance to recover. Humans, however, can use technology to pursue prey far below the limits that other predators would. In many areas of the world, the problem is simply too many people for the available resources. The example given on Panama is instructive.

Alien species often do well in a new habitat because there are no exact competitors for them, and the new habitat often does not have appropriate predators or specific diseases to affect the alien species. Examples are almost too numerous to list; Ricklefs gives several, to which I might add the locally significant zebra mussel and the gypsy moth. Because of the great impact they may have on the environment, such introduced species often become keystone species. The zebra mussels, for instance, have completely changed the biota of Lake Erie.

Almost any time you clear away native vegetation, you will get soil erosion. This is a particular problem in rainy areas - such as the tropical rain forests - or where slopes are steep (such as in mountains). We have numerous examples of soil erosion locally; and soil erosion is the number 1 cause of water pollution in the United States. Of course, any area which is eroding rapidly is unable to provide any environmental "services" and actually tends to degrade nearby aquatic systems.

Ricklefs doesn’t come out and say it, but irrigation almost never works quite the way it is intended. Unless you are very careful and put in a rather elaborate (= expen$ive) system, you will have either water table lowering, salinization, water pollution, disease, or some combination of these. In the US, this is probably one of the biggest forms of "corporate welfare". Face it - why should a farmer living in Ohio pay taxes so someone in California can grow alfalfa in the desert with inexpensive irrigation water? A true capitalist would say that the California farmer should invest his or her own money to irrigate the crops, and if the crops can still be produced at a competitive price, then that farmer will make a profit. Otherwise, they should get out of the business. Any business majors want to take a closer look at these issues?

Whenever fertilizers are applied to agricultural lands, it is inevitable that some will run off into groundwaters and surface waters. Ricklefs makes a mistake in calling this artificial enrichment eutrophication, when in fact it is better termed cultural eutrophication. This distinction is necessary since eutrophication is a natural process, although under natural conditions it usually takes thousands of years. Eutrophied waters support a high level of plant and plankton life; when these die the decay of the resulting detritus may use up all the oxygen in the water, and lead to a fish kill. Cultural eutrophication is a problem in lakes, streams, rivers and even the oceans (at least in local areas). In the oceans, cultural eutrophication has been linked to the growth of the organisms responsible for red tides. In nature, these organisms secrete toxins which kill fish and other aquatic life, the red-tide organisms thrive in the water which is enriched by the nutrients leaching from the dead sea life. With cultural eutrophication, these organisms can thrive in more areas, and cause fish kills more often.

Humans alter the balance of ecological processes, often in such a way that allows material toxic to organisms to accumulate. These toxins themselves then further alter ecological processes. Acids are released as a result of mining (which exposes chemicals which then oxidize to form acids) or as a result of burning fossil fuels. Burning the fuels (which contain sulfur and nitrogen as well as carbohydrates), nitrous oxides, sulfur dioxide, and carbon dioxide are released. All of these form acids when exposed to water in the atmosphere; the precipitation that forms from this water is thus acid. Acid rain is a bigger problem than acid drainage because the area affected by acid rain is huge - everything downwind of the source, including both terrestrial and aquatic habitats. Rainwater normally has a pH of 6; acid rain may be as acid as pH 3. Because a change of pH from 6 to 5 means a 10x increase in hydrogen ions, it follows that pH 3 is 1,000 times as acidic as pH 6. Acids leach minerals from the soil, degrade human-built structures, change the availability of minerals in the soil and water, make plants susceptible to frost damage, and, of course, physically burn or injure living organisms. With fish, at least, it must also be remembered that even though the adult fish might be able to tolerate acid conditions, the larval fish or eggs might not. Heavy metals such as lead, mercury and cadmium are also important toxins. Heavy metals usually target the nervous system; they get into the environment by smelting of ores, disposal of wastes, in chemical pesticides, and in leaded gasoline. They are particularly nasty because many plants concentrate them from the surrounding soil or water, and they tend to biomagnify as they move through the food chain. Even lower levels may destroy critical species in the ecosystem; fungi in particular are susceptible to low doses of heavy metals. Toxic organic compounds include many pesticides and materials such as PCB’s. If used on farm fields, and if they break down before they leave the field, they do relatively little damage to the environment. Problems occur when these materials reach natural ecosystems or when they persist long enough to move from level to level in the food chain. Sometimes these materials can be removed by applying engineered organisms in bioremediation, but if you think about it, this kind of treatment can be dangerous in itself. To reduce the need to use pesticides, programs such as integrated pest management (IPM) and biocontrol are often used. These methods stress knowledge of the pest and the crop to apply just the right amount of pesticide (if any) at just the right time. Often pesticides can be avoided by simply changing cultural practices such as the day the crops are planted or harvested. Oil spills are another problem you are well aware of, Ricklefs makes an interesting point in that the overall production of "new" hydrocarbons in the oceans dwarfs the amount of oil spilled every year; it is the localized nature of the oil spills that causes the problems. Radiation is a problem, particularly the ionizing radiation, which has enough energy to damage biological molecules. Again, the problem is when humans concentrate radioactive materials and they are subsequently released into the environment in concentrated form. Of course, if there ever were to be a nuclear war, radiation would be the least of the problems ecosystems would face.

Acid rain may affect a region, but it is the most far-reaching of the problems we have studied so far. The other problems we looked at tend to be local in scope. Two problems bear special notice because they affect every ecosystem on the planet. They are destruction of the ozone layer and global warming.

Ozone (O₃) is created when normal (O₂) is broken apart by sunlight and the free O’s combine with O₂’s to form O₃’s. At ground level, ozone is a potent toxin because it has great oxidizing power. In the upper levels of the atmosphere, however, it is of benefit because it absorbs ultraviolet (UV) radiation. UV radiation from the sun has enough energy to damage biological molecules such as DNA. If your skin gets too much UV, the gene that prevents cancer may be damaged and skin cancer will result. UV can also cause cataracts, and, more worrisome, can damage the photosynthetic complexes in plants and algae. Normally, the ozone in the upper atmosphere absorbs the UV, however, chlorine and other molecules that get into the upper atmosphere break down ozone and allow UV to come through. This effect is particularly noticeable at the poles, and lately every winter ozone holes have been noticed at the poles. This is more of a problem at the South Pole, and a number of human settlements are now routinely exposed to elevated UV levels. Chlorofluorocarbons (CFC’s) are the primary source of the chlorine in the upper atmosphere and various treaties have been signed to phase out their use.

Humans have stepped outside the normal density-dependent restrictions that control population growth. Despite crowding, improved agriculture, transport of food using fossil fuels, and reduced mortality due to public health and advanced medicine have all allowed human populations to maintain high birth rates and low death rates. What happens next?

1. Find an official listing of all endangered and threatened Odonata in the United States and in Ohio. Type up and submit the list.

2. Go to the Ohio Odonata Society web pages and examine the Ohio distribution of the various dragonfly and damselfly species. Choose 3 species; one that is threatened, one that is endangered, and one that is common, and explain your reasoning for placing each species in its category.

3. Obtain information on the habitat and national distribution of the species you chose as endangered in Ohio. Is it endangered nationally? Why is it endangered in Ohio? How might we help it survive in Ohio? Should we? Be specific in your plans.