Ecology and Environmental Science
 
Learning Objectives
 
Text Assignment pages: 63-79, 87-92, 115-137
 
Required reserve Reading
 
Optional Reserve Readings (counts toward writing section)
 
One of the hallmarks of living things is their organization. Biologists have classified living things into several levels of organization in biology
I . Sub-biological levels: atom - molecule - compound
II. Biological levels:
  1. Suborganismal/organismal levels: cell - tissue - organ - organ system - organism
  2. Superorganismal levels: population - community - ecosystem - biosphere (or ecosphere)

 
Environmental science is generally associated with the levels : organism to the biosphere.
 
Cells (smallest living entity of life), tissues (group of cells that perform a special function), organs (several groups of tissues that form a discrete body that performs a function, the stomach for example), organ systems (groups of organs that do a major task, like digestion)
 
organisms are the fundamental units of living things. At the level of the individual is the level at which many biological processes work (via survival, reproduction, etc.).
 
populations are all individuals of one species in a defined area. (species definition: all individuals that potentially can mate with each other and produce fertile offspring.)
 
communities: A community is all populations in a defined area that interact (via predation, competition, etc.). There are no rigid boundaries to populations and communities, like organisms).
 
ecosystems: an ecosystem consists of all of the interactions within an community, along with all interactions of the living community with the nonliving physical environment: cycling of nutrients and the flow of energy.
 
biosphere or ecosphere consists of all ecosystems on earth, a thin layer on the surface of the earth.
 
When imbalances occur at any level, all things are affected above it. If you wipe out a level of organization, all the levels below it are gone too (take away the forest: the ecological community living there is destroyed). So, one of the goals of environmental biology (maybe the principal one) is to identify ways to avoid upsetting the balance of the biological systems that support us. When problems do occur, the task of the environmental biologist is to suggest how to deal with the problem (or problems) in the most constructive way possible.
 
The earth is remarkably resilient. It can dilute, break down, and recycle many of the chemicals we add to the air, water, and soil as long as we don't overload these natural processes. It can replenish topsoil, water, air, forests, grasslands, and wildlife as long as we don't use these resources faster than they are renewed. Think of the earth's resources as our savings account C our natural capital. As long as we live off the interest on this capital, we and other species can be sustained.
 
We face a complex mix of interrelated problems. We recycle and reuse little of what we extract from the earth and change into products. Instead we dump the chemicals produced by resource extraction and use into the air, water, and soil, hoping they won't build up to harmful levels. We also produce products that the earth's natural processes can't recycle for us. We will come back to these problems later.
 
I. Introduction to Ecology
The word ecology was coined in 1865 (defined by Ernst Haeckel) from the Greek (oikos meaning "house") to designate the study of organisms in their natural homes. More specifically, it means The scientific study of distributions and abundances of organisms, and the study of the interactions of organisms with one another and with the physical and chemical environment in which they reside.. There are almost as many definitions of ecology as there are ecologists, but this previous definition is a pretty good one.
 
The word "ecology" is often misused in the popular press or equated with "environmentalism" or activism. While many ecologists are active in the environmental movement, ecology as a science is not dependent on –or necessarily always in agreement with-the ideas espoused by various environmental action groups.
 
Ecologists try to understand organisms as they relate to their environment. They can approach this from a number of different levels:
 
A) An ecological community is a set of all of the interacting species present in a given place or habitat. An ecosystem is the ecological community and its nonliving environment, interacting with each other.
All ecosystems are characterized by the concepts of (1) nutrients cycle within ecosystems, and (2) energy flows through ecosystems. Ecosystems are the minimal entities that have all of the properties that can sustain life- no individuals, populations, or even species have this attribute. It takes all of the interactions of the ecological community within itself and with its nonliving environment in order to sustain life. No organism is known to produce its own food and recycle all of its wastes.
 
B) Ecosystems
When any species is carefully studied in nature, it becomes evident that it is not independent of other living things but is one of a system of interacting and interdependent parts which form a large unit. Ecologists use the term ecosystem to indicate a natural unit of living and non-living parts that interact to form a stable system in which the exchange of materials between living and non-living parts follows a circular path. Ecosystems are hard to define, either structurally (by species location) or functionally (by species interactions). A small puddle and a large forest can be an ecosystem. Terrestrial ecosystems are often defined by watersheds , the area of land drained by one stream.
 
The classic example of an ecosystem is that of a small pond. The nonliving parts include water, dissolved oxygen, carbon dioxide, inorganic salts (such as phosphates and chlorides of sodium, potassium, and calcium) and a host of organic compounds. The living parts (organisms) may be subdivided according to their role in the system, these levels are known as trophic levels (= feeding levels.) A trophic level consists of all of the species that are the same number of feeding levels away from the ultimate source of energy (the sun in most cases). A trophic level (trophic = feeding) is the feeding level of an organism in a web. All members of a trophic level feed on individuals from the next level down.
 
sun--->grass --->insect----> mouse---->snake---->hawk
 
There are a total of five trophic levels in the above, with five energy transforming steps (we do not count the sun as a trophic level).
 
C) Trophic levels
1.Producers: Also called autotrophs and are the green plants that produce organic compounds from simple, inorganic substances. There are two types of producers in a pond; the larger plants that are rooted or float on the surface and the phytoplankton or microscopic floating plants that give water its greenish tint.
 
Photosynthesis and respiration, biological production
 
Photosynthesis: organisms that make their own food by capturing light energy and storing it as a form of potential energy (in the chemical bonds that hold atoms together in a molecule of glucose). Green plant are photosynthetic (or autotrophic). They combine CO2 and water to form glucose. Oxygen gas is given off as a byproduct.
 
6 CO2 + 6 H2O + light energy ----> C6H12O6 + 6 O2
carbon dioxide gas + water + light -----> glucose + oxygen gas
 
Respiration is the reverse reaction: plants and animals break down glucose and other energy containing molecules, releasing the chemical energy for work within the body (maintaining activity, growth, etc.)
 
C6H12O6 + 6 O2 --------> 6 CO2 + 6 H2O + energy
 
Remember: autotrophs have to have respiration too!!!!.
 
Primary production: This term refers to the amount of organic matter (biomass) found in an area that was produced by plants. It is measured as the amount (tons, grams, etc.) per unit area (acre, square meter, etc.) Primary productivity is a rate function; it refers to the total amount of organic matter produced by plants per unit area over time. Gross primary productivity (GPP) is the total amount of organic matter per unit area that was produced. Some of these biomass was used by plants in respiration (R) . By subtracting respiration from gross production, you get the net primary productivity (NPP, the net plant biomass per unit area per unit time).
 
GPP = NPP + R
 
Secondary production means the same as primary production, except now we are referring to the amount of heterotrophic biomass (primarily animals) in an area. Secondary productivity means the same as in primary productivity, except now we are talking about the production of animal tissue per unit area per unit time
 
2.Consumers: Also called heterotrophs because they get at least some of their food prefabricated in the form of organic matter (created by other living organisms). Consumers are divided into several groups.
Primary consumers (herbivores): animals that eat plants
Secondary consumers (carnivores): animals that eat animals that eat plants
;Tertiary consumers (carnivores): animals that eat animals that eat animals
Omnivores: animals that eat both plants and animals (they reside at several trophic levels)
Detritivores: organisms that eat dead organic matter, such as leaves and sticks (detritus).
 
Decomposers: Heterotrophic bacteria and fungi which breakdown the organic compounds of dead organisms and return the material to the producers in a form they can use (such as CO2, nitrates, etc.).
 
No matter how large and complex an ecosystem may be, it can be shown that these three major living parts as well as the nonliving component are present.
 
Some plants can be carnivorous! Pitcher plants and Venus flytraps capture insects and other small organisms in traps, these traps contain digestive enzymes that break down animal tissues. These plants are also autotrophs, but they live in nitrogen poor habitats and thus need animal protein as a nitrogen source.
 
D) Food chains:
The transfer of food energy from its ultimate source in plants through a series of organisms, each of which eats the preceding and is eaten by the following, is known as a food chain. The number of steps in a food chain is limited to perhaps 4 or 5 because of the great decrease in available energy at each step (in part to the laws of thermodynamics). Food chains are thus linear chains of who eats whom, the pathways of the flow of energy (food) and transfer of nutrients through the community, from one organism to another.
The percentage of the food energy consumed that is converted to new protoplasm and thus available as food energy for the next organism in the food chain is known as percentage efficiency of energy transfer.
The first step in any food chain, the capture of light energy by photosynthesis and the production of energy-containing foods by plants, is relatively inefficient - only about 0.2% of the incident light energy is stored as food. The efficiency of energy transfer when one animal eats a plant or another animal is a little higher, ranging from 5% to 20%. However, on average, only about 10 percent of the high-quality chemical energy available at one trophic level is transferred and stored in usable form in the bodies of the organisms at the next trophic level. This is sometimes called the ten percent rule. The remaining 90% of the chemical energy transferred from on trophic level to another is degraded and lost as low-quality heat to the environment. (Remember the laws of thermodynamics!)
Most organisms belong to more than one food chain and may even occupy different feeding positions or trophic levels. So, in reality, we have food webs.
 
E) The ultimate size of any animal population is limited by:
a) the length of the food chain, b) the percentage efficiency of energy transfer at each step in the chain, and c) the amount of light energy falling upon the earth. Thus humans can increase our supply of food energy only by shortening our food chain. China eats grain instead of meat, steak is a luxury ecologically as well as economically.
 
The most important thing to remember about energy flow in ecosystems is that it is linear, or one-way. That is, energy can move along a food chain or web from one organism to the next as long as it is not used for metabolism. When energy is used for metabolism and other forms of work, it becomes unavailable for use by any other organism in the ecosystem (remember the laws of thermodynamics?)
 
F) Ecological pyramids
In any food chain, there is loss of energy at each step. It follows that there is usually a smaller amount of living biomass in each successive step of the food chain. Thus a food chain may be visualized as a pyramid; each level is much smaller than the one on which it feeds. There are three pyramids.
 
1) If you count the number of organisms in the different trophic levels, you find that (normally) there are more plants than herbivores than carnivores, a pattern called the pyramid of numbers.
 
2) Because predators are usually larger than the ones on which they prey, a pyramid of biomass can also be constructed (usually on dry weight). Thus animals at the base of the pyramid are small in mass and abundant in numbers; where as those at the apex are large in mass and few in numbers; with those in between showing a progressive increase in size and decrease in number. [On average, these is about a 90% reduction of biomass for each trophic level]
 
3) A pyramid of energy indicates the energy content (usually in kilocalories) of the biomass of each trophic level. Remember: most food chains are short because of the dramatic reduction in energy content that occurs at each trophic level. If you were to have a level 20 consumer, it would take the entire ocean to support one individual. This is why most food webs have only three to five levels.
 
You can have an inverted pyramid of numbers and biomass, but you cannot have an inverted pyramid of energy (again, remember the laws of thermodynamics).
 
If all of us eat as herbivores, is this necessarily better ? We would then need to clear more land for agriculture, invest more capital in production systems, etc. If populations increased, we would still create greater drain on earth's resources, including an increased pressure on other living things by disrupting the ecosystems, and an increase in pollution. We thus do not deal with root of population problem: overpopulation
 
II. Community interactions
 
A) Species may affect each other directly through food chains, or indirectly through other complex relationships. One species may affect the environment in such a way so as to make it more or less suitable for other species, even though the species do not directly interact. These are called community-level interactions. During the 18th and 19th centuries, sea otters were almost hunted to extinction for their fur. When the sea otters were wiped out, the sea urchins (previously kept in check by sea otter predation) increased in numbers, eating and dislodging all of the kelp in the nearshore area. Kelp beds produce habitat for many other species in the habitat, and some species reproduce there. When the sea urchins removed the kelp, this drastically reduced the number of species present. When sea otters were brought back, they ate the seas urchins, and the kelp beds (and eventually other species) came back. The sea otter does not directly interact with kelp (they do not eat kelp), but their presence allows the kelp community to thrive. This indirect effect is called keystone predation, the otter is a keystone predator). A keystone species is one whose presence or absence dramatically affects the rest of the community. This is the main reason why wolves are being reintroduced into parts of North America: the large predators on land are the keystone species. Without them, the numbers of prey populations increase, affecting the rest of the community and the environment and in some ways perhaps harming us. Deer and small mammals (mice and rats) and turkeys are going out of control in many places: the mammals carry ticks that transmit a variety of diseases to humans (Rocky Mountain spotted fever, Lyme disease, etc.)
 
B) Types of species interactions
The members of two different species may directly affect each other in any one of several different ways (Interspecific interactions):
  However, it is incorrect to assume that the host-parasite and predator-prey relationships are invariably harmful to the host or prey as a species. If the predators remove the aged and the sick, they tend to benefit the entire prey population (more food for the survivors, less of a chance of disease from the sick conspecifics, a selection force that weeds out the weak and the sick). In addition, predation, by keeping population numbers down allows for increased diversity of organisms to live in an area (keystone predation)
 
C) Competition and competitive exclusion
 
One ecological principle (formulated by Georgii Gause, but Garrett Hardin coined the term in 1960) is called the competitive exclusion principle. This principle holds that two species with the exact same ecological requirements cannot occupy the same habitat indefinitely. One species usually is slightly better than the other species in using the ecological resources it needs to survive, eventually driving the other species to extinction. In other words, no two species can coexist in the same niche. The same species does not always win at competition, If two species are grown separately , they may use the entire resource. However, when the two species occur together, one drives the other to extinction locally. Sometimes, however, the two appear to coexist, because they use the habitat in different ways (they have slightly different niches).
 
 
D) Symbiosis
 
Not all species compete to the detriment of others, some species cooperate where both benefit. This symbiotic association is called mutualism (you book calls symbiosis to be a synonym of mutualism. Symbiosis in the narrowest sense of the word means mutualism. In the broadest sense, symbiosis means any interaction between two species.) Ruminants (such as cows and reindeer) and intestinal bacteria - both benefit from the association
 
Can be facultative (i.e., they can live apart - legumes (bean plants) and nitrogen fixing bacteria) or obligate (like termites and their intestinal ciliates that break down the cellulose in the wood for them. The two cannot live separately). Pollination is a form of mutualism: the bees get pollen and nectar, the flower gets pollinated.
 
E) niches and habitats: A niche is like the 'job' or occupation of an organism: its functional role in the community, and includes in the definition the exact environmental conditions it requires. The British ecologist Charles Elton defined this term. The organism's habitat is like its 'address, the location (physical location ) of the species. If two or more species are present in a habitat, they occupy different niches.
 
An ecological niche is sometimes hard to identify, but it can be measured in terms of temperature and moisture tolerances, food requirements, mode of acquiring food, nest sites, etc.
 
The fundamental niche is the environment a species would occupy in the absence of direct competition the realized niche is the actual range it occupies in the presence of competitors . Species B's fundamental niche is shown in (b), but when it coexists with species A, its realized niche is smaller, as shown in (c).
 
F) Some common community/ecosystem level processes
 
Succession and disturbance: Succession is the gradual, somewhat predictable change in the plant community over time. Primary succession starts from bare rock, it is the establishment and development of an ecosystem. A few colonizing species settles on the rock (such as lichens) and weeds. They live off of the rock, breaking it down and building up soil (soils consists of weathered rock grains, dead organic matter (humus), water, and many small living organisms). Over time, the colonizing species are replaced with other species, who build up the soils further. Each community is replaced in turn (weeds are replaced with grasses, and grasses with shrubs, and shrubs with trees) until the dominant vegetation type (the climax community) develops.
 
Secondary succession occurs after an area have been disturbed (by farming, fire, flooding). Some of the community has been removed, and succession 'starts over', but not from scratch. Thus secondary succession is the reestablishment of the original ecosystem. One type of secondary succession is old field succession ( 9.6). After the farm field is abandoned, secondary succession occurs. First, the weeds establish (they may sprout up from the many seeds that have lain dormant in the farm field's soils). Over the years, grasses and perhaps trees take over the field, and it reverts back to its original community. Secession is a very slow event, taking 50 to hundreds of years to occur.
 
Over time, the number of species (diversity) increases with succession (Fig. 9.7). At the climax community, the actual number of species may be slightly lowered, due to the various populations of earlier colonists going extinct. The greatest storage of nutrients in the ecosystem and the greatest buildup of soils are occurs in the middle of succession.
 
Fire: Fire is a major disturbance, and a large fire may burn large areas of forest or grassland, where secondary succession may start over. However, fire can be important; by frequent burning all of the dead leaf litter, it can prevent a large buildup of leaf litter, which could cause a catastrophic fire. Many plants, particularly many pine trees, are adapted to fire, they are able to withstand a small, coller fire that does not catch the upper branches on fire. Fire actually helps some pines to disperse their seeds, or prevent competition with grasses. Fire as a disturbance may actually benefit diversity.
 
G) Biological diversity
 
1) Actually three definitions: diversity of habitats in an area (habitat diversity), the number of genetic varieties within species (genetic diversity), the number and relative abundance of species in an area. (species diversity).
 
2) Species diversity is a combination of two concepts: species richness (the number of species present), and species evenness (the relative proportion of members of each species). Merely counting the number of species present is not sufficient to describe the diversity. Diversity has to do with the relative chance of seeing different species as it does with the actual number of species present. A community where each of the species is equally abundant is more diverse than a community with the same number of species, yet one species makes up most of the individuals encountered.
 
3) Some species are more abundant or more widespread than others.
Exotic species: species introduced to a new are, zebra mussels, for example.
Endemic species: species that are found only in one particular native habitat, often one location
Ubiquitous species: found in a wide variety of ecosystems and habitats throughout an area
 
4) The exact number of species on the planet is not known: this is probably one of the more important numbers, according to E. O. Wilson (American ecologist). There are about 1.5 million named species, of these, insects, other arthropods, nematodes, molluscs, protozoans, bacteria, fungi, and flowering plants (dicots and monocots) are the most abundant. Birds (9,000)and mammals (4000) are ACTUALLY VERY FEW, AND MOST BIRDS AND MAMMALS ARE NAMED ALREADY. There may be anywhere from 2 to 10 million actual species on the planet at this time.
 
H) Why preserve diversity?
1. ethical reason: the other species are also alive. Who are we to destroy nature?
2. aesthetic and emotive reason: their beauty and the benefits we derive from observing them. You can look at many monumental vistas in nature (such as the Grand Canyon) and feel this.
3. economic/medical reason: the direct and indirect ways they benefit us, particularly for building, for medicine, and for food.
4. ecological reason: the health of the ecosystem depends on all species of the community. Natural communities help recycle our nutrients and remove toxic materials, refreshing and replenishing our air and water.
5. intellectual reason: what they can tell us about life and ourselves (we are animals after all).
6. religious/moral reason: the duty we owe to nature, depending on religious or moral beliefs. In addition, the responsibility we owe future generations.
7. recreational reason: the need to get away from it all, to exercise and enjoy nature from a recreational point of view.