18 December 1995
Third Examination: Community and Systems Ecology
A. The nature of the community
1. Briefly describe the major differences between the pattern of succession of an algae on a rocky shore from that which happens in an area recently uncovered by the retreat of glacial ice.
The first plants to settle in the marine environment are the spores of algae such as Gelidium, Gigartina, Ulva, and other small red and greens. These spores then germinate in the vegetative plants. They are able to settle because of the bacterial film on the substrate. In competition with them are the larvae of barnacles and mussels. If the latter settle first, then they shade out or prevent the algae from growing. For the terrestrial habitat, the first organisms to settle out are lichens and/or annuals that are able to grow in nitrogen poor substrates. This therefore is the major difference, aquatic succession is not related to nitrogen availability from the substrate, but simply to the nature f the substrate, whereas in terrestrial systems, nitrogen availability is an import determinant of what will happen. From this point on there are some differences in the sizes of the plants, as in terrestrial ecosystems plant size gets larger as one approaches the climax community, whereas in marine systems, there is no real change in the size of the organisms.
2. Define the following terms with respect to community structure:
a. climax
The climax community is the community that is defined as the end sere. It is characterized by low rates of productivity and low turn over, and a large amount of recycling. The species belonging to the climax community are long lived species and in terms of strategy are "k" selectors rather than "r" selectors. Climax species are replaced by themselves as compare to subclimax species which are replaced by a different suite of species.
b. facilitation
Facilitation is the situation where the presence of one species enables another species to succeed the first. If the example of glacial succession is used, the first colonizers increase the nitrogen content of the soil and as a result enable plants that are not able to produce their own nitrogen, to grow in what was initially a nitrogen poor environment
c. allogenic succession
Allogenic succession relates to events where the pattern of succession is determined by colonizers outside of the system. One characteristic example of allogenic succession is what happens in cow dung. There are certain species of plants and animals that inhabit this material. After the material is released from the cow, it falls to the ground where some of the seeds int he material germinate and begin to grow. This produces an "island" of different species from what is happening around the dung.
d. gradient analysis
In gradient analysis one assumes that a community is simply an association of organisms that are located in the area being sampled. As a result, if one looks at the distribution of any one member of that community, one would see that the members of that species are distributed along a gradient of some environmental parameter, eg. temperature, soil pH, etc. Therefore the community is simply the location where the gradients of al lthe species that are found there, overlap.
e. diversity indices
Diversity indices not only measure the number of species present, but also the numbers of individuals belonging to a species. If we only looked at species richness ( a measure of the total number of species in a community) we would have a biased vision of that community, as some species may be abundant, others not so abundant. If we take into this measure the number of individuals belonging to a species we have an added measure of the diversity of the community
B. The flux of energy through a community
1. Define the following terms (give the units of measure if appropriate):
a. primary productivity
Primary productivity is a measure of the amount of photosysnthesis/chemosynthesis that takes place in a community. It is a measure of the amount of carbon fixed in the community. It is usually measured in gms carbon/m2/day
b. biomass
Biomass is a measure of the amount of living (or perhaps living and dead biomass) found in a community. It is not a rate measure, but simply a mass per unit of area measure or an energy per unity of area measure (kg/hectare or gm/m2)
2. By means of a diagram indicate the relationship between leaf temperature, rate of photosynthesis (gross and net) and respiration.
This is a diagram with leaf area along the x-axis and rate of photosynthesis/respiration along the y-axis. Photosynthesis and respiration are convex and concave measures and the area between the two represents the net gain. As is evident from the diagram there is one leaf area where photosynthesis is maximized and respiration is minized and thus the total gain is maximal. This point varies for all species dependent upon leaf geometry, and photosynthetic efficiencies.
3. Compare and contrast the primary production in a grassland and in the near shore temperate ocean. Include in your answer information about the nature of the producers, their annual cycle, rates of consumption, etc.
The primary producers in a grassland are the grasses. They are usually at least annuals, but more often perrenials. Much of the energy is tied up in dead material on the ground surface, as at the end of the season the above ground biomass falls over and as the material being decomposed. In contrast, in ocean systems, the producers are small phytoplankton which have a life span of a day or two. When the nutrients are gone, they are gone. Because they live in a volume, upon death if not eaten, they disappear from the volume due to sinking. Thus their nitrogen is not recycled, but is loss to the system. The grazers in both systems are of different sizes. Those in the ocean are only slightly larger than their food items, whereas in the grassland, the grazers may a good deal larger (eg., bison). It seems as if the grazers in a grassland do not control the grass abundance although they may increase abundance due to cropping and salivary growth enhancers. The opposite seems somewhat true of ocean systems, although in this case the decrease in phytoplankters is more due to a loss nutrients for growth rather than a decrease in numbers due to grazing.
4. By means of a simple diagram, indicate the path of energy through a simple ecosystem. Indicated the losses and gains to each component of the system.
The members of a simple ecosystem are the producers, the consumers and the decomosers. All lavels have inputs, eg., sunlight for the first, live organisms for the second and a dead/particulate matter for the third. All levels have losses, consumption for the first, death or consumption by a higher level of consumers for the second and consumption or death for the decomposers. All have a respiratory loss. All may have a flux out of the community, eg., coral reef or stream communities. All set aside energy for growth.
C. Flux of matter through a community
1. What are the main differences between the fluxes of energy and the fluxes of matter in communities?
Energy is constantly being recycled, whereas matter is used only once. With every conversion of matter to energy, there is some loss in the process. The usable energy, heat energy, contributes to the entropy of the system. If we think of the matter as the constituent atoms that is composed of, then we find that the individual atoms are recycled, even though in the chemical processes associated with the atoms, there is a loss of matter as some of the matter is converted to energy to drive the system.
2. We spent some time describing the nitrogen budget for the Hubbard Brook Experimental Forest. What were the main compartment for nitrogen in that system? When the system was partially perturbed, e.g., by clear cutting of one of the drainages, what was the outcome with respect to changes in nitrogen in the system? What did this indicate as to the relationship between nutrient cycling and inputs and outputs in the system?
The main compartments for nitrogen in that system are the above ground plant parts, leaves, branches and trunks; the below ground parts, roots; the nitrogen in the leaf litter; and the nitrogen in the soil that has been added by decomposing leaves. The inputs essentially come from nitrogen (in the form of nitrites and nitrates ) from the air and materials like dust, etc. that contain nitrogen in one form or the other. The materials are essentially recycled in the system. If the forest is clear cut, then since the biomass is taken out of the system, the nitrogen is removed from the system. Another aspect that has been noted is that nitrogen in the stream flow also increases immediately after clear cutting, indicating that the change in vegetation also affects the way in which nitrogen is cycled in the system.
3. Take one of the major elements and briefly describe its regular cycle and then describe how we humans have modified that cycle.
Carbon--Carbon is fixed by photosynthetic plants. Some of the carbon will be in a form usuable by the consumers, eg., glucose, amino acids, other will not be immediately usuable, eg., cellulose. The organic material is passed from one level to the next by consumption. There are losses at each step. Not all material is eaten, not all material is assimilated. These losses get transferred to the decomposers. Decomosers reduce materials back to their elemental form. Often they can't keep up with the amount being added and the organic material is mineralized by other processes or may be fossilized. Humans perturb the system by either removing the carbon from the system directly, cutting down trees, harvesting plants and transferring it to other systems (eg. sewerage treatment plants associated with towns and cities) or somewhat indirectly through forest or grass fires. This transfers the carbon to a different comartment, eg., the atmosphere or to the ocean where there are other pathways that the material can travel.
D. Islands, Areas and Colonization
1. What is the general rule about the relationship between the island size and the number of organisms?
The general rule is that as the island is larger in size, there are greater numbers of species. Associated with the rule is the rule of distance, i.e., the greater the island is away from the mainland, the fewer the species.
2. The above is usually explained in terms of a. habitat diversity, b. equilibrium theory and c. rates of evolutionary change. Briefly describe each of these explanations and giving a biological example for each.
a. Habitat diversity--one might assume that larger habitats possess a greater diversity of habitats, e.g., as soil type is dependent upon the underlying geological strata, the larger the area, the more geological strata present.
b. equilibrium theory--this states that the number of species arriving at an island should reach an equilibrium point with respect to the number of species going extinct.
c. rates of evolutionary change--this states that the longer a species has been present on an island the greater the chance that it has undergone evolutionary change. That evolutionary change might include the production of many new species or at least a few more than had originally arrived. Thus the number of species on an island could be due to the age of the island and not simply the number of arrivals and departures
3. Mac Arthur and Wilson's equilibrium theory makes some predictions about species turnover on islands. What are these predictions? How would you test for them? Is such a test feasible?
Their prediction is that distance and size determine the number of species on an island. This has been tested emirically by sampling programs on islands of different size and different distances from the mainland. This has been tested experimentally by removal of species form mangrove islands off the coast of Florida. Therefore, a test is feasible. What one has to discount though is the differences in the habitats provided by different islands, eg. tropical island versus one off the coast of Greenland (itself and island) and how long the island has been around (Madagascar versus Krakatoa).
4. In what ways would a better understanding of island biogeography lend itself towards nature conservation?
The most important aspect is an understanding of what size plots of land are most suitable for the conservation of organisms of different body size and different life histories. For example, to maintain shrew or vole diversity, we would only need a plot size of a few hectares, yet to maintain wolves or other large carnivores, we would have to preserve thousands of hectares.
E. Go to the ecology home page and answer the following questions based on data on that home page (http://oz.plymouth.edu/~lts/ecology.html). You can use any program on the computer to help in answering the question.
1. What is the average age of the trees in the Pemigewasset Riverside Park? Is there any correlation between dbh and age? Attach a printout that includes a scatter graph of this relationship.
The average age of trees in the stand is 40.21 years. There is only a weak correlation between dbh and age (0.36).
2. Examine the data sheet for leaf drop in Plymouth. Write a short results section and send that section to me by e-mail (lts is my e-mail address).
Results:
Twelve of the trees examined were Sugar Maples. They ranged in elevation from 110 meters above sea level to 183 m. There seemed to be no relationship between the total loss of leaves and elevation. There was a looser relationship between latitude and loss of leaves. With a couple of exceptions, those trees further north tened to loose their leaves and leaf color earlier. The maples lost not only color earlier than the beech tree, but also their leaves. As of the 13th of Novemenber the Beech tree still retained 28% of all its leaves, whereas all the maples had lost their leaves by the 31st of October.
3. Examine the data sheet for the leaf area index. Write an abstract for that data sheet (assume that you have written all the other sections of the paper prior to this activity). Use the word processing abilities of the computer and type for me a title, your name and address and the abstract. Use the format that you would use if you were to submit this paper to Ecology.
Leaf Area Index of Selected Tree Species in Central New Hampshire
Larry T. Spencer
Natural Science Department
Plymouth State College
Abstract: The effectiveness of a tree species in garnering energy from the sun is related to number of leaves possessed by the tree and the geometry of those leaves on the tree. A measure of this effectiveness is called "leaf area index", the ratio of total leaf area to area of the shadow of the tree crown that would be present at mid-day with the sun directly overhead. This study examined the LAI of trees in central New Hampshire, one conifer (Pinus strobus) and a couple of Sugar Maples. For a small tree, all leaves were counted and measured (leaf length). Leaf area was determined by removing a selected sample of leaves from a tree and determining leaf area by scanning and use of NIH Image, a image processing program on the Macintosh computer. A regression was run on the relationship between leaf area and leaf length. A similar protocol was used with the conifer. The pine had the smallest LAI (0.79) and the Sugar Maple a lot larger LAI (4.3). At first hand, this difference might indicate a higher level of productivity by the Sugar Maple, as the maple should theoretically capture more of the energy coming from the sun. Data from another experiment though showed that maples loose their leaves at the end of October, yet the pines retain their needles all year round and thus have an extended growing season.
4. Examine the data sheet for the exercise on weed species in the intervale fields. Calculate a species diversity index for this data set. Do this on the proportional numbers of plants. We will make some assumptions on this matter that may not be true, but for this exercise have some utility. The plot was 256 m2 (16 x 16). If a plant was found in the first m2, then multiply it by 256, in the second m2, then 128, the third m2 then 256/3, i.e., the multiplier is 256 divided by the accumulative area sampled at that point. Use the Shannon diversity index (H = - summation of PilnPi where i goes from 1 to S [S is the number of species present and P is a proportion and ln is the log to the base 10]). Show me your work by either attaching a printout or your worksheet.
Plot Sp. Unmow # of ind # Diversity Sp. Mow # of # Diversity
# plts/field ind plts/field
1 11 256.00 2816.00 -0.931 9 256.00 2304.00 -0.906
2 1 128.00 128.00 -0.054 1 128.00 128.00 -0.066
3 1 85.33 85.33 -0.040 0 85.33 0.00 0.000
4 2 64.00 128.00 -0.065 0 64.00 0.00 0.000
5 4 32.00 128.00 -0.076 1 32.00 32.00 -0.024
6 2 21.33 42.67 -0.028 1 21.33 21.33 -0.017
7 0 16.00 0.00 0.000 1 16.00 16.00 -0.014
8 1 8.00 8.00 -0.006 2 8.00 16.00 -0.016
9 3 6.40 19.20 -0.015 1 6.40 6.40 -0.007
10 5 4.00 20.00 -0.017 1 4.00 4.00 -0.004
11 6 2.00 12.00 -0.011 1 2.00 2.00 -0.002
12 7 1.33 9.33 -0.009 1 1.33 1.33 -0.002
13 2 1.00 2.00 -0.001 1 1.00 1.00 -0.001
3398.53 1.254 2532.07 1.059