Ecology Name _______________
25 November 1996
Second Lecture Examination--Part Two of Collinvaux

A. Creatures: Each of the following species appeared in Part Two. Briefly describe how the organism was used by an ecologist to make an ecological point. List also, if possible, the ecologist(s) who used the organism.
1. Two species of paramecia
The ecological point illustrated by the two species of paramecia is that of competition and competitive exclusion. When one or the other is raised separately with ad libidum resources, it shows logistic growth. When both are grown together, one wins and the other looses. If a refugeum is provided for the looser, both survive. These studies were done by Gause and others.
2. Warblers
Warblers are used to illustrate the concept of competition and character displacement. Robert MacArthur studied five species of sympatric warblers that feed on bugs in conifers. They divide up the space in the trees so that they are visiting different locations in the tree for their food items. This allows for greater number of species to utilize a common resources through niche specificity.
3. Red wing blackbirds
Red wing blackbirds can be used to illustrate the points of sexual dimorphism and territoriality. Males arrive at the summer habitats first and setup and maintain territories against aggressors. They actively solicit females to nest in their territories. Males are differentially colored from the females. Their strategy is to attract as many females as possible. Females seek out the most fit males and mate with them in hopes to improve their own fitness and that of their progeny. Orians at the University of Washington has done many of these studies.
4. Monarch butterflies
Monarchs illustrate the point of mimicry and signaling. Their use of milkweed plants as food allows them to sequester alkaloids in their body tissues. They announce their distastefulness to predators by their black and yellow coloration. This pattern of coloration is mimicked by viceroy butterflies, or at least we thought so until a few researchers determined that this species of butterfly is also able to produce alkaloids, even though they don’t eat milkweeds. Bates and Mueller.
5. Wolves
Wolves, particularly those from the Isle Royale National Park are used to illustrate the concept of predation, the concept of cropping, and the concept of diversity maintenance. They normally only prey on the old and infirmed. The cropping normally has no effect on prey species population sizes. By cropping a variety of species, the wolf enhances the overall diversity of a habitat. Many studies have been done by David Mech and colleagues.
6. Corixid beetles
Corixid beetles were used by Hutchinson to illustrate the concept of biodiversity. Hutchinson while at the shrine of Santa Rosalia found only two species of corixid beetles. He wondered why those two and not other species. His paper goes on to propose that diversity is related to food chain/web lengths and the amounts of energy passed from one trophic level to the next.

B. Hypotheses:
1. Briefly describe three of the hypotheses or models that have been proposed to explain the concept of sex. All involve the concept of cost and benefit. Can the cost of sex be reduced by inbreeding? Why or why not? What about hermaphrodism?
Collinvaux lists at least three hypotheses. They are:
a. ecological--niche separation, enhancement of fitness
b. genetic--minimization of deleterious mutations
c. primordial--sex has been with us since the very start of life via symbiotic relationships that enabled the symbionts to offset the mutagenic effects of ionizing radiation

One of the major costs of sex is the fact that the female only passes on 1/2 of her genome to her offspring (the cost of meiosis). Inbreeding would reduce this cost because offspring potentially could have a higher percentage of female genes in their genomes because of relatedness. Of course, the major problem is that the genetic load of deleterious genes would also increase.

Hermaphrodism also supplies a solution to the problem of the costs of meiosis in that all offspring, if selfing occurred, would contain exactly the same genes as the parent. This is not usually the outcome in hermaphrodites because gametes show only differential maturation, but are also exchanged between different individuals in the population by cross fertilization.
2. One might hypothesize that plants should only produce allelochemics when non-stressed, or when under strong herbivory. What data do we have to support these statements? What are some of the costs to the plants of making such materials?
The evidence shows that when plants are stressed, they produce fewer allelochemicals. It also shows that when strong herbivory is not prevalent, they also produce fewer chemicals. The reasoning associated with this is that production of toxic chemicals has a cost to the plant; cost of manufacture (if not the end product of an existing regular pathway), cost of sequestering, and the physiologic costs if they are negatively metabolically active in the producing plant. Another cost might be that of producing a specialized herbivore who is no longer bothered by the chemical (e.g., monarchs and alkaloid producing plants). Specialized herbivores may do more damage than generalized herbivores.
3. When working towards a global theory of species diversity, two proposed hypotheses are the rejuvenating catastrophe hypothesis and the intermediate disturbance hypothesis. Briefly describe the differences and similarities between the two hypotheses. What evidence do we have to support either?
A rejuvenating catastrophe is like an ice age or a hurricane. By knocking an ecosystem back to an earlier stage of development, in the long run may lead towards a change in the diversity of the system. This hypothesis deals with a broad geographic region, whereas the intermediate disturbance hypothesis deals with a localized geographical region. In this hypothesis, diversity is maintained and enhanced by gap production through treefall. In each of the gaps, succession is reset to an earlier stage. If an area has many of these disturbances scattered throughout, the overall diversity of the region is increased. Numerous studies have been done on gaps in tropical rainforests and the North American continent is a living laboratory for the rejuvenating catastrophe hypothesis due to the presence of glaciated and non-glaciated areas and because we can time the past episodes of glaciation.

C. Concepts:
1. Some would support the maintenance of constant numbers of organisms via density dependent mechanisms. What evidence can be used to support this idea? What evidence is contrary to that idea? What does the concept of the “Red Queen” have to say about this matter?
Most populations seem to maintain themselves through time at relatively stable numbers. This is particularly true of bird populations for which we have a long record, partly through numerous bird count studies. Bird apparently control their numbers by controlling number of clutches per year and number of eggs per clutch. In years when large numbers of offspring would be detrimental, they reduce the number of clutches and number of eggs per clutch. Density dependence is contrary to the idea of external non-biotic controls on population size. Ecologists on the other side of the fence (e.g., Andrewartha and Birch and Australian grasshoppers) believe numbers of individuals are controlled by external events such as weather conditions. Oscillation in numbers of many species support this density independency. The Red Queen hypothesis says that organisms can never become most fit to a particular set of conditions as the set of conditions is constantly changing. An organisms therefore appears to be running in place, but never gaining. This would be antithetical to a concept of density dependence.
2. What did Hutchinson’s paper “Homage to Santa Rosalia” have to say about species diversity? How does diversity vary with latitude? from shallow sea to deep ocean? If Hutchinson were alive today, what points do you think he might make about a general theory of diversity?
Hutchinson tied his paper to ecological energetics, a field that was quite active at the time he wrote the paper. He set limits to potential diversity via limits imposed by lengths of food webs/chains and ecological efficiencies.
Diversity decreases with increasing latitude. It is highest in equatorial regions and decreases towards the poles. Diversity increases with increasing depth, reaching a maximum in the deeper regions of the ocean (with respect to infaunal creatures. Even in the deep ocean it shows some of the same features as latitudinal distribution on land (i.e., high in equatorial ocean, low in polar oceans)
Hutchinson would probably agree with Collinvaux. We know more of the fine details as to how ecosystems function, but we are still no closer to a general theory to explain diversity.
3. Coevolution has occurred a number of times, but some of the strongest evidence has been obtained from plant-insect relationships. Explain what is meant by the term “coevolution” and describe briefly how plant-insect relationships support our understanding of the topic.
Coevolution is where one organism enhances its fitness with respect to another species when at the same time the other species reacts to changes in the first. The relationship between the two species may be positive, neutral or negative, but often is positive. A number of examples can be used:

milkweeds and monarchs
flower structure and bee pollination
flower location and arrangement and pollination.

All examples show a ‘tit-for-tat” kind of relationship between the associated species with increasing specialization amongst the species pairs as coevolution takes place (e.g., Yucca moth and yucca plant)

D. Terms: Define the following terms in an ecological sense.
1. logistic curve
The kind of growth curve where a population reaches a maximum size that is related to the carrying capacity of the environment. The curve is sigmoid in shape and show high rates of growth initially followed by linear growth. As the population approaches the carrying capacity, growth rate decreases until reaching zero.
2. competitive exclusion
No two similar species can occupy a single niche at one moment in time
3. displacement
A morphological or behavior attribute that undergoes changes when two species are competing for a single niche. This change or displacement changes the niche requirements of one of the competing species.
4. hermaphrodite
An organism that contains both sex/reproductive structures (male and female organs)
5. lek
The space where a male member of species shows his fitness and attracts mates. In Prairie grouse, the most fit males occupy the best locations and attract the greatest number of females.
6. cropping
The culling of a prey species by a predator or herbivore that in the long run enhances the diversity of a particular environment.
7. clutch
A nest full of eggs laid by a bird or a turtle
8. mimicry
An organism that pretends to be something that it isn’t by evolving to look like something nasty or distasteful
9. territoriality
The non-random occupancy of a particular geographic space that enhances the fitness of the species. Usually males, but not always.
10. Keystone species
A species that exerts a controlling influence over the ecosystem is resides in by cropping the ecosystem and enhancing its diversity.