Lect 25, Questions -Queen of the Trees PDF

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Fall 2015: Biology 106 Required Assignment in lieu of lecture session 25. Rather than use lecture time for this video, lecture 25 is converted into an assignment since the video is available on-line and you can watch it at any time. Read the questions below before watching the video – you need to look for certain things that might be shown for only a few moments. Video: “The Queen of Trees.” Observations on the ecology of community structure and species interactions. Access this video at: https://www.youtube.com/watch?v=xy86ak2fQJM Assignment: “The Queen of Trees:” The following questions deal with your observations and understanding of important ecological aspects of this video. Prior to watching the video, read and think about these questions because you’ll have to make very careful observations. The reason that you will have to observe and follow the dialogue closely is that there is no obvious or stated answer to a number of these questions, so in many cases you will have to develop your responses by combining several sets of observations. Remember, the process of science begins with observations, and this is to encourage you to develop those skills. 1. When the video is just beginning, even before the title, you will see close-ups of the leaves of the Sycamore Fig tree. As the camera pans the tree, carefully notice the leaves – some are entire, while other have one or many holes or sections missing – perhaps eaten by some leaf feeding insect. These views of leaves will be repeated numerous times throughout the video. With this image in mind, think about this question: Why is nature green? If leaves are food for herbivores, why is it that all the green leaf material is not consumed? What other examples of herbivory (plant eating) and frugivory (fruit eating) are illustrated during this presentation? 2. The Sycamore Fig flowers and fruits several times per year without regard for season. Further, each Sycamore Fig tree in the community fruits independently from all the other Sycamore Fig trees. Note that this video is taking place in tropical Kenya, so what signals might there be to indicate an annual cycle? What is the significance of this apparent random pattern of fruiting behavior? In thinking about your answer, consider the relative length of life of the interacting species, i.e., the wasp being the “Queen’s courier” and the tree. 3. The fig wasp is a highly specific pollinator and without it, no species of fig tree could exist; nor without the fig trees, the wasp species could not exist. Although the size differences between these interacting species are enormous, there is total dependence of the fig on the wasp and visaversa. If this is an example of a species-specific interaction and there are thousands of species of figs in the world, what evolutionary ideas can we explore about this kind of interaction? Why are there so many species of figs? Are there other examples of such pollinator-plant species specificity? 4. In this region of tropical Africa, the figs thrive along the banks of rivers. Carefully look at the various scenes of aerial footage, such as flying over a river showing the extent of the trees distribution. All the vegetation that we see is not just Sycamore Figs but numerous other plant species as can be distinguished by shape and color differences. What can we surmise about the distribution of these Sycamore Fig trees and the importance of different mechanisms of predation and seed dispersal? 1

5. The commentator indicated that the Sycamore Fig starring in our story is a 100-year-old tree, and we can observe that it looks like many of the other apparently well-aged individuals spaced out along the river. Yet, there seems to be very few smaller trees except where a fig fruit has fallen and then we see a vast number of seedlings germinating from that fruit. What are the forces of age-dependent mortality on the Sycamore Fig? What factors would be important in the survivability of a Sycamore Fig from seed to mature tree? What type of distribution pattern of mature trees would we expect among Sycamore Figs? 6. The Sycamore Fig acts as a hunting ground or a home to a large number of animal species, many of which are dependent upon the tree for nourishment. In general, Sycamore Figs feed a greater variety and animals than any other tree in this African habitat. Of the various interactions that are described and illustrated in this video, which are important to the life cycle of the tree and which are purely independent and unimportant to its survival and reproduction? 7. Note that every few months the tree drops a fruit crop consisting of about a ton of figs that form a thick mat of fruit on the ground. What are the consequences of having so much fruit available during one short period of time? What does this observation tell us about the distribution of mature Sycamore Figs? What is the relationship between the probability of seed survival and the distance from the parental tree? 8. Fig fruits are rather strange. The white flowers are on the inside, not exposed, forming, as the commentator stated, a “secret garden.” Why would these flowers be white? Where are the ovules? Where is the ovary? Is there another mechanism by which pollination could occur? What are the similarities and what are the differences between the fig flower and fruit and that of the typical angiosperm? 9. Note that the announcer states that the delicate perfume produced by the figs attracts only those female fig wasps that are laden with pollen. Where did these female wasps get the pollen? Why aren’t the male wasps attracted to the figs? Were these female wasps virgins or had they already mated? 10. Each fig fruit, being an inside-out “secret garden,” contains many hundreds of flowers, some destined to escape the parasite’s ovipositor and become fig seeds, while others are parasitized when the parasite lays its egg in the flower’s ovary. The fig responds to chemicals deposited (a venom) with the wasp’s egg that induce the plant to develop a gall. The gall is a growth of the plant which houses and nourishes the next generation of wasps. By producing a gall, the fig tree becomes the surrogate mother of the wasps and nourishes their development. What would happen if the parasites were so successful that all ovaries were successfully attacked? What are the hyperparasites doing? Are there other examples of gall production induced by wasps? 11. Note the announcer’s comments about the occurrence of rains, such as their being late. What does that have to do with seasonality? Does it affect the Sycamore Fig tree? Why would this be important in tropical habitats? What would happen if the reproductive cycle of the Sycamore Figs were synchronized with the occurrence of rains? 12. Notice that the ground under the crown of the Sycamore Fig becomes covered with a thick layer of fallen brown leaves at the end of the fruiting cycle. What can we learn from this observation when we consider the trophic level interactions and consequences of producing left over primary productivity? What happens to these materials at the decomposer level? Do left 2

over organic materials accumulate? Should we consider the world as being “brown” as opposed to “green” because of the importance of the decomposers? 13. Trees photosynthesize in order to provide nourishment and energy for their own wood, fruit and leaf production. Natural selection is a strong form of selection acting on plants that are being eaten and loosing photosynthetic potential. As a result of millions of years of herbivore attacks, fig trees evolved a foul tasting and sticky latex sap that interferes with the consumers. However, again as a result of natural selection, the herbivores evolved counter-defense strategies to overcome plant defenses. Explain this apparent evolution of a strategy of attack, defense, counter-attack, and counter-defense between interacting species. What, would you hypothesize is the next stage in this story? Do we see such strategies among other systems of interacting species? Describe the various adaptations evolved by herbivores to overcome the described plant defenses. 14. The commentator states, “...fermenting fruits attract vinegar flies...” This statement introduces a whole other aspect to the energy flow through this ecosystem, that is a food web based on the decomposing portion of the tree’s photosynthetic energy (as fruits, leaves and wood). Here we see fallen sugar-containing fruits that become inoculated with yeasts, which feed on the sugars and convert some of that stored energy into alcohol. Can you describe the nature and extent of this portion of the food web and its energy flow? How distinct is this food web from other fluxes of energy illustrated in the video? 15. Hyperparasites are wasps that attack other parasitic wasps that live within the developing fig. Since they cannot enter the “secret garden” as did the pollinator wasps, they must attack from the outside and enter through the wall of the fig fruit. Using their long ovipositors, these hyperparasites drill through the fig fruit wall, locate the previously parasitized flowers that now contain developing galls, lay eggs on the developing fig wasps, and subsequently consume that wasp and take over that gall. In what ways are these hyperparasites dependant upon the survival of their host wasps? What factors determine the population density of the hyperparasites? 16. The commentator discusses the observation that ants are the “allies of fig trees” because they patrol and protect the tree and fruits from attack by some herbivores. However, the ants also function as “farmers,” actually “herders,” of bugs of the leafhopper genus Hilda. The bugs graze as if they were sheep, and the surface of the fig fruit serves as a sheep pen. The leafhopper nymphs tap into the phloem containing sap under pressure, which passes rapidly through their gut and is expelled, providing honeydew, which is consumed by the ants. Consider the evolution of this interaction. Would you consider the ants to be allies of the plants, or simply an opportunistic exploiter taking advantage of the most readily available sources of energy? Is this a case of alternative feeding strategies? What is the effect of this behavior on the Sycamore Fig? 17. Seed distribution and dispersion: The commentator indicates that no fig seedlings germinate under the Queen. Why would this be? Fig seeds, however, are dispersed by various vertebrates such as fruit bats, green pigeons and fish. How would observations of the dispersal of fruits and the success of the seeds in developing into a tree relate to the idea that it is very difficult to establish human agricultural monocultures in tropical habitats? What would be the consequences of establishing monocultures of fig trees? 18. When cicada nymphs emerge from the soil, they crawl up the tree, molt into adults and feed briefly on sap by tapping into the phloem, producing copious amounts of honeydew much like 3

the much smaller leafhopper Hilda nymphs. They mate, deposit their eggs on the tree stems, then die. Many species take advantage of their honeydew as source of plant sugars. In what way does the appearance of cicadas alter the interactions between other species? What can we say about the leafhoppers that were being herded and groomed by the ants? In what way does this affect the Sycamore Fig? What were the cicadas doing before they emerged as adults? Question 18, FYI: This phenomenon parallels stories related in the Bible and Qur’an where “manna from heaven” served as food for the Israelites. Current explanations indicate that the “manna” was most likely the crystallized honeydew of certain scale insects. 19. A male fig wasp emerges from its gall before the females emerge. Why is that? He has powerful jaws and enormous reproductive capabilities with the potential to mate many of his sisters. The wingless male never leaves the fig fruit and is not adapted to exist outside the fruit, having no wings and highly reduced eyes and antennae. However, the male is so well endowed reproductively, that he can inseminate neighboring females housed in their galls without leaving his gall. In some fig species the male wasps actually battle to the death with other males in order to dominate the reproduction within that fruit. Why are powerful jaws needed? What would be the advantage of such male-male competition? Would this sib-mating behavior cause inbreeding within the wasp population? What is the genetics of the wasp parasite? 20. The commentator refers to the wasps as the “Queen’s couriers” and the wasps’ “gift to the Queen.” A plant, after all, requires a mechanism to deliver pollen from a mature individual flower to a flower that is just developing. In fact, the plant is seducing the insect to act as its messenger of gametes. Be sure that you understand the complete cycle of pollination in the figwasp interaction. What are the essential components in getting pollen from one generation of fruit to the next? What is the role of the two sexes of wasps and what is the exact sequence? 21. The Sycamore Fig tree has an enormous reproductive potential where perhaps as many as 100,000 figs are produced per reproductive cycle, each fruit producing large numbers of wasps, each of which as the potential of producing many offspring. What does this power of reproductive potential tell us about the forces of mortality active on these two very different populations? Are mortality rates related to longevity? How can you describe the “reproductive strategies” of these two very different species? 22. What is the role of nematode worms in the scope of this story? Is there an apparent effect of the wasp being parasitized (infected) with a nematode worm? How does this fit into the waspfig pollination story? Is this a case of simple opportunism by the nematode? 23. The hornbills described in this video show a reproductive pattern common among bird species, where eggs are laid over a period of time and have different hatching times. What are the consequences of the hornbill’s chicks hatching at different times? Would this hatching behavior be an evolved phenomenon? What do we mean by a distinct pecking order? What if the rains followed a different pattern and were not delayed? 24. Describe the density-dependent and/or density independent factors influence the density of fig wasp parasites and their hyperparasites? 25. How many puns did you catch?

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