Horror of horrors! Club Med makes the scene at Grotto Beach, San Salvador, Bahamas. See other beautiful phenomena from the Bahamas.
|
|
Introduction
Leaf cutter ants are one of the most influential organisms of the Neotropical rainforests. Their complicated social structure and development of agriculture have made them an interest and mystery to the many people who have ventured through the rainforests. Some of the many aspects of the leaf cutter ants that are apealing to those who may pass by a colony are their busy highways to transport plant pieces, the aggresive soldier ants, and the mutualistic relationship that they have developed with the cultivated fungus.
Ants are one of the only insects that are completely social, meaning that every ant is dependent on her colony, made of her sisters, for survival. Ants are almost entirely blind, so their world is run by chemical smells and tastes, making them well adapted for life underground. They will release pheromones to alert each other of danger, location of food, and to help perform colony tasks together. Most colonies only have one queen who is the mother of the colony, her job is to constantly lay eggs to keep the colony populated.
Leafcutter ants are one of the most socially advanced insects on the planet, one colony can number up to 7 million individuals. Their nests are very large and complicated, some can be up to 30 meters across and over 6 meters deep. The agriculture of fungus that is used by these ants predates human agriculture by about 50 million years which has evolved into a complex symbiosis. Multilane highways are easy to spot leading to the nests, the ants use these trails to transport plant fragments which are used to feed their fungus living below the ground. There are two main types of leafcutters in Costa Rica- Atta and Acromyrmex, Atta cephalotes is the most common species found in the country. One colony can harvest as much vegetation as an adult cow everyday and in one year leafcutters harvest 12-17% of the total leaf production in Costa Rica, each species may specialize on up to fifty different types of plants. Leafcutter ants have become an agricultural pest, attacking important crops such as banana, sugar cane and corn. The ants do not actually feed on the plants, but use the plant pieces as a fertilizer for their fungus crop which is their primary source of food, they will use plant juices as a supplement to their diet.
Leafcutters are very dependent on the fungus for their nutrition becuase they are unable to digest cellulose. The cultivated fungus is very specialized becuase it is only found in the nests of leafcutter ants. The fungus of leafcutters has been identified as Leucocoprinus gongylophorus, but this is not an accurate identification since it has lost the ability to make reproductive structures which are usually used to identify fungi. The fungus must rely on the ants for reproduction, when a new colony is started the queen leaves her parent colony taking a piece of fungus with her to start a new garden. Essentially the ants and the fungus are dependent upon the queen for reproduction and she is dependent on them for food, they have developed a complete obligatory mutualism. The worker ants bring the leaf pieces into the nest where smaller workers can process the leaves by chewing them into pulp and adding digestive secretions from their abdomen. Then there are even smaller workers that place the pulp into the garden so that it may be quickly consumed by the fungus. There are swellings that form on the fungus, called gongylidia, which are rich in glycogen and they are harvested by the ants to feed the queen, larva, and themselves. Most ants cultivate the fungus as a mycellium, which is a multicellular phase, but there have been some ants found to cultivate the fungus as masses of yeast, which is the unicellular phase.
There are five types of ants in the caste system of leafcutters, all determined by their diets as larvae. The five castes are queen, soldiers, workers, minima, and the males. The queen is the heart of the colony, she can live to be 20 years old, may grow to be two inches long, she lays millions of eggs, colonizes new colonies, and mostly produces females. Then there are the soldiers which usually do not number more than a 1,000 in each colony, they fight to the death with their huge mandible to protect the colony and they remove debris from the nest. The workers are the next down in the caste system, the largest cut leaves and carry them back to the nest, some are scouts for new vegetation sources, smaller workers process the plant pieces, some leave chemical trails and they can live for about one year. The minima are the smallest of the ants and they harvest the fungus, feed the larva of the queen, or may ride along on the plant pieces to clean off parasitic eggs of flies, so that they do not enter the nest. The males are the lowest of the castes and they are only produced about once a year, they fly in swarms and mate with new queen and die.
The colony reproduces itself once a year at the start of the rainy season. The queen can collect up to 300 million sperm from the males that she has produced, she then kills the males and burrows into the soil to never return to the surface. Many of the first offspring starve or are eaten before the colony has a chance to get started, usually only about 1% survive. Once the colony has made it through the first year the queen will start to produce soldiers and the castes will become more complex. It takes about three years for a colony to be fully established and functional.
Hypothesis
The larger colonies will be more complex, have a more developed caste system, and will use more biomass than a smaller colony.
Methods
The nests were first choosen dependent on their accessibility from the trail and then general observations were first made. These general observations included the size and length of the pathway and the size and type of vegetation being carried. We recorded the plant part that was being carried and made very loose observations of the piece sizes, calling them small, medium or large. A point was picked on the trail and the number of ants that passes in 15 seconds was recorded, along with the number of soldiers, workers and minima. Then a series of disturbances were created on the pathway to record the reaction of the ants. The disturbances included; water thrown on the ants, organic matter layed in their pathway,trail repeatedly racked with a stick, holes covered, and stomping on the ground. The number of sodier ants were counted at a specific point under normal conditions and after a disturbance. Then comparisions were made of the development of castes to the visible size of the nest.
Results
After making these observations and creating situations each colony was compared. It was observed that the large pathways were associated with the larger nests, but there was no correlation between nest size and food size, food type, or their reaction to disturbances. The number of ants that passed to and from the nest was consistent with the nest size. The nests that were classified as large based on observable physical size had between 30 and 45 workers pass in 15 seconds and the small nests had only 15 to 25 workers pass in the 15 second period. This same consistency was also observed for the soldiers and minima. The disturbance of water caused the ants to stop for a moment and then continue, organic matter in their path caused them to simply go around or climb over, racking the pathway forced them to move their path around that area, when their holes were covered they crawled through or around the barrier and stomping on the ground caused a reaction out of the soldiers which would quickly come towards the stomping and attack. Their were many more soldiers that responded to the stomping in the large nests and a few small nests did not have any soldiers that responded. After all disturbances it was observed that the number of soldiers increased outside of the nest. From the observations made there was consistency in the actually physical size of the nests and the observable development of the colony.
Discussion
All of our observations were made in Corcovado Park because the leafcutter ants cannot live in the high altitudes of Monteverde. The period of time that was spent in Corcovado was not ideal for observing ants because there was a lot of rain and the ants do not work while it is raining, when it is about to rain or if it has just rained. It would have been very beneficial to the research if more time could have been spent collecting data at each nest and more days spent actually out looking for colonies. It was felt that the data would have gained more validity from visiting each colony multiple times over multiple days and if it were possible to observe the colony below ground. These observations were not able to be made because of time and equipment limitations.
Conclusion
The hypothesis was correct that larger colonies are more complex, have a higher caste system, and use more biomass than a small colony. This is believed to be becuase the smaller colonies are younger and have had less time to develop their castes and grow in number and nest size. There were many observations and tests that were not able to be taken which may have altered this conclusion and should be taken into consideration.
Bibliography
Kricher, John. A Neotropical Companion. Princeton University Press, Princeton, NJ. 1997.
Mertl, Amy. The Fabulous Leafcutters.(Pamphlet from butterfly garden)
Mueller, Ulrich G., Stephen A. Rehner, Ted R. Schultz. The Evolution of Agriculture in Ants, www.sciencemag.org, vol. 291. 1998. Tropical Ecosystems of Costa Rica Course Packet, ed. Hays Cummins. p121-124
Next Article
Previous Article
Return to Topic Menu
DOWNLOAD the Paper Posting HTML Formating HELP SHEET!
We also have a GUIDE for depositing articles, images, data, etc in your research folders.
Article complete. Click HERE to return to the Pre-Course Presentation Outline and Paper Posting Menu. Or, you can return to the course syllabus
WEATHER & EARTH SCIENCE RESOURCES |
|
OTHER ACADEMIC COURSES, STUDENT RESEARCH, OTHER STUFF
|
|
TEACHING TOOLS & OTHER STUFF
 |
It is 3:17:32 AM on Monday, November 23, 2009. Last Update: Wednesday, December 10, 2008
Listen to a "Voice Navigation" Intro!
(Quicktime or