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What effect does human disturbance have on the liquid characteristics and macroinvertebrates within a Heliconia flower bract?

 

 

Woodrow Wilson National Fellowship Foundation

Environmental Science Institute

Costa Rica

July 2000

 

 

Charles Lee

Annmarie Merager

Carmen Nunez

Miles Robinson

 

INTRODUCTION

Heliconias are a genus of striking flowering plants that are native only to Central and South America and some of the islands of the South Pacific, with approximately 40 species occurring in Costa Rica.  Heliconias attain their most vegetative growth in the humid lowland tropics below 1500 feet, with their greatest numbers being found in the mid elevation and rain cloud forest habitats.  Few occur above 6000 feet. 

 

Each erect shoot of the Heliconia is composed of a stem and leaves and it is often terminated by an inflorescence.  Each inflorescence of tank Heliconias contain on average 6-20 bracts that are often filled with a liquid substance.  The liquid substance is thought to defend the plan’s reproductive structures from herbivores (3).  The flower within the bract of the Heliconia is hermaphroditic, having both male and female reproductive parts.  Heliconias bloom in January to September with a peak in April to May.   Heliconias grow to a height of 5-15 feet in a habitat of full sun to 40% shade.

 

Most conspicuous members of the genus inhabit open sites in secondary growth along roadsides, riverbanks and patches of light in the forest.  With increased destruction by man of the tropical rain forest, these species readily invade and colonize the newly opened areas.  To the natives of the regions where they occur naturally, their abundance lends them to be considered as weeds, or used as favorite ornamental garden plants.  The focus of this project is to investigate what effect human impacts may have on the liquid characteristics and macroinvertebrates in the bracts of Heliconia in different areas of disturbance near San Vito, Costa Rica.  Testing sites include the Wilson Botanical Gardens, a sun coffee plantation, and the primary forest area.  Ammonia, phosphate, and nitrate tests levels were measured as chemical indicators of biological life within the bracts.  pH testing is used as a chemical indicator of change occurring within the bracts and different locations of study.  We measured the amount, type, and diversity of macroinvertebrates to determine life within the bracts. 

 

After the orientation sessions to the Wilson Botanical Gardens the investigators of this project became interested with liquid volume held in the bracts of the Heliconia plants.  We hypothesized that liquid characteristics can be used as indicators of life processes occurring within the immediate area of the Heliconia.  We hypothesized that the more human disturbance in an area, the less macroinvertebrates there would be in the bracts, therefore allowing the Heliconia to flourish in disturbed areas (i.e. coffee fields, roads, etc.) due to the plant’s ability to colonize newly opened areas.  

 

MATERIALS

·        Hydrion pH paper (scale 0.0 – 13.0)

 

APPARATUS

 

PROCEDURE

 

Protocol

            Three different sample sites were be used:

1.)    Wilson Botanical Gardens

2.)    Coffee Plantation

3.)    Forest

 

From each sample site, two inflorescences of similar length (.1 M – .8 M) and height from the ground (1 M – 6 M) were selected.  We sampled all plants between 8:00 am and 11:00 am.  Two bracts from the top, middle, and bottom of the inflorescence were sampled.

 

Testing

 

Temperature           

Place a thermometer in the water or water like substance of one of the two top, middle, and bottom bracts.  Allow the thermometer to remain for 2 minutes.  Remove and record temperature.

 

pH *

Remove a small portion of Hydrion pH paper with a scale of 0.0 – 13.0. 

Dip the paper in the water sample and compare the color to the pH color

scale on the bottle. 

                       

Ammonia*

Using a LaMotte water testing kit, fill the 5.0 mL test tube to the line with sample water.  Add 4 drops of Ammonia Nitrogen Reagent #1.  Cap and mix.  Add 8 drops of Ammonia Nitrogen Reagent #2.  Cap and mix.  Insert test tube into the Ammonia Nitrogen Comparator.  Match sample color to a color standard.  Record as ppm Ammonia Nitrogen.

 

Phosphate*

Using a LaMotte water testing kit, fill test tube to the 5mL line with the sample water.  Use the 1.0 mL pipet to add 1.0 mL of the VM Phosphate Reagent to the test sample.  Cap and mix.  Wait 5 minutes.  A yellow color may appear at this point.  Use the pipet to add 3 drops of the Reducing Reagent to the mixture.  Invert to mix the contents.  If Phosphate is preset, a blue color will form immediately.  Insert the test tube in the VM Phosphate Comparator.  Match sample color to a color standard.

 

Nitrate*

Using a LaMotte water testing kit, fill test tube to the 2.5 mL mark with the sample water.  Add Mixed Acid until the tube is filled to the 5.0 mL mark.  Cap and mix.  Wait two minutes.  Using the .1g spoon to add one level measure of Nitrate Reducing Reagent to the mixture in the test tube.  Invert the test tube 50-60 times in one minute.  Wait 10 minutes.

 

Macroinvertebrates          

Using tweezers, examine each of the sample bracts for macroinvertebrates.  Use a stereomicroscope to identify and count each species. 

 

Height - Ground to Top of Inflorescence                                                          

Using a tape measure, measure in meters from the ground to the top of the sample inflorescence.                       

 

Height - Inflorescence Length

Using a tape measure, measure in meters from the bottom to the top of the inflorescence.              

 

Percent Canopy Cover

Using a digital camera, photograph the canopy directly over the Heliconia plant.  From this photograph, calculate the percentage of canopy covered.

 

*  An aspirator was used to extract the water content of each of the bracts.  The water content was then stored in plastic vials and returned to the lab for testing of pH, density, ammonia, phosphate, and nitrate.

 

RESULTS

With the given test kit, we found ammonia levels to be high in the garden, intermediate in the coffee plantation, and undetectable in the forest.  The nitrate levels were approximately 9 ppm in the forest and undetectable in the garden and coffee plantation.  Average inflorescent length was greater in the coffee plantation and less in the forest, probably due to increased canopy cover.  The quantity and diversity of macroinvertebrates was higher in the forest, less in the garden, and few in the coffee plantation.

 

CONCLUSION

It was assumed when starting this investigation that the substance in the bracts of the heliconia was primarily rainwater, collected by the plant.  While this may be partially true the amount of nutrients particularly phosphates indicates some other source or contribution by the plant.  The variable amounts of the nutrients, nitrates, ammonia and phosphates in the bracts may be due to dilution or concentration of this plant contributed material.

 

There was some variation in the amount and kinds of organisms from the top to the bottom of the inflorescence, which may have been due to the length of time the inflorescence was open and the availability of food.  The top inflorecenses were open only a short time and had less time to acquire a diverse fauna.  As the flower develops, some of the flowers appeared to lose their seeds or have seeds that were deteriorated and rotted. 

 

There was a definite difference between the kinds and numbers of organisms found in the bracts in the forest and in the coffee plantation.  The diversity and abundance of the organisms in the garden, a human disturbed site, was similar to what was found in the forest.  In the coffee plantation there were fewer species.  The coffee plantation, a sun plantation, probably did not have the diversity of macroinvertebrates to colonize the flowers.  In addition, the introduction of the pesticides and herbicides in the plantation would also affect the relative kinds and numbers of individuals.  In the forest, there were a vast number of organisms and a wide variety of species, even between the two sample plants.  The abundance of the variety of species that can colonize the bracts was indicated by this bloom of fauna.  While there were similar species in the two forest samples, there were different species in each.  In the garden sample, which had more liquid and perhaps more dilution by rainwater because the bracts were larger, there were also a lot of species and numbers of organisms.  The presence of large numbers of mosquito larvae in the garden specimen may be a result of the presence of more liquid or water habitat that mosquitoes can inhabit.  There were no mites or nematodes on these samples, which may indicate that either the species were not in the garden to colonize or that the environment was not compatible with the needs of the individual species. 

 

 

CLASSROOM APPLICATION

A research project of this nature can be easily incorporated into many science curricula due to the variety of disciplines being addressed.  Both biological and chemical properties were tested in the project to compare the natural versus disturbed areas.  By having students work in small groups on authentic research, the instructor can observe the student’s understanding of scientific processes and the scientific method.  This investigation demonstrated to the researchers that there are significant differences between the human disturbed and the climax forest even at very small, almost invisible level, significant changes.  Discussing these differences is important, but actually collecting and analyzing these differences makes this situation much more believable and convincing.  At the high school level, similar investigations of more natural habitats in the area and farmland can give the students experience with this loss of diversity.  A connection with the student through this investigation makes a stronger impression.  Concepts need to be internalized to be of use to the person developing a conceptual framework.  Less complex invitations could also be done at the middle school level.

 

The problems of loss of biodiversity are one of the major global problems.  Before this problem can be addressed with solutions, people need to be convinced this is a problem.  The research done here, demonstrated this loss of biodiversity.  Looking closer the investigator finds that within the plant there is a world of life.  This world, nearly unseen, is greatly disturbed with a significant loss of biodiversity and actual numbers of organisms.  This investigation can be the starting point for discussion and research.  Students will be looking beyond the obvious and see the subtle changes that will ultimately impact us all with this loss of biodiversity.  It is important to connect the student the problems and this investigation is a way to do that. 

 

In order to incorporate this into the classroom, the students would need to have significant background knowledge of the plant species they are investigating, as well as significant knowledge about the role of macroinvertebrates play in biodiversity. 

 

 

 

REFERENCES

1.  Beletsky, Les.  (1998)  Costa Rica The Ecotravellers’ Wildlife Guide.  Academic Press.  San Diego, CA.

 

2.  Berry, Fred, and Kress, W. John.  (1991)  Heliconia an Identification Guide.  Smithsonian Institution Press.  Washington and London.

 

3.  Wooton, J. Timothy, and Sun, I-Fang.  (1990)  Bract Liquid as a Herbivore Defense Mechanism for Heliconia wagneriana Inflorescences.  Biotropica 22 (2): 155-159.

 

 

 

The investigators of this project would like to express appreciation to the Office of Tropical Studies, the Woodrow Wilson National Fellowship Foundation, and Rodolfo Quiros for the opportunity to study in the Wilson Botanical Garden.

 

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