The mean steam density and area of occupancy of the three above species in the 50 hectare plot on Barro Colorado Island.


This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

C:\Users\owner\Documents\VUW 2015\BIOL 327\essay\map inga nobilis.pngIntro Barro Colorado Island is a very diverse ecosystem which is broadly studied by biologists due to its unique ecology and its natural tropical forests which have been undisturbed by humans. The island is a national reserve with a land area of 1,500 hectares, protected since 1923. In 1980 a permanent forest plot was set up by the Smithsonian Tropical research institute to better understand tropical forest biology. (1) The plot has an area of 50 hectares and composed of approximately 306 species. Barro Colorado Island has a tropical climate with high humidity, temperatures and an annual rainfall between 1815mm to 4469mm. (1) Most of the rainfall occurs in the rainy season from April to December meaning the dry season has minimal rainfall and extreme temperatures up to 31° c. The 50 hectare plot in which the plot lies is on a generally flat plateau 140m above sea level. (1) The site has a canopy composed of trees ranging from 20m to 50m tall. The plot is also occupied by approximately 40 non flying mammalian species including few large predators, and large herbivores including Tapirs, Deer and peccary which feed on the native plants. Other insect populations may also damage the plant life on the plot site, however insectivorous birds limit such damage.(1) Fig 1

Studied species Inga Nobilis belongs to the family Fabaceae which consists of a wide variety of trees and shrubs that are easily identified by its production of legumes. (2) Inga Nobilis is a large perennial tree growing up to 15m tall, found widely distributed in Mexico, Colombia, northern Venezuela, Puerto Rico, Panama and west of South America at elevations from 0 to 1460m. (3 Fig 1) Fabaceae are mostly entomophilous plants and produce flowers attractive to insects for pollination. However the sub fleshy legumes produced by the tree are consumed by a wide variety of animal dispersers such as Tapirs, deer and many birds. (4)

Pentagonia macrophylla belongs to the family Rubiaceae which consists of a wide variety of shrubs, trees, lianas or herbs which are identified by their opposite leaf arrangement. (5) Pentagonia macrophylla is a tree which grows up to 7m tall, found widely distributed in Peru, Ecuador, Colombia, Panama and Costa Rica at elevations from 0 to 2000m. (6, 7) Rubiaceae are mostly entomophilous plants and produce attractive flowers that attract insects, but most commonly ants for pollination and seed dispersal.(6, 5) P. Macrophyla is often located in mature forest or mountainous areas that are often very humid with alluvial soils. (7) However P. macrophyla is significantly damaged by butterfly species. (8)

Trichilia Tuberculata belongs to the family Meliaceae that consist of mostly trees, shrubs and is recognized by its leaves and thick water fruits. (9) Trichilia Tuberculata is a tree which grows up to 30m tall, found in Panama, Bolivia, Brasil, Central America, Guatemala and tropical South America at elevations of 0 to 250m. (9, 10) Meliaceae consists of plants that are entomophilous and have flowers that predominantly attract butterflies and bees for pollination. (12) The seed of T. Tuberculata is often dispersed by large mammals and birds in the area. T. Tuberculata is usually located in moist forests that have above 2,500 mm annual precipitation and usually near the Pacific coast (9).

Aims of Study

I aim to use statistical analysis to find out the flowing: 1: To Find out the mean steam density and area of occupancy of the three above species in the 50 hectare plot on Barro Colorado Island.

2: To observe aggregation of the species

3: To test if any of the following species had a negative or positive association or correlation with one another

4: To test if any of the following species is dependant or effected by its environmental factors and if this influenced the abundance of each species in the 50 hectare plot

Method The questions we aimed to answer were analysed using excel and spss a statistical analysis programme. My first question was answered using excel, whereby the =average function was first used to find the mean plot stem density per species. I then used the =sum(plots occupied/ total plots*100) function to give me the percentage of plots each species occurred. This was further refined to the number of plots each species occupied by using the =sum(plots occupied% / 2) function again. Question number two was also answered in excel by using the stem density of each species to find the variance by the =var function and highlighting the stem density data for the desired species. The variance was then used to find intraspecific aggregation between the species by using the following equation in excel by using the =sum(variance/mean) function again.

The third question was also answered using excel and its data analysis tools. Once navigated to the data analysis tools, correlation was selected and the desired species were compared producing a Pearson’s correlation (r). Unfortunately a chi squared test and Phi coefficient couldn’t be carried out because many of my cells contained 0 values, rendering a chi squared test unreliable. The final question was analysed using spss to compare the stem densities of each species with its environmental factors. This was accomplished by running a backwards elimination on a linear regression model at the 95% significance level. By doing this variables that didn’t have a significant influence on the distribution of the species were eliminated, leaving only the factors that did influence the species distribution.

Results Question 1: The mean stem density of each species was calculated T. Tuberculata = 66.45 I. Nobilis = 3.88 and P. Macrophyla = 2.27. From this data we can see a significant difference between T. Tuberculata and the other two speciies however minimal difference between I. Nobilis and P. Macrophyla (figure 2). The area of occupancy of each species was also calculated: T. Tuberculata : 50 hectares of the 50 hectare plot (100%), I. Nobilis : 46.5 hectares (93%) and P. Macrophyla : 40.5 hectares (81%)(figure 3).

Question 2: Aggregation was measured by finding the variance and dividing it by the mean giving us an index of dispersal (I). T. Tuberculata I= 27.2246472, I. Nobilis I= 2.494893824 and P. Macrophyla I= 1.741499994 (Fig 4).

Species ( fig 4)

Index of Dispersal Value ( I )


T. Tuberculata


Aggregated (Variance > Mean )

I. Nobilis


Aggregated (Variance > Mean )

P. Macrophyla


Aggregated (Variance > Mean )

Question 3: Since a Chi squared test was unreliable to analyse my data due to low values a Pearson’s correlation was conducted to find correlation between species. The correlation between T. Tuberculata and I. Nobilis was P = 0.136135 (figure 5). The correlation between I. Nobilis and P. Macrophyla was P= 0.383783 (figure 6). The correlation between T. Tuberculata and P. Macrophyla was P= 0.08015 (figure 7).

Question 4: When a backwards elimination on a linear regression model was conducted at the 95% significance level variables that didn’t significantly effect the distribution of the species were eliminated based on low F value. For T. Tuberculata (fig 8) the gradient variable was the only variable eliminated. For I. Nobilis the wetness and gradient variable were eliminated (fig 9). For P. Macrophyla all of the variables were eliminated (fig 10).

Fig 8 below

Fig 9 below

Fig 10 below



1: 2: Fabaceae. (2015). InEncyclopaedia Britannica. Retrieved from

3:, (2015).Biodiversidad de Costa Rica. [online] Available at: nobilis [Accessed 3 Jun. 2015].

4: Fayaz, A. (2011).Encyclopedia of tropical plants. Richmond Hill, Ont.: Firefly Books.

5: "Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 12, July 2012.

6:, (2015). Tropicos | Name - Pentagonia macrophylla Benth.. [online] Available at: [Accessed 3 Jun. 2015].

7: CONTAINS 'Pentagonia macrophylla' (pentagonia habitat and world wide distribution)

8: Encyclopedia of Life, (2015). Pentagonia macrophylla - Information on Pentagonia macrophylla - Encyclopedia of Life. [online] Available at: [Accessed 3 Jun. 2015].

9:, (2015). Biodiversidad de Costa Rica. [online] Available at: tuberculata#usesManagement [Accessed 3 Jun. 2015]. (hight, distribution and habitat) 10:, (2015). Tropicos | Name - !Trichilia tuberculata (Triana & Planch.) C. DC.. [online] Available at: [Accessed 3 Jun. 2015].

11:, (2012). Trichilia tuberculata (Triana & Planch.) C. DC. — The Plant List. [online] Available at: [Accessed 3 Jun. 2015].

12: Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 11th May’.

Writing Services

Essay Writing

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.