Determination Of The Type Of Symbiotic Relationship Between Spanish Moss (Tillandsia Usneoides) And The Host Species The Southern Live Oak (Quercus Virginiana)

Abstract

In this lab, the relationship between Spanish moss (Tillandsia usneoides) and one of its host species, the Southern live oak (Quercus virginia) was observed on a portion of the University of Florida campus in Gainesville, FL. Spanish moss is an atmospheric epiphyte and the Southern live oak is a hardwood tree. Some possible interactions between the two species were neutralism, commensalisms, mutualism, and parasitism. It was hypothesized that the relationship would be commensalism, with Spanish moss benefited and the Southern live oak neither benefited nor harmed. The type of symbiotic relationship was determined using two factors, the relative health of the host oak tree and its relative load of Spanish moss. A two-way X2 test for independence was performed using the data recorded. Calculations gave a X2 value of 0.61 and p-value between 0.1 and 0.5, with one degree of freedom and the level of significance, α, equal to 0.05. Since the p-value was greater than the α value, the lab observations failed to reject Ho, and the conclusion was that the data supported no interaction between Spanish moss and the Southern live oak. Therefore, the lab observations did not support the hypothesis of commensalism between the two species.

Introduction

In this lab, the interaction between the two species Spanish moss (Tillandsia usneoides) and the Southern Live Oak (Quercus virginiana) were observed and the type of relationship was determined using field observations of live oaks with Spanish moss on them and recording the relative load of Spanish moss and the relative health of each tree observed. This is important in order to study the effects of epiphytes on host plants, and the possible environmental implications that such relationships would have, such as whether or not the Spanish moss is harming the oak trees. This study could be helpful to serve as a basis for other epiphyte and host interaction studies, particularly for endangered plants which may go extinct if not helped. Spanish moss is considered an atmospheric epiphyte, absorbing nutrients and water from the surrounding air and nearby host plant. It is found in the subtropics from the southeastern United States to Argentina and Chile (Luther 1997). Southern Live oaks are a hardwood tree native to the southeastern United States and are one of the more common types of large hardwood trees on the University of Florida campus. It was assumed that the two species, given their very close physical contact, would have some effect on each other, and would have a symbiotic relationship; otherwise their relationship would be one of neutralism (Doubrava 1999). If symbiotic, their relationship would be commensalistic, mutualistic, or parasitic. Commensalism is a relationship in which one organism benefits while the other is neither benefited nor harmed. Mutualism is a relationship in which both organisms benefit. And parasitism, a special form of predation, is when one species benefits while the other is harmed. In parasitism, the host species is generally larger than the parasite and the parasite tends to benefit without killing the host (Vliet 2004). Neutralism, which is rare in nature because most organisms exhibit some effect on the other, is when neither species is affected (Richardson 2000). In all three symbiotic relationships it is assumed that the Spanish moss is benefited since being on the live oak gives it access to more sunlight and possibly more rain then it would otherwise get if below the tree canopy. It is predicted that the relationship between the live oak and the Spanish moss is commensalistic, with the Spanish moss benefiting and the live oak neither benefited nor harmed, since my background research led me to a study conducted that showed commensalism between Spanish moss and its host species (Callaway 2002). This would mean that there should be a relationship between the two species, and the amount of moss on the oak trees should not affect the health of the oak trees. A statistical test will be used to determine the relationship between the two species.

Materials and Methods

To determine the type of symbiotic relationship between Spanish moss and the live oak trees, I examined 52 large live oak trees within the area near the biology lab classroom and classified them as being either healthy or unhealthy and whether or not they had a light or heavy load of Spanish moss. Healthy trees were defined as having more than 80% deep green leaves with no noticeable brown leaves and no significant dead branches, and possibly showing new growth. Unhealthy trees showed significant decline, with many dead branches, brown leaves, and hardly any or no new growth. Trees with a heavy load of Spanish moss were those with over 50% of the canopy being covered by Spanish moss and significant Spanish moss covering lower branches. Trees with a light load had less than 50% of the canopy covered and little Spanish moss covering lower branches. After recording the relative health and load of each tree, the results were analyzed using the Chi-squared statistical test. The expected number of each type of tree (e.g. healthy and heavy load), represented by e in the equation, was compared to the observed number of individuals, represented by o in the equation, for each type of tree using the two way X2 test for independence:

X2= Σ (o-e)2/e

From the results I determined what type of symbiotic relationship was best shown by the Spanish moss and live oaks. Ho in this experiment was that there was no interaction between Spanish moss and its host. Ha in this experiment was that there was interaction between Spanish moss and its host.

Results

The chi-squared test was used