Thorns Lab Report

Introduction

When looking into certain trees with thorns it is found that the thorn lengths and densities differ. An excellent example of an area where the same species grows different sizes of thorns would be in the Kruger National Park (KNP). The KNP is part of a savanna biome. A species of acacia titled the Acacia grandicornuta, commonly known as the horned thorn, is widely spread in the KNP but it has previously been observed that the thorn sizes differ based on where the tree is situated. Some horned thorn trees have bigger thorns whereas some have smaller thorns.

In the KNP there are two main areas where one would look to determine if the above suspicion of Acacia grandicornuta trees equipping themselves with larger thorns as a response

It has an irregular V-shaped canopy. The bark is black, it has white flower-balls and flat sickle-shaped pods (Eco Travel Africa, n.d.). The thorns have aposematic colouring. Aposematism is the use of bright colours to advertise that an organism is dangerous or unpalatable (The Amateur Entomologists' Society, n.d.). The conspicuous colour of the thorns becomes a visual sign to animals who would attempt to feed on it (Lev-Yadun, 2001). The animals begin to recognize the thorns and avoid eating the tree on which they are displayed therefore decreasing the rates of consumption for that

Milewski, 1990). Some plants contain secondary plant substances which are by-product chemicals of primary metabolism not directly involved in photosynthesis (Krebs, 2008), Secondary plant substances include a class of organic compounds with a nitrogen base known as alkaloids (Merriam-webster, 2015). Well-known alkaloids are nicotine, tobacco and caffeine which make the plant repugnant (Krebs, 2008) thus lowering the rate of herbivory. Further research has been conducted since the year 2008 which confirms the statements on plants made by Krebs.

Trees, as a response to herbivory, have equipped themselves with structures for protection. These structures include prickles, thorns, spines and trichomes (Pallardy, 2015). If these structures are developed or enhanced as a response with means to prevent herbivory then those structures would be said to be induced by the herbivory. Thorns are therefore thought to be an induced defense structure as they are enhanced in areas where there are larger populations of herbivorous animals who attempt to feed on the