Page 1





PRÉCIS FOR LECTURE 20 PRESENTED BY DR. IAN THOMAS MAIN IDEAS 1. Plant classification 2. Environmental gradients 3. Niches 4. Biodiversity PLANTS CLASSIFICATION THE RAUNKIÆR SYSTEM Dr. Thomas discussed how plants classification can be deduced using a range of systems and be used as an approximation for identifying an ecosystem. The Raunkiær system which was developed by Christen C. Raunkiær is a method of plant classification based on the different biological structures of a plant’s reproductive system and the ideal conditions in which it grows most in. 1. Phanerophytes - Plants that project stems into the air with reproductive systems placed there. 2. Chamaephytes - These plants do not grow far up from the ground with reproductive systems also quite close to the ground. These include most ground cover and low lying plants. 3. Hemicryptophytes - These plants possess reproductive systems that are close or at the soil level. 4. Cryptophytes are plants wherein the reproductive is hidden from the open air be it soil or wate. They can be broken down into Geophytes (underground), Helophytes (under marshy water) and Hydrophytes (underwater). PLANT FUNCTIONAL TYPES Plant functional types (PFTs) are a classification that rely on the climactic and functional conditions of a plant. In Australia for example, fire plays a large role on reproductive regimes. Obligate/Faculative Seeders - Plants that do/do not require reproduction via reseeding. Obligate/Fuculative Resprouters - Plants that do/do not reproduce by resprouting. ENVIRONMENTAL GRADIENTS These are changes that occur across landscapes on an environmental scale. Examples of these include temperature, soil chemistry and precipitation. Populations tend to respond to these rather sensitively and more consistently than compared to communities and will be shown via distribution changes. A population/community will try to shift to the optimal gradient condition when a change occurs. NICHES Dr. Ian illustrated how species spread out of points of origin and will expand to fit into niches - a species’ share of a habitat and the resources in it. Plant species cooperate through this by avoiding overlap between niches. Fundamental niches are the maximum of a species’ living condition while a


realized niche is the optimum living condition. Species can potentially immigrate and speciate in isolation to fit another niche via the process of allopatry. BIODIVERSITY Endemism is where a species exists in one particular location specifically and happens on a regional and local scale. Things to consider: - Endemism depends on isolation over a temporal and spatial scale caused by tectonic plate activity and glacial cycles over time. - Biodiversity is the amount of living diversity in a given area. - Biodiversity is also a good scale for levels of productivity in an ecosystem. - As a general rule, as one moves away from the equator, biodiversity declines. This can be seen where rainforests are centered around the equator and have a high level of productivity (Latitudinal Gradient). - Some level of disturbance to an ecosystem is good in maintaining optimum biodiversity (Intermediate Disturbance Hypothesis). IN RELATION TO THE LANDSCAPE FUNCTION REPORT Biodiversity as a concept as discussed by Dr. Thomas is particularly useful in the landscape function report as it can aid in determining the condition of an ecosystem given that biodiversity has the potential to be used as an indicator for human impacts and their influences.


Natural Environments Précis