BOT 141: Basic Principles of Botany - ECOLOGY •Before delving into the subject matter of Ecology, it will be important for us to understand what the word Ecology means. • The word “ecology” has its origin from two Greek words: -oikos which means a house, home, dwelling place or habitat of an organism and -logos meaning a branch of study. • Literally therefore, it is the study of living organisms with their environments (house, home, habitat etc.) • The environment of organisms includes both physical, biological and non-biological environments which these organisms interact with. • Therefore, in a broader sense, ecology is the science that studies the interactions between living organisms and their environment. • It involves their mode of life, habits, effects upon each other and their habitats as well as the effects of the environment upon the organisms. • In summary, ecology is the science that deals with the living organisms as they are found in their natural habitats (i.e. homes). SCOPE OF ECOLOGY • Basically, ecology is a biological science since it is concerned with the interrelationship of organisms with their environment (including the non-living environment). • Ecology as study is not restricted to biology alone wanders into other subject areas gathering bits and bits of information to expand its own base. • For instance, the spatial distribution of organisms on the earth demands a good knowledge of geography, demography, mathematics and statistics. • The study of soil organisms and their relationships with the soil requires a good knowledge of pedology (soil science). • In the vein, the study of man as an organisms brings into the fold of ecology several other fields such as anthropology, sociology, economics etc. • Today, at global level, man is concerned with the maintenance and sustainability of his environment and therefore a good knowledge of environmental law becomes important. • Also, the relationships between developing foetus and the mother as in most animals requires a good knowledge of medicine, veterinary medicine, nursing and health management. • What about Theology? Our relationship with the unseen God. • From the above, we could see that ecology as a subject is an interdisciplinary synthetic science. It is difficult to set limit to its scope except that (for convenience) it remains a biological science dealing with living organisms. SUB-DIVISIONS OF ECOLOGY • Ecology can be sub-divided into many but varying ways. • However, the traditional sub-division of ecology are plant and animal ecologies. These two sub-divisions can not be justified due to their interdependences. • Another approach divides ecology as autecology (i.e. ecology of single individual or population) and synecology (i.e. ecology of more than one but different species of organisms or communities). • This approach has been modify to reflect different levels of community organisation. • Thus, we talk of population and community ecologies and indeed ecosystem ecology. ECOLOGICAL CONCEPTS • At this point, it with be important for us to understand some important ecological terms or concepts: - Population: This refers to a group of organisms of the same species, living together in a particular area and can interbreed among themselves. - Community: This is a natural assemblage of several species population in a given area. - Sample: This refers to part of a whole/entity taken to represent the whole/entity. - Ecosystem: Is a complex interacting systems of communities with their physical environments. ECOSYSTEM • As stated earlier, it is a complex interacting systems of communities with their physical environments. • It consists of the biotic and abiotic components. • This concept is central to the study of ecology and indeed many scholars refer to ecology as the study ecosystem. • Functions of the ecosystem include among others (a) to allow energy flow and cycling/recycling of minerals and (b) stabilizing the system in order to ensure continuity of life. Components of the Ecosystem Biotic component: This refers to the living organisms in the ecosystem. Abiotic component: refers to the physical (or non- living) environment in the ecosystem. Biotic Component Living organisms are grouped as either (a) Autotrophs or (b) Heterotrophs. Autotrophs • These refer to organisms that produce their own for as well as for other organisms. • They are better referred to as Producers. • They include all photosynthetic green plants (with chlorophylls) and chemosynthetic bacteria and algae. Heterotrophs STOPPED 2/10/15 • These organisms depend directly or indirectly upon the autotrophs for their food. • They can be further subdivide into Phagotrophs and Osmotrophs Phagotrophs • These include all organisms that ingest and digest their food inside their bodies. • Generally, they are referred to as Consumers. • They include the: - Herbivores (plant eating organisms) - Carnivores (animal/flesh eating organisms) and - Omnivores (organisms that eat all kinds of food). Osmotrophs • These include all organisms that secrete digestive enzymes exo-cellularly to break down food into simpler forms and then absorb the digested food. • They are mostly parasitic and saprophytic bacteria and fungi. • These organisms are generally called Decomposers because of their role in the decomposition of dead organic matter. • However, it is important to note here that parasites and some consumers (insects and worms) are not decomposers, but they help in the decomposition and break down of dead organisms into smaller bits. • Based on the above, heterotrophs are better sub- grouped as Biophages (i.e. feeding on living organisms) and Saprophages (i.e. feeding on dead matter) Abiotic Component • The physical environment and its several interacting variables make up the abiotic component of the ecosystem. • It includes: -Lithosphere -Hydrosphere -Atmosphere and -Radiant Solar energy. The position and movement of the earth as well as the gravitational force are additional components of the environment. Energy Flow • Energy is required for proper functioning of the ecosystem and all organisms need energy to survive • At any given time in an ecosystem, energy flow is unidirectional. • The solar energy is the chief source of energy in the ecosystem as the energy used for all life processes are obtained from it. • This energy is fixed by green plants by converting the light to chemical energy via photosynthesis and make it available to other organisms as food. 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6CO₂ +6H₂O • Since heterotrophs can not fix this energy from the sun, they use the plants as their energy source. • Thus, series of feeding relationships will be established – this feeding relationship is called the food chain. • The energy fixed in each feeding step/stage is lost in to other steps as heat which cannot be re-utilized. • The first step in the production of food by plants is called Gross production or Gross photosynthesis. • Out of the energy fixed in this production, some are lost during respiration by plants. The remaining amount is used in building up of tissues and organs by plants and the balance is called Net production or Net photosynthesis. • During digestion of food by animals, complex organic molecules are broken down to simpler ones and new compounds re-synthesized. • As a result, a good percentage of energy is again lost as heat while a little fraction is stored in the animal tissues. • Consequently, energy transfer along the food chain follows an average of 10% rule, i.e. about 10% energy is fixed in successive higher trophic levels. • Example, if a plant fixes 1000 kcal of energy, the herbivore will store only 100 kcal in its body (others will be lost as heat in faeces, respiration etc). Similarly, carnivore feeding on herbivore will only make available 10 kcal energy to the next trophic level and in that order. • This explains in part, at least, the reasons for the limited number of links in food chain. Food Chain and Food Web • As noted earlier, energy flow is a sequence of steps from one organism to another in terms of energy fixed and stored in a food chain. • A food chain is a chain that shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. • Every organism needs to obtain energy in order to live. For example, plants get energy from the sun, some animals eat plants, and some animals eat other animals. • A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. • A food chain starts with the primary energy source, usually the sun. Plant → Man This the simplest food chain. • Another food chain is as shown below: Grass → Ant → Toad → Snake → Hawk → Man Trophic level 1st 2nd 3rd 4th 5th 6th The arrow shows the direction of energy flow in the food chain From the above examples, we will observe that food chain is unidirectional. • Each organism in the food chain occupies a position. The position of any organism in the chain represents its trophic level. • Primary producers are the base of every food chain – these are called autotrophs. Food Web • In food web, organisms' position in the food chain can vary as their diet varies. -For example, when a bear eats berries, the bear is functioning as a primary consumer. -When it eats a plant-eating rodent, it functions as a secondary consumer. -When it eats salmon, it functions as a tertiary consumer (this is because salmon is a secondary consumer, since salmon eat herring that eat zooplankton that eat phytoplankton, that make their own energy from sunlight). • In any food web, energy is lost each time one organism eats another. Because of this, there have to be many more plants than there are plant-eaters. There are more autotrophs than heterotrophs, and more plant-eaters than meat-eaters. Schematic drawing of a food web • A food web (or food cycle) represents feeding connections in an ecological community and hence is also referred to as a consumer-resource system.