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Biotic and Abiotic Factors Different Approaches to the Study of Ecology • Ecology is the study of an organism or organisms and their relationship to the environment. • An organism’s environment consists of the physical, chemical and biological factors with which it interacts. • The mollusks seen at the right must deal with changes in temperature, tides, wave action, predators and competition for food. Each plays its own role or niche. How can we study Environmental Interactions? • At the most basic level, an ecologist may be interested in the interactions of a single organism and its environment. • Population ecologists focus on factors that affect populations of organisms that are found in a specific area. (i.e. What determines the reproductive success of wood storks in South Florida.) • At the community level of study one is interested in understanding the interactions between populations of different species living in an area. For example, what determines composition and distribution of trees in a hardwood hammock? An Ecosystem Approach • At a fourth level, studies may examine an ecosystem. • The ecosystem includes all the organisms in an area and all of the abiotic factors that affect them. • In South Florida there are many ongoing studies of the Everglades ecosystem, as biologists, geologists, hydrologists and atmospheric scientists work together in efforts to understand how all the parts of it relate to each other. Without this knowledge we cannot hope to preserve, protect or manage the unique natural environment that is South Florida . Abiotic factors are the non-living Components of the Environment • Abiotic factors include: – Sunlight – Water – Temperature – Wind – Soil/substrate – Special events such as: • Fires • Hurricanes • Floods • Volcanic eruptions • Tsunamis The atmosphere has a tremendous effect on the distribution of plants and animals. Global patterns of circulations affect rainfall patterns and the prevailing wind directions. Changes in air circulation over the Pacific Ocean can lead to events, such as El Nino, which have global repercussions (i.e. torrential rains in the Andes and severe drought in Australia) Regional climate affects biological communities • The unequal heating of the earth’s surface leads to the global patterns of rainfall and winds. At the equator there is maximum heating of the earth’s surface. This causes hot air to rise, and as it rises it cools, forming clouds and increasing precipitation. At high altitudes the air cools and moves away from the equator. At the mid-latitudes this cool air sinks back to the surface. This results in both the trade winds and relatively dry conditions. Prevailing wind patterns, set ocean currents in motion. • The patterns of wind flow can be seen in the figure at the right. Land masses can interrupt these patterns at a local or regional level. • Ocean currents are created by the flow of winds, and cause great patterns of circular flow in the oceans. The Gulf Stream is one such current. Without the heat in this mass of water, the climate of northern Europe would be much cooler. This would alter the biological communities found there. Rain shadows greatly affect the availability of moisture! • As previously stated, land masses affect atmospheric movements. Rain shadow effects are seen when moist oceanic air masses encounter mountains. The moist air is forced up, cools, and releases its moisture in the form of rain. On the back side of the mountains, the cooled air decends towards the surface, but is no quite dry. This may create arid or semi-arid conditions. Other Abiotic Factors • Temperature also affects the distribution of plants and animals. • As a rule, temperature are lower as you move towards the poles or as you climb in elevations. For this reason arctic or sub-arctic plant communities can be found at high elevations in the tropics. • In the temperate latitudes living organisms must be able to tolerate the temperature extremes of summer and winter. This could range from 90’s in the summer to well below freezing in the winter. • In the tropics there is very little seasonal change and many organisms have a narrow range of temperature tolerance. Years ago an important paper was publish titled ‘ Why mountain passes are higher in the tropics’. What does that mean?? • It means that in the tropics differences in elevation can be barriers to the distribution of species. The temperature at which you can live may prevent your population from moving from one suitable habitat to another, because of the temperature zones through which you would need to pass in a vertical migration. Other Abiotic Factors • Here are some abiotic factors that you may not have thought about. – Calcium: The lack of availability of calcium will restrict the distribution of land snails. If there is no calcium a shell can’t be secreted. – Sand: the size of the sand grains in the soil can impact animal that are burrowers. – Nitrogen: Not just nitrogen, but nitrate (NO 3). This is the form of nitrogen used by plants. When nitrate is not readily available in the soil, some plants supplement it with a meat diet. (insectivorous plants). Biotic Factors • A living organism is also affected by the living components of its environment. • Competition exists for available food resources. • Predators feed on members of the population. • Microbes can bring diseases. (If time travel were possible, and you could be transported to the Cretaceous Era to look at dinosaurs, don’t be afraid of fear Tyrannosaurus, fear the microbes. You would have no immunity to them!!) • There may be competition for nesting space. • Plants may compete for the light needed to carryout photosynthesis. • These are many other biological factors determine the success of an individual or species.
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