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Download 1. Ecology Introductory Concepts
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The Nature of Ecology Ecology is the scientific study of the interactions between organisms and their environment that determine their distribution and abundance Ecologists employ a variety of techniques to investigate: • The relationship between a single species and the environment • The relationships that exist between individuals of different species within a community, and also between them and their environment • The changes that take place in the abundance, distribution and activity of species Ecology is a multidisciplinary science encompassing the techniques and concepts of physiology, chemistry, mathematics, physics and biogeography Temperature, rainfall and light intensity are the major environmental factors in determining the nature of the biome High temperatures, abundant rainfall and roughly constant day length throughout the year produce tropical rain forests Tropical Rainforest Tropical forests are characterised by having the greatest diversity of species of all world biomes; they occur near the equator with high temperatures and abundant rainfall and roughly constant day length throughout the year Savannah Savannahs are tropical grasslands with scattered or clumped trees; the climate is tropical semi-humid, with a rainy season in the summer and a long dry season during the winter months Deserts High daytime temperatures and light intensity, little rainfall and strong winds characterise the deserts – the harshest environments within the biosphere; organisms colonising these areas are specialised to withstand the xerophytic conditions Tundra Arctic tundra is located in the northern hemisphere, encircling the north pole and extending south to the coniferous forests of the taiga Characteristics of the tundra are a cold climate, low biotic diversity and simple vegetation structure Ecosystem Structure An ecosystem is a natural unit which consists of several habitats and their communities; it thus consists of both abiotic and biotic components and encompasses all their interactions The habitat of an organism is its place of residence; this is where it lives, such as at the bottom of a lake, in a cave or within a tree hole A population is a group of individuals of the same species which occupy a particular habitat A community is a collection of different populations which occur together in both space and time The environment of organisms is the set of conditions that surround them and encompasses their abiotic (non-living) and biotic (living) environments An organism’s environment may be subdivided into abiotic and biotic components The biotic environment consists of producers, consumers and decomposers and, biotic factors include all the interactions that exist between them such as competition and predation The abiotic environment includes light energy, water availability, pH, soil characteristics, temperature, atmospheric gases, aspect and altitude The Ecological Niche The ecological niche of a population is its role within the community and is defined as the sum total of all aspects of a population’s existence, i.e. its habitat, activities and requirements together with its effects on both the abiotic and biotic environments Ecological niches are the outcome of evolution; species acquire a range of adaptations through natural selection and these establish the range and boundaries of the ecological niche for that species Every organism of a particular species is adapted to survive within a range of environmental conditions The range of environmental conditions within which organisms survive are described as tolerance ranges and include factors such as temperature, light intensity and rainfall Niche Overlap and Competition When organisms share the same habitat and have the same functional roles or requirements for a particular resource, then niche overlap occurs When the niches of two species overlap, there is competition for limited resources such that the greater the overlap, the more intense the competition In extreme cases, where two species have identical niches, competition can be so intense that the different species are unable to coexist and one species may totally out-compete the other – The Competitive Exclusion Principle Competition between members of different species (interspecific competition) is generally less intense than that observed between members of the same species (intraspecific competition) Competitive exclusion is often avoided by dividing up environmental resources, such that each competitor exploits different portions of the resource or utilises them at different times; this is described as Resource Partitioning Chthamalus populations are potentially able to grow at all levels of the rocky shore (fundamental niche) Chthamalus is more tolerant of high temperature and desiccation than Balanus and is therefore able to survive the conditions on the upper shore The upper distribution limits for both species are largely determined by their tolerance to these abiotic factors – temperature and desiccation The lower distribution limit (realised niche) of Chthamalus is determined by competition for space with the faster growing Balanus ; Balanus balanoides dominates the middle intertidal zone where it outcompetes the slower growing Chthamalus Various biotic factors appear to be responsible for determining the lower distribution limit of Balanus balanoides