AQA A Level Biology复习笔记7.4.5 Ecosystems

Ecosystems

• Species do not exist by themselves in their own isolated environment, they interact with other species forming a community
• The species within a community interact with each other and the environment they live in, forming ecosystems
• There are both living (biotic) and non-living (abiotic) components within an ecosystem
• An ecosystem can be defined as:

A relatively self-contained unit consisting of a community (or multiple communities) of species interacting with each other and with the non-living components of their environment

The dynamic nature of ecosystems

• Many features within ecosystems are in a constant state of change
• These changes can occur over a wide range of time scales, from quick changes (e.g. in weather or a population explosion of a species, as occasionally occurs in locusts) to very slow changes (e.g. the erosion of rock, eventually leading to soil formation or evolution by natural selection, eventually leading to speciation)
• Both the biotic and abiotic components within ecosystems are dynamic
  • Some examples of each are given below

   

Biotic components

• There is a constant flow of energy within ecosystems. For example, the process of feeding ensures that energy can move between organisms:
  • Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers, who are themselves eaten by tertiary consumers
  • When organisms die or produce waste products, the organic matter is broken down (decomposed) by organisms such as bacteria and fungi

   

• Species numbers are constantly fluctuating within ecosystems, as populations decline (through death and emigration) or grow (through birth and immigration)
  • These factors mean that the population size of a particular species constantly varies around the theoretical carrying capacity depending on factors such as interspecific or intraspecific competition, geographical location and the time of year

   

Abiotic components

• There is also a constant flow of nutrients within ecosystems as they are continually recycled (e.g. the carbon, nitrogen and phosphorus cycles)
• Water is also constantly cycled in ecosystems via the water cycle
• Other aspects of weather that can affect communities of species, including abiotic factors such as temperature and wind, are also very dynamic

Implications

• The main implication of the dynamic nature of ecosystems is that this means they can be very complex to study and understand
• Biological studies of ecosystems must try to take the effects of all the biotic and abiotic factors into account in order to understand how these factors interact with each other and the different extents to which they affect species populations and communities
  • In a very complex ecosystem, such as a tropical rainforest, this can be almost impossible to do and biologists may be forced to focus on some of the main biotic and abiotic factors and potentially disregard less ecologically significant factors
  • Even the components of a relatively simple ecosystem, such as a desert, can still be sufficiently dynamic to make studying them a complicated and time-consuming process

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